Study On Concrete Structure Corrosion Mechanism And Protection In Salinity Dry Environment With Great Temperature Difference

The harsh natural environment on saline-alkaline land of western China causes various degration of building materials. A survey shows that: a large number of structures have been built in poor conditions with varying degrees of damage and the damage trend is speeding up. Particularly, , the corrosion of concrete material in concrete bridge structures constructed on saline-alkaline land of western area is intensified due to the effects of salinity and other factors. It is not only a major scientific and technical issue, but also a major social problem that how to ensure the durability of concrete materials and service life of bridges in the region.Based on some concrete bridge structure protection projects in the west, the influence of different mineral admixtures on the durability of concrete bridges is discussed in the thesis by use of local raw materials. The electric flux, chloride diffusion coefficient experiment as well as results of MIP analysis and micro-hardness analysis were used to evaluate the durability and microstructure of concrete.The permeability and durability of concrete were studied, Moreover the influence of various factors is also studied, like protective coating on concrete permeability, anti-corrosion properties and microstructure of the concrete. The results showed that:1. The high quality mineral admixtures (fly ash slag, etc.) can not only refine the pore size of concrete, improve the performance of concrete, reduce slump loss of concrete, but also improve the strength of coagulation and the density of concrete by a secondary hydration reaction and a micro-aggregate effect. At the same time, the slag-fly ash concrete with superplasticizers shows good chloride resisting properties. Compared with other types of concrete, microhardness of double-added additives was significantly higher than that of other concrete, and the width of ITZ decreases in dry areas with large temperature difference.2. Protective coating can effectively prevent or retard aggressive medium into concrete. Compared with other protective coatings, the cement-based capillary crystalline waterproof coating is better for enhancing the corrosion resistance properties of the concrete. Strength and permeability of the concrete can be improved obviously and concrete density was significantly increased through the use of the cement-based capillary crystalline waterproof coating.3. If the concrete structures are protected with internal or external measures, it would be effective to prevent or retard the penetration of corrosion medium in concrete. The internal protection system is mainly composed of fly ash, blastfurnace slag and superplasticizers; the external protection system is mainly formed by the concrete protective coating, such as cement-based capillary crystalline waterproof coating. If the external protective system is destroyed, the concrete internal protection system can still prevent harmful chemical reaction, thereby to protect the bridge concrete structure further.