Synthesis and exposure of multisource solid waste‐based porous geopolymer composites with hollow Al ₂ O ₃ microspheres

Abstract In this paper, we proposed a method for utilizing multisource solid wastes to create a valuable product of porous fly ash/red mud/slag‐based geopolymer composite, combining hydrogen peroxide foaming and hollow Al 2 O 3 microspheres (HAMs). The effects of high temperatures (600–1200°C), hydrogen peroxide addition, and HAMs on the microstructure characteristics of the porous composites were examined. Before exposure, the composites had an amorphous matrix with high porosity ranging from 32.5% to 75.2% and a compressive strength between 0.72 and 22.38 MPa. The strength was improved by the fractured spheres, crack deflection, and a good bond state between the HAMs and the matrix. After being exposed to temperatures above 800°C, the samples crystallized to porous ceramics with compressive strength improvement. The composites had the lowest thermal conductivity of 0.393 and 0.248 W/(m·K) before and after exposure, respectively. This hybrid composite exhibited high properties even after exposure, which provided a simple fabricating method for porous geopolymer ceramic used in insulation areas.