Research On Deterioration Of Bond Behavior Of Reinforced Concrete Beam Caused By Corrosion Expansion

In reinforced concrete structure,the premise that two kinds of materials with different physical properties can work together is that there is enough bond stress between them.Bond interface damage will lead to the performance degradation of reinforced concrete structure,and even lead to direct failure of the structure.Therefore,it is a hot topic for many scholars to study the bond behavior of reinforced concrete for a long time.In this paper,based on the research of corrosion expansion of reinforced concrete at home and abroad,two-dimensional and threedimensional random pitting corrosion models of reinforced concrete are established by using cellular automata（CA）method based on the electrochemical corrosion theory of reinforced concrete.The CA model focuses on the accumulation form and volume of steel corrosion products.Through the introduction of relevant parameters to achieve the numerical simulation of the corrosion morphology which is consistent with the existing test results,it provides a new idea and method for the study of steel corrosion and the structural mechanical properties.Based on the plastic damage theory of concrete,two-dimensional and three-dimensional concrete corrosion expansion models are established respectively to study the influence of uniform corrosion,non-uniform corrosion and pitting corrosion on the damage process of concrete.Based on the corrosion expansion of reinforcement,the numerical simulation of the drawing process is carried out innovatively.The distribution and variation of the bond force in the drawing process are analyzed,and the influence of three different corrosion expansion conditions on the bond performance of steel-concrete beams is compared.The main work and achievements of this paper are as follows:（1）Based on the theory of metal electrochemical corrosion,a non-traditional kinetic method（without strictly defining physical equations or functions）is used to establish a CA model suitable for simulating the corrosion of steel bars by defining the local reaction rules in the space.It can not only realize the simulation of different corrosion pit morphology,but also obtain the accumulation morphology and volume of corrosion products of steel bars,The ratio of the volume of corrosion expansion products to the volume of dissolved metal is highly consistent with the experimental results.The two-dimensional cellular automata program is extended to three-dimensional,and the metal corrosion in the cell space of hexahedron（plane corrosion）and cylinder（curved surface corrosion）is discussed.The correctness of corrosion morphology in cylindrical coordinate system and the universality of CA model are demonstrated.The CA program established in this paper is highly visible and can be used for numerical study of various steel corrosion and related fields.（2）In order to study the influence of pitting corrosion on the failure process of reinforced concrete,and compare it with uniform corrosion and non-uniform corrosion,the pitting corrosion morphology and product accumulation morphology of reinforced concrete were generated by using the established CA model.The corrosion pit and product data are extracted into lst Opt software,and the product morphology data fitting function expression is imported into the commercial software ABAQUS,which is applied to the concrete inner wall as the corrosion expansion displacement field,and finally the concrete damage under different corrosion expansion conditions is obtained.By analyzing the damage evolution process of concrete under different corrosion expansion conditions,the crack propagation path and ultimate failure mode are predicted,which are consistent with the relevant test results.It is found that the pitting corrosion has the greatest damage to the concrete protective layer under the same corrosion rate,but its damage is only limited to the concrete protective layer area under the rebar,and the final failure mode may be the mixed failure of crushing and pulling in the local protective layer area;The damage area of concrete caused by uniform corrosion is the largest.The damage area is not only distributed on the side of the protective layer,but also on the side far away from the protective layer.The final failure mode may be the breakage and spalling of the protective layer;The damage area of concrete caused by non-uniform corrosion is mainly concentrated on one side of the protective layer,but the damage is also more serious on the section parallel to the protective layer and passing through the center of the reinforcement circle.The final failure mode may be the delamination failure of the whole protective layer or the splitting failure of the concrete protective layer.（3）The axisymmetric pull-out model of two-dimensional steel-concrete members and the pull-out model of three-dimensional reinforced concrete beams are established.By inserting bonding elements into the steel-concrete interface,the different working conditions such as no corrosion expansion,uniform corrosion expansion,non-uniform corrosion expansion and pitting corrosion expansion are simulated,which can not only study the performance degradation of the bonding interface caused by corrosion expansion,moreover,the influence of drawing process on the damage evolution of concrete can be studied.By comparing and analyzing the damage evolution process and bond slip curve under different corrosion conditions,it is found that no matter which form of corrosion expansion will have a negative impact on its bond performance,and pitting corrosion expansion has the greatest impact and the strongest destructive.In this paper,the cellular automata model based on the theory of metal electrochemical corrosion fully considers the randomness of pitting corrosion morphology and the accumulation shape and volume of corrosion products,which makes up for the deficiency of the existing cellular automata method which only focuses on the morphology of corrosion pits and ignores the accumulation of corrosion products.In addition,this paper investigates and realizes the damage effect of pitting corrosion on concrete,and fully studies the influence of uniform corrosion,non-uniform corrosion and pitting corrosion on the damage evolution of concrete.On the basis of concrete corrosion damage,the influence of three corrosion conditions on the bond performance of reinforced concrete is further studied,which provides a new idea and method for the study of bond performance deterioration of steel-concrete structures.The conclusions of this paper can provide a reference for evaluating the performance of steelconcrete members with uniform corrosion,non-uniform corrosion and pitting corrosion,and have theoretical significance and application value for the study of bond performance degradation of steel-concrete members in engineering.