Study On Chloride Ion Transport Mechanism Of Concrete In Submarine Tunnel Under The Interaction Of Multi-salts And Multi-fields

The submarine tunnel has become an all-weather channel connecting the strait and the bay because it does not hinder the shipping of ships and minimize the impact on the marine ecological environment.At present,more and more submarine tunnels have been completed,under construction,and proposed construction.According to previous engineering cases,offshore structures at home and abroad have been subjected by harmful substances in varying degrees in the marine environment.The subsequent maintenance or reconstruction has caused a huge economic burden.So the durability of offshore structures have drawn great attention.Due to the complexity of the service environment of submarine tunnels,the research on concrete chloride diffusion coefficient,which is the key index to evaluate the durability of the submarine tunnel concrete,has gradually shifted from single physical field test to multi-field simulation.Therefore,this paper takes the concrete of the subsea tunnel as the research object,and supported by the China Postdoctoral Science Fund(No.2015M571601),simulates the physical environment of multi-salt(chloride and sulfate)and multi-field(concentration field and pressure field).By introducing the theory of micro-fluid mechanics and seepage mechanics of porous media,the chloride ion transport equation of concrete under the coupling of multi-salt and multi-field was established,and the solution function of the transport equation was deduced,using the existing research results and simulation tests to modify the chloride ion transmission coefficient,then distribution function suitable for describing the evolution of chloride ion concentration over time and depth under multiple salt and multi-field coupling was established,and use laboratory simulation experiments verify the correctness and effectiveness of the chloride ion distribution function.The model established in this paper can directly guide the design of the durability of the proposed seafloor tunnel under the current depth of less than 100m and the prediction of the remaining life of the existing or building submarine tunnel.Based on the analysis and research,some conclusions are drawn.(1)The existence of sulfate obviously delays the transmission process of chloride ion in concrete,but the retarding effect of sulfate on the diffusion of low water-binder ratio to chloride ion of concrete is not as obvious as that of high water cement ratio concrete.(2)The lower hydrostatic pressure(0.5 MPa)can make the chloride concentration distribution curve of concrete with high water-binder ratio tend to be anti-S-type,and the chloride transport process tends to dominate convection.(3)Concrete with low water-binder ratio or fly ash can resist high hydrostatic pressure(1MPa),which can reduce the chloride concentration within a certain depth of the concrete surface,and can effectively reduce the seepage velocity of composite salt solution inside the concrete,making chlorine the transfer of ions is mainly dominated by convection and diffusion dominated.(4)Using COMSOL simulation software to establish the simulation model of chloride ion transmission in concrete can effectively simulate the effect of aggregate on chloride ion transmission in concrete.(5)The depth of chloride ion transport decreases linearly with the increase of aggregate content,but the interfacial effect can promote chloride ion transport.When the aggregate content is lower,the aggregate effect on the chloride ion penetration plays a dominant role,but with the increase of the aggregate content,the interface effect becomes more obvious.