Abstract: Serpentine shielded concrete is a neutron shielding material that can maintain high crystal water content even under high temperature condition for a long time, but its compactness is low and it lacks boron element that can effectively absorb thermal neutrons. As a source of boron, boric acid is an effective material for producing shielded concrete. However, in cement-based hydration systems, the addition of boric acid can inhibit the cement hydration process, leading to deterioration of material strength and durability. This study induced the formation of high boron content and crystalline water content of boric acid in cement slurry by modifying high concentration boric acid solution. The boron content in the system was increased while the inhibitory effect of boric acid on cement hydration was relieved. The effect of modified high concentration boric acid solution on workability, mechanical properties, high-temperature residual compressive strength, microstructure and shielding performance of serpentinite shielded concrete was studied. The results show that the addition of modified high concentration boric acid solution has no adverse effects on the setting time, mechanical properties at room temperature, and high-temperature residual compressive strength of serpentine shielded concrete. After adding modified high concentration boric acid solution, the high-temperature residual compressive strength at 400 ℃ of serpentinite shielding concrete increases by 43.5%, the half value layer at room temperature decreases by 31.7%, and the half value layer decreases by 21.4% after insulation at 350 ℃ to constant weight, enhancing the shielding ability of neutron rays.

Key words: serpentine shielded concrete, neutron shielding property, high-temperature residue compressive strength, modified high concentration boric acid solution, gowerite, setting time