Alkali activated sawing tuff wastes as sustainable mortars for Cultural Heritage

Zeolitized Tuff (such as Neapolitan Yellow Tuff), thanks to aesthetic features and their good technological properties, has been the predominant building material in the historical architecture of Naples since the Roman and Greek ages (VI century B.C.). This lithotype contributes significantly to the vast monumental heritage found throughout the Campania region, particularly in Naples, whose historic city center of approximately 17 km² is the largest in Europe. These naturally occurring rocks are usually cut into prismatic blocks, causing the formation of massive amounts of powder-like wastes related to cutting and polishing operations, which represents a serious environmental problem. An alternative to the typical solution as supplementary cementitious materials is provided by raw materials for alkali activated binder production. Alkali activated materials (or geopolymers) are obtained through a chemical reaction of an alumino-silicate powder with a highly concentrated aqueous alkali hydroxide and/or silicate solution, to produce synthetic amorphous-to semicrystalline alkali alumino-silicate new phases. These materials are of great interest because of their high sustainability and reduced energy requirement in their production. It has been proven that any material, whether natural or synthetic, rich in silica and alumina can be utilized as a precursor for geopolymerization. The aim of this paper is to explore the possibility to produce innovative and eco-friendly mortars re-using sawing tuff powders. Accordingly, sawing tuff wastes and metakaolin were alkali activated to obtain sustainable binders, which were characterized by X-ray diffraction, infrared spectroscopy and thermogravimetry analysis. Technical performance of the alkali activated binders, such as water absorption, open porosity and capillary absorption, was measured in accordance with European Standards’ prescriptions. Mineralogical characterization and the FTIR spectra confirmed the tuff interaction with alkaline activators. Preliminary data demonstrated that alkali activated tuff-based products are compatible and technically consistent with the existing historical materials and with the traditional repairing mortars too.