Monitoring early hydration of calcium sulfoaluminate clinker

Abstract Initial hydration and setting were continuously monitored in calcium sulfoaluminate clinker (KCSA) mixed with water or 2 M NaOH with isothermal conduction calorimetry, ultrasonic pulse velocity (UPV) measurement, the Vicat apparatus, and (in- and ex-situ) X-ray diffraction. P-wave acceleration (ap) proved highly useful to detect very rapid initial reactions, not generally perceptible with other techniques. Setting in the water-hydrated KCSA pastes was mediated by ettringite formation. Flash setting due to calcium aluminate hydrate precipitation was observed in the 2 M NaOH-hydrated clinker. Ye’elemite reacted most intensely at later times in both pastes, inducing AFt and AH3 precipitation and the formation of smaller proportions of other calcium aluminate hydrates that densified the matrix.