“The desirable characteristics of such textures will be predominately negative texture coupled with good microtexture and excellent macrotexture,” says Scofield. NCGS can now be found at seven sites in five states. There are three test sections near MnROAD; one in suburban Chicago; one in Norman Okla.; one near Abilene, Kansas; and one near Omro, Wis.

Other test sections have been established this year in Washington state and in Arizona.

All surfaces are still performing as intended. As of 2009, ACPA’s figures show that OBSI testing was conducted on 288 pavement sections consisting of 126,720 lineal feet (24 miles) of concrete pavements across North America. The surfaces were evaluated with two goals in mind; first, to benchmark current surface texturing practices, and second, to develop insight into the acoustic longevity of textures. The acoustic longevity will become increasingly important as quiet pavement technology becomes integrated into noise mitigation.

Recent sound results from the MnROAD test sections indicate that NGCS pavements are running in the range of 99 dB(A) to 101 dB(A). By comparison, conventional diamond ground sections ranged up to 104 dB(A).

One test section in Kansas shows that an NGCS surfaces has produced 99 dB(A) and 100 dB(A) in two different tests. By comparison, an Astro-Turf drag surface ranges up to 102.5 dB(A) and an exposed aggregate surface ranges up to 104.5 dB(A).

A renewable surface

At MnROAD, Diamond Surface Inc. constructed a surface casually called NGCS LITE, which was designed as a renewable surface. It was developed to provide additional microtexture on existing NGCS surfaces if the need arose to do so. With the large land size (between the grooves) of the NGCS surface, the texture wear has been assumed to be less than for a conventional diamond-ground surface. So, NGCS is expected to have a long life by comparison. v

by Daniel C. Brown, Contributing Editor

In association with ACPA

(American Concrete Pavement Association)

How the Mechanistic-Empirical Pavement Design Guide Helps Optimize Concrete Pavements

The M-E PDG can account for numerous variables in concrete pavement design

In its simplest terms, concrete pavement design optimization considers the performance benefits of various components versus their cost.

Design optimization can be thought of in various ways, says Michael Ayers, PhD, Director of Education for Design and Construction at the American Concrete Pavement Association (ACPA). Those include:

Achieving long life;

Lowering initial cost;

Minimizing maintenance and rehabilitation costs; and

Developing a sustainable, environmentally-sound pavement system.

Until recently, pavement designers were mostly limited to the 1993 AASHTO Pavement Design Procedure. Although many agencies are still using the 1993 protocol, it has limited inputs and is not ideal for optimizing pavement design.

Concrete pavement design optimization considers the performance benefits of various components versus their cost.

By contrast, the current AASHTO Interim Mechanistic-Empirical Pavement Design Guide (M-E PDG) has many more input parameters, which allow designers greater influence over pavement performance. The M-E PDG combines empirical or observed pavement performance data from a number of sources – primarily the Long-Term Pavement Performance Studies done under the Strategic Highway Research Program, and mechanistically-calculated pavement response parameters.

“When you combine those two elements, it gives you the flexibility to account for various types of design optimization,” says Ayers. The variables to be considered depend on the design method used in the analysis. The M-E PDG has the capacity to consider support conditions (including subbases for concrete pavement), concrete materials and properties, load transfer (both longitudinal and transverse), and numerous other criteria.