Advances in Pavement Performance Enhancement with Dry Process Engineered Ground Tire Rubber

Ground Tire Rubber, or GTR, is gaining popularity as a recycled mixture component and performance-enhancing asphalt mix modifier in multiple U.S. states. This noticeable increase in usage has been driven by recent advances in production technologies, material specifications, modern asphalt mixture performance testing, cost-savings, and favorable field performance comparisons with polymer modified asphalt mixes. This paper details laboratory and field investigations of recent GTR designs, demonstration projects, and routine construction projects in Georgia, Virginia, Texas, Wisconsin, Illinois, and Missouri, including high-profile interstate and Tollway paving projects with up to 15 years of performance experience. Both terminal blend and dry process rubber asphalt modification techniques are investigated, with the latter involving a chemically engineered, dry GTR system designed to impart workability and performance characteristics beyond that achieved with simple GTR addition. Mix lab testing methods and procedures will be discussed, and recommendations will be presented regarding BMD with dry process rubber. Mixture performance and field tests indicate that GTR-modified, stone-mastic asphalt (SMA), open graded, and dense graded mixes can perform similarly to polymer-modified mixtures, but at significantly lower modification costs. Field data, economic data, and contractor feedback from several states will be presented, along with brief discussion of the application of an engineered crumb rubber (ECR)-modified mix used at ASCE Headquarters in Reston, VA.