Relationship between compressive strength and UPV of GGBFS based geopolymer mortars exposed to elevated temperatures

Geopolymers are innovative materials possessing properties similar to normal OPC, while having less environmental impact. The current research was conducted on GGBFS based geopolymeric mortars. The effects of sodium silicate to sodium hydroxide ratio on the compressive strength of the mortars at 1 and 7 days before and after exposure to the elevated temperatures of 200 °C, 400 °C, 600 °C, and 800 °C were investigated. Additionally, the relationship between Ultrasonic Pulse Velocity (UPV) and compressive strength was investigated for before and after exposure to elevated temperatures. It was found that the sodium silicate to sodium hydroxide ratio had little or no effect on the compressive strength change between 1 and 7 days. However, the compressive strength generally increased with increasing sodium silicate content. Similar trend was observed for elevated temperature exposure, in that the strength increased with increasing sodium silicate to sodium hydroxide ratio, while the overall behavior was such that the compressive strength decreased as the temperature exposure increased. UPV measurements showed similar behavior, which indicated that relationship between UPV and compressive strength was exponential and R2 was between 0.95 and 0.98.