es

Thermal Control of C t

nd Code

Concre

t

e

ology an e Techn oncret C
Overview

es nd Cod

 Hot weather concreting

 “External” influences

ology an

 Mass concrete

 “Internal” influences

e Techno oncret C
Hot Weather Concretin

ACI 305 DefinitioACI 305 Definitio

Definitio

“Hot weather is any combination of

Hot weather is any combination of

- high air temperature- high concrete temperature high concrete temperature- low relative humidity- wind velocit

y

- solar radiation...that tends to impair the quality fresh or hardened concrete.”
Hot Weath

C tW 

oncre

te 

W
Questions You Ask Yo

Questions Questions You Ask Yo

Yo

During Hot Weather ?

 What are the effects 

weather on concrete 

 Why are these effects im

the quality of the finished product?
Hot Weather Concreting Probl

Hot Weather Concreting ProbFresh properties Fresh properties

 Increased W

Demand

 Accelerated  Faster Set T Rapid Wate

Evaporation

 Plastic Shrin Difficulties c

entrained ai

 Increased po

thermal crac
Hot Weather Concreting 

Problems

– Hardened Pr

Hardened Pr

 Decreas Drying S Decreas

Durabili

 Increase

Permea
Evaporation of Surface of Surface

Moisture from 

Concrete

 When the rate of evaporation 

exceeds 0.2 lb/ft2 per hour precautionary measures should be taken.

 The use of supplementary 

cementing materials may lower this value.

Concrete Temperatur

Concrete Temperatur

 ACI 211.1 For every 100 l

Cement expect approxima10-15

oF temperature rise 

Heat of Hydration.

 Use tepid f water 

for curing

 After curing, let surface d

sl l ow

y t d th 

to re

duce the poss

of crazing or cracking.
Effect of Concrete Tempera

Water Requirement Water Requirement
Effect of Concrete Temper

on S tti Ti S

etting Time
Effect of Concrete Tempera

on Strength on Strength
Strength vs. Curing Temperat
Adjust the mix for Hot Weather

 Use of SCMs (fly ash, slag cement)

(Can be a double edged sword Can be

a double edged sword)

 Retarders Cool concrete materials Cool concrete materials Moisten aggregates Cool concrete Cool concrete Add plastic fibers
Adjust Placement Pract

Adjust Placement Pract

 Dampen subgrade Reduce the time of 

transport, placing and finishing

 Erect temporary 

windbreaks and sunshades

 Fog over the concrete 

immediately after placing

 Cover concrete


Effect of Temperature of Mate

Concrete Tem

peratures

0.22(

Ta

M

a + 

Tc

M

c) + 

Tw

M

w + 

Twa

Mwa

0 22(

M

M ) M

M

T

=

0.22(

M

a + 

M

c) + 

M

w + 

Mwa

T = temperature of the freshly mixed concrete = temperature of the freshly mixed concreteTa, Tc, Tw, and 

Twa = temperature in °C (°F) of ag

cement, g, added mixin

g water, and free water o

aggregates, respectivelyM

a, M

c, M

w, and 

Mwa = mass, kg (lb), of aggre

cementi i l dd d i i d 

ing materials, add

e

d mixing water, an

d

water on aggregates, respectively

Effect of Ice on 

Temperature of Concre

0.22(

Ta

M

a + 

Tc

M

c) + 

Tw

M

w + 

Twa

Mwa 

– 

0.22(

M

a + 

M

c) + 

M

w + 

Mwa + 

Mi T (oC)

=

a

c

w wa i

0.22(

Ta

M

a + 

Tc

M

c) + 

Tw

M

w + 

Twa

Mwa 

– 

0 22(

M

+

M ) +

M

+

M

+

M T 

(oF)

=

0.22(

M

a

+

M

c) +

M

w

+

Mwa

+

Mi
Placing & Finishing Concrete 

Hot Weather Hot Weather

 Cool equipment Dampen/ cool

- subgrade

- forms- rebar

 Scheduling: evening or night tim

construction

 Windbreaks Sunshades


Fogg g in
Questions on Hot Weat

Concreting?
What is Mass Concret

What is Mass Concret
What is Mass Concret

What is Mass Concret

“Any volume of concrete with dimenlarge enough to require that measutaken to cope with generation of hehydration of the cement and attendahydration hydration of the cement and attenda

attenda

volume change, to minimize crackinvolume change, to minimize crackin

American Concrete Institute (ACI) 

• Thick: Foundations, columns

radiation shielding etc radiation radiation shielding shielding, etc.

