Concrete production has a significant environmental impact, mainly due to the high CO₂ emissions associated with Portland cement manufacturing and the extraction of raw materials, such as limestone and clay. In parallel, iron ore mining generates large quantities of waste rock, an inert by‑product removed during the extraction process, which is typically stockpiled in piles, pits, or dams, requiring extensive disposal areas and long‑term environmental management. The reuse of this abundant material in cementitious materials presents a promising strategy to reduce both environmental burden and cement consumption. This study investigates the incorporation of iron mining waste rock as a partial cement replacement in concrete, focusing on the effects of substitution on physical and mechanical properties. Concrete mixtures were produced with 20% and 30% of the cement replaced by waste rock, and consistency, fresh density, compressive strength, Young’s modulus, water absorption, voids content, and hardened density were evaluated. In support of the mixture design, the waste rock was briefly characterized and its cement performance index determined through standardized compressive strength comparisons, which indicated that the material does not act as a reactive addition and that its contribution is primarily physical. Concrete mixtures with waste rock showed slight reductions in consistency, density, and compressive strength compared to the reference mixture; however, these losses were not critical and remained within acceptable ranges for general applications. Other physical and mechanical properties also exhibited minor reductions with increasing replacement levels. The results demonstrate the technical feasibility of using iron mining waste rock as an inert filler in concrete, enabling partial cement replacement without significant loss of performance, and support more sustainable construction practices by promoting the reuse of mining by‑products, in line with circular economy principles.