Preparation of recycled sand from WRSG and compressive and flexural behavior of recycled aggregate concrete

The use of both recycled coarse aggregates (RCAs) and recycled sand (RS) derived from weathered residual soil of granite (WRSG) into concrete has the potential to greatly enhance the recycling of construction and demolition waste. However, the characterization of RS from WRSG and the compressive and flexural performance in fresh concrete containing RCAs and RS have not been thoroughly investigated. In this study, clay content, fineness modulus, chemical compositions, mineral compositions, and pore structure of RS from WRSG were tested. On this basis, the optimized preparation parameters of RS were suggested. The compressive behavior, flexural behavior, and cement hydration degree of recycled aggregate concrete (RAC) simultaneously containing RS and RCAs were investigated comprehensively. A stereological model was proposed to explain the results related to cement hydration. The results showed that: (a) the optimized preparation could substantially lower the clay content of RS; (b) RS was more porous than natural sand (NS), resulting in a higher water absorption during mixing; (c) the compressive strength of concrete containing RS developed faster than the concrete with NS; (d) at day 90, the compressive and flexural strength of the concrete containing RS were not less than those of the concrete with NS; and (e) RS was shown to have a greater influence on the hydration degree of cement paste than RCAs, due to RS significantly reducing the average value of inter-aggregate spacing in concrete, making the cement paste more susceptible to the internal curing effect induced by the water in aggregate pores.