Mechanical properties of ready-mixed concrete incorporating fine recycled aggregate

Experimental research was conducted to investigate the replacement ratio and water absorption of fine recycled aggregate (FRA) on the fresh and hardened properties of recycled aggregate concrete (RAC). Two types of FRA, originating from construction and demolition wastes of concrete structures, were used in this study - FRAL with a lower water absorption ratio of 5.83% and FRAH with a higher water absorption ratio of 7.95%. The fresh and hardened properties of RAC with different replacement levels of FRAL (0%, 30%, 60% and 100%) and FRAH (35% and 70%) were studied. In considering practical applications of FRA concrete, all the concretes were obtained from a local ready-mix plant in Daejeon, Korea. The paper reports the results of tests for slump, air content, compressive strength, splitting tensile strength, modulus of rupture, drying shrinkage, creep, flexural performance, shear performance and bond performance. The results show that the slump and compressive strength of ready-mixed concrete with 100% replacement of FRAL were 10% and 13% lower than the respective values for conventional concrete. RAC prepared with FRAH showed a more marked reduction in strength compared with the FRAL RAC. A replacement level of FRA of more than 30% has a negative effect on the drying shrinkage, creep and bond performance of concrete, whereas the shear and flexural performance of beams with 70% and 100% replacement of FRAH and FRAL were similar to those of conventional concrete beams. It may be concluded that, for structural concrete of medium compressive strength, the substitution of FRA with water absorption ratio in the range 5.8-8.0% does not seem to seriously affect the mechanical properties of concrete for replacement ratios up to 30%.