Experimental analysis of mechanical properties of CSA mortar incorporating hydrophobic agents

Abstract

Various methods have been proposed to improve the durability of cement composites by reducing water absorption. One such method involves imparting hydrophobicity to cement composites. However, research on imparting hydrophobicity has primarily focused on Ordinary Portland Cement (OPC). This study investigated the properties of rapid-hardening CSA (Calcium Sulfoaluminate Cement) composites by imparting hydrophobicity using PDMS and TEOS. The evaluation of CSA cement included mechanical properties, microstructure, and water absorption due to hydrophobicity. The mixing ratio of the hydrophobic material was fixed at 0.5 % of the cement volume, and the PDMS content varied from 25 % to 90 %. As the PDMS content increased, the setting time also increased, but the change in initial setting time was negligible within the range where effective hydrophobicity was maintained. The incorporation of the hydrophobic solution significantly reduced the degree of length change, while the compressive strength decreased by up to 15 %. Additionally, the average capillary pore size and water absorption rate in the treated mortar both decreased, resulting in increased water repellency and a negative capillary force. These results provide guidelines for the development of CSA mortar formulations that balance water resistance and mechanical properties, and suggest CSA cement mortar as a suitable material for environments where water repeatedly penetrates and is absorbed. © 2025 The Author(s)