Effects and Mechanisms of Al Powder, Soybean Oil, and Expanded Polystyrene on Performances of Novel Foamed Geopolymers Utilizing Multiple Solid Wastes

To address the challenges of high energy demands of cement and high costs of alkali activated materials in the preparation of foam concrete, this study innovatively uses all solid waste to prepare foamed geopolymers (FGs). A systematic investigation was conducted to investigate the effects of aluminum (Al) powder, soybean oil, and expanded polystyrene (EPS) on physical, mechanical, and thermal properties of a novel FG through the alkali activation of ground granulated blast-furnace slag (GGBS) and red mud (RM), employing alkaline solid wastes such as municipal solid waste incineration fly ash (MSWIFA) and carbide slag (CS). Comprehensive material characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis with derivative thermogravimetry (TG-DTG), and scanning electron microscopy coupled with electron diffraction spectroscopy (SEM-EDS), were employed to analyze the reaction products and elucidate the mechanisms by which aluminum powder, soybean oil, and EPS influence the hydration process. The resultant material showed favorable characteristics, achieving a compressive strength of 0.89 MPa, a dry density of 474.5 kg/m3, and a thermal conductivity of 0.0801 W/(m·K). The formation of aluminum hydroxide gel during the initial stages of aluminum powder hydration temporarily hinders strength development but subsequently enhances strength at later stages. Additionally, soybean oil was found to optimize the material’s pore structure while moderating the kinetics of the hydration reaction. This study could provide a theoretical foundation for the FG preparation, contributing to the green and low-carbon advancement of the construction materials industry.