Experimental Study On Properties Of Iron Ore Concrete Mixed With Boron Carbide After Sub-high Temperature

Radiation shielding concrete plays important role in the nuclear field.The application environment of radiation shielding concrete is complex and changeable.The harsh temperature environment is one of the main reasons for accelerating the aging of concrete.Radiation shielding concrete was affected by sub-high temperature environment due to factors such as nuclear power plant radiation heating,baseline accident heating and pipeline heat conduction.Therefore,improving the stability of the performance of radiation shielding concrete in complex environments is of great significance for maintaining nuclear safety and prolonging the service life of nuclear power plants.Boron carbide material is a new type of anti-radiation material,which is resistant to radiation and high temperature,and stable in nature.The research on it anti-radiation abilities and mechanical properties when added to concrete have laid certain foundation,but it needs further explorations when combined with the different properties of concrete in complex temperature environments.Iron ore concrete is one of the main classifications of radiation shielding concrete.The bulk density and apparent density of hematite and limonite sand were measured.Formulated iron ore radiation shielding concrete that meets the compressive strength grade of C50 and density grade of RS2 by design of mix proportion.The apparent density and slump of fresh concrete were measured by the performance test.The boron carbide material and sub-high temperature environment were used as control variables respectively in the experimental investigation.The mass of 5% of the boron carbide material substituted with the limonite sand.Researched the thermal performance of iron ore radiation shielding concrete in different sub-high temperature points and the changes in mechanical and durability properties before and after 5 days of sub-high temperature treatment at 145℃.Combined with bubble parameters and microscopic morphology,analyzed the influence rule and mechanism of boron carbide on the macro performance of iron ore concrete before and after sub-high temperature.It is found that iron ore concrete mixed with boron carbide had outstanding advantages in anti-deterioration ability after being subjected to sub-high temperature environment.The main research results are as follows:(1)The working performance test showed that the boron carbide material increased the slump of iron ore concrete and slightly reduced the apparent density.The study of thermal parameters showed that the specific heat capacity and thermal conductivity of iron ore concrete mixed with boron carbide decreased significantly after 105℃.The specific heat capacity and thermal conductivity decreased by 54.5% and 17%.The thermal diffusion coefficient decreased by 6.8% and the apparent density decreased by 25% in the range of 25-145℃.Boron carbide material made the specific heat capacity,thermal conductivity and thermal diffusion coefficient of iron ore concrete and other thermal parameters change less under the influence of temperature.It was beneficial to the stability of temperature,reduced the generation of concrete cracks,and ensured the radiation protection performance was relatively stable.(2)The test results of compressive strength and flexural strength showed that the iron ore concrete mixed with boron carbide had the highest ratio of bending-compressive strength after sub-high temperature.Boron carbide material increased the increase amplitude of flexural strength of iron ore concrete by 3% and increased the increase amplitude of ratio of bending-compressive strength by 5.4% and inhibited the increase amplitude of compressive strength in the sub-high temperature environment.The results of electric flux test and carbonization test showed that the addition of boron carbide can effectively inhibit the chloride ion permeability resistance and carbonization performance deterioration of iron ore concrete under sub-high temperature environment.The increase of electric flux and carbonation depth of iron ore concrete under sub-high temperature were inhibited by 57% and 30.6% by boron carbide materials.It has obvious effect on preventing corrosion of steel bars and cracking of concrete,and was beneficial to prevent the attenuation of concrete radiation protection performance.(3)The correlation of macro properties was explored through the variation rule of micro properties after sub-high temperature.The fluctuation of concrete properties was small at room temperature when 5% boron carbide was substituted for fine aggregate.Experimental study on bubble parameters and microscopic morphology showed that the addition of boron carbide had the filling effect obviously after sub-high temperature,reduced the bubble chord length,reduced the bubble spacing,optimized the bubble structure,and improved the stability of bubble parameters of iron ore concrete after sub-high temperature.It was good for keeping the shielding performance stable.The improvement of bubble parameter stability of iron ore concrete by boron carbide at sub-high temperature is the main reason to inhibit the decrease amplitude of the specific heat capacity,thermal conductivity and other thermal parameters as well as the chloride ion permeability and carbonization resistance after sub-high temperature.