Coupled Model And Simulation Study Of Chloride Transport In Concrete Considering Binding Effect

A large number of concrete structures are located in the coastal areas of China,and the ingress of chloride ions from the marine environment into concrete,leading to steel corrosion,is the main factor causing the deterioration of concrete structures.Some of the chloride ions that enter the concrete will undergo complex physicochemical interactions with cement hydration products and become bound to concrete,while the portion of free chloride ions present in the pore solution is generally believed to cause steel corrosion.Therefore,the study of the durability of concrete structures needs to take into account the effects of chloride binding.Concrete structures are typically subjected to a complex service environment involving multiple factors such as temperature,stray currents,and erosive ions.Both the transport and binding processes of chloride ions can be affected by these coupled factors.The establishment of a coupled model considering these factors is of great significance for simulating the distribution of chloride ions inside concrete and conducting research on the durability of concrete structures.The main research contents of this paper are as follows:(1)Based on thermodynamic models including the phase equilibrium model and surface complexation model,the physical and chemical interactions between cement-based materials and chloride ions are explored using PHREEQC software.The effects of chloride concentration,temperature,and p H of solution on the amount of cement hydration products and adsorbed ions on the surface of C-S-H gels in concrete are analyzed.And then the change rules of chemical bound,physical bound,and total bound chloride ions are obtained,and the chloride binding isotherms under different environmental conditions are fitted.(2)The basic equations and corresponding boundary conditions for thermo-electro-chemomechanical coupling systems of porous media are defined.Based on the work-energy transfer principle and the energy conservation law,the Hamilton-type variational principle for thermoelectro-chemo-mechanical coupling systems is established.The Hamilton-type generalized variational principle for thermo-electro-chemo-mechanical coupling systems is established using the Lagrange multiplier method.The accuracy of the established variational principles is verified by deriving the stationary value conditions.Based on the established variational principles,the equivalent weak form for thermo-electro-chemo-mechanical coupling systems suitable for finite element analysis is derived.(3)Based on Fick’s law and the multi-field coupling theory established in this paper,the transport process of chloride ions in concrete under different environmental conditions is simulated by COMSOL software.The distribution of chloride ions inside the concrete is obtained,and then the service life of concrete structures is predicted and the evolution of the substances inside the concrete during the transport of chloride ions is also investigated.