Durability And Service Life Prediction Of Coated Steel Bars In Concrete Under Severe Condition

The concentration of chloride ion and sulfate ion in groundwater in the eastern coastal areas of China is high,which is harmful to the durability of concrete structures.Prestressed high strength concrete pipe piles(PHC pipe piles)is a concrete component for building foundation construction,which is made by pre-tensioned pre-stressed technology.PHC pipe piles is in underground saltwater environment for a long time and in wet-dry cycle with the change of groundwater level.Therefore,the PHC pipe piles in service will be eroded by chloride and sulfate,which will decrease the service life of PHC pipe piles.As a result,it is necessary to improve the durability of PHC pipe piles.In addition,the modified diffusion law is often used to predict the service life of concrete structures by means of medium transmission,but it may not be applicable to the concrete diffusion law of PHC pipe piles under the action of groundwater level fluctuation and multi-ion coexisting saltwater.Therefore,it is very important to study the durability of concrete of underground pipe piles and to accurately evaluate their service life.In this paper,the corrosion resistance of pipe pile concrete mixed with corrosion inhibitors and coated steel bars under the action of underground saline water is studied.The corrosion current density icoor(muA cm-2)of steel bars during corrosion process is obtained by linear polarization resistance(LPR).Based on the corrosion current density test results and Wiener process,the service life of coated steel concrete is studied.The main contents are as follows.(1)The critical chloride ion concentration of bare steel bar,2% PCI-2015 corrosion inhibitor,8% PCI-2016 corrosion inhibitor,8% PCI-2016 rust inhibitor+1% graphene and coated steel bar were studied.The results showed that the critical chloride ion concentration of bare steel bar,2% PCI-2015 corrosion inhibitor,8% PCI-2016 rust inhibitor+1% graphene and coated steel bar were 0.1 mol/L,0.6 mol/L,1.5 mol/L,1.7 mol/L and 2.2 mol/L,respectively.(2)The corrosion current densities of steel bars under accelerated dry-wet cycling test of artificial seawater were studied by adding migratory corrosion inhibitors PCI-2015,PCI-2016,graphene and PCI-2016,as well as coated reinforced concrete specimens.The the anti-rust effect of of steel bar from good to bad is as follows:coated steel bar,double-doped graphene and PCI-2016,single-doped PCI-2016 and single-doped PCI-2015.(3)Taking the corrosion current density of steel bar measured at different time as the durability degradation of reinforced concrete,the process parameters of Wiener random process are estimated by Bayes estimation method.The reliability function and probability density function of concrete specimens are obtained,and the service life model of reinforced concrete based on Bayes method of Wiener process is established.(4)The process of service life prediction is programmed with MATLAB language,and a computer software with graphical user interface is developed.By inputting the measured corrosion current density data,the service life of reinforced concrete at different reliable levels can be calculated.The calculated service life of reinforced concrete specimens under different conditions is close to the actual engineering situation,which shows the validity of the service life prediction method and calculation software established in this paper.