Climatic effect on resilient modulus of recycled unbound aggregates

The effect of temperature on plastic strain and resilient modulus (MR) of different sources of recycled asphalt pavement (RAP) and recycled concrete aggregate (RCA) was evaluated from the results of laboratory temperature-controlled MR 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 MR of RAP under cyclic loads but had a negligible effect on plastic strain and MR of RCA. Freeze–thaw cycles steadily reduced the MR of RAP; however, long-term freeze–thaw cycles increased the MR of RCA. Thermal preloading reduced the plastic strain and increased the MR 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.