Effect of kaolin pretreatment on the structure and properties of metakaolin phosphate-based geopolymers

This study focused on the preparation of metakaolin-based phosphate-activated geopolymers (MKPGs) using kaolin pretreated at 950 degrees C for varying times as a precursor. It was found that kaolinite quickly transformed into amorphous metakaolin (MK) and then transitioned from a disordered phase to an ordered phase, resulting in precipitation of kyanite and mullite with increasing calcination time. The formation of the kyanite phase had an adverse effect on geopolymerization, which caused a decrease in the strength of the MKPGs. The precipitation of the mullite phase hindered the geopolymerization reaction between phosphoric acid and MK, and the geopolymer failed to solidify. As the calcination time increased from 10 min to 60 min, the compressive strength of the geopolymers increased and then decreased. The maximum strength of the geopolymers created from MK calcined for 30 min was 132.1 MPa.