Development of high-performance heavy density concrete using different aggregates for gamma-ray shielding

Abstract

Primary and secondary containment structures are the major components of the nuclear power plant (NPP). The performance requirements of the concrete of containment structures are mainly radiological protection, structural integrity and durability, etc. For this purpose, high-performance heavy density concrete with special attributes can be used. The aggregate of concrete plays an essential role in modifying concrete properties and the physico-mechanical properties of the concrete affect significantly on its shielding properties. After extensive trials and errors, 15 concrete mixes were prepared by using the coarse aggregates of barite, magnetite, goethite and serpentine along with addition of 10% silica fume (SF), 20% fly ash (FA) and 30% ground granulated blast-furnace slag (GGBFS) to the total content of OPC for each mix. To achieve the high-performance concrete (HPC- grade M60), All concrete mixes had a constant water/cement ratio of 0.35, cement content of 450 kg/m3 and sand-to-total aggregate ratio of 40%. Concrete density has been measured in the case of fresh and hardened. The hardened concrete mixes were tested for compressive strength at 7, 28 and 90 days. In some concrete mixes, compressive strength was also tested up to 90 days upon replacing sand with the fine portions of magnetite, barite and goethite. The attenuation measurements were performed by using gamma spectrometer of NaI (Tl) scintillation detector. The utilized radiation sources comprised 137Cs and 60Co radioactive elements with photon energies of 0.662 MeV for 137Cs and two energy levels of 1.173 and 1.333 MeV for 60Co. Some shielding factors were measured such as half-value layer (HVL), tenth-value layer (TVL) and linear attenuation coefficients (μ). Experimental results revealed that, the concrete mixes containing magnetite coarse aggregate along with 10% SF reaches the highest compressive strength values exceeding over the M60 requirement by 14% after 28 days of curing. Whereas, the compressive strength of concrete containing barite aggregate was very close to M60 and exceeds upon continuing for 90 days. The results indicated also that, the compressive strength of the high-performance heavy density concrete incorporating magnetite as fine aggregate was significantly higher than that containing sand by 23%. Also, concrete made with magnetite fine aggregate improved the physico-mechanical properties than the corresponding concrete containing barite and goethite. Therefore, high-performance concrete incorporating magnetite as fine aggregate enhances the shielding efficiency against γ-rays.