Effect of graphite powder on the mechanical, durability and electromagnetic shielding performance of cement mortar incorporating ball-milled waste iron mill scale

Abstract The rapid growth of wireless communication systems, radar technologies, and electronic devices has increased the demand for cementitious materials capable of mitigating electromagnetic interference (EMI) while maintaining adequate structural performance. This study investigates the influence of graphite powder on the mechanical, durability, and electromagnetic shielding performance of cement mortar incorporating a fixed 15% replacement of ball-milled waste iron mill scale. Graphite powder was incorporated at 0–5% by weight of cement. The effects of graphite content on flowability, mechanical properties, durability, electromagnetic shielding effectiveness, and microstructure were systematically evaluated. Compared with the control mix, the incorporation of 2% graphite powder increased the 28-day compressive, flexural, and tensile strengths by approximately 7.2%, 10.6%, and 13.0%, respectively, while simultaneously reducing water absorption, chloride permeability, and sulphate deterioration, indicating improved durability. Electromagnetic shielding effectiveness increased progressively with graphite content, reaching a maximum of 45.4 dB in the X-band frequency range. However, under the fixed 15% ball-milled waste iron mill scale replacement condition, the BW15-G2 mix provided the optimum balance between mechanical performance, durability, and electromagnetic shielding effectiveness, achieving 37.6 dB shielding performance. SEM observations revealed a denser matrix with refined pore structure, while XRD qualitatively indicated enhanced hydration product development in the optimized mix. Response surface methodology demonstrated that curing period predominantly influenced strength development, whereas graphite content governed matrix refinement and overall performance. The developed models and optimum graphite content are applicable only within the investigated fixed 15% ball-milled waste iron mill scale replacement level. The developed multifunctional cement mortar shows promising potential for EMI-sensitive infrastructure, including hospitals, data centres, telecommunication facilities, and defence structures.