Construction of rubber-modified asphaut pavements

Public road agencies are currently evaluating hot mix applications of PlusRide™ and Arm-R-Shield™ modified asphalt pavements. The processes use reclaimed rubber from ground automotive and light truck tires to reduce reflective and thermal cracking, suppress traffic noise, increase resistance to studded tire wear, and reduce the environmental impact of tire disposal. The projects constructed to date have primarily been experimental because the capital cost for this surfacing alternative ranges from 1.5 to 2 or more times the cost of conventional asphaltic concrete. A literature review of the construction practices and a questionnaire survey of contractors are used to determine why the construction costs of the modified mixes have been so high. One of the factors is the increase in financial risk perceived by contractors who bid on these types of pavements. Another cost factor, especially with the PlusRide™ system, is the unusual aggregate gradation required by the process. Still another concern is the increased mixing temperatures and times required by both rubber-modified products. For Arm-R-Shield™, the high cost of the mix primarily reflects the cost of the asphalt-rubber binder supplied by the manufacturer. These costs could be reduced by development of specifications which limit the contractor’s risk, such as the use of conventional aggregate gradings, requiring minimum increases in mixing temperature and time, and allowing competition between rubber-modified asphalt suppliers.