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by using cold water for admixture and curing.
to keep concrete materials under shade to prevent sun heat.
to pour the concrete within the design mix time.
In addition to the above details , I would like to say :
By using retarders additives we can increase the hardness time of concrete for giving larger duration to mix concrete components or mortars as well as to reduce hardness speed which reduce hydration heat
I agree with my colleagues Yaqoub Alomar and hatem labib:
keep concrete materials under shade to prevent sun heat, cold water for admixture and curing, using retarders additives and working in night shift
1. Cool aggregates and mixing water added to the concrete to reduce its initial temperature.
2. Protect the concrete surface with plastic sheeting
3. Use of additives
4. Curing
A- By using admixtures to the concrete that decrease the temperature degree .
B-By adding cold water and ice during mixing.
C- By cast the concrete at the night or early mornning to avoid high temperature.
In order to avoid harmful effect of high temperature in concrete, temperature of ingredients should be controlled so that the temperature of produced concrete is lower. Mixing water has the greatest effect on lowering of temperature of concrete. The use of chilled water or flaked ice in mixing produces adequate reduction in concrete temperature
The National Ready Mixed Concrete Association (NRMCA) defines hot weather concreting as anytime during high temperatures in which special precautions need to be taken to ensure proper handling, placing, finishing and curing concrete. During the summer months you will most generally experience problems that require precautions being taken for hot weather concreting, but the associated climatic factors of high winds and dry air can occur at any time. These conditions often produce a rapid rate of evaporation of moisture from the surface of the concrete and an accelerated set time among other problems.
Hot weather is a major factor to consider when planning a concrete project. Too often it is assumed that not much can be done to combat hot and dry conditions. Many times the addition of large amounts of water is used to fight off rapid set times or to ease the placing and finishing process. These assumptions and practices often times prove to be detrimental to the concrete.
Problems that can occur due to high temperature, high wind and low humidity are:
· Increase slump loss, making concrete more difficult to place and finish.
· Accelerated set time, decreasing the amount of finish time.
· Increasing the potential for plastic and drying shrinkage cracking.
· Decreased air content.
· Reduced strength if water is added to offset slump loss.
· Thermal cracking may result from a rapid drop in concrete temperature when placed on a hot day followed by a cool night.
There are several methods to avoid high temperature problems in concrete. As concrete is the mixture of coarse aggregate, fine aggregate, cement and water. All these ingredients are required to be control from hot atmosphere then we will be able to maintain the temperature of concrete within in the permissible limits. Aggregates should be stored at the place where the direct heating of sun could not reach. Secondly ice blocks can be used during the preparation of concrete so as to avoid the high temperature problems. If all these things are not available then concrete activity should be carried out at night instead of day time. In this way we can overcome this problem and we can used the chillier system to make the water for mix cold
hello fellow engineers,
High temperature problems arise in mass concrete works like thick rafts, concrete dams which is different from hot weather concreting. Use low heat portland cement or PPC by adding further quantity of PFA or GGBS to slow down the rate of hardening process of concrete. Never use OPC alone. Following may be adopted for best work.
1. Avoid concreting in hot weather. Do all shuttering, bar bending etc works in daytime and start concreting from6PM and complete concreting job.
2. use ice or nearly zero degree water .
3. use Flyash (PFA) confirming to grade-I.
4. keep all aggregates under shade.
5. use hessian cloth all-round the transit mixer and wet it
6. Cover exposed surfaces with plastic sheet to minimize evaporation.
7. use appropriate admixture.
8. even after taking above precautions, thin elements likely to get cracks, specially slabs/roads/canal lining which are having more exposed surface. sprinkle/wet with water and refinish the surface.
9. Follow guide lines given by Prof P K Mehta to get durable concrete.
10. NOTE THAT "SLOW SETTING GIVES LONG LIFE"
Avoid casting concrete in times of high temperature
Protect the concrete surface with plastic sheeting
by using cold water for admixture and curing
There are lots of solutions for the high temperature of concrete now the question is how to control temperature of fresh concrete or hardened concrete?
To control the temperature of fresh concrete use:
1- flaky ice up to70% of water as per ACI in some cases we can go upto100% in Makkah and madina we have done it
2- zero temperature water
3- Nitrogen ( Expensive)
4- adding fly ash by % of cement
5- Cooling the aggregates by shading and sparying cold water
To control the temperatur of hardened Concrete:
1- minimize the use of cement and replace it with other cementitious materials such as fly ash to control heat of hydration
2- pour of the concrete at night
3- cure and protect the concrete from direct sun light
Following precautions can be taken while concreting in hot weather.
1. Aggregates storage shall be covered, temperature of aggregates can be brought down by frequently water sprinkling.
2. Mixing water shall be from chilling plants temp5-7 degree Celsius, ice flakes can be used.
3. Transit mixers shall be covered with moist hesian cloths.
4. Adequate care can be taken at pouring point, by covering fresh finished concrete with polythene sheets.
5. Curing compound or chemical can be used for covering semi-hardened concrete.
6. Water curing by sprinkling or wet hesian cloths shall be started as soon as concrete is fully set.
