Microstructure and hydrophobic characteristics of calcium sulfoaluminate cement paste incorporated with PDMS and TEOS agents

Abstract

Hydrophobicity is a technique that improves durability by preventing the absorption of water and contaminants into cement composites. In this study, hydrophobicity was imparted to Calcium sulfoaluminate (CSA) cement, and the change in properties of the CSA cement composite (CSAC) by the hydrophobic material was investigated. For imparting hydrophobicity, a hydrophobic solution with different mixing ratios of polydimethylsiloxane (PDMS) and tetraethyl orthosilicate (TEOS) was prepared and mixed with CSA cement. PDMS and TEOS produce water and ethanol through hydrolysis and polycondensation reactions. As a result, ethanol reduces the consumption of ye'elimite and suppresses the formation of ettringite, and as the ratio of TEOS increases, the consumption of ye'elimite further decreases. This can lead to a decrease in the physical properties of CSAC. In addition, calcium silicate hydrate (CSH) gel generated by TEOS forms more networks of interconnected spheres as the ratio of TEOS increases. Hydrophobicity was greatest when the ratio of PDMS and TEOS was 7:3, and when the hydrophobic solution was mixed at more than 1% of the cement weight, there was no significant difference in hydrophobicity. Consequently, a hydrophobic CSAC was achieved, which is expected to expand the usability of CSA cement.