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Hot Weather Concreting

Presented by:

Tom Pelo

Area Sales Leader

BASF Construction Chemicals

Admixture Division

ACI 305 Definition of Hot Weather

• Any combination of high ambient temperature, high concrete temperature, low relative humidity, wind velocity and solar radiation that impairs the quality of concrete by accelerating the rates of moisture loss and cement hydration

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Necessary Components for Good

Concrete Construction

• Good Design

• Good Specifications

• Good Materials

• Good Construction

• Good Inspection

• Good Testing

• Good Maintenance & Repair

• Matching Expectations

Detrimental Hot Weather Conditions

Higher ambient temperature

Higher concrete temperature

Lower relative humidity

Wind

Solar radiation

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Effects of Hot Weather on Concrete

Higher concrete temperature

• 55 – 65 ° F during winter

• 80 – 90 ° F during summer

Concrete water demand goes up

Concrete rate of slump loss is increased

Concrete rate of setting is decreased

Concrete strength is decreased

• Increased permeability

• Decreased durability

Hot Weather Concreting Problems

Greater water demand

Increased rate of slump loss

Retempering at jobsite

Potential for cold joints

Fast setting

Plastic shrinkage cracking

Difficulty placing, compacting and finishing

Control of air content

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Effect of Concrete Temperature on Water Demand

Effect of Concrete Mix Temperature on Water Requirement

310(184)

300(178)

290(172)

280(166)

270(161)

260(154)30

(0)40(4)

50(10)

60(16)

70(21)

80(27)

90(32)

100(38)

110(44)

Concrete temperature, °F (°C)

Slump: 3 in. (76 mm) Max. size agg.: 1½ in. (38 mm)

Effect of Concrete Mix Temperature on Water Requirement

Wat

er c

onte

nt,

lb p

er c

u y

d (

kg p

er m

)

3

Effect of Concrete Temperature on Slump

Effect of Concrete Temperature on Slump

40 60 80 100 120

Per

centa

ge

chan

ge

in w

ater

requir

emen

ts p

er 1

-inch

chan

ge

in s

lum

p

Concrete temperature, °F

0

5

4

3

2

1

6

0

5

4

3

2

1

6

Cement Content: 517 lb/yd³ (307 kg/m³)4½ + ½ % air; Aggregate top size: 1½ in. (38 mm)

°C10 20 30 40 50

Slu

mp, in

100

50

150

Slu

mp, m

m

Slump

Water requirement

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Concrete Setting Times

Setting Time of Concrete at Various

Temperatures

Setting Time of Concrete at Various

Temperatures

Temperature

100°F (38°C)

90°F (32°C)

80°F (27°C)

70°F (21°C)

60°F (16°C)

50°F (10°C)

40°F ( 4°C)

Approximate

Setting Time

2 hours

3 hours

4 hours

6 hours

8 hours

11 hours

14 hours

Effect of Concrete Temperature on Time

of Set

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Concrete Temps vs Humidity vs Plastic Shrinkage Cracking

Setting Time of Concrete at Various

Temperatures

Typical Concrete Temperatures for Various

Relative Humidities Potentially Critical to

Plastic Shrinkage Cracking

Concrete temperature

°F (°C)

105 (41)

100 (38)

95 (35)

90 (32)

85 (29)

80 (27)

75 (24)

Relative humidity

%

90

80

70

60

50

40

30

Effect of Curing Temperature on Strength

Development

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Effect of Curing Temperature on Strength

Development

Effect of Initial Curing of Test Specimens

on Strength DevelopmentExecutive Summary

Initially curing PCC test cylinders in saturated lime water provides more consistent surrounding temperature, a record of the surrounding temperature and rigidly conforms to T-23-93 section 9.2.1, preventing moisture loss. This is a practical curing method that leads to more consistent 28-day compressive strength. More consistent results will reduce costs associated with unnecessary over-design of PCC mixes, further testing of in-place PCC, and the time consuming claims process.

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Effect of Initial Curing of Test Specimens

on Strength Development

Data Source: CRMCA Test Fest, Grand Junction, CO, 8/29/13

Effect of Material Temperature on

Concrete Temperature

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Ways to Lessen the Effect of Hot Weather

on Concrete

Supplementary cementitious materials

Cool aggregates

Chemical Admixtures

Ice

Time of Placement

Reduce the time of transport, placing, or finishing

Use sunshades and/or windscreens

Prompt curing of concrete during the placement

Necessary Components for Good

Concrete Construction

• Good Design

• Good Specifications

• Good Materials

• Good Construction

• Good Inspection

• Good Testing

• Good Maintenance & Repair

• Matching Expectations

www.concrete.org

3/4/2015

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Necessary Components for Good

Concrete Construction

• Good Design

• Good Specifications

• Good Materials

• Good Construction

• Good Inspection

• Good Testing

• Good Maintenance & Repair

• Matching Expectations

www.concrete.org

Definition of Curing

ACI 308 Guide to Curing Concrete

1. The process by which concrete matures and develops hardened

concrete properties over time as a result of continued hydration of

the cement in the presence of sufficient water and temperature.

