Influence of duration of heat curing and extra rest period after heat curing on the strength and transport characteristic of alkali activated class F fly ash geopolymer mortar

In the study, the influence of heat curing duration and rest period after heat curing duration on the strength and transport characteristics of alkali activated fly ash (AAFA) mortar were investigated. A local class F type fly ash, CEN reference sand, sodium hydroxide and potable water were used in preparation of cement-less fresh geopolymer mortar mixture. Mixture ratios (in mass basis) were 3, 1, 0.29, and 0.1 for sand, fly ash, water and sodium hydroxide, respectively. Some samples were cured at 75 °C temperature for 4 h, 1, 2, 3 and 7 days; then, they were tested after heat curing period. Additionally, some of the equivalent samples were kept in the laboratory at 23 ± 2 °C temperature with 50 ± 5% relative humidity, until 28 days after their initial heat curing period. Then, they were tested at 28 days for combined curing conditions. The measured properties of AAFA mortar were unit weight, porosity, capillary water absorption, water absorption capacity, flexural-bending and split tension strength, compressive strengths and abrasion resistance. It was observed that the strengths of mortar were significantly increased with the increase in heat curing duration. A significant strength development was also observed after rest period. As a result of the study, high strength and abrasion resistant AAFA geopolymer mortar was produced. However, transport properties of AAFA geopolymer mortar found to be not as good as mechanical properties.