Effect of Recycling Agents on the Laboratory Performance of Asphalt Mixtures Containing Recycled Asphalt Shingles

The use of recycled asphalt shingles (RAS) as a partial replacement for aggregates and petroleum-based virgin asphalt cement binder has gained interest; however, many state departments of transportation are still cautious about adopting high RAS content in their designs because of construction concerns and durability issues. The objective of this study was to conduct a comprehensive laboratory evaluation of asphalt mixtures containing RAS with and without recycling agents. The study used post-consumer waste shingles. Five 12.5-mm asphalt mixtures were designed to meet Superpave (R) design criteria, with three of the five mixtures containing no recycling agents and two mixtures containing recycling agents (a naphthenic and a vegetable oil). Laboratory testing evaluated rutting performance, moisture susceptibility, fracture resistance, and the critical cracking temperature of laboratory produced mixtures. The testing used the Hamburg loaded-wheel tester, the semicircular bending test, and the thermal stress restrained specimen test in addition to the dynamic modulus test. The results from the experimental program indicated that asphalt mixtures containing 5% RAS without recycling agents had similar performance compared with the control asphalt mixture containing no RAS at high, intermediate, and low temperatures. The inclusion of RAS with and without recycling agents showed an improvement in rutting performance with no adverse effect on moisture sensitivity compared with the control mixture without RAS. However, because the use of recycling agents increased the recycled binder ratio, the intermediate- and low-temperature performances of the mixture were adversely affected.