The present paper reports results of an experimental investigation on physicomechanical and microstructural characteristics of fly ash based geopolymer composites exposed to elevated temperature. The changes in compressive strength, weight loss and microstructure of geopolymer paste and mortar specimens were studied after exposing them to oven temperature at 300°C, 600°C and 900°C. The experimental results showed that residual properties of specimens are highly dependent on Si:Al and Na:Al ratio of the geopolymer mix. The compressive strength of mortar specimen deteriorated rapidly beyond 300°C. However, in paste specimen reduction in compressive strength was observed up to 600°C but further heating improved compressive strength due to viscous sintering of specimen. Thermo-gravimetric analysis (TGA) revealed that specimen loses its weight at elevated temperature due to dehydration, de-hydroxylation and densification processes occurred during transient heating from room temperature to 900°C. XRD analysis of specimen showed formation of new compound such as Nepheline and Albite at 900°C. The Si:Al and Na:Al ratio of geopolymer mix also influenced homogeneity of the microstructure as observed in SEM investigation. The results obtained in the current research indicated that fly ash based geopolymer composites are highly resistant to elevated temperature exposure.
Fly ash, geopolymer, weight loss, compressive strength, TGA, microstructure
