Effect of ettringite seed crystals on the properties of calcium sulphoaluminate cement

Polycarboxylate superplasticizers have been applied in calcium sulphoaluminate (CSA) cement-based materials to obtain a good workability, while the concomitant retardation in hydration results in a slow early strength development after setting. Ettringite seed crystals synthesized in this research are expected to work as seed nucleus and accelerate the hydration of CSA at early ages in the presence of polycarboxylate-ether (PCE) superplasticizer. The effect of ettringite seed on setting time, rheological properties, compressive strength, volume changes, phase development and microstructure of CSA pastes was experimentally investigated. Results showed that the addition of ettringite seed crystals indeed promoted the hydration and significantly improved the compressive strength and microstructure of CSA pastes at early ages, while reduced the setting time, the yield stress and plastic viscosity. Compared with the control paste, 3-h compressive strength of CSA paste containing 4% ettringite seed increased by 290%. The compressive strengths increased with increasing ettringite seed content less than 1% at all curing ages, with an adequate setting time and rheological properties. (C) 2019 Published by Elsevier Ltd.