Biomass bottom ash waste and by-products of the acetylene industry as raw materials for unfired bricks

This research aims to study the feasibility of using wastes: biomass bottom ash resulting from the combustion process of a mix of pine-olive pruning in power generation plants, and Geosilex, a by-product obtained in the acetylene industry, as raw materials in the manufacture of unfired bricks. These materials were characterized physically, chemically and mineralogically. Different proportions of raw materials have been investigated; biomass bottom ash (100-20 wt %) and Geosilex (0–80 wt %). The specimens were obtained by compression at 10 MPa and cured for 28 days in water. The physical, mechanical and thermal properties of the unfired bricks have been evaluated. Optimum results have been obtained for specimens with 70–60 wt % of biomass bottom ash and 30–40 wt % of Geosilex, presenting the best mechanical properties, with compressive strength values of 52 MPa and thermal conductivity of 0.52–0.57 W/mK, respectively. These unfired bricks presented a greater quantity of hydrated calcium silicates and hydrated calcium aluminates that provide mechanical properties. This fact is due to that these specimens had the optimal amount of pozzolanic materials, Ca(OH)2 present in the cementing agent Geosilex and SiO2 and Al2O3, present in the ash. Recycling these raw materials in unfired bricks implies significant economic and environmental benefits owing to wastes are used as substitutes for natural raw materials.