hot and cold weather concrete and freeze-thaw resistance ......cold & hot weather & freezing...

Structural Engineers Assn. of OhioCold & Hot Weather & Freezing

September 14, 2012

Ken Hover, P.E., Cornell [email protected] 1

Hot and Cold Weather Concrete andandFreeze-Thaw Resistance

Ken Hover, P.E.Cornell University

High Low

Evap

orat

ivit

y

High HotDry

ColdDry

Concrete Temperature

Low HotWet

CoolWet

High Low

Evap

orat

ivit

y

High

Moisture Effects

Temperature Effects


Low

Temperature Effects The Weather Challenge in OhioThe Weather Challenge in Ohio


September 14, 2012


Columbus, Ohio Monthly Average Temperatures

http://www.city-data.com/city/Columbus-Ohio.html

Why Concrete TemperatureConcrete TemperatureMatters

1.) Reaction only proceeds in a “water-filled space”

2.) Rate of reaction exponentially dependent on temperature

3.) Volume depends on extent of reaction and loss of water

Hydration

2

3

4

-10 0 10 20 30 40

Concrete Temperature (C)

ydra

tio

n R

ate

d t

o L

ab C

ure

200 %

11C 36C23C

0 20 40 60 80 100 120

0

1

Concrete Temperature (F)

Rel

ativ

e H

Co

mp

are d

50 %

100 %

52 F 96 F73 F

ydra

tio

n R

ate

d t

o L

ab C

ure


of

Fre

ezin

g

2

3

4

-10 0 10 20 30 40


Rel

ativ

e H

Co

mp

are d

Ris

k

0 20 40 60 80 100 120

0

1


September 14, 2012


Net lossdue tofreezing

8

12

16

-10 0 10 20 30 40Concrete Temperature (C)

Set

tin

g T

ime

d t

o L

ab C

ure

0 20 40 60 80 100 120

0

4


Rel

ativ

e

Co

mp

are d

TemperatureandandStages in the Life of Concrete

52F = 50% Hydration rate compared to73F Lab Temp

52FC = 200%Set Time compared to73F Lab Temp



TemperatureandandWater Demand for Workability Increased Water Demand with

Higher Concrete Temperature

About 1 gallon / yard per 10 degrees F


September 14, 2012


TemperatureandandCompressive Strength

3000

4000

5000

6000

ve S

tren

gth

(p

si)

Curing Temperature (C)

20

30

40

ve

Str

eng

th (

MP

a)

13 23 32 41 49

Curing Temperature ( F)

0

1000

2000

Co

mp

ress

iv

0

10 Co

mp

ress

iv

55 73 90 105 120

1 day strength

3000

4000

5000

6000

ve

Str

eng

th (

psi

)

Curing Temperature (C)

20

30

40

ve

Str

en

gth

(M

Pa)

13 23 32 41 49

28 day strength

Curing Temperature ( F)

0

1000

2000

Co

mp

ress

iv

0

10 Co

mp

res

siv

55 73 90 105 120

1 day strengthb lConstructability

Problems!

52F = 50% Hydration rate compared to73F Lab Temp

52FC = 200%Set Time compared to73F Lab Temp



These Observations Lead to Concrete Temperature

Specifications


September 14, 2012


40 50 60 70 80 90 100 110 120

High Low28

-day

Opt

imum

Std

. Lab

Cur

e

Spe

cifie

d M

ax.

F Spe

cifie

d M

in.

