Effect of calcium sulfoaluminate cement on the hydration process and water resistance of phosphogypsum slag cement

The hydration properties and water resistance of phosphogypsum slag cement with different contents of calcium sulfoaluminate cement (CSA) were investigated through the tests of setting time, fluidity, pH of pore solution, flexural strength, compressive strength, water absorption, softening coefficient, hydration heat, and hydration products. The results indicate that as the CSA cement content increases, the fluidity of the cement paste decreases, the setting time shortens, the pH of the pore solution decreases, and the cumulative heat release in 3 d increases. Early age flexural and compressive strengths of the cement paste continuously increase with higher CSA cement content. The addition of CSA cement delays the hydration of phosphogypsum slag cement to a certain extent, but the pH of the pore solution shows an upward trend as hydration progresses. The softening coefficient of phosphogypsum slag cement increases to some extent with increasing CSA cement content, while the water absorption of the cement mortars initially decreases and then increases. As the CSA cement content increases from 0% to 15%, the cumulative heat release of the cement paste at 3 d rises from 78.4 J g −1 to 124.8 J g −1 , which remains lower than that of typical low heat Portland cement. • Adding CSA cement accelerates the setting time and reduces the fluidity of cement paste. • With added CSA cement, the heat release of phosphogypsum slag cement stays low. • A certain amount of CSA cement can improve the water resistance of phosphogypsum slag cement.