Preventive measures of steel reinforcement in chloride environment
1. Strictly control the test and thicken the protective layer
It is suggested that the quality inspection department take "fresh mixed mortar method" and "hard mixed mortar method" as the necessary testing process of engineering quality inspection.The total amount of chlorine in raw materials should be controlled within the limit value.On this basis, the thickness of protective layer should be appropriately increased.A large number of engineering practices and tests show that the chloride ion concentration in the depth of 12mm of concrete surface in chloride environment is much higher than the depth range of 25-50mm.Therefore, the thickness of concrete protective layer should be no less than 38mm and preferably no less than 50mm for projects in chlorine environment. Considering construction deviation, the design thickness of protective layer should be 65mm.2. Select raw materials and rust inhibitors
2. In the selection of cement to choose slag, ash, fly ash cement.The low Ca2 content of cement stone in these cement can prevent the dissolution and dissolution of cement stone by chlorine salt, and prevent the alkali aggregate reaction between chlorine salt and cement stone, resulting in expansion salt with low strength and low cementing force, as well as the resulting looseness, exposed bone and falling off of concrete.The coarse aggregate should choose carbonic acid rock gravel with high alkalinity as far as possible. On the one hand, it can have high strength cementing force with cement, and on the other hand, it can form a highly alkaline environment, so that the passivation film of the steel bar interface is in the passivation state for a long time.Fine aggregate should be as far as possible to use river sand to prevent sea sand into the chlorine salt.On this basis, corrosion inhibitors suitable for engineering characteristics are preferred. NaNO2 composite corrosion inhibitors are recommended to be used, which can generate Fe3O4 oxidation film in alkaline environment and prevent the corrosion of steel bars by Cl- ions.
3. Three component cementing material and coating
Reducing the permeability of corrosive medium in concrete is one of the most direct ways to prevent Cl- from entering the surface of rebar.The usual method is to add a certain amount of micro-silica powder, fly ash or ground slag into the concrete.Cement, micro - silicon powder, fly ash as three - component cementing materials.Concrete made of three components has very low permeability and high Cl- permeability resistance, and has low heat and economy.Micro silicon powder can improve the wear resistance of concrete, micro silicon powder and fly ash can effectively reduce the active aggregate content and total alkali content, so as to avoid the alkali aggregate reaction.In addition, concrete surface coating is the first line of defense against steel corrosion.The coating on concrete surface can effectively prevent corrosive medium from immersing in a certain period of time, but it cannot be widely used due to its limited service life.At present, the cement - based polymer coating and mortar layer are the first choice for concrete surface protection.
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