Experimental Study On The Resistance Of Chloride Ion Penetration Of Ultra-high Performance Concrete

At present,there is no uniform standard and specification for the evaluation of the resistance of UHPC to chloride ion penetration in China.Therefore,by testing the UHPC chloride ion migration coefficient under different mix ratios,the water-binder ratio,The influence of silica fume content,steel fiber type and content,and coarse aggregate content on the resistance of UHPC to chloride ion penetration will help further research on UHPC.And in recent years,there have been a large number of researches on UHPC containing coarse aggregates,but most of them are about their mechanical properties.The research on the influence of coarse aggregates on the permeability of UHPC is relatively lacking,which hinders the inclusion of coarse aggregates to a certain extent.The promotion and application of aggregate ultra-high-performance concrete,and the addition of coarse aggregate will inevitably affect the permeability of UHPC.Therefore,by studying the influence of UHPC on the permeability of coarse aggregate under different amounts of coarse aggregate,the promotion of coarse aggregate The application of high-performance concrete provides a theoretical basis for subsequent related research.The research results are as follows:（1）With the increase of the water-binder ratio,the expansion of the concrete increases;when the amount of silica fume increases from 20%to 30%,the expansion of the concrete increases first and then decreases;long steel fibers The increase of the amount of short steel fiber will cause the decrease of concrete fluidity,and the amount of steel fiber is the main factor affecting the flow performance of UHPC.As the amount of coarse aggregate increases,the fluidity of the concrete gradually decreases.（2）The strength of UHPC decreases with the increase of water-binder ratio;silica fume contributes the most to the increase of UHPC compressive strength when the amount of silica fume is about 25%;in addition,the increase of steel fibers has a strong promotion of compressive strength effect.（3）When more and more coarse aggregates are added,the compressive strength of UHPC increases first and then decreases.Under normal temperature curing conditions,when the amount of coarse aggregate is small（400kg/m³）,the compressive strength of the test piece reaches the maximum value of 149MPa,which is 6%higher than that of the blank group.Under hot water curing conditions,this group of test pieces the compressive strength reaches 184MPa.（4）Under standard curing conditions,the chloride ion migration coefficients corresponding to water-binder ratios of 0.16,0.17,and 0.18 are 6.92×10^-14m²/s,8.87×10^-14m²/s,and 13.53×10^-14m²/s,respectively.As a result,when the water-to-binder ratio increases,D_RCM increases accordingly.When the amount of silica fume gradually increases（20%,25%,30%）,the corresponding UHPC chloride ion migration coefficients are 11.12×10^-14m²/s,8.87×10^-14m²/s,7.97×10^-14m²/s,indicating that its chloride ion permeability will weaken with the increase of silica fume content.Under thermal conditions,UHPC chloride ion migrat ion coefficient is greatly reduced.When the curing time increases,the D_RCM value decreases and the UHPC’s resistance to chloride ion penetration will continue to increase.（5）Under standard curing conditions,the UHPC chloride ion migration coefficient of steel fiber and coarse aggregate is basically in the order of 10^-13,while the UHPC chloride ion migration coefficient of unmixed steel fiber and coarse aggregate is basically in the order of 10^-14 Under thermal conditions,the measured chloride ion migration coefficient is about half of that under standard conditions.（6）In the group not mixed with steel fiber or coarse aggregate,the average penetration depth of chloride ions is smaller,and the penetration depth of chloride ions increases with the increase of the water-gel ratio.For the group with added steel fibers,the average penetration depth of chloride ions is about 2-3 times that of the group without added steel fibers and coarse aggregates.At the same time,the surface rust is more serious.