Nonlinear Diffusion Of Harmful Ions Of Concrete Structure In Marine Environment

There are three main factors that affect nonlinear diffusion of harmful ions in concrete structure in the marine environment: The first factor is continuous hydration of unhydrated cement particles.New hydration products are produced by unhydrated cement particles continuous hydration.These new hydration products fill pores of concrete and hinder the diffusion of harmful ions.The second factor is reaction between harmful ions and cement hydration products.New products are reacted by cement hydration products and harmful ions by diffusion into the mixed cement in concrete pore solution.These new reaction products inhibit the diffusion of harmful ions,too.The third factor is erosion damage of harmful ions.The expansive force acting on the concrete pore walls is caused by the new reaction products.When the new reaction products and the diffusion of harmful ions are increased,the expansive force of pore wall causes micro cracks.It leads more harmful ions to diffuse.At last,it leads the structure to damage,while service life of concrete structure is not up to the design life.This paper mainly studies nonlinear diffusion model of harmful ions of concrete structure under influence of three factors.The specific contents are as follows:Firstly,the evolutions of density,elastic modulus,compressive strength and tensile strength as well as pore structures of concrete in the late water immersion are studied.These evolutions are leaded by unhydrated cement particles continuous hydration.First,the evolutions of mass,wave velocity,compressive strength,tensile strength and porosity of concrete were detected regularly by experimental methods during continued hydration process in this study,and then according to chemical reaction equation of cement hydration,related reaction rate equation as well as mass conservation,the new evolution models of mass,elastic modulus and porosity were suggested.Finally,the experimental data are substituted into the theoretical model.The results show that the theoretical model is in good agreement with the experimental data,and the theoretical model can well describe the concrete hydration evolution characteristic of the elastic modulus and porosity under long-term continuous hydration.Secondly,the evolutions of density,elastic modulus and pore structures of concrete with different mix proportion in different concentration solution are studied.Firstly,the evolutions of mass,wave velocity and porosity of concrete in different concentration solution were measuredregularly by experimental methods during the process of erosion.Then according to chemical reaction equation of cement hydration,related reaction rate equation as well as mass conservation,the new evolution model of mass of concrete samples in sodium chloride solution was suggested.Finally,the evolution of porosity and elastic modulus of concrete in sodium chloride solution are theoretically analyzed.Thirdly,the new evolution model of porosity and erosion damage were introduced into the effective diffusion coefficient of diffusion equation.The diffusion equation was solved numerically by the finite difference method.The numerical results were compared with the experimental results.The results show that the numerical results are very close to the experimental results.In the marine environment,harmful ions diffusion rate depends on the erosion damage,and the rate of erosion damage is related to the chemical reaction rate.Finally,the evolutions of wave velocity,tensile strength and resistivity of conductive concrete in the late water immersion and in different concentration solution are studied.Firstly,the evolutions of mass,wave velocity and resistivity of conductive concrete in the late water immersion were measured regularly by experimental methods during the process of immersion.Then according to the experimental datas,the content of conductive graphite was determined.In order to improve the mechanical properties of conductive concrete,the amount of silica powder was determined by experiments.Finally,electrical conductivity of conductive concrete was measured in chlorine salt and sulphate erosion.The results show that electrical conductivity of conductive concrete is not affected by the erosion of harmful ions.