A review of eggshell and fish scale powders as sustainable supplementary cementitious materials for concrete

The environmental burden of Portland cement production, together with the growing accumulation of food and aquaculture waste, has intensified interest in sustainable supplementary cementitious materials. This review critically evaluates egg shell powder (ESP) and fish scale powder (FSP) as bio-based cement replacements, emphasizing their calcium carbonate– and hydroxyapatite-driven mechanisms and defining reliable performance thresholds for concrete applications. A structured narrative review of peer-reviewed literature published between 2010 and 2024 was conducted, covering material processing, chemical composition, fresh properties, mechanical performance, durability behavior, and microstructural characteristics of ESP- and FSP-modified concretes. Reported results were normalized relative to control mixes and synthesized using replacement-level grouping and effect-size analysis to enable cross-study comparison. The synthesis shows that ESP performs optimally at 7.5–10% cement replacement, achieving 8–12% improvements in compressive strength, up to 18% reductions in permeability, and enhanced sulphate and carbonation resistance through filler, nucleation, and pore-refinement effects. Replacement levels near 15% represent an upper practical limit, beyond which consistent losses in workability and strength are observed. FSP exhibits optimal behavior at 1.5–3% replacement, providing 10–15% gains in tensile and flexural strength and up to 15% improvement in chloride resistance, attributed to hydroxyapatite integration and collagen-assisted interfacial densification; higher dosages offer limited additional benefit and significantly impair workability. Life-cycle assessments indicate that ESP and FSP can deliver net CO₂ reductions of approximately 7–9% and 2–4%, respectively, at optimal dosages when preprocessing energy demands are controlled. Overall, ESP and FSP provide complementary, dosage-sensitive enhancements and viable pathways for partial clinker reduction in low-carbon concrete, though standardization of preprocessing and long-term durability evaluation remains essential for large-scale adoption.