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3/4/2015
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CRMCA SOUTHERN MARKETING
O
COLD WEATHER CONCRETE PRACTICES
SUCCESSFULCOLD WEATHER
CONCRETING
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ACI DEFINITION OF COLD WEATHER
Cold Weather - A period when, for more than 3 consecutive days, the
following conditions exist:
• The Average daily air temperature is less than 40 ºF (5 ºC), and
• The air temperature is not greater than 50 ºF (10 ºC) for more than
one-half of any 24 hour period.
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9
U.S. FREEZE / THAW ZONE MAP
Annual average number
of days temperatures
fall below 32 °F (0 °C)
Less than 30
30 to 90
91 to 150
151 to 210
More than 210
10
Temperature, °F Approx. Setting Time, hrs.
70 6
60 8
50 11
40 14
32 Concrete Freezes
CONCRETE FREEZES!
Setting Time of Concrete at Various
Temperatures
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11
Effect of Early Freezing
12
A 10 degree drop in
concrete temperature
will DELAY set time by
approximately
2 – 2 ½ hours
Rule of Thumb
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Increased Contractor
Labor Costs
Extended Concrete Setting Times
14
Increased Contractor Labor Costs
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15
• Prevent damage to concrete due to freezing at early stages
• Assure that the concrete develops the required strength for safe removal of forms
• Maintain curing conditions that foster normal strength development
• Limit rapid temperature changes
• Provide protection consistent with the intended serviceability of the structure
OBJECTIVES OF SUCCESSFUL
COLD WEATHER CONCRETING
• Materials
• Mix Design
• Placement Conditions
• Curing conditions and length of time
• Protection
What Can We Influence
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• GOAL is to ACCELERATE and INCREASE
Maximum Temperature
• Provide concrete with predictable setting
times
• Maintain Air entrainment and workability
• Minimize Plastic and Drying shrinkage
Materials & Mix Design
Speed up the early hydration (heat gain) of
concrete can be obtained by using one or more
of the following:
• Additional portland cement
• Use Type III Cement
• Hot water
• Heat Aggregate
• Use of calcium chloride
• Use of a non-chloride accelerating admixture
Cold Weather Concreting (Producer)
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19
0
2
4
6
8
10
12
14
12:35
10:40
8:55
Effect of Cement Content on Setting Time
Performance
Concrete and Ambient Temperature: 50 °F (10 °C)In
itia
l Tim
e o
f Se
t -
Ho
urs
Cement Content, lb/yd³ (kg/m³)
420 (250) 520 (310) 600 (355)
20
An increase of 1
sack of cement, will
improve the set time
by about 1 hour
Why?
Lower unit water
content
Rule of Thumb
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21Age of Test, Days
Com
pre
ssiv
e S
trength
, % o
f 28 D
ay,
73°F
(23°C
) Cure
d C
oncre
te
40
20
0
60
80
1 3 7
Mixed and
cured at 55°F (13°C)
Age of Test, Days
Com
pre
ssiv
e S
trength
, % o
f 28 D
ay,
73°F
(23°C
) Cure
d C
oncre
te
40
20
0
60
80
1 3 7
Mixed and
cured at 55°F (13°C)
Early Age Compressive Strength for
Type I and Type III Cement
22
Early Age Compressive Strength For
Type I and Type III Cement
Age of Test, Days
Com
pre
ssiv
e S
tren
gth
, %
of
28 D
ay,
73°F
(2
3°C
) C
ure
d C
oncre
te
40
20
0
60
80
1 3 7
Mixed and
cured at 40°F (4°C)
Type III
Type I
Early Age Compressive Strength for
Type I and Type III Cement
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“An accelerating admixture is a material
added to concrete for the purpose of
reducing the time of setting and
accelerating early strength development.”
“Accelerating admixtures are useful for
modifying the properties of concrete,
particularly in cold weather, to:”
Chemical Admixtures for Concrete
ACI 212.3
24
• Expedite the start of finishing operations
• Reduce the time required for proper curing
and protection
• Increase the rate of early strength
development to permit earlier removal of
forms and earlier opening of construction
for service
Chemical Admixtures for Concrete
ACI 212.3
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Accelerated setting time characteristics
• Earlier finishing of slabs
• Increased early and ultimate strength
• Reduced protection time in cold weather
• Earlier stripping and reuse of forms
Accelerating Admixtures
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Calcium Chloride
Accelerating admixtures containing calcium chloride
Non-chloride accelerating admixtures
Non-chloride accelerating admixtures for use in
concrete placed in sub-freezing temperatures
Classes of Accelerating Admixtures
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• Concrete should never be placed on a
frozen subgrade
• On a frozen subgrade, heat will migrate
rapidly away from the bottom of the
concrete retarding setting time
• Thaw the subgrade not just the surface
• Reschedule for a warmer day!!
