Microstructural and Strength Characterization of Acid-Resistant Cement Mortar Incorporating Crab Shell Powder and Recycled PET

Environmental pollution caused by marine shell waste and plastic disposal, together with carbon dioxide emissions from cement production, has increased the demand for sustainable construction materials. This study investigates the microstructural characteristics and acid resistance of cement mortar incorporating crab shell powder (CSP) as a partial cement replacement and recycled polyethylene terephthalate (PET) plastic as a fine aggregate replacement. X-ray diffraction (XRD) analysis identified portlandite, quartz, belite, and tobermorite phases, providing insights into hydration and microstructural development. X-ray fluorescence (XRF) analysis revealed slight variations in the major oxide composition and clinker compounds, supporting the potential use of CSP as a supplementary cementitious material. Durability performance was evaluated by immersing mortar cubes in hydrochloric acid (HCl) and sulfuric acid (H₂SO₄) for 56 and 92 days. Weight loss and compressive strength were assessed to determine the effects of CSP and PET replacement levels. The results indicate that moderate CSP incorporation improves acid resistance and durability, whereas excessive replacement causes deterioration of the cementitious matrix. A CSP replacement level of up to 15% by weight of cement is identified as a promising option for sustainable mortar production. This approach offers potential benefits through waste valorization and reduced reliance on conventional cement and natural fine aggregates.