Recycling Iron Ore Tailings as Sand Replacement in Cement Mortar: Effects on Strength, Durability, and Microstructure

Iron ore tailings (IOT), an abundant by-product of iron ore beneficiation, pose serious economic and environmental challenges due to their large-scale disposal. This study investigates the potential of IOT as a partial replacement for natural sand in mortar at levels of 10%, 20%, 30%, and 40%. A comparison was made between two size fractions of IOT obtained from Duqm, Oman. Along with the fresh properties, the mechanical performance was evaluated through compressive strength and flexural strength tests. Durability was characterized using ultrasonic pulse velocity (UPV), water absorption, porosity, capillary water absorption (sorptivity), and acid resistance tests using 5% sulfuric acid (H 2 SO 4 ). Microstructural features were examined using scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS), and phase composition was analyzed through X-ray diffraction (XRD). Results indicated that replacement levels between 20% and 30% provided optimal performance, with 28-day compressive strength improvements of 6%–15% and a 6.5% increase in flexural strength compared to the control mix. Mortars with up to 40% replacement demonstrated mechanical properties comparable to the control. Durability performance also improved, as evidenced by reductions in porosity, water absorption, and sorptivity, as well as enhanced UPV. Acid resistance tests confirmed comparable weight and strength losses relative to the control. Microstructural analysis revealed denser cement matrices and more compact interfacial transition zones (ITZ) in the optimum mixes. Overall, IOT incorporation offers a technically viable and potential waste valorization strategy for mitigating natural sand shortages and reducing industrial waste accumulation.