Mechanical and gamma-ray shielding performance of waste ceramic substituted magnetite concrete under high temperatures

To synergistically enhance radiation shielding performance while promoting resource sustainability, this study developed a high-density radiation-shielding concrete by substituting magnetite fine aggregate with waste ceramic fine aggregate at volumetric replacement ratios of 0%, 20%, 40%, 60%, 80%, and 100%. The thermal response (25 ℃, 300 ℃, 450 ℃, 600 ℃) was systematically evaluated in terms of mass loss ratio, ultrasonic pulse velocity（UPV）, macro-mechanical properties, microstructural evolution, and gamma-ray linear attenuation coefficient (μ) characteristics. Multi-scale mechanisms were elucidated via scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results demonstrate that moderate ceramic incorporation optimizes internal humidity distribution and reinforces the interfacial transition zone (ITZ). The 60% replacement mixture exhibited optimal comprehensive performance within 300–450 ℃, with significantly higher compressive strength, splitting tensile strength, and UPV than the control (0% replacement), indicating superior thermo-mechanical stability. Even under extreme 600 ℃ exposure, although compressive strength slightly decreased, splitting tensile strength remained higher than that of the control. SEM analysis revealed reduced ITZ porosity and enhanced densification in the 60% mixture; at 300 ℃, secondary hydration, triggered by internal curing, generated C-S-H gel that effectively filled and “healed” thermally induced microcracks. Gamma-ray shielding performance was evaluated using the μ and the mass attenuation coefficient (μₘ). At different temperatures, as the replacement ratio increased, μ showed a decreasing trend, whereas μₘ showed an increasing trend. In conclusion, the 60% waste ceramic replacement ratio achieves synergistic optimization among load-bearing capacity, thermal-damage tolerance, and radiation-shielding efficiency, offering a green functional material with environmental compatibility and high-temperature service reliability for nuclear facilities, civil defense projects, and medical radiation shielding structures.