Cold-Weather Concreting. Cold Weather When air temp. is at or below 5°C or when there is a probability of it falling below 5°C within 24 hours of placing

Cold-Weather Concreting


Cold Weather

When air temp. is at or below 5°C or when there is a probability of it falling below 5°C within 24 hours of placing —

CSA A23.1



Effect of Freezing Fresh Concrete Up to 50% reduction of ultimate

strength can occur if frozen — within a few hours before reaching a str. of 3.5 MPa

Frozen only once at an early age —

With curing nearly all strength can be restored

Less resistance to weathering More permeable


Relationship Between Initial Set and Casting Temperature


Relationship Between FinalSet and Casting Temperature


Relationship Between Slump and Casting Temperature


Effect of Temperature on Strength Development


Effect of Low Temperatureon Strength


Early-Age Strength


Retaining Heat of Hydration



Type 30 High-early-strength cement

Additional portland cement (60 to 120 kg/m3 )

Chemical accelerators

Methods to accelerate strength gain:



Effect of F/T on Strength of Non-Air-Entrained Concrete



Permissible Concrete Temperatures at Placing

Thicknessof Section, m

Temperature, °C

Minimum Maximum

Less than 0.3

0.3-1

1-2

More than 2

10

10

5

5

35

30

25

20

CSA A23.1


Effect of Temperatures of Materials on Concrete Temperature

0.22(TaMa + TcMc) + TwMw + TwaMwa

0.22(Ma + Mc) + Mw + Mwa

T =

T = temperature of the freshly mixed concrete, °C

Ta, Tc, Tw, and Twa = temperature in °C of aggregates, cementing materials, added mixing water, and free water on aggregates, respectively

Ma, Mc, Mw, and Mwa = mass, kg, of aggregates, cementing materials, added mixing water, and free water on aggregates, respectively



Max. Permissible Temp. Differential Between Concrete Surface and Ambient Air — Wind up to 25 km/hr.

Thickness of

concrete,

m

Max. permissible temp. differential, °C

L to H ratio of structure

0 3 5 7 20 or more

0.3

0.6

0.9

1.2

1.5

29

22

18

17

16

22

18

16

15

14

19

16

15

14

13

17

15

14

13

13

12

12

12

12

12


Checking Fresh Concrete Temperatures


Checking Hardened Concrete Temperatures


Temperature of Test Cylinders


Recommended Duration of (A) Concrete Temp. in Cold Weather

Air-entrained concreteAir-entrained concrete

Service category

Protection from early-age freezing

For safe stripping strength

Convent. concrete,

days

High-early strength concrete,

days

Convent.

concrete, days

High-early-strength concrete,

days

No load, not exposed, favorable moist-curing

2 1 2 1

No load, exposed, but later has favorable moist-curing

3 2

3 2

Partial load, exposed 6 4

Fully stressed, exposed

See next slide (B)


Recommended Duration of (B) Concrete Temp. in Cold Weather

Fully stressed, exposed, air-entrained concreteFully stressed, exposed, air-entrained concrete

Required % of standard-cured 28-day strength

Days at 10°C Days at 21°C

Type of portland cement

Type of portland cement

10 I or GU

20 II or MS

30 III or HE

10 I or GU

20 II or MS

30 III or HE

50 6 9 3 4 6 3

65 11 14 5 8 10 4

85 21 28 16 16 18 12

95 29 35 26 23 24 20


Cold-Weather Insulation, Aboveground


Thermal Resistance (R) for 10-mm Thickness ofness of Material

Board and SlabsDensity

kg/m3(m2 . °C)/W

Expanded polyurethane 24 0.438

Expanded polystyrene 29 0.277

Mineral fiberboard 256 - 272 0.204

Plywood 545 0.087Loose fill

Wood fiber, soft woods 32 - 56 0.231

Vermiculite 112 - 131 0.148


Insulating Blankets

Thermal resistance of mineral fibre blanket (50 to 70-

mm thick)

1.2

(m2 ·°C)/W


Insulating Concrete Forms (ICF)


Insulated Column Forms

High-density plywood

Rigid polystyrene

Rough plywood


Enclosures

Wood Canvas Tarpaulins Polyethylene Film


Heated Enclosure


Direct-Fired Heater


Indirect-Fired Heater


Hydronic Systems


Maturity Concept

M = (C + 10) t

where M = maturity factor = summation C = concrete temperature, °C t = duration of curing at temperature

°C, usually in hours



Video

Concreting on Ground

Documents

Cold-Weather Concreting. Cold Weather When air temp. is at or below 5°C or when there is a probability of it falling below 5°C within 24 hours of placing