• Thin: High Performance (HP

Self Consolidating Concrete (SCC), Grout, Patching mate
W ki D fi i i Working 

D

efi

n

i

t

ion

• Minimum Dimension (Thickness

– No consensus (21⁄2 ft to 7 ft)– ACI 301 ACI 301

-09 will likely say 09 will likely say

≥ 4 

• Cement Content

– Usually not considered – ACI 301 ACI 301

-09 will likely recomm

09 will likely recomm

recomm

a limit
Key Considerations Key Considerations

 Maximum tem

perature

 Can reduce strength and durability

 Tem

perature difference

 Can result in thermal cracking
Maximum Temperature Maximum Temperature

 Often limited 

 No consensus between agencies Safe limit: 160

°F 

(70

°

C

)

 Delayed Ettringite Formation (DEF)

 Concrete mid i x 

design

 Cement (type and quantity) Pozzol( d ) ans 

(type an

d percentage

)
Delayed Ettringite Forma

(DEF)

 Concrete cured at excessively 

high temperatures may develo

p g DEF because ettrin

gite 

decomposes – or does not form at high temperature. 

 Later it forms/reforms after Later it forms/reforms after

the concrete is hard, and may cause expansion.

 DEF i t th t i l DEF is a 

term th

a

t is properly 

applied only to curing at elevated temperatures. It 

d t l t bi t does no

t apply 

to ambien

t

curing.
Expansion of Paste awa

from Aggregate
DEF potential?

 The heat of hydration of cement 

raise the concrete tem

perature to 

above 160°F

 The critical temperature for DEF l

somewhere between 160°F and 1(depends on the cement)

 This is particularly true for cemen

with high fineness( > 400m

2/kg), 

C S hi h C A d hi h lk li t 

3

S, hi

g

h

C

3

A, an

d hi

g

h alk

ali con

t

SO

3/Al

2

O

3 ratio > 0.7
Maximum Temperature

 100% C 70/ 

30 

Cemen

 25/75 

Cemen
Maximum Temperatu

Estimation

Max. Temp. = Initial Temp. + Temp. Rise - L Initial Temperature Initial Temperature

 As low as economically practical (Payback 

 Temperature rise depends on mix design

 Equivalent cement content 

 Loss (Early heat loss) 

 Minimal for placement >5 ft thick 2-6 F per day, depends on R value, dimen
Equivalent Cement 

Content

 1lb/yd

3 of cement = 1 lb/yd

3 equiv. cemen

 1 lb/yd

3 of Class F ash = 0.5 lb/yd3 equiv. ce

1 lb/ d

3 f Cl C h 0 8 lb/ d

3



1 lb/

y

d i 

3

o

f Class 

C as

h = 

0.8 lb/

y

d

3 equiv. c

 1 lb/yd

3 of Slag (50%) = 0.9 lb/yd3 equiv. ce

 1 lb/yd

3 of Slab (75%) = 0 8 lb/yd3 



1 lb/yd of Slab (75%)

=

0.8 lb/yd equiv ce

equiv. ce

 Tem

perature Rise in Concrete

 16°F per 100 lb/yd3 equiv. cement
For example For example

...

