Effect of limestone powder in manufactured sand on the hydration products and microstructure of recycled aggregate concrete

In this paper, X ray diffraction test and Scanning electron microscope test were designed to investigate the effect of limestone powder (LP) in manufactured sand on the hydration products and microstructure of full recycled coarse aggregate concrete samples. The results showed that most of LP was inactive, except only a small quantity of LP participated in the hydrating reaction at mid-late period. This small amount of LP did not change the composition of hydration products but varied their morphology. Some amount of LP filled in the pore structure of cement matrix and in the interface between recycled coarse aggregate and new harden cement paste, improving the compactness of the cement matrix and the interfacial transition zone. The nucleation around the LP who filled in the pore structures was also observed, and the hydration products gradually formed and subsided on the surface of these LP and accelerated the cement hydration.