High-Temperature Resistance of a Red Clay-Based Geopolymer Reinforced by Basalt Fiber

A red clay-based geopolymer is prepared with the addition of SiO2-coated basalt fiber, which possesses high compatibility in gel structure because of their similar chemical compositions. The evolution in the microstructure of the geopolymers is studied at temperatures up to 1000 °C. The analyses are conducted by 29Si NMR spectroscopy, 3D full-field strain measurements (XTDIC), and an ultrasonic echo material testing system (UMS). At calcination of 1000 °C, the compressive stress of the geopolymers is significantly reinforced by the basalt fiber, which increases from 6.8 to 12.9 MPa. The geopolymers with the basalt fiber give a 2 times higher compressive strength than the unreinforced samples. The enhancement in thermal stability of the geopolymers might derive from the stretching of the basalt fiber at the nanoscale, so that it delays the expansion of microcracks, which dissipate huge thermal energy and avoid concentration of thermal stress. This study helps to mitigate thermal damage of geopolymers exposed to elevated temperatures and promote the development of geopolymers with desired thermal resistance for application.