Study on the effect and mechanism of cement-based material retarder on red mud-based hybrid alkali activated cement

Abstract

In this paper, the effects of sodium gluconate (SG), sodium hexametaphosphate (SHMP) and sodium tripolyphosphate (STPP) on the rheological behavior and mechanical property of red mud-based hybrid alkali activated cement (RM-HAAC) were discussed, and their hydration process were analyzed. Hybrid alkali activated cement has great potential in solid waste utilization and carbon reduction. This study aims to provide valuable reference and guidance for the engineering application of red mud-based hybrid alkali activated cement, and shed light on the utilization of red mud. The results showed that: sodium gluconate could effectively delay the hydration rate of red mud-based hybrid alkali activated cement, which the initial setting time was delayed by 109.8% when the dosage was 0.5 wt%. Sodium hexametaphosphate can promote the hydration rate, which the initial setting time decreases by 25.5% when the dosage is 0.5 wt%. When the content of sodium tripolyphosphate is lower than 0.3 wt%, it has little effect on the hydration rate, while when the content is larger than 0.3 wt%, it has a certain promoting effect. The rheological property of red mud-based hybrid alkali activated cement could be represented by the H–B fluid model. Sodium gluconate increases the fluidity of the slurry, while sodium hexametaphosphate and sodium tripolyphosphate decrease the fluidity. The 28-day compressive strength of red mud-based hybrid alkali activated cement has been improved under the influence of retarder. Sodium tripolyphosphate has the largest 28-day strength with an increment of 18.8%. Microscopic analysis shows that sodium gluconate hinders the hydration process of red mud-based hybrid alkali activated cement mainly through complexation encapsulation and adsorption, and sodium hexametaphosphate and sodium tripolyphosphate promote the hydration process mainly through hydrogen bond bonding between phosphate and alkali activated cementitious materials.