Concrete Foundation

400 lb/yd

3 cement and 200 lb/yd

3 class F fly 

70°F delivered concrete

6 ft thick 6 ft thick

Equivalent cement = 400 + 0.5*200 = 500 lb/Tem

perature Rise = 500*16/100 = 80

°

F

Maximum Temperature = 80+70-0 = 150°F
Temperature Differen

Limited to minimize (or prevent) thermal crackin

Temperature difference between interior and surfTemperature difference between interior and surf

Crack width is a function of the temperature diffe
Thermal Cracking Thermal Cracking

 Undesirable, but sometimes una Mostly a durability concern Severe can be a structural issue “Tolerable” limits in ACI 224R
E Th l C ki Extreme Thermal Cracking
More Extreme Therm

More Extreme Therm

Cracking
Somewhat Extreme Therm

Somewhat Extreme Therm

Cracking
T i l Th l C ki Typical Thermal Cracking
More Typical Therma

More Typical Therma

Cracking

Temperature Difference 

Temperature Difference 

 Often limited to a maximum of 3

 Generalized “rule-o

f-thumb”

 Worked for unreinforced dams i

E 75+ urope 75+ years ago

 May not prevent thermal crackin Extends construction time Extends construction time

 Stepped limit

 Steps up with age (35 Steps up with age (35

-45

-60

°F)

 Shortens construction time Can lead to thermal cracking Can lead to thermal cracking

 Tailored limit
Tailored Temperature 

Difference

 Calculation based on ACI 207.2R Performance-based approach Acco nts for concrete’s abilit to Acco

unts for concrete’s ability to

withstand higher thermal stresses as in-place strength increases

 Based on concrete properties Based on structure and design Can be used to prevent cracking or Can be used to prevent cracking or

limit crack widths
Temperature Differen

( ) cont.

)

806070

Diff., °F

4050

Temp. 

102030

llowable Calculated (Exam

Specified 35

°

F

0

10

0 1000 2000 3000 4000 5000 600

AlSpecified 35 F

In-Place Compressive Strength, psi
Temperature Differenc

Time Savings

180140160

re, °F

100120

mperatu Calculated dT

6080

Te

0 10 20 30 40 

Time, Days
Temperature Control 

Strategies

- Use a Reduc

Use

a Reduc

Heat Concrete

 Type I/II, II or V Cement Slag Cement 120

140160180

atu re , °F

 Slag Cement

 50% to 75% replacement

 Fly Ash (Class F) 60

80

100

120

0 5 10 

Tem p e r

 25% to 40% replacement 0 5 10 

Recall that:

1lb/yd3 of cement = 1 lb/yd3 equiv. cement

1 lb/yd3 of Class F ash = 0.5 lb/yd3 equiv. cement

lb/ d3 f l h lb/ d3 1 lb/

y

d3 o

f Class C as

h = 0.8 lb/

y

d3 equiv. cement

1 lb/yd3 of Slag (50%) = 0.9 lb/yd3 equiv. cement

1 lb/yd3 of Slab (75%) = 0.8 lb/yd3 equiv. cement
Temperature Control Stra

–

Pl C i i

lace Concrete 

in Li

 Thick placements take a Thick placements take

a long time to 

time to 

 Multiple distinct placements Thin lifts allow early heat loss Thin lifts allow early heat loss

 Reduced maximum temperature  Faster cooling Faster cooling
Temperature Control 

Strategies

– Precool the Precool the

Concrete

 Precool aggregates

 Evaporative cooling is a very low 

cost solution cost solution

 Chilled mix water 

 Low cost (need chiller plant) Max. reduction of about 5°F

 Substitute ice for mix water

 More expensive More expensive Can be labor intensive  Max. reduction of about 20°F 
Temperature Control 

Strategies

– Precool the Precool the

Concrete (Cont.)

 Liquid Nitrogen (LN2)

 Can re-cool concrete 

multiple times

 Adds time and drum 

rotations 

 Cool onsite or at batch 

plant

 Can be expensive Can be expensive Can be dangerous
Temperature Control 

Strategies 

– Coo

ling Pip

 Remove internal heat after Remove internal heat after

concrete placed

 Reduces maximum tem

perature 

 Reduces cooling time 3⁄4” plastic cooling pipes Grouted afterwards 
Temperature Control 

Strategies 

– Coo

ling Pip

 Large supply of natural water Large supply of natural water

(river, lake, ocean, ground water)

 Chiller
Temperature Control Stra

– Insulation

 Insulation retains surface 

heat to control the temperature difference temperature difference

 Necessary in summer 

and winter and winter
Things to Avoid Things to Avoid

 Water Curing Improper Insulation Improper Insulation Early Removal of 

Insulation
Example: 10 ft dia colum

Example: 10 ft dia. colum

 Performance specifications

 674 pcy minimum cementitious 150

°F maximum temperature 

 No thermal cracking Tailored tem

perature difference
Example (cont ) Example (cont

.

