Climatic effect on resilient modulus of recycled unbound aggregates

The effect of temperature on plastic strain and resilient modulus (M-R) of different sources of recycled asphalt pavement (RAP) and recycled concrete aggregate (RCA) was evaluated from the results of laboratory temperature-controlled M-R tests, with a conventional Class 5 aggregate serving as the control. Freeze-thaw tests were also conducted on samples of RAP and RCA. Five years (spring-summer-fall-winter) of field falling weight deflectometer (FWD) tests were conducted on three pavement sections with RAP, RCA, and Class 5 as the unbound base course. Laboratory test results showed that temperature rise increased plastic strain and reduced M-R of RAP under cyclic loads but had a negligible effect on plastic strain and M-R of RCA. Freeze-thaw cycles steadily reduced the M-R of RAP; however, long-term freeze-thaw cycles increased the M-R of RCA. Thermal preloading reduced the plastic strain and increased the M-R of the compacted RAP. Construction of a pavement system made with RAP is thus recommended during warm seasons to induce thermal preloading. The elastic modulus back-calculated from the FWD tests did not show a consistent trend with respect to temperature change. No significant change on elastic modulus of RAP, RCA, and Class 5 aggregates due to freeze-thaw cycles was observed over five years.