The effect of liquid-to-binder ratio and wastewater sludge powder content on workability and compressive strength of fly ash-based geopolymer mortar

Abstract

This study examines the effect of alkali liquid-to-binder ratio (L/B) and wastewater sludge powder from a beverage factory (WP) content on the properties of fly ash-based geopolymer mortar. The L/B ratios of 0.55, 0.65, and 0.75 were used and fly ash was replaced by WP at ratios of 0, 20, 40, 60, 80, and 100 percent by weight of fly ash. The tests of flow value, compressive strength at 7 days, and unit weight were conducted. The results showed that an increase in the L/B ratio increases the flow value of fresh geopolymer mortar while the compressive strength tends to decrease. The unit weight tends to increase when the L/B ratio rises from 0.55 to 0.65 and then decreases with the increased L/B ratio to 0.75. For the WP contents, the result showed that the flow value, compressive strength, and unit weight tend to decrease with the increase in WP contents. However, the compressive strength of the geopolymer mortar with the L/B ratio of 0.75 increased with an increase in WP content at 20% of WP by weight, then the compressive strength decreased according to the amount of WP. The strength activity index values of geopolymer mortars containing less than 40% WP are higher than 75%. The L/B ratio of 0.65 is the optimum ratio for geopolymer mortar fabrication and the appropriate WP replacement content depends on the need for further use. The use of WP in fly ash-based geopolymer mortar is considered a beneficial use of waste from industrial factories which helps reduce disposal costs including reducing the use of cement in construction.