Behaviour changes of ground granulated blast furnace slag geopolymers at high temperature

In this paper, the thermal performance of ground-granulated blast furnace slag (GGBFS) geopolymers is investigated. The geopolymers were prepared with sodium-based alkali activator and exposed to elevated temperature (200 to 1000°C) after 28 d of curing at room temperature. The unexposed geopolymers exhibited excellent compressive strength of 95 MPa. The compressive strength reduced to 8·9 MPa at 800°C and increased to 19·8 MPa at 1000°C. The strength regained by 122·5% as compared to the residual strength at 800°C. The crack reduction and partial melting in geopolymers treated at 1000°C signifies crack healing at elevated temperature, which in turn increases the compressive strength. In addition, the formation of crystalline phases of gehlenite (Ca₂Al₂SiO), mayenite (Ca₁₂Al₁₄O₃₃) and larnite (Ca₂SiO₄) filled the geopolymer matrix and formed an ordered structure. This further enhanced the strength and high-temperature stability of GGBFS geopolymers.