Sustainable Utilization of Mill Scale in High-Calcium Fly Ash Geopolymer Concrete: Mechanical, Durability, and Radiation Shielding Properties

This study evaluated the impact of mill scale (MS), a steel manufacturing waste product, as a replacement for natural fine aggregate (up to 100% by volume) in high-calcium fly ash-based geopolymer concrete (GC) and ordinary Portland cement concrete (CC). We compared the workability, compressive strength, splitting tensile strength, modulus of elasticity, density, water absorption, porosity, ultrasonic pulse velocity, thermal conductivity, acid resistance, chloride penetration, and radiation attenuation (gamma rays and fast neutrons) of the resulting materials. Results showed that GC and CC with 100% MS achieved 28-day compressive strengths of 23.6 MPa and 35.2 MPa, respectively, representing 58% and 90% of the strengths of plain GC and CC. MS-modified GC exhibited superior acid and chloride resistance compared to CC. Importantly, MS enhanced radiation shielding, with GC and CC containing 100% MS, demonstrates the best performance, suggesting its potential use in radiation-shielding construction materials.