A sustainable foamed material preparation via ettringite-targeted mineral transition of industrial solid wastes

Foamed material (FM) is widely considered efficient energy-saving building insulation material. Using solid waste as raw material and removing the autoclave process will further promote the green degree of FM. This study proposes a sustainable FM preparation via ettringite-targeted mineral transition of industrial solid wastes. A solid-waste-based sulfoaluminate clinker (SSC) was prepared for the first time entirely using industrial solid waste. Then, the synergistic effect and mechanism of SSC with high-content by-product gypsum were investigated. The most suitable matching scheme for preparing FMs based on SSC and by-product gypsum was finally determined. Results revealed that the different mineral compositions of the gypsum after calcination affected the hydration process of SSC in the mixture. The occurrence of unstable expansion is a threshold effect, mainly induced by the formation of ettringite exceeding the critical amount. When SSC was blended with by-product gypsum treated at 80 or 600°C, the mixed paste showed long-term volume stability. Under the similar initial rheological properties of paste and a fixed dosage of H2O2, the specific compressive strength, pore size distribution and water absorption of FM were significantly deteriorated with the increase of gypsum content. When by-product gypsum (treated at 80°C) utilization approached 65%, the FM still exhibited good properties: 534 kg/m3 density, 2.69 MPa 7-d compressive strength, 14.4% 24-h water absorption, and 0.143 W/m·K thermal conductivity. Moreover, the synergistic complementarity of ettringite with other components enhanced the performances of FM. This study expands a novel avenue for the large-scale and high-value utilization of industrial solid waste, especially by-product gypsum.