The disposal of massive amounts of demolished concrete and excavated soil, and the consumption of large amounts of cement and natural aggregates for concrete have restricted urban development. Recycled lumpaggregate concrete (RLAC), containing recycled lumps (RLs), recycled coarse aggregates (RCAs), and recycled sand (RS), is a potential solution. However, the higher crushing index and clay content, along with the lower fineness modulus and apparent density of RS derived from weathered residual soil of granite (WRSG) compared to natural sand, have raised concerns regarding the performance of RLAC. In this study, the compressive behavior and permeability of RLAC were investigated. The positive effect of WRSG-derived RS on RLAC permeability was quantitatively revealed for the first time, and the underlying mechanisms were elucidated. The quantitative effect of RS on the compression behavior and its engineering acceptability were also clarified. The results showed that: (a) The use of WRSG-derived RS had a slight effect on the compressive strength of RLAC. However, the presence of clay minerals with poor elastic modulus in RS led to a reduction in the elastic modulus of RLAC, with a maximum decrease of 6.1%, which is acceptable for practical applications. (b) The promotion of RS to cement paste hydration, adequate filling of RS in the cement paste, and tight mechanical interactions between RS and the cement paste contributed to a denser mortar microstructure. The permeability coefficient of RLAC and the porosity of harmful pores (>100 nm) in fresh mortar were reduced by 86% and 55%, respectively, with 70% RS utilization. (c) When the water-cement ratio of fresh concrete was 0.36 or 0.45, although the impermeability grade of the RLs was only P4, the RLAC still had an impermeability grade of P12, which can satisfy almost all the engineering impermeability requirements.

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.