Pyroclastic volcanic ash as a potential precursor of alkali-activated binders - A case study from Tajogaite (La Palma, Canary Islands) volcano eruption

Abstract

The volcanic eruption of Tajogaite in La Palma (Canary Islands, Spain) produced approximately 200 Mm3 of fine lapilli and ash. Using this volcanic ash (VA) to produce alkali-activated binders (AABs) fosters a sustainable approach to binder manufacturing, aligning with the principles of a circular economy and reducing reliance on non-renewable resources. The feasibility of using VA as a sole precursor for the formulation of sustainable AABs was evaluated based on its composition and physical-chemical properties. To this end, a comprehensive physicochemical characterization of VA was carried out and the physical, mechanical, and environmental properties of the binders formulated were analyzed. The physical-chemical analysis reveals the neoformation of typical secondary reaction products, such as NASH and (C,N)ASH gels. The microstructure analysis reveals that the AABs formulated using 6 M and 8 M NaOH activator solutions contain homogeneously dispersed unreacted VA particles within the binder matrix, providing increased cohesion and mechanical strength. The highest compressive resistance of AABs formulated using only VA as the precursor was achieved with a 6 M NaOH activator solution and a curing temperature of 60 ◦C, reaching a strength of 16 MPa. Although alkaline activation enhances the release of some metals and metalloids contained in the VA, the study of the environmental requirements at the end of the life cycle of the formulated AABs allows them to be classified as nonhazardous materials.