Metakaolin-based geopolymers for stone conservation: preliminary results on alkaline activation

Abstract. Geopolymers are inorganic and versatile alternative binder. They exist in a wide range, varying from a material which behaves like mortars to a material with properties like ceramics. This makes them a potentially innovative alternative to repair mortars. In this research the activation of metakaolin-based geopolymers is explored in the context of stone conservation. A set of reactivity tests are performed to evaluate activators and compatibility with a lime-based binder. The physico-chemical properties of the binder are investigated, in combination with low proportions of standardized aggregates of marl powder, limestone powder and quartz sand. The most promising mixtures absorb water relatively slowly due to the relative small pore sizes. The samples have a high open porosity and therefore a lower density when compared to results found in literature from geopolymers with aggregate, but the results are comparable to geopolymers without aggregates. The compressive strength is comparable to currently used repair mortars. This study shows that metakaolin with lime-based binders could be investigated in the future as alternative binder in stone repair mortars.