Comprehensive utilization of blast furnace slag, municipal sludge and kaolin clay in building brick manufacture: Crystalline transformation, morphology observation and property assessment

Abstract

At present, the comprehensive utilization of bulk industrial solid waste has attracted wide attention. The recycling of industrial solid waste in building materials not only provides valuable insights for the management of solid waste, but also alleviates the over-exploitation of natural clay resources in the construction industry. In this study, municipal sludge (MS) and blast furnace slag (BFS) were incorporated into kaolin clay (KC) to synthesize sustainable composite bricks, and the sintering effects and engineering properties of bricks were adjusted by changing BFS dosages. The results indicated that the addition of BFS would promote liquid glassy phase production in bricks due to the higher content of alkali/alkaline-earth metal oxides, and the ingredient, viscosity and content of liquid glassy phases could also be regulated through varying the dosage of BFS (0-15%), thereby affecting the pore structure, particle arrangement/consolidation and performance of bricks. Among all synthesized bricks, the optimum dosages of BFS, MS and KC for satisfying the building standard thresholds were 10%, 40% and 50%, with corresponding linear shrinkage, porosity, density, water absorption, compressive and flexure strengths of 12.97%, 18.15%, 1.83 g/cm³, 0.82%, 15 MPa and 38 Mpa, respectively. Finally, mechanism analysis further demonstrated that the formation and evolution of liquid glassy phases were the key responsibility for adjusting the brick micromorphology and performance. Based on this study, using MS and BFS in brick manufacturing benefited the value-added utilization of industrial solid wastes, clean protection of environments and sustainable production of building materials, providing a reference for the process optimization and potential application of MS and BFS wastes in masonry construction.