Understanding the thermal behaviour of MSWI bottom ash foamed ternary geopolymer: The fundamental role of pore structure

Porous materials are widely used in refractory applications, but conventional foaming relies on energy-intensive equipment or chemical agents, increasing cost and carbon footprint. Municipal solid waste incineration bottom ash (MSWI BA) provides a low-carbon alternative, as its inherent metallic aluminium can produce foams in the alkali environment. However, uncontrolled gas generation may lead to expansion cracks within the matrix during hardening. In this study, a novel method is proposed to develop a porous Class F fly ash based geopolymer with inhibited crack formation by incorporating steelmaking byproduct ladle slag, which regulates the foaming process induced by MSWI BA. Through adjusting precursors composition, the pore structure is tailored, and systematically characterized to correlate with drying shrinkage, mechanical performance and thermal behaviour. Results indicate that the tortuosity of capillary network is the key factor retarding moisture loss of samples, which in turn affects drying shrinkage, with ultimate values as low as 306 microstrain. Moreover, interconnected macropore structure is found to determine thermal cracking resistance. After 1000 °C exposure, highly connected macropore structure largely maintains the structural integrity of samples, enabling an approximately 200% enhancement in compressive strength relative to room temperature performance. Accordingly, a conceptual model is proposed to understand the influence of pore structure on moisture movement at both ambient and elevated temperatures. This work offers practical insights into waste valorisation and pore structure design, guiding the customization of porous geopolymer to achieve enhanced high temperature performance.