Placing Concrete on Ground
Concrete bleeding
Bleed water can freeze on surface
Bleed water capillary channels can freeze within the concrete
Cold subgrades
Rapid migration of heat from concrete will affect setting time
Uneven settlement may occur, causing cracking
Plastic Concrete Problems in Cold Weather
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Surface crusting which can cause:
Blisters
Delamination
Scaling (premature/over finishing)
Finishing Problems in Cold Weather
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All snow, ice and frost must be removed from
forms, reinforcement and other embedments
Must protect from all sides
Use of Type III cement, additional cement and/or
non-chloride accelerators will reduce the length
of protection period, HOWEVER, know the effects
each will have on the plastic and hardened
properties
Cold Weather Concreting Above Ground
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1
2
4
Minimum Concrete temperature as placed and maintained
Minimum concrete temperature as mixed for indicated air temperature
Air Temperature
-
Above 30 °F
Below 0 °F
<12 in. 12-36 in.
55 °F 50 °F
60 °F 55 °F
3 0 to 30 °F 65 °F 60 °F
70 °F 65 °F
Table 3.1 – Recommended Concrete
Temperatures
37
DURATION OF RECOMMENDED PROTECTION FOR % OF
STANDARD-CURED 28-DAY STRENGTH
50 6 9 3
65 11 14 5
85 21 28 16
95 29 35 26
Percentage of
Standard-cured
28-day strength
At 50 °F (10 °C), days
Type of Cement
I II III
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8.1 – Introduction ― “Newly placed concrete
must be protected from drying so that adequate
hydration can occur. Normally, measures must
be taken to prevent evaporation of moisture
from concrete. During cold weather, when the
air temperature is below 50 ºF(10 ºC),
atmospheric conditions in most areas will not
cause excessive drying.”
Concrete Curing
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8.2 - Curing during the protection period
When dry heating is used, the concrete should
be covered with an impervious material or
curing compound.
Water curing is not recommended.
Concrete Curing
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Things to watch
Carbonation CO2
Vent or have heat source from outside
Watch Carbonation from other trades equipment
Watch blowing hot air across a fresh slab
Heating
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8.3 - Curing following the protection
period “…if a curing compound is applied
during the first period of above-freezing
temperature after protection is removed,
the need to conduct further curing
operations if the temperature should rise
above 50 ºF(10 ºC) is eliminated.”
Concrete Curing
46
Effect 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
Com
pre
ssiv
e st
reng
th,
perc
ent
of
28-
day
moi
st-c
ure
d c
oncr
ete
Effect of Curing on Compressive
Strength
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Cylinders should be protected and stored in
protective area between 60°F and 80°F for the first
24 hours.
Record field storage conditions with a high / low
thermometer.
Field cure cylinders for form removal should be
representative of the structure and not used for
quality assurance.
Recommend using maturity meter for in place
strength data.
Testing
49
110
100
80
60
40
20
0
3 6 9 12 18 24
Sta
nd
ard
28
-Da
y C
om
pre
ssiv
e S
tren
gth
Age at which specimens were frozen, in hours
Effect of Freezing on 28-Day
Compressive Strength
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“Work on your project named here shall
conform to all requirements of ACI
306.1,Standard Specification for Cold Weather
Concreting, published by the American
Concrete Institute, Detroit, Michigan, except
as modified by the requirements of these
Contract Documents.”
Sample Cold Weather Spec.
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The entire team must:
Plan ahead
Be prepared
Be concerned
Schedule work
Instruct and inspect
Successful Cold Weather Concreting
Practices
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Quality concrete can be successfully placed at low ambient temperatures
ACI 306R Guide, ACI 306 specification and ACI 308 Guide should be followed
More cement, Type III Cement, heat and/or accelerating admixtures may all be used to accelerate concrete setting time and increase early strength development
Conclusions and Recommendations
53
“Cold Weather Concreting”
Reported by
ACI Committee 306
“Standard Specification for Cold Weather Concreting”
Reported by
ACI Committee 306
“Standard Practice for Curing Concrete”
Reported by
ACI Committee 308
Resources
