Experimental evaluation and multi-objective optimization of hybrid steel–shape memory alloy fiber reinforced concrete for enhanced mechanical and microstructural performance

Abstract

This study presents a comprehensive experimental investigation and multi-objective optimization of Hybrid Steel–Shape Memory Alloy Fiber Reinforced Concrete (HS–SMA FRC) designed to enhance mechanical performance and material efficiency. M40-grade concrete mixes incorporating steel fibers, NiTi-based SMA fibers, and hybrid combinations at volume fractions of 0.5% and 0.75% were evaluated. Mechanical properties, including compressive strength, split tensile strength, flexural strength, bond strength, and modulus of elasticity, were assessed at 7 and 28 days. The results indicate that hybrid fiber systems outperform mono-fiber and control mixes, with the 0.75% HS–SMA FRC mix achieving the highest compressive strength (64.25 MPa), split tensile strength (10.80 MPa), and flexural strength (12.5 MPa), attributed to synergistic crack-bridging and stress redistribution mechanisms. Microstructural observations using SEM and EDS suggest improved fiber–matrix bonding and a denser interfacial transition zone, supporting the observed mechanical enhancements. A hybrid optimization framework combining Response Surface Methodology (RSM) and NSGA-III was implemented to identify optimal trade-offs among performance parameters, with model-predicted results indicating efficient material configurations. However, the findings are limited to material-level behavior under monotonic loading conditions, and the optimization results are not experimentally validated. The study provides a robust foundation for developing high-performance hybrid fiber reinforced concrete with potential applicability in advanced structural systems.