Effect of calcium sulphate dihydrate on early hydration of amorphous C12A7

To promote the utilization of amorphous C12A7, this work aims to clarify the effects of calcium sulfate dihydrate (CaSO4 · 2H2O) on early hydration characteristics of amorphous C12A7. The hydrated pastes were characterized with XRD, TG-DTG, FTIR, and SEM. Results showed that the content of CaSO4 · 2H2O influences both the rate and the products of hydration in amorphous C12A7. The setting time of amorphous C12A7 paste is delayed significantly in the presence of CaSO4 · 2H2O. The main products for the specimens with less CaSO4 · 2H2O were low-sulfur calcium sulfoaluminate (AFm) and gibbsite (AH3), whereas the main product was altered from AFm to ettringite with the increase in CaSO4 · 2H2O content. According to the compressive strength, the optimum dosage for CaSO4 · 2H2O lies between 35% and 50%.