3D In Situ Study On Corrosion Expansion Cracking Of Concrete Structres In Coastal Environment Based On Real Distribution Information In Cover

In this paper,based on the National Natural Science Foundation project ?The study on 3D non-uniform corrosion induced cracking based on actual local characteristics of reinforced concrete structure in marine environment?(51878413),the corrosion of steel bars caused by chloride ion invasion is explored in the coastal environment.Many scholars have conducted experiments or theoretical studies on this,but there is still a lack of extraction of real and effective information within cover.The conclusions obtained cannot be generalized,even if the extraction is limited to the two-dimensional plane,or the test piece is damaged,and a large number of researches are based on the assumption of “ignoring the material factors of the member”.They rarely pay attention to the influence of the actual distribution information within concrete on the durability of the reinforced concrete members,and cannot describe the rust and damage behavior of the real concrete members.The rust expansion theory cracking model cross-test verification proved to be inconsistent.Therefore,this paper introduces cement mortar specimens with initial defects at different locations,conducts accelerated electrification corrosion test and dry-wet cycle test in accordance with the characteristics of coastal chlorine salt corrosion.In different corrosion stages,the ?CT technology is used to test the inside of reinforced concrete specimens.The cracking process is carried out in three-dimensional in-situ,non-destructive and dynamic analysis.The main conclusions of this paper are as follows:(1)Comparing the strip and round hole defect specimens,the cracks of the strip defect specimens are mainly cruciform or inline type distribution,and the round hole shape defect specimens are mainly herringbone distribution.From the aspect of corrosion rate,the corrosion rate of the strip defect test piece is always larger than that of the round hole shape,and the cracking time is earlier;(2)Comparative two different test methods of electrochemistry and dry-wet cycle,except that the corrosion products in the dry-wet cycle test are non-uniformly distributed,and the corrosion products in the electrochemistry are except the interface defects,and the other specimens were uniform distribution.Compared with the maximum crack width of the electrochemistry specimens,the lower corrosion rate can achieve a larger crack width under the dry and wet cycle conditions.In the same way,in the dry-wet cycle environment or the electrochemistry conditions,the corrosion rate of the interface defect in the early is much higher than that in the middle,surface and non-defect specimens;(3)By comparing the maximum crack width,through crack volume,all crack volume,maximum corrosion thickness and other cracking indicators,it is shown that the volume of all cracks in the specimens(R~2 > 0.94)is a better parameter to reflect the actual corrosion level of the steel.The maximum width of the through crack(R~2 > 0.87)also has a good evaluation and easier to measure.And ?CT technology provides an accurate method to calculate the volume expansion rate.The rusting products around the steel bars containing the defect specimens are rusted and cracked at the initial stage(? = 5%).The volume expansion ratio is as follows: surface 1.92 > middle 1.87 > interface 1.64(bar),surface 2.05 > middle 1.96 > interface 1.68(round hole shape);(4)According to the experiment results,the prediction model of the critical cracking time established by the research group is fitted and corrected,and a more accurate prediction model of the corrosion cracking time of the cover with initial defects at different positions is obtained.Under the same conditions,the critical cracking is performed.The order of time is: interface > middle > surface.