0 10 20 30 40 50


C

75

80

per

atu

re (

F)

National Highway InstituteConcrete Materials Module

University of Nevada at Reno, 1997

25

0 30 60 90 120Minutes after Batching

60

65

70

Co

ncr

ete

Te

mp

15

20

Heat of HydrationHeat of Hydration

Heat of Hydration

Heat of Hydration

6 Sack Mix =6 Sack Mix =

564 lb x 190 BTU =

107,000 BTU / CY

4 – 150 W lamps

564 lb Cement / CY

640 Watts / CY


September 14, 2012


Cold Weather ConcretingCold Weather Concreting ydra

tio

n R

ate

d t

o L

ab C

ure


of

Fre

ezin

g

2

3

4

-10 0 10 20 30 40


Rel

ativ

e H

Co

mp

are d

Ris

k

0 20 40 60 80 100 120

0

1

Hot Weather ConcretingHot Weather Concreting


September 14, 2012


Moisture MattersMoisture Matters

1.) Reaction only proceeds in a “water-filled space”

2.) Rate of reaction exponentially dependent on temperature

3.) Product depends on extent of reaction and loss of water

Hydration

Surface Drying and ShrinkageSurface Drying and Shrinkage

How soon until this concrete starts to dry?Concrete Slab on Ground in dry air

1.) Bleed water appears on concrete surface

2.) Bleed water evaporates

3.) Drying of concrete surface


September 14, 2012


Pre

ssu

re

Low Humidity Air

vapo

ratio

n

Water Temperature

Wat

er V

apor

Ev

WIND

Texas Evaporation

0 10

0.20

0.30

ativ

ity

/hr

0.05 lb/ft2/hr, Va. SF Overlay

-0.20

-0.10

0.00

0.10

0 90 180 270 360Days From Jan 1

Eva

po

ra

lb/f

t2/

Freeze Thaw Damage andDeicer Scaling Resistance


September 14, 2012


Control porosity by controlling water

Control Finishing

Curing & Shrinkage control

Freeze Thaw Damage and Deicer Scaling Resistance

Curing & Shrinkage control

Temperature Control

Frost-Resistant Aggregate

Air-Entrained Paste

Air Entrained Concrete

• Concrete to which a detergent has b i t ti ll dd d f thbeen intentionally added for the purpose of stabilizing air bubbles formed during the concrete-mixing process.

Air VoidDisadvantages

• Strength Reduction– Porous Paste

• Aggregate InterfaceR i d C ti• Required Compensations– Lower water content– Admixtures– Higher cement content

• Cost• Heat• Shrinkage


September 14, 2012


Clustering of Air BubblesDisadvantages

• Stickiness

• Finishing Problems– Bleeding Plastic Cracking Delaminations– Bleeding, Plastic Cracking, Delaminations

• Variable Volume – Yield problems

• Interaction with other admixtures

ACI 302 - Construction of Floors

• Entrained air not recommended when smooth, dense, hard troweled finish required

ACI 301 S ifi tiACI 301 - Specification

• Intentionally entrained air should not be incorporated in normalweight concrete slabs to be given a smooth, dense, hard troweled finish.

Porous Paste

Random

Air Voids

Air Voids

point: freezing begins

Ice Expands

High Pressure

Low Pressure

p

Water and Ice move in direction of least resistance

The longer the flow path,

The higher the pressure

High Pressure

Low Pressure

High Pressure

The Longer the line, the higher the pressure for a given pumping rate.


September 14, 2012


The LESS permeablethe concrete,

The higher the pressure

High Pressure

Low Pressure

High Pressure

pressure

The smaller the hose diameter, the higher the pressure for a given flow rate.

How far can water and ice travel in the capillary pores until the pressure cracks

the paste?

“0.010 INCHES

OR THEREABOUTS”

10 mil poly slab underlayment

~ 10 mils~ 10 mils

~ 10 mils

~ 10 mils

Double thickness = 20 mils

“0.020 INCHES

OR THEREABOUTS”


September 14, 2012


Does a Large Air Void protect more paste than

a Small Air Void?

YES!

Costs200-250 psiPer percent

This is why we want the air

voids!

Protected Paste:Asset

Air Void Volume:Liability

Air Volume

And leads to other problems

like delayed bleeding and

blisters


a Small Air Void?

Does a Small Air Void protect

more pastePER PERCENT

Air Volumethan a Large Air

Void?

YES!

The smaller the air void, the higher the ratio of Asset/Liability!

Absolutely!


a Small Air Void?

