Formation mechanism of early strength in geopolymer based on molar ratio of mineral components

Abstract

X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to observe the compound change law of geopolymer reaction and the hydration reaction of calcium silicate by adjusting the molar ratio of SiO2/Al2O3, CaO/Al2O3 and Na2O/Al2O3 in the geopolymer. Then the compound synergistic effect of geopolymer reaction and the hydration reaction of CaSiO3 was explored. Furthermore, the formation mechanism of early strength in geopolymer was revealed. The results show that the geopolymer reaction products contain a certain amount of quartz component. The physical properties and chemical properties of quartz are very stable and the quartz strength is high. The products of hydration reaction of CaSiO3 are mainly CaSiO3 hydrate whose internal structure is loose. With the mole ratios of SiO2/Al2O3 and CaO/Al2O3 increasing, the degree of geopolymer reaction increases first and then decreases, and the degree of hydration reaction of CaSiO3 increases first and then stabilizes and is greater than the degree of geological polymer reaction. When the SiO2/Al2O3 molar ratio is 3.8 and the CaO/Al2O3 molar ratio is 2.750, the compound synergistic effect of geopolymer reaction and hydration reaction of CaSiO3 is the best. At this time, the proportion of quartz in geopolymer is about 66wt%, the proportion of CaSiO3 hydrate in geopolymer is about 24wt% and the mechanical properties are good.