Cold-Weather Concreting

CVLE 519

Concrete Technology

Dr. Adel El Kordi

Professor

Civil and Environmental Engineering

Department

Faculty of Engineering

Cold Weather

Average daily temperature <5ºC (40ºF) for 3

successive days

Stays <10ºC (50ºF) for more than ½ of any

24h period.

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Hydration Basics

Cement Particle

Early Stage of Hydration

Hydration Stages (73 ºF)

Effect of Freezing Fresh Concrete

Up to 50% reduction of ultimate strength can occur if frozen —

Within a few hours

Before reaching a strength of 3.5 MPa (500 psi)

Frozen only once at an early age —

With curing nearly all strength can be restored

Less resistance to weathering

More permeable

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Rule of Thumb

“For every 10°C (18°F) reduction in

concrete temperature, the times of

setting of the concrete double...”

Relationship Between Initial Set and Casting Temperature

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Relationship Between Final Set and Casting Temperature

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Effect of Casting Temperature on Slump

Relationship Between Slump and Casting Temperature

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Setting Times at Different Temperatures

27.6 MPa

3.4 Mpa

Whoops!!!

Effect of Temperature on Strength Development

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Effect of Low Temperatures on Strength

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Effect of Cement Type on Early Age Strength in Cold Weather

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Retaining Heat of Hydration

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Heat of hydration is useful in

winter concreting as it

contributes to the heat needed

to provide a satisfactory

curing temperature; often

without other temporary heat

sources, particularly in more

massive elements.

Cold-Weather Concreting

Methods to accelerate strength gain:

Type III or (HE) high-early-strength

cement.

Additional Portland cement (60 to 120

kg/m3).

Chemical accelerators

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Air-Entrained Concrete

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21

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Durability of Non-Air-Entrained Concrete

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Concrete that is not air

entrained can suffer

strength loss and

internal as well as

surface damage as a

result of freezing and

thawing.

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Example of a concrete floor that was saturated with rain, snow, or water and

then frozen, showing the need for air entrainment. This could also result in

greater deflection of the floor and a surface that is less wear-resistant.

Durability of Non-Air-Entrained Concrete

Effect of Temperature of Materials on Concrete Temperatures

0.22(TaMa + TcMc) + TwMw + TwaMwa

0.22(Ma + Mc) + Mw + MwaT =

T = temperature of the freshly mixed concrete,

°C (°F)

Ta, Tc, Tw, and Twa = temperature in °C (°F) of

aggregates, cement, added mixing water, and

free water on aggregates, respectively

Ma, Mc, Mw, and Mwa = mass, kg (lb), of

aggregates, cementing materials, added mixing

water, and free water on aggregates,

respectively

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Temperature of mixing water needed to produce heated concrete of

required temperature.

Checking Fresh Concrete TemperaturesControl Test

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• Thermometer with a metal sensor suitable for checking

fresh concrete temperatures.

Checking Hardened Concrete Temperatures – Control Test

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Measuring Hardened concrete temperatures below the

surface with a glass thermometer.

Temperature of Test Cylinders

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Concrete test cylinders must be maintained at a temperature between 16°C and

27°C at the jobsite for up to 48 hours until they are taken to a laboratory for

curing. For concrete mixtures with a specified strength of 40 MPa or greater,

the initial curing temperature shall be between 20°C and 26°C

Recommended Concrete Temperatures-Air-Entrained Concrete

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Cooling After Protection

Section size, minimum dimensions, mm.

Less than

300 300 to 900 900 to 1800

Over

1800

28°C 22°C 17°C 11°C

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To avoid cracking of the concrete due to sudden temperature change

near the end of the curing period, ACI Committee 306 requires that the

source of heat and cover protection be slowly removed. The maximum

allowable temperature drop during the first 24 hours after the end of

the protection is given in Table

Recommended Duration of Concrete Temperature in Cold Weather–Air-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-curing2 1 2 1

No load, exposed, but

later has favorable moist-

curing3 2

3 2

Partial load, exposed 6 4

Fully stressed, exposed See next slide

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Recommended Duration of Concrete Temperature for Fully Stressed, Exposed, Air-Entrained Concrete

Required

percentage

of standard-

cured 28-day

strength

Days at 10°C (50°F) Days at 21°C (70°F)

Type of portland

cement

Type of portland

cement

I or

GU

II or

MS

III or

HE

I or

GU

II or

MS

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

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Cold-Weather Insulation, Aboveground

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Thermal resistance (R) of insulation required to

maintain the concrete surface temperature of

walls and slabs aboveground at 10°C or above for

7 days. Concrete temperature as placed: 10°C.

Maximum wind velocity: 24 km/h (15 mph). Note

that in order to maintain a certain minimum

temperature for a longer period of time, more

insulation or a higher R value is required (adapted

from ACI 306).

Insulating Materials

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Heat and moisture can be

retained in the concrete by

covering it with commercial

insulating blankets. The

effectiveness of insulation can

be determined by placing a

thermometer under it and in

contact with the concrete. If

the temperature falls below

the minimum required on Line

4 in Table 14-1, additional

insulating material, or material

with a higher R value, should

be applied.

Thermal Resistance, R, for (10-mm Thick) Insulating Materials

Board and Slabs (m2·K)/W(°F·hr·ft2)/Bt

u

Expanded polyurethane 0.438 6.25

Expanded polystyrene 0.277 4.0

Mineral fiberboard 0.204 2.94

Plywood 0.087 1.24

Loose fill

Wood fiber, soft woods 0.231 3.33

Vermiculite 0.148 2.13

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Insulating Concrete Forms (ICF)

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Insulated Column FormsHigh-density plywood

Rigid polystyrene

Rough plywood

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With air temperatures down to

23°C, concrete was cast in this

insulated column form.

Direct-Fired Heater

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Indirect-Fired Heater

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Hydronic Systems

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Heating Materials

Water

Aggregates

Admixtures Protect from freezing

Agitate if necessary

Maturity Concept

Metric: M = (C + 10) t

where

M = maturity factor

= summation

C = concrete temperature, degrees Celsius

t = duration of curing at temperature C, usually in hours

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Thermocouples and wiring at various

depths in a caisson.Automatic temperature recorder.