Influence of various metakaolin raw materials on the water and fire resistance of geopolymers prepared in phosphoric acid

Different formulations of geopolymers were synthesized in acidic media (phosphoric acid) starting from three different raw metakaolin materials to identify compositions of interest. Four different property groups were highlighted based on the most favorable thermal and water resistance properties (while maintaining acceptable mechanical properties). The groups were related to the chemical composition, setting time and setting temperature of the synthesized geopolymers. Indeed, mechanical strength was determined by chemical composition, such as the aluminum content and the amount of water in each sample. The results showed that the sample with Si/Al ≥ 1 and Al/P = 1 exhibited compressive stress to rupture values ranging between 66 and 120 MPa and was thermal resistant. Water resistance with a mechanical strength of 50 MPa was obtained for the samples with Al/P = 1 or 4 and Si/Al ≤ 1. This work highlights the possibility of selecting a specific property associated with the mechanical performance for an acidic geopolymer.