Mechanism of retarder on hydration process and mechanical properties of red mud-based geopolymer cementitious materials

The effects of sodium gluconate, sodium hexametaphosphate, and sodium tripolyphosphate on the hydration process, rheological properties, and mechanical strength of red mud-based geopolymer cementitious materials were studied by hydration microcalorimeter, infrared spectrometer, and X-ray diffraction. The results show that all the three retarders can delay the hydration and hardening rate of the slurry of red mud-based geopolymer cementitious materials, and sodium gluconate has the most significant effect on the hydration rate. The rheology of the slurry shows the Herschel-Buckley model. The introduction of retarders will reduce the yield stress and increase the shear thickening characteristics of the slurry. Under the action of retarder, the 3-days compressive strength of red mud-based geopolymer cementitious materials decreases significantly, while the 28-days compressive strength has little change. Sodium gluconate can improve the 28-days compressive strength to a certain extent. Microscopic analysis showed that retarding agent blocked the hydration rate of red mud-based polymer gel mainly through adsorption, encapsulation and complexation.