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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.

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Long-term filtration tests were conducted to assess the hydraulic compatibility of the recycled concrete aggregate (RCA) and nonwoven geotextile that is typically used in underdrains. The RCA samples used in this study were collected from a single facility, but with different ages (aged in the laboratory). Geotextile samples were also exhumed after each test and evaluated for reduction in their serviceability. The laboratory tests showed that aging does not adversely affect the hydraulic properties of the RCA in long-term filtration tests. The results showed that the previously defined serviceability criteria based on gradient and permeability ratios are not relevant to evaluate the hydraulic compatibility of RCA/geotextile tested in this study due to the existence of turbulent flow regime. An alternative limiting ratio called herein hydraulic conductivity ratio (HCRLFT) is proposed and validated with long-term filtration tests performed with natural aggregates. An acceptance criterion of HCRLFT ≤ 4 is suggested to assess the compatibility of RCA (or natural aggregate)/nonwoven geotextile systems.