Strength, Sulfate Resistance, and Microstructural Characteristics of Concrete With Partial Cement Replacement Using Eggshell Powder and Wheat Straw Ash

This study explores the partial replacement of ordinary Portland cement (OPC) with a composite of eggshell powder (ESP) and wheat straw ash (WSA) in C‐25 concrete, focusing on mechanical performance and durability. Cement was replaced with varying proportions of ESP and WSA, and the concrete mix was prepared following ACI guidelines. Chemical analysis identified WSA as a Class F pozzolan, containing 86.97% combined oxides (SiO 2 , Al 2 O 3 , Fe 2 O 3 ). Experimental tests assessed consistency, workability, compressive and flexural strength (at 28 and 56 days), acid resistance, and microstructure (via SEM and XRD). As the ESP–WSA content increased, consistency improved while workability decreased. The blend containing 15% ESP and 5% WSA achieved compressive strength comparable to the control (33.5 MPa) and maintained flexural strength. All blended mixes demonstrated improved resistance to sulfuric acid. SEM analysis revealed a denser microstructure with reduced free lime, while XRD results indicated lower portlandite content and inhibited ettringite formation, confirming pozzolanic activity. Overall, replacing 20% of cement with 15% ESP and 5% WSA enhanced durability without compromising strength, supporting the use of these agrowaste materials as sustainable cement alternatives.