Strength Development of Heat Cured and Ambient Cured Sodium Hydroxide Activated Fly Ash Based Geopolymer

Compressive strength development of class F fly ash geopolymer activated by sodium hydroxide was compared between initial heat curing at 75oC for 24 hours and the ambient medium. Class F geopolymeric mortar was produced with standard Rilem sand, sodium hydroxide, and water. Mortar mixtures ratios were 3, 1, and 0.288 for sand, fly ash, and water, respectively. Some samples were cured in laboratory conditions; some samples were heat cured for 24 hours at 75oC. Ambient curing medium result with non-measurable low compressive strength up to 7 days, however significant strength development observed in longer curing time up to six months. Heat curing developed higher strength at all times than ambient curing did. It was concluded that heat cured geopolymer samples could be utilized in construction materials, while utilization of non-heat cured samples was not practical due to its longer curing duration needs.