New software promises to put whitetopping on the map: A new software product is forthcoming to help highway agencies and others evaluate portland cement concrete as a viable alternative for pavement overlays

Public Roads, July-August, 2002 by Robert Otto Rasmussen, George K. Chang, J. Mauricio Ruiz, W. James Wilde, Patricia Kim Nelson, Jason Dick, Dan K. Rozycki

Mending deteriorated asphalt pavements with portland cement concrete is a familiar technology Highway engineers used whitetopping--concrete overlays placed on top of asphalt--as early as 1918. Offering benefits that include long life and superior bonding to underlying material, whitetopping overlays grew in popularity through the mid-1970s, and ultra-thin whitetopping burst onto the scene in the early 1990s. Until recently, however, pavement engineers had no one clear resource or set of guidelines that they could refer to when determining where, when, or how to use whitetopping as a pavement option.

In 2001, to fill this knowledge void and help validate whitetopping as a viable alternative, the Austin, TX-based transportation engineering firm, The Transtec Group, developed design, construction, and rehabilitation guidelines for whitetopping. Capitalizing on state-of-the-art computer modeling technologies, the firm is developing a Windows [R]-based software that pavement practitioners can use to analyze and compare different whitetopping strategies. Balancing cutting-edge research, field-tested best practices, and construction and traffic restraints with economics, the project team's goal is to help make whitetopping a more competitive alternative for roadway construction and rehabilitation projects. By June 2002, the white- topping software was nearing the beta testing stage.

Through Thick and Thin

Highway engineers have met great success using conventional whitetopping overlays--20 centimeters (8 inches) or more--for more than 60 years. And for the last 10 years, ultrathin whitetopping--5 to 10 centimeters (2 to 4 inches)--has satisfied the need for an effective low-cost overlay for intersections and low-traffic and low-speed applications. What was missing, according to Jim Mack, executive director of the American Concrete Pavement Association - Northeast Chapter, was a unified program to design thin overlays from 5 to 20 centimeters (2 to 8 inches).

"Conventional and ultra-thin whitetopping overlays are based on two different technologies and bonding interactions," Mack says. "The computer program will bridge the gap between ultra-thin and conventional whitetopping, enabling pavement engineers to design whitetopping overlays effectively for any road application from residential streets to high-volume interstates."

With the whitetopping software, pavement practitioners will be able to analyze all three whitetopping applications-ultra-thin, thin, and conventional. The software will help construction and materials engineers, construction supervisors, and contractors produce more effective concrete mixtures, pavements, specifications, and repairs using whitetopping overlays. The product will help engineers choose the proper overlay thickness, joint spacing, and the optimum surface preparation.

"We want States to think about whitetopping as another tool that they can use to rehabilitate roadways, but they need to know how to use it properly," says Ken Fults, director of the materials and pavement section in the Construction Division of the Texas Department of Transportation (TxDOT). "The software will enable States to make better and more rational decisions about whitetopping."

A Systems Approach to Pavement Engineering

A virtual bible for all things whitetopping, the software demonstrates the inherent value of approaching the world of whitetopping through a systems approach. Rather than view the processes of white-topping design, construction, and rehabilitation as independent sets of procedures--which easily could have led to authoring three different sets of guidelines--the software developers elected to employ a systems approach to the project.

By integrating all three sets of procedures into one unified software program, the project team created a practical and reliable one-stop-shop That will enable State highway agencies, contractors and pavement designers to design and build-white topping overlays efficiently, based on the best data on materials, cost, and safety available in the industry.

Highway engineers used a similar approach when developing the original philosophy behind the asphalt industry's Superpave[TM], which combines, three distinct components--binder specification mix design, and performance prediction testing--into one comprehensive system.

"The whitetopping software will be for the concrete industry what Superpave[TM] is' for the asphalt industry," Bob Risser, executive director of the Michigan Concrete Paving Association, says. "But more than just a set of design principles, the white-topping software will provide a usable tool that highway agencies can use on a daily basis to explore pavement overlay alternatives."

A New Overlay Option

Highway engineers traditionally perceive portland cement concrete pavements as an option for new construction only, primarily for heavy-duty pavements. But for pavement rehabilitation, agencies generally view hot-mix asphalt (HMA) overlays as the first option, regardless of the existing pavement structure. HMA overlay designs, however, are not usually as robust as concrete. Economics and construction restraints often drive the design of HMA overlays, resulting in typical thicknesses of 10 to 15 centimeters (4 to 6 inches), independent of the design procedure. Many agencies regard an HMA overlay as an intermediate fix before major rehabilitation or reconstruction is required. In many cases, the length of service is expressed as a minimum requirement but not geared to any type of service-related distress.