Durable Mortar Mixes Using 50% of Activated Volcanic Ash as A Binder

Volcanic ash (VA) is an abundant resource in many world regions that can be used as a supplementary cementitious material (SCM). However, its low reactivity limits its applications as a replacement for Portland cement. In this study, the improvement of its reactivity was evaluated through the calcination of VA (CVA) at 700 °C, alkali activation with Na₂SiO₃, CaCl₂, and Na₂CO₃, as well as its combination with other SCMs (lime, fly ash, and blast-furnace slags). Additionally, the effect of curing was analysed under different regimes: standard moist curing and heat curing. The use of alkaline activators, especially 2% Na₂SiO₃ and 1% CaCl₂, along with thermal curing (70 °C for 3 days) in mortars containing 50% VA, resulted in compressive strengths at 28 days, significantly higher than those obtained for mortars with non-activated VA or those cured under moist conditions. Furthermore, the addition of 10% fly ash (FA) and 5% slag (EC) to the mortars also led to the largest improvements in compressive strength. In addition, mortars cured at 70 °C exhibited lower shrinkage and improved resistance to acid attacks, particularly in those manufactured with CVA and 1% CaCl₂. This study concludes that it is possible to optimise the design of mortars with 50% VA in replacement of ordinary cement based on activation and curing methods. These methods improve early-age strength, reduce shrinkage and water absorption, and enhance acid resistance.