2. The action taken to maintain moisture and temperature conditions in

a freshly placed cementitious mixture to allow hydraulic-cement

hydration and, if applicable, pozzolanic reactions to occur so that

potential properties of the concrete develop.

3. The curing period is defined as the time period beginning at placing,

through consolidation and finishing, and extending until desired

concrete properties have developed

MOISTURE, TEMPERATURE, TIME

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Definition of Curing

ACI 308 Guide to Curing Concrete

• Initial Curing: action taken after placing during to

prevent loss of moisture from the concrete surface

– Fogging

– Liquid-applied evaporation reducers

– Windscreens / sunshades

Plastic Shrinkage Cracking

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Fogging

Fogging

18,000 CFM (510 CMM) generated by

15 HP fan.

• 12,000 square feet (1,115 square

meters) coverage.

• Oscillator gives 0-40 degrees of

movement.

• Adjustable angle of throw 0-50 degrees

of height adjustment.

U.S.: 3 Phase / 15 HP fan / 480 Volt / 60

Hertz. Full load current is 21 amps. 30

Kw gen set is recommended.

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Fogging

40-50 PSI constant pressure needs to be

delivered to the unit.

• 1-1/2" (38.1 mm) cam-and-groove

quick disconnect female coupling for fire

hose provided on machine.

• 30 brass nozzles (also available in

stainless and nylon).

•Droplet size 50-200 microns.

• Throw 150 feet (45 meters)

Fogging

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Fogging: for smaller jobs……

Originally designed for dust suppression, these Buffalo Turbine Air Misters are suited for evaporative cooling of small, localized work areas.

Surface Evaporation Reducers

Monomolecular Film – will enhance quality of concrete

Reduces surface moisture evaporation

Reduces crusting, plastic shrinkage cracks

Eliminates need for added water – compensate for rapid evaporation

Increases amount of surface handled per finisher

Reduces overall finishing costs

Not a finishing aid

Not a curing compound for hardened concrete

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Liquid-applied evaporation reducers

Hot Weather Facts

• An increase in wind velocity, reduction in humidity and high temperature

Results in water evaporating from concrete surface

Can lead to crazing and shrinkage cracks

Create a weak surface prone to dusting and poor abrasion resistance

May result in a poor finished surface

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ACI 305Evaporation Will Increase by 300%

If humidity & wind stays the same with air temperature change from 60-90°F (16-32°C)

If air temperature & wind remain the same with humidity decrease from 90–70%

Combination of all the above – evaporation will increase by 900%

If air temperature & humidity stays the same with wind speed increase from 5-20 mph (8-32 km/h)

Plastic Shrinkage Cracking PotentialEffect of Concrete and Air Temperatures, Relative Humidity

and Wind Velocity on the Rate of Surface Moisture

Evaporation from Concrete

90F (32C)

deg C

Air temperature, deg F

kg/m

²/hr

40 50 60 70 80 90

2.0

3.0

4.0

100

1.0

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Rate

of

evapora

tion,

lb/s

q f

t/hr

5 15 25 35

Win

d velocit

y 25 mph (4

0 km

/hr)

20 mph (3

2 km/hr)

15 mph (2

4 km/hr)

10 mph (16 km/hr)

5 mph (8 km/hr)

2 mph (3 km/hr)

0

Concrete temperature 100F (38C)90F (32C)

80F (27C)

70F (21C)

60F (16C)40F (4C)10

20

30

40

50

60

70

80

90

Relative humidity

100 percent

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Plastic Shrinkage Cracking Potential

Bridge Deck placement, Albuquerque, New Mexico

Plastic Shrinkage Cracking Potential

Portable Weather Station on bridge deck

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Plastic Shrinkage Cracking Potential

Plastic Shrinkage Cracking Potential

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Definition of Curing

ACI 308 Guide to Curing Concrete

• Final Curing: actions taken after final finishing to prevent

the loss of moisture and to maintain proper temperature

in order to foster normal strength development

– External source of water (fogging, ponding)

