Co-valorisation of construction and demolition waste and basalt powder as raw materials in geopolymers

The development of environmentally friendly and sustainable geopolymer materials has been experimented, aiming to simultaneously valorise two types of industrial wastes, namely unsorted construction and demolition waste (CDW) and basalt powder. Metakaolin (MK) was used as an aluminosilicate source together with these scarcely reactive precursors to optimise the geopolymerization process. The effect of CDW/basalt ratio on the overall properties of the obtained geopolymers was compared. Microstructure, porosity and mineral phases of alkali-activated products were investigated by SEM, MIP, FTIR, and XRD. Additionally, compressive strength tests and thermal characterisation up to 1000°C were carried out. Microstructural features typical of geopolymers and compressive strength up to 37 MPa were achieved with CDW/basalt ratios ranging from 3 to 1. The prepared materials remained thermally stable up to 600–650 °C. Beyond this temperature, they underwent shrinkage due to viscous flow followed by expansion; nonetheless, increasing the basalt content reduced the tendency for surface fracturing. Based on these results, combining basalt with CDW appears to be an effective approach for producing sustainable geopolymer products.