Substitution of slag with waste-derived precursors for alkali-activated mortars

In this study, three wastes (almond shell biomass ash (ABA), mining sand (MIN), and municipal solid waste incineration fly ash (MSWI)) were investigated as innovative precursors for alkali-activated mortars. Initially, ground granulated blast furnace slag (GGBFS) was partially substituted with ABA, MIN, and MSWI FA at increasing percentages (0%, 25%, 50%, 75%, and 100% by mass) in pastes activated with 4M and 8M NaOH solutions. Then, the most promising wastes and substitution levels were selected to manufacture mortars using calcareous sand. Mortars were cured under controlled conditions (temperature of 20 ± 1 °C and relative humidity > 95%) and their compressive strength (Rc) was evaluated after 2, 7, 28, and 90 days of curing. Results demonstrated that the NaOH molarity influences workability and mechanical performances of the mortars. ABA emerged as the most promising precursor due to its high potassium content. Indeed, the replacement of GGBFS with 25% ABA contributes significantly to the development of mechanical strength since the additional potassium increases the availability of alkalis