Experimental Study On The Detection Of Corrosion Of Double Steel Bars In Concrete By Infrared Thermal Imaging

Reinforced concrete is one of the most widely used building materials in China,and steel corrosion is the main reason for the durability failure of concrete structures.The problem caused by steel corrosion threatens people ' s lives and property safety.Therefore,accurate detection of steel corrosion in concrete is of great significance to evaluate the durability of structures.Detection methods of steel bar corrosion in concrete can be divided into two categories: damage detection and non-destructive detection,both methods have their own advantages and limitations.Based on the basic infrared thermography,this study carried out the non-destructive test on the corrosion degree of double reinforcements in concrete with different corrosion ratio of reinforcements,different concrete cover and different reinforcement spacing.In the region where the temperature is stably distributed along the axial direction of the reinforcement in the thermal image,the temperature data on a line segment perpendicular to the longitudinal axis of the reinforcement are extracted,this line segment is called temperature measurement line.Analysis of the relationship between the temperature difference(difference between temperature peak and initial temperature)at the midpoint of the reinforcements and the corrosion ratio,the concrete cover and the reinforcement spacing.Thus,the feasibility and accuracy of the infrared thermal imaging nondestructive testing method with tungsten wire heating as the heat source to detect the corrosion degree of double reinforcements in concrete are analyzed.The main research of this paper is as follows:(1)Experimental study on steel corrosion in concrete based on infrared thermography:The reinforcements were cut and grooved,filled with silica gel with thermal conductivity and placed with tungsten wire to make uniform heating reinforcements as the external excitation heat source for infrared thermography detection test.The infrared thermography non-destructive testing test was carried out under the concrete cover of 30 mm,40mm,50 mm,reinforcement spacing of 60 mm,70mm,target corrosion ratio of 0 %,3 %,5 %,7 %,9 %,12 %.Accelerated corrosion test of steel bar by full immersion and external current after casting.Heating test and infrared thermography test for all specimens,and obtaining temperature data of specimen surface during testing.(2)Recording corrosion cracks on concrete surface of corroded specimens,the figures shows that the greater the corrosion ratio,the greater the crack width.The value of s/c is used to illustrate the mutual influence of corrosion of two reinforcements and the law of crack development.The results show that when s/c ? 2,18 longitudinal cracks are located at the bottom,and only 2 longitudinal cracks are located at the side.When s/c ?1.75,there are 33 longitudinal cracks on the side and only 5 longitudinal cracks on the bottom.Moreover,the smaller the s/c is,the greater the interaction between reinforcements is,and the more prone to transverse cracks in the concrete between reinforcements The failure mode of concrete is more likely to be layered spalling.(3)Infrared thermography test results show that: The temperature difference at the midpoint of reinforcement decreases with the increase of reinforcement corrosion ratio,there is also a negative correlation between temperature difference and concrete cover.Through the collected temperature data,the corrosion ratio and temperature difference of each series of specimens were fitted and analyzed,and the quantitative relationship between corrosion ratio and temperature difference was obtained.When the reinforcement spacing is60 mm and 70 mm,the corrosion ratio,concrete cover and temperature difference of each specimen are fitted and analyzed,and the quantitative relationship between corrosion ratio,concrete cover and temperature difference is obtained.The goodness of fit of the relationship obtained by analysis is reliable.When the concrete cover is 30 mm,40mm and50 mm,the influence of reinforcement spacing on temperature difference is analyzed.The experimental results show that it is feasible to explore the infrared thermal imaging method to detect the corrosion degree of double steel bars in concrete.The research results of this paper can provide a theoretical and experimental basis for the subsequent infrared thermal imaging technology to detect the degree of corrosion in concrete.