• Whether the precast slabs are placed together or individually has a dramatic effect on installation costs.

• There needs to be sufficient time between finalizing the detail and the installation to allow for casting and curing of the slabs.

• To gain the benefits of longevity with the precast concrete, wet curing requirements should be tightened up. The standard at the time of the project required wet cure of 14 days.

• Utah DOT’s generic option needs additional design work, drawings and details to reduce risk in bidding. Included should be casting tolerances, requirements for dowel bar caps, reinforcing steel, joint tolerances, details on how to deal with tie bars and offset transverse joints, bedding grout and encasement grout.

• Any asphalt patching requirements should be included in project documents.

• Finishing requirements (i.e., a broom finish) should be included in project documents.

• Minimum length of slabs to be allowed to remain in place should be clarified.

• Additional slab removal instruction should be provided.

• Vertical placement tolerances should be increased to allow for a little bit of settlement. On the project, some slabs ended up below the grinding plane.

• Bedding grout is essential to slab stabilization. On the project, traffic caused even the shimmed slabs to squirm and settle a little bit if the grout had not been installed.

• Acceptance testing should be included and encasement grout strength verified.

• Tie bars, No. 5 bars at longitudinal joints, were a construction complication.

Drilling increased work exposure to traffic and was a time-consuming part of the process. The need for and benefit from these tie bars should be re-evaluated.

Additional information on the project can be obtained from Scott Nussbaum at snussbaum@utah.gov, Barry Sharp of Central Materials at rsharp@utah.gov, or David Stevens of Research at davidstevens@utah.gov.

Benefits of High-Friction Pavements

According to a 2010 Virginia Tech Transportation Institute (VTRC) report, high-friction driving surfaces offer long-term performance and a positive benefit-to-cost ratio. The report, Field Performance of High-Friction Surfaces was authored by Edgar de León Izeppi, Ph.D., senior research associate, Center for Sustainable Transportation Infrastructure; Gerardo W. Flintsch, Ph.D., associate professor of civil and environmental engineering, and director, Center for Sustainable Transportation Infrastructure Virginia Tech Transportation Institute; and Kevin K. McGhee, P.E., associate principal research scientist, VTRC.

Great attention has been focused on the new concept of pavement preservation, even in place of capacity improvements. As interest in pavement preservation via thin high-performance asphalt overlays grows in this decade, focus will fall on such high-friction driving surfaces as an option for thin-lifts.

The goal of the researchers was to develop guidance for agencies when they consider a high-friction surface (HFS) for low-skid resistance pavements, or where there is a need for high friction.

“HFS systems are specially designed thin surface treatments that provide significant additional skid resistance [for] pavements and bridge decks without significantly affecting other qualities of the surface such as noise, ride quality, or durability,” the authors write.

In addition to an overview of HFS locations and climatic conditions, the authors recount experiences reported by user agencies, and summarize key HFS service-level indicators, such as friction and texture. Agency experiences include a sample benefit-cost analysis from an installation in Wisconsin that justified an HFS application through crash reductions that resulted following the measured increase in skid resistance.

“Optimal surface conditions should exhibit sufficient friction and texture depth to reduce roadway highway accidents,” the researchers write. In the context of pavement management, HFS pavements are becoming an appealing alternative to conventional pavements as these systems can increase friction and improve texture immediately after placement without significantly affecting other pavement qualities, such as noise or durability, they say. Such high-friction surfacings consist of high-polished stone value aggregates mixed with some type of resin to hold the aggregate particles together and bond them to the existing pavement surface.