During the life of concrete structure in its service should keep the required strength, and other functions, concrete structure also must be able to withstand all kinds of erosion damage, this is often referred to as the concrete durability. But I wasn't referring to concrete durability during the use of for the infinite long, also is not a concrete can resist all kinds of damage. Daily maintenance has an important influence on the durability of concrete. Due to the strength of the concrete structure is increased gradually, the durability of concrete may also be considered to be naturally improve. But, in fact, strength and durability are two different concepts, reflect the different aspects of concrete performance. For the majority of concrete structure, strength and durability should be considered during the design phase, sometimes the durability has become main design parameters.
2.1 the permeability of concrete
In concrete, the permeability is an important indicator, it refers to gas, liquid pressure or ions, the chemical potential or electric fields, in the concrete to the difficulty of the infiltration, proliferation or migration. Concrete permeability is the main reason of the concrete in a large number of pore and fracture. The pore structure of concrete including cement paste pore, pore in the aggregate, aggregate and will be exempted from inspection as antithesis pore, poor construction can also lead to parts of honeycomb structure.
Due to the permeability of concrete determines the gas, liquid and the ease of soluble hazardous substances into concrete, a direct impact on the carbonation of concrete steel corrosion, erosion, and the freezing-thawing resisting ability, so it is one of the most important factors that affect the durability of concrete structures, the durability of concrete permeability to evaluation.
2.2 concrete alkali aggregate reaction
JianJiLiao response refers to the concrete raw materials (including cement, aggregate, admixtures and mixing and mixing water, etc.) in the alkaline substances react with the active ingredient, generate expansive material (material) or swell caused by concrete inside the expansion stress and cracking phenomenon. With general JianJiLiao response is after some years after the concrete forming gradually, the results cause the loss of concrete durability, serious when still can make concrete lost use value, and the reaction is occurred in the concrete, therefore, the damage caused by this reaction are difficult to prevent, and difficult to prevent, more is not easy to repair and saving, so called the concrete cancer.
2.3 concrete chloride ion erosion
Chlorine salt compounds is one of the most harmful erosion sex, can lead to damage of concrete rapidly eroded. Due to the slurry properties of pore fluid, the concrete substrate characterized by strong alkali. Slurry hole fluid contains large amounts of alkali, its pH may only 13. But chlorine salt solution with strong acidity and erosion resistance, erosion intensity depends on chlorine salt solution concentration and combine with chlorine ion of cationic species. The chlorine salt erosion process need to chloride ion penetration into concrete microstructure, and require the precipitation from the cement hydration phase has a reverse movement of ions. Therefore the pore structure and permeability of concrete to chloride ion erosion has very important influence. The chloride ion erosion for cement concrete pavement and bridge panel has obvious damage effect, including the use of deicing agent after spalling of concrete surface damage and corrosion of the internal reinforcement.
2.4 the sulfate attack of concrete
Nature exist all sorts of sulfate and sulfate in the industrial production has also been used light reflex. Sulfate solution will be in contact with the concrete structure or into the concrete matrix, and the cement hydration reaction product, lead to the expansion of the concrete, cracking and spalling damage, and then lose concrete structure integrity and stability.
Concrete under sulfate macro performance degradation is due to the formation of new phase in the process of erosion and the disappearance of the old phase microstructure change as a result of, therefore, through the microscopic methods such as XRD analysis of corrosion products to explore the mechanism of sulfate erosion and the performance degradation of macro explain the reason for evaluation method research has important guiding significance.
3.1 the choice of raw materials
The strength of the cement materials and engineering properties, it is through the condensation of cement mortar, hardening of formation, cement stone once damaged, the durability of concrete were damaged, so the cement should pay attention to the choice of varieties of cement concrete performance, select small alkali content, low hydration heat, dry shrinkage of small, heat resistance, water resistance, corrosion resistance, good cement antifreeze performance, combined with the specific situation to choose. Cement strength are not the only standard to concrete strength and performance, such as low grade cement can also make high grade concrete. Choose the cement strength at the same time, therefore, the project should be considered its engineering properties, sometimes, its engineering properties are more important than strength.
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