Study On Chloride Corrosion Resistance Of High Performance Concrete Under Dry Wet Cycle

A vast territory and abundant marine resources in China.In order to make full use of marine resources,we need to carry out a large number of marine engineering construction.The reinforcement inside the reinforced concrete structure is very vulnerable to chloride ion erosion,resulting in the damage and damage of the whole structure.When the reinforced concrete structure is in long-term service in the environment rich in chloride ion such as the ocean,its service life will be greatly affected.In order to avoid the early retirement of reinforced concrete structures due to chloride ion corrosion,it is a general trend to further study new concrete with good corrosion resistance.Ultra high performance concrete(UHPC)is a new type of cement-based composite material with excellent durability such as impermeability and chloride ion corrosion resistance.If this material is applied to the environment with high chloride ion content such as ocean,deicing salt environment and salt lake,it will avoid the loss of human,material and financial resources caused by the damage and damage of concrete structure due to the bad service environment.Therefore,it is of great significance to study the compressive strength,damage degree and chloride ion transmission law of ultra-high performance concrete under the coupling action of chloride salt dry wet cycle.Based on the research on the durability of ultra-high performance concrete by a large number of scholars at home and abroad,this paper focuses on the anti chloride ion corrosion performance of ultra-high performance concrete under dry wet cycle:(1)The experiment designs the corrosion of ultra-high performance concrete under the dry wet cycle coupling action of three groups of chlorine salts with different concentrations: a(16%NaCl solution),B(5% NaCl solution)and C(10% NaCl solution),and the cube strength change rate,mass change rate and stress-strain relationship are discussed,The results show that the cube compressive strength and quality of UHPC increase first and then decrease,but the variation range is small in the whole test process,and the cube compressive strength and quality are relatively stable.At the same time,the complete stress-strain curve equation of ultra-high performance concrete suitable for the mix proportion in the test is proposed.(2)Based on Fick’s first and second laws,the experimental analysis of ultra-high performance concrete subjected to the coupling effect of dry and wet cycle of chloride salt is carried out.Combined with the actual working conditions of the test,the influencing factors affecting the diffusion coefficient of chloride ion in ultra-high performance concrete,the distribution law and diffusion model of chloride ion are discussed.The results show that the ultra-high performance concrete has good resistance to chloride ion corrosion.After 360 days of chloride salt dry wet cycle,the chloride ion concentration measured in the specimens is low.The chloride diffusion coefficient decreases with the increase of depth from the surface,and the lower the chloride concentration is;The chloride ion diffusion coefficient at the same depth increases gradually with the increase of dry wet cycle,and the greater the chloride ion concentration.(3)Using the comprehensive concrete crack defect tester,the plane test is carried out on three kinds of 100mm×100mm×400mm prismatic specimens after the dry wet cycle of different concentrations of solution,the changes of sound time and sound velocity are analyzed and studied,and the damage degree and damage layer thickness of ultra-high performance concrete after different chlorine salt dry wet cycle under different salt solution concentrations are obtained.The results show that the damage of ultra-high performance concrete is not serious after being eroded by chloride under the action of dry wet cycle,and the damage layer thickness of Cube Specimens in the same concentration solution increases slowly with the increase of dry wet cycle;In the same dry wet cycle,the damage layer thickness of the test piece is as follows:group a > group C > group B > clear water group.(4)The microstructure changes of ultra-high performance concrete are analyzed from the micro level by using XRD and SEM technology.The results show that the interior of ultra-high performance concrete is dense and has few pores.With the increase of dry wet cycle,the interior pores of concrete will be filled with cementitious materials and tend to be more dense.It is verified that the durability performance of ultra-high performance concrete at the macro level after the coupling effect of chloride dry wet cycle.