The water is added arbitrarily at the construction site, and the management of the construction site is not strict
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When pouring concrete, the falling distance or the thickness of pouring layer is too large
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Whether the quality defects and strength of concrete increase regularly or not requires the construction unit to carefully organize and implement the concrete pouring, vibrating, curing, covering protection and other processes, and construct in strict accordance with the corresponding standards and specifications, so as to ensure the concrete strength and engineering quality
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If the concrete strength is lower than the formwork removal strength and the formwork is removed too early, it is easy to crack in the tension area and even damage in the compression area, resulting in safety accidents; if the concrete strength is lower than the formwork removal strength and the formwork is removed too early, it will increase the creep of the concrete and lead to structural deformation; if the concrete strength is lower, it is easy to collapse or local collapse in the process of formwork removal The collapse phenomenon weakens the section of the component and affects the bearing capacity and appearance quality; because of the low strength of the concrete, the ability of the concrete and the reinforcement to work together is poor, under the self weight of the component, construction load and other vibration, it is easy to cause the reinforcement to slide in the concrete, so as to reduce the binding force of the reinforcement; premature formwork removal leads to premature water loss on the concrete surface and accelerate the carbonation of the concrete surface The durability of concrete is reduced
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Moreover, if the free falling height is too high, the concrete will have great impact force, which will bend the reinforcement and make the stirrups of the vertical members dislocation, which will affect the mechanical performance of the members
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Improper concrete vibration sequence and method, concrete vibration not in accordance with the specified sequence, improper vibration method or local missing vibration, will lead to local sand and stone concentration, so that the concrete is loose and not dense, honeycomb holes or local holes will appear, especially in the parts with dense reinforcement, which is prone to honeycomb, exposed reinforcement and other adverse diseases
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In short, commercial concrete is a semi-finished product
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The construction site requires too large slump
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The earlier the drying time, the more serious the shrinkage cracking, the looser the structure, the greater the loss of strength, the greater the carbonation of concrete surface, and the lower the durability
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And the habit of, a quality problem is often pushed to the concrete mixing station, according to the following construction, can blame the laboratory concrete control is not good? 1
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Source: Internet.
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When pouring concrete, the reinforced concrete column, wall and other projects poured from the top, if it is too high, the coarse aggregate in the concrete will separate from the concrete and fall on the outside or bottom of the concrete pile, or in the process of pouring, the coarse aggregate will fall first, and the mortar will fall behind, causing the segregation of the concrete and squeezing the coarse aggregate In the corner of the floor, it is easy to form “honeycomb”, “pockmarked surface”, “rotten root” or cause uneven distribution of sand and stone
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Due to the dense reinforcement in the concrete structure, the construction unit, in order to facilitate the construction, requires too large concrete slump, which causes aggregate precipitation, and some structural pastes are dense, resulting in uneven strength and poor compactness of concrete structure, which affects the bearing capacity of concrete
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Whether the concrete strength has regular occurrence and development, whether the concrete surface defects can be controlled, whether the concrete durability can meet the service life, these are closely related to the construction technology, construction details and the maintenance of concrete on the construction site
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It is a necessary condition for cement hydration reaction that concrete members are not cured
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In some sites, water pipes and water guns are even used to directly add water into the hopper of the pump truck, which seriously affects the quality of the concrete mixture, increases the water cement ratio of the concrete, increases the free water and interlayer water, increases the void ratio of the hardened concrete paste, weakens the interfacial adhesion between the cement and aggregate in the concrete, and reduces the strength and durability of the concrete
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In order to facilitate the construction, the workers often add raw water to the mixed concrete, which has not been approved and verified by the technical management personnel of both parties, and the second mixing is not carried out after adding water
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In the construction process, because of the ideological and technical defects, the construction unit often produces various defects to the concrete components, such as honeycomb, pockmarked surface, cracks, exposed reinforcement, holes and so on, but without reinforcement, it will cause lifelong defects of the concrete project and affect the service life of the building, and the concrete entity detection It affects the real judgment of concrete performance
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Improper pouring management and uneven distribution will result in uneven sand and stone in concrete components due to improper pouring sequence and distribution, affect the concrete strength of components and defects such as honeycomb, pockmarked surface and holes, cause hidden dangers to engineering quality, and may also constitute major quality accidents
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If the humidity is not enough, the concrete will lose water and dry, which will affect the normal hydration of cement, or even stop hydration
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Therefore, the ambient humidity has a significant impact on the normal development of concrete strength
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Sprinkling raw water to the concrete surface increases the water cement ratio of the concrete surface, increases the voids of hardened paste, makes the concrete surface loose, reduces the strength and anti carbonization ability of the concrete surface, and causes the concrete surface to dust, return sand and crack
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In order to facilitate the surface finishing, the workers at the construction site do not stop the phenomenon of sprinkling raw water, which seriously affects the quality of concrete
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