Using sulphoaluminate cement and calcium sulfate to modify the physical–chemical properties of Portland cement mortar for mechanized construction

Abstract

The mortars with Portland cement (PC), sulphoaluminate cement (CSA) and calcium sulfate (C S¯) have the potential to improve mechanized construction efficiency and apply in high chloride environments. To better understand the performance of the mortars, this work investigated the roles of sulphoaluminate cement replacing Portland cement ratio (CRPR) and calcium sulfate to sulphoaluminate cement ratio (CCR) on the physical–chemical properties of the PC-CSA-C S¯ system. Results show that the variation of CRPR or CCR affects the setting time, strength, water absorption and chloride diffusion of the mortars. In the hydration process, it is found that aluminate (C3A) in PC and ye’elimite (C4A3S¯) in CSA compete in the reaction with C S¯ to form ettringite (AFt), and this competition affects the hydration and pore structure of the cementitious system. The volume of pores over 20 nm increases with CRPR, but declines with CCR. Moreover, compared with pore structure, ettringite (AFt) content and the hydration degree of alite (C3S), monosulfoaluminate (AFm) content has better effect on blocking chloride diffusion.