Effects of Partial Substitution of Ordinary Portland Cement With Stone‐Cutting Dust, Limestone, and Natural Pozzolana on Compressive Strength and Microstructure

Rapid industrialization and urban growth have driven a rising demand for cement, yet ordinary Portland cement (OPC) production remains energy‐intensive and a major source of CO 2 emissions. The partial substitution of OPC with supplementary cementitious materials (SCMs) offers a sustainable route to reduce environmental impact, production costs, and enhance performance. This study investigates the effects of replacing OPC with stone‐cutting dust (SD), natural pozzolana (NP), and limestone (L) individually and in ternary blends on the compressive strength and microstructure of cement mortars. OPC was partially substituted with SD and NP at 10%–40% and with L at 5%–20%. Ternary blends containing SD, NP, and L replaced OPC at 25%–40%. Compressive strength was measured at 2, 7, 28, and 56 days, and microstructural analysis was performed at 28 days using scanning electron microscopy (SEM). Commercial OPC and Portland pozzolana cement (PPC) served as control samples. Results showed that strength development increased with curing age for all mixes. Optimal performance was recorded at lower substitution levels particularly 10%–20% NP, 5%–15% L, and ≤25% SD achieving 28‐day strengths comparable to or exceeding OPC. High replacement levels (≥35%) reduced strength due to dilution of reactive clinker phases. Ternary blends demonstrated synergistic effects when reactive pozzolanic material and fine limestone were balanced, producing dense microstructures with refined pores and abundant calcium–silicate–hydrate (C–S–H) gel. SEM observations confirmed that improvements in compressive strength were associated with increased C–S–H formation, reduced calcium hydroxide (CH), and better particle packing in optimized mixes. These findings indicate that SD, NP, and L can be used effectively in partial substitution of OPC to produce environmentally friendly cement with satisfactory mechanical performance. Optimized blends can reduce OPC content by up to 25% without compromising strength, supporting sustainable construction practices while promoting the utilization of locally available industrial by‐products. PPC was only used as a microstructural reference to compare hydration morphology with blended OPC systems, while OPC was utilized as the mechanical control for compressive strength evaluation.