Cement-free building materials: mix design and properties in view of their application in civil engineering

This PhD thesis deals with a new class of cement-free building materials known as geopolymers, obtained through the reaction of a low-calcium solid aluminosilicate source in alkaline conditions. With the aim to go forward on the research on geopolymers and to pursuit sustainable products, this thesis focuses on low-calcium coal fly ash geopolymers activated at room temperature. By varying the type of aggregates, it was possible to test and characterize traditional and lightweight mortars as well as composites for different areas of application. In view of developing products potentially ready for the market, geopolymers were produced, characterized and tested according to the conventional procedures used for cementitious binders. A preliminary investigation of using commercially available superplasticizers to improve the workability of geopolymer mortars and to facilitate the in-situ applications was carried out. The research was then dedicated to the development and characterization of fibre reinforced geopolymer matrix (FRGM) composites for strengthening existing reinforced concrete and masonry structures. An extensive study of thermal properties and high temperature behaviour of geopolymers was reported. The mechanism of cracking induced by high temperature exposure was studied. Afterwards, composites containing recycled refractory particles were developed to enhance the thermal dimensional stability of geopolymers. Furthermore, lightweight mortars were obtained using expanded perlite as fine lightweight aggregate and studied as passive fire protection systems for steel elements. Fly-ash based geopolymers proved to be versatile materials that can be tailored according to the desired final performances. The experimental findings highlighted that in all the investigated cases, optimized fly ash-based geopolymers resulted promising and competitive products. In particular, geopolymers used as both FRGM composites and fireproofing materials showed performances comparable and in some cases better than those of commercial products currently used in these fields.