Research On The Influence Of Steel Concrete Interface Defects On Concrete Corrosion-Induced Cracking

The corrosion of reinforcement is the most important factor affecting the service life of reinforced concrete structure.As the third phase of reinforced concrete structure,the transition zone of reinforced concrete interface has an important influence on the corrosion process of steel bars in concrete.The current academic circles ignore the influence of reinforcement concrete interface transition area on the research of concrete corrosion leading to early service life of concrete The sound.This study focuses on the corrosion process of reinforced steel in concrete under chloride environment.It is significant to analyze the role of the transition zone between reinforced concrete interface and extend the service life of reinforced concrete structure.In this study,the influence of the defect on the corrosion product distribution and the cracking of concrete caused by the expansion of corrosion products was studied.Two layers of horizontal reinforcement height are designed to obtain the interface defects of different sizes of reinforced concrete.The experimental cycle is accelerated by adding DC power supply and 1.5% chloride and dry wet cycle.The size of the interface defect and the thickness of corrosion products in each experimental period are analyzed by taking back scattering electronic images to quantify the size of the defects in the interface of the reinforced concrete under different reinforcement heights and the thickness of corrosion products in each experimental period The crack producing part and development law,the corrosion morphology of the steel bar was observed in the broken specimens at different experimental periods,and the elastic modulus of corrosion products around the steel bars was analyzed by nano indentation technology.The main conclusions are as follows:During the forming of concrete,the aggregate sinks and bubbles float up due to the action of inserting,vibrating and vibrating.The bubbles in the concrete are blocked by the horizontal arrangement of steel bars in the process,which leads to the size of the transition area of the lower reinforcement concrete interface larger than other parts,and will increase with the increase of the horizontal reinforcement distribution height and the system water cement ratio.When the water cement ratio is 0.4,when the height of the reinforcement is increased from 20 mm to 170 mm,the defect size of the lower interface of the reinforcement increases from 0 μ m to 411.48 μ m;when the water cement ratio increases from 0.4 to 0.55,the area size of the lower interface of the 170 mm reinforcement increases from 411.48 μm to 980.11 μm.(2)The corrosion process of steel bars in concrete will be accelerated by adding DC current,and the corrosion around the reinforcement is not uniform.Although the test piece is connected in parallel,because of the defect of the interface between the steel bar and the concrete,the upper reinforcement in the same test piece is more seriously rusted than the lower reinforcement,and the bottom side of the steel bar is the most serious place.The corrosion products are generally brown yellow,and with the corrosion deepening,the rust gradually gathers and develops into black.The corrosion of the upper and lower steel bars of the specimens with DC power supply is relatively uniform in the initial stage of corrosion.With the corrosion,the uneven corrosion of the reinforcement becomes more and more obvious.For the samples with chlorine salt,the water glue ratio has little effect on corrosion.(3)The interface defect size of upper reinforcement is larger due to the high height of reinforcement distribution,which is prior to the corrosion of the lower reinforcement,so corrosion and cracking occurs around the upper reinforcement.Generally,the rust expansion crack appears from the steel section,and the upper layer of steel bar is spread from the upper part of the steel bar to the top of the test piece,while the lower layer of the rust expansion crack appears at the bottom of the steel bar and spreads to the bottom of the specimen,and finally develops into the crack along the reinforcement.Because the size of the interface defect of the upper reinforcement bottom is large,although the corrosion is the priority,the larger interface defects contain some corrosion products,which delay the occurrence of the rust expansion cracks.Therefore,the rust expansion cracks are generally located on the side and upper part of the upper reinforcement,and no rust expansion cracks are found in the concrete directly below the reinforcement section direction.The defect size of the lower interface of the lower layer is small,and the corrosion cracks usually appear on the lower side of the steel bar after the corrosion occurs at the lower part of the reinforcement.The small mass loss of steel bars(about0.38%-0.56%)can lead to the occurrence of rust expansion cracks.(4)When the rust crack runs through the concrete cover,the crack width reaches the maximum value on the concrete surface.Rust will move outward along the expansion crack and fill in the pores of concrete around the reinforcement.The distribution and morphology of aggregate in concrete will affect the width and direction of the crack.(5)Nano indentation technology shows that the elastic modulus of corrosion products around the reinforcement is different,and the elastic modulus of corrosion products on the lower side of the upper reinforcement is smaller than that of the lower side.This indicates that the corrosion products on the upper side of the steel bar exert greater expansion force on the surrounding concrete.The side shows that the larger transition zone of the steel bar concrete interface provides expansion space,which delays the expansion crack It’s produced.