Timely blueprint will direct research into pavement management and preservation

Anew “roadmap” indicating the direction of research in pavement management and pavement preservation is coming at just the right time, as states begin to openly curtail capacity improvements in favor of pavement preservation.

Chip seal is a fundamental pavement preservation process, here placed in Minnesota.

The Pavement Management Roadmap (FHWA-HIF-11-011) was articulated in 2011 by the Federal Highway Administration (FHWA) and helps identify the steps needed to address current gaps in pavement management – thus preservation – and to establish research and development initiatives and priorities.

Pavement preservation is a network-level, long-term strategy that enhances performance and extends pavement life by using a variety of cost-effective surface treatments, and its successful application is intertwined with effective pavement management.

For states fleeing to pavement preservation, the issue is money. As cash streams dwindle, state DOTs are compelled to use available funds to preserve their existing road network with a goal of improving their pavement condition indices (PCIs).Take these examples:

• Missouri DOT has put citizens on notice that it will spend money to preserve the existing system, and that the days of major capacity rebuilds – like the massive New I-64 total expressway rebuild in St. Louis, where reconstruction resulted in the complete closure of portions of the expressway in 2008 and 2009 – are over.

In its five-year plan of June 2011, the Missouri Highways and Transportation Commission chose to reduce the size of DOT staff by 1,200, close 131 facilities and dispose of more than 740 pieces of equipment.

Unit of American Asphalt and Grading Company places slurry seal as part of year-long work with the City of Las Vegas in 2009

“By 2015, the proposed direction will save $512 million for vital transportation improvements,” the plan’s executive summary states. “As of Sept. 30, we had eliminated 667 staff positions, closed 23 facilities and disposed of 245 pieces of equipment. Those moves have allowed us to save $177 million since March of 2010 when the initial plan was put into action. More than $64 million of that money has been used to improve the state’s rural roads.”

In his November 2011 address to the Asphalt Emulsion Technologies Workshop sponsored by the Asphalt Emulsion Manufacturers Association, MoDOT chief engineer David Nichols, P.E., said given current cash flow, system preservation would take priority over capacity improvements, as one of three goals.

“We are committed to keeping our roads and bridges in good condition for as long as we can with the resources we have, keeping our citizens safe, and delivering outstanding customer service,” Nichols said in St. Louis. He added that, in January 2012, MoDOT was going to seek legislative authority to create a public-private partnership with a goal of rebuilding I-70 from St. Charles to Kansas City as a toll highway, as tolls were the only way the project could be paid for given current funding levels.

• Wyoming DOT in November announced a strategy of preserving the state’s highways and bridges during the state’s current transportation funding crisis.

Asphalt rejuvenator is placed on U.S. 25 near Jackson, Miss., using a BearCat 2,000-gallon distributor on an abraded surface.

“In anticipation of major funding decreases, WYDOT is making sweeping changes,” says director John Cox. “WYDOT has shifted its focus away from the kind of reconstruction and improvement projects we’ve been doing for the past four decades into more of a survival mode.”

In a video released by the American Association of State Highway & Transportation Officials (AASHTO), Cox says changing the department’s focus to preservation will make the decline in the condition of the state’s highways more gradual. “Our primary goal is to preserve the existing highway system as long as possible,” Cox says. “What that does is it kind of staves off the inevitable, because sooner or later we’re going to have to take care of the system by getting underneath the pavement and reconstructing pavements.”

However, this approach will also result in fewer safety improvements to highways and a smaller number of projects designed to accommodate increasing traffic volumes, he says.

• Ohio DOT’s director said in October that his state was shifting to preservation. In today’s lean times, system preservation has become the priority for ensuring serviceable pavements, says director Jerry Wray, P.E., P.S., also in an AASHTO video.

New ‘Roadmap’ points path to improved pavement management and preservation in the decade to come.

In the video, Wray explores Ohio’s strategy for preserving its highways and bridges during the current transportation funding crisis “There’s a limited amount of resources for an unlimited amount of wants, desires and needs,” Wray says. “We have to focus on the basics: What improves safety, the economy, and the quality of life for the people of Ohio.”

ODOT is working to be leaner, more efficient, and more effective. “We have a responsibility to all Ohioans to get the best value and highest rate-of-return for every dollar we spend,” Wray says. Like Missouri, that also will include public-private partnerships, which due to a change in Ohio law are now allowed.

New ‘Roadmap’ is a Guide

As more governments drift toward pavement preservation, they will become part of a national approach to pavement preservation which was bolstered in 2011 by the release of FHWA’s national Pavement Management Roadmap.

The roadmap is authored by Kathryn A. Zimmerman, Linda M. Pierce and James Krstulovich of Applied Pavement Technology, and helps identify the steps needed to address current gaps in pavement management, and to establish research and development initiatives and priorities.

While the roadmap nominally considers pavement management, the ability to preserve pavements economically via enhanced pavement management is a fundamental part of the roadmap.

“Unfortunately, decreases in the purchasing power of available funding, coupled with reduced funding levels, have led to deteriorating network conditions within most transportation agencies at the same time that demand for these facilities is increasing,” the introduction states. “As a result, many transportation agencies are shifting their priorities from a focus on system expansion to an increasing focus on system preservation. In fact, a number of agencies have recognized the cost-effectiveness associated with the use of preventive maintenance treatments to slow the rate of deterioration and to postpone the need for the most costly rehabilitation strategies.”

Pavement preservation is changing how road agencies work, the introduction says, and this is reflected in the examples of Missouri, Wyoming and Ohio above. “[T]he shift towards pavement preservation has not been entirely free from problems,” the introduction says. “For example, organizations that had previously separated the maintenance and capital improvement decision processes have had to overcome these institutional barriers in order to develop effective improvement programs that include preventive maintenance treatments.

“As a result of these and other changes impacting transportation agencies, the role of pavement management is changing,” the roadmap says. “In the past, pavement management was primarily considered to be used for assessing and reporting pavement conditions, prioritizing capital improvements, and estimating funding needs. Today, pavement management has the potential to fulfill a much broader (and more significant) role within a transportation agency.”

In addition to the more traditional roles it serves, pavement management can provide a link to maintenance and operations through the analysis of pavement preservation options. And it can provide the pavement performance data required to evaluate and calibrate the mechanistic-based performance models for use within a specific transportation agency.

A Vision for 2020

The roadmap attempts to clarify what the next 10 years will mean for agency pavement investments in its Vision for Pavement Management in 2020.

“Pavement management will make use of a new generation of technology so agencies are less dependent on manual labor for data collection,” the vision statement says. “Pavement management tools will allow agencies to communicate effectively with stakeholders, using clear statements that are tied to agency goals and pavement worth.

“Within an asset management framework, pavement management will be used for investigating decisions and program options in both private and public sectors,” the roadmap envisions. “A pavement management analysis will consider new materials and construction/design practices, as well as other factors that influence project and treatment selection, including safety, congestion and sustainability. As a result of these changes, pavement management will be robust, comprehensive and credible, and will address agency needs at the project, network and strategic levels.”

Asset management goes hand-in-hand with pavement management and pavement preservation. It provides a coordinated approach to managing infrastructure assets over the course of their entire life cycle, thus improving performance, increasing safety and providing greater value to the community.

With an asset management approach, optimal decisions on what would be the most effective mix of preserving, maintaining, renewing or replacing infrastructure components are based on accurate data, economic analysis and sound engineering.

Decisions are also supported by performance measures and performance-based goals. “The availability of quality data has had a tremendous impact on an agency’s ability to compare different investment options and to make sound business decisions that consider both engineering and economic factors,” says Nastaran Saadatmand of FHWA’s Office of Asset Management.

Short/Long-Term Needs

FHWA developed the roadmap through three regional workshops held in Phoenix, Dallas and McLean, Va., in 2010. Stakeholders participating in the workshops included representatives from state and local highway agencies, Canadian government agencies, academia and private industry.

Twenty-three short-term needs (the next five years) and 24 long-term needs (the next five to 10 years) were identified and prioritized by participants. Meeting these needs would require more than $14.5 million in funding. Needs were grouped by four theme areas:

• Use of Existing Tools and Technologies;

• Institutional and Organizational Issues;

• The Broad Role of Pavement Management; and

• New Tools, Methodologies and Technology.

Top short-term needs outlined in the roadmap include communicating pavement management information and benefits, developing and using effective performance measures, improving the skills of pavement managers, developing automated condition data processing tools, and developing methods to quantify the benefits of pavement management.

The long-term needs include ones that will require research to improve existing practices. Priority long-term needs include defining and calculating the effect of pavement preservation treatments on pavement life, defining the impact of pavement management investment levels on benefits, using pavement management data to support design activities, developing performance models that consider a series of pavement preservation treatments, and developing a method for effective modeling of structural condition.

The roadmap also looks at the steps required to make these identified priorities a reality, noting that “the successful implementation of the roadmap demands a focused, cooperative approach among national and international organizations,” the document says.

The roadmap is available online at www.fhwa.dot.gov/infrastructure/asstmgmt/index.cfm, along with an accompanying Executive Summary (Pub. No. FHWAHIF-11-014). Download your copy at www.fhwa.dot.gov/asset/hif11011/hif11011.pdf.

Bridge Preservation Guide

A new guide to bridge preservation also was released in 2011 and is available for download.

Published in May 2011, the new Bridge Preservation Guide: Maintaining State of Good Repair Using Cost-Effective Investment Strategies provides an overview of preventive and systemic preservation activities for bridge structures.

Bridge preservation is defined as actions or strategies that prevent, delay or reduce deterioration of bridges or bridge elements, restore the function of existing bridges, keep bridges in good condition and extend their life, according to the guide.

Like pavement preservation, effective bridge preservation actions are intended to delay the need for costly reconstruction or replacement actions by applying preservation strategies and actions on bridges while they are still in good or fair condition and before the onset of serious deterioration. Bridge preservation encompasses preventive maintenance and rehabilitation activities.

An effective bridge preservation program:

• employs long-term strategies and practices at the network level to preserve the condition of bridges to extend their useful life;

• has sustained and adequate resources and funding sources; and

• has adequate tools and processes to ensure that the appropriate cost-effective treatments are applied at the appropriate time.

Download the new Bridge Preservation Guide at www.fhwa.dot.gov/bridge/preservation/guide/guide.pdf.

High-Volume Road Preservation

In addition to the Bridge Preservation Guide, new guidance is now available for the preservation of high-volume roadways.

Even as road agencies have turned to pavement preservation to extend the life and improve the condition of their roadway networks, the use of many strategies has been restricted to lower-volume roadways, with little use on high-volume roads. To remedy this, a new report has been issued by the Second Strategic Highway Research Program (SHRP2), Guidelines for the Preservation of High-Traffic-Volume Roadways.

The guidance provides information to help expand agencies’ ability to use varied treatments to best meet the preservation needs on higher-volume roadways. As the guidelines note, “most preservation treatments will have the same beneficial effects on a pavement regardless of traffic volumes.”

Barriers historically inhibiting the greater use of preservation treatments on high-traffic-volume roadways have included increased performance expectations, increased risk of failure associated with the durability of treatments under higher traffic volumes, and lack of agency experience with certain treatments.

The guidelines include details on factors affecting project and treatment selections for pavement preservation, including traffic level, pavement condition, climate and environment, work zone duration restrictions, expected treatment performance and relative costs.

A sequential approach for evaluating possible preservation treatments for an existing pavement and identifying the preferred one is presented in the guidelines, diagramming how data sources and project constraints are considered.

Also presented is information on pavement distresses and how the various preservation treatments can address them. The treatments are described in initial feasibility matrices that outline possible applications for specific distresses and the treatments’ ability to prevent or slow pavement deterioration or to restore functionality or surface characteristics.

Download the document at http://www.onlinepubs.trb.org/onlinepubs/shrp2/SHRP2-S2-R26-RR-2.pdf.

2012 National Conference on Pavement Preservation

A national conference on pavement preservation will be held in Nashville in August. FP2, Inc. – in collaboration with the National Center for Pavement Preservation – will sponsor the National Pavement Preservation Conference which will be held Aug. 27- 30.

The national conference theme, Road Trip: Driving the Message for Change, promotes the idea that spending money to keep good roads in good condition is a cost-effective way to save America’s highways. Communicating the importance of preserving our highway investment will be an important conference objective.

The Renaissance Nashville Hotel is the venue for 2012, and is located in the heart of downtown near popular attractions. Building on the success of the First International Conference on Pavement Preservation in April 2010 in Newport Beach, Calif., this conference incorporates the first combined meetings of the Midwestern, Northeast, Rocky Mountain West and Southeast Pavement Preservation Partnerships, to examine advancements in current practice and new treatment technologies that offer improved reliability and enhanced performance.

For more information, visit www.nationalpavement2012.org or call (517) 432-8220.

The multiple values of accelerated bridge replacement

A section of the I-15 Prairie Crossing superstructure is moved toward placement in Utah in October, 2009.

The cost of user delays in an era of unbridled traffic congestion is driving today’s fast-paced bridge erection technology, and it’s being encouraged by the Federal Highway Administration (FHWA) in partnership with active state DOTs.

Those state DOTs are accelerating bridge replacement via use of prefabricated bridge components that are either placed on site, or assembled on site into a superstructure and then installed in one swift action.

The fast-tracking of bridge replacement via prefab sections is only one of a series of major advancements happening in bridge technology. Others include:

* Fiber-reinforced polymer (FRP) composites continue their inroads into bridge design, at the expense of precast concrete and lightweight aggregate. Three new design themes emerged in 2011 as focus areas for the American Association of State Highway and Transportation Officials (AASHTO) Subcommittee on Bridges and Structures: rigidified FRP tube arches, hybrid composite beams, and reinforced thermoplastics technology.

* The growing acceptance of self-consolidating concrete (SCC) is making erection of conventional precast, post-tensioned structures – and those using FRP components – easier as they greatly reduce the need to vibrate concrete mixes into complex steel reinforcement, either in-plant for precast, or on site for poured-in-place.

* Both precast and cast-in-place concrete proponents look forward to concrete-grade coal fly ash escaping designation as a “hazardous waste” as sought by the Environmental Protection Agency (EPA). The classification of fly ash as hazardous waste could introduce chaos into the production of high-performance concrete for bridges.

Every Day Counts

Fast-paced bridge replacement using precast components is a high priority for FHWA and is a critical part of its Every Day Counts (EDC) initiative.

“Every Day Counts reflects a new sense of urgency we bring to our work,” said FHWA Deputy Administrator Greg Nadeau at the second International Warm Mix Conference in St. Louis in October (warm mix asphalt also is being promoted through the EDC program).

EDC aims to make highway and bridge building more efficient and effective, Nadeau said. “FHWA doesn’t deliver projects; we support our partners who support a more effective delivery of the federal-aid highway program.”

That includes fast replacement of bridges by use of what FHWA calls prefabricated bridge elements and systems (PBES) technology, he said. “As a result, bridges are built faster, and with much less disruption to the traveling public and, importantly, to commerce,” Nadeau said. “These techniques and technologies are going to have to be deployed, especially in areas that are experiencing significant congestion. We want to rapidly deploy technology that makes sense.”

With prefabricated bridge elements and systems, many time-consuming construction tasks no longer need to be done sequentially in work zones, FHWA says.

These PBES superstructures are assembled adjacent to or away from the jobsite to limit construction in the right-of-way, as is the conventional practice. “An old bridge can be demolished, while the new bridge elements are built at the same time offsite, under controlled conditions, then brought to the project location ready to erect,” FHWA says.

Benefits, FHWA says, include:

* Reduction of on-site construction time;

* Reduction of environmental impacts;

* Improved work zone and worker safety;

* Lowered initial and life-cycle costs; and

* Improved product quality via a better-controlled manufacturing or assembly environment and cure times, and easier access to components in a plant facility.

“Prefabricated bridge elements especially tend to reduce costs where use of sophisticated techniques would be needed for cast-in-place work, such as in long water crossings or higher structures like multi-level interchanges,” FHWA says.

But while precast, post-tensioned concrete I-beams and box girders have been used in repetitive bridge construction for decades — as in lengthy causeways along the Gulf Coast and in Florida, for example — what is new is the near-complete assembly of bridge superstructures from manufactured components on the jobsite but out of the right-of-way.

“The lion’s share of the construction work is done off-site, usually in a nearby staging area, and the new bridge superstructure is lifted or ‘rolled’ into place,” FHWA says. “This method takes advantage of precast elements to minimize the impact of the project on motorists by reducing the time needed for roadway work zones.”

Prefab elements for a superstructure will include: deck panels, both partial and full depth, precast or steel stay-in-place; I-beams with more efficient designs; and composite decks. Substructure prefab elements can include: pier caps, columns and footings; abutment walls, wing walls and footings; and bent caps.

“Increasingly, innovative bridge designers and builders are finding ways to prefabricate entire segments of the superstructure,” FHWA says. “A substructure system may consist of individual piers or prefabricated bent caps supported by prefabricated columns and/or prefabricated abutment elements. Total prefab bridge systems offer maximum advantages for rapid construction and depend on a range of prefabricated bridge elements that are transported to the work site and assembled in a rapid-construction process.”

An Early Adopter

Famously, the Utah DOT was an early adopter of prefabricated superstructure technology. In October, 2009 – as part of its Corridor Expansion (CORE) program – Utah used giant self-propelled modular transporters (SPMTs) to move bridge spans into place at Pioneer Crossing over I-15 at American Fork, south of Salt Lake City.

A south bridge span over I-15’s northbound lanes for a new diverging diamond interchange was moved into place with SPMTs on a Friday night, and a span over the southbound lanes was moved into place just two days later on Sunday night. Then, the existing four-span bridge was dismantled without reducing the Interstate’s three-lane capacity in each direction.

Then, on a weekend in June, 2010, the north bridge for the interchange was moved into place from a staging area in the northwest quadrant outside the interchange southbound ramp, over a quarter-mile from the bridge. The span over the southbound lanes of I-15 was moved into place on a Friday night, and the span over the northbound lanes was moved into place on the following Sunday night. These bridges over I-15 are the largest multi-girder spans moved with SPMTs in the United States.

The two spans of the north bridge had been constructed on temporary support piers in the staging area. Then, the SPMTs were moved under one 186-foot-long span, with nine 96-inch prestressed concrete Washington State bulb tee girders in the cross section. The span had a 45-degree skew and weighed 2,100 tons. Two lines of SPMTs had to be configured to support the massive span at each end.

Special tower stand jacks raised and lowered the span off the temporary supports and onto the new substructure elements, respectively. Chains were also used to help control the distance between the double lines of SPMTs. On the top of the bridge, piano-like wire was placed at the diagonals of the span to measure any span distortion. To avoid overstressing the deck concrete, only inches of distortion was allowed. The span superstructures were placed late Friday evening into early Saturday morning, and late the following Sunday night into early Monday morning, with minimal traffic restrictions and lane closures.

MassDOT: 14 in 10 Weekends

This summer, Massachusetts DOT achieved a remarkable bridge replacement record, with 14 bridges replaced in Medford, Mass. over 10 weekends from June to August with its I-93 “Fast 14” Rapid Bridge Replacement Project.

Because MassDOT used cutting-edge accelerated bridge construction techniques and materials to replace the bridges, all the bridge and associated work was completed over a five-month period.

“Using conventional methods, it would have taken at least four years to replace all 14 bridges, and during those four years drivers would have had to endure long-term lane closures,” MassDOT says. “MassDOT executed a traffic management plan and a comprehensive communications plan to minimize construction-related congestion and community impacts during construction, which was limited to off-peak hours.”

The innovations MassDOT used to accelerate the bridge replacements include design/build procurement, a prefabricated bridge elements system and a special rapid-setting concrete. “By replacing the bridges with modular superstructure units that were fabricated off-site, MassDOT eliminated years of work in the roadway,” the agency says.

This project was showcased by FHWA, receiving national attention for the innovation it used to get the bridges built so quickly and safely, and for limiting major impacts to road users to off-peak hours.

Prefab Speeds

Access Overpass

Even before Utah and Massachusetts, the Georgia DOT used extensive prefabricated bridge elements and systems to radically reduce the time and cost of a new bridge over I-85 in Troup County, as part of an improvement to provide access to a new Kia vehicle assembly plant there.

On the Utah I-15 project, a self-propelled modular transporter (SPMT) moves superstructure into position between bridge bents.

Georgia DOT Commissioner Gena Evans said at the project’s dedication in December, 2008 that the project was an enormous achievement, considering a tight, 18-month construction timetable that had to be met. Work was finished more than 30 days ahead of that schedule in the largest design-build construction project initiated by Georgia DOT.

“This effort proves that design-build can be successful when applied to the right projects,” Evans said. “Georgia DOT is proud to have played a role in helping to bring new jobs and improved mobility to the area.”

Though Kia was located near I-85, access to the highway was limited. Existing roads could not accommodate the estimated thousands of additional daily auto and truck trips, and a bridge was needed. To expedite construction, Georgia DOT chose prefabricated bridge elements and systems.

“With PBES, innovation could be incorporated into the design without increasing the user costs,” the DOT says. “Conventional bridge construction, using cast-in-place technology and traditional contracting methods, would have required 30 months. With PBES, the project was completed in only 16.5 months.”

