Further insights into calcium sulfoaluminate cement expansion

There is still an ongoing debate on the mechanisms of expansion of calcium sulfoaluminate (CSA) cements, which can be either favorable e.g. in shrinkage compensating construction materials or deleterious in cases of excessive expansion. In order to expand on previous studies, CSA cements with molar ratios (M) of calcium sulfate/ye’elimite of 0.1, 1, 1.5 and 2 were investigated from 30 minutes to 182 days. All systems showed expansion, and expansion was found to increase with increasing gypsum content. The sample with M = 2 showed a high expansion and severe cracking after 1 day of hydration. Based on the pore solution chemistry crystallization pressures were calculated, which revealed that not only ettringite, but also the other hydrate phases present (AH3, strätlingite, CAH10, monosulfate) may contribute to the total crystallization pressure. The percolation pore radii obtained by mercury intrusion porosimetry were used to calculate hydrostatic tensile stresses. It was found that in all investigated systems the hydrostatic tensile stresses exceeded the 1 d tensile strength, which is in line with the fact that all samples showed expansion.

Author: C.W. Hargis, B. Lothenbach, C.J. Mueller, F. Winnefeld

Section: Science and production

Keywords: calcium sulfoaluminate cement, expansion, durability, pore solution, thermodynamic modeling