Compactness and hardened properties of machine-made sand mortar with aggregate micro fines

Abstract

Machine-made sand (MS) has become a hot topic in construction materials due to the depletion and scarcity of natural river sand. Aggregate micro fines (AMF) of varied contents were included in MS during the manufacturing process. To quantify the filling role of AMF in MS mortars, a physical packing model together with the related mathematical model of fresh mortar was established by considering the water as a void component in fresh mortar mixture. A total 42 MS mortar mixes with different water-cement (W/C) ratios (0.45, 0.5, 0.55, 0.6), different sand-cement (S:C) ratios (1:1, 2:1, 3:1) and different contents of AMF (0 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%) were prepared. The effects of AMF on the bulk density and compactness of fresh mortar, flexural and compressive strength, pore structure and microstructure of hardened mortar were investigated. The results show that the changing trend of compactness of fresh mortar is in consistent with the results of the bulk density and mechanical properties of the mortar. The optimal contents of AMF are found to be dependent on the W/C and S:C ratios. Our results show that, when S:C = 2.5:1, the optimal contents of AMF by weight of MS are 5 wt%, 10 wt%, 15 wt%, and 20 wt% for the mixes with the W/C ratios of 0.45, 0.5, 0.55, and 0.6, respectively; when the W/C = 0.5, the optimal AMF contents are 5 wt%, 10 wt%, and 15 wt% for the mixes with the S:C ratios of 1:1, 2:1, and 3:1, respectively. The results of mercury intrusion porosimetry (MIP) and electron backscattered diffraction (EBSD) show that the AMF can modify the pore structure and enhance the interfacial transition zone (ITZ) of mortar.