Effect of Calcium Chloride Solution on Performance of Calcium Sulphoaluminate Cement at –10 ℃

The influence of cold CaCl₂ solution on the setting behavior, strength development, mineralogical composition, microstructure, and chloride content of calcium sulphoaluminate (CSA) cement at –10 ℃ was investigated. The results show that there is a significant and persistent temperature peak in CSA cement pastes mixed with 16% and 28% cold CaCl₂ solution, so CSA cement can hydrate continuously. The temperature peak retards from 90 min to 150 min as the solution concentration increases from 16% to 28%. The pastes with 16% CaCl₂ solution set quickly and the compressive strength is high (initial setting time 15 min and final setting time 24 min, compressive strength 41.0 MPa at 1 day and 85.2 MPa at 28 days); while the pastes with 28% CaCl₂ solution set slowly and the compressive strength is low (initial setting time 85 min and final setting time 155 min, compressive strength 24.3 MPa at 1 day and 57.7 MPa at 28 days). Ettringite is the primary hydration product and its morphology is needle in hydrated pastes with 16% CaCl₂ solution. The Friedel՚s salt turns to be dominant and the morphology is hexagonal plate in hydrated pastes with 28% CaCl₂ solution. There is little binding chloride for 16% CaCl₂ solution and 0.95% binding chloride for 28% CaCl₂ solution. In the presence of CaCl₂ solution, the CSA cement can hydrate continuously at –10 ℃ . Furthermore, a shorter setting time and a higher strength can be obtained in CSA cement pastes mixed with 16%‒20% CaCl₂ solution.