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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.

Potentialities and suitability of metakaolin-based geopolymers in Cultural Heritage have been explored. In particular, in order to evaluate their possible use as restoration materials in conservation of historic manufactures, mortars have been prepared by adding aggregates of Italian ornamental stones to alkali-activated metakaolin with binder/sand ratio of 1:1. To improve workability, geopolymer binders have been synthesized from metakaolin and sodium silicate solution with water/solid weight ratios between 0.33 and 0.66 and SiO 2 /Al 2 O 3 and Al 2 O 3 /Na 2 O molar ratios of 3.70 and 1.04, respectively, and characterized by several techniques, including mechanical strength tests according to UNI EN 196-1. All binders display good mechanical properties, with compressive and flexural strength values as high as 72 MPa and 6 MPa, respectively, and decreasing with increasing water/solid ratio. The increase of water in geopolymer formulation has little negative effect on the aluminosilicate gel development and on the strength of these materials. Mortars display a homogeneous and compact matrix, bonded (silicoaluminate aggregates) or interlocked (carbonate) with aggregates. Their compressive strengths fall in the masonry mortars class M20 range. Their pore size distribution guarantees good breathability and adaptability to the substrate. The final materials mimic the original stones, with good aesthetic compatibility.