Abstract: In this paper, the effects of the ratio of fly ash to powder, the mass fraction of alkali activator and the modulus of alkali activator on the hydration reaction, setting time and mechanical properties of the geopolymer material were studied. The microstructure of the material was characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The results show that with the decrease of the ratio of fly ash to powder, the hydration reaction rate of the geopolymer material is accelerated, the setting time is shortened, and the compressive strength and flexural strength are increased. With the increase of the mass fraction of alkali activator, the hydration reaction rate of the geopolymer material is accelerated, the setting time is shortened, the compressive strength is increased, and the flexural strength is first increased and then decreased. With the increase of the modulus of alkali activator, the hydration reaction rate of the geopolymer material slows down, the setting time prolongates, and the compressive strength and flexural strength decrease continuously. The results show that when the ratio of fly ash to powder is 2:8 and the mass fractions of sodium oxide and silicon oxide are 5.25% and 4.20%, respectively, the compressive strength and flexural strength of the 28-day geopolymer material reach 68.90 MPa and 11.50 MPa. The microscopic test results further prove that with the decrease of the ratio of fly ash to powder, the increase of the mass fraction of alkali activator and the reduction of the modulus of alkali activator, the microstructure revealed by SEM gradually tends to be dense, which is consistent with the change of macroscopic mechanical properties. The results of EDS and FTIR show that C-A-S-H gel is the main component of the hydration products of different ratios of geopolymer material. The conclusion of the study provides a theoretical basis for the popularization and application of geopolymer material.
Keywords: geopolymer material; mechanical properties; setting time; hydration heat; microstructure