Sustainable development of geopolymer technology for cultural heritage application: synthesis set-up and morphological characterization

The term "geopolymer" describes a wide variety of natural or synthetic composite materials showing a polymeric structure. They are materials similar to ceramics, whose components are mainly aluminum-natural silicates. The geopolymerization takes place in three phases: dissolution of the aluminosilicate source, polycondensation of aluminosilicate oligomers and finally precipitation of geopolymeric particles, which form a gel. The sol-gel synthesis is an eco-friendly approach to functionalize geopolymers, without high temperature treatments, perfectly in accordance with the principles of circular economy and green chemistry. [1] The present work concerns the modification of the geopolymer at the chemical and nanostructural level, through the condensation process in alkaline conditions [2]. The alkoxysilane agents may be chosen for the implementation of specific properties of the geopolymer materials that allow the production of various types of coatings, such as protective coating, reflective or anti-reflective coatings, refractory linings, coatings with controlled porosity, all these properties may result determining in the restoration of cultural heritage. The morphology of the geopolymer surface depends on the degree of cross-linking of its molecular structure and varies according to the quantity and type of alkoxysilane added. The methods of functionalization of the geopolymers described in this work are the following: a) the treatment of the geopolymeric surface, post-drying, through the application of the sol-gel directly on the monolith, for a modification of the surface properties; b) the pre-treatment of the geopolymeric mixture, through the addition of the selected alkoxysilane, can induce a homogeneous consolidation of the molecular structure, implementing the properties of the entire monolith.