The Research Of The Process About Corrosion-induced Cracking Of Concrete Cover

The corrosion-induced cracking of concrete cover is extremely unfavorable to the structural durability and structural properties,and it is an important problem to be solved urgently in the project.Through the study of the process and the influencing factors of the corrosion-induced cracking of concrete cover,it can provide the conditions for the durability assessment and the residual service life prediction of the e xisting concrete structures,and also provide a theoretical basis for improving the design level of structural durability.This paper focuses on the following studies:Firstly,the finite element software ANSYS is used to simulate and analyze the process and the influencing factors of the concrete cover cracking caused by a single uniform corroded steel reinforcement at the middle and the corner zones,respectively.The results show that the single middle located corroded steel reinforcement can cause longitudinal cracks of concrete cover,while the single corner located corroded steel reinforcement can cause the corner area of concrete cover spalling;The corner located corroded reinforcement is more likely to crack concrete cover than that at middle zones.The larger concrete tensile strength and the relative thickness of concrete cover are,the harder the concrete cover cracking will be.In addition,based on the numerical simulation results,a calculation model is established for the critical corrosion e xpansion force of a single corroded steel reinforcement.Through the relationship between the critical corrosion expansion force and the critical corrosion rate,a calculation model of the critical corrosion rate of a single corroded steel reinforcement can be obtained.It is proved by the experimental results that the calculation model of the critical corrosion force is effective and the numerical simulation method in this paper is also reasonable and reliable.Secondly,the finite element software ANSYS is used to simulate and analyze the process and influencing factors of the concrete cover cracking caused by multi-strand uniform corroded steel reinforcements(one row and double rows).The results show that when the horizontal clear spacing of the corroded steel reinforcements is small,it is easy to cause the concrete cover spallation damage.When the horizontal clear spacing of corroded steel reinforcements is increased to a certain extent(s/c＞3),the cracking failure mode of the concrete cover and the critical corrosion expansion force of multi-strand uniform corroded steel reinforcements are the same as that of a single corroded steel reinforcement.The diameter of steel reinforcements has little influence on the cracking failure of concrete cover.The greater concrete tensile strength and thickness of the concrete cover are,the more difficult the concrete cover is to crack.The critical corrosion expansion force of double-row corroded steel reinforcements which can cause the concrete cover spallation damage in the direction of each row of steel reinforcements is basically the same as that of the single-row corroded steel reinforcements,that is,the rows of steel reinforcements has no effect on the critical corrosion expansion force of the steel reinforcements.Based on the numerical simulation results,a calculation model is established for the critical corrosion expansion force of multi-strand uniform corroded steel reinforcements.Based on previous research results,a calculation model is further established for the critical corrosion rate of multi-strand uniform corroded steel reinforcements.Finally,the finite element software ANSYS is used to simulate the process and influencing factors of the concrete cover cracking caused by a single uniform corroded steel reinforcement at the middle zones with consideration of the stirrup(the stirrup and the concrete are respectively in rigid and bond-slip state).The results show that the cracking propagation patterns of the concrete cover of cross section with the confinement of the stirrup is the same as that without no stirrup.The outer surface of the concrete cover completely cracks along the axis without no stirrup,while the outer surface of the concrete cover with the confinement of the stirrup firstly crack s at the farthest distance from the stirrup along the axis,and then the cracks are gradually developed from both ends to the middle position.The critical corrosion expansion force of the steel reinforcement with the confinement of stirrup is improved in comparison with that with no stirrup,which is obvious that the stirrup can effectively inhibit and postpone the development of cracks in concrete cover.By comparing the rigid connection with bond-slip between stirrup and concrete,it is concluded that the critical corrosion expansion force of the steel reinforcement under actual conditions can be obtained,when the stirrup and the concrete are in the bond state.The yield strength of the stirrup has no effect on the critical corrosion expansion force of the steel reinforcement.Increasing the diameter of the stirrups and controlling the spacing of the stirrups in a certain range will increase the critical corrosion expansion force,which is beneficial to postpone the expansion of the cracks in the concrete cover and improve the design level of the structural durability.