Interaction of metakaolin-based geopolymers with natural and artificial stones and implications on their use in cultural heritage

Alkali activated materials, and geopolymers in particular, have proven to be a valid alternative to traditional binders, due to their significant mechanical performances, durability and environmental advantages. The present paper describes the results of a research project, initiated in order to explore the potentiality and suitability of metakaolin-based geopolymers within the domain of cultural heritage. SEM-EDS analyses were utilized in order to evaluate the interaction of geopolymers with natural and artificial stones by assessing the variations at the boundaries due to differences in the minero-petrographic and chemical compositions of natural and artificial stones. Three ornamental stones widely used in the historic Italian architecture were selected: Pietra Serena (sandstone), Pietra di Angera (dolostone) and Pietra di Noto (limestone). Widespread construction materials, such as concrete and brick were also included in the study. Furthermore, the interaction between geopolymers and historic elements, such as decorative stones and/or mortars, were also studied, in order to evaluate a possible application of these materials within the realm of restoration, as well as for the conservation of historic manufactures. The results revealed that adhesion appears to be satisfactory in the case of all analyzed materials. Silicoaluminate phases partially dissolve and increase the availability of Si and Al within the interface, resulting in a strongly interlinked whole, whereas carbonate phases and rocks supply Ca, which changes the local composition of the binder