The I-85 bridge was planned as a four-span concrete structure with eight columns per bent. Prefabricated elements were used for the substructure’s columns, pier caps and deck beams. The bridge components were cast off-site and shipped to the site on conventional semi-trailers. Each component was carefully cast to within a 0.25-inch tolerance so connections made in the field would fit precisely.

“We’re doing some innovative things, using precast, prestressed columns and caps on the bridge in order to expedite the work,” said then-Georgia DOT District 3 engineer Thomas Howell. “It’s a first in this district. The pieces were actually cast at a yard and brought out, instead of forming and pouring them on-site.”

Safety data sets were collected before, during and after construction to ensure that the innovations did not increase risks. With PBES, no worker injuries were reported. A single motorist incident involved minor vehicle damage with no personal injury. The cost savings with PBES were equally compelling, saving nearly $2 million, or 45 percent, of what the interchange would have cost if it had been built conventionally.

FRP Composites Refined

Even as concrete and steel bridge construction is accelerated via new technologies and techniques, fiber-reinforced polymer (FRP) bridge materials continue to make inroads as their engineering is refined.

Three new FRP technologies were in the spotlight in 2011, with rigidified FRP tube arches, hybrid composite beams and reinforced thermoplastics technology this year being named as focus areas by the AASHTO Subcommittee on Bridges and Structures’ Technical Committee T-6: Fiber Reinforced Polymer Composites.

Concept of the superstructure placement for the I-93 ‘Fast 14’ Rapid Bridge Replacement Project in Medford, Mass. completed in the summer of 2011.

Maine DOT has volunteered to be the lead state, taking on the next step in the implementation process, which will include conducting a market analysis and developing a marketing plan for implementation. Other state DOTs represented on the team include Massachusetts, Michigan, Missouri and New York, along with the Maine Composites Alliance and the University of Maine.

“For nearly 30 years, FHWA has supported research and development technology transfer, deployment and standardization of FRPs as a promising solution for bridge construction and rehabilitation,” Louis N. Triandafilou, P.E., FHWA Office of Infrastructure team leader, Bridge & Foundation Engineering Team, said this summer.

“After a long history of worldwide research, use of FRP composites in seismic retrofits and bonded repairs has become almost commonplace,” Triandafilou said. “Also, highway agencies are applying this technology to a growing number of projects involving bridge deck panels and reinforcing bar and prestressing applications. However, despite widespread government and industry support, there has been little self-sustaining, competitive deployment of this technology.”

Nonetheless, several emerging FRP composite technologies could play an important role in future rehabilitation and replacement, Triandafilou said. “Some promising emerging approaches are focused field applications of rigidified FRP tube arches, hybrid composite beams and reinforced thermoplastics.”

FRP is a general term for polymer-matrix composites reinforced with cloth, matting, strands or other fibers, Triandafilou said. FRP composites consist of thermoset resins, which, once cured, cannot be returned to an uncured state. Reinforced thermoplastic resin composites, on the other hand, can be softened repeatedly by heating or hardened by cooling. In the softened state, workers can reshape these composites by means of molding or extrusion. “FRP and reinforced thermoplastic composites have the potential to create cost-effective, durable and long-lasting bridge structures,” Triandafilou said.

* Rigidified FRP tube arches are derived from a kit consisting of three main components: carbon- and glass-FRP composite tube arches, a self-consolidating concrete (SCC) mix design, and corrugated fiberglass panels, Triandafilou reports. “Once on site, workers inflate the 12- to 15-inch- diameter diam tubes and bend them around arch forms,” he said. “The crew then uses a vacuum-assisted transfer molding process to infuse the tubes with resin. The tubes, which cure in a matter of hours, function as stay-in-place forms for the SCC, eliminating the need for temporary formwork, and provide structural reinforcement for the concrete in the longitudinal direction, in shear, and as confinement, eliminating the need to install rebar.”

* Hybrid composite beams combine the properties of concrete, steel and FRP composites in beam fabrication, Triandafilou says. “This combination results in stronger and lighter-weight bridge members,” he said. Hybrid composite beams offer the possibility of cost-effective spans and corrosion resistance, he added.

* Reinforced thermoplastics consist of 65-percent high-density polyethylenes blended with 35-percent polystyrene or polypropylene glass fibers, Triandafilou says. “The resulting materials have a high resistance to corrosion, rotting and insect infestation, making them excellent candidates for replacing deteriorated railroad ties,” he added. “Reinforced thermoplastics also possess favorable durability and toughness characteristics without chemical additives. Favorable engineering properties such as flexural, compressive and shear stress make these materials a viable alternative for highway bridge applications.”

SCC Boosts

Concrete Bridges

Self-consolidating concrete (SCC), also known as self-compacting concrete, is a highly flowable, non-segregating concrete that spreads into place, fills formwork, and encapsulates even the most congested reinforcement, all without any mechanical vibration, reports the National Ready Mixed Concrete Association (NRMCA). Its use is simplifying bridge construction both in the field and precast bridge component fabrication in the plant.

SCC is defined as a concrete mix that can be placed purely by means of its own weight, with little or no vibration. Adjustments to traditional mix designs and the use of superplasticizers creates flowing concrete that meets tough performance requirements, NRMCA says. If needed, low dosages of viscosity modifier can eliminate unwanted bleeding and segregation.

The flowability of SCC is measured in terms of spread when using a modified version of the slump test (ASTM C 143), according to NRMCA. The spread (slump flow) of SCC typically ranges from 18 to 32 inches depending on the requirements for the project. The viscosity, as visually observed by the rate at which concrete spreads, is an important characteristic of plastic SCC and can be controlled when designing the mix to suit the type of application being constructed.

In precast concrete components, SCC has the ability to eliminate inadequate consolidation in thin sections or areas of congested reinforcement, which leads to a large volume of entrapped air voids and compromises the strength and durability of the concrete. Because SCC is designed to consolidate under its own mass, it has the potential to eliminate this problem.

However, with SCC, when the flow rate is high, the potential for segregation and loss of entrained air voids increases. This can be fixed by designing a concrete with a high fine-to-coarse-aggregate ratio, a low water-cementitious material ratio (w/cm), good aggregate grading and a high-range water-reducing (HRWR) admixture. Viscosity modifying admixtures (VMAs) also are used to reduce the tendency for segregation and enhance the stability of the air-void system.

For the rigidified FRP tube arches described above, the SCC mix incorporates HRWRs to achieve enhanced flowability, and VMAs to achieve stability, eliminating aggregate segregation. The mix also includes set retarders (for stabilizing hydration), shrinkage reducing admixtures, and 0.375-inch pea gravel aggregate.

In a September, 2011 technical paper from the Illinois Center for Transportation, University of Illinois at Urbana-Champaign, Transfer and Development Links in Prestressed Self-Consolidating Concrete Bridge Box and I-Girders, authors Bassem Andrawes and Andrew Pozolo said the American precast industry has taken significant strides to adopt SCC in commercial projects, though concern about early-age bond behavior has limited the material’s application in prestressed members.

Placement of fiber-reinforced polymer (FRP) deck panels on steel girders of a 125-foot through-truss bridge at Maryland S.R. 24, north of Baltimore, near Rock Creek State Park.

To explore the application of SCC in Illinois bridge construction, Illinois DOT and the Illinois Center for Transportation sponsored a three-phase study investigating the bond behavior of steel strands in pretensioned bridge box and I-girders. In the first phase, 56 pullout tests were conducted to compare the performance of seven-wire strands embedded in SCC to that of strands in conventionally consolidated concrete blocks.

In the second phase, transfer lengths of prestressing strands in two 28-foot SCC hollow box girders and two 48-foot SCC I-girders were determined experimentally. In the third phase, development lengths of strands in the four girders were determined through a series of iterative flexural tests.

They found that pullout test results at various ages showed strand performance in SCC to be comparable with strand performance in the conventionally consolidated concrete.

I-girders were found to perform adequately in both shear and flexure even when the embedment lengths were lower than the predicted development length values, which ranged from 73.9 to 81 inches. “With satisfactory pullout behavior and adequate transfer and development lengths, it is reasonable to conclude that the SCC mixture in this study had sufficient bond to prestressing strands,” the authors conclude.

Defending Use of Fly Ash

The Environmental Protection Agency has taken aim at coal combustion fly ash used in precast and cast-in-place concrete, a move that seriously concerns the people who design and build bridges.

Fly ash is the residue of the burning of pulverized coal in thermal power plants. The ash particles are collected mechanically or by electrostatic precipitators. Fly ash is a pozzolan, meaning it is a siliceous and aluminous material that, in the presence of water, will combine with an activator (lime, Portland cement or kiln dust) to produce a cementitious material, according to Fly Ash Facts for Highway Engineers, a publication of the FHWA and authored by the American Coal Ash Association (ACAA).

Fly ash use on federal-aid highway projects was encouraged by its classification as a “recovered” product under the federal Resource Conservation and Recovery Act (RCRA), which generally mandates use of fly ash in cement or concrete in construction projects using $10,000 or more of federal funds.

The pending EPA classification of fly ash as hazardous waste has the potential to disrupt this accepted use of fly ash in the production of high-performance concrete. But legislation protecting fly ash was approved this October by the U.S. House of Representatives, and at press time awaited action by the U.S. Senate Environment and Public Works Committee.

Five Democrat and five Republican senators have filed the bipartisan Coal Residuals Reuse and Management Act (S.1751), creating national disposal standards for coal ash while protecting the material from a hazardous waste designation.

S.1751 is patterned after the bill of the same name that passed the House of Representatives in mid-October, with 37 Democrats voting yes.

Sen. John Hoeven (R-N.D.) observed that states can manage the disposal of coal byproducts with good environmental stewardship while permitting beneficial uses like building bridges, roads and buildings that are stronger and less expensive.

“Years of research have shown that coal ash should not be regulated as a hazardous waste,” said Sen. Kent Conrad (D-N.D.), a cosponsor of the legislation. “Doing so would only force unworkable requirements on our state’s utilities, resulting in serious economic consequences and the loss of good-paying jobs.”

What percentage of RAP is best? It depends.

Processed, ground reclaimed asphalt shingles await addition to asphalt mix near Waco, Tex., and are a low-volume adjunct to RAP.

T here are powerful inducements today to reuse reclaimed asphalt pavement (RAP) in a variety of applications. And the big question about RAP has shifted from whether it belongs in mixes at all, to how much can safely be accommodated in a mix.

It is this question that is driving an enormous amount of attention and research today. Many road agencies are closely observing the research as they permit higher percentages of RAP in a mix. Environmental legislation at the state level also is compelling higher percentages of RAP.

In the meantime, research continues on the questions of to what degree does the residual asphalt on RAP replace performance-graded (PG) binders; how will larger percentages of RAP impact the type of PG binder that should be specified for a Superpave mix in a particular location; and how important is the processing and analysis of RAP stockpiles in allowing higher percentages of RAP in asphalt mixes.

New guidance was released this year and last from the Federal Highway Administration (FHWA) and the National Cooperative Highway Research Program (NCHRP) on higher amounts of RAP in asphalt mixes.

An abundance of reclaimed asphalt pavement (RAP) – combined with constrained virgin aggregate resources and costly liquid asphalt binder – has caused the industry to define higher levels of RAP in asphalt mixes.

Today, critical-performance mixes – such as those for surface or friction courses – typically get a lower percentage of RAP allowed than the intermediate or leveling courses just below them. It’s being demonstrated that warm-mix asphalt (WMA) modifiers can permit higher percentages of RAP in a mix, and that warm mixes are very friendly to RAP. Use of a rejuvenator can allow vastly higher percentages of RAP in noncritical intermediate courses. And foamed asphalt- or asphalt emulsion-stabilized bases can use 100-percent RAP, as was done in a major recycling project on Interstate 81 in Virginia this year.

In 2009, researchers at the National Center for Asphalt Technology (NCAT) estimated that across the United States, RAP usage varied considerably, but the average RAP content was estimated to be around 15 percent. Boosting that average could reduce greenhouse gas emissions from roadbuilding substantially, National Asphalt Pavement Association (NAPA) president Mike Acott says. “Use of 25-percent RAP reduces total lifecycle greenhouse gas emissions by 10 percent, which equates to 2 million tons [of carbon dioxide] offset annually,” he says.

And more emissions reduction is possible, Acott implies: “A singular quality of asphalt cement in that it is rejuvenated when RAP is incorporated into new pavement, becoming an integral part of the binder. In view of the high reuse/recycling rate in lead states, including a preponderance of evidence that the quality of asphalt pavements incorporating RAP is equal to or better than pavements using all virgin materials, there is ample opportunity to double the quantity of RAP used within five years.”

A late-2010 survey of state DOTs, reported in May 2011 and conducted by the RAP Expert Task Group, reported maximum allowable percentages of RAP in mixes.

Boosting the amount of RAP in mixes is a line item in the National Asphalt Road Map: Commitment to the Future, produced in 2007 by NAPA; FHWA; American Association of State Highway & Transportation Officials; Asphalt Institute; and National Stone, Sand & Gravel Association.

The asphalt road map lists Item No. 4.09: Develop High RAP Content Mix Design Procedure as one of its needed high-priority research projects. The road map also urges study on use of recycled materials other than RAP in asphalt mixes.

A May 2011 survey by RAP Expert Task Group found maximum allowable percentages of reclaimed asphalt shingles (RAS) permitted in asphalt mixes.

“The use of RAP in recycled asphalt pavement is well accepted practice by many federal, state and local agencies,” the road map says. “In many areas, almost all hot-mix asphalt (HMA) contains at least some RAP. However, with a few exceptions, the amount of RAP that can be added in hot plant mix asphalt mixtures is limited to relatively low percentages and in some areas the use of RAP is prohibited in certain types of mixtures, such as surface courses. Typically, the maximum percentage of RAP allowed is anywhere from 15 to 30 percent by weight of HMA mixture.”

The road map anticipates considerably higher percentages being implemented. “Laboratory and field studies have been performed on HMA with much higher percentages of RAP,” the road map says. “These investigations have concluded that HMA materials with percentages in excess of 50 percent can be produced to perform the same as ‘virgin’ mixes. It has been well established that agencies that are not currently allowing RAP into their HMA mixtures and those that are only allowing small percentages of RAP can safely increase the amount of RAP used without fear of shortening pavement life, provided that best practices are followed. . . . [T]he state-of-the-practice relative to the mix design procedures using high RAP content mixes needs to be established.”

RAP millings from Virginia’s I-81 are fed into adjacent portable cold recycling plant to make foamed asphalt base using 100-percent RAP.

To this end, last year, the leaders of trade associations that represent 150 million tons a year of asphalt recycling signed a cooperative agreement aimed at doubling the rate of reuse/recycling of asphalt pavements within five years.

Principal signatories to the agreement were NAPA and the Asphalt Recycling & Reclaiming Association (ARRA). Letters of support were provided by the FHWA and EPA. Under the agreement, NAPA and ARRA pledge to support each other’s efforts to deal with common challenges and build on each other’s strengths regarding asphalt recycling issues.

“Asphalt pavement is America’s most recycled material,” says NAPA’s Acott. “There are more than 18 billion tons of asphalt pavement already in place on the roads, streets and highways of this country. These same roads that Americans use every day are also a resource that future generations can use. Our goal is to increase the rate of recycling even further.”

“Reclaiming and recycling asphalt roads brings America the best possible pavements while conserving precious natural resources,” says Mike Krissoff, executive director of ARRA. “The members of both ARRA and NAPA are proud of the industry’s long track record of delivering quality and value.”

Complications

Efforts to boost RAP usage are restrained by the fact that larger-than-conventional doses of RAP – without binder adaptation – can complicate long-term mix performance.

On Virginia’s I-81 recycle project, foamed asphalt base is produced in KMA 220 portable cold mix plant and is taken immediately to project for placement and compaction as base.

One “rap” against RAP is that its composition varies because it’s sourced from a wide variety of locations. Therefore, advance knowledge of the composition of the residual binder in RAP – along with the separate stockpiling of different varieties, or blending of varieties to create a consistent product – is necessary for creation of reliable mixes.

One way to boost use and consistency of RAP in asphalt mixes is for producers to maintain sheltered, blended RAP stockpiles and, if needed, to reprocess, or fractionate, the RAP into individual gradations. Sheltered stockpiles are favored because RAP doesn’t shed water as easily as virgin aggregate.

The processing, or “fractionation,” of RAP replicates conventional best practices for virgin aggregate processing. With fractionation, RAP is screened, with oversize broken into smaller fractions and each stockpiled separately. Fractionated RAP may result in more uniform mixes, in which RAP fractions can be isolated, in contrast to general stockpiles in which large and smaller fractions may become segregated.

Long ago it was established that RAP was not just a “black rock,” but that its residual asphalt – oxidized and brittle as it is, and in varying amounts – still provides a bituminous portion to the overall mix design, permitting addition of a lesser amount of expensive liquid asphalt binder. The Asphalt Institute (AI)stated components of RAP have value, particularly true of asphalt binder, and the residual asphalt can reduce the amount of new asphalt binder in a mixture. A mix with 20-percent RAP with 5-percent asphalt content can result in a 1-percent savings in new asphalt binder, AI says.

RAP = Stiffer Mixture

Excessive amounts of RAP in the mixture can have substantial effects on pavement performance. Use of 15-percent or more RAP can result in a significant increase in stiffness of the mixture, which can enhance durability. But the use of RAP in hot-mix asphalt also can negatively affect low temperature cracking characteristics of the pavement.

“The aggregate in RAP should be considered as if it were just another stockpile of virgin aggregate,” states the Washington State DOT in an online tutorial. “RAP aggregate properties, as with virgin aggregate properties, may limit the amount of RAP that can be used in a particular mixture.”

The residual binder in RAP must be taken into account when designing a mix, WashDOT says. “The effect of RAP asphalt binder must be considered when using RAP in Superpave mix design (or any mix design),” the tutorial states. “RAP asphalt binder will blend with virgin asphalt binder in most any mix design, and the resulting properties of this blended asphalt binder must be understood.”

The reason is that RAP asphalt binder already is significantly aged because of its previous field life, WashDOT says. “This aged binder is generally stiffer than virgin asphalt binder and thus will cause the resultant binder blend to become more viscous (stiffer),” the tutorial says. “This, in turn, will cause the HMA to be more viscous.”

Therefore, successful RAP mix designs incorporating RAP above 15 percent by weight should analyze the stiffness of the existing residual binder in the RAP, and compare it to the stiffness of the virgin liquid binder, along with the proportions of each in the final product.

In their 2010 Transportation Research Board paper, A Backcalculation Method to Determine “Effective” Asphalt Binder Properties of RAP Mixtures, Thomas Bennert, Ph.D., senior research engineer, Rutgers University’s Center for Advanced Infrastructure and Transportation (CAIT), and Raj Dongré, Ph.D., Dongré Laboratory Services, Fairfax, Va., observe that it’s important to understand the effect that RAP has on the final asphalt mixture performance.

“Current recommendations for the use of RAP in asphalt mixtures follow those developed under NCHRP Project 9-12, Incorporation of Reclaimed Asphalt Pavement in the Superpave System,” they write. These include: no change in binder selection necessary for RAP percentages less than 15 percent; select a virgin binder grade one grade softer than normal for RAP percentages between 15 and 25 percent; and follow recommendations from blending charts when RAP percentages are greater than 25 percent. The results were based on laboratory testing of asphalt mixtures containing approximately 5-percent asphalt binder and using non-fractioned RAP.

‘Tiered’ Approach to Higher RAP

Similarly, New Jersey has taken an incremental approach in raising allowable percentages of RAP in its mixes, with evaluation of the residual RAP binder required for doses higher than 15 percent.

In his 2010 presentation, Higher RAP Mixes in New Jersey: Changes in Mix Design and Production, CAIT’s Bennert describes the efforts that New Jersey DOT is undergoing to incorporate higher levels of RAP in mixes while maintaining pavement durability.

New Jersey DOT has established “tiers” describing increasing levels of RAP in mixes.

• Tier 1: 10- to 15-percent RAP. Asphalt binder grade for the mixture is selected for the environmental and traffic conditions the same as required for a mixture with all virgin materials. With RAP limited to 15 percent or less, it is not necessary to determine the properties of the RAP binder. No [PG] grade adjustment is made to compensate for the stiffness of the asphalt binder in the RAP.

• Tier 2: 16- to 25-percent RAP. The asphalt binder grade can also be selected using an appropriate blending chart if the supplier chooses to adjust the binder selection to compensate for the stiffness of the reclaimed asphalt binder. Extraction and recovery of RAP binder with binder testing is required. Regardless of the method used to select binder grade, adjust binder grade as necessary to meet mixture performance requirements

• Tier 3: 26- to 40-percent RAP. The binder grade for the new asphalt binder is selected using an appropriate blending chart for high and low temperatures. Extraction and recovery of RAP binder and testing is required on a minimum of five samples. Adjust binder grade as necessary to meet mixture performance requirements.

