Recycling in Building Materials: Analysis of the Possibilities and Results of Using Recycled Glass Sand in Autoclaved Materials

The construction industry is particularly responsible for the appearance of the earth and the environment and for its partial degradation related to climate warming through the production of cement, brick burning, and the processing of substrates for the production of building materials (lime, gypsum, polystyrene, processed materials, etc.). An important aspect of the 21st century has been the overproduction and excessive use of natural resources, including sand. The purpose of this article is to analyze the possibility of using glass sand as a substitute for quartz sand in the production of materials resulting from hydrothermal treatment (so-called silicate bricks). The article is a review of the research conducted since 2016 on laboratory tests on the modification of silicate mass with glass sand from recycled bottle glass, the properties of the mass modified in this way (hydration temperature, consistency, and humidity of the mixture), its physical and mechanical properties, and its structural and potential durability, which is related to, e.g., the direction and degree of crystallization of the C-S-H phase. Tests of compressive strength, density, water absorption, oxide composition (XRF), structure (XRD), microstructure (SEM), and porosity (CT analysis using computer tomography) were carried out. A special point of the research was the use of geochemical modeling code in the form of the GEMS-PSI program in the process of analyzing the modification of silicate mass by glass sand, which is beneficial in limiting ineffective modifications, thus saving time, money, and energy. Studies have shown that the use of glass cullet has a positive effect on the consistency of the modified raw material mass, on the density (1.6–1.75 kg/dm 3 ), and on the compressive strength (15.729–20.3 MPa), while the crystallization of the C-S-H phase occurs in the direction of natrolite and gyrolite, less frequently towards the M-S-H or brucite phase.