A comparative study of high- and low-Al2O3 fly ash based-geopolymers: the role of mix proportion factors and curing temperature

Developing sustainable and low-CO2 emission construction materials is of essential importance for reducing the environmental footprint of cement industry. In this work, ordinary circulating fluidized bed combustion fly ashes with different Al2O3 concentrations were used to prepare geopolymer. Upon XRD, SEM, FTIR and TG/DSC characterizations, the factors, including Si/Al ratio, the additional water/solid ratio, modulus of alkali activator (molar ratio of SiO2/Na2O) and curing temperature, had been investigated to reveal their influences to the mechanical and microstructural properties of geopolymers. For low-Al2O3 fly ash, the optimal synthesis conditions (curing temperature = 80 °C, Si/Al = 2:1, modulus = 1.5, additional water/solid ratio = 0.1) were obtained. Geopolymers modified with high-Al2O3 fly ash possess superior performance than that of low-Al2O3 fly ash modified samples, in terms of compressive strength and microstructure. This study proves that the application of lowAl2O3 fly ash can be used as a substitute material for geopolymer cement manufacture