What are the influencing factors of reinforcement corrosion in concrete?

1. Strengthen the influence of itself

The nonuniformity of steel bars is caused by the difference of chemical composition or crystal structure, the difference of stress level, the discontinuity of passivation film or the difference of surface pollution. These non-uniformity can lead to the existence of potential difference and the formation of corrosive cells.


2. Chloride effect

Chloride ion can accelerate the corrosion of reinforcement, which has been proved in a lot of engineering practice. Although there are different views on its mechanism, it is generally believed that chloride ions will destroy the passive film on the surface of steel bars and cause local corrosion of steel bars.


3. Carbonation

Carbonation refers to the action of CO in air and calcium hydroxide in concrete. Therefore, the reinforcement from the passive state into the active state, resulting in concrete pulverization, steel cover fall off. With the decrease of pH value, aluminate chloride is no longer stable, releasing chloride ion and increasing the depth of free chloride ion.

In the form of gas phase, CO2 in the air diffuses into the pores of concrete partially filled with water through the coarse capillary channels in concrete, and then neutralizes with calcium hydroxide dissolved in pore fluid. The optimum air relative humidity of concrete carbonization is 50% - 75%. The main factor affecting the carbonation rate is the density of concrete, namely impermeability, which is related to the water cement ratio of concrete and the amount of cement per unit.


4. The role of oxygen and water

Oxygen participates in the cathodic reaction in the electrochemical corrosion process of steel, so the corrosion rate of steel is controlled by the diffusion process of dissolved oxygen in water. Water can not only accelerate the carbonation of concrete, but also provide conditions for the corrosion of steel bars. In addition, the corrosion of reinforcement in concrete is also affected by environmental factors such as temperature and stray current.

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