Indiana Justifies More RAP

Use of larger amounts of RAP – and thus changes in a state’s RAP acceptance spec – can be justified by adjusting the type of PG grading used for a Superpave mix, say Matthew Beeson and Michael Prather, Indiana DOT, and Gerry Huber, Heritage Research Group, in their 2011 TRB paper, Characterization of Reclaimed Asphalt Pavement in Indiana: Changing INDOT Specification for RAP.

But doing so requires intensive study of the binder properties in the existing storehouse of RAP across the state, and comparing them to the properties of new asphalt binders being used in the state.

“Interest has been growing to increase reclaimed asphalt pavement usage by increasing the allowable percentage that can be used in hot-mix asphalt,” Beeson, Prather and Huber say. “[Indiana DOT] undertook a detailed evaluation of asphalt binder properties in RAP and the properties of new asphalt binders being supplied to INDOT.”

Asphalt binder was recovered from 33 RAP samples taken across the state, and characterized for low temperature and high temperature grade [for Superpave mixes], they say. “New asphalt binder properties were obtained from more than 200 quality acceptance samples that covered three minus-22 grades and three minus-28 grades,” they said in January. “The data were analyzed to determine the maximum amount of RAP that could be added. Up to 22-percent RAP could be added without changing the original grade of binder. By shifting to a minus-28 grade, the allowable RAP increased to 38 percent. These findings supported the findings of a North Central Superpave Center study on five asphalt plants.”

The result was enough confidence in the existing RAP and its interaction with virgin PG binders that Indiana DOT was able to change its RAP acceptance specs upward. “On the basis of this information, INDOT changed the specification for RAP to allow up to 25-percent binder substitution without changing the normal binder grade of minus-22, and up to 40 percent if the binder was changed to a minus-28 grade.”

WMA and RAP

As WMA is an unfolding technology, its interaction with RAP is being studied in an ongoing investigation. The Effect of Warm Mix Asphalt on RAP in Hot Mix Asphalt is being undertaken by Rutgers’ Bennert and Nazhat Aboobaker of the New Jersey DOT.

The project is intended to determine how RAP can be used at typical and higher percentages in warm-mix asphalt. “One of the critical issues facing warm-mix asphalt is the lack of a formal mixture design procedure,” the researchers say. “If warm-mix asphalt is to replace or be used in conjunction with hot-mix asphalt in the future, a laboratory mixture design procedure for warm-mix asphalt must be established.”

Key issues that will be addressed during the research project are: the appropriate RAP percentages due to potential of decreased RAP and virgin asphalt binder blending with WMA; possible mixture design modifications for WMA technologies and additives, including foamed asphalt; possible recommendations for minimum production temperature and storage times of warm-mix asphalt; and acceptance procedures for allowing the use of current and new WMA technologies and additives. The project began Mar. 1, 2010, and is set to end April 30, 2012.

A Limit to RAP Content?

Use of larger quantities of RAP in highways might be attractive today due to the obvious savings in material costs, but that might lead to trouble “down the road,” say José P. Aguiar-Moya and Jorge A. Prozzi, Ph.D., University of Texas-Austin, and Feng Hong, Ph.D., P.E., Texas DOT, in their January 2011 TRB paper, RAP: Save Today, Pay Later?

In Texas, the DOT allows up to 30-percent RAP in base mixtures and up to 20-percent RAP in surface mixtures. “There are many advantages that are associated with the use of RAP, including economic benefits due to the reduction in virgin asphalt binder and new aggregates required, environmental benefits associated with the use of a recycled material, significant energy savings, and short-term performance benefits due to increased rutting resistance,” the authors say. “However, field observations have raised some concerns in terms of the long-term performance of mixtures containing RAP compared to those of virgin mixes.”

In order to address these concerns, the authors used data from FHWA’s Long-Term Pavement Performance (LTPP) project’s SPS-5 experiment in Texas to quantify and compare the field performance of pavement sections containing RAP to those of those that don’t.

Based on the SPS-5 data, simple performance models were developed for rutting and cracking of the pavement structure. The models were then used to statistically quantify the effect of RAP on each type of distress and to estimate the expected pavement life of a given overlay, with and without RAP.

“As expected, the results indicate that there is a significant gain in rutting resistance when using RAP,” the authors say. “However, pavements containing RAP develop cracking earlier, and at a faster rate, so short-term savings may be offset by additional overlays later in the life of the pavement. This raised the following concern: Are we saving today to pay later?”

The authors conclude that RAP may not be always the most economical solution, and that lifecycle cost analysis is imperative to assess the real benefits and costs of the various alternatives. “The interim results indicate that, under particular scenarios, the use of RAP might not be the most economic choice,” the authors say. “Where and how much RAP should be used should be determined through a case-by-case analysis.”

The authors don’t want to discourage higher amounts of RAP in mixes, but emphasize that pavement designers need to be cautious with the use of RAP and to take into consideration that pavement structures with RAP might deteriorate faster in the long run, mainly in cases where RAP is used in thin overlays.

“Increasing RAP percentages is not always the solution,” they write. “Consequently, it is important that proper deterioration models be developed and calibrated for the different regions where RAP is used so that proper economic analysis is applied for determining whether or not to use RAP in each specific project. Pavement managers should consider that using RAP today may result in initial construction savings, but the long-term maintenance and rehabilitation costs might overshadow these initial benefits.”

ETG Guides RAP Use

Also guiding the effort toward higher percentages of RAP is the Reclaimed Asphalt Pavement Expert Task Group, or RAP ETG. Created in 2007 by the FHWA, the RAP ETG is composed of materials specialists from FHWA, state DOTs, AASHTO, NAPA, NCAT at Auburn University in Alabama, and other stakeholders.

Its mission is to advance the use of RAP in asphalt paving applications by providing information emphasizing the production of high-quality, high-RAP mixtures, the performance of asphalt mixtures containing RAP, technical guidance on high-RAP projects and RAP research activities.

In September 2011, activity of the RAP ETG was the subject of an FHWA Tech Brief titled High Reclaimed Asphalt Pavement Use (the ETG defines high RAP as 25-percent or more RAP in an asphalt mixture by weight of the total mix).

The Tech Brief contains the latest responses to a biannual survey on RAP use conducted by the RAP ETG. With the assistance of AASHTO, the survey was conducted in 2007, 2009 and 2011. “In 2007, the typical hot-mix asphalt mixture contained about 12-percent RAP,” the document states. “From 2007 to 2009, about 27 states increased the amount of RAP permitted in asphalt mixtures, and, as of 2009, 23 states have experience with high-RAP mixtures. As of 2011, the majority of state highway agencies (more than 40) allow more than 30-percent RAP; however, only 11 report actually using 25-percent RAP or more.”

The RAP ETG Tech Brief also lists recent documents that articulate new technical information on higher RAP contents. Download it by searching for “FHWA-HRT-11-057.”

Earlier in 2011, the FHWA rolled out a definitive document that maintains that, based on an evaluation of pavements containing 30-percent RAP through the LTPP program, performance of pavements containing up to 30-percent RAP is similar to that of pavements constructed from virgin materials with no RAP.

The April 2011 report, Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice (Publication No. FHWA-HRT-11-021), provides new guidance on best practices when using RAP, and documented information about long-term performance of high-RAP pavements.

The state of the practice for RAP use across the United States, as well as common challenges for increasing the use of RAP, are identified. Authored by FHWA’s Audrey Copeland, best practices for the use of RAP are presented for developing specs, and for sourcing, processing, stockpiling, testing, designing, evaluating, producing and placing high-RAP mixtures. Ways to attain best performance for high-RAP mixtures are presented. Download the report by searching for “FHWA-HRT-11-021.”

When Politics Drives RAP Use

While other states adopt a tiered approach to higher percentages of RAP, California is using legislation to aggressively adopt higher RAP in HMA specifications.

The California Asphalt Pavement Association (CalAPA) reported in October 2011 that Caltrans’ acting director Malcolm Dougherty says the state transportation department is “moving aggressively” to adopt new standards to permit more RAP usage on state highway jobs.

The pledge comes as assembly speaker pro tem Fiona Ma is pressing Caltrans in legislation to allow up to 50-percent RAP in mixes. In an August 10, 2011 letter to Dougherty, Ma said she was “disappointed” by an earlier letter to her office from Caltrans indicating a lengthy process involved in evaluating a move to a higher RAP standard.

In his official response dated September 5, Dougherty said his department “recognizes the benefits of using a higher percentage of [RAP]. Caltrans is moving aggressively to introduce specifications and guidelines that will incorporate a higher percentage into our projects, while ensuring long-term performance of our paving materials.”

Dougherty announced that the department has accelerated an internal deadline, from June 2012 to November 2011, to develop a specification for 25-percent RAP, which will be incorporated into pilot projects in 2012 and evaluated. Current Caltrans specifications limit RAP to 15 percent of mixes.

“Industry’s reaction to the news was mixed,” CalAPA reports. “On the one hand, industry representatives were glad that Caltrans was recognizing the need to increase RAP limits, but the incremental approach and relatively slow pace of the changes bred frustration.”

CalAPA reported Bill Williams of Bo Dean & Co., an asphalt producer in Santa Rosa, as having said, “There is no known reason why Caltrans should limit high percentage RAP to 25 percent. I believe that 25 percent is achievable without fractionalization, especially when incorporated with warm-mix asphalt technology. Caltrans should not limit our ability to move toward a greener asphalt that creates better roads.”

RAP Basics

Reclaimed asphalt pavement – cold-milled using dedicated, high-performance machines that remove deteriorated pavement, improve overhead clearances and reveal curbs to enhance drainage – is one of the most recycled products in North America.

Stockpiles of RAP are commonplace at asphalt plants and even alongside construction projects. The self-propelled cutting machines mill off aged, cracked asphalt pavement in varying depths and widths, and convey the RAP to dump trucks which haul to stockpiles. From there, RAP is reused as inexpensive road base, added to virgin hot-mix asphalt as a tested material, used for driveways, bike paths, recreational trails and much more.

Asphalt pavement is unquestionably the nation’s most widely recycled product, reports the Asphalt Pavement Alliance, an industry coalition. APA says about 100 million tons of asphalt pavement are reclaimed each year during resurfacing and widening projects, and more than 95 percent of that total is reused or recycled.

Use of RAP saves valuable aggregate resources. While in America there are plenty of construction aggregates in place in the ground, virgin aggregate extraction sites are finding it more and more difficult to obtain mining permits.

Existing quarries or gravel pits once outside of a city now are being overwhelmed by new suburbs and neighbors who don’t like living near quarries and will fight any kind of expansion. This also puts the future supply of virgin aggregates at risk.

But RAP already contains existing aggregates that have been acquired, permitted, shot, loaded, crushed, screened, stockpiled, reloaded and hauled – at great expense – thus their reuse saves time, money and resources. Use of RAP also eliminates costly landfilling of the material, which was the practice prior to the popularizing of RAP use in the last two decades.

Moreover, big jumps in the cost of asphalt and asphalt paving – in addition to increased pressure for an environmentally sustainable transportation infrastructure – have boosted the use of RAP in asphalt mixes. RAP significantly lowers the overall cost of bituminous road mixes while providing substantial environmental benefits.

Higher use of RAP is another way to lower production of greenhouse gases in road construction, said National Asphalt Pavement Association president Mike Acott at a House hearing in 2009.

“Consumption of fuels in the process of acquiring and processing raw materials accounts for a significant share of the greenhouse gas emissions associated with producing asphalt pavement material,” Acott told the House in March. “Therefore, it is possible to reduce greenhouse gas emissions simply by incorporating RAP in new pavement.”

No need for a lowboy to haul this excavator

An excavator capable of reaching highway speeds even greater than those permitted on many local highways? Indeed, says Gradall, announcing its new XL 4100 IV hydraulic excavator comes equipped with the new AutoDrive system, featuring a six-speed automatic Allison transmission. Powered by a 245-horsepower Mercedes Tier 4 Interim engine, the XL 4100 IV reaches highway speeds of 60 miles per hour. Push-button controls in the undercarriage truck cab allow the operator to select between Gradall, “John Deere” or SAE joystick patterns. Once at the jobsite, the AutoDrive’s new transfer case allows the excavator to be remotely repositioned from the seat in the upperstructure cab, at a maximum 5 miles per hour. Introducing a new highly-visible yellow paint scheme, the XL 4100 IV telescoping excavator is available with either a 6×4 or 6×6 drive train. Maximum boom reach at grade is 30 feet 3 inches, maximum dig depth is 20 feet 3 inches and maximum loading height is 17 feet 2 inches. The boom crowd force is rated at 21,940 pounds and, unlike on conventional excavators, remains constant throughout the dig cycle.

Power Pavers

When a full-size slipform paver is too much

With its new compact slipform concrete paver model, Power Pavers is offering an economical solution to a market issue based on material supply. “With the ability to pave up to 7.5 meters (24 feet 7 inches) wide, the SF-1700 was developed to react to the contractor demand for two-pass paving in many highway applications,” says Fred Hite, general manager of the Power Pavers subsidiary of Power Curbers Inc. “In many developing countries, concrete supply is an issue, so paving in two passes is more practical than one pass.” By reducing the engine size and mainframe width of the company’s leading SF-2700 model, Power Pavers was able to develop the SF-1700, which comes standard with a 160-horsepower Cummins engine, 12 Wyco vibrators, and a spread auger and tamper bar. Within a month of introduction, Power Pavers placed units in three countries, says Hite, and “we are getting great reports from our customers who have put them to work.”

Maxwell Products

Meltable crack sealer

Nuvo Gap from Maxwell is a rubberized hot-pour patching material for wide cracks, potholes, rutting and depressed broken-up areas, and around manholes, gutters and drains. It creates a load-bearing, weather-resistant, durable bond. The sealant’s PolySkin packaging is a fully-meltable container that absorbs completely into the product, so there’s no need for opening or cutting.

Progressive Turf Equipment

Mowing where no person should go

Slope-Pro from Progressive Turf Equipment is a remote-controlled, self-contained, tracked mower capable of either rough-cut or finished-cut mowing. It is designed to mow difficult and sloped areas without risk to equipment, terrain or operator, regardless of weather conditions. It features an ultra-low center of gravity for good stability and maneuverability, allowing the mower to cut on slopes as steep as 50 degrees while being remotely operated and realize an increase in productivity over manual cutting.

Vaisala

Free online road calculator for RWIS

The RoadDSS Value Calculator from Vaisala is a free online tool that evaluates potential cost and community savings to using various road weather information systems (RWIS) or road decision support systems. The calculator asks 12 questions about road maintenance operations. Once the user has input infrastructure and cost information, the calculator uses embedded algorithms to produce calculated savings based on referenced study findings. The report provides a breakdown of all direct and indirect cost savings, including safety aspects (such as potential accident reductions) and environmental aspects (such as carbon and other pollutant reductions). A user can adjust any of the information that has been input into the calculator to better tailor their end report.

New Pig

Dust- and grit-free absorbent mats

The Pig Universal Absorbent Mat Pack from New Pig absorbs and retains oil, coolants, water, gasoline, solvents and other liquids. The mat is dust- and grit-free, so it does not contaminate or damage hydraulics, parts or sensors. The mat pack contains three 15-by-20-inch pads. Each pack of three absorbs up to a half-gallon.

Navistar international

Air compressor for Class 4/5 trucks

The Terrastar Underhood kit (V900109) is a VR70 vehicle-mounted air compressor (VMAC) system, delivering 70 cfm and up to 175 psi. Developed for the Class 4/5 International Terrastar vocational truck, the system is said to fill the gap left when GM discontinued the 4500/5500 chassis. At press time, the kit was slated to be available for orders by the end of October.

Cimline

Better routing for cracksealing

The PCR-30 Router from Cimline’s Pavement Maintenance Group has “better routing for better cracksealing,” according to the company. The router, shown at the recent American Public Works Association (APWA) expo, has an electric start, 30-horsepower Kohler engine and a patent-pending, quick-stop, anti-kickback braking system. The drum is sturdy with heavy-duty roller bearings. The machine’s height-adjustable, shock-mounted handles eliminate vibrations. A lower, wider stance provides stability, and start-up and operation are simple. For a walkaround video of the router go to New Road Products in the Better Roads Digital Edition.

Badger Equipment

Self-propelled mounted excavator

The 470 TM from Badger Equipment isn’t a new concept. The truck-mounted telescoping excavator concept has been around since the 1950s. But this mounted excavator is designed to be driven on the highway. At Better Roads press time, production was slated to start Oct. 1 for the 215-horsepower, Tier 3 machine (with Tier 4i production beginning after Jan. 1.). The mounted excavator is a self-propelled machine, with an automatic transmission, and comes in two- and four-wheel drive. “It can be driven from the upper cab or in a ‘creep’ mode from the back of the cab,” Paul Marxen, Badger Equipment sales and marketing manager, told Better Roads at APWA. For a walkaround video go to New Road Products in the Better Roads Digital Edition.

Atlas Copco

Stands up to heavy-duty construction

Atlas Copco’s XAS 750 JD7 Tier 4a rotary-screw portable compressor generates 750 cfm of free air delivery at normal working pressure and 100 psi at normal working pressure. Powered by a 200-horsepower John Deere six-cylinder diesel engine, it is Tier 4a compliant and designed for heavy-duty construction environments. The XAS 750 JD7 has an air receiver capacity of 16.7 gallons. With a fuel tank capacity of 78 gallons, the electronically-controlled, water-cooled engine has fuel consumption of 8.2 gallons per hour at 100-percent load. This offers a significant improvement over the previous model. In order to meet the new Tier 4a emission standards, the engine uses Exhaust Gas Recirculation (EGR) technology to reduce NOx (nitrogen oxide) emissions. A particulate filter is then used to remove the increased amount of particulate matter.

Pexco/Davidson Traffic Control Products

Traffic bollards that never rust

X-Last polyurethane composite bollards from Davidson Traffic Control Products, a division of Pexco, fully comply with the function of preventing vehicles from entering prohibited zones. The bollards’ extreme flexibility makes them nearly impossible to break, and when hit and knocked down they return to their full, original upright form, according to the manufacturer. The bollards are solid color throughout and never need painting or refinishing, and because they are plastic, they do not rust.

Cargill

Deicing the white stuff the green way

Cargill has received the “Design for the Environment” (DfE) designation from the U.S. Environmental Protection Agency (EPA) for its ClearLane enhanced deicer, a green-colored deicing product. Traditional sodium chloride has been enhanced with a blend of salts and organic additives to provide increased performance while reducing the user’s environmental impact. Lab data and customer usage experience show this composition can help lower the amount of salt used per application by 30 to 40 percent, according to Cargill, which means less salt is distributed into the environment when compared to regular road salt.

GVM Snow Equipment

Four-wheel steering, three modes

GVM Snow Equipment’s PowerPlatform multi-purpose machine maintains a road-legal 102-inch tire width and can reach road speeds up to 45 mph. The four-wheel-drive machine offers four-wheel steering with three steering modes: front steering, coordinated steering and crab steering. The unique frame design allows the PowerPlatform to turn with a 9-foot-shorter radius than a pickup truck, allowing the vehicle to turn around on a two-lane road intersection and maneuver through cul-de-sacs. The forward-mounted cab features floor-to-ceiling glass and carries 26,000 pounds of cargo at 45 mph, and 44,000 pounds at lower speeds. Powered by a 260-horsepower Cummins 6.7L Tier III engine mated with a ZF six-speed power shift transmission, the PowerPlatform possesses an efficient mechanical drive train. A 43-gpm hydraulic accessory flow is standard. For an interview by Better Roads editors and video walkaround of a control system from GVM, go to youtube.com/user/BetterRoadsmag#p/u.

Nanotech era draws closer

By Tom Kuennen, Contributing Editor

Nanotechnology offers long-term promise to boost performance of our highway, road and bridge infrastructure. New research is expanding and new applications are materializing. More recently, the long-term environmental impacts of nanomaterials are being studied. But implementation is going to take a long time.

The impact of nanotechnology on highway, road and bridge transportation infrastructure is just beginning. Nanotechnology involves the characterization, engineering and fabrication of matter at the molecular nanoscale, to improve existing products and to make feasible new materials and processes.

Nanoscale crystal seeds speed up concrete hardening. BASF’s X-Seed hardening accelerator makes additional heat superfluous and the concrete is particularly strong and durable. Magnification 960:1 (by 12 cm in width).

Nanotechnology embraces the nanoscale; that is, the range of dimensions from approximately 1 nanometer to 100 nanometers (1 to 100 billionths of a meter). One nanometer is 100,000 times smaller than the width of a human hair. That’s a molecular domain in which devices and systems exhibit properties that aren’t seen at larger scales. In that domain of quantum physics, clusters of atoms and molecules exhibit properties quite different from those found at larger scales. These properties have applications for pavement and bridge infrastructure.

“Nanotechnology should not be implemented in the pavement engineering arena merely because it is a new technology,” states Wynand Jacobus van der Merwe Steyn, Department of Civil Engineering, Tshwane University of Technology, Pretoria, in his paper, Development of Auto-Luminsecent Surfacings for Concrete Pavements. “[T]he application of nanotechnology should allow the engineer to deliver a better product to the client. This may, for instance, be a more cost-effective product, a more technologically suitable product or a safer product.”

