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OUTLINE
ACI definition of cold weather
Setting time of concrete at various temp.
Effect of cold weather on concrete
Precautionary measure for conc. in cold weather
Conclusion
ACI DEFINITION
Cold Weather - A period when, for more than 3 consecutive days,
the following conditions exist:
The Average daily air temperature is less than 40 ºF (5 ºC), and
The air temperature is not greater than 50 ºF (10 ºC) for more
than one-half of any 24 hour period.
SETTING TIME OF CONCRETE AT VARIOUS TEMPERATURE
Temperature, °F Approx. Setting Time , hrs.
70 6
60 8
50 11
40 14
32 Concrete Freeze
PROBLEM OF COLD WEATHER ON CONCRETE
Delay setting time
Freezing of concrete at early age
Placing concrete on ground
Plastic concrete problem
1. DELAY SETTING TIME
The rate of hydration of cement depends upon the ambient temperature.
If the ambient temp. is low , hydration process will go slow.
Than concrete takes a longer time to set and to develop strength.
2. FREEZING OF CONCRETE AT EARLY AGE
When the temp. of concrete falls below
freezing point , the free water held in the
plastic conc. Freeze.
Due to freezing of water , conc. Expand and
hydration of cement will be stopped.
3. PLACING CONCRETE ON GROUND
Concrete should never be placed on a frozen subgrade
On a frozen subgrade, heat will migrate rapidly away
from the bottom of the concrete retarding setting time
Thaw the subgrade not just the surface
4. PLASTIC CONCRETE PROBLEM
Concrete bleeding
Bleed water can freeze on surface
Bleed water capillary channels can freeze within the concrete
Cold subgrades
Rapid migration of heat from concrete will affect setting time
Uneven settlement may occur, causing cracking
1. HOT WATER
During cold weather, it may be necessary to heat
one or more of the concrete materials (normally we
use hot water).
An increase in water temperature of 50oC will
result in a rise in concrete temperature of
approximately 10-15oC.
The temperature of the water added should be no
more than 60-80oC.
2. TYPE III CEMENT
Type III cement is a form of Portland cement.
Type III cement achieves about 70% of its 28 day
strength after 3 days. That is indeed a little
faster thanType I.
3. AIR ENTRAINING AGENT.
Air entrainment is the intentional creation of tiny
air bubbles in concrete.
Air-Entrained concrete has higher durability than
the ordinary concrete under freezing conditions.
Modify the pore structure of the concrete and
improve the resistance to frost attack.
4. ACCELERATING ADMIXTURES
Earlier finishing of slabs
Increased early and ultimate strength
Reduced protection time in cold weather
Earlier stripping and reuse of forms
B. PROTECTION IN FIELD
Delayed Removal of formwork
For slower rate of gain strength formwork is required to be kept in place for
longer time
Covering the concrete surface
During cold weather, all conc. Surface shall be covered as soon as the conc.
Has been placed in order to prevent the
i. Loss of heat
ii. Prevent freezing