Sustainable surface coating strategy for the interface compatibilization of hybrid high-density polyethylene microfibers and geopolymer-based composite: A versatile path for an efficient brittle to ductile-like transition

Geopolymer-based mortars (GMs) are known for their high compressive strength, but their brittleness under tensile and bending loads has limited their structural applications. To overcome these challenges, enhancing the fiber-matrix interface in fiber-reinforced GMs is crucial to achieve better load transfer. In this study, we employed an eco-friendly, non-invasive, and scalable surface coating method by dispersing metakaolin particles on the fiber surface. The fibers' chemical structure, morphology, thermal stability, and mechanical properties were analyzed, confirming the successful treatment with no major defects. When incorporated into GMs at 0.3 wt %/binder, the treated fibers achieved remarkable mechanical improvements, including a 1065 % increase in flexural toughness, a 190 % rise in flexural strength, and notable strain-hardening behavior, marking a transition from brittle to ductile-like failure. Additionally, the flexural modulus, split tensile strength, and compressive strength increased by 92 %, 154 %, and 7 %, respectively. These results demonstrate the effectiveness and the potential of such a simple and sustainable fiber compatibilization strategy in developing durable, highperformance fiber-reinforced geopolymer composites for construction applications.