Valorization of brick waste by alkali-activation: A study on the possible use for masonry repointing

Alkali-activation of brick waste has recently been proposed as a sustainable route to develop pastes/mortars with tailored mechanical properties and pore system. In this study, the suitability of using pastes from brick waste alkali-activation for repointing existing masonries (i.e., filling the most external part of mortar joints, lost due to deterioration processes) was investigated. Five different formulations (having SiO2/Al2O3 molar ratio ranging from 1.4 to 0.4) and two different curing temperatures (room temperature and 50\ua0\ub0C) were investigated. Open porosity and efflorescence formation were found to decrease for decreasing SiO2/Al2O3 ratio. Curing at high temperature generally favored geopolymerization and reduced efflorescence formation. Pastes with SiO2/Al2O3=0.8 and 0.9 exhibited open porosity and water vapor permeability fairly similar to those of historic lime-based mortars, thus proving to be potentially compatible with them. Further optimization of the mix design seems however necessary to reduce the formation of efflorescence