Effects of nano- and micro-cellulose on Ca(OH)2 formation: Implications for lime-based binders

Air lime-based mortars and plasters are preferred for the restoration of historic masonry due to their high compatibility, and for modern constructions given their lower environmental impact. However, their slow setting (via carbonation) and their limited strength hinder their widespread use. This study explores the influence of nano- and micro-cellulose additives dosed during lime slaking on the formation and textural/structural features of calcium hydroxide. The alkaline degradation of the additives, along with their interaction and adsorption/ occlusion during heterogeneous and homogeneous precipitation of calcium hydroxide was studied. Both additives foster the non-classical crystallization of portlandite via amorphous phases, resulting in plate-like crystals in the case of nano-cellulose, whereas more reactive micro-cellulose promotes the stabilization of a dense liquid precursor, and upon its dehydration, the stabilization of amorphous calcium hydroxide. Ultimately both additives lead to the formation of potentially more reactive nano and mesostructured Ca(OH)2 particles.