1】 Concrete is not acid resistant. There is acid resistant concrete, which is another matter. DBJ test of DPS of permanent concrete shows that it is good in acid and alkali resistance, freezing and thawing resistance and chloride ion resistance, which conforms to the structural performance.
Carbonation of concrete: it is a kind of chemical corrosion that concrete is subjected to. The CO2 gas in the air penetrates into the concrete and reacts with the alkaline substance to generate carbonate and water, which reduces the alkalinity of the concrete. The process is called concrete carbonation, also called neutralization. The chemical reaction is Ca (OH) 2 + CO2 = CaCO3 + H2O. During the hydration process of cement, a large amount of calcium hydroxide is generated, so that the concrete voids are filled with saturated calcium hydroxide solution. Its alkaline medium has a good protective effect on the reinforcement, and makes the surface of the reinforcement generate insoluble Fe2O3 and Fe3O4, which is called purification membrane. After carbonization, the alkalinity of the concrete will be reduced. When the carbonization exceeds the protective layer of the concrete, the concrete will lose its protective effect on the reinforcement and the reinforcement will start to rust in the presence of water and air.
Generally, concrete carbonation will not directly cause the deterioration of its performance. For plain concrete, carbonation can also improve the durability of concrete. However, for reinforced concrete, carbonation will reduce the alkalinity of concrete and increase the number of hydrogen ions in concrete pore solution, thus weakening the protection of concrete against reinforcement.
2】 In the seaside, because the air contains a large amount of chloride ions, the penetration of chloride ions will greatly aggravate the corrosion of concrete structures.
① Invasion of chloride ions: when water is saturated, concrete will be neutralized due to the penetration of carbonate gas and chloride ions.
② Corrosion of reinforcement: the reinforcement is corroded due to water, gas, chloride ion, etc. Even if it is not neutralized, the phosphorus content in the surface layer of the reinforcement will cause corrosion of the reinforcement.
③ Crack generation: concrete cracks occur due to corrosion and volume expansion (2.5 times) of reinforcement.
④ Strength reduction: corrosive substances will further immerse from the crack to accelerate the corrosion and volume expansion of the reinforcement, thus reducing the strength of the concrete.
In a word, corrosion will reduce the strength of the concrete structure, thus greatly shortening the service life of the bridge.
With the exception of fire-resistant concrete, the heat resistance of concrete leads to a reduction in strength.
Portland cement concrete is a mixture of solid, liquid and gas phases. At a high temperature of more than 100 ℃, the liquid phase water will be vaporized and expand, resulting in surface explosion and internal structure damage. At the same time, high temperature will decompose some hydration products of cement hydration, such as calcium sulfoaluminate (ettringite). Under the action of these two kinds of damage, the compressive strength (including tensile and flexural strength) of concrete will decrease.
3】 It can be seen that the concrete structure damage caused by carbonization of concrete and corrosion of reinforcement can not be ignored. DPS with excellent characteristics is not only a waterproof agent for the structure, but also an anti-corrosion protection agent for the concrete structure. It combines with a large number of alkali ions to more fully generate crystalline gel, seal pores, compact the structure, and become a part of the concrete. It is an integral waterproof of the concrete structure, and the effect is the same as the life of the building.