Synergy of hybrid glass–PVA fibres in sustainable one-part geopolymers: mechanical, durability and microstructural performance

One-part geopolymers are promising sustainable alternatives to ordinary Portland cement, but their brittleness and limited tensile strength limit their structural use. While previous studies primarily utilise high-modulus steel fibres, which compromise workability and are prone to corrosion, there is limited research on the effectiveness of low and medium modulus fibres. This study systematically investigates the influence of low-modulus polyvinyl alcohol (PVA) fibres and medium-modulus glass fibres, both individually and in hybrid forms, within fly ash and slag-based one-part geopolymer composites at 2% fibre volume. Results show that PVA fibres greatly improve tensile ductility and shrinkage control but increase porosity, whereas glass fibres enhance compressive strength and reduce shrinkage yet introduce brittleness. Notably, hybrid fibre reinforcement provides synergistic crack-bridging, raising flexural strength by 11% and enhancing crack resistance. Microstructural analyses reveal robust fibre-matrix interactions. Overall, hybridisation of fibre types and lengths addresses brittleness and demonstrates substantial promise for sustainable structural applications.