Improved early-age and late-age performances of calcium sulphoaluminate cement with the presence of calcium nitrate

Abstract

In calcium sulphoaluminate (CSA) cement, the belite (β-C2S) exhibits low hydration activity. In this study, to promote the hydration of β-C2S and improve the late-age performance of CSA cement, Ca(NO3)2 is introduced into CSA cement as an accelerator. The hydration and performance of the CSA cement were investigated. The results demonstrate that Ca(NO3)2 decreased the water demand for normal consistency. In addition, the dissolution of ye'elimite (C4A3$) and the formation of ettringite (AFt) are inhibited within the hydration age of 0–30 min, leading to a prolonged setting time. Inversely, the hydration of C4A3$ and formation of AFt is boosted in the following hydration period, which enhances the 6 h, 12 h, and 1 d compressive strength. In addition, Ca(NO3)2 promotes hydration ofβ-C2S in CSA cement at 28 d, which improves the late-age compressive strength. For the CSA cement with Ca(NO3)2, the capillary pore volume of the hardened cement paste decreases, which could improve the permeability and corrosion resistance. Therefore, Ca(NO3)2 is an appropriate admixture to improve both the early-age and late-age performances of CSA cement.