Porosity and Sorptivity on Performance of Fly Ash Based Geopolymer Mortars in Nitric Acid

This paper reports the effect of apparent porosity and sorptivity on durability of fly ash based geopolymer mortar specimens in Nitric acid solution. Geopolymer mortar specimens were manufactured by activating a Class F fly ash with a mixture of NaOH and Na₂SiO₃ containing Na₂O in the range of 5% to 8%. A 10% Nitric acid solution was used to immerse the geopolymer mortar specimens and durability was evaluated on the basis of changes in weight and residual compressive strength at the end of 24 weeks. Specimens containing lesser Na₂O were found to possess higher apparent porosity and water sorptivity. Geopolymer mortar specimens still retained substantial compressive strength even after 24 weeks in Nitric acid solution. Loss of weight and reduction in compressive strength were higher for specimen with higher porosity and water sorptivity. Results obtained in the experimental program indicate that porosity and sorptivity of geopolymer mortar specimens influences the performance of geopolymer mortars in Nitric acid.