Study On Microstructure Characteristics And Critical Chloride Concentration On The Surface Of Steel Bar

Reinforced concrete is the most widely used structural material in today’s civil engineering field.However,reinforced concrete also has the problem of durability.Reinforcement corrosion is the main factor affecting the durability of concrete structures,serious corrosion will lead to damage to the concrete structure.Although the factors that cause corrosion of the steel are multifaceted,examples of the destruction of a large number of reinforced concrete structures show that they are mainly derived from chloride ions and carbonization.Based on the above understanding,this paper taked the HPB300 circular steel bar with diameter of 10 mm as the research object,and choosed simulated concrete pore solution and real concrete.In addition,XPS,XRD,SEM and other microstructural testing methods were used to study the corrosion of steel,and the microstructure characteristics of the steel bar under the action of carbonization and chlorination were discussed,which clarified the effects of microstructure on the corrosion failure mechanism of steel bars.At the same time,combined with natural potential test technology of reinforced and macro verification method,we investigated the effect of surface morphology of the steel,reinforced concrete water cement ratio,steel protective layer thickness on the critical chloride concentration in concrete,which revealed the critical chloride concentration under different conditions to make steel depassivation.The main research results are as follows:1.There are FeOOH and FeO in the corrosion of steel bars in simulated chloride salt solution.The corrosion of steel bars in simulated carbonized solution is mainly FeOOH,Fe3O4 and Fe2O3.The corrosion of steel bars in simulated carbonized chloride compound solution is mainly FeOOH,Fe3O4,FeOOH and FeCl3.The content of FeOOH in the corrosion products of the steel is always the highest,and it is more than 60%.2.The corrosion period of the steel bar in the concrete structure is longer than that in the simulated concrete pore solution,and the microstructure and composition of the reinforced concrete are different.When the reinforced concrete structures in corrosive environment,and the corrosion of the steel bar with the steel surface passivation film structure of FeO and Fe3O4 arecompact will be transformed into Fe3+,and the Fe3+will form Fe3+-Ca2SiO4 complex and Ca2SiO4 hydration products of cement and steel corrosion.However,with the increasing degree of corrosion of steel Fe3+-Ca2SiO4 salt content will be gradually reduced,then Fe3+will be transformed into other forms of corrosion.3.Corrosion of steel in concrete under chloride environment,the corrosion productions are mainly FeOOH,FeO,Fe3O4,FeCl2 and Ca2FeOCl3.Corrosion of steel in concrete under carbonation environment,the corrosion productions are mainly Fe3O4,Fe2O3 and FeO,and the corrosion will be attached to a layer of CaCO3.Corrosion of steel in concrete under carbonation chloride environment,the corrosion productions are mainly for FeO,Fe3O4,Fe2O3 and Ca2Fe2O5 double salt.4.The concrete protective layer thickness and water cement ratio have effects on the critical chloride concentration.Critical chloride concentration greater protection layer thickness of rebar depassivation is bigger,and the critical chloride ion concentration water cement ratio is the smaller the ambassador of rebar depassivation.Steel surface with the black oxide,can effectively delay the corrosion of reinforcement,under the same conditions,increases the critical chloride concentration of rebar depassivation.In this paper,the microstructure characteristics of steel corrosion and the critical chloride concentration under different influence factors are studied,which has important guiding significance for preventing the corrosion of concrete structures.