A high-strength red mud–fly ash geopolymer and the implications of curing temperature

In response to the requirement for the comprehensive utilization of industrial waste, high-strength geopolymers were prepared from red mud (RM) and Class 1, 2, and C fly ash (FA) rich in active substances (FA1, FA2, and FAC, respectively) in the presence of an alkali activator (AA). Increasing the curing temperature from room temperature (22 °C) to 60 °C rapidly increased the strength of the geopolymer, while maintaining a certain level of humidity during curing inhibited crack formation in the geopolymer. The use of a sodium hydroxide (NaOH) solution improved the strength of the geopolymer. However, an excessively high concentration of NaOH solution induced considerable efflorescence. The strength of the geopolymer prepared with a mixed solution (MS) composed of a NaOH solution and a water glass (WG) solution increased as the concentration of the MS increased and reached 63.5 MPa when the NaOH concentration in the MS was 10 mol/L.