Effects of the addition of slaked lime to alkali-activated pastes based on volcanic ashes from Mt. Etna volcano (Italy)

This study provides experimental insights into the optimization of alkali-activated materials (AAMs) carried out in situ at the restoration site of Monreale Cathedral, Italy. Volcanic ash from Mt. Etna volcano (Italy) was used as a precursor to obtain AAMs. Standard and modified pastes with a small amount of slaked lime paste were compared in terms of setting time, rheology, mineralogy, chemical morphology, and mechanical performance. The modified pastes exhibited a faster setting time, superior mechanical strength and rheological properties. Mineralogically, no difference was observed between the two pastes for the small amount of slaked lime paste added very close to the detectable limit (<2 wt%). Moreover, its addition causes slight differences in the morphology of the gel without changing the chemical composition of the Na2O-CaO-Al2O3-SiO2-H2O ((N,C)-A-S-H)) type. The results obtained may be useful for the development and optimization of building materials (especially for restoration purposes) where appropriate physico-mechanical performance is required.