The effect of temperature, time of curing and Na2O/SiO2 molar ratio on mechanical and chemical properties of geopolymer cement

The geopolymer cement is a suitable alternative material for Portland cement due to their environmental compatibility, low curing temperature, and high strength. In this research, Kaolin was used as a raw material for the construction of a geopolymer cement, while sodium hydroxide was an alkali hydroxide. Kaolin is calcined at 750 °C to obtain meta-kaolin. Geopolymer samples were prepared at various curing temperatures (25, 50, and 75 °C), different curing times (3, 7, 21, 28, and 60 days) and with different activator ratios (0.6-0.9). The thermal analysis of kaolin was done via DTA/TGA. Investigation on the geopolymer cement structure and phases were performed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and magic angle spinning nuclear magnetic resonance (MAS-NMR). Also, the effects of temperature and time of curing and Na2O/SiO2 molar ratio were studied. The results showed that the maximum compressive strength was 115MPa, which obtained at a molar ratio of Na2O/SiO2=0.9, a curing time of 60 days, and a curing temperature of 75 °C. The microstructure of cement was studied using scanning electron microscopy (SEM)