Retardation effect of elevated temperature on the setting of calcium sulfoaluminate cement clinker

The hydration of calcium sulfoaluminate (CSA) clinker at 5, 20 and 40 °C was characterized by a combination of XRD, DTA-TG and ESEM analysis (also with backscattered electron imaging, BEI). Meanwhile, the setting times and compressive strength development were studied. It was interesting to notice that elevated temperature retards the setting of CSA clinker and decreases compressive strength prominently, while it promotes the hydration heat releasement and hydration degree. With the temperature rising from 5 °C to 40 °C, the amount of ettringite formed after 1 d decreases by half, but alumina gel increases by more than 4 times, accompanying with a more inhomogeneous microstructure and higher porosity. ESEM observations indicate that such massive alumina gel covers on the unreacted particles and other hydrates, which could account for the retardation of elevated temperature on the setting of CSA clinker.