)

 Specially designed 

concrete

 Tight Schedule Used Cooling Pipes Used Maturity
Example (cont.) 130

150

Ambient Air Surface 

p( ) Water Outlet

 Using Calculated temp. 

d ff l

90

110

Temperature, °F difference, Columns 

sufficiently cool in 5 to 6 days 50

70

0123

T

y

Time, Day

• If 20°C(35°F) temp differential F) temp differential differential

specified...

– cooling time increased by 50%– could not meet spec without c

could not meet spec without without c

c

pipes 
Example:

Cl A l i Column Analysis

Concrete in the

Bottom Half of

the Column

Concrete at Top CL

of Column

Full-height Cooling Pipe (4 total)

Hoop/Tie Reinforcing (not all shown)

CL

CL

Su

P

Plan View of the Column

(not to scale)
Day = 0
Assumed Placement Conditions

Concrete Mix No. 1 with 330 pcy slag and 330 pcy cementCooling Pipes Installed and OperatedAverage Air Temperature = 70°F Initial Concrete Temperature = 80°FCooling Water Temperature = 70°FR-2.8 Surface Insulation

Predicted Temperatures (See Drawing No. 3 for Thermocouple Locations)Center Thermocouple = 137°FS f Th l 123°F Surface Thermocouple = 123°FPipe Thermocouple = 117°FLargest Temp. Diff. = 20°F Day = 1
Assumed Placement Conditions

Concrete Mix No. 1 with 330 pcy slag and 330 pcy cementCooling Pipes Installed and OperatedAverage Air Temperature = 70°F Initial Concrete Temperature = 80°FCooling Water Temperature = 70°FR-2.8 Surface Insulation

Predicted Temperatures (See Drawing No. 3 for Thermocouple Locations)Center Thermocouple = 150°FS f Th l 129°F Surface Thermocouple = 129°FPipe Thermocouple = 124°FLargest Temp. Diff. = 26°F Day = 2
Assumed Placement Conditions

Concrete Mix No. 1 with 330 pcy slag and 330 pcy cementCooling Pipes Installed and OperatedAverage Air Temperature = 70°F Initial Concrete Temperature = 80°FCooling Water Temperature = 70°FR-2.8 Surface Insulation

Predicted Temperatures (See Drawing No. 3 for Thermocouple Locations)Center Thermocouple = 146°FS f Th l 123°F Surface Thermocouple = 123°FPipe Thermocouple = 121°FLargest Temp. Diff. = 25°F Day = 3
Assumed Placement Conditions

Concrete Mix No. 1 with 330 pcy slag and 330 pcy cementCooling Pipes Installed and OperatedAverage Air Temperature = 70°F Initial Concrete Temperature = 80°FCooling Water Temperature = 70°FR-2.8 Surface Insulation

Predicted Temperatures (See Drawing No. 3 for Thermocouple Locations)Center Thermocouple = 139°FS f Th l 116°F Surface Thermocouple = 116°FPipe Thermocouple = 116°FLargest Temp. Diff. = 23°F Day = 4
Assumed Placement Conditions

Concrete Mix No. 1 with 330 pcy slag and 330 pcy cementCooling Pipes Installed and OperatedAverage Air Temperature = 70°F Initial Concrete Temperature = 80°FCooling Water Temperature = 70°FR-2.8 Surface Insulation

Predicted Temperatures (See Drawing No. 3 for Thermocouple Locations)Center Thermocouple = 131°FS f Th l 109°F Surface Thermocouple = 109°FPipe Thermocouple = 111°FLargest Temp. Diff. = 21°F Day = 5
Assumed Placement Conditions

Concrete Mix No. 1 with 330 pcy slag and 330 pcy cementCooling Pipes Installed and OperatedAverage Air Temperature = 70°F Initial Concrete Temperature = 80°FCooling Water Temperature = 70°FR-2.8 Surface Insulation

