The Research On The Deteriorated Mechanisms Of Reinforced Concrete In Stray Currents And Chloride Ion Coexisted Corrosion Environment

The concrete structure of subway project usually is in stray currents and chloride ion coexisted corrosion environment. Because of stray currents and chloride ion mutual promoter action on the concrete durability deterioration, the concrete durable problem of this kind of project is more serious, and its durable deteriorated mechanism is also more complex than the single factor function. In this thesis, the deteriorated characteristic and mechanism of reinforced concrete, as well as the corresponding high durable material preparation have been researched in system and depth. There are important theory and practice guiding meaning of the results of this research for the durable design and the application of the subway and so on the underground project concrete material.The main research work and compliments of this paper are:Through the systematic research on the electrochemical equivalent and the corrosion characteristic of the steel bar, as well as the corresponding physical mechanics performance degeneration characteristic of reinforced concrete under stray currents and chloride ion coexistent environment, the deteriorated characteristics of reinforced concrete, such as steel bar corrosion speed quick, the corrosion degree serious as well as the quick deteriorated characteristic of the concrete compressive strength and the elasticity ratio have been obtained. Simultaneously used the electrochemistry test technology, verified the change rule that the limiting concentration value of the chloride ion to initiate the steel bar corrosion was reduced with stray currents intensity increased, the attribute method of chloride to initiated the steel bar corrosion was proposed: [Cl^-]/[OH^-] = 2.33e^0.12A. The reinforced concrete corrosion destruction model had been established under this environmental condition, compared with the sole factor influence similar model, this new model to the reinforced concrete corrosion destruction process, specially rusts away the induction period, had carried on a more detailed description: the induction period should divide into two stages, the first stage is the induction period of expansion, mainly induces the steel bar corrosion by the stray current; The second stage is the induction acceleration period, this stage mainly induces the steel bar corrosion by the chloride ion.The influence rule of the stray current on the binding chloride ion stability has been researched in depth. The results show that stray currents are disadvantage for the cement motor binding chloride ion. The transition trend of chloride form binding to freedom is more obviously with the stray current intensity increased. Uses the single mineral preparation, the C-S-H gel preparation and the microscopic testing method such as X-ray Diffractometer (XRD), thermogravimetric analysis (TG), the superficial electric potential, to verifies the stray currents to the binding chloride ion stable adverse effect mainly related with the chloride ion stability which solidified by the physisorption form, the Stern gel electric double layer theory is used to carry on the detailed elaboration and the analysis to this kind of influence mechanism. In addition, according to the transition characteristic of chloride form binding to freedom with stray currents influence, a method for separated the binding and free chloride ion is found.The systematic research has carried about the effect of stray currents on the migration process of chloride ion into concrete. The migration characteristic that chloride ion is accelerated to the steel bar surface region gathering under the stray currents influence. By analyzed the distributed characteristic of the electric field of stray currents in the concrete interior, and according to the electricity transfusion theory and Energy Dispersive X-ray Analysis (EDXA) and so on the microscopic test analysis result, proposed "the diffuse and electromigration" hypothesis to the explanation to migration mechanism of chloride ion in concrete interior under the stray currents influence. Based on the influence of stray currents on binding stability and distribution of chloride ion, the chloride ion to the concrete internal transport equation has been established.According to the reinforced concrete deteriorated characteristic and mechanism under the stray current and chloride ion coexisted corrosion environment, the design method and requirements for concrete are proposed: 56 days electrical resistivity≥100 kΩ·cm, 28 days flux≤350C, and chloride ion diffused coefficient between 0.5×10^-13m²/s and 0.8×10^-13m²/s .Embarks from the material study angle, according to the material compound preparation principle, a new kind high performance concrete was prepared, which is able to fit for the requirement of high electrical resistivity and anti-chloride ion permeability for subway concrete by compound uses mineral admixtures, lightweight aggregate and insulation polymer. Its 56 days electrical resistivity is 110.5 kΩ·cm, 28 days flux is 350 C.