Nanotechnology can focus on improving the general properties (e.g., strength, durability) of current materials, the ability to use marginal materials, or the novel application of nanotechnology to enable a safer transportation environment, Steyn says.

Nanomaterials and Construction

Nanomaterials offer significant advantages for the construction industry at large, from making more durable concrete to self-cleaning signs or windows. “The advantages of using nanomaterials in construction are enormous,” says Pedro Alvarez, chair of the Department of Civil and Environmental Engineering at Houston’s Rice University. “When you consider that 41 percent of all energy use in the U.S. is consumed by commercial and residential buildings, the potential benefits of energy-saving materials alone are vast.”

But widespread use in building materials comes with potential environmental and health risks when those materials are thrown away. Those are the conclusions of a study published by Rice University engineering researchers in the July 2010 issue of ACS Nano.

“[T]here are reasonable concerns about unintended consequences,” Alvarez says. “The time for responsible lifecycle engineering of man-made nanomaterials in the construction industry is now, before they are introduced in environmentally relevant concentrations.”

In fact, in a 2010 report, Nanomaterials in the Construction Industry: A Review of Their Applications and Environmental Health and Safety Considerations, Alvarez and co-authors Jaesang Lee, a postdoctoral researcher at Rice, and Shaily Mahendra, an assistant professor at UCLA, find that nanomaterials will likely have a greater impact on the construction industry than any other sector of the economy, following biomedical and electronics applications.

Nanomaterials, they find, can strengthen both steel and concrete, keep dirt from sticking to windows, kill bacteria on hospital walls, make materials fire-resistant, drastically improve the efficiency of solar panels, boost the efficiency of indoor lighting and even allow bridges and buildings to “feel“ the cracks, corrosion and stress that will eventually cause structural failures.

But the authors warn of potential adverse health and environmental effects of widespread use of nanomaterials. In some cases, the very properties that make the nanomaterials useful can cause potential problems if the material is not disposed of properly. For example, titanium dioxide particles exposed to ultraviolet light can generate molecules called “reactive oxygen species“ that prevent bacterial films from forming on windows or solar panels. This same property could endanger beneficial bacteria in the environment.

FHWA Coordinates Research

The Federal Highway Administration (FHWA) has been studying applications of nanotechnology to highway infrastructure for more than a decade.

In 2009, FHWA’s Exploratory Advanced Research (EAR) program hosted a workshop to identify interests and capabilities for nanoscale research that can be applied to highways. The workshop attracted experts from FHWA, university transportation research centers, federal labs and other organizations that are conducting nanoscale research.

The workshop helped shape the scope of FHWA’s further investment in nanoscale research, and supported the development of strategic roadmaps that could outline funding needs for future nanoscale research for highway infrastructure.

“We expect the nanoscale workshop to lead to an overall increase in research targeted at highway program needs,” says David Kuehn, EAR program team director at FHWA. “The workshop was an ideal opportunity to collaborate and leverage nanoscale technology that is being developed for other industries and to accelerate our ability to solve long-term highway research questions.”

“There are multiple potential nanoscale applications in highways,” FHWA says in a 2010 report on the workshop, Nanoscale Approaches for Highway Research. “For example, concrete is a material containing pores on a nanoscale, a result of the chemical reaction between cement and water. Repeated exposure to deicing chemicals causes oxidation, cracks and long-term deterioration to occur in the structure. Utilizing nanotechnology to create smart self-healing materials and structures could lead to less-frequent and faster construction, as well as to increased durability and improved performance, all helping to prevent catastrophic failure.”

Nanotechnology’s ability to produce minuscule MEMS, or microelectronic and mechanical systems, would permit stakeholders to constantly monitor materials, and also could offer improved predictive performance models. “During construction, nanotechnology can allow for embedding increasingly smaller sensors throughout a structure or pavement,” FHWA says. “These sensors could be used for long-term monitoring of corrosion and could offer an invaluable tool in monitoring bridges. By using a car-mounted data reader, information from the embedded sensors could then easily and safely be collected as the vehicle passes.”

As Alvarez, Lee and Mahendra observe, some of this research should be aimed at the environmental aspects of widespread use of nanotechnology, FHWA says. There is concern that unleashing these products on a widespread basis could have unanticipated consequences like something out of a science fiction novel.

Yet nanotechnology in transportation infrastructure also offers environmental benefits, FHWA observes. “[Nanomaterials have the] ability to monitor mobile source pollutants during construction and operations by using nanoscale devices to bind with road-based pollutants,” FHWA says. “Low-cost environmental sensors could monitor the air, water and soil quality, and the technology could allow large-scale monitoring of the operation to continually map pollution levels.”

In a new line of research, nanomaterials such as thin-film technologies may boost use of recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP), in addition to reducing alkali-silica reactivity (ASR) in concrete.

“Nanoscale research could lead to an increased use of recycled materials in pavements through a better understanding of bonding at the boundaries of different materials and the design of very thin coatings to improve the workability and durability of recycled materials, which would also help to reduce costs,” FHWA says. “Nanoscale research also could result in the development of smaller, lower-cost sensors, which would use substantially less energy. Self-powered sensors also would contribute to the efficiency and reduced environmental impact of the highway network.”

Concrete Leads Nanoresearch

By far, the most activity in nanotechnology research for pavement and bridge infrastructure has taken place in the concrete industry. There, research is aimed at optimizing concrete strength and durability using nanomaterials, and condition monitoring via MEMS imbedded in the concrete matrix.

For years, the minuscule size of a particle of microsilica admixture has benefited concrete, as the smaller the silica particle size, the greater the surface area that is presented for reaction within the curing concrete. The much smaller size of nanoparticles now makes possible a geometric increase in performance, and that’s one of the areas of research.

Research in concrete nanotechnology has been well-organized. A workshop at the University of Florida in August 2006 was attended by more than 70 participants, with more than 30 presentations, and focused on the development of a Roadmap for [Nanotechnology] Research for Concrete-Based Materials. The roadmap is destination-oriented, with clearly defined outcomes that will greatly enhance concrete technology and the uses of concrete in structures, including housing, bridges, tunnels and pavements.

That 2006 roadmap identifies research needs such as:

• development of high-performance cement and concrete materials as measured by their mechanical, durability and shrinkage properties;

• development of sustainable and safe concrete materials and structures through engineering concrete for different adverse environments, reducing energy consumption during cement production, and enhancing safety with nanoengineering of concrete materials;

• development of intelligent concrete materials through the integration of nanotechnology-based, self-sensing and self-powered materials and cyber infrastructure technologies;

• development of novel concrete materials through nanotechnology-based innovative processing of cement and cement paste; and

• development of fundamental multiscale model(s) for concrete through advanced characterization and modeling of concrete at the nano-, micro-, meso- and macroscales.

The workshop was followed with a September 2007 conference in Arlington, Va. And, in 2008. a Center for Nanotechnology in Cementitious Systems (CNCS) was created at Iowa State University. The CNCS uses nanotechnology to improve sustainability and performance of concrete roads and structures. The cross-disciplinary nature of the center opens the door to exciting research in this new area, including nano devices that could one day monitor and report on the state of hydration in a mixture and correlate that with the risk of cracking, or predict when traffic can be placed on a pavement.

Other nano-based materials or devices could be used to modify or control the rate of hydration to allow for changes in construction practices or prevent weather-related damage during construction, CNCS says.

In the future, CNCS researchers hope to support 10 graduate students through research projects. Initial projects are being developed, including analysis of the effects of shrinkage-reducing admixtures on the morphology of hydrated cement paste and the properties of air voids entrained in the mixture.

Finally, in May 2010, the First International Conference on Nanotechnology in Cement and Concrete was held in Irvine, Calif. More than 100 delegates from 17 countries and 27 states heard 37 technical papers covering nanotechology in concrete.

Concrete Nanoscale

Nanomaterials can boost strength and resistance to permeability in concrete, according to Celik Ozyildirim, P.E., Ph.D., principal research scientist, and Caroline Zegetosky, graduate research assistant, Virginia Transportation Research Center (now Virginia Center for Transportation Innovation and Research), in their paper Exploratory Investigation of Nanomaterials to Improve Strength and Permeability of Concrete.

“Concrete containing various supplementary cementitious materials (SCMs) such as silica fume, fly ash and slag has improved properties,” they write. “Nanomaterials, new SCMs with possible applications in concrete, have the smallest particle size (less than 100 nm). Nanomaterials are reactive because of the small size and large surface area of the particles, and they have great potential in improving concrete properties such as compressive strength and permeability.”

Ozyildirim and Zegetosky studied a variety of nanomaterials in concrete and compared them to conventional concrete, and concrete containing common SCMs. “The potential benefits of using nanomaterials over other SCMs are high reactivity and cost-effectiveness; in addition, smaller amounts are necessary, resulting in less cement replacement,” they write.

Concretes containing nanosilica and nanoclay were prepared in the laboratory, and compared to concretes containing conventional silica fume, fly ash, slag or only Portland cement. Specimens were tested for compressive strength and permeability. The microstructure of selected concretes with improved compressive strength and permeability was analyzed to explain the improvements.

“The results of this study indicate that some of the nanomaterials tested have potential in concrete applications,” Ozyildirim and Zegetosky write. “The microstructure of the nanosilica concrete was denser and more uniform than the conventional concrete microstructure. In addition, the nanosilica had the largest improvement in both compressive strength and permeability among the nanomaterials tested.”

Download their study from the Virginia DOT at virginiadot.org/vtrc/main/online_reports/pdf/10-r18.pdf

Nanocrystals and Concrete

The private sector has been quick to lead the way to nano-enhanced concretes. For example, a new product, X-Seed crystals from BASF, makes concrete cure faster and reduces carbon emissions.

X-Seed has innovated production of precast-concrete components by serving as a curing accelerator, which the company says not only allows precast concrete units to be produced more rapidly and in better quality, but considerably reduces energy consumption and the associated emission of carbon dioxide (CO2) greenhouse gas.

Cement is produced by pyroprocessing limestone, clay and minerals at high temperatures to produce cement clinker. Pyroprocessing consumes enormous amounts of energy, and releases large amounts of CO2 from combusting the fuel (principally coal or natural gas) and from the chemical reaction the combustion enables. Finally, the coarse-grained clinker is ground into a fine, gray cement powder that hydrates after mixing with water. Calcium silicate hydrate and other compounds crystallize out of the cement during this process to form a compact stone matrix in which aggregates and sand are embedded.

Concrete products are manufactured by placing the uncured concrete mix into forms. Only when the concrete has cured sufficiently can the mold be opened and the component removed. At ambient temperatures (68 degrees F) it can take up to 12 hours to cure, which is valuable production time, during which the formwork cannot be reused. To speed production, the mold often is heated with steam. Although this accelerates production, it also demands much additional energy. Moreover, this treatment can lead to internal thermal stresses, discolorations and a coarser surface of the finished concrete part.

“X-Seed makes heat curing, with all its disadvantages, largely superfluous,” says Dr. Michael Kompatscher, responsible for BASF’s European precast concrete component market. “With this additive, concrete hardens just as fast at 20 degrees C (68 degrees F) as it otherwise does at 60 degrees C (140 degrees F), by a adding something that’s already present in the concrete anyway – calcium silicate hydrate (CSH).”

Countless millions of tiny CSH crystals with a diameter of several nanometers are suspended in liquid in X-Seed, BASF says. Because of their nanosize, more very homogeneously distributed crystallization seeds can be accommodated in the same mass, and thereby promote faster growth. When the concrete cures, further molecules from the cement can attach themselves to these CSH “seeds.” The resulting crystals grow more densely and finally interlock to form the compact cement stone.

When conventional cement hydrates, the CSH seeds first have to form spontaneously from several molecules released from the cement, which accidentally come into contact with each other. X-Seed negates this first barrier to crystallization by providing an excess of these tiny crystal seeds. Another factor is that the CSH crystals form in a more homogeneously distributed manner.

Both these effects of the synthetic crystal seeds halve the time to formwork removal at 68 degrees F from about 12 to six hours, without any detectable differences in the final product, BASF says.

Zeolites and WMA

Warm-mix asphalt (WMA) technologies are a family of processes that produce low-energy asphalt mixes that can be placed at significantly lower temperatures than conventional hot-mix asphalt. At least one additive for warm-mix asphalt operates at the nanoscale, Aspha-Min.

Zeolites are nanoporous crystalline alumino-silicates with important attributes. A zeolite is a constituent of a group of commercially valuable minerals – metamorphosed crystals of hydrated aluminum silicates – of interest to industry for a variety of applications. Zeolites have large vacant spaces or cages in their structures that allow space for large, positively charged ions such as sodium and potassium, and even entire molecules such as water.

Aspha-Min is a synthetic zeolite compound, which releases water (H20) into the asphalt mix to improve workability at lower temperatures. Aspha-Min is available as a very fine, white-powdered form in bags or in bulk for silos. The percentage of water held by the zeolite is 21 percent by mass and is released in the temperature range of 212 to 392 degrees F.

By adding 0.3-percent Aspha-Min to the preheated mixture of sand and stone at the same time liquid asphalt is being introduced, a water-based vapor is created. The water released from the crystal causes the binder to expand to a kind of foam, permitting better workability and coating of aggregates at lower temperatures. Tests indicate that 54 degrees F reduction in temperature equates to a 30-percent reduction in fuel energy consumption.

Thanks for the MEMS

Nanotechnology for transportation infrastructure goes beyond engineered materials, into appliances manufactured at the nanoscale. These nanotechnology-driven sensors and instruments – microelectronic and mechanical systems, also called microelectromechanical systems (MEMS) – have the ability to detect motion and monitor corrosion, cracking and performance of structures and pavements under service loads and conditions.

In their 2008 paper, Applicability of Microelectronic and Mechanical Systems (MEMS) for Transportation Infrastructure Management, investigators Kelvin C.P. Wang and Qiang Li, Department of Civil Engineering, University of Arkansas-Fayetteville, describe the application of MEMS for pavements and bridges.

“With the tremendous advancement in technology, it is possible to employ devices embedded in structural members for real-time monitoring of infrastructure health,” they say. “Micro-electromechanical systems are miniature sensing or actuating devices [that] can interact with their environment to either obtain information or alter it. With remote query capability, it appears such devices can therefore be embedded in structures to monitor distresses such as cracking.”

MEMS merge the functions of sensing and actuating with computation and communication to locally control physical parameter at the micro-scale, yet cause effects at much grander scales, they observe. MEMS as devices have static or movable components with some dimensions on the scale of a micrometer, and can be either sensors, actuators or passive structures.

“Sensors are transducers that convert mechanical, thermal or other forms of energy into electrical energy; actuators do the exact opposite,” Wang and Li write. “Passive structures are devices in which no transducing occurs. A fourth classification, hybrid systems, is used for specialized applications. Micromachining and integrated circuit technologies are the foundation of sensors and actuators as well as of MEMS or microsystems.”

MEMS produce smart materials and structures technology, and their applications include structural control, condition or health monitoring, damage assessment, structural repair, integrity assessment and more recently in asset management, preservation and operation of civil infrastructure, they write. “The potential benefit here is improved system reliability, longevity, enhanced system performance, improved safety against natural hazards and vibrations, and a reduction in lifecycle cost in operating and managing the infrastructure. There is no doubt MEMS can . . . assist engineers in infrastructure management to have real-time or quasi-real-time information on the health of the infrastructure.”

In bridges, MEMS technologies are well-suited to improve the performance, size and cost of sensing systems, they say. “MEMS can be used in both monitoring and testing of transportation infrastructure systems,” they write, adding applications in bridge engineering are underway.

In pavements, MEMS have the capability of supplementing, if not replacing, nondestructive testing of pavement condition, they suggest. “Recently, vigorous efforts have been devoted into developing sensing technologies and nano-technology in infrastructure condition monitoring,” write Wang and Li. For crack monitoring purposes, a MEMS transducer has been developed for an ultrasonic flaw detection system, which can be used to detect the initiation of a crack.

Geometrically smaller size of nanoparticles increases the relative surface area available to react with cement in concrete.

Also, networks of nanosensors embedded in roadways could provide real-time information to better manage congestion and incidents, or to detect and warn drivers about fast-changing environmental conditions such as fog and ice. “In recent years, more and more attention has been paid to MEMS-based moisture sensors,” they write. It’s clear that MEMS will play a big role in the intelligent highway systems of the future.

Nanotechnology is leading to self-cleansing signs. The so-called “lotus effect” – which describes the self-cleansing surface of the lotus leaf, which takes place at the molecular level – is being replicated in lotus effect-based self-cleansing nano materials into traffic and work zone signage, and in particular traffic-control devices, which require labor-intensive periodic washing to remove road grime and enhance visibility.

Cleaner air from pavements: Titanium dioxide nanoparticles in both concrete and asphalt pavement surfaces have the ability to remove – via photocatalytic reaction – nitrogen oxides and sulfur dioxide from the atmosphere.

“On a hydrophobic, easy-clean surface, particles of dirt are just moved around by moving water, but on a lotus-effect surface, dirt and grime are collected by water drops and rinse off,” Wang and Li write. “Coatings that mimic the properties of the lotus leaf may well lead to signs that shed dirt and never need washing.”

Thin Film Technologies

Nanoscale research could lead to an increased use of recycled materials in pavements through a better understanding of bonding of different materials, and the design of very thin coatings to optimize use of reclaimed materials.

In their 2010 Transportation Research Board paper, New Possibilities and Future Pathways of Nanoporous Thin Film Technology to Improve Concrete Performance, Jose F. Muñoz of the Department of Material Science and Engineering, University of Wisconsin–Madison, and Richard C. Meininger and Jack Youtcheff of the Pavement Materials and Construction Team at FHWA’s Turner-Fairbank Highway Research Center, find that nanoporous thin films (NPTFs) may improve the interfaces between aggregate and cement paste.

“Aggregates are often considered as inexpensive inert filler material in concrete,” the authors write. “However, the mixture of the aggregate with the cement paste creates one of the most vulnerable areas of concrete, the interface of aggregate and cement paste. The judicious application of nanoporous thin films on the aggregate’s surface is an effective way to improve those interfaces.”

The most recent work on concrete shows that the use of different types of NPTF can induce changes in different properties of concrete or in an aggregate’s mineralogy, the researchers say. The observed improvements in mechanical properties such as compressive, flexural and tensile strengths, modulus of elasticity and drying shrinkage can ameliorate longitudinal and transverse cracking, corner breaks, punchouts and D-cracking, they write.

Improving Traffic Safety

Nanotechnology also has a role in improving transportation safety, according to Satish V. Ukkusuri, Ph.D., assistant professor, and Gitakrishnan Ramadurai, graduate student, Rensselaer Polytechnic Institute, in their 2009 TRB paper, A Comprehensive Review of Emerging Technologies for Congestion Reduction and Safety.

Looking ahead 20 years, the researchers identified future technologies, and focused on nanotechnology, as well as other emerging fields. “Nanosensors have potential to track bioterror agents, stress in materials and detect polluting agents in the atmosphere and tailpipes,” they say. “Nanosensors could be used in transportation to monitor pavement conditions, bridge conditions, pollution deduction, bioterror agent detection and air-quality monitoring.”

The feasibility of “cyberliths,” or “smart aggregates,” as wireless sensors embedded in concrete or soil is being studied. Researchers at Johns Hopkins University’s Applied Physics Laboratory have developed a robust wireless-embedded sensor, suitable for long-term field monitoring of corrosion in rebar, particularly in bridge decks, they say.

“Nanomaterials that are of interest in transportation include carbon fibers that are 100 times stronger than steel, nanocoating of metallic surfaces to prevent corrosion, and nano reinforcements in vehicle bodies, pavements and other transportation infrastructure,” Ukkusuri and Ramadurai write. “Automatic healing materials have potential to be used in guardrails that heal themselves, or concrete or asphalt that heal their own cracking.”

Road Science Tutorial

Nanotechnology Will Transform Infrastructure Will Impact Materials, Monitoring, Maintenance, Safety and Durability

Thin Open-Graded Surfacings Drive Market

By Tom Kuennen, Contributing Editor

Now, more than ever, thin open-graded friction courses (OGFCs) are driving the market for drainable, high-friction, noise-attenuating asphalt mixes.

A thin crumb, rubber-modified, open-graded wearing course is placed on California Highway 1 near Fort Bragg; the mix incorporated a warm-mix additive to ensure workability, following the two-hour drive to the Pacific Coast from the plant.

This new generation of OGFCs is being bolstered by the advent of high-performance “spray” pavers that place thin, polymer-modified OGFCs quickly and with great consistency, and by new materials that halt the potential “draindown” of liquid asphalt within an open-graded mix.

The use of these new OGFCs also is expanding as a result of the general trend toward pavement preservation, as cash-strapped road agencies realize that it’s a lot cheaper to extend pavement life by spending limited funds on preservation techniques at the right time, rather than allow a road to deteriorate to the point of failure, with costly reconstruction the only option.

A conventional OGFC is a layer of asphalt that incorporates a skeleton of uniform aggregate size with a minimum of fines. It features an open aggregate structure in which larger-sized aggregate is held in place by polymer-modified and fiber-modified Superpave performance-graded liquid asphalts. Most OGFCs are 3/4-inch thick, and never thicker than 2 inches.

