Mechanical and microstructural evaluation of cement mortar incorporating ball-milled iron mill scale using response surface modeling

Abstract Incorporating industrial by-products into cementitious materials provides a sustainable solution to reduce the reliance on natural aggregates. This study investigates the feasibility of using ball-milled waste iron mill scale (B-WIMS) as a partial replacement (0%–30%) for fine aggregate in cement mortar. Mechanical properties, microstructural characteristics, and sustainability indicators were evaluated using a two-factor response surface methodology framework considering B-WIMS content and curing periods of 3, 7, and 28 d. The results show that an optimum replacement level of 15% B-WIMS achieves superior performance, with compressive, flexural, and tensile strengths of 50.1 MPa, 8.5 MPa, and 4.6 MPa at 28 d, respectively, representing significant improvements over the control mix. Microstructural analysis using scanning electron microscopy (SEM), x-ray diffraction (XRD), and FTIR suggests the formation of a denser matrix with improved particle packing and reduced portlandite content. Phase identification was primarily supported by XRD, while SEM provided complementary morphological insights. Analysis of Variance results indicate that curing period is the most influential factor governing strength development ( p < 0.0001), while B-WIMS content shows significant quadratic effects. The developed models demonstrated strong predictive capability ( R 2 = 0.78–0.98). Despite a slight increase in embodied energy, improved strength-to-energy and strength-to-carbon ratios confirm enhanced eco-efficiency. Overall, B-WIMS offers a promising approach for sustainable mortar development.