Behavior of fly ash geopolymer as fire resistant coating for timber

This paper presents an innovative application of fly ash geopolymer as fire resistant coating of timber. Sodium (Na) and potassium (K) activated fly ash geopolymer coatings with carbon fiber (CF) and basalt fiber (BF) reinforcement were evaluated for suitability as fire resistance coatings of pine timber. It was found that both Na-based and K-based fly ash geopolymers coated timber having 2 mm coating thickness exhibited comparable fire resistant in terms of char depth under direct fire where an elevated temperature of approximately 1100 °C was maintained for 10 minutes. The char depth was reduced by 35-45% by doubling the geopolymer coating thickness. The K-based geopolymer coating exhibited less damage in terms of fewer cracks after exposure to fire than the Na-based coating, which was shown to be due to a lower shrinkage and lower thermal conductivity. The addition of both CF and BF in K-based geopolymer coated timber exhibited better fire resistance, in terms of smaller char depth, than the unreinforced geopolymer coatings. The addition of 1.5% CF in 4 mm thick K-based geopolymer coating exhibited between 67% and 79% reduction in char depth than equivalent coatings without reinforcement. The surface cracking of CF reinforced K-based geopolymer coating after exposure to fire was less compared to geopolymer paste only coating due to bridging of cracks by CF.