Effect of mechanical loading on gas permeability and radiation shielding properties of concrete with low-clinker cement

Concrete shielding structures in nuclear facilities must maintain both radiation attenuation capacity and transport barrier performance throughout their service life. Although gas permeability and radiation shielding properties have been widely investigated, their coupled evolution under load-induced damage remains insufficiently understood, particularly for concretes with low-clinker cements. This study evaluates the combined effects of low-clinker cement type, aggregate type, and mechanical preloading on the gas permeability and gamma-ray shielding performance of concretes intended for nuclear applications. Six mixtures were produced using CEM II/C-M (V–F–LL) and CEM V/A (S–V) cements combined with magnetite, basalt or limestone aggregates. Gas permeability was measured using the Cembureau method on specimens subjected to progressive preloading up to 90% of the splitting tensile strength. Gamma-ray attenuation parameters were determined using a 137 Cs source (0.662 MeV), and microstructural observations were performed by SEM. Aggregate type was the dominant factor governing shielding performance. Magnetite concretes exhibited the highest compressive strength, the lowest gas permeability, and the highest attenuation coefficients, reaching μ = 0.258 cm⁻¹ and HVL = 2.68 cm. CEM V concretes generally showed lower permeability than the corresponding CEM II concretes. Mechanical preloading increased gas permeability, particularly above approximately 80% of the splitting tensile strength, indicating the formation of connected microcrack networks. Simultaneously, a reduction in attenuation factor was observed, demonstrating that load-induced damage adversely affected shielding effectiveness. A relationship between the increase in permeability and the reduction in attenuation factor was identified, suggesting a transition from pore-controlled to crack-controlled behaviour. The results demonstrate the suitability of concretes with low-clinker cements for shielding applications and provide new insight into the coupling between damage development, transport properties, and radiation shielding performance.