The South China Sea is far away from mainland China,and a major problem facing engineering construction in the South China Sea is the lack of construction materials such as river sand,gravel and fresh water.On the premise of not destroying the original ecological environment of the islands,using coral in situ around the islands and reefs instead of traditional concrete aggregates is a feasible solution.However,the chloride ion corrosion of coral aggregate concrete prepared from loose and porous coral is particularly serious in the high temperature,high humidity and high salt environment of the South China Sea.Studying the impact of coral aggregate on the chloride ion transport process,and establishing a mesoscopic transport model for coral aggregate concrete are of great significance for controlling the chloride ion erosion process of coral aggregate concrete and achieving the durability design of coral aggregate concrete.In this paper,Rapid Chloride Migration Test(RCM)and Mercury Injection Test(MIP)were carried out.Based on the theoretical analysis of the test results,numerical simulations were conducted at the mesoscale using COMSOL Multiphysics software to explore the chloride ion transport laws and mechanisms of coral aggregate concrete in the underwater and tidal regions of the ocean.The main research contents and results are as follows:(1)Based on the RCM test results,the influence of coral aggregate on the chloride ion diffusion resistance of concrete was analyzed: the introduction of coral aggregate significantly reduces the chloride ion diffusion resistance of concrete,and the chloride ion diffusion coefficient of coral aggregate concrete increases linearly with the increase of the volume fraction of coral coarse aggregate.Introducing the n-phase inclusion spheres theory and combining with the RCM test results,it can be obtained that the chloride ion diffusion coefficient of coral aggregate phase in coral aggregate concrete is about twice that of coral sand mortar phase after 28 days of curing.The MIP experiment was used to compare the pore structure of coral sand mortar and river sand mortar.The results showed that the porosity of coral sand mortar was close to twice that of river sand mortar,and the porosity of coral sand mortar was significantly higher than that of river sand mortar in the pore size stages of capillary and transition pores.(2)Based on the method of random extension,a generation algorithm of random convex polygon aggregate model was constructed.The chloride ion transport processes at the mesoscopic level of ordinary aggregate concrete(OAC)and coral aggregate concrete(CAC)were simulated and compared using COMSOL Multiphysics software.Simulation studies on chloride ion diffusion in coral aggregate concrete under different coarse aggregate area fractions and different aggregate shape characteristics were conducted.The results show that: the diffusion process of chloride ions is blocked by ordinary aggregates,while chloride ions can rapidly diffuse to the deep layer through coral aggregates;the higher the area fraction of coral aggregate,the lower the surface chloride ion concentration and the higher the deep layer chloride ion concentration after the chloride ion diffusion process and the difference of deep layer chloride ion concentration increases with the increase of simulation exposure time;the shape of aggregates has little effect on the diffusion process of chloride ions,the sharper the coral aggregate shape is,the faster the chloride ion diffusion rate is.(3)A coupled moisture-chloride ion convection-diffusion transport model was established,the numerical simulation study of chloride ion transport under dry and wet cycle conditions of coral aggregate concrete(CAC)was carried out.The results show that:the peak value of chloride ion waveform in the surface layer decreases with the increase of coral aggregate area fraction,while the chloride ion concentration in the deep layer increases with the increase of coral aggregate area fraction;the chloride ion concentration under dry and wet cycling conditions is higher than that under pure soaking conditions,and the peak value of chloride ion waveform and the chloride ion concentration in the deep layer increase with the increase of dry and wet cycle ratio. |