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 degrees C) to 60 degrees 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.