Effect of protogenetic anhydrite on the hydration of cement under different curing temperature

- We investigated using protogenetic anhydrite instead of added gypsum to make cement.
- The optimum content of protogenetic anhydrite in cement increased with increasing temperature.
- Curing temperature made the concentration of sulfate ion in pore solution changed.
- Higher temperature increased the risk of delayed ettringite formation in cement paste.

Compared with the added gypsum, protogenetic anhydrite is the anhydrite in clinker and cement admixture. And using protogenetic anhydrite as the setting retarder instead of added gypsum to make cement could be an effective way to make full use of clinker and wastes with high sulphur content. However, the high temperature sensitivity of solubility property of protogenetic anhydrite may result in unhydrated anhydrite exist in cement paste under high curing temperature at early age, and that may make a bad influence on the properties of cement. This work investigated the effects of protogenetic anhydrite on the long-term strength, volume stability and hydration products of cement paste under different curing temperature. It is shown that higher curing temperature caused the greater value of optimum content of protogenetic anhydrite in cement, and protogenetic anhydrite could not make the bigger volume expansion and worse strength of cement than gypsum when the high curing temperature being used. But curing temperature caused the dissolution of protogenetic anhydrite change and influenced the concentration of sulfate ion in the pore solution of hardened cement paste. The results of XRD patterns showed that the risk of delayed ettringite formation in hardened cement paste cured at high temperature had been increased. The results will be helpful to understand the role of protogenetic anhydrite in cement, and further promote the use of clinker and wastes with high sulfate.