Mechanical and microstructural properties of phosphate-based geopolymers with varying Si/Al molar ratios based on the sol-gel method

Abstract Phosphate-based geopolymers with different Si/Al molar ratios were synthesized using Al2O3-nSiO2 powder obtained by the sol-gel method. The influence of different Si/Al molar ratios on the synthesis process and geopolymer properties was studied. The physical and mechanical properties of the geopolymer were evaluated using the three-point bending resistance test. With increasing Si/Al molar ratios, the flexural strength increased and reached a maximum value at an Si/Al ratio of 2.5 and then decreased. However, the reaction speed and curing speed slowed with increasing the Si/Al molar ratioratios. When the Si/Al ratio equaled 1.5, the geopolymer exhibited high expansibility, and the speed of reaction increased. Additionally, its compressive strength reached 2 MPa after 5 min. This study is of great significance for the application of geopolymers in practical emergency rescue projects, such as water gushing in tunnel engineering and pipeline gushing in hydraulic engineering.