The increasing consumption of cement and the growing generation of metallic waste have highlighted the urgent need for developing sustainable concrete incorporating recycled materials. Although numerous studies have independently investigated the effects of microsilica or waste iron shavings on concrete properties, limited research has examined their combined influence on both the mechanical performance and durability characteristics of concrete. Consequently, a significant research gap remains regarding the synergistic behavior of these two materials. Therefore, the present study aimed to experimentally investigate the combined effects of microsilica and waste iron shavings on concrete performance and to identify the optimum mixture exhibiting the best overall performance within the investigated range. To this end, concrete mixtures containing 4% and 8% microsilica as partial replacements for cement and 3%, 5%, and 7% waste iron shavings as partial replacements for fine aggregate were prepared. Compressive strength, splitting tensile strength, flexural strength, water absorption, density, and electrical resistivity were evaluated at curing ages of 7, 28, and 90 days.

The results indicated that replacing cement with 8% microsilica increased the 90-day compressive strength by approximately 29% compared with the control mixture. Furthermore, incorporating 3% waste iron shavings enhanced the compressive strength by approximately 22%, whereas increasing the iron shaving content to 7% resulted in a reduction in strength and an increase in water absorption. However, considering the overall performance in terms of mechanical properties and durability indicators, the mixture incorporating 8% microsilica and 3% waste iron shavings exhibited the most balanced and favorable performance. Overall, the findings demonstrate that the controlled incorporation of waste iron shavings in the presence of microsilica can simultaneously enhance the strength and durability of concrete through a synergistic effect, providing an effective approach for producing sustainable concrete with improved engineering performance.