Why Monitor Concrete Temperature?And How?

Peter Taylor

What Are We Talking About?

• Maturity• Isothermal Conduction Calorimetry• Field Semi-Adiabatic Calorimetry• Heat of Hydration• Setting Time

Definitions

• Isothermal (constant temperature)• Adiabatic (no energy transfer)• Semi-adiabatic (some, known, energy

transfer)

Maturity

• Using a time/temperature function to estimate strength (or other property)

• No thermal control

Why?

•• Replaces TemperatureReplaces Temperature--Matched Matched Curing of Cylinders in Thermal Curing of Cylinders in Thermal Control PlansControl Plans

•• Can Reduce Construction TimeCan Reduce Construction Time

• Use laboratory testing to develop a relationship

• Monitor concrete using temperature probes

How?

Note: Maturity testing does not indicate quality of concrete

ASTM C1074 Maturity

•• TimeTime--Temperature Factor (Temperature Factor (°°FF··hr)hr)

•• Equivalent Age (days)Equivalent Age (days)

t)T-(T=Mt

0=to

te=Mt

0=t

T1-

T1Q-

sa

Footing Example

0

10

20

30

40

50

60

0 1 2 3 4 5 6 7

Time, Days

Tem

pera

ture

, °C

Center Top Bottom

7 Day Equivalent Age7 Day Equivalent Age

But…

•• Maturity relation required for each Maturity relation required for each mixmix

•• Provides an estimate of a property Provides an estimate of a property based on indirect measurementsbased on indirect measurements

Calorimetry

• Measuring heat in paste mixtures to assess hydration kinetics

• i.e. How do system chemistry, admixtures and SCMS influence hydration

• Isothermal

How?

How?

Heat sink

Test Sample

Reference Sample

Peltier Sensors

Why?

0

5

10

15

20

25

0:00:00 6:00:00 12:00:00 18:00:00 24:00:00

Time of Hydration (hrs)

J/gh

Sample "1PA"Sample "2PA"Sample "3PA"Sample "4PA"Sample "5PA"Sample "6PA"

Why?

Hydration Profile

0.00

3.00

6.00

9.00

12.00

15.00

0:00:00 6:00:00 12:00:00 18:00:00 24:00:00

Time of Hydration (hrs)

J/gh

Sample "5P"Sample "5C"Sample "5F"Sample "5S"

Why?

Effect of Water Reducer Dosage on Hydration

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0:00:00 6:00:00 12:00:00 18:00:00 24:00:00

Time of Hydration (hrs)

J/gh

No Adm WRA x1

WRA x2

Why?

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25 30 35 40 45

Time of Hydration (hours)

Hea

t (m

V)

But…

•• Small paste samplesSmall paste samples

•• Fixed temperatureFixed temperature

•• May not flag all aluminate reaction May not flag all aluminate reaction problemsproblems

•• Takes up to 24 hoursTakes up to 24 hours

•• Other techniques?Other techniques?

Field Semi-Adiabatic Calorimetry• Measuring heat in mortar /concrete

to assess hydration kinetics• i.e. Is the system hydrating?• Semi(ish) adiabatic

How?

Why?

Why?

Gary KnightGary Knight

But…

•• CoarseCoarse

•• Takes timeTakes time

Heat of Hydration

• Measuring heat generated by a cementitious system (paste)

• Used for heat calculations in mass concrete

• Adiabatic / Semi adiabatic

Why?

How?

•• ASTM C ASTM C 186186

•• CalorimeterCalorimeter

•• Concrete Concrete cubecube

How?

0

50

100

150

200

250

300

350

0:00 24:00 48:00 72:00 96:00 120:00 144:00 168:00

Time of Hydration, hrs

J/g

CTLGroupCTLGroup

But…

•• Not standardizedNot standardized

•• yetyet

Time of Set

• Using temperature monitoring to measure time of set

• Semi-adiabatic

Why?

CTLGroupCTLGroup

0

1000

2000

3000

4000

5000

0 2 4 6 8

Hours

Pene

trom

eter

, psi

90

95

100

105

110

115

Tem

pera

ture

, °F

ASTM C 403Thermocouple

Initial set

Initial Set

0

5

10

15

20

0 5 10 15 20ASTM C 403, hours

Ther

moc

oupl

e, h

ours

CTLGroupCTLGroup

• Useful data can be collected•For characterizing materials•Investigating interactions•Tracking uniformity•Timing finishing activities•Tracking hydration

• Use the right equipment for the right application

Summary