Cold Weather

Concreting

Nebraska Concrete & Aggregate Association

2019 Quality Concrete Conference

January 9 & 10, 2019

Cold Weather Concrete

Requires Experience

Cold Weather

ACI 306R-16 Committee Definition

• Cold weather conditions exist when

the air temperature has fallen to, or is

expected to be 40ºF or less during

the protection period

OK… so what is the

“Protection Period”?

• The protection period is defined as

the time required to prevent concrete

from being adversely affected by

exposure to cold weather

ACI 306 Chapter 7 says…

• 500 psi – 1 freeze-thaw cycle

– Air entrained and not exposed to water

saturation

• 3500 psi – Repeated freeze thaw

cycles

– Air entrained and not exposed to water

saturation

Rule of Thumb

Concrete temperature

above 50° F for 7 Days

Durability of Non-Air-

Entrained Concrete

Overworked, Densified Surface Paste

Trapped Moisture Layer Entrained Air

Bubbles

H2O

Effect of Freezing

Fresh Concrete

• Up to 50% reduction of ultimate

strength / durability can occur if

frozen before reaching a strength of

500 psi (3.5 MPa)

• Frozen only once at an early age —

– With curing nearly all strength

can be restored

– Less resistance to weathering

– More permeable

Effect of Freezing

Fresh Concrete

• It’s a race between the concrete

temperature and heat loss

– Includes the internal heat generated

from the hydration of the cementitious

• At a point after hydration the

concrete is strong enough to resist

freezing

• Very little hydration takes place

below 40° F

Relationship Between Initial

Set and Casting Temperature

Setting Time of Concrete at

Various Temperatures

“Concrete Construction”, March 1990

Temperature Approximate

Set Time

70°F 6 Hours

60°F 8 Hours

50°F 11 Hours

40°F 14 Hours

30°F 19 Hours

20°F Set Does

Not Occur

Rule of Thumb

For each 10°F reduction in

in temperature, set time is

increased by 1/3

Relationship Between Slump

and Casting Temperature

Effect of Low Temperatures

on Strength

Successful cold weather

concrete projects depend on

concrete that is properly

Produced

3P’s Placed

Protected

What Can We Do?

Goals for Cold Weather Concreting Practices

• Maintain curing conditions that foster normal strength development • Prevent damage due to early freezing • Limit rapid temperature changes that induce thermal stresses • Assure development of concrete engineering properties to meet project requirements

Cold-Weather Concreting

• Type III or HE high-early-strength

cement

• Additional portland cement

• 100 to 200 lb/yd3

• 10 to 15°F gain in heat of hydration

per 100 cwt

• Chemical accelerators

Methods to accelerate heat / strength

gain:

Typical Set Times

with

Chemical Accelerators

POZZOLITH NC 534 TIME OF SET

0

500

1000

1500

2000

2500

3000

3500

4000

0 100 200 300 400 500 600 700 800 900

Time (Minutes)

Pe

ne

trati

on

Re

sis

tan

ce

Control 10 oz./cwt 20 oz./cwt 30 oz./cwt 40 oz./cwt

POZZOLITH 122-HE TIME OF SET

0

500

1000

1500

2000

2500

3000

3500

4000

0 100 200 300 400 500 600 700 800

Time (Minutes)

Pe

ne

trati

on

Re

sis

tan

ce

Control 16 oz./cwt 32 oz./cwt 48 oz./cwt 64 oz./cwt

Chloride Based Time of Set Non-Chloride Based Time of Set

ACI 306 Recommended Concrete

Temperatures Air-Entrained Concrete

Thickness of section

Line

Condition

Less

than

12”

12” to

36”

36” to

72”

Over

72”

1

2 3

Min.

temp. of

fresh

concrete

Above

30°F

0°F to

30°F

Below

0°F

60°F

65°F

70°F

55°F

60°F

65°F

50°F

55°F

60°F

45°F

50°F

55°F

4

Min. temp. of fresh

concrete as

placed and

maintained

55°F

50°F

45°F

40°F

ASTM C 1622 offers more guidance for concrete temperatures

Effect of Temperature of Materials on

Concrete Temperatures

0.22(TaMa + TcMc) + TwMw + TwaMwa

0.22(Ma + Mc) + Mw + Mwa

T =

T = temperature of the freshly mixed concrete, °F (°C)

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

aggregates, cement, added mixing water, and free

water on aggregates, respectively

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

cementing materials, added mixing water, and free

water on aggregates, respectively

Concrete Temperature Analysis with Hot Water

Input: Moisture Batch Temperature

Material Content Weights F

Cement - 564 lbs./cy 100

Fly Ash - 0 lbs./cy 75

Coarse Aggregate 1.0 % 1800 lbs./cy 60

Fine Aggregate 2.5 % 1300 lbs./cy 60

Water - 30.0 gals./cy 140

Concrete Temperature: 82.8 F

Concrete Temperature Analysis with Ice

Input: Moisture Batch Temperature

Material Content Weights F

Cement - 564 lbs./cy 100

Fly Ash - 0 lbs./cy 75

Coarse Aggregate 1.0 % 1800 lbs./cy 60

Fine Aggregate 2.5 % 1300 lbs./cy 60

Water - 30 gals/cy 140

Ice in lieu of water 80 lbs./cy

Adjusted water 20.4 gals/cy

Concrete Temperature: 64.4 F

Concrete Temperature Prediction Model

Gotta have a Plan!

Cooling After Protection

Maximum Allowable Temperature Drop

During the First 24 Hours (ACI 306)

Section size, minimum dimensions

(in.)

Less than

12” 12” to 36”

36” to

72”

Over

72”

50°F 40°F 30°F 20°F

Checking Fresh Concrete

Temperatures

Temperature of Test

Cylinders

ASTM C-31 states

maintain temperature

60°F - 80°F at the

jobsite for up to 48 hrs.

Retaining Heat of Hydration

Cold-Weather

Insulation,

Aboveground

Insulating Blankets

Thermal resistance of

mineral fiber blanket

(2 to 2.75-in. thick)

1.2

(m2·K)/

W

7

(°F·hr·ft2)/

Btu

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

Caution!

CO2 can cause

carbonation!

Indirect-Fired Heater

Hydronic Systems

Maturity Concept

Metric: M = (C + 10) t

Inch-Pound: M = (F – 14) t

where

– M = maturity factor

– = summation

– C = concrete temperature, degrees

Celsius

– F = concrete temperature, degrees

Fahrenheit

– t = duration of curing at temperature C

(F), usually in hours

Concreting on Ground

Remember the 3 P’s

Produce, Place, & Protect

And you will never spin your wheels

Thank You

For Your Time Today!