Simulation Study On Chloride Ion Transport Mechanism In Cement-based Materials Under High Water Pressure-chlorine Coupling

The subsea tunnel has become an all-weather channel connecting the straits and bays,because it's advantages in both unobstructed shipping and environmental protection.At present,more and more reinforced concrete subsea tunnels have been built or proposed,so the structural durability of subsea tunnel is highly valued.Due to the complexity of the service environment of subsea tunnel,the research method of evaluating chloride diffusion coefficient in concrete is gradually changing from single physical field test to multi physical field simulation.Therefore,this paper simulates the physical environment of the multi field(chloride concentration field and hydrostatic pressure field)of the subsea tunnel,and the Nernst-Planck equation is introduced on the basis of Fick's second law,and the chloride ion transport equation in cementbased materials under multi-field coupling is established,the definite solution function of the transmission equation under certain boundary conditions was determined,and the chlorine ion transmission coefficient was corrected by using existing research results and simulation tests.The correctness and effectiveness of the distribution function of chloride ion is verified by the combination of traditional physical experiment and multi physical field simulation.Through the research and analysis,this paper draws the following conclusions.(1)The water-cement ratio has a great influence on the chloride ion penetration process in cement-based materials under hydrostatic pressure.With the increase of water-cement ratio of cement-based materials,the penetration depth of chloride ion is deepened,and both have high correlation.(2)Under the action of different hydrostatic pressure,the penetration depth of chloride ion has a very obvious change,and its depth is deepened with the increase of the hydrostatic pressure.(3)The influence of aggregate content on chloride transport depth is studied quantitatively.The results show that the tortuosity effect of aggregate significantly inhibits the transmission depth,and the transport depth of chloride decreases linearly with the increase of aggregate content.(4)The interface effect of the concrete interface zone promotes the transmission of chloride ion.When aggregate content is low,the inhibition effect of aggregates on chloride ion penetration is dominant,and the interfacial effect is not obvious.However,with the increase of aggregate content,the interfacial effect is more and more obvious.(5)The simulation model of chloride ion transport of cement based materials is established by COMSOL software.It can effectively simulate chloride ion transport process and change rule in cement based materials under hydrostatic pressure and aggregate volume fraction changing.