Influence of siderite aggregate substitution on chloride resistance, durability, and gamma-ray shielding of heavy concrete.

This study investigates the effect of replacing natural aggregates with siderite (10%, 20%, 30%, and 100%) in heavyweight concretes designed for radiation shielding. Both fine (0-4 mm) and coarse (4-16 mm) siderite aggregates were used, while the binder composition (cement + GGBFS) and water-to-binder ratio (w/b ≈ 0.40) were kept constant. Mechanical, durability, and radiation shielding properties were evaluated through compressive strength, abrasion resistance, ultrasonic pulse velocity, freeze-thaw resistance, high-temperature exposure, chloride migration, and gamma-ray attenuation tests at 1173 and 1333 keV. The results indicate that siderite incorporation generally improves compressive strength, density, and durability-related performance. These improvements may be associated with a more compact internal structure, as reflected by reduced water absorption potential (indirectly inferred from transport-related behavior), lower chloride migration, and higher ultrasonic pulse velocity values. A strong inverse relationship between compressive strength and chloride migration (R² = 0.97-0.87) confirms improved transport resistance, where GGBFS likely contributes to chemical chloride binding, while siderite mainly enhances physical aggregate packing. Gamma-ray shielding performance also improves with increasing siderite content, with coarse aggregate systems showing superior attenuation compared to fine ones. Overall, siderite-modified concretes demonstrate strong potential for durable and radiation-shielding structural applications.