Performance and microstructural evaluation of sustainable self-compacting concrete incorporating eggshell powder and fly ash as environmentally sustainable cement replacements

In the pursuit of sustainable construction practices, this study evaluates the potential of eggshell powder (ESP) and fly ash as partial replacements for cement in self-compacting concrete (SCC). ESP, rich in calcium carbonate, and fly ash, known for its pozzolanic properties, were used at replacement levels of 5–20 % and 20 %, respectively. Comprehensive experiments assessed the fresh properties (slump flow, V-funnel, L-box, and J-ring), mechanical strength (compressive, split tensile, and flexural) at 7 and 28 days, and durability under acid exposure (HCl and H₂SO ₃). Microstructural analyses via SEM and EDX confirmed the improved hydration and densification in the optimally dosed mixes. The findings revealed that replacing 10 % of the cement with ESP, along with 20 % fly ash, achieved the best performance, yielding a 14.7 % increase in compressive strength at 28 days compared to the control, enhanced tensile and flexural strengths, and superior acid resistance. However, higher ESP dosages (>10 %) led to strength and durability reduction due to increased porosity and excess unreacted CaCO₃. The study demonstrates that optimized blends of ESP and fly ash can produce high-performance, eco-efficient SCC, providing a practical route toward circular economy practices and a reduced carbon footprint in concrete construction.