Study on mechanical properties of kaolin-based geopolymer with various Si/Al ratio and aging time

Geopolymers are a class of aluminosilicate-based ceramics that contain 3D network synthesized by condensation of tetrahedral aluminosilicate units, produced by the aluminosilicate raw materials and alkaline activators. The Si/Al ratio and aging time are the crucial parameters which influence the reaction degree of geopolymerization process and the reaction time, affecting the final properties, respectively. Here, we investigated the effect of Si/Al ratio and aging time on the microstructure and mechanical properties of kaolin-based geopolymers, where SEM, XRD, and piston on three ball test were applied at the different Si/Al ratio and the aging time. Given the higher ratio of Si/Al and longer aging time, geopolymer-based matrix was densified and high crystalline phases were evolved. Furthermore, the highest flexural strength of specimen, with the Si/Al ratio of 2.49 and aging time of 1 day, was 19.5 MPa.