Geopolymers: Innovative Materials for Conservation Work

In restoration works it is important to use products that are compatible with materials composing the Cultural Heritage artworks. The majority of these materials (ceramics, mosaics, mortars, stones) are made of natural inorganic raw materials. In the conservative interventions of these artworks will be important to use inorganic compounds that have chemical composition, microstructure and porosity similar to the original materials. For these reasons, we are setting up geopolymer products that simulate natural porous materials. Geopolymers are artificial inorganic polymers synthesized by alkali activation of materials rich in SiO2 and Al2O3 (e.g. metacaolin, fly ashes, natural minerals, blast-furnace slags). The main characteristics of geopolymeric binder are based on some important ratios: Si/Al; alkalis/Al2O3 and H2O/alkalis [1]. The reaction, called geosynthesis or geopolymerization, takes place at low temperature (<300°C). The binder, similar in aspect to the injection mortar, could be used alone, but the physical and mechanical properties can be improved adding different types of aggregates, fillers, inorganic pigments, organic dyes and additives. The main characteristic of geopolymers is the possibility to tailor them in function of the final application. In the restoration and preservation field the geopolymers can be used to replace pieces, to make copies but also to realize new artistic objects. At present, we deal with the realization of lightweight movable panels as support for mosaics and wall paintings fragments, the production of colored geopolymers to be used as mosaic tesserae for integration works and the realization of masterpieces, copies and new artistic objects. All the products obtained were characterized by means of mechanical tests and from microstructural point of view (such as observations at electron microscope, porosimetric analyses, etc ..). In addition, release of soluble salts and colorimetric analyses were investigated in order to know the behavior of the materials exposed to chemical stresses and different environmental conditions. Results of mechanical tests performed on geopolymeric composites are interesting (compressive strength=50 MPa; flexural strength=10 MPa) and comparable to those of commercial products. No significant changes in the speciation and in the concentration of released ions suggests a good stability of geopolymers in basic and acid environments.