Post on 21-Jul-2020
transcript
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