Effect of volcanic ash and a C-S-H nano-additive on the manufacture of cementitious systems

Volcanic ash (VA) has been used as pozzolan with lime or cement since the Roman Empire. The 2021 volcanic eruption in Spain provided an opportunity to investigate the reactivity of freshly deposited ash. The present research work proposes studying the VA produced at the Cumbre Vieja volcano (La Palma Island, Canaries, Spain), denominated VAP. These natural waste materials exhibit pozzolanic properties, which make them suitable for use as a partial cement substitute. VA typically exhibits moderate to slow reactivity in early curing stages. VAP’s pozzolanic behaviour was studied using the Frattini test, pH and electrical conductivity in lime/VAP suspensions, and mechanical tests in mortars (15 %, 25 % and 35 % wt% Portland cement replacements with VAP). The use of nanoparticles (nanoC-S-H) as an accelerator of the mechanical properties in the mortars with VAP was analysed at short curing ages. The compressive strength values of the mortars with VAP and the nano-additive (2 % vs. the binder) showed that nanoC-S-H effectively enhanced mortars’ early-age mechanical properties (measured by ultrasonic and compressive tests). At a low water/binder ratio, the strength values of the VAP-containing mortars were similar to those of the mortars containing 100 % Portland cement as a binder. All the tests support using ash from the recent eruption as a viable option for producing cement-based systems. Notably, the use of a C-S-H-based nano-additive significantly improved early-age mechanical performance. • Adding nanoC-S-H greatly enhances the early strength of the mortars with VA. • Cumbre Vieja VA ha potential as a partial cement substitute. • The VA and nanoC-S-H mortars have comparable mechanical properties to pure cement. • We confirm that Cumbre Vieja VA use in sustainable cement systems is feasible.