The Development Of Corrosion And Cover Cracks Of Concrete In Marine Environment

Cracking caused by corrosion of steel bars in concrete structures is one of the main reasons for structural durability failure,among which the chloride corrosion in coastal environment is the most significant.The rust product produced by the corrosion of steel bars is 2-6 times the volume of iron consumed,resulting in excessive internal pressure in the concrete,which eventually leads to cracking of the concrete until the structure is destroyed.Most scholars adopt the criterion of judging that cracks occur on the surface of reinforced concrete members when the circumferential tensile stress of concrete reaches the ultimate tensile strength of concrete,but the cracking criteria for internal cross section of concrete based on limit deformation are less analyzed.Although some scholars have put forward many models of chloride ion corrosion of reinforced concrete,the relationship between cracks in concrete rust expansion cracking is rarely studied.In recent years,there are many scholars who pay attention to the microscopic characteristics of reinforced concrete corrosion,but the analysis of the components of concrete corrosion products after different corrosion conditions is insufficient.In this paper,through experimental research combined with theoretical analysis and numerical simulation,the cracking criterion,crack spacing and corrosion product composition of non-uniform corrosion of steel bars in concrete are studied.The specific research contents are as follows:(1)By dry-wet circulation accelerated corrosion method to accelerate the corrosion of concrete specimen,using environmental scanning electron mirror(EMS)and energy spectrometer(EDS)nondestructive testing method test and quantitative description of the distribution of reinforcement corrosion along the direction of concrete cross section,discusses the corrosion after the element concentration distribution in concrete,and compared under the condition of different dry-wet circulation ratio,the composition and development process of concrete corrosion product.(2)Based on the mathematical model of angle probability distribution(von Mises distribution model),a modified probability distribution function model is established to represent the distribution law of corrosion products,which is compared with the existing corrosion distribution model.On the basis of this model,through the thickness of corrosion products and the limit radial displacement of concrete,a new Cracking Criterion of concrete cracking is put forward;and a new Cracking Criterion of concrete cracking is also established In the finite element analysis model,the non-uniform distribution model of corrosion products of reinforced concrete is used as the basis of displacement loading of the model,and the process of rust cracking of reinforced concrete is simulated.The numerical analysis shows that the simulation results are in good agreement with the theoretical model results.(3)The cracking and shrinkage of concrete is restricted by the bond force between reinforcement and concrete,and the second crack will be produced at a certain distance away from the crack.Different from the existing research on crack development law,based on the mechanical equilibrium relationship of differential element,the mechanical analysis model of concrete crack is established in this paper.Based on the mechanical theory,the mechanical analysis of concrete after cracking is equivalent to the stress diagram of differential element in elastic-plastic mechanics.Based on the mechanical balance relationship,the concrete crack prediction model is established.Then,compared with the existing simulations and experimental results,the development of cracks at the interface between steel bar and concrete under chloride-induced corrosion in different locations of steel bar is verified.The results prove that the model proposed in this paper can effectively predict the location of crack with error less than 8%.