Evaluation of the effects of bismuth oxide (Bi₂O₃) micro and nanoparticles on the mechanical, microstructural and γ-ray/neutron shielding properties of Portland cement pastes

This study presents a comparison of the effects of micro-Bi₂O₃ and nano-Bi₂O₃ powders on the mechanical, microstructural and gamma / neutron shielding properties of Portland cement pastes. Cement pastes with various ratios of cement (up to 30 wt-%) replaced with Bi₂O₃ micro and nanoparticles were prepared. Consistency, compressive strength, water accessible porosity and mercury intrusion porosimetry tests were performed, in order to characterize their engineering properties. In addition, experimental and theoretical evaluations of γ-ray and neutron shielding properties were performed. The results showed that the incorporation of Bi₂O₃ powders gradually leads to a decline in cement pastes’ compressive strength and an increase in their porosity, as the amount of powder is increased. However, the deterioration rate varies depending of type of powder used, in favor of nano-Bi₂O₃. Gamma attenuation tests results indicate that the addition of Bi₂O₃ powders enhances the shielding capability of pastes, in the energy range of interest (0.08–2.614 MeV). However, the effects of particle size on γ-ray attenuation are negligible in that energy range. Slow neutron attenuation study showed that the addition of nano-Bi₂O₃ improved the shielding ability of cement pastes, with enhancements ranging between 15.3% and 25.5% for samples with 5 and 30 wt-% nano-Bi₂O₃, respectively. In conclusion, this study shows that the addition of nano or micro-Bi₂O₃ is effective in producing lead-free cementitious composites with improved γ-ray and neutron shielding properties. Unlike gamma shielding, nano-sized Bi₂O₃ has a better ability to attenuate neutrons, in comparison to their micro-sized counterparts.