Click the blue words above to pay attention to the concrete slump
. 
Concrete slump mainly refers to the plasticizing and pumpable properties of concrete
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The main factors affecting concrete slump are gradation change, water content, weighing deviation of weighing instrument, dosage of admixture, and the temperature of cement
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Slump refers to the workability of concrete, specifically to ensure the normal construction, including the water retention, fluidity and cohesion of concrete
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Workability refers to whether the concrete is easy to operate and even dense
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It is a comprehensive performance, including fluidity, cohesiveness and water retention
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The main factors affecting workability include useful water, water cement ratio, sand ratio, cement type, aggregate condition, time and temperature, admixture, etc
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The standard of concrete slump is not clear
.
No specification gives a strict standard, only a recommended standard
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Because in the concrete construction, different parts, different reinforcement ratio, different climate or different construction technology will affect the concrete slump that can be constructed
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But the general principle is to reduce the concrete slump as much as possible under the condition that the construction technology and concrete forming requirements can be guaranteed
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Because the concrete collapse will cause a lot of problems, such as: the pouring concrete strength is easy to produce problems, the vibrator is not easy to make the concrete vibrate dense, the concrete segregation and holes are easy to appear
.
As mentioned above, slump is also restricted by construction technology and construction position
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For example, if the reinforcement ratio in the concrete is very high, the temperature is too high, the transportation distance is too long, and the pumping concrete is used, the construction can not be carried out because the slump is too small
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The slump should be determined according to the actual situation of the site, which can not affect the construction too small, and can not affect the concrete quality too much
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Influence factors of concrete slump 1
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Influence of concrete raw materials on water washed sand in Shahe River
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Due to different storage time and batches, the water content is unstable, and there are great limitations in determining the water content through tests
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Generally, the water content of coarse aggregate is relatively stable, but sometimes it changes
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The reason is that aggregate plants are mostly open storage, and the water content of aggregate changes after rain, When mixing concrete, the different water absorption of aggregate will lead to different degrees of deviation of concrete slump
.
2
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Machinery and mixing time affect the concrete
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Long mixing time will increase the water absorption of aggregate, reduce the free moisture in concrete clinker, and cause the loss of concrete slump
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Concrete mixing machinery measurement system error will also cause concrete slump loss
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Concrete mixing ratio is obtained through accurate calculation and repeated trial adjustment
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Any kind of material will change the specific surface area of material in the unit due to inaccurate measurement
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The greater the specific surface area of material changes, the greater the slump loss over time
.
3
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Due to the influence of concrete transportation machinery, the longer the transportation distance and time of concrete mixer truck, the less the free water content of concrete clinker due to chemical reaction, water evaporation, aggregate water absorption and other reasons, resulting in the time loss of concrete slump, and the loss of mortar due to concrete belt conveyor and tumbling barrel, This is also an important reason for the loss of concrete slump
.
4
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In the process of concrete pouring, the longer the concrete clinker reaches the warehouse surface, the more free water in the concrete clinker will be reduced rapidly due to chemical reaction, water evaporation, aggregate water absorption and other reasons, resulting in slump loss, especially when the concrete is exposed to the belt conveyor, the larger the contact area between the surface and the external environment, The rapid evaporation of water has the greatest impact on the slump loss of concrete
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According to the actual measurement, when the air temperature is about 25 ℃, the slump loss of concrete clinker can reach 4cm in half an hour
.
5
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The influence of concrete pouring time is different, which is also an important reason for concrete slump loss
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In the morning and evening, the temperature is low, and the water evaporation is slow; in the afternoon and noon, the temperature is high, and the water evaporation is fast
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The faster the water loss is, the greater the slump loss of concrete is, and the worse the fluidity and cohesion of concrete are, and the more difficult the quality is to guarantee
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