Reaction kinetics of red mud-fly ash based geopolymers: Effects of curing temperature on chemical bonding, porosity, and mechanical strength

The reaction kinetics of red mud-class F fly ash based geopolymer (RFFG) was investigated through understanding the influence of curing temperature on the formation of geopolymer gel, porosity, and the development of mechanical properties. Chemical bonding, mineralogy, mechanical properties and porosity of RFFG during a curing period of up to 120 days were assessed with Fourier transform infrared spectroscopy, X-ray diffractometer, unconfined compression tests, and micro-CT and N2-BJH techniques, respectively. The geopolymer gels were found to develop via a three-stage process: dissolution-Al-rich gels (I), Al-rich gels-Si-rich gels (II) and Si-rich gels-tectosilicate networks (III). The mechanical strength is largely governed by the development of geopolymer gels and affected by porosity, both of which are influenced by curing temperature. The early mechanical strength of RFFG is enhanced by elevated curing temperatures, but the long-term strength can be compromised by higher porosity resulted from an excessively high curing temperature.