No abstract

Mechanical and hydraulic properties of recycled concrete aggregate (RCA) were evaluated for use as backfill in mechanically stabilized earth (MSE) walls. Large-scale drained triaxial tests, direct shear tests and pullout tests were performed to obtain mechanical properties of RCA interacting with various geosynthetics. Long-term filtration (LTF) tests were performed to evaluate hydraulic conductivity of RCA-geotextile systems. Results showed that the RCA had an internal friction angle of 49°, which was within the typical range. The RCA-uniaxial geogrid had the highest interface friction angle of 36° – and the interface friction angles of RCA-biaxial geogrid, RCA-nonwoven geotextile, and RCA-woven geotextile were 32°, 26° and 22°, respectively. Reinforced RCA showed comparable pullout capacity to reinforced sand. No slippage was observed between the RCA and geotextiles or geogrids, and the failures occurred mainly due to rupture of the geotextiles and geogrids during the pullout test. Results of the LTF tests showed that, over a filtration period of 2500 h, the ratio of mean hydraulic conductivity of RCA only to that of RCA-nonwoven geotextile and RCA-woven geotextile systems remained between 0.91 and 3.2, suggesting that the clogging of the geotextiles with RCA was minimal.

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 backcalculated 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.

No abstract