Effects of sodium gluconate on hydration reaction, setting, workability, and strength development of calcium sulfoaluminate belite cement mixtures

Fast setting is an important reason restricting the applications of eco-friendly calcium sulfoaluminate belite (CSAB) cement. To help spread the application of CSAB cement, this study investigated the influence of sodium gluconate (SG) as a setting retarder on the setting, workability, and strength development of CSAB cement mixtures. Quantitative X-ray diffraction (QXRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were performed to understand the effects of SG on the hydration and microstructure of CSAB cement mixtures. The results showed that SG effectively extended the setting time and improved the workability of CSAB cement pastes since it retarded ye'elimite hydration and impeded the loss of workability caused by ettringite formation. Low dosages (<= 0.5%) of SG increased the unconfined compressive strength (UCS) of CSAB cement mortars at all ages (from 2 h to 90 days) due to the reduction in void content, fast diminishment of the retarding effect at early ages, and slight acceleration on belite hydration at later ages. However, high dosages (>= 1%) significantly degraded the UCS of CSAB cement mortars at all ages since high dosages of SG strongly retarded ye'elimite hydration at early ages and caused a looser microstructure at later ages.