| Topic : Smart construction engineering |
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Construction Planning & Management |
Project Management |
THINKERS and ONLY THINKERS……………!!!!!!!!!!!
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Activity:
157 views;
last activity : 11 01 2010 10:14:40 +0000
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Proper thermal analysis
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Low heat generating concrete mixtures & cooling pipes
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Using thermocol
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ice
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Thermal Insulation
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CONTROLLING CONCRET TEMPARATURE.
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Put insulation of wet gunny sheets on transit mixer
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Transport At Night
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Cooling of concrete is a very expensive method. So it is very important to first analyze the need to do it and to what extent it must be done. Proper thermal analysis need to be done before taking any decision. That will help us decide the extent of cooling that we need to do. The following points can be considered for cooling of concrete after thermal analysis is done. 1. Use of supplementary cementitious material like fly ash or slag will help in reducing the heat of hydration. This was the total heat generated will also be less as compared to concrete with only cement. Subsequently the placing temperature can also be more as the total heat generated is less. 2. The lead time from the batching plant to the pouring point needs to be considered as the temperature of concrete will increase during transit. It means that if we have to place the concrete at 20C then considering the transit time the concrete has to be produced at a lower temperature. 3. Transit mixes should be covered with wet hessian cloth. This will not allow the temperature of concrete to increase fast. 4. For cooling of concrete, chilled water can be used in concrete. Also chilled water should be sprinkled on aggregate in the bins in order to reduce the aggregate temperature.This way temperature can be lowered upto 5-6C. 5. If chilled water cannot fulfill the requirement then ice can be used as a replacement of water.This will help to reduce the concrete temperature substantially. This way temperature can be lowered by another 8-9C. 6. In case of dam concrete where the placing temperature requirement is 10C, there the aggregate need to be inundated in chilled water to bring the temperature of aggregate down to about 12-14C. Then chilled water and ice needs to be used to achieve the required temperature. 7. Cooling pipes are also used in dam concrete for post concreting cooling. But this is rarely done in India. 8. In case the quantity of cooled concrete is very less and setting up a chilling plant and ice plant is not economical then liquid nitrogen can be used for cooling of concrete. It is a very effective method for cooling of concrete but is quite costly. |
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Its a very good description of the subject. We are very much concerned on the heat of hydration and the most accepted and easiest way is the replacement of cement either with Fly-Ash or GGBFS to as much as 55%. This not only results good quality concrete but also reduces its making cost to a large extent. Further, special concrete like SSC will support the cause. Another important thing to be taken care of is the concrete pump efficiency. The frequency of strokes of the Pump should be monitored closely that can bring big effects in concrete temperature.
yes all RMC suppliers are taking care of these points.
Superb and sufficient. This ideate can be closed now.
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Interesting :) We need to do proper analysis to determine the most best method to restrict temperature increases and subsequent temperature drops to levels just safely below values that could cause undesirable cracking. For structures of limited complexity satisfactory results may be obtained by roller compacted concrete thermal control options. |
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If thermocol are packed in the transit mixture the temperature of concrete can be maintained at the same temperature as it is during concrete preparation. |
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Mr. Charles,
It is only idea for maintaining concrete temperature. This idea have to studied in depth by the truck manufactures so that the transport of concrete mixture will be within the required temperature. i can elaborate by saying that the transit mixture container have to be lined with thermocol either on inner side or outside, so that the concrete mixture will be with in the prescribed temperature.
Mr perumal, could you pls elaborate this idea in detail I am interested in the details
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Ice is one of the solution commonly used .Any other better ones pls to bring down temp by 8-10 degrees |
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Takiling about Thermocol insulation:
Thermocl line on outer surface only, is possible but with a thin metalic sheet as an integrated part of the drum. It will ensure your company signatures etc.
But, this will increase the cost & load on the chasis and better done at manufacturers end.
Inner surface is exposed to concrete and generates friction while rotating, thus damaging any type of insulation.
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Hi !! The ideas were funtastic, but soon the situation will change globally, as far as insulation is concerned to arrest the ambient effect. 1. Insulating the drum with wet gunny cloth gives a very bad look and could cause corrossion in due course. 2. Insulating the drum with thermocol is totally a design aspect of the drum that may increase the total load. 3. Thermal insulation material coating (Micro alumina grain rich) which is generally used on satilites, is not that costly; but a periodical application. This will give a good thermal protection. Hence, the use of fiber drums with good thermal protection, resonably long life, reduced static weight in the chasis, easy repairs and low repair cost. Apart from the following cooling ideas: 1. Water jacket to cement silos. 2. Areation chambers in the silos: for cooling & keeping the cement bed in fuidized state for free flow down. 3. Water cooled air jets in aggregate bins. I appreciate and wel-come some practical innovative ideas. Dheer |
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High concrete temperatures increase the rate of hydration, thermal stresses, the tendency for drying shrinkage cracking, permeability, and decrease long-term concrete strengths, and durability as a result of cracking. There are an increased number of failures as the air temperature at placement increases problems in fresh concrete are likely to include: Increased water demand; Increased rate of slump loss and corresponding tendency to add water at the job site; Increased rate of setting, resulting in greater difficulty with handling, compacting, and finishing, and a greater risk of cold joints; Increased tendency for plastic shrinkage cracking; and Increased difficulty in controlling the entrained air content.
There are a number of mitigation measures that can be used to minimize the potential of experiencing problems associated with hot weather concreting, of which the following are only a few examples : The use of concrete materials and proportions with satisfactory performance in place under hot weather conditions; Use cooled concrete, which can be achieved by using chilled mixing water, ice in the mixture, the use of liquid nitrogen to cool the mixing water or the concrete mixture, or the cooling of the coarse aggregate. The use of a concrete consistency that allows rapid placement and effective consolidation at high temperatures; Schedule placement activities during the times of the day or night when the weather conditions are favorable; Minimize the time to transport, place, consolidate, and finish the concrete; and Protect the concrete from moisture loss at all times during placement and during its curing period.
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Putting wet gunny bags around the drum of transit mixer is practical and widely used to control temprature of concrete during trnasportation. Other methods given by friends are good but some times may not be practical. |
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In the day temperature is high!! Do concreting / transportation at night to control temperature. |
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