The document discusses concrete construction in cold weather. It defines cold weather as periods when the average daily temperature is below 40°F for more than 3 days. Concrete sets more slowly at lower temperatures, taking approximately twice as long to set at 40°F compared to 70°F. Precautions are needed to prevent freezing of plastic concrete and ensure proper strength gain. Methods include using Type III cement, air entrainment, heated materials and forms left in place longer during curing to insulate concrete from cold temperatures.

1. COLD WEATHER
CONCRETE

2. 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

3. ACI DEFINITION
ColdWeather - 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.

4. SETTING TIME OF CONCRETE AT
VARIOUS TEMPERATURE
Temperature, °F Approx.SettingTime , hrs.
70 6
60 8
50 11
40 14
32 Concrete Freeze

5. PROBLEM OF COLD WEATHER ON
CONCRETE
 Delay setting time
 Freezing of concrete at early age
 Placing concrete on ground
 Plastic concrete problem

6. 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.

7. 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.

8. 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

9. 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

10. PRECAUTIONARY MEASURE FOR
CONCRETE IN COLD WEATHER
A. Use of materials
B. Precautions in field

11. A. MATERIAL USED IN FIELD
 Use of type III cement
 Air entraining agent
 Admixture

12. 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.

13. 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.

14. 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.

15. 4. ACCELERATING ADMIXTURES
 Earlier finishing of slabs
 Increased early and ultimate strength
 Reduced protection time in cold weather
 Earlier stripping and reuse of forms

16. 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