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Because of their wide range of concrete materials, low cost, high compressive strength, can be poured into various shapes, and a good fire-resistant and difficult to weathering, low maintenance costs, the building structure in the world today has become the most widely used in building materials. The main drawback is that the concrete tensile poor, vulnerable to cracking. A large number of engineering practice and theoretical analysis shows that almost all of the concrete structures are working with cracks, but some very small cracks, or even invisible to the naked eye (<0.05mm), the general structure of the use of the absence of any major harm, can be allowed to Exist; some cracks in the load or the use of external physical, chemical factors, and have continued to expand, caused by carbonation of concrete, peeling protective coating, corrosion of steel, concrete strength and stiffness has been weakened, reducing durability, even when serious Collapse accident, against the normal