Expansion Characteristics of Calcium Sulfoaluminate Hydrates

In contrast to the general belief that formation of calcium trisulfoaluminate hydrate is accompanied by expansion even under conditions of restraint, Chatterji and Jeffery speculated that formation of calcium monosulfoaluminate hydrate is mainly responsible for the expansion phenomenon. Because of the importance of calcium sulfoaluminate hydrates in sulfate disruption of portland cement concretes and in expansive cements used for making crack-resistant concretes, the author, using data reported by Chatterji and Jeffery, attempted to reproduce their results. Some additional experiments were made to test the validity of their hypothesis. The results of the experiments showed that in every case, under conditions of restraint, it was formation of calcium trisulfoaluminate hydrate and not calcium monosulfate hydrate that caused significant expansions, which is contrary to the hypothesis of Chatterji and Jeffery.