Predicted Temperatures (See Drawing No. 3 for Thermocouple Locations)Center Thermocouple = 123°FS f Th l 104°F Surface Thermocouple = 104°FPipe Thermocouple = 106°FLargest Temp. Diff. = 19°F Day = 6
Assumed Placement Conditions

Concrete Mix No. 1 with 330 pcy slag and 330 pcy cementCooling Pipes Installed and OperatedAverage Air Temperature = 70°F Initial Concrete Temperature = 80°FCooling Water Temperature = 70°FR-2.8 Surface Insulation

Predicted Temperatures (See Drawing No. 3 for Thermocouple Locations)Center Thermocouple = 116°FS f Th l 99°F Surface Thermocouple = 99°FPipe Thermocouple = 101°FLargest Temp. Diff. = 17°F Day = 7
Assumed Placement Conditions

Concrete Mix No. 1 with 330 pcy slag and 330 pcy cementCooling Pipes Installed and OperatedAverage Air Temperature = 70°F Initial Concrete Temperature = 80°FCooling Water Temperature = 70°FR-2.8 Surface Insulation

Predicted Temperatures (See Drawing No. 3 for Thermocouple Locations)Center Thermocouple = 110°FS f Th l 95°F Surface Thermocouple = 95°FPipe Thermocouple = 97°FLargest Temp. Diff. = 15°F Day = 8
Inspector’s Guide to Ma

Concrete 

– Bef l ore P

lace

 Read contractor’s thermal contro Identify initial concrete temperat Identify other rejection criteria Verify cylinder storage area Verify placement equipment Schedule 

personnel and duties

 Verify installed temperature sen Verif

y p gpp 

 o

peration of coolin

g

pipes 
Thermal Control Plan 

( ) TCP

)

 Submittal item

 Must be approved before placement

 Demonstrates contractor’s methods t

 Comply with mass concrete specificat Ensure maximum temperature under 

specified limit) 

 Mi i i / h l ki ( Mi

nimize

/prevent t

hermal cracking 

(s

temperature difference limit)

 Ensure proper curing Ensure proper curing
Contents of a TCP Contents of

a TCP

 Specification Requirements Concrete Placements covered by TCP Concrete Mix Design Predicted Temperatures in Placement

 Assumptions used  Temperature ranges (air, concrete, et Prediction method  Anticipated results
Contents of a TCP (co

Contents of

a TCP (co

 Construction Practices

 Placement method (pump, etc.) Rejection temperature for delivered c Curing method Insulation (materials and installation) Cooling pipe details (if used)

MaterialsInstallationOperation
Contents of a TCP (co

Contents of

a TCP (co

 Construction practices (cont.)

 Temperature monitoring

EquipmentFrequencyR ti epor ng

 Corrective measures

 Completion riteria Completion criteria
Prepour Temperature S

Veri

fication

 Correct e

q p ui

pment and locations

 Per the thermal control plan Typically at center of mass of placemen 2-3” below surface (top or side) Away from pipes, piles, etc. Backup sensors

 Functioning (good data) Wires protected
Prepour Cooling Pipe 

Veri

fication

 Pro

per locations

 Per the thermal control plan Uniform layout

 Water flows through all pipes No leaks Flow rate
Inspector’s Guide to Ma

Concrete 

– During P

lace

 Verify fresh properties Verify concrete temperature wit Verify proper vibration Form pressure issues? Watch cooling pipes and temper

sensors

 Revibration Finishing Curing
Inspector’s Guide to Ma

Concrete

– During Therm

During Therm

Control Period

 Fully insulated concrete and form Cooling pipes operating properly All temperatures within limit Temperature differences within  Contractor adjustments, if neces
Inspector’s Guide to Ma

Concrete

– After Therm

After Therm

Control is Complete

 Cooling pipes grouted, cut below 

and patched

 No thermal cracking Repairs (if necessary)
Summary

 Concrete gets hot!! Concrete gets hot!! Extra measures are needed to 

prevent excessive temperatureand temperature differences.

 Many approaches to thermal 

cont l ro

 Insulation always needed Temperature sensors for Temperature sensors for

verification of thermal control
Questions on Mass 

Concrete?