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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
10
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
3/4/2015
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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