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What are the notes when pouring fresh concrete in hot weather? With today's hot climate, the concrete pouring process also has many difficulties and leads to the phenomenon that causes the concrete to lack water leading to cracking, the quality of concrete becomes reduced, the workability of the concrete mix. The concrete will decrease rapidly leading to the construction process becomes more difficult. So there are ways to prevent this phenomenon, with Dufago concrete learn the methods below as follows:
With hot climate, the workability of the concrete mix will decrease rapidly, making the construction process more difficult. The addition of water to concrete at the construction site to improve the above condition, although recommended as very dangerous, is still used. Adding water at the construction site will increase the water/cement ratio, reducing the strength and durability of the concrete.
To ensure that the reduction in strength of concrete building materials caused by hot weather is within the allowable limits. The temperature of fresh concrete should be strictly controlled. At some projects in Vietnam, it is required, the initial temperature of fresh concrete should be from 30 - 32 .oC. Besides reducing the strength and durability of concrete, the high initial temperature of fresh concrete also leads to some negative effects:
– Faster hydration of cement is the cause of early curing of concrete – resulting in rapid decrease in workability of concrete.
– The surface of concrete dries very quickly especially under the effect of wind, sunlight and low relative humidity.
– To avoid water loss, concrete needs to be cured or continuously moistened on the surface. If dehydration occurs, cracks due to plastic shrinkage will appear. In addition, the above process leads to the fact that the cement cannot be completely hydrated. Continues to degrade the ultimate strength of the outer layer of concrete which is soon dehydrated. Reduces the durability of concrete.
Method of controlling the initial temperature of fresh concrete
Method to reduce the temperature of fresh concrete
– Cool the aggregate by covering and moistening the aggregate
– Use of ice during mixing/using water chiller
– Cool the concrete mix with liquid nitrogen
Preparation plan for concrete pouring
– The process of pouring concrete must be closely combined with the concrete construction process to minimize the delay of pouring blocks.
– There must be adequate preparation of equipment and labor so that the concrete can bend and compact quickly.
– The foundation and formwork must not absorb water from the concrete. Formwork should be moistened before placing concrete. But it must be avoided that the mold and the foundation are sprayed with too much water, causing water stagnation.
– If the conditions for being able to work in hot weather cannot be met, the work should be postponed to a cooler time of the day. For example: construction at night.
– Set extender admixtures can be used to reduce the disadvantage of fast hydration cement, but they will prolong the setting time of the concrete a little. The use of setting extender admixtures also requires an extended curing time as they increase the risk of plastic shrinkage cracking. The foundation and formwork must not absorb water from the concrete. Formwork should be moistened before placing concrete. But it must be avoided that the mold and the foundation are sprayed with too much water, causing water stagnation.
– If the conditions for being able to work in hot weather cannot be met, the work should be postponed to a cooler time of the day. For example: construction at night.
– Set extender can be used to reduce the disadvantage of fast hydration cement. They will prolong the setting time of the concrete a little. The use of setting extender admixtures also requires an extended curing time as they increase the risk of plastic shrinkage cracking.
When is it allowed to dismantle the formwork?
The formwork can only be removed when the concrete structure has reached sufficient material strength to stabilize the structure. Normally, people often consider the time from 3 to 4 weeks to be wrong when pouring in normal conditions (20 - 30 minutes).oC ) is enough to unload the formwork, but if possible, leave it as long as possible.
There are many cases where dismantling the formwork before the prescribed time limit has collapsed the structure, causing serious accidents. After dismantling the formwork, it should be noted that the commercial concrete only reaches the static load strength (i.e. its own weight) but it will take a long time to withstand the action (load and weight of the items). Other fixtures and equipment In case it is necessary to remove the formwork early, it is advisable to continue to support members such as floors, beams and main beams with wooden or metal supports.
CONTACT INFORMATION – CONSTRUCTION SERVICES DA NANG- QUANG NAM- QUANG NGAI
Phone number: 0915 737937 – pouring concrete Danang Consulting phone number: 0899154747 – pouring concrete Quang Nam Consulting phone number: 0935103935 – pouring concrete Quang Ngai Address: 233 Dien Bien Phu – Hoa Khe Ward – Thanh Khe District – City. Danang Website: https://dufago.com.vn Dufago's fanpage Concreting in Da Nang, Quang Nam, and Quang Ngai 
