Research On Radiation Shielding Concrete

Concrete which contains water,cement and high density aggregates,is widely used in building construction such as nuclear power stations and particle accelerators instead of other radiation shielding materials because it is a kind of cheap,shaping easily and high compressive strength composite materials.The mechanical properties,thermal stability, radiation shielding effectiveness and key construction techniques of radiation shielding concretes prepared with different aggregates and boron containing additives were investigated in this paper adapting new situation demands of large underground civil defense engineering.Through study the setting time,compressive strength, the hydration water content and the PH value of cement paste which contains different boron containing additives and through XRD, SEM microscopic test method,the influence of the introducing way of boron element on the hydration of cement was emphtically studied. The results indicate that the borax can greatly prolong the setting time of cement,the boron oxide lightly prolong the setting time of cement,but can greatly reduce the mechanical properties of cement paste and the boron glass has no negative effect on the setting time and mechanical properties of cement paste.The reason is that the soluble boron existing in the borax and boron oxide react with calcium forming calcium borate films which cover the surface of cement particle preventing cement hydration.The C50 steel slag concrete with a density of 2750kg/m3, C60 crushed granite stone and steel concrete with a density of 3200kg/m3and C70 steel concrete with a density of 4300kg/m3 were prepared by these measures including using heavyweight aggregates,optimizing concrete match ratio,adding boron containing additives and high range polycarboxylate water reducer.Through XRD,SEM microscopic test,compressive strength test after high temperature and thermal expansion analysis,the thermal stability of cement paste,mortar and radiation shielding concretes were studied. The results indicate that the compressive strength after high temperature of cement paste and concrete firstly increases and then decreases with temperature increases below 300℃,and reach a maximum at 300℃, the compressive strength of concrete decreases greatly above 300℃,and some concrete sample burst above 500℃.The XRD spectrum of cement-based materials amended by slag and silica fume changed obviously after 700℃,the diffraction apex of ettringite disappeared, the diffraction intensity of Ca(OH)2 weakened remarkably and the diffraction intensity of CaO increased lightly.The thermal expansion curve of cement paste contain slag and silica fume and mortar firstly increases,then decreases as the temperature continued to rise,and at high temperature the shrinkage rate of cement paste is much greater than that of the mortar.The reason is that the thermal expansion of aggregates contained in mortar restricts the shrinkage of cement paste.Making radiation shielding concrete with heavy aggregates should use new production technology which include design low slump, secondary batching method,strict control vibration time,strengthening maintenance and so on.The concrete contain steel slag,crushed granite stone, steel and boron glass has good shielding property.This study has important theoretical significance and practical engineering value in civil defense engineering construction under the new situation.