The OGFC’s open structure of 15 percent or more voids allows water to drain right through the driving or friction course to an impervious intermediate course below, and out into roadside ditches. The result is the near-complete elimination of tire spray and hydroplaning, making a safer pavement and saving lives. It also results in a quieter pavement as noise is attenuated within the gaps between the aggregate. OGFCs should be elevated above the shoulder, as the water drains onto the shoulder and hence to a roadside ditch.

A Variety of Names

Today’s spray-applied OGFCs are known by a variety of names. Oklahoma DOT has expanded the use of what it calls spray-applied ultra-thin bonded wearing courses. In Nevada, they’re known as ultra-thin asphalt concrete surfacings (UTACS, pronounced “you-tacks”), which are gap-graded wearing courses, bonded to the surface by a warm polymer-modified membrane, followed immediately by the hot, gap-graded, ultra-thin asphalt concrete friction layer.

UTACS are similar to Caltrans’ bonded wearing course, “a gap- or open-graded, ultra-thin hot-mix asphalt mixture applied over a thick polymer-modified asphalt emulsion membrane,” to quote the agency. “The emulsion membrane seals the existing surface and produces high binder content at the interface of the existing roadway surface and the gap- or open-graded mix, all in one pass.” Recently, Caltrans has been increasing its use of crumb rubber-modified emulsion for these OGFCs in lieu of polymer modifier.

Such bonded wearing courses are primarily used in high-traffic areas as a surface treatment over hot-mix asphalt or Portland cement concrete pavements. They are placed over structurally-sound pavements as a maintenance treatment, but may also be used in new construction and rehabilitation projects as the final wearing course.

In a bonded-wearing course such as those specified by Caltrans, a polymer-modified asphalt emulsion membrane seals the existing pavement while bonding the gap-graded or open-graded mix to the surface. The thicker nature of the membrane allows it to wick upwards into the mix, filling voids in the aggregate and creating an interlayer of high cohesion that does not delaminate or bleed, if applied correctly.

A predecessor of today’s thin, open-graded wearing course designs is NovaChip, an ultra-thin, bonded, gap-graded wearing course placed by a specialized paver in one pass. This exclusive pavement process applies an ultra-thin hot-mix wearing course over a polymer-rich asphalt emulsion. The process rapidly secures the lift to the existing surface and allows for minimal traffic delays. Originally developed by a French contractor, the patent for NovaChip is currently owned by Colas S.A. and is licensed for use in the United States by Road Science LLC of Tulsa.

But what’s not happening today is an increase in deeper-lift OGFCs. While most states that use them place OGFCs as thin asphalt lifts at 3/4-inch depth or less, the Oregon DOT has been placing 3/4-inch open-graded mixes in structural layers of 2 inches or more for about 30 years, reports Dr. Steve Muench, et. al., at the University of Washington-Seattle, in a June 2011 report for the Oregon DOT. He adds the Washington State DOT has used similar mixes since the early 1990s, although more sparingly. Due in part to the damage done to OGFCs by studded tires used in Oregon, the report recommends that use of 3/4-inch OGFCs be discontinued in the state (see below).

OGFCs for Cold Weather?

Typically, OGFCs tend to be confined to states without severe winters, as it’s perceived that water trapped within the drainable layer can expand and cause the open-graded layer to ravel, or create dangerous icing, leading to accidents.

One cold weather state, Wisconsin, recently looked at OGFCs as used and discontinued by northern-tier states and provinces, and received a recommendation that it not proceed.

“OGFC has historically not been used in Wisconsin due to concerns about its performance in a climate with a large number of freeze-thaw cycles,” says Richard E. Root, P.E., Root Pavement Technology, in his 2009 Wisconsin Highway Research Program report, Investigation of the use of Open-Graded Friction Courses in Wisconsin. “Questions also exist about the cost/benefit of these mixtures.”

The study’s primary objectives were to determine if the OGFC mixture could be successfully used in the Wisconsin climate. After a literature review that listed many northern-tier states that had started “new generation” OGFCs, but had since discontinued them, Root concluded that Wisconsin should avoid them.

“While the use of OGFC mixtures in warm southern climates has been successful, this pavement has not proven to have the same successes in the northern freeze/thaw environment,” Root says. “None of the states or Canadian provinces with climates that duplicate Wisconsin’s use OGFC mixtures. On a routine basis, it is recommended that Wisconsin should not currently build pavements with an OGFC surface.”

This summer, Oregon had reason to abandon OGFCs altogether. In June, a technical report – Open-Graded Wearing Courses in the Pacific Northwest: Final Report by Stephen T. Muench, Ph.D.; Craig Weiland; Joshua Hatfield and Logan K. Wallace of the Department of Civil and Environmental Engineering, University of Washington – suggested that use of the 3/4-inch open-graded hot-mix asphalt (previously referred to as “F-Mix”) be curtailed.

“The best estimated service life of [Oregon] DOT 3/4-inch open-graded HMA ranges from 14 years (< 5,000 ADT) down to seven years (> 100,000 ADT), which is less than comparable dense-graded mixes,” Muench and researchers wrote in June. “The primary mode of distress is raveling and studded tire wear. Reduced service life, along with uncertain and unquantified safety benefits and a possible greater risk of early failure lead to a recommendation to discontinue use of 3/4-inch open-graded HMA in Oregon as a standard surface mix.”

Open-graded wearing courses used elsewhere in this country are not likely suited for use by Oregon DOT, due to their susceptibility to studded tire wear, they say, and the writers don’t recommend their adoption. “If 3/4-inch open-graded HMA does continue in use,” the writers say, “recommendations are [to] quantify its benefits, restrict its use to low-traffic routes (< 30,000 ADT), recalibrate the state’s pavement management system’s expected life to be more in line with observed historical life, and require the use of a windrow pick-up machine or end-dump transfer machine when paving OGFCs.”

Download the new research at http://ntl.bts.gov/lib/41000/41300/41329/SPR680.pdf

Binder Modification Key

Open-graded friction courses have been used since 1950 in the United States to improve the frictional resistance of asphalt pavements, promote drainage of water from pavement and thus reduce tire spray, and reduce noise from the tire/pavement interface.

Spaces within the “open-graded” or “gap-graded” mix — and amounting to as much as 20 percent of the mix or more in some European mixes — help drain water and attenuate tire noise.

OGFCs are attaining a new popularity as states take a look at refined mix designs incorporating additives like polymer modifiers, rubber asphalt, fibers and hydrated lime. But it wasn’t always this way.

Prithvi S. “Ken” Kandhal and Rajib B. Mallick of the National Center for Asphalt Technology (NCAT) at Auburn University published a 1998 survey, Open-Graded Asphalt Friction Course: State of the Practice. The survey showed that, when these pavements were introduced in the 1950s, some states had problems with them. Improvements in OGFCs have made a vast difference. “These improvements have been achieved with the help of good design and construction practices,” they write.

The secret is modification of the asphalt binder. “A vast majority of agencies report good experience using modified asphalt binders,” Kandhal and Mallick say.

Georgia’s experience reflects the OGFC survey. “Early mixes used were very susceptible to premature failure due to weathering,” state Georgia DOT researchers in the DOT’s Progress in Open-Graded Friction Course Development, presented at the Transportation Research Board annual meeting in 1998.

Because of early problems, Georgia put a moratorium on OGFCs in 1982. Likewise, Washington State DOT tried smaller stone-sized (3/8-inch) mixes as thin (0.15-foot) wearing courses in the 1980s and early 1990s, but discontinued their use because of excessive studded tire wear problems.

Porous asphalt pavement is similar to open-graded friction courses (OGFC) but is meant for static loads and environmentally-sustainable stormwater drainage. A mix for the parade ground at U.S. Marine Corps Recruit Depot at Parris Island, S.C., contained Evotherm warm-mix additive instead of fibers.

But in the 1990s, Georgia developed a mix that incorporates a high degree of single-sized coarse aggregate, polymer-modified asphalt binder, stabilizing fibers and hydrated lime.

“This mix has been used extensively statewide since 1993,” the DOT reports. Now Georgia, pleased with its success, is urging other state DOTs to reassess OGFCs. “[Agencies] should reconsider the possibility of using this modified OGFC on high-volume-traffic facilities,” they say. “It is now Georgia DOT policy to use modified OGFC as the final ride surface on all Interstates and on state route projects that have daily traffic volumes exceeding 20,000 and are not in a reduced speed zone area.”

Modified vs. Standard Binders

After Georgia, use of polymer-modified — and more recently, rubber-modified — binders for OGFCs has become common. But the use of polymer or crumb rubber modifiers in OGFC binder may come at a cost: the ability of the pavement to drain water, at least in 4.75-mm nominal maximum aggregate size (NMAS) mixes.

That’s what Qing Lu, assistant professor, Department of Civil and Environmental Engineering, University of South Florida, and John T. Harvey, professor, Department of Civil and Environmental Engineering, University of California-Davis, say in their 2011 Transportation Research Board paper, Laboratory Evaluation of Open-Graded Asphalt Mixes with Small Aggregates and Various Binders and Additives.

Their paper is part of ongoing research to develop alternative asphalt surface mixtures that are quieter and durable without much sacrifice of safety, they say.

Five binder types (PG 64-16, PG 58-34PM, PG 76-22PM, asphalt rubber and PG 76-22TR) and two additives (hydrated lime and cellulose fiber) were selected for a 4.75-mm NMAS gradation, they write. A series of laboratory tests were conducted to evaluate their pavement surface performance-related properties, including acoustic absorption, texture, resistance to raveling, moisture sensitivity, permeability, friction, resistance to permanent deformation and resistance to reflective cracking.

“Results show that using polymer-modified or rubberized binders instead of unmodified binder in the 4.75-mm NMAS open-graded mixture reduces permeability,” they write, “but increases acoustic absorption, with the mixture containing asphalt rubber binder showing the most acoustic absorption improvement.”

Using asphalt rubber also can enhance the mix’s resistance to moisture damage or premature failure, raveling, rutting and potential resistance to reflective cracking. “There are also preliminary indications of friction improvement by replacement of conventional binder with asphalt rubber binder in the small-size aggregate open-graded asphalt mix,” Lu and Harvey say.

Rubber-Modified OGFC Binders

Rubber-modified binders for OGFCs now are seen on the west coast (California) and the east coast (South Carolina), as well as in the epicenter in Arizona.

On Napa Valley’s Silverado Trail, a specialized paver places tack coat at the rate of 0.17 to 0.20 gallons per square yard in advance of rubber-modified open-graded friction course.

Modified asphalt cement binder is required in OGFCs to prevent draindown of the binder and achieve the necessary level of adhesion and mix stability, reports the Asphalt Rubber Technology Service (ARTS) at Clemson University. “Although typically a polymer is used as the modifying additive to the asphalt cement binder, crumb rubber made from scrap tires may also be used as an alternative modifier,” according to the university.

The South Carolina rubber-modified open-graded friction course is placed 3/4- to 1-inch deep, with a crumb rubber content of 12 percent by weight of the liquid asphalt, or 0.85 percent by weight of the mix.

There, OGFC can be placed on either asphalt or concrete pavements, and it consists of roughly 93-percent crushed stone, 7-percent modified asphalt binder and a small amount of stabilizing fibers, Clemson’s ARTS says.

A next-generation polymer-modified open-graded friction course is placed on a Clark County, Nev., street.

“Rubber-modified open-graded friction course has all the same advantages as polymer-modified OGFC,” ARTS says. “Compared to concrete and standard asphalt dense-graded pavements, it has significantly lower noise levels, it has less surface water in wet weather, and it is generally safer in wet weather due to the better visibility and decreased hydroplaning, resulting from the lack of surface water on the pavement surface.”

In addition to sharing all the advantages of OGFC with its polymer-modified counterpart, rubber-modified OGFC also costs slightly less than conventional polymer-modified OGFC, ARTS says, adding when used in OGFC, scrap tires can be used at a rate of approximately 1,000 tires per mile of two-lane pavement.

Fighting Draindown with Fibers

While modifiers will help keep liquid asphalt binder from moving within an open-graded mix, it still may puddle at the bottom of a haul truck, or settle lower in the lift of mix just placed. This “draindown” of asphalt seriously compromises the durability of OGFCs.

The problem of draindown of liquid asphalt is solved by use of fibers – typically cellulose, but also mineral filler – which are used to hold the binder in place.

Tack coat eliminated: Movable bars spray polymer-modified emulsion tack coat in advance of thin-lift open-graded UTACS friction course in Clark County, Nev.

While cellulose fibers are most often used, new research indicates that polyethylene fibers may do the same thing in OGFCs. In the technical paper Characterization of OGFC Mixtures Containing Reclaimed Polyethylene Fibers written by V.S. Punith, of the Asphalt Rubber Technology Service at Clemson University, and A. Veeraragavan, Department of Civil Engineering, Indian Institute of Technology, Madras, and published last year in the Journal of Materials in Civil Engineering, it was reported that polyethylene fibers derived from recycled low-density polyethylene (LDPE) tote bags performed in OGFC mixes.

Polyethylene fibers recycled from LDPE bags collected from domestic waste improved OGFC mixes without fibers, they say. “Draindown test results indicated that OGFC mixtures with polyethylene fibers can be effectively used to retard draindown of the binder and mineral filler,” they write. “[T]est results indicated that OGFC mixtures with reclaimed PE fibers showed improvement in tensile strength and improved resistance to permanent deformation, fatigue-induced damage, and moisture susceptibility, when compared with mixtures without fibers.”

Draindown in Porous Mixes

While porous asphalt pavements are open-graded to encourage water drainage, they differ from open-graded friction or wearing courses by structure and function. Yet, they pose many of the same challenges as OGFCs, including binder draindown.

Porous asphalt pavement is an environmentally-sustainable infrastructure design that helps property owners manage stormwater effectively and inexpensively. They are specified for static traffic areas such as parking lots, and aren’t suitable for wearing courses.

Typically, a porous asphalt pavement will be composed of, from the bottom, an uncompacted soil subgrade that will optimize infiltration of water into the aquifer; a geotextile fabric that will permit water to pass but preclude movement of fines up into the structure; a stone recharge bed with same-sized aggregate and 40 percent voids; an optional stabilizing or “choker” course of single-size crushed stone smaller than that in the recharge bed; and an open-graded asphalt surface with 20-percent voids that permit stormwater to flow through the pavement into the stone recharge bed.

While OGFCs shoot for voids of 15 percent to control spray and noise, porous asphalt pavements let water drain directly into a recharge layer below, and the air-void target is 20 percent. The porous asphalt “green grinder,” or parade ground, constructed at the U.S. Marine Corps Recruit Depot at Parris Island, S.C., in May 2011 was not intended to reduce spray, hydroplaning or noise, but simply to provide the most efficient means of draining water from the paved surface and into the soil, while avoiding conventional detention ponds.

While fibers conventionally are used to stabilize porous asphalt mixes, an innovative warm-mix asphalt design for Parris Island saved money by eliminating fibers required for stability of the open-graded mix. The porous asphalt design also eliminated the expense of creating a detention pond and associated environmental requirements.

The elimination of fibers from the Parris Island mix was achieved by use of a warm-mix asphalt additive, Evotherm 3G from MWV Asphalt Innovations, which adds lubricity to individual microscopic asphalt particles, permitting production of asphalt at significantly lower temperatures than conventional mixes.

Evotherm stops the draindown of liquid asphalt by virtue of the lower mixing temperature it enables. “We were able to make the mix at 285 degrees F, instead of 350 degrees, which completely eliminates the problem of draindown,” says Dean Frailey, business development manager, MWV Asphalt Innovations. The mix was emerging from the truck at approximately 275 degrees and from the screed at about 245 degrees. No liquid asphalt was visible in the truck bed as mix was fed to a material transfer vehicle ahead of the paver.

CRM Binder in California

Crumb rubber-modified binder was used recently for an ultra-thin, open-graded wearing course in California’s Napa Valley. In the town of Napa, a 10-year-old asphalt overlay on the Silverado Trail was showing signs of wear over a 2.9-mile section. There was minor cracking, some raveling and a few areas required full-depth asphalt patching. But for the most part, the road was in good shape; it was structurally sound.

To preserve the road and extend its life, Caltrans turned to an ultra-thin bonded wearing course. In this process, a Roadtec SP-200 paver sprays a tack coat down just in front of the spreading augers, and the screed levels off a 3/4- to 1-inch-thick layer of open-graded hot mix.

On California Highway 50 between Placerville and South Lake Tahoe, an ultra-thin bonded wearing course lasted seven years, says Brian D. Toepfer, maintenance engineer, Caltrans. “I think it [performs] better than a mill-and-fill, and it is a lot less expensive.”

On the Silverado Trail, the Construction Division of Telfer Oil, Martinez, Calif., used the specially-equipped paver to spray down a heavily polymer-modified emulsion at a rate of 0.17 to 0.20 gallons per square yard. “The emulsion is similar to a PMCRS-2H emulsion, which is a standard chip sealing emulsion,” says Karl Meyers, general manager of Telfer’s Construction Division.

The paver immediately followed the emulsion with a 7/8-inch-thick layer of open-graded hot mix made with PG 64-16 liquid asphalt that was modified with crumb rubber. The target value for binder content was 8.5 percent, and the top-size aggregate in the mix was 3/8 inch. It also contained a small amount of sand.

Static compaction with two double-drum rollers followed the paver. “You have to run two rollers because you need to hit the temperature range on compaction, which is 180 to 280 degrees,” Meyers says. “That thin lift behind the screed is cooling fast, and you want to release the road to traffic quickly. Plus, the paver is moving at 70 to 100 feet per minute, so you need to run two rollers behind.”

The process has a number of advantages, Meyers says. “You are not getting any tack coat dragged around the city, you get an outstanding bond with the hot mix, you are forming a waterproof membrane, there is no water splash, and you can release the road quickly to traffic,” he says.

Polymer-Modified UTACS

In the meantime, a specialized paver has given a Las Vegas asphalt contractor entry into the growing market of ultra-thin asphalt concrete surfacings in Nevada and throughout the Southwest.

However, to correctly place UTACS or other bonded wearing courses, the right kind of paver is needed: One that has the ability to spray asphalt emulsion onto a pavement, and then immediately place a thin overlay on top. Las Vegas Paving found the Super 1800-2 with optional SprayJet module from Vögele fit the bill.

With its new Super 1800-2 SprayJet paver, Las Vegas Paving now is able to undertake pavement preservation contracts as agencies like Clark County, Nev., use available funds to prolong the life of pavement structures in its desert locale.

Las Vegas Paving acquired its Super 1800-2 SprayJet in early 2010, and has been using it for UTACS ever since. “We were the new kids on the block with this process,” says Clark Webster, general superintendent. “2010 was our first year paving UTACS, and we were concerned that interest would not last, but agencies are still interested.”

Late in 2010, Las Vegas Paving was applying a UTACS to busy Jones Avenue between Tropicana Avenue and Russell Road for the Clark County Department of Public Works. This 2,700-ton job involved three lanes each way, including shoulders and turn pockets. “Jones Avenue is a piece of a larger contract we have with the county, with each piece being anywhere from 15,000 to 20,000 square yards of UTACS,” Webster says. “Jones was a 1-inch deep UTACS, with almost 100-percent passing 1/2-inch with some fines.”

On Jones, warm polymer-modified emulsion was being sprayed directly ahead of the screed via spray bars on each side of the Super 1800-2 SprayJet at a rate of 13/100-gallon per square yard. “It’s not unlike a prime or tack coat, but it provides much more coverage,” Webster says. “And no one can run on it. The Super 1800-2 places the coat behind the wheels but ahead of the material, so cars or our haul vehicles can’t drive over it and pick up the sticky, polymer-modified emulsion. It gives us the best of both worlds – we are able to use a polymer-modified emulsion without having the mess of tires tracking it everywhere.”

The benefits of high-tech transportation may be surprisingly affordable today

By Tom Kuennen, Contributing Editor

T he move toward intelligent trafficways has only just begun, and there is no end to the high-end applications that are being installed or are planned for the future.

At a March press conference at the Las Vegas-area FAST Traffic Management Center of the Regional Transportation Commission of Southern Nevada, Rudy Malfabon, deputy director, Nevada Department of Transportation, discusses the highway funding needs of the state, flanked by Jacob Snow, RTCSN general manager, and Frank Moretti, director of policy and research for TRIP, The Road Information Program.

Last year, RoadScience covered how, after nearly two decades of development, intelligent transportation system (ITS) technologies were finally going mainstream. This included the outlook for self-controlling “autonomous” vehicles that respond to environmental and vehicle cues, and the use of ITS to track vehicle movements to manage traffic volume and impose congestion pricing, both goals of IntelliDrive, a service mark of the U.S. Department of Transportation (see “ITS Finally Here!,” July 2010, pp 12-21).

But there also are relatively low-cost methods of increasing traffic volumes, and moving traffic faster via intelligent systems, that are available to agencies from coast to coast. The following is an overview of some of these accessible technologies for state, city and county road agencies.

