Intermittent curing of fly ash geopolymer mortar

Abstract

The research work focuses on the production of type F fly ash based geopolymer using intermittent curing. Two different types of soluble sodium silicate and Na(OH) solution with three different mole ratios were used with a fixed ratio. Two different fly ash-to-alkaline liquid activator ratios were used with and without additional water content. Two different resting periods were checked prior to starting the curing regime. The curing temperature was set at 70°C applied intermittently on 4 steps for 6h each per day followed by 18h rest at ambient temperature. Twenty-one different geopolymer mixtures were cast using a mixture of fly ash and natural sand at a fixed ratio. The gain of compressive strength was checked at age 24, 48, 72, and 96h and 7days. Intermittent curing proved to increase the compressive strength of all geopolymer mortar at the end of each curing step. Thirteen geopolymer mixtures exceeded the Egyptian Code of Practice limit set for the 7-day compressive strength at 27MPa. The UCS is directly proportional to the increase of the specific gravity of the soluble sodium silicate used, the age, the Na(OH) solution mole concentration, the alkaline liquid activator-to-fly ash ratio, the resting period and the Na2O-to-SiO2 mole ratio. Yet, it is inversely proportional to additional water content, H2O-to-Na2O mole ratio and the water-to-geopolymer solids ratio.