"The higher RAP content on this particular job will save DelDOT approximately $2 per ton on liquid asphalt costs, and we'll still meet their PWL (percent within limits) specifications for density (93 percent minimum) and rideability specifications," Lester says.
Time to move forward
Jim Pappas, who heads up DelDOT's materials and research engineering office, says the project could very well be the beginning of how the road agency builds future projects.
"Our specifications have allowed 20-percent RAP up to this point, but the (asphalt) industry came to us with a higher RAP content recommendation and we agreed as long as the performance characteristics were the same," Pappas says. "We've been very involved with the Delaware Asphalt Pavement Association, participating in their quarterly meetings, and we just felt it was time to pursue the approach in an effort to control the rising cost of materials. We would like to implement this new design specification on all our projects if it performs as well as it should. We chose a project that must support a high volume of traffic (200,000 vehicles daily) and the research (loaded wheel test) we received shows that this mix design should support the traffic load without any significant rutting problems."
To ensure that the high-RAP mix meets DelDOT specifications, QA/QC incentives will be awarded, with 70 percent tied to material quality based on air voids, AC content and gradation, and 30 percent tied to compaction density. Density incentives are paid 100 percent if compaction achieves 93 percent minimum and rideability meets the International Roughness Index specifications.
The project is also generated substantial interest from the Federal Highway Administration, which brought in a mobile testing lab to monitor the project. The FHWA testing planned for the project will mirror that of DelDOT and Diamond Materials. Although FHWA testing will not be as frequent as that of DelDOT and Diamond Materials' lab technicians, the results will be shared with DelDOT and will also be used as resource material for a national data base source other road agencies can access.
"We really think this project is going to be very successful and if all goes well we could in fact rewrite our mix specifications for 2009 projects," Pappas says. "And with the price of AC climbing to over $500 per ton, we anticipate a savings of over $200,000 on a project like this. It's a very big project and one that will provide a lot of insight as we move forward in developing more cost-effective ways to build and maintain quality pavements for the state of Delaware."