Mesoscale-strength model for steel fiber-reinforced recycled aggregate concrete: coupled experiments and self-compiled six-phase simulations

Abstract

In alignment with the global imperative toward sustainable construction, recycled aggregate concrete (RAC) has emerged as a promising alternative to conventional concrete. However, its inherently inferior mechanical performance poses a significant barrier to broader engineering adoption. To counteract this deficiency, this study investigates the mechanical enhancement mechanisms of steel fiber-reinforced recycled aggregate concrete (SF-RAC) through a synergistic experimental–computational framework. A comprehensive experimental program was conducted to systematically evaluate the influence of critical mix parameters—namely, the water-to-cement ratio (W/C), steel fiber volume fraction (S-F), and recycled coarse aggregate (RCA) content—on the compressive and tensile behavior of SF-RAC. All mixtures were prepared with 100% RCA replacement of natural coarse aggregates, while the coarse aggregate volume fraction was varied at three levels (0%, 30%, and 45%) to investigate its influence on fiber reinforcement. Parallelly, a high-fidelity mesoscale numerical model was developed via a custom-built computational platform, explicitly resolving six distinct constitutive phases: steel fibers, old and new mortar matrices, old and new interfacial transition zones (ITZs), and virgin as well as recycled aggregates. The numerical model was calibrated using experimental data from three water-to-cement ratios (0.45, 0.50, and 0.55) and validated specifically for W/C = 0.55, confirming its predictive capability within this practical range. Leveraging mesoscale insights, a semi-empirical strength model was formulated to estimate both compressive and tensile strengths of SF-RAC as explicit functions of fiber inclusion and mix proportioning. The proposed model is applicable for SF-RAC with 100% RCA replacement, coarse aggregate volume fractions of 30–45%, steel fiber contents of 0–1.0%, and water-to-cement ratios of 0.45–0.55; extrapolation beyond these ranges should be undertaken with caution. The integrated findings not only deepen the mechanistic understanding of fiber reinforcement in recycled matrix systems but also furnish a quantitative design tool for performance-driven optimization of SF-RAC in sustainable infrastructure applications.

Graphical abstract

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