2. Introduction
In the laboratory testing of concrete , All test are done in controlled
situation but in actual at site, control in temperature is Difficult.
According to IS code 7861 part I And II, the temperature of concrete
is must in range of 25.6°C to 35°C. In this range of concrete the
strength is much better and more economical and eco-friendly.
When temperature gets different from the standard temperature
then strength is also gets different. In Hot weather conditions it
accelerates the cement hydration reaction & In cold weather
conditions it Show the cement Hydration process.
4. Detrimental Conditions
• High ambient temperature
• High concrete temperature
• Low relative humidity
• Wind velocity
• Solar radiation.
5. Difficulties in Hot Weather
• Increased water demand.
• Accelerated slump loss.
• Increased rate of setting.
• Increased tendency of plastic shrinkage cracking.
• Critical need for prompt early curing.
6. Hot Weather Concreting
• Certain precautions should be taken in order to reduce the difficulties
in hot weather conditions.
• Temperature ranging from 10 to 15˚C is desirable, but such
temperatures are not always practical.
• Many specifications require that concrete when placed should have a
temperature of less than 29 to 32˚C.
7. Precautions Depends on
• Type of construction.
• Characteristics of the materials being used.
• The experience of placing and finishing crew in dealing with the
atmospheric conditions in the site.
8. Precautions
• Use materials and mix proportions that have a good record in hot
weather conditions.
• Cool the concrete or one or more of its ingredients.
• Use a concrete consistency that allows rapid placement and
consolidation.
• Reduce the time of transporting, placing, and finishing as possible.
• Schedule concrete placements to avoid extreme weather, such as at
night or during favorable weather conditions.
• Consider the methods to limit moisture loss during placing and
finishing such as sunshades, wind screens, fogging, and spraying.
9.
10. Effect of High Concrete Temperature
• increase the rate of setting and shorten the length of time within
which the concrete can be transported, placed, and finished.
• Setting time can be reduced by 2 or more hours with a 10°C increase
in concrete temperature
• There is an increased tendency for cracks to form both before and
after hardening.
• Rapid evaporation of water from freshly placed concrete can cause
plastic-shrinkage cracks before the surface has hardened.
• .
11. • Cracks may also develop in the hardened concrete because of
increased drying shrinkage due to higher water contents or thermal
volume changes as the concrete cools
12.
13. Cooling Concrete Materials
• Lower the temperature of concrete materials before mixing.
• The contribution of each material is related to
• Temperature.
• Specific heat.
• Quantity of each material.
14. Supplementary Cementious Materials
• The use of supplementary materials (fly ash, ground granulated blast
furnace slag) can help in hot weather conditions.
• These material slow the rate of setting as well as the rate of slump
loss.
15. Controls for Hot Weather
• Using a concrete mixture that is properly proportioned for conditions
• Consider the use of a set-retarding admixture to control set times.
The use of fly ash can also reduce the effects of fast-setting concrete.
• Have manpower and equipment
• Add water only once—adjust the slump when the truck first arrives
and follow through with prompt placement.(For drying shrinkage
cracking)
• To minimize plastic shrinkage cracking, keep the surface wet (not
saturated) by applying moisture with a fog sprayer until the final
curing method is ready to be applied.
16. Admixtures
• A retarding admixtures can be very helpful in delaying the setting
time, despite increased rate of slump loss resulting from their use.
• A hydration control admixture can be used to stop cement hydration
and setting. As a general rule a 5°C to 9°C temperature rise per 45 kg
of Portland cement can be expected from the heat of hydration.
17. EFFECTS OF LOW TEMPERATURE
What Happens When Concrete Freezes?
• Pore water in concrete starts to freeze around -1°C (30°F)
• As some water freezes the ion concentration in the unfrozen water
goes up, further depressing the freezing point.
• At around -3 to -4°C enough of the pore water will freeze so that
hydration will completely stop. and depending on the extent of
hydration, and thus the strength of the concrete, the forces generated
by the expansion of ice may be detrimental to the long term integrity
of the concrete.
18. COLD WEATHER CONCRETE
Definition
• A period when for more than 3 successive days, the following
conditions exist:
• The average daily air temperature is less than 40°F, and
• The air temperature is not greater than 50°F for not more than one
half of any 24 hour period.
19. Effects of cold weather on concrete
• Delayed Setting
• Freezing of Concrete at Early Ages
• Repeated Freezing and Thawing of Concrete
• Stresses Due to Temperature Differential
20. Cold weather can be divided into three
catagorias
The severity or the weather determines the precautions to be taken.
For this purpose cold weather can be divided into three catagorias
1. When the temperature is below 5°0 but does not fall below
freezing point,
2. When frost occun at night only and is not very severe, and
3. When there is severe frost day and night
21. TEMPERATURE CONTROL
• The most direct approach to keeping concrete temperature up by
controlling the temperature of ingredients. The contribution of each
ingredient to the temperature of concrete is function of the
temperature. specific heat, and quantity used of that ingredient. The
aggregates and mixing water exert the most pronounced effect
temperature of concrete. Thus. in cold weather, all available means
shall be used for maintaining these materials at a high a temperature
practicable.
22. Ingredients
• Aggregates : When aggregates in stockpiles are heated by Iteam
pipes, exposed surfaces of aggregate shall be covered with tarpaulins
as much as practicable to maintain uniform distribution of heat and to
prevent formation of frozen crusts.
• Water: water is heated to a temperature in excess of 40’c.
• Cement: for extreme weather use Rapid hardening cement.
• If loss of effectiveness of air entraining admixtures is noticed due to
hot water. the admixture may be added to the batch only after water
temperature has been reduced.
23. Recommended Practices and Basic
Principles
• Planning
• Curing and Protection
• Temperature Records
• Heated Enclosures
• Exposure to Freezing and Thawing
• Slump
• Truck Travel Time
• Hot Water
• Hydration in Cold Weather
• Acceleration of Concrete
1. Calcium Chloride as an
Accelerator
2. Air entraining agents
24. References
• BIS 7861 part I
• BIS 7861 part II
• A Cade study under IJARS – INTERNATION JOURNAL OF ADVANCE
RESEARCH IN SCIENCE AND ENGINEERING BY PROFF. ASIF HUSSAIN.
