Experimental Research On The Electric Accelerated Corrosion Method And The Current Efficiency

Corrosion of reinforcement is one of the most important factors that affects the loading capacity of RC-members. However, Corrosion of reinforcement in reinforced concrete members takes a long time to progress. Therefore, in order to study the residual loading capacity of reinforcement corroded RC-members in a short period, it is necessary to find ways to replicate reinforcement corrosion within the laboratory by applying accelerated corrosion methods on designed specimens. And the main purpose of this thesis is to figure out an efficient way to acquire deteriorate RC members and study the electrochemical mechanism during this processIn this thesis, various acceleration corrosion methods developed in different literatures are summarized and evaluated. The external and internal factors affecting the accelerating corrosion process are also discussed in detail. Based on the comparison one acceleration corrosion method had been chosen and improved in this thesis. The acceleration corrosion method is electrolysis with DC power supply and the rebar works as anode. Several problems had been observed in details and beneficial conclusions had been proposed.In the actual service condition, as part corrosion of RC members is more common in nature, locally electric accelerated corrosion of reinforcement by attaching cathode material on the target corrosion area is used in this thesis, and solution circulation system is introduced to improve the shortcoming of this electric accelerated corrosion method. 18 specimens( 150 ′150 ′300mm) with single re-bar are corroded by the electric accelerated corrosion method mentioned above. The result shows the locally electric accelerated corrosion of reinforcement by attaching cathode material on the target corrosion area, which is improved by applying the solution circulation system, can maintain the humidity of the specimen’s surface. Thus, it is able to keep the resistance of the concrete in a low level. And a low voltage which means safer can be used to achieve the nominal current intensity. Besides, instead of setting up a large electrolytic tank for large scale RC members, the solution circulation system has a solution tank which is movable and replaceable at any time.Corrosion of reinforcement happened out of the target corrosion area is found in the experiment described above. In order to represent the corrosion range away from the target corrosion area, a parameter named Diffusion Angle, is put forward. And the experimental value of the Diffusion Angle is given in this thesis based on the experiment data.The Faraday’s Law that is applied to predict the electric accelerated corrosion result has been proved to be inaccurate, which means other reactions happen simultaneously with the corrosion of reinforcement and consumes the current quantity applied. A parameter Current Efficiency, mentioned in different literatures, is used to represent this inaccuracy. This thesis explains possible reactions happened on the reinforcement during the electric accelerated corrosion process by the E-lg|I| figure and the E-p H figure of iron-water system based on the electrochemical theory.An electric accelerated corrosion test consists of 52 small reinforcement pieces and 36 mortar specimens with different cover depth is carried out to study the factors affecting the Current Efficiency. A gas collected device is set up to collect gases during the test. Result shows the Current Efficiency and valence state of iron oxide(a parameter used in the Faraday’s Law) is influenced by the current density and voltage applied, p H of solution, chloride concentration and cover depth of reinforcement, etc. A corrected parameter λ, which describes the relationship between parameter α(α=and parameter n(n is the valance state of iron oxide), is used on the Faraday’s Law for a better prediction of electric accelerated corrosion result. And the experimental value of the corrected parameter λ is given in this thesis based on the experiment data.4 RC beams( 250 ′200 ′1300mm) are corroded applying the method that locally electric accelerated corrosion of reinforcement by attaching cathode material on the target corrosion area, which is improved by applying the solution circulation system. Result shows that the improvement that applying the solution circulation system has advantages on large scale specimen as well as on single re-bar specimen. And the Faraday’s Law corrected by the correct parameter λ makes a more accurate prediction of the electric accelerated corrosion result. Besides, the loading test result indicates that this electric accelerated corrosion method is practical to acquire corroded specimens for the study of deteriorated RC structures.