Development and characterization of sustainable mortar using industrial iron waste as an alternative to sand with Portland limestone cement

The significant carbon dioxide emissions from ordinary Portland cement production, as well as the increasing accumulation of iron ore tailings (IOTs) and associated environmental and health problems, are of concern. This study aims to address these issues by using iron ore tailings as a partial replacement for natural sand, combined with Portland limestone cement (PLC) to create a more sustainable and environmentally friendly mortar. Two types of iron ore tailings, a coarser type with lower iron oxide content (IOT−1) and a finer type with higher iron oxide content (IOT−2), are used as a partial replacement for natural sand in PLC mortar mixes at replacement levels ranging from 0% to 40%. After a thorough characterization of the raw materials, the mortar mixes were evaluated in terms of fresh properties, mechanical performance, durability, and microstructural characteristics using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results confirmed that a 20% replacement level is optimal for both types of iron ore tailings, resulting in compressive strength increases of 23.0% and 16.5% for the coarser and finer types, respectively, at 28 days. However, mechanical strength showed improvement even up to a 40% replacement level compared to the control mix. In general, the IOT−1, which had a low iron oxide content, performed better than the IOT−2. Durability assessment confirmed the enhanced performance at the optimal replacement level, represented in higher ultrasonic pulse velocity (UPV) and lower water absorption, porosity, and sorptivity. Overall, the findings demonstrate that iron ore tailings can effectively replace up to 40% of natural sand in PLC mortars, contributing to sustainable industrial waste management and reducing the environmental impact associated with the production of cementitious construction materials.