Chloride Ion Transport In Coral Concrete Under Bending Stress And Steel Corrosion Research

The ocean is a key factor driving the development of a major country.The new lightweight aggregate concrete-coral concrete,which is prepared by using coral debris and coral sand as coarse aggregate and seawater mixing method,has a wide application prospect in Marine engineering construction because of its convenient materials,economy and high efficiency.However,in practical engineering,coral concrete structures are often subjected to the coupling action of seawater and bending stress,and the structural damage accumulates continuously,providing a convenient channel for the invasion of harmful substances.As a result,the reinforcement corrosion of coral concrete structures in the island environment is serious,which often cannot meet the service life requirements.In order to explore the rule of reinforcement corrosion and service life of Coral Aggregate Seawater Concrete(CAC)structure under the coupling effect of bending stress and Marine environment,the bending stress loading test was carried out on coral aggregate seawater concrete(CAC)structure by self-made equipment.The influence of bending stress on corrosion of different kinds of steel bars in coral concrete with different thickness of protective layer was studied.AB AQUS finite element analysis software was used to simulate the stress and stress state of reinforced coral concrete member model under bending stress.The corrosion of different kinds of steel bars under bending stress was analyzed by polarization curve and electrochemical impedance spectroscopy.The free chloride ion concentration(C_f)and apparent chloride ion concentration(C_s)at different depths and test times of coral concrete under bending stress were measured,and the chloride ion diffusion coefficient(D)was calculated to construct the chloride ion diffusion model of coral concrete under bending stress.The main research results are as follows:(1)Firstly,by testing the polarization curve of coral concrete reinforcement under bending stress,the failure process of different protective layer thicknesses and different kinds of reinforcement in chlorine salt environment is qualitatively analyzed.The results show that:With the increase of concrete protective layer thickness and bending stress,the polarization resistance(R_p)of self-corrosion potential value of reinforcement in CAC gradually increases,while the corrosion current density(Icorr)and steel corrosion rate(Vcorr)gradually decrease.It indicates that the concrete protective layer thickness and bending stress can be reduced appropriately.It can effectively reduce the corrosion rate of reinforcement and improve the corrosion resistance of reinforcement.However,when the thickness of the protective layer increases to a certain range,the change rate of the above parameters tends to be stable and even starts to decline,indicating that the corrosion protection effect of reinforcing steel bar by increasing the thickness of the protective layer is more significant when the thickness of the protective layer is small,but the corrosion protection effect decreases when the thickness of the protective layer is large.(2)Three electrode method was adopted to measure the electrochemical impedance spectrum analysis of the reinforcement in coral concrete.It was found that with the extension of exposure time,the radii of the high frequency capacitive reactance arcs in the Nyquist plot were gradually decreasing,the intersection points of the high and low frequency capacitive reactance arcs gradually shifted to the right,and the low frequency capacitive reactance arcs gradually contracted to the real part of the impedance,and the Bode impedance modulus and the absolute value of the maximum phase Angle were also gradually decreasing.This indicates that,with the extension of time,the steel bar in CAC gradually occurs blunt rust,and the corrosion rate increases gradually.(3)The chloride ion diffusion behavior in coral concrete under bending stress was studied.The results show that the decreasing relationship between chloride content and diffusion depth of CAC conforms to Fick’s second diffusion law.With the increase of erosion time,the surface chloride ion concentration increases slightly,but eventually becomes stable.The bending stress has no obvious effect on the surface chloride ion concentration.The flexural stress accelerates the development of microcracks in concrete structures,increases the porosity and accelerates the erosion rate of chloride ions in concrete.The flexural stress inhibits the formation and development of microcracks in concrete structures,reduces the porosity,and reduces the erosion rate of chloride ions.