Effect of long-term drying on the performance of sulfoaluminate cement

Abstract

The effect of continuous drying for 360 days on the performance of sulfoaluminate cement (SAC) with different contents of gypsum was investigated, with ordinary Portland cement (OPC) selected as the control. First, the compressive strengths and deformation of mortars dried at 40 °C for different times were tested. Meanwhile, for the hardened cement pastes dried under the same condition, the mineral phase, micromorphology, and pore structure evolutions were monitored. Results indicated that the compressive strength of SAC mortars showed a significant decrease after 360 days of drying, whereas the compressive strength of OPC mortar was still higher than that before drying. Moreover, the SAC mortars with high gypsum content exhibited significant shrinkage after drying. This was because the ettringites lost crystal water during the drying process, and the crystallinity decreased gradually until they were amorphous. Meanwhile, the ettringites showed a shriveled morphology after drying, and became weaker than before drying. Besides, both the pore size and total porosities of the SAC hardened cement pastes showed a noticeable increase after 360 days of drying. However, the hydration products of OPC were stable under the same dry condition. This study provides direct evidence to explain the mechanical strength reduction of SAC in service.

Keywords

• Sulfoaluminate cement
• Long-term drying
• Compressive strength
• Hydration product
• Microstructure