Microstructure and microchemistry of fully-reacted geopolymers and geopolymer matrix composites

The processing, intrinsic microstructure and properties of geopolymer materials and geopolymer composites made with basalt fibers (chopped and fiber weaves) have been investigated. Curing of geopolymers was achieved by one of three routes, viz., pressureless curing, warm pressing, and curing in a high pressure autoclave. The materials were fabricated at ambient temperatures up to (40-80°C). Using fiber reinforcement, the bending strength and work of fracture of geopolymer materials have been increased from an average of 2.8 MPa to 10.3 MPa and 0.05 kJ/m² to 21.8 kJ/m², respectively. Electron microscopy studies (SEM, TEM/EDS, in situ hot stage TEM) were made of the intrinsic geopolymer. The microstructure of fully reacted geopolymers consists of amorphous nanoparticulates separated by nanopores whose features are of the order of ≤10 nm. The microchemistry frequently observed by TEM/EDS corresponded to a silica (SiO²) to alumina (Al²O ³) ratio of 4:1. In situ, hot-stage TEM observations made during heating for 4 h up to 1000°C showed that the nanosized microstructure was stable, although continuous evolution of gas, presumably H₂O, was noticed upon heating. These materials are inorganic polymers cured at ambient temperatures which remain microstructurally stable to above 1000°C.