Amorphous self-healed, chopped basalt fiber-reinforced, geopolymer composites

Geopolymer composites containing refractory, chopped basalt fibers and low-melting glass were made and systematically heat-treated at higher temperatures. Potassium-based geopolymer of stoichiometric composition K₂O·Al₂O₃·4SiO₂·11H₂O was produced by high shear mixing from fumed silica, deionized water, potassium hydroxide, (i.e., water glass) and metakaolin. With the addition of low-melting glass (T_m ~815°C) the flexure strengths of the composites increased to ~6 MPa after heat treatment above 900°C to 1100°C. A Weibull statistical analysis was performed showing how the amorphous self-healing effect of the glass frit significantly improved the flexure strength of the geopolymer and ceramic composites after high-temperature exposure. At temperatures up to 900°C, the geopolymer-basalt composite remained amorphous and the low-melting glass frit flowed into the dehydration cracks in the geopolymer matrix. This type of composite could be described as amorphous self-healed geopolymer (ASH-G). At ~1000°C, the geopolymer converted to primarily a crystalline leucite ceramic, but the basalt fiber remained intact, and the melted glass frit flowed and sealed the cracks developed at that temperature. This type of composite could then be described as amorphous self-healed ceramic (ASH-C). A temperature of 1150°C was determined to be optimum as at 1200°C the basalt fibers melted and the strength of the reinforcement was lost in the composites. The amorphous self-healing effect of the glass frit significantly improved the room temperature flexure strength of the heat-treated geopolymer-based composites.