Review:dual-performance behaviour of geopolymer surface coatings—fire retardancy and abrasion resistance potential

Abstract Geopolymer surface coatings have emerged as promising and sustainable protective barriers against thermal and mechanical stresses. Derived mainly from industrial by-products and aluminosilicate sources such as fly ash, slag, metakaolin, and silica fume, these materials offer high thermal stability, good adhesion, and ceramic-like structural integrity, making them highly suitable for surface applications. This review provides a comprehensive and critical analysis of geopolymer coatings with dual-performance potential in fire retardancy and abrasion resistance. A unifying conceptual framework is presented to show how the cross-linked aluminosilicate network contributes to both properties through its influence on thermal stability, matrix compactness, interfacial bonding, and resistance to crack propagation. Crucially, the review highlights that the relationship between fire retardancy and abrasion resistance is not always fully synergistic, as increased porosity may improve thermal insulation but weaken matrix compactness and wear resistance. The available literature indicates that high-silica, dense geopolymer systems generally offer the greatest potential for balanced fire protection and mechanical durability. However, direct abrasion testing remains limited with many studies relying on indirect indicators such as hardness and adhesion. The field is further constrained by inconsistent testing methods, limited long-term durability data, scale-up challenges, and the continued use of chemically complex petrochemical additives in advanced formulations. Overall, geopolymer coatings show strong potential as dual-performance protective systems, but further progress requires standardized evaluation methods, multi-objective optimization, and stronger validation under realistic service conditions.