Comparative performance of raw and calcined limestone dust as partial Portland cement replacements in cement paste

Abstract This study investigates the performance of natural limestone dust (LD) and calcined limestone dust (CLD) as partial replacements for Portland cement (PC) in cement paste. Cement pastes containing 0%, 10%, 20%, 30%, and 40% LD or CLD were prepared and evaluated. The reference PC paste was prepared at a water-to-cement ratio (w/c) of 0.30, whereas the LD- and CLD-blended pastes were prepared at a fixed nominal water-to-binder ratio (w/b) of 0.26. The w/b ratio of 0.26 was selected based on a previous experimental study of CLD-containing blended binders, which demonstrated suitable mixing behavior and favorable compressive-strength performance at this ratio. The physical, mechanical, and microstructural properties of the cement pastes were evaluated using specific gravity, bulk density, Vicat penetration behavior, setting time, compressive strength, X-ray diffraction (XRD), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS). The results showed that CLD replacement levels of up to 20% generally produced higher early-age and 28-day compressive strengths than the corresponding LD mixtures, with strength values approaching those of the reference PC paste. Increasing LD and CLD replacement levels also affected the specific gravity, bulk density, penetration behavior, and setting time of the cement pastes. XRD and SEM/EDS analyses provided qualitative evidence of changes in crystalline phases and microstructural features associated with the incorporation of CLD. Overall, CLD exhibited promising potential as a partial replacement for Portland cement across the replacement levels investigated. Further studies are required to evaluate the long-term durability and environmental performance of CLD-containing cement pastes.