Corrosion protection technology of reinforced concrete structures
Corrosion protection technology of steel reinforcement in chloride environment
The purpose of anti-corrosion technology research is to make the time from the use of the structure to the beginning of corrosion of internal steel bars as close to the design life as possible.In order to completely avoid the corrosion of Cl-, the most ideal way is to keep the concrete isolated from the chlorine environment fundamentally, which is impossible in fact.What is important is how to effectively control the total amount of chlorine salt, so that it is limited within the specified range.Based on the electrochemical behavior of reinforcing steel bar in chlorine salt environment research results and corrosion mechanism, think who can effectively prevent PH decline, ensure reinforced concrete interface on the passivation film is not activated, maintain the electric double layer interface potential constant, avoid the happening of depolarization steel surface, can effectively control the occurrence of corrosion, namely anti-corrosion technology.This paper summarizes the anti-corrosion technology as follows:
1. Cl- limit value in concrete
The so-called "limited value" refers to the maximum allowable value in concrete.The research shows that the total limit value of Cl- should be less than 0.18%, equivalent to 0.55kg/m3, which is equivalent to the limit value of the United States and 8% lower than the standard value of Japan civil engineering society. The research results are basically consistent with the standard value of developed countries in the United States and Japan.In addition, the total amount of Cl- also directly affects its diffusion rate in concrete. The diffusion process can be described by the following equation:
We can figure it out from the normal distribution.In this way, the relationship between Cl- diffusion and service life can be established by using the diffusion equation, and then concrete durability design or inspection evaluation can be carried out based on this, and the relationship between diffusion rate and Cl- concentration is also determined.
2. Limit the current density and ph of the rebar interface
Limiting the current density of the rebar interface is the basic index to ensure the constant potential, that is, the critical value to transform the passivation state to the activation state of the rebar interface protective film.The critical value is not less than 10A/cm2, while strong alkalinity is the best environmental condition for the rebar interfacial protective film, and the best ph value is not less than 11.5.
3. Define concrete crack width and water-cement ratio
Cracks in the concrete allow corrosive media to pass through the concrete protective layer and enter the steel reinforcement surface.The crack width of concrete protective layer must be limited, and the crack value of high-performance concrete should be 0.2mm. The value of ordinary concrete should be appropriately reduced.To reduce the diffusion rate of Cl-, the permeability of concrete must be reduced. The most effective way to control the permeability of concrete is to control its water-binder ratio, which is generally limited to 0.35 ~ 0.45.
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