Evaluating the effectiveness of limestone and eggshell waste as cement replacements - a review.

The increasing focus on environmental sustainability has sparked global interest in substituting cement with materials derived from industrial and agricultural waste. As cement manufacturing is a major source of CO₂ emissions, and waste generation continues to rise, repurposing these byproducts as Supplementary Cementitious Materials (SCMs) presents an eco-friendly solution. This approach not only reduces environmental harm and conserves natural resources but also improves the properties of cement-based composites. This review explores the potential of Waste Limestone Powder (WLP), an industrial byproduct, and Powdered Eggshell (PES), an agricultural waste rich in calcium carbonate (CaCO₃), as partial cement replacements. The study critically examines existing literature on the physical, chemical, and morphological properties of WLP and PES, along with their effects on the workability, mechanical strength, durability, and microstructure of mortar and concrete. According to a study of the literature, WLP increases packing density and provides hydration nucleation sites, improving workability and compressive strength when utilized at a replacement rate ranging from 10 to 20%. PES, which contains up to 95% CaCO₃, performs best at 5-10% replacement and helps with early strength and microstructural densification. Higher levels, however, may make the material less workable and durable because of decreased pozzolanic reactivity and greater water demand. Microstructural analyses using SEM, XRD, and TGA confirm that both WLP and PES function as fillers, with crystalline CaCO3 enhancing performance, and can be used as a SCM in construction. Findings suggest that these waste materials exhibit notable cementitious characterization, offering a sustainable and eco-friendly approach to cement reduction in construction applications.