Strength and stiffness of compacted crushed concrete aggregate

A comprehensive series of drained triaxial compression tests were performed on crushed concrete aggregate (CCA) moist as compacted. When compared to ordinary natural well-graded gravelly soils, the peak strength and stiffness increase more significantly with dry density, while the effect of the degree of saturation during compaction is much less significant. In a range of confining pressure of 30–600 kPa, the strength and stiffness of well-compacted CCA is similar to, or, in some cases even higher than, typical selected high-class backfill materials (e.g., well-graded gravelly soil of crushed quarry hard rock). The strength and stiffness of CCA with a maximum particle size D_max=37.5 mm obtained from a typical concrete crushing plant are noticeably lower than CCA sieved to D_max=19 mm compacted using the same energy. However, when compacted to the same dry density, the original CCA exhibits the strength and stiffness higher than the sieved CCA. Effects of the strength of original concrete on the strength and stiffness of compacted CCA are insignificant, while the strength and stiffness of compacted CCA are, respectively, noticeably higher than, or similar to, the original concrete aggregate (i.e., natural gravelly soil) compacted using the same energy. All these results indicate that well-compacted CCA can be used as the backfill material for important civil engineering soil structures requiring a high stability while allowing a limited amount of deformation.