Pore structure development of cementitious materials with manufactured sand from various lithologies and differential effect of CaO–MgO blend expansion agent

Abstract

With intensifying the contradiction between the demand and supply of nature sand (NS), the extensive utilization of manufactured sand (MS) as a substitute has become prevalent in various projects. The pore structure development plays a crucial role in early-age shrinkage of concrete, but research on pore structure development of cementitious materials incorporating diverse lithologic MS is still lacking. This study examined the effects of MS powders and particles from diverse lithologies on pore structure, along with the differential impacts of CaO–MgO blend expansion agent (CMEA) on the pore structure of mortar containing MS from different lithologies. The results demonstrated a significant reduction in the peak value of pore size distribution and porosity in cement paste after incorporating MS powder, particularly with the most pronounced effect observed in tuff powder. In mortar, the incorporation of tuff manufactured sand (TMS) also led to a substantial decrease in both the peak value and peak area. However, the pore size distribution peak value and areas of limestone manufactured sand (LMS) mortar were slightly higher than those of NS mortar at 3 and 7 days. In comparison to cement pastes, the secondary peak proportion in mortars increased by approximately 4–5 percentage points at 28 days. Furthermore, the harmful pores and severely harmful exhibited varying degrees of increase in diverse lithologic MS mortar after incorporating CMEA, with the highest increase observed in NS mortar and the smallest increase observed in TMS mortar.