Experimental Study On The Effect Of The Rainfall On The Distribution Of Chloride In Concrete

The durability of the reinforced concrete structures in the coastal salt fog area is caused by chloride ion erosion.The transport of chloride ions in concrete is affected by various factors,among which water transport is one of the important factors.Precipitation affects the degree of saturation of the concrete and causes the transport of moisture,which affects the distribution of chloride ions in the concrete.It is of great significance for the durability and safety of concrete structures to carry out studies on the concentration of chloride ion in the surface layer of concrete and the internal chloride transport law.In this paper,an indoor artificial rainfall system was used to study the effect of different rainfall conditions on the transport of chloride ions in concrete.The transmission model of chloride ions in concrete under rainfall was established and numerical calculations were performed.The existing coastal structures in the salt fog area were selected.Core samples were taken at typical locations of the structure and the actual structure was affected by chloride ions in the rain and flowing water environment.The results show:(1)Rainfall time and rainfall intensity have a significant effect on chloride ion concentration in the surface layer of concrete.The longer the rainfall time,the greater loss of surface chloride ion concentration,the greater amount of chloride ion loss in the surface layer,the greater depth of the convection zone;The greater the rainfall intensity,the greater loss of surface chloride ion concentration,the greater amount of chloride ion loss in the surface layer,but the same effect depth;the chloride ion distribution characteristics of different saturated concrete are different,the lower the saturation,the more obvious the effect of rainfall,and the decrease of chloride ion concentration faster.(2)Using COMSOL finite element software to solve the model,it is shown that the calculated results of the chloride ion transport model under rainfall are consistent with the experimental results.(3)Rainfall time,rainfall intensity and saturation have significant effects on chloride binding ability.The longer the rainfall time,the smaller the chloride binding ability,and the greater the intensity,the smaller the chloride binding ability;It shows a decreasing trend with saturation decreases,but it does not decrease indefinitely and tends to a stable value.(4)Rainfall has a significant influence on the micro-morphology structures of concrete.The longer the rainfall time,the more leaching ofCa(OH)2,the more obvious the deterioration of the pore structure,and the greater the porosity;the lower the saturation under the same rainfall,The greater the amount of Ca(OH)2 leaching.Rainfall can delay the time when the chloride ions in the concrete penetrate into the surface of the steel bar,and has a positive effect on the improvement of the durability of the concrete structure.(5)The actual concrete structure in the coastal salt fog area and the concrete in the bridge deck area under the action of rainfall,the distribution of chloride ions on the surface of the concrete appears convection zone phenomenon.The difference of chloride ion concentration in concrete in the tidal area of bridge piers is mainly caused by the scouring strength of different water flows.Through MIP experiments,it is found that water scouring has a significant effect on the porosity of concrete,the stronger the scour action,the greater the porosity.Simultaneous erosion also causes the leaching of calcium hydroxide in the concrete pores,with the effect of rain on the type of effect.