In spring, the temperature difference between day and night is large, the temperature is changeable, and the weather is dry and windy
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Strong wind and high temperature make fresh concrete lose more water and increase plastic shrinkage
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Due to the large slump, high sand ratio and large amount of cementitious materials of commercial concrete, especially the pumping concrete, the shrinkage of concrete is intensified
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According to the characteristics of spring construction, the corresponding technical measures should be taken to ensure the quality of concrete
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The construction unit should do the following: 1
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Vibration method
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In the construction process, the concrete should be fully vibrated, so that there is no leakage of vibration, but the vibration
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Over vibration of concrete results in delamination and segregation, surface laitance, uneven settlement and shrinkage of concrete, and cracks appear at the junction of structural thickness
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Leakage vibration is not conducive to concrete compaction, resulting in concrete honeycomb, pitted surface and other defects
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The time of concrete vibration should be determined according to the workability of concrete
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The concrete should be fully vibrated, and its signs are: there is slurry on the concrete surface, no bubble overflow, the concrete is full of test mold, and no significant sinking
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2
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According to the characteristics of commercial concrete, the construction personnel of secondary vibration and multiple plastering should have a large slump and a long setting time (generally 8-12h) of commercial concrete
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They should do a good job of secondary vibration and plastering to make the plastic shrinkage cracks heal in time and fully
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The second vibration can eliminate the inner delamination caused by plastic settlement, block the continuous channel left by bleeding, improve the interface structure of aggregate, and improve the strength and permeability resistance of concrete
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In the dry spring, the surface of concrete mixed with high-efficiency retarding and water reducing agent is dried, the water evaporates quickly, and a “hard shell” is formed on the surface
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When the air temperature is high and the evaporation is large, the method of spraying water mist at the edge can solve the “crust” phenomenon of concrete
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3
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After the on-site curing concrete is poured, it shall be immediately covered with plastic film after the first leveling, so as not to let the moisture evaporate, and the moisture conservation shall be carried out by relying on the moisture of the concrete itself
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If the surface is not covered and watered in time, the water on the surface will evaporate rapidly, and it is easy to produce shrinkage cracks
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Especially in the case of low relative humidity and high wind speed, shrinkage is more likely to occur
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Some data show that when the wind speed is 16m / s, the evaporation rate of water in concrete is four times of that without wind
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At present, some construction sites in the pouring of concrete, can not be timely covered insulation maintenance
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Generally, it will be covered only after the last time of plastering
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There are still many construction sites that are not covered at all, or only send people to water every few hours
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After the first troweling, it should be covered with plastic film immediately to prevent the moisture from evaporating, and it should rely on the moisture of the concrete itself for moisture conservation
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When the second troweling is needed, uncover the film and cover it after troweling
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Moisturizing curing shall not be less than 7 days, and the curing time for projects with special requirements such as impermeability shall not be less than 14 days
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4
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The time and sequence of formwork removal should be paid attention to when concrete formwork is removed
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For beams, wallboards and other structures, the formwork removal time should be appropriately extended, and measures should continue to be taken for maintenance after formwork removal
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Moreover, it is not easy to carry out construction or pile up heavy objects on the floor, so as to reduce or avoid shrinkage deformation cracks of reinforced concrete structure
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5
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As for the setting time, the temperature in spring is changeable, the temperature difference between day and night is large, and the temperature at night is low, which is easy to prolong the setting time
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Therefore, attention should be paid to the heat preservation and maintenance work
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Commercial concrete companies also take measures to strictly control the slump and dosage of admixtures, especially when using retarded superplasticizer, pay more attention to the influence of temperature on the setting time of concrete
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If the slump loss of concrete is large and the workability cannot meet the construction requirements, please inform the commercial concrete company in time for adjustment
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Do not add water or admixtures to adjust the slump of concrete in the construction site, so as to avoid concrete quality problems..
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