The payoff can be quite good for low-cost applications, like synchronized traffic signals. “Transportation agencies that have invested in ITS have found that every $1 spent on technologies like synchronized and adaptive traffic signals returns nearly $40 or more to the public in time and fuel savings,” says Scott Belcher, president and CEO, ITS America, the public/private sector organization that advocates for and coordinates intelligent transportation technologies.

In the Canton/Akron, Ohio area, new variable message signs give traffic times and will be tied into statewide ITS, where current messages can be displayed in real time.

Variable message signs, video cameras and loop detectors are among the more popular means where state agencies are implementing intelligent transportation technologies.

Loop detectors are electrical voltage sensor wires buried in the driving course. They determine that a vehicle has passed via changes in electrical voltage caused by the metallic body of the passing vehicles. When linked to a regional transportation center’s computer, software can determine the speed and volume of vehicles on a pavement by analyzing how much time elapses between activation of two sets of wires.

If the traffic center computers detect congestion, video cameras can look for the cause of the congestion and this information can be displayed on variable message boards to advise motorists and to suggest alternate routes.

In the Canton/Akron region, the Ohio DOT is developing an ITS that will use variable message signs, and it will be integrated into the statewide ITS website at www.buckeyetraffic.org. The site lists lane closures and restrictions, road weather conditions, webcams, relative traffic speeds, what each variable message sign says in real time, and much more.

By the end of September, webcams and variable message signs on major routes in the area will be connected to the system. In the Canton/Akron metro area, some 64 web cameras have been installed, with 18 variable message signs on the way, primarily on Interstate routes. This summer, 18 electronic message signs on those same routes are being installed.

Mobile Phones and More

One way agencies are using existing infrastructure to leverage intelligent transportation is enhanced use of smart phones.

Boston’s Street Bump uses a smart phone’s accelerometer and GPS system to detect when a driver hits a pothole, and then sends that information to city officials; users activate the app using this icon on their Android-based smart phone.

For example, in June, ITS America recognized the New Jersey Department of Transportation and Turnpike Authority with its Smart Solution Spotlight award for the agency’s use of a smart phone “app” to provide New Jersey commuters with more accurate and timely information about traffic conditions, weather situations and safety advisories.

Drivers on New Jersey’s most heavily traveled highways may download a free smart phone application called Trumpit, developed by ITS America member HNTB, to receive audio-based traffic, weather and public safety alerts customized to their commute.

The free Trumpit app for iPhones, Androids or BlackBerrys allows drivers to hear audio alerts that can be tailored to their commutes through the My511 feature at the www. 511nj.org website. When an alert tone sounds on a driver’s phone, the driver can listen to it by pressing a single button.

NJDOT plans to use global positioning systems in smart phones to deliver traffic alerts for any roadway on which drivers are traveling without having to sign up for that specific road through the app, anticipated for later in 2011.

Smart phones may also offer more than just an outreach function; they may also enable intelligent highways or traffic monitoring, analysis and response.

The Integrated Vehicle-Based Safety Systems (IVBSS) project involved light-vehicle and heavy-truck field operational tests of the effects of a prototype-integrated crash warning system on driver behavior and driver acceptance.

Because digital phones and smart phones emit radio signals that reveal the locations of their owners, future traffic management systems may be able to collect the data and disseminate traffic information more easily and quickly.

Listening posts, in conjunction with cell phone base stations, would permit traffic management personnel to triangulate the location of each vehicle containing mobile phones, and by time-stamping the radio signals, the listening posts could algorithmically determine the speed, direction and location of each mobile device-bearing commuter on a particular highway.

Then, traffic control could send to the mobile devices personalized traffic updates, along with GPS-produced maps advising commuters of alternate routes and traffic information to the affected commuters’ phones.

This already is happening in New York City, where the city’s Metropolitan Transportation Authority has been using “NEXT TRAIN 00 MIN” displays in stations to maintain patron confidence in train arrivals. But in early June 2011, The New York Times reported that a web development firm called Densebrain says it can do the same thing at practically no cost, by analyzing how people lose phone service when they head underground.

“Densebrain’s project works by taking note of which cellphone tower a phone is communicating with,” The New York Times reports. “It then looks for disruptions in service followed by significant changes in location. If a phone located near Times Square suddenly loses service and reconnects at Prince Street and Broadway 15 minutes later, then it has almost certainly traveled there using the N or R trains. This type of data, when taken from large numbers of phones and analyzed algorithmically, could give an accurate look at the performance of the entire subway system in real time.

“Urban planners, technology companies and officials from local governments see potential in projects like these that mine data collected from phones to provide better public services,” The Times reports.

Can You Hear Me Hit That Pothole Now?

Boston is developing a system that will use sensors in Android-based smart phones to provide a real-time “snapshot” of pavement conditions such as potholes.

The system, called Street Bump, uses a smart phone’s accelerometer and GPS system to detect when a driver hits a pothole, and then sends that information to city officials. Such a system will have the ability to help government agencies collect data that would have required in-pavement network sensors.

“It is unlikely that we are going to be able to invest in that sensor system,” says Chris Osgood, co-chairman of the Mayor’s Office of New Urban Mechanics in Boston, which is responsible for establishing Street Bump, as reported in The New York Times. “But what we’ve recognized is that many, many constituents have already invested in a sensor platform,” that is, their smart phones.

The interior of Integrated Vehicle-Based Safety Systems (IVBSS) heavy truck; the vehicle was instrumented to capture detailed data on the driving environment, driver behavior, warning system activity and vehicle kinematics.

The Boston Urban Mechanic Profiler (Street Bump) prototype app was developed in partnership with Fabio Carrera, a Worcester Polytechnic Institute professor who has partnered with the City of Boston on a variety of projects focused on collecting and using data to improve city operations.

Taking advantage of the sensors on Android-system smart phones, Street Bump will provide the city with a near-real-time picture of Boston’s road conditions and the location of its potholes. When launched and recording, Street Bump collects information from the phone’s sensors to record the time, the phone’s location, its orientation, its speed, its bearing and its acceleration. These readings are automatically uploaded to the Street Bump website.

In early 2011, the app was in prototype form, simply recording and uploading data from the sensors. In collaboration with InnoCentive and Liberty Mutual Insurance, Boston was preparing to launch a challenge to design the algorithms needed to convert the data into actionable information.

Adaptive System Cuts Commutes

Adaptive traffic systems coordinate traffic signals along a corridor based on prevailing conditions, yielding smooth, more-balanced traffic flow and enhanced arterial capacities, and can help agencies get extra capacity out of existing roadways.

Reacting to real-time traffic loads, adaptive signal control accelerates travel times, enhances intersection safety, and lowers fuel consumption and exhaust emissions.

In the past year, in San Diego suburb San Marcos, Calif., an adaptive traffic system has reduced delays on San Marcos Blvd. by up to 46 percent, with an average fuel reduction of 8 percent, according to Jack Stack, a traffic consultant who drives the route.

The federally-funded, $670,000 system – which was completed in early 2010 after three years of installation – links signals at 17 major intersections along a 3.6-mile segment of San Marcos Blvd., and was installed by McCain Inc., of Vista, Calif. McCain’s analysis found motorist stops decreased 39 percent and drive times dropped an average of 20 percent, according to the San Diego Business Journal.

Another way to lower the cost of intelligent transportation is to spread its cost over multiple city agencies, providing a unified view of urban needs and providing a coordinated approach toward operations. That’s the goal of the new IBM Intelligent Operations Center for Smarter Cities.

The IBM Intelligent Operations Center monitors and manages city services, providing operational insight into daily city operations through centralized intelligence. “Now cities, government agencies and enterprises can optimize operational efficiencies and improve planning,” the firm says.

Introduced in June 2011, the IBM Intelligent Operations Center for Smarter Cities is intended to provide cities of all sizes a “holistic” view of information across city departments and agencies. “By infusing analytical insights into municipal operations through one central point of command, cities will be able to better anticipate problems, respond to crises and manage resources,” IBM says.

Through a unified operations center, cities will be able to:

• accurately gather, analyze and act on information about city systems and services, including public safety, transportation, water, buildings, social services and agencies;

• analyze real-time information to better model and anticipate problems to minimize the impact of disruptions to citizens; and

• integrate real-time information from across multiple city systems to enable collaborative decision-making for rapid response to events and incidents.

The system can integrate city management of services such as transportation, public safety, water, building and energy management within the Intelligent Operation Center.

The system will use analytical technologies to provide travelers with real-time traffic information across multiple modes of traffic, so that they can choose the best route for their commute. For example, the Intelligent Operations Center allows analysts to anticipate traffic disruptions and model “what if” scenarios, providing options to minimize traffic congestion. Automated directives can trigger communication and collaboration across the city departments and out to citizen alerts.

Pinpointing No-Pass Zones

Technology can be applied to road safety issues as well. No-passing zones on highways traditionally have been circumscribed using engineering judgment, but in today’s legal environment, a new program permits no-passing zones to be determined using line-of-sight equipment.

A no-passing zone study is required for proper striping of two-lane roadways, according to MasterMind Systems. “Changes to roadways and growth of foliage in the right-of-way lends itself to having the study performed every several years,” the firm says. “Aside from the protection from lawsuits, proper zoning makes your roads safer for the traveling public.”

MasterMind uses a two-vehicle, sight-light method to establish no-passing zones caused by vertical or horizontal curves. All data are collected using the firm’s RoadMaster NPZ system. Sight height and zone lengths are set according to a state’s Manual on Uniform Traffic Control Devices, or MUTCD specs. Zone lengths and intersection approach zones can be customized to specifications.

Then, no-passing zone graphical logs can be created showing the location and parameters of each no-passing zone in the state, and can be accessed publicly from an online GIS map. “Logs normally display 1 mile per page, but can be scaled to 1/4-, 1/2-, 1-, 2- and 3-mile-per-page scales,” MasterMind says. “These roadlogs also make T-marking, or indexing, the road a simple procedure. Lineal footage, paint and bead quantities can be easily calculated.”

Wireless-Linked Vehicles Tested At Speedway

Even as these technologies appear from coast to coast, the U.S. DOT continues to explore wireless vehicle-to-vehicle communications, using auto race tracks to do so on a safe, controlled basis.

In June 2011, the DOT announced the selection of Michigan International Speedway (MIS) near Detroit as one of only six venues in the country to host testing for wireless vehicle-to-vehicle safety communication technologies. Other “clinics” will be held in Minneapolis; Orlando; Blacksburg, Va.; Dallas and San Francisco. 

In August 2009, the Michigan DOT and the Center for Automotive Research began to use the MIS road course as a test facility for connected vehicle technology.

“MDOT’s partnership with MIS will position Michigan as a leader in the development of connected vehicle technology,” said Kirk T. Steudle, Michigan transportation director in 2009. “This concept provides a unique opportunity to shape the future of transportation by improving safety and mobility on heavily traveled highways.”

Earlier in 2011, RITA – the Research and Innovative Technology Administration of the U.S. DOT – conducted the Connected Vehicle Technology Challenge, a national competition seeking ideas for using wireless connectivity between vehicles to make transportation safer, greener and easier.

RITA is soliciting ideas for products or applications that use Dedicated Short Range Communications (DSRC), an advanced wireless technology similar to WiFi but faster and more secure. DSRC can communicate basic messages – such as alerts about imminent crash situations or roadway hazards – from one vehicle to another in a fraction of a second with minimal interference and without manipulation by the driver. The spectrum used by DSRC technology has been reserved by the Federal Communications Commission for transportation applications.

DSRC will be the basis for a future system of connected vehicles that will communicate with each other as well as the surrounding infrastructure, such as traffic signals, work zones and toll booths. According to a National Highway Traffic Safety Administration report, wireless Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communications will make for safer driving.

Not Professional Drivers on a Closed Course

This month at Michigan International Speedway, RITA will begin testing of wireless connected vehicle warning devices with ordinary drivers in normal roadway situations.

“Connected vehicle technology has the potential to address 81 percent of all unimpaired driver-related crashes,” says RITA administrator Peter Appel. “We must take a serious look at how this technology will work in the real world to create a safer transportation system.”

The Connected Vehicle Safety Pilot Program includes six driver clinics, in which motorists will be monitored in a controlled environment, and a model deployment during which drivers will test the safety technology with volunteer drivers in one geographic region without any restrictions.

The two components of the program include:

• Safety Pilot Driver Clinics: During these tests, which will take place in six locations in the United States, regular drivers will test cars with built-in wireless safety warning devices in a controlled environment. The goal will be to see how motorists handle various alert messages such as in-car collision warnings, do-not-pass signals and warnings that a car ahead has stopped suddenly.

• Safety Pilot Model Deployment: This trial will include up to 3,000 vehicles fitted with devices that will communicate with other vehicles and the surrounding infrastructure, while operating on everyday streets in a highly-concentrated area where the cars will regularly interact with each other. Motorists will be able to tell when another vehicle fitted with a wireless safety device has moved into their immediate driving area, and they will get warnings if either car is in danger of crashing.

The Connected Vehicle Drive Clinics at Michigan International Speedway are part of a DOT research program held in conjunction with the National Highway Traffic Safety Administration, and the private-sector Crash Avoidance Metrics Partnership Vehicle Safety Communications Consortium, a research effort of eight automobile manufacturers.

The program is aimed at developing technology that will help vehicles avoid crashes by communicating with nearby vehicles and with roadway infrastructure such as traffic signals, dangerous road segments and grade crossings. This is achieved by alerting the driver when there is a risk of a crash or other safety driving hazard.

But before real-world testing is undertaken, agencies must test in a safe, controlled environment, and this is where the MIS facility serves this critical role. In Michigan, some 100 local drivers will be recruited for the clinic, which will take place in controlled locations around the racetrack. Each clinic will include about 16 cars equipped with technology applications that drivers will evaluate as they use the vehicles in a controlled environment designed to simulate real roadways and intersections.

The trials will take place along the speedway’s road course, some of which will be outfitted with temporary traffic signals to mimic city streets and roads. Movable traffic lights will allow agencies to test anywhere on the track’s pavement throughout the 1,400-acre property.

After the driver clinics are completed, the DOT plans to deploy thousands of wirelessly-connected vehicles to test how the technology performs in a real-world driving environment. The model deployment is scheduled to begin in fall of 2012 at a site that will be selected through an open competition.

Previous to the six field tests involving actual drivers off the street, NHTSA completed study of Integrated Vehicle-Based Safety Systems (IVBSS), and in June 2011 released a final report.

The project involved light-vehicle and heavy-truck field operational tests of the effects of a prototype-integrated crash warning system on driver behavior and driver acceptance. Both platforms included three integrated crash-warning subsystems, forward crash, lateral drift and lane-change/merge crash warnings. The light-vehicle platform also included curve-speed warning.

The integrated systems were introduced into two vehicle fleets of 16 light vehicles and 10 Class 8 tractors. The light vehicles were operated by 108 volunteer drivers for six weeks, and the heavy trucks were driven by 18 commercial-truck drivers for a 10-month period.

Each vehicle was instrumented to capture detailed data on the driving environment, driver behavior, warning system activity and vehicle kinematics. Data on driver acceptance are collected through post-drive surveys and debriefings.

The University of Michigan Transportation Research Institute analyzed the data and found that the integrated crash warning system results in improvements in lane-keeping, fewer lane departures and increased turn-signal use.

Both the passenger car and commercial drivers accepted the integrated crash warning system and benefited from improved awareness of vehicles around them. No negative behavioral-adaptation effects of using the integrated system were observed in either driver group.

You may download the report at nhtsa.gov/DOT/NHTSA/NVS/Crash%20Avoidance/Technical%20Publications/2011/811482.pdf

A war is being waged on noise generated by pavements and highways.

By Tom Kuennen, Contributing Editor

Today, highway noise is considered an undesirable emission, just as if it were a noxious gas out of the tailpipe. But road designs can do much to attenuate highway noise.

These include active methods to quell noise created at the pavement-tire interface, such as variable transverse groove patterns on concrete and the new Next Generation Concrete Surface (NGCS), and thin and thick open-graded or porous asphalt friction courses.

But they also include passive methods, such as sound walls, vegetation screens, earth berms, recessed pavements, or combinations of the foregoing.

And even as the techniques of active and passive highway noise suppression are refined, methods used to measure noise are getting more sophisticated amid a political climate of less tolerance for highway noise in our cities and neighborhoods.

Keeping it Down

New solutions are coming in to play to control noise from America’s Interstate highways, primary highways and arterial streets. Road agencies are spending more on noise mitigation. On new or capacity improvement projects, sound walls that were once considered an extravagance are now standard procedure.

Engineers are finding that the best solution to highway noise is a combination of sound wall, appropriate vegetation and a quieter pavement surface. Any combination of the three elements will help, because noise barriers can cost an average of $3.9 million per mile, according to current estimates by the Washington State DOT, with lower costs for rural barriers, and higher for urban.

Producing a low-noise diamond ground surface – the NGSC – requires creating uniform and consistent negative-land profiles

Highway noise barriers can be of many configurations, including recycled plastic, wood, evergreens, gabion walls and precast concrete panels. Trees — such as stands of thick evergreens — have the potential to replace noise barriers, and are aesthetically pleasing, but are effective only in deep stands, requiring additional strips of right-of-way, as much as 100 feet wide.

Efforts to limit highway noise have focused on barriers. But because most of the noise originates at the tire-pavement interface, use of “quiet pavements” to quell noise there makes sense.

For portland cement concrete pavements, texture is added to improve friction and driver control, but done incorrectly it can add to pavement noise. Tine or groove depth, width, spacing and orientation are all major factors affecting tire-pavement noise. Transverse tinings with uniformly spaced tines a half inch or greater have been found to produce an objectionable tone, with pressure spikes at specific frequencies, that users interpret as a tire “whine.” Randomly varying the transverse tine spacing, or skewing it, can reduce the tonal-quality problems.

Sophisticated asphalt pavement designs – such as polymer-modified, open-graded friction courses (OGFCs) – offer greater tire-pavement noise reduction than conventional asphalt mixes. Also, their porous nature also allows fast drainage of water and eliminates the problems of tire spray, glare and hydroplaning.

Even as the industry improves noise suppression practice, a new rule from the Federal Highway Administration takes effect this month (July 13). Articulated last year, the final rulemaking for 23 CFR 772, Procedures for Abatement of Highway Traffic Noise and Construction Noise, fine-tunes expectations for highway noise reduction and describes a three-part approach to highway noise:

• Noise-Compatible Planning. Local governments should regulate land uses to restrict noise-sensitive uses adjacent to highways.

• Source Control. EPA noise regulations set the maximum noise level 50 feet from the centerline of travel at 80 A-weighted decibels.

• Highway Project Noise Mitigation. FHWA sets a five-step process for transportation agencies managing highway project planning and design to identify and abate highway noise impacts.

Download a summary of the new rules at environment.fhwa.dot.gov/strmlng/newsletters/sep10nl.pdf The complete final rule may be accessed at]edocket.access.gpo.gov/2010/2010-15848.htm

A recap of current federal and state initiatives in noise suppression – including a look at sound-absorbing noise walls – appears in the December 2010 ROAD SCIENCE (see Gaining Influence in 2011, December 2010, pp. 9-17).

Next-Generation Concrete Surface

This year, the concrete industry launched a portland cement concrete surface that will suppress noise from concrete pavements while enhancing friction and smoothness. A refinement of the pavement diamond-grinding process, the Next Generation Concrete Surface (NGCS) is being promoted by the International Grooving & Grinding Association and its allies, the American Concrete Pavement Association, Portland Cement Association and Purdue University.

New-generation sound wall on Windsor-Essex Parkway in Ontario boasts aesthetic pattern and clear, transparent panels which obviate ‘Berlin Wall’ look

When this innovative surface was used on an urban highway in Duluth, the response was overwhelming, IGGA reports. “Residents have called in asking how the roads became so quiet and it has even made the front page in the local newspapers,” says IGGA Executive Director John Roberts.

The best way to understand the difference in the sound level with NGCS is to experience it; a high-traffic freeway with 240 vehicles will now sound comparable to only 120 vehicles of traffic, a substantial reduction in sound, IGGA reports. This is a considerable decrease for areas with a greater need for quieter roads, such as urban or residential areas.

The NGCS is a diamond saw-cut surface designed to provide a consistent profile absent of positive or upward texture, resulting in a uniform land profile design with a predominantly negative texture. NGCS is a hybrid texture that resembles a combination of diamond grinding and longitudinal grooving.

On-Board Sound Intensity measurement processing of sound at tire-pavement interface creates graphic – integrated with Google Earth image – reporting existing highway noise performance.

The texture is most easily constructed in a two-pass operation using diamond-tipped saw blades mounted on conventional diamond-grinding and grooving equipment. Testing has shown that these textures can be used for both new construction and rehabilitation of existing surfaces.

The construction method has two separate operations, reports the Washington State DOT in its April 2011 report, Evaluation of Long-Term Pavement Performance and Noise Characteristics of the Next Generation Concrete Surface. The first operation creates a flush ground surface and eliminates the joint or crack faults while providing lateral drainage by maintaining a constant cross-slope between grinding extremities in each lane.

The second operation provides the longitudinal grooves, Washington DOT reports. The longitudinal grooves are 0.125 inches wide, and 0.125 to 0.375 inches deep. The longitudinal grooves are spaced approximately 0.5 inches center-to-center. The grooves are constructed parallel to the centerline.

