Novel Cement-Free UHPC with High Gamma-Ray Resistance Using Calcium Oxide–Activated Slag, Iron and Barite Powders, and Steel Fibers

This study focuses on the development and evaluation of a novel cement-free gamma-ray-resistant ultrahigh-performance concrete (UHPC), known as UHPC-CAS. UHPC-CAS is composed of calcium oxide–activated slag, iron and barite powders, and steel fibers, making it a type of ultrahigh-performance geopolymer concrete (UHPGC). In this study, the effects of replacing silica sand with varying percentages of iron and barite powders on the mechanical and radiation properties of UHPC-CAS were investigated. The optimal replacement ratio of iron powder was found to be 50%, resulting in the highest compressive, tensile, and bending strengths among all mixtures without fibers. Furthermore, the UHPC-CAS samples reinforced with steel fibers and containing barite powder exhibited a more pronounced softening zone than those containing iron powder. With 100% iron powder and 3% steel fibers, UHPC-CAS achieved superior resistance to gamma rays, as evidenced by the highest attenuation coefficient of 0.234 cm and the lowest half-value layer of 2.96 cm. This research demonstrates the potential for developing sustainable cement-free UHPC for use in nuclear facilities and other applications requiring high radiation shielding.