Elevated-temperature performance, combustibility and fire propagation index of fly ash-metakaolin blend geopolymers with addition of monoaluminium phosphate (MAP) and aluminum dihydrogen triphosphate (ATP)

Thermal performance, combustibility, and fire propagation of fly ash-metakaolin (FAMK) blended geopolymer with the addition of aluminum triphosphate, ATP (Al(H₂PO₄)₃), and monoaluminium phosphate, MAP (AlPO₄) were evaluated in this paper. To prepare the geopolymer mix, fly ash and metakaolin with a ratio of 1:1 were added with ATP and MAP in a range of 0–3% by weight. The fire/heat resistance was evaluated by comparing the residual compressive strengths after the elevated temperature exposure. Besides, combustibility and fire propagation tests were conducted to examine the thermal performance and the applicability of the geopolymers as passive fire protection. Experimental results revealed that the blended geopolymers with 1 wt.% of ATP and MAP exhibited higher compressive strength and denser geopolymer matrix than control geopolymers. The effect of ATP and MAP addition was more obvious in unheated geopolymer and little improvement was observed for geopolymer subjected to elevated temperature. ATP and MAP at 3 wt.% did not help in enhancing the elevated-temperature performance of blended geopolymers. Even so, all blended geopolymers, regardless of the addition of ATP and MAP, were regarded as the noncombustible materials with negligible (0–0.1) fire propagation index.