The NGCS is being promoted following three years of research at the Minnesota Road Research Project (MnROAD), the world’s largest and most comprehensive outdoor pavement laboratory.

In early 2011, new NGCS test sections were constructed at the Virginia Tech Transportation Institute’s Smart Road test facility near Blacksburg, Va. In January 2011, three test strips situated on two test areas were constructed, including a conventionally diamond-ground section, and an area that was conventional followed by longitudinal grooving of each half of the lane using two different groove spacings of 0.5 and 0.75 inches.

New Texturing Guide Specs

Also this spring, two new approaches were articulated for guide specifications for reducing tire-pavement noise on PCC pavements.

In the May 2011 publication, Concrete Pavement Specifications for Reducing Tire-Pavement Noise, – developed by the Concrete Pavement Surface Characteristics Program (CPSCP) and published by the National Concrete Pavement Technology Center (CPTC) at Iowa State University – authors Robert Otto Rasmussen and Richard Sohaney of The Transtec Group, and Paul Wiegand of the Institute for Transportation at Iowa State, describe method-based (prescriptive) specs and end-result specs for suppressing PCC pavement-generated noise.

For the methods-based specs, four guide specifications (GS-1 through GS-4) have been developed. “[They] correspond to the four most commonly used concrete pavement textures: diamond grinding, drag (artificial turf), longitudinal tining and transverse tining,” the authors write. “The practices described in the specifications have been demonstrated to increase the likelihood of constructing a durable, quieter concrete surface. Central to the specification is guidance for texturing the concrete surface, given that texture geometry has a paramount effect on tire-pavement noise. Guidance is also provided for curing to improve strength and durability of the surface, and thereby improve texture durability.”

For the end-result specs, a recommended practice (PP-1) has been developed that includes guidance and sample specification language for owner agencies to evaluate tire-pavement noise of new concrete pavement surfaces. “The overall sound intensity level measured with the onboard sound intensity (OBSI) test method is designated as the quality characteristic,” the authors write.

The authors single out transverse tining technique as a major culprit in PCC pavement noise. “Both longitudinal and transverse tining are routinely used by owner-agencies, particularly for high-speed facilities,” Rasmussen, Sohaney and Wiegand wrote in May. “Achieving a quieter concrete surface is possible, but requires additional control, particularly for transverse tining, which is often associated with some of the loudest concrete pavements.”

When using tined textures, grooves are imparted in the surface of a pavement while the concrete is plastic, they say. For best results, application of a drag pre-texture should be followed by subsequent tining.

“For longitudinal tining,” the authors write, “the nominal spacing of the tines is 3/4 inch. For transverse tining, nominal spacing of 1/2 inch is specified. The nominal depth of the tined grooves in the plastic concrete is 1/8 inch.”

The Tech Brief may be downloaded from the CPTC at cptechcenter.org/publications/surface_char_specs_tech_brief.pdf and the individual guide specs can be found at cptechcenter.org/projects/surface-characteristics/index.cfm

New Ways to Measure Noise

Integral to concrete’s new attack on noise is a shift from measuring sound pressure remotely, to sound intensity directly at the source, the tire-pavement interface.

The key recommendations developed by the Concrete Pavement Surface Characteristics Center are largely based on tire-pavement noise tests conducted worldwide using microphones right at the tire moving on the pavement, write Rasmussen, Sohaney and Wiegand in a companion Tech Brief issued in May, Measuring and Reporting Tire-Pavement Noise Using On-Board Sound Intensity (OBSI).

“OBSI measures tire-pavement noise at the source using microphones in a sound-intensity probe configuration mounted to the outside of a vehicle, near the tire-pavement interface,” they say. “Measurements are performed while the test vehicle drives across the pavement of interest.”

Sound and noise can be a relative experience. A rock concert produces sound levels at about 110 decibels. A quiet night actually produces some 30 decibels of sound. But only levels above 85 to 90 decibels are thought to pose health risks.

Sound levels are measured exponentially. One expert describes it this way: Assuming two planes with the same individual sound level (3 decibels) are added for every double. If a plane taking off creates 100 decibels of noise, two planes would make 103 decibels, four planes 106 decibels, and eight 109. Highways, roads and streets routinely produce decibel readings of from 65 to 85 decibels.

When a sound level (such as 90 dBA) is reported, it is most often a measure of the amplitude of sound pressure changes, the authors add. “Sound intensity is different from sound pressure in that it has both amplitude and an associated direction,” they write, making it a more meaningful criterion for analyzing noise emissions.

Benefits of OBSI include:

• The directional characteristic of the probe makes it better-suited for measuring a specific noise source, while attenuating sounds from other sources in other directions (such as engine or exhaust noise);

• Sound intensity is much less contaminated by “random” noise, such as wind noise generated as the vehicle is moving; and

• Because sound intensity measures the acoustic energy propagating away from the source to the roadside, it correlates well with sound measured at the roadside (known as pass-by or wayside measurements).

The new Tech Brief may be downloaded atcptechcenter.org/publications/surface_char_specs_tech_brief.pdf

OGFCs Quell Noise at Surface

Open-graded friction courses offer state DOTs a better-performing, driver-friendly pavement. These new-design OGFC pavements feature an “open” aggregate structure (without fines) in which larger-sized aggregate is held in place by polymer-modified and fiber-modified Superpave performance-graded liquid asphalts.

This open structure of 15 percent or more voids allows water to drain right through the driving or friction course to an impervious intermediate course below, and out the side and into edge drains or roadside ditches. The result is the near-complete elimination of tire spray and hydroplaning, making a safer pavement.

Also, because noise generated at the tire/pavement interface is attenuated within the spaces between the aggregate, they are significantly quieter pavements. The noise reduction can be on the order of 3 to 5 decibels.

An OGFC describes a layer of asphalt that incorporates a skeleton of uniform aggregate size with a minimum of fines. Typically, OGFCs in the past have a void content as low as 12 percent and as high as 15 or 16 percent. But the new generation of OGFCs that are being built in Europe have considerably higher air void contents, up in the range of 17 to 22 percent. They are more open, with more voids.

Most OGFCs are 3/4-inch thick, and never thicker than 2 inches. The OGFC should be elevated above the shoulder, as the water drains onto the shoulder and hence to a roadside ditch. Open-graded, proprietary thin surfacings such as Novachip and its clones qualify as OGFCs.

In dense-graded asphalt mixtures, reports The Asphalt Institute, a thin film of asphalt plus compaction effort – are required to keep the mix glued together. In short, the final density of dense-graded mixes is a direct measure of the strength and durability of the mix. But the OGFC mix, according to the AI, uses a grading of mostly 3/8-inch stone, the idea being to build up a thick film of asphalt on the stone without the mixture draining or flushing. The asphalt film thickness is usually four to six times that of a dense-graded mix.

“If properly designed, the asphalt in an OGFC does two jobs,” AI says. “First, it acts as a binder or glue. Second, since the mix is open to water and air, it acts as a waterproofing agent and protective coating to resist oxidation and rapid aging of the asphalt cement itself.”

Today’s OGFCs are polymer-modified and include spun mineral or cellulose fibers to preclude drain-down of asphalt binder during transport and placement. Use of polymer modifier or fiber does not preclude the other; instead, each complement the other in the liquid asphalt. The fibers disperse evenly, and despite their tiny size, overlap and form a mat, which keeps the liquid asphalt from draining from the top to the bottom of the layer before it cools, not unlike the action of gauze in keeping a wound from seeping.

But an application in May 2011 in South Carolina showed that fibers can be eliminated from an open-graded porous asphalt pavement. Use of Evotherm warm-mix asphalt additive permitted an open-graded mix that did not require addition of mineral or cellulose fibers to prevent draindown, a substantial savings. It also permitted elimination of lime as an adhesion promoter resulting in substantial savings.

Sound Walls Go Mainstream

From a start as an extravagance decades ago, sound walls now have gone mainstream, as they are seen more and more on new urban and suburban expressway projects, and as retrofits on existing highways.

The FHWA requires DOTs to complete a sound study any time it plans to add through lanes to an existing highway or change the location of a road. “Sound walls can help lessen the noise impacts of the roadway improvement and provides noticeable sound reduction for houses closest to the highway,” says the Missouri DOT.

A sound wall can reduce noise levels from 5 to 10 decibels. In Missouri, communities are eligible for a sound wall only if noise levels are at 66 decibels or above. According to the Washington State DOT, 66 decibels was chosen as the impact threshold because researchers have shown that above this level, conversation between two people standing 3 feet apart and speaking in a normal voice is impaired.

Missouri criteria for construction of a sound wall includes:

• the sound wall must reduce noise levels by at least 5 decibels for all benefited homeowners,

• the sound wall must benefit more than one homeowner,

• the sound wall must be 18 feet or less in height,

• the sound wall must not pose a traffic safety hazard, and

• the majority of the benefited residents must agree that a sound wall is desired.

Sometimes state and local agencies will cooperate in construction of sound walls for existing freeways. For example, Missouri will conduct a sound study to review the need for sound mitigation near existing highways when cities and counties participate in the cost of the design and the construction of the wall. The local government agency must provide 50 percent of the design and construction cost. MoDOT will provide the 50 percent matching funds. If the construction cost of the sound wall project exceeds $30,000 per benefited resident, the local government agency must pay 100 percent of the cost above $30,000.

Sound walls can be a costly undertaking. In Washington State, the DOT estimates current construction costs are averaging $53 per square foot. “This translates into a 14-foot-high wall costing about $3.9 million per mile,” the DOT says. “Construction costs for rural barriers may be lower and urban barriers may be much higher. The higher urban costs are associated with the existence of other infrastructure – like retaining walls or water pipes – that may need to be retrofitted or moved to allow the placement of barrier.”

A Choice of Materials

Precast concrete panels – due to their quick erection capability in the field – constitute the bulk of sound walls today. Precast panels also permit aesthetic textures to be integrated into a project. They can be as bland as an imitation of hewn concrete block, or as attractive as a motif incorporating Native American designs, as seen often in the American Southwest.

Concrete panels and block are muscling out competing materials like wood, steel and plastic on a national basis, but in doing so quite often are going up against each other in bids. In 2000, concrete and block represented almost two-thirds of total material usage, according to a spokesman for the FHWA Office of Environment and Planning.

Because of the growth in sound wall applications, and the fact that highway noise barriers can be so expensive, barrier design must as efficient and cost-effective as possible. That’s why FHWA released, in March 1998, a state-of-the-art model for predicting noise impacts in the vicinity of highways, the FHWA Traffic Noise Model.

The current Version 2.5 was released in April 2004. The FHWA TNM is a computer program that incorporates advances in personal computer hardware and software to improve upon the accuracy and ease of modeling highway noise, including the design of effective, cost-efficient highway noise barriers. For more information, visit fhwa.dot.gov/environment/noise/traffic_noise_model

Although precast concrete and masonry are the leading materials for sound walls, wood often is thought of first for sound walls. Other competing materials include steel, plastic and recycled products. The concrete products industry is fighting against lower-priced materials by promoting lifecycle costing versus competing materials.

Wood has declined in usage because of durability problems compared to concrete, difficulties in cleaning of graffiti, and the disfavor of use of imported wood from tropical rain forests, which had been the prime source. Wood also suffers because preservatives such as creosote emit volatile organic compounds to the atmosphere.

Use of alternate materials may have been boosted with the January 1999 Transportation Research Board-sponsored publication of Noise Barriers Using Recycled-Plastic Lumber (Hag-Elsafi, Elwell, Glath and Hiris).

This paper, out of the New York State DOT, described use of “lumber” fashioned from recycled plastic extruded into classic lumber sizes, and placed in wood or steel frames. They mentioned then-competitive costs per square meter of $161-194 for plastic lumber with wood frames, and $226-269 with steel frames.

Diamond Grinding vs. Micromilling

By Tom Kuennen, Contributing Editor

Diamond grinding of Portland cement concrete pavements and micromilling of bituminous asphalt pavements are superficially similar in concept, but that’s just about the only thing they have in common.

Diamond grinding is applied to I-88 near Albany, N.Y.

Diamond grinding of aging Portland cement concrete (PCC) pavements renews the pavement’s skid-resistance, and provides a smoother-riding pavement. And the resulting smoother profile reduces dynamic loading on the pavement, thus extending its service life.

On the other hand, micromilling, or fine-tooth milling – using conventional cold mills with fine-tooth drums and hardened teeth – can remove imperfections from an asphalt surface and prepare it for a super-smooth thin asphalt overlay in a manner superior to conventional cold milling. In some cases, it can even be used instead of grooving or grinding pavements.

Following several years of research, promotion has begun for a new permutation of the diamond grinding process, the Next Generation Concrete Surface (NGCS). As promoted by the International Grooving and Grinding Association (IGGA), the NGCS is said to suppress noise from concrete pavements while enhancing friction and smoothness. The NGCS is being promoted following three years of research at the Minnesota Road Research Project (MnROAD), the world’s largest and most comprehensive outdoor pavement laboratory.

Early in 2011, new NGCS test sections were constructed at the Virginia Tech Transportation Institute’s Smart Road test facility near Blacksburg, Va. In January, three test strips situated on two test areas were constructed, including a conventionally-diamond-ground section, and an area that was conventional followed by longitudinal grooving of each half of the lane using two different groove spacings, of 0.5 and 0.75 inches respectively.

Each of the two test areas were ground one-lane wide and 528 feet long, and will allow the institute to study the impact of grinding and grooving on profiler measurements and on friction test results. In addition, the sections allow the future evaluation of splash and spray, as the Virginia Tech facility has this capability as well.

Diamond Grinding PCC Pavements

Diamond grinding is a concrete pavement preservation technique that corrects a variety of surface imperfections on concrete pavements, and should be used in conjunction with other pavement preservation techniques, reports IGGA.

It involves the removal of a thin layer of the cured concrete surface using a dedicated, self-propelled machine with closely-spaced diamond-coated circular saw blades. Diamond grinding restores rideability by removing surface irregularities. The immediate effect of diamond grinding is a significant improvement in the smoothness of a pavement, and a significant increase in surface macrotexture with improvement in skid resistance, noise reduction and safety.

The value of diamond grinding is borne out by a California Department of Transportation (Caltrans) study, conducted to quantify the expected longevity of a diamond-ground PCC pavement, and its overall effectiveness under various weather conditions and construction practices. In the study, Caltrans reported that diamond grinding “is a viable and cost-effective rehabilitation measure when properly applied. Diamond grinding not only extends the service life of a concrete pavement, but it also reduces tire-pavement interface noise and improves texture and skid resistance. Because the pavement is much smoother after grinding, highway user costs are also reduced through improved fuel efficiency and lower vehicle maintenance costs.”

Diamond grinding provides a smooth surface that can reduce dynamic loading and increase pavement longevity, IGGA reports. Increased pavement life will be obtained by reducing the roughness, IGGA maintains, and can be demonstrated using the American Association of State Highway & Transportation Officials (AASHTO) 1993 Pavement Design Equation. In that equation, serviceability is analogous to smoothness, which means that increased serviceability (a smoother pavement) will result in more equivalent single-axle loads carried by the pavement, the association says.

Diamond-ground surfaces have been found to reduce accident rates, IGGA reports. The Wisconsin DOT, working with Marquette University, found that the overall accident rate for diamond-ground surfaces was only 60 percent of the rate for nonground surfaces. The diamond-ground pavements provided significantly-reduced accident rates up to six years after grinding.

While creating a smoother pavement, diamond grinding does not affect the fatigue life of a pavement and does not raise the pavement surface elevation. Grinding also does not affect the hydraulic capacities of curbs and gutters on municipal streets, unlike bituminous overlays that fill curb and gutter, and reduce their drainage capabilities, IGGA says. Diamond grinding can be applied only where improvement is needed, and can be performed during off-peak hours.

Micromilling Asphalt Pavements

Unlike diamond grinding, micromilling pavements do not require a dedicated machine, as they can be applied by a conventional asphalt cold mill fitted with a fine-tooth drum.

Micromilling, or fine milling, by Pavement Products and Services, provides super-smooth base for overlay while correcting cross-slope problems on I-185 in Greenville, S.C.

This is particularly important when placing so-called thin HMA overlays, microsurfacing or other spray surface treatments. There, micromilling is preferred to a conventional drum because the latter provides a “peaks-and-valleys” pattern that will be relatively high and deep. If an agency is not placing a lift that’s thicker than 1 to 1-1/4 inches, the rough surface can reflect through to the paved surface. But with 5/16-inch bit spacing (or less) – the definition of a fine-toothed drum – an owner or contractor can minimize the potential reflection of the peaks and valleys through the thin lift surface.

Georgia DOT’s micromill spec – Section 432: Mill Asphaltic Concrete Pavement (Micro-Mill) – describes micromilling of existing asphalt concrete pavement to remove wheel ruts and other surface irregularities, and restore proper grade and/or transverse slope of pavement as indicated in the plans or as instructed by the engineer.

“The planed surface shall provide a texture suitable for use as a temporary riding surface or an immediate overlay with OGFC [open-graded friction course] or PEM [porous European mix] with no further treatment or overlays,” Georgia DOT says in its spec, and limits use of the micromilled pavement as a temporary riding surface to a maximum of seven days.

Control systems and a full lane-width, fine-mill drum allows Pavement Products and Services to correct pavement cross-slope using micromilling on I-185.

• equipped with a cutting mandrel [drum] with carbide-tipped cutting teeth designed for micromilling bituminous pavement to close tolerances;

• equipped with grade and slope controls operating from a stringline or ski and based on mechanical or sonic operation;

• capable of removing pavement to an accuracy of 1/16 inch (1.6 mm);

• furnished with a lighting system for night work, as necessary; and

• provided with conveyors capable of side, rear, or front loading to transfer the milled material from the roadway to a truck.

Prior to commencement of the work, Georgia DOT requires a 1,000-foot test section with uniformly-textured surface and cross section as approved by the engineer.

Next Generation Concrete Surface

While concrete diamond grinding has been limited to smoothing rough concrete surfaces, the Next Generation Concrete Surface offers a new application for enhancement of PCC pavement smoothness, friction and, especially, noise created at the tire-pavement interface. That’s important, because noise is more and more considered an emission into the environment that must be controlled.

TexOp Construction uses a fine-toothed drum to prep President George Bush Turnpike near DFW Airport in advance of NovaChip overlay; the contractor alternative provided significant savings over diamond grinding originally planned by owner North Texas Tollway Authority.

The NGCS is a diamond saw-cut surface, designed to provide a consistent profile absent of positive or upward texture, resulting in a uniform land profile design with a predominantly negative texture. NGCS is a hybrid texture that resembles a combination of diamond grinding and longitudinal grooving.

The texture is most easily constructed in a two-pass operation using diamond-tipped saw blades mounted on conventional diamond grinding and grooving equipment. Testing has shown that these textures can be used for both new construction and rehabilitation of existing surfaces.

The construction method has two separate operations, reports the Washington State DOT in its April 2011 report, Evaluation of Long-Term Pavement Performance and Noise Characteristics of the Next Generation Concrete Surface. The first operation creates a flush ground surface and eliminates the joint or crack faults while providing lateral drainage by maintaining a constant cross slope between grinding extremities in each lane.

The second operation provides the longitudinal grooves, Washington DOT reports. The longitudinal grooves are 0.125 inches wide and 0.125 to 0.375 inches deep. The longitudinal grooves are spaced approximately 0.5 inches center to center. The grooves are constructed parallel to the centerline.

Patch-and-Grind Option

Another variation of diamond grooving and grinding is “patch-and-grind.” Cook County, Ill., in the heart of the Chicago metro area, reports great success serving its road users by using the patch-and-grind method of concrete pavement restoration.

Patch-and-grind involves full- or partial-depth concrete pavement patching and joint repair, followed by diamond grinding of the entire pavement. The patching addresses structural issues such as cracked panels and spalled joints, while the diamond grinding addresses the functional deficiencies.

Patching without diamond grinding can result in poor rideability and is not an attractive alternative when considering the most effective use of the taxpayer’s money, IGGA reports. But the patch-and-grind repair method has proven to be a lower-cost construction alternative when compared to a full reconstruction, the association says. Motorists also realize the benefit of the shorter construction duration.

The Cook County Highway Department has used diamond grinding on a growing number of projects and the technique has migrated into adjoining Lake County, Ill. Full reconstruction of these pavements would have cost the taxpayers three times more than the patch-and-grind technique, IGGA says. A full reconstruction costs approximately $45 to $50 per square yard, while a patch and grind costs approximately $15 a square yard.

“When a typical full reconstruction of a lane-mile costs $1 million, the use of patching and grinding makes sense because it can be done at a fraction of the cost, provides long-lasting repairs and creates far less inconvenience to the motoring public,” says John Beissel, P.E., assistant superintendent, Cook County Highway Department.

Micromilling Fixes Cross Slopes

Micromilling with cold mills isn’t limited to preparing asphalt pavements for thin asphalt overlays. South Carolina is taking a leadership position on micromilling to correct cross slopes, and it shows in the increase of fine milling jobs undertaken by one contractor, Pavement Products and Services (PPS), Piedmont, S.C.

