Hybrid steel and carbon fiber reinforcement enhances mechanical performance and sustainability of cementitious composites

This study investigates the synergistic effects of hybrid steel fiber (SF) and carbon fiber (CF) reinforcement on the mechanical, microstructural, and sustainability profiles of cementitious composites. While fiber-reinforced mortars are known for enhanced ductility, the multi-scale interaction between macro-scale SF and micro-scale CF remains under-explored in the context of simultaneous environmental and economic optimization. Experimental results demonstrate that the hybrid integration of 0.37% SF and 0.10% CF achieves a superior flexural-to-compressive strength ratio, attributed to a hierarchical crack-arrest mechanism. Microstructural analysis via Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscopy (SEM) confirms that CF acts as a pore-refiner, densifying the interfacial transition zone (ITZ). Furthermore, a cradle-to-gate Life Cycle Assessment (LCA) and cost-efficiency analysis were integrated into a novel 'Performance Index' (PI) to resolve the trade-offs between technical performance and sustainability. The findings reveal that optimized hybrid systems provide a more sustainable alternative to mono-fiber systems, offering a balanced solution for high-performance and eco-friendly construction materials.