Engineered combinations of volcanic ash and waste glass for sustainable alkali activated materials

The environmental sustainability of new materials and production processes is of crucial importance nowadays. This study examines the use of mixtures of volcanic ash collected from street sweeping following pyroclastic eruptions of Mt. Etna, and waste glass fines derived from the recycling process of glass containers, for the manufacturing of dense blocks. These materials can be activated using a low molarity NaOH aqueous solution (3 mol/L) followed by a drying process at 75 °C for 3 days. Additionally, these same mixtures can be used for the preparation of lightweight foams through limited incorporation of sodium perborate and surfactant. The resulting solid products exhibit competitive strength-to-density ratios compared to commercial construction materials. Strength evaluations were conducted using three-point bending tests (0.47–5.93 MPa) and compression tests (7.82–22.77 MPa). Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM-EDS) reveal a complex hardening mechanism. This mechanism involves unreacted particles that are not strictly bound by gel, resulting from condensation reactions of components released in solution during alkaline attack. Regarding the cold consolidated foams, their morphology may take them suitable for application as sorbents for contaminants as well as thermal insulators (λ = 0.137 W/m·K).