“South Carolina has a lot of ‘flat’ roads,” says Douglas E. Limbaugh, the company’s project manager. “The cross slopes are out of balance. So, we will surface-plane or micromill an inch or two off the road, to get the aged asphalt off, and once that’s done, variable surface-plane or cross-slope correct the main lines or roadways.”

By doing the planing in two stages, the company eliminates the drop-offs that would result in doing the work in one pass. “Motorists don’t have to drive with more than a 1-inch drop, and in the meantime they get a better surface to drive on,” Limbaugh says.

In 2010, PPS was cold-milling day and night with fine-tooth drums. For example, in March 2010, during the day, the company was micromilling the I-185 expressway just southwest of downtown Greenville, S.C., and at night, was using some of the same equipment to micromill I-85 west of the city.

“Using our fine-tooth drums, we are removing an inch from I-185, then coming back the same day and fine-milling a second inch,” Limbaugh says. “We then will go to isolated areas and cross-slope correct there.” That project represented two 50,000-square-yard lifts, 100,000 total.

The I-85 work – three lanes both north and south – that night was part of a total 1.4 million square yards of 1-inch micromilling, and 295,000 square yards of variable surface planing for cross-slope correction. “We will be using two full-lane cold mills with 12.5-foot drums, and a half-lane micromill.”

The South Carolina DOT uses the terms “surface planing” but the same term applies to “fine milling” and “micromilling,” Limbaugh says. “The spacing on the cutter drum must be 0.2 inches, which translates to 5 mm spacing,” he said. “It means from chevron to chevron, or tooth mark to tooth mark, you have to have 5 mm or less.

“The state also requires tolerances of 1/8 inch from high to low on the tooth marks, so you can’t just put a thousand-tooth drum out there and run 80 feet per minute,” Limbaugh says. “You have to go at a steady pace, because that will leave as smooth a surface as you can. In ride quality, it’s comparable to a porous friction course.” On top of that, for cross-slope correction, the state imposes a rideability spec.

As standard bids are cut to the bone, these contractors strive to earn smoothness bonuses, which PPS makes easier by its fine milling. “We are setting them up not to fail, but to win, by giving them a superior surface,” Limbaugh says.

Fine-Mill Grooving Substitute?

Micromilling with a fine-tooth drum also can be used on driving surfaces just to restore friction and smoothness.

For example, fine milling or texturing may be appropriate for a county that does not have a lot of money to mill out and pave its roads completely, and they may just want to shape up the roads and remove some rutting and areas where asphalt is shoved in intersections. “A fine milling drum can be put in a cold mill and used to repair that driving surface,” says Jeff Wiley, senior vice president with equipment manufacturer Wirtgen America. “The county will have bought some time while being able to open a road to traffic immediately.”

With a narrower drum on a smaller cold mill, fine milling is also useful for removal of road markings, or for prepping pavements for road-marking application.

But in limited instances – at least when a pavement is prepped for an overlay – micromilling with a fine-tooth drum can replace diamond grinding of existing pavement. For example, not too long ago, micromilling was used instead of the specified diamond grinding of the driving surface of the President George Bush Turnpike north of Dallas.

There, the President George Bush Turnpike is a major east-west route in the northern half of the Dallas Metroplex, and is a 30.5-mile, six-lane, limited-access toll highway that passes through or along the cities of Garland, Richardson, Plano, Dallas, Carrollton, Farmers Branch and Irving.

The turnpike owner – the North Texas Tollway Authority – planned to overlay a section of the expressway with NovaChip proprietary open-graded friction course. But such thin lifts – with maximum 3/8-inch stone – require extremely well-prepared and even surfaces for placement. Any irregularity in the existing pavement will reflect through the thin surfacing immediately.

Conventional surface prep for worn pavements previously involved diamond grinding the pavement to precise tolerances. But cold milling subcontractor TexOp Construction, Roanoke, Tex., in conjunction with its general contractor APAC, proposed to cold-mill using a 2-meter (6.56-foot) fine-tooth drum to prepare and level the aged asphalt pavement surface prior to the thin surfacing.

The project already had been designed with diamond grinding in the contract, so a change order was the means to get the cold mill on the project instead of a diamond grinder. On this particular job, fine-texturing with a cold mill saved the authority a significant sum over diamond grinding. Also, the diamond grinders were asking for a minimum 60 days, and the contractor was on track to finish the same area in 10 to 14 days.

“There was a very high cost to the diamond grinding,” says Danny Simpson, vice president and managing partner, TexOp Construction. “Also, the time it would take to do the diamond grinding was excessively long. We proposed to do the job in a much shorter period of time at a lower cost, but with the same benefit as the diamond grinding, 20 days versus 60 days, giving them exactly the same ride in a third of the time.”

First, both the turnpike authority and the Texas DOT requested a test section. “We did a test project for Texas DOT using the fine-texture drum,” Simpson says. “People came out, took a look and liked what they saw, including the smoothness of the ride and the pattern of the drum. They were skeptical until they saw the process work.”

A strong foundation is the key to a strong pavement structure

By Tom Kuennen, Contributing Editor

A pavement is only as strong as its foundation. Without an adequate base or foundation, a road simply cannot stand up to long-term traffic volumes, increasing vehicle weights and speeds, and the assault of the elements.

Strong subbases bolster the base and pavement layers above.

While the concept of a subbase is simple, the reality is that in today’s world of advanced technology, a subbase design and construction can be complex and demanding. Subbase design may require analysis of existing, virgin and reclaimed materials, application and mixing of stabilization chemicals, installation of stabilization fabrics, and measurement of compaction using “smart” technology built into dirt rollers. Subbases must also be drained and protected from frost.

For new alignments, stabilize the subgrade prior to work on subbase, base and pavement layers.

And the new philosophy of mechanistic-empirical design, as articulated by the American Association of State Highway & Transportation Officials (AASHTO) with the National Cooperative Highway Research Program (NCHRP), is bringing a new rigor to the design and construction of subbases.

The result will be better-performing pavement structures.

Damage from Inadequate Subbases

Subbases inadequate for the traffic loads they carry will manifest their shortcomings in a variety of ways.

A new Cat 160M2 motor grader preps the subbase prior to base placement.

The most common clue to base failure-related pavement woes in is fatigue cracking. Fatigue, or bottom-up, cracking results when traffic load stresses propagated to asphalt pavement foundations cause foundation cracks to work their way upward through the pavement.

In asphalt pavements, it’s manifested as a series of interconnected cracks resembling an alligator hide, hence its popular name alligator cracking. It develops into many-sided, sharp-angled pieces, usually less than 12 inches on the longest side.

If not stabilized, expansive subbase and base layers will heave and destroy pavement.

Low-severity fatigue cracking characterizes an area of cracks with no or only a few connecting cracks. The cracks are not spalled nor sealed, and pumping of base materials out the cracks is not evident. In moderate fatigue cracking, the interconnected cracks form a complete pattern, cracks may be slightly spalled and may be sealed, and pumping is not evident. High-severity fatigue cracking is an area of moderately or severely spalled interconnected cracks forming a complete pattern, the pieces of which may move when subjected to traffic loads. Cracks may be sealed, and pumping may be evident.

In portland cement concrete (PCC) pavements, longitudinal cracking describes cracks that are mostly parallel to the pavement centerline, and are attributed to subgrade heaving that pushes upward against the rigid slab and cracks it.

“Daylighted” permeable base – exposed here at the shoulder – is a lower-cost PCC pavement drainable design that doesn’t require separation fabric or drainage systems.

Base and subbase layers that are composed of expansive soils with an abundance of clay must be stabilized, frequently done with cement. This is particularly true of soils in Louisiana, Texas and the American Southwest. Expansion of these base and subbase layers will cause heaving in the pavement, forcing it upward, causing it to fissure and break. The pavement likely will have to be completely reconstructed.

Layers of Pavement Structure

The pavement structure is composed of layers beginning with the subgrade, topped by the subbase, the base course, and lastly one or more surface courses. On roads with lighter traffic loads, the surface course(s) may rest directly on the subbase.

The surface courses can be a single course of PCC, although simultaneous twin lifts of PCC are being studied (see “Research that Can Change the Way We Work,” April 2011, pp. 26-39); or one, two or even three courses of hot-mix asphalt or its warm- and cold-mix permutations. These will rest on base and subbase layers that can be unbound, bound, or stabilized by a variety of methods, including cement- or lime-slurry, dry cement or lime, asphalt emulsion, or foamed asphalt.

The subgrade is the graded, prepared ground beneath the subbase layer. It’s been described as the point at which excavation ceases and construction starts, and supports the entire pavement structure and traffic loads.

In practice, the subbase becomes the main load-bearing layer of the pavement, evenly spreading the traffic loads across the subgrade. The materials used may be soil-aggregates, unbound granular material, or bound granular material.

Soil-aggregate subbases consist of soil from the subgrade, combined with mineral aggregate present on the road surface, with or without additional aggregate. ASTM D1241-07, Standard Specification for Materials for Soil-Aggregate Subbase, Base and Surface Courses describes soil-aggregate as: sand-clay mixtures; gravel; stone or slag screenings; sand; crusher-run coarse aggregate consisting of gravel, crushed stone, or slag combined with soil mortar; or any combination of these materials. These subbase materials are spread, shaped and compacted in accordance with Department of Transportation (DOT) contract documents.

They differ from granular subbases, which are composed of granular material that may be present on the roadbed, plus a specified quantity of virgin aggregates – with or without recycled materials – that meet strength, abrasion and gradation specs. The granular mixture is placed on a subgrade, uniformly moistened, shaped and compacted to spec.

Aggregates used in granular base and subbase applications generally consist of sand and gravel, crushed stone or quarry rock, slag, or other hard, durable material of mineral origin, according to the Federal Highway Administration (FHWA). The gradation requirements vary with type base or subbase.

“Granular base materials typically contain a crushed stone content in excess of 50 percent of the coarse aggregate particles,” according to the FHWA. “Cubical particles are desirable, with a limited amount of flat or thin and elongated particles. The granular base is typically dense-graded, with the amount of fines limited to promote drainage.”

Granular subbase is also dense-graded, but tends to be somewhat coarser than granular base, FHWA says. The requirement for crushed content for granular subbase is not required by many agencies, FHWA says, although provision of 100-percent crushed aggregates for base and subbase use is increasing in premium pavement structures to promote rutting resistance.

“A granular subbase course is that part of the pavement structure constructed to provide a foundation for the base course, to distribute the superimposed loading to the subgrade and to provide drainage beneath the base and surface courses,” states the Wisconsin DOT in its Construction and Materials Manual. “It usually consists of natural sand or a mixture of sand with gravel, excavated and constructed with grading equipment as an item under a grading contract.”

Before placing the subbase material, the subgrade or foundation must be properly prepared, the Wisconsin DOT says. “It should be smooth, shaped to conform to required crown and grade, and be compacted to the required density.”

Where travel of the placing equipment ruts or disturbs the foundation, means must be employed to correct these conditions ahead of placing the subbase material, the Wisconsin DOT warns. “If the subbase is constructed on a rutted foundation, the roadbed will not drain properly and areas of weakness may develop in the pavement structure. Placing, shaping and compacting the subbase material to conform for its full width to the required grade, section and density is necessary for satisfactory construction of the proposed base course. The inspector should frequently check the subbase course for correct depth and spread.”

Draining the Subbase

Wisconsin DOT warns of the danger of water in pavement structures. It’s commonly said that “water is the enemy of pavements.” Therefore, whatever can be done to keep water out of the pavement structure is effort well spent.

As noted below, saturated pavement structures will actually pump water and base fines out of HMA fatigue cracks or along the sides of PCC slabs, indicating subbase and base layers in dire straits.

Pavement structures will contain water in its free state, as capillary water between the granular material, bound moisture, or water vapor. Free water is the form of most concern, engineers say, because it can do the most harm and is the only form of water that can be significantly removed by gravity drainage.

The subgrade, granular subbase and other pavement layers always are constructed with cross slope to facilitate drainage. Rain or melt water will enter pavement through cracks and joints in the driving surface. A properly designed pavement will use gravity to encourage water to find its way through voids in the granular base and subbase following the slope, to either exit the structure into side ditches, or into a built-in pavement drain that will take it to ditches and ultimately to a creek, wetland or bioswale.

Permeable road bases are made of an open-graded granular material that allows free flow of water through the subbase or base layer, and then out to a drainage appurtenance. The permeable base may be unbound or bound, as in the case of the cement-treated permeable base – which adds structural strength – and may be separated from the subgrade by an impermeable drainage fabric that keeps fines from migrating from the subgrade into the subbase.

‘Daylighted’ Permeable Bases

Optimal use of fabric requires a drainage system, but a lower-cost design for PCC pavements — the “daylighted permeable base” — allows free draining of water to roadside.

“Daylighted permeable bases are well-suited for roadways with flat grades (1 percent or less) and shallow ditches, where it is difficult to outlet drainage pipes at an adequate height above the ditch,” says the FHWA in its 2009 Tech Brief publication, Daylighted Permeable Bases.

“Daylighted permeable bases have been used for more than 20 years in the United States to remove infiltrated water from pavement structures,” FHWA writes. “[W]hen appropriately used, designed, constructed and maintained, daylighted permeable bases have the potential to perform just as well as edge-drained permeable bases, for about the same or even lower cost.”

Two types of materials have been used for daylighted permeable bases, FHWA says. The first is an unstabilized large-sized stone, also called a rock base, typically constructed about 18 to 24 inches thick. The second type of material is a permeable base gradation such as would be used for an edge-drain system, either untreated or treated with asphalt or portland cement, and typically constructed about 4 to 6 inches thick. The permeability requirements and asphalt or cement content required to maintain long-term stability are the same for daylighted permeable bases as for edge-drained permeable bases, FHWA says.

A permeable daylighted base needs a suitable separator layer beneath it to prevent subgrade fines from migrating up into and clogging the base, but not necessarily a fabric, FHWA reports. “This may be an appropriately graded untreated aggregate subbase, an appropriate geotextile fabric, or a layer of subgrade soil treated with sufficient lime or cement to achieve good long-term stability and resist erosion,” the agency says.

Download the complete report at fhwa.dot.gov/pavement/concrete/pubs/hif09009/hif09009.pdf

Impact of New Design Guide

Part of the new complexity of subbase design, and ultimately construction, derives from the ongoing adoption of new highway pavement design procedures set forth in the Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures, Final Report (NCHRP, 2004), now referred to as the Mechanistic-Empirical Pavement Design Guide (MEPDG), and in the process of adoption by DOTs from coast-to-coast.

Mechanistic-empirical are big words that describe a very simple concept. Mechanistic refers to the interaction between the materials and structure of a pavement, and how it stresses and strains under load deflection. The MEPDG paradigm relates these pavement mechanics to empirical or experimental performance data obtained in field or lab.

The guide uses mathematical models to describe this relationship, and the primary basis for all mechanistic-based pavement performance predictions methods is cumulative axle load applications.

“The benefit of a mechanistic-empirical approach is its ability to accurately characterize in situ material (including subgrade and existing pavement structures),” says the Washington State DOT in its online tutorial. “This is typically done by using a portable device to make actual field deflection measurements on a pavement structure to be overlaid. These measurements can then be input into equations to determine existing pavement structural support (often called backcalculation) and the approximate remaining pavement life. This allows for a more realistic design for the given conditions.”

The existing 1993 edition of the AASHTO Guide for Design of Pavement Structures is based on empirical equations derived from the well-known, but outdated, AASHTO Road Test. This program conducted performance testing between 1958 and 1960 of a limited number of structural sections at one location, Ottawa, Ill., and based on much-reduced traffic levels compared those of the 21st century.

Under the new design guide, a designer of any pavement must first consider site conditions such as traffic, climate, subgrade, existing pavement condition for rehabilitation and construction conditions in proposing a trial design for a new pavement or rehab. Then, using the software, the trial design will be evaluated through prediction of key distresses and smoothness. If the trial does not meet the demanded performance criteria, the pavement design must be revised until it does.

The new guide also incorporates procedures for performing traffic analyses, includes options for calibrating to local conditions, and incorporates measures for design reliability. Engineers can use the guide to analyze common causes of pavement distress, including fatigue, rutting and thermal cracking in asphalt pavements, and cracking and faulting in concrete pavements.

Reclaimed Materials in Bases

There is no question that recycled concrete aggregate (RCA) also may be used in road subbases and bases, so long as it is treated as an engineered material — that is, crushed, screened, processed and tested as though it were a virgin aggregate. (See Better Roads, Two for the Price of One, April 2010, pp. 16-29.)

In that Road Science Tutorial, we reported that TxDOT has researched and used RCA with good success for about 17 years. In the years 2006-2008, TxDOT saved approximately 1.8 million tons of virgin aggregates by incorporating RCA in cement treated base, flexible base, continuously reinforced concrete pavement (CRCP), filter dams, gabion walls, concrete traffic barriers, flowable fill and select backfill for mechanically-stabilized earth walls. “This equates to an estimated savings of $12.6 million from reduced or eliminated landfill and virgin aggregate associated costs,” TxDOT reports. “Savings from using RCA has the potential to increase tenfold based on current availability of RCA.”

But recycled aggregate from structures may perform just as well as RCA from demolished highways, say Dana V. Martin and Gregory W. Halsey, undergraduate research assistants, and Jeffrey S. Melton, research assistant professor, Department of Civil Engineering, University of New Hampshire-Durham, in their 2011 Transportation Research Board paper, Comparison of Building Derived Aggregate in Comparison to Crushed Stone.

Use of recycled concrete aggregate for road construction has become a widely accepted practice throughout the United States, and has proven to be an excellent substitute for crushed stone in road base applications. More than 45 states allow its use in highway construction, they write, adding the most common source of RCA is from the demolition of highway infrastructure. “While the use of RCA has become commonplace,” they say, “the use of building-derived aggregate (BDA) in roadway construction has not.”

BDA derives from the construction and demolition industry, which generates millions of tons per year throughout the United States, the researchers say. An inherent trait of BDA is that there are a variety of other materials present, such as brick, porcelain, cement-based masonry units and other inorganic materials, they write.

“The presence of these other materials has created a barrier in the use of BDA for roadway construction,” say Martin, Halsey and Melton. “The AASHTO standard for the use of crushed concrete in road base applications, M 319, allows only 5-percent brick by mass to be used.” But it’s common for BDA to have up to 10-percent brick by mass present, they write, which has precluded its use. The presence of nonconcrete materials in BDA has created a perception that it does not perform as well as RCA or crushed stone.

Their research, performed at the University of New Hampshire and funded by FHWA through the Recycled Materials Research Center there, has shown that BDA is a usable substitute for crushed stone. As it is also important to understand the long-term effects of using BDA, their study quantifies the longer-term performance and associated effects of using BDA in road construction.

On the other hand, the stiffness increase was almost 50-percent more than that of the crushed rock, and did not decrease with time, they say. “If this trend continues,” they report, “it would suggest that the presence of so-called deleterious materials like brick and tile is not significant, and that the BDA can be used as base course aggregate.”

Reclaimed asphalt pavement (RAP) is useful as an additive to crushed angular aggregate or pit-run granular soils for road subbases and bases in Montana, according to research from Montana State University.

In research prepared for the Montana DOT, Evaluation of the Engineering Characteristics of RAP/Aggregate Blends, by Robert L. Mokwa and Cole S. Peebles, Department of Civil Engineering, Montana State University-Bozeman, research and tests were conducted to evaluate the suitability of such RAP blends.

The study examined changes that occur in the engineering properties of aggregate materials when mixed with RAP. In addition to a thorough evaluation of published literature on the subject, an extensive suite of laboratory tests were conducted using four different aggregates blended with asphalt millings over a broad range of mix percentages.

Laboratory investigations suggest that the engineering properties of RAP-blended soils are comparable with those of virgin aggregates, they say.

“Gradation analyses indicate that the addition of RAP to virgin materials does not significantly change the particle size distribution,” Mokwa and Peebles say. “The outlook for the continued implementation of RAP as an additive to granular base and subbase materials for use in highway construction looks promising. Results from the extensive suite of laboratory tests indicate that blending asphalt millings with granular cohesionless material, like crushed aggregate or pit-run cohesionless soil, results in only minor changes to the engineering properties of the virgin material.”

Also, pit-run steel slag is extensively used for subbase construction in some areas, especially where weak subgrade conditions exist.

Steel slag is a crushed product having hard, dense, angular and roughly cubical particles. “Steel slag meets the requirements of ASTM D 694 and D 1241, of national agencies, and of local highway departments for macadam and crushed aggregate bases,” reports supplier Phoenix Services, Uniontown, Pa. “Local highway department standards or the producer’s recommendations are applicable for both base and subbase courses.”

Steel slag for use in bases and structural fills — where very high stabilities are required — may require proper selection, processing and aging (weathering) before use, Phoenix says. “Steel slag may contain free lime (CaO or MgO) that may cause the slag to be expansive or cause differential movement when used as a base,” Phoenix reports. “Steel slag is not recommended for use in rigid, confined applications such as concrete aggregate, base or fill under structures or floor slabs, or backfill against structures or bridge abutments.”