Reinforced concrete Bridges 'disease' strengthening maintenance manuals

Reinforced concrete Bridges 'disease' of reinforcement of reinforced concrete bridge maintenance manuals diseases the main causes are the following six kinds of circumstances: 1 the intensity of the original design standard is low, waterproof and antifreeze performance is not strong, waterproof concrete can not meet the waterproof requirement, small permeability coefficient, surface concrete protective layer thickness too thin, and select material is lax, construction mixing unevenly, vibrating untrue, often the existence of honeycomb pitting surface defects, thus the compactness of concrete is poorer, adverse stress structure reinforcement effective protection, causing the local crack of cast-in-place concrete ( Shrinkage crack, plastic deformation cracks) From happening. 2 temperature stress to defects in micro cracks of concrete, the water vapor in the air under the action of capillary seep into the microfracture, if through the coating to steel surface, under the action of water and oxygen corrosion cell formation, the passivation membrane, cause steel corrosion. In coastal areas of concrete Bridges, the invasion of the chloride ion accelerate the corrosion of steel bar is the main cause. This is after the first crack corrosion. Another kind of situation is due to the compactness of concrete is poor, the presence of free water to the porous body of reinforcement corrosion to occur in the first, the corrosion of the reinforcing bar volume expansion, will inevitably produce expansion stress, its force in the direction of the necessity to concrete thin protective layer cracking, ahead of formation, the cracking of steel and a protective layer peeling, it is a reflection of the first after the corrosion cracking. 3 chemical pollution environment, there are two situations: one is that when there are cracks, carbon dioxide in the atmosphere of CO2 and calcium hydroxide in the concrete Ca ( 哦) 2 will happen chemical reaction, generate neutral calcium carbonate, makes concrete carbonation its PH 12. Will be reduced to less than 9, 5 is reinforcement corrosion lead to rust. Second, in recent years due to atmospheric environmental pollution increasingly serious acid rain damage to concrete structure, our country's acid rain area has reached more than 30% of the land area, SO2 and SO3 sulphur trioxide further oxidation of sulfur dioxide, all can make the concrete neutralization and carbide, also can directly produce chemical corrosion of reinforcement, and at the same time produce sulfate erosion on concrete further expansion. So the acid rain area than carbide to the harm of reinforced concrete structures is more serious. 4 freeze-thaw cycle of concrete structure damage occurs mainly in cold area, when the concrete structure has the loose hole defects such as crack, honeycomb pitting surface, moisture intrusion, encountered below freezing expansion of frozen, frozen surface produces roughly 9% expansion stress, the internal compression deformation defects. And when the environment temperature, freezing surface heated to melt and make its under tension, loop repeatedly so freezing thawing, as used in the pore of tensile stress is greater than the ultimate tensile strength of concrete, can produce large crack and split. Also often frozen by the snow on the bridge deck, in order to prevent the wheels skid, ensure traffic safety, often use a lot of salt to melt the snow, if the bridge cracks, salt water intrusion will inevitably make the reinforcement from being destroyed by chloride ion corrosion, which in turn lead to bridge deck on large area concrete fracture, serious still can extend to the girder, if the girder crack, also will be subject to disease. Alkali aggregate reaction (5 AAR response) , mainly is the gradation of the concrete mixed materials, alkali content ( Sodium oxide Na2O, kali K2O) On the high side, and aggregate the active ingredient in ( Silicon oxide, carbonate, etc. ) React to produce silica gel, swell after produce internal stress, leading to concrete cracking, this disease is known as 'cancer' of concrete. Actually can be prevented, as long as strictly when select material, waterproof measures to do better, can avoid to produce the condition. 6 solution erosion, mainly due to concrete structure itself is not dense, although sometimes cracks is invisible to the naked eye, but often can be water seepage, the concrete structure parts of the calcium hydroxide dissolved, its concentration is declining, Ca (in the solid phase 哦) 2 continue to by dissolution and decompose the CaO, CaO and soluble in water and wash away with water, leading to the structure of cement stone is destroyed, decrease of PH value, the porosity increases, inevitably cause steel corrosion disease occurs, the concrete surface of the drum stripping will appear.