Effect of calcium sulfoaluminate cements composition on their durability

Abstract

Calcium Sulfoaluminate Cements (CSA) are considered as an alternative to Ordinary Portland Cement (OPC) for some applications. There is still a lack of knowledge on their durability and degradation mechanisms. The goal of this study is to investigate the influence of CSA cement composition on CSA cement paste durability. In addition to a commercial cement, two CSA cements with different amounts of ye'elimite (50 and 75 w.t. %) were synthetized for this study Three cement pastes were prepared and leached for one year in pure water at a temperature of 20 °C. The leachates were analyzed by ICP/AES and the cement pastes were characterized by X-Ray Diffraction (XRD), thermogravimetric analysis (TGA/DTG), Mercury Intrusion Porosimetry (MIP), and Scanning Electron Microscope (SEM). The results show that the leaching mechanism is first dissolutive than diffusive independently of the composition of calcium sulfoaluminate cement. Before leaching, the paste generated by the cement containing 50 w.t. % of ye'elimite had the highest porosity and was the only one to contain Stratlingite. During leaching, this material exhibited the lowest decalcification rate and showed the smallest degraded zone after one year of degradation. This study reveals that the presence of stratlingite has an important role in improving the durability of calcium sulfoaluminate cement paste.