– Burlap (poly-coated burlap)

– Plastic film

– Liquid membrane-forming compounds

Difference Between Initial and Final

Curing

Window of initial curing

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ACI 308 Recommended Duration of Final

Curing

Effect of Proper Curing on Hardened

Concrete

• Increased Strength

• Increased Watertightness

• Increased Abrasion resistance

• Increased Freeze-thaw resistance

• Increased Volume stability

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Effect of Moist Curing on StrengthEffect of Curing on Compressive Strength

Age, Days

125

100

75

50

25

0

150

3 7 28 90 180

Moist-cured entire time

In air after 7 days

In air after 3 days

In air entire time

% o

f 28

co

mp

ress

ive s

tren

gth

Effect of Proper Curing on Hardened

Concrete

Increased oxygen permeability at the surface of concrete can be accompanied by increased carbonation, which weakens the paste.

Which part of the concrete seems to most vulnerable to scaling???

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Extending the Service Life of Concrete

Pavements

Effect of Proper Curing on Hardened

Concrete

Phenolphthalein is used by petrographers as a pH indicator. Lower pH is an indication that the surface has carbonated, often prematurely.

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Curing Methods

Saturated Wet Coverings

Curing Methods

Liquid membrane-forming compounds

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Curing Methods

Liquid membrane-forming compounds

Curing Methods

Liquid membrane-forming compounds

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Curing Methods

Is this an adequate application of liquid membrane-forming compound?

Type of liquid membrane-forming

compounds

Curing Compounds - ASTM C309

• Type I – Clear without fugitive dye

• Type ID – Clear with fugitive dye

• Type 2 – White pigmented

• Class A – wax based

• Class B – resin based

• Shall not allow concrete to lose more than 0.55 kg/m2 of water in 72

hours

• White pigment shall exhibit a reflectance of at least 60%

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Type of liquid membrane-forming

compounds

Cure & Seal Compounds - ASTM C1315

• Type I – Clear

• Type 2 – White pigmented

• Class A – non yellowing

• Class B – moderate yellowing

• Class C – may undergo severe darkening and has no requirement

relative to yellowing

• Shall not allow concrete to lose more than 0.40 kg/m2 of water in 72

hours

• Cure & Seals last long and serve to prevent ingress of water

Hot Weather Concreting Resources

http://www.concrete.org/BookstoreNet/SearchResults.aspx?CATEGORY=HOT+WEATHER&SEARCH_STATUS=ACTIVE

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Hot Weather Concreting

Questions?

Pop Quiz

An increase in concrete temperature is likely to

result in:

□ A reduction in setting time

□ A decrease in slump for a given quantity of mixing

water

□ A reduction in strength at later ages

□ All of the above

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Pop Quiz

An increase in concrete temperature is likely to

result in:

□ A reduction in setting time

□ A decrease in slump for a given quantity of mixing

water

□ A reduction in strength at later ages

■ All of the above

Pop Quiz

An increase in cement temperature of 27 oF:

□ Does not change the concrete temperature

□ Changes the concrete temperature by 3 oF

□ Changes the concrete temperature by 9 oF

□ All of the above

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Pop Quiz

An increase in cement temperature of 27 oF:

□ Does not change the concrete temperature

■ Changes the concrete temperature by 3 oF

□ Changes the concrete temperature by 9 oF

□ All of the above

Pop Quiz

Of these concrete materials, which is the easiest to

cool?

□ Cement

□ Coarse Aggregate

□ Fine Aggregate

□ Water

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Pop Quiz

Of these concrete materials, which is the easiest to

cool?

□ Cement

■ Coarse Aggregate

□ Fine Aggregate

□ Water

Pop Quiz

A decrease in concrete temperature is likely to lead

to:

□ a reduction in setting time

□ a decrease in slump for a given quantity of mixing

water

□ an increase in strength at later ages

□ all of the above

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Pop Quiz

A decrease in concrete temperature is likely to lead

to:

□ a reduction in setting time

□ a decrease in slump for a given quantity of mixing

water

■ an increase in strength at later ages

□ all of the above

Pop Quiz

The addition of water to concrete on the jobsite to

compensate for reduced slump due to higher

temperature can cause:

□ a reduction in compressive strength

□ increased drying shrinkage

□ increased permeability

□ reduced durability

□ all of the above

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Pop Quiz

The addition of water to concrete on the jobsite to

compensate for reduced slump due to higher

temperature can cause:

□ a reduction in compressive strength

□ increased drying shrinkage

□ increased permeability

□ reduced durability

■ all of the above