Does a Small Air Void protect

more pastePER PERCENT

Air Volume|than a Large Air

Void?

YES!

Absolutely!

The smaller the air void, the higher the ratio of Protected Paste Volume/Air Content

•Large number of small voids

•Well distributed in paste

Wanted:

•Well distributed in paste•Prefer bubbles around 5 mils•< About 10 mils to nearest bubble•Air vol about 18% of paste vol


September 14, 2012


Characteristics of AE ConcreteCharacteristics of AE Concrete

••44--8% air bubbles by volume of concrete8% air bubbles by volume of concrete

••1 to 2 ft1 to 2 ft33 Air bubbles / CYAir bubbles / CY

••1010--15 billion air bubbles / CY15 billion air bubbles / CY

Characteristics of AE ConcreteCharacteristics of AE Concrete

••44--8% air bubbles by volume of concrete8% air bubbles by volume of concrete

••1 to 2 ft1 to 2 ft33 Air bubbles / CYAir bubbles / CY

••1010--15 billion air bubbles / CY15 billion air bubbles / CY1010 15 billion air bubbles / CY15 billion air bubbles / CY

••2 million in2 million in22 of air bubble surface area / CYof air bubble surface area / CY

••1500 SY of bubble surface area / CY1500 SY of bubble surface area / CY

••Bubble Size Matters!Bubble Size Matters!

1010 15 billion air bubbles / CY15 billion air bubbles / CY

••2 million in2 million in22 of air bubble surface area / CYof air bubble surface area / CY

••1500 SY of bubble surface area / CY1500 SY of bubble surface area / CY

••Bubble Size Matters!Bubble Size Matters!

How much Air do you need?

• How much paste do you have to protect?

H i th ?• How severe is the exposure?

• Who are you asking?

6

7

8

9

10

11

en

t in

Co

ncr

ete

(%

)

90 95 100 105 110 115 120Water Content kg/m3

Average Bubble Radius = 7 mils


430 in2/ in

3

500 in

2/in3

600 in2/in3

0.007 in.

0.006

0.005

w/c = 0.45

250 260 270 280 290 300 310 320 330 340 350Water Content lb/CY

1

2

3

4

5

6

Re

qui

red

Air

Co

nte




750 in2/in3

1000 in2/in3

0.004

0.003


September 14, 2012


60

80

100

120

Durability Vs. Spacing Factor

y F

acto

r

0.008

0

20

40

60

0 0.005 0.01 0.015 0.02 0.025 0.03

Computed Spacing Factor

Du

rab

ilit

y

Materials Issues

• Frost-Resistant Aggregate

• w/c or w/cm 0.45

• Controlled water content• Controlled water content

• Air content 18-22% of paste content

• Periodic check of air bubble size

• Periodic check of air bubble stability

• Control the water

SCM’s and Scaling• Slag/FA/OPC concrete can be scale-

resistant.

• Air quality key. Charcoal is the problem.

• Cure for at least 7 days• Cure for at least 7 days.

• Finish on time. (Delayed Bleeding)

• Slag & Fly Ash may be more sensitive to poor construction practice than OPC.

• Late season placement needs protection

Construction Issues

• Control water

• Periodic check of air stability

• Timing of finishing operations• Timing of finishing operations

• No surface water addition

• Wet curing


September 14, 2012


Standard Specs won’t produce scaling resistance! p g

Specifying Freeze-Thaw Resistance

• W/C max = 0.45 (in-place)

• Air content = 18% paste vol

• In place spacing factor max 0 010• In place spacing factor max 0.010

• Check ability of materials to stabilize a satisfactory air void system

Specifying Scale Resistant Concrete

• W/C max = 0.45 (in-place)• Wet cure 7 days (truly wet)• Air vol = 20% of paste volAir vol 20% of paste vol• Spacing factor < = 0.008 inches• Check ability of materials to stabilize a

satisfactory air void system • Timing of Finishing is critical

– Not too soon / not too late

hot and cold weather concrete and freeze-thaw resistance ......cold & hot weather & freezing...

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