coefficient of thermal expansion of concrete pavements - kohler.pdf · erwin kohler ramon alvarado...
TRANSCRIPT
![Page 1: Coefficient of Thermal Expansion of Concrete Pavements - KOHLER.pdf · Erwin Kohler Ramon Alvarado David Jones University of California Pavement Research Center Coefficient of Thermal](https://reader035.vdocument.in/reader035/viewer/2022062911/5c09025409d3f2a9648c892c/html5/thumbnails/1.jpg)
Erwin KohlerRamon Alvarado
David Jones
University of California Pavement Research Center
Coefficient of Thermal Expansion of Concrete Pavements
TRB Annual Meeting, Washington D.C.January 24th, 2007
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Importance of CTE for pavements
• Joint opening LTE• Thermal curling cracking• Joint sealant perf. spalling• Even potential for
catastrophic failures such as blow ups
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FHWA CTE Testing
• FHWA has CTE from over 1,800 samples• Lab cast and drilled cores from LTPP
sections • Result from 670 tests is that CTE ranges
between 5.0 and 7.0 microstrain/°F. • Objective: validating data for the
Mechanistic-Empirical Pavement Design Guide (ME-PDG)
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TxDOT CTE Testing
• Concretes made with coarse aggregates from > 30 sources in Texas
• Large variance in CTE with concrete containing river gravels,
• More consistent CTE with crushed limestone aggregates
• Objective: improve reinforcement design and construction specs for CRCP
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CTE in ME-PDG
• Transverse crack predictions highly dependent on the assumed CTE value
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Variable Factor Levels
1 COTE (2) 4 × 10-6/ºF 7 × 10e-6/ºF
2 Axle Load Spectra (2) Urban Rural
3 Traffic Volume (1) TI: 16
4 PCC Thickness (2) 9 in. 12 in.
5 Base Type (1) Cement Treated Base
6 Dowels (2) Dowels No Dowels
7 Shoulder Type (3) Asphalt Shoulders Tied Shoulders Widened Truck Lane
8 Joint Spacing (2) 15 ft. 19 ft.
9 Climate Regions (3) Mountain Valley South Coast
10 Subgrade Type (1) SP 11 Strength (1) 626 psi Total Number of Cases: 288
Experiment to Study Effect of CTE
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Effect on cracking and faulting
• 4 × 10-6/ºF corresponds to limestone or granite aggregate; • 7 × 10-6/ºF corresponds to quartzite, cherts
4 7
0
20
40
60
80
100
% Slabs Cracked
0.0
0.2
0.4
0.6
Faulting (in.)
4 7CTE (x10-6/ºF)CTE (x10-6/ºF)
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Testing Procedure
AASHTO TP60 + recommendations by Texas DOT
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Steps to test CTE
1. Specimen preparation : - 100mm (4 inches) diameter cores- Cut flat surfaces top and bottom- Length from 165 to 210mm (6 ½ to 8 ¼ inches)
2. Submerge specimen in limewater for at least 2 days.
3. Measure exact length of the specimen4. Specimen is placed in the testing frame which
is submerged in water5. Test
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Steps to test CTE (cont’d)
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Steps to test CTE (cont’d)
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Temperature sequenceStep Temperature Duration
1 10°C 30min
2 Change from 10°C to 50°C
2hr 15min
3 50°C 30min
4 Change from 50°C to 10°C
2hr 15min
5 10°C 30min
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Software’s screen capture
5.11
5.12
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Thermal cycling
1. The thermal cycling is automatically repeated three times to obtain more stable readings, as explained later
2. Each cycle takes ~6 hours entire test is ~18 hours.
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Frame correction• Correction to account for
thermal deformation on the frame that supports the LVDT.
• Correction obtained using cylinders of known CTE:–3 stainless steel 304 –3 aluminum 6061 T-6
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Regression to determine CTE
Test 1, rising: CTE=6.40y = 0.002x - 0.0449R2 = 0.99995
Test 1, falling: CTE=6.10y = 0.0019x - 0.0382R2 = 0.9994
Test 2, rising: CTE=6.63y = 0.002x + 0.0797R2 = 0.9999
Test 2, falling: CTE=6.60y = 0.002x + 0.0805R2 = 0.9997
-0.05
0
0.05
0.1
0.15
0.2
10 15 20 25 30 35 40 45 50 55Temperature (C)
Rel
ativ
e di
spla
cem
ent (
mm
) .
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Effect of consecutive thermal cycles
• Better regressions are obtained with consecutive thermal cycles
• Reduction in the difference between the rising and falling CTE
• Lower CTE
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Effect of consecutive thermal cycles
0.99700
0.99750
0.99800
0.99850
0.99900
0.99950
1 2 3
Thermal Cycle
R2
5.4
5.5
5.6
5.7
5.8
5.9
6.0
1 2 3
Thermal CycleC
TE (m
icro
stra
in/F
) .
Rising(heating)
Falling(cooling)
CTE decreases with additional cycles:3rd CTE is lower than 1st CTE in 76% of cases3rd CTE is lower than 1st CTE by 0.1 /°F in 48% of cases3rd CTE was on average 0.15 /°F lower than 1st CTE
R2 CTE
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3rd CTE vs 1st CTE
4.0
4.5
5.0
5.5
6.0
6.5
7.0
4.0 4.5 5.0 5.5 6.0 6.5 7.0
1st CTE (10-6/°F )
3rd
CTE
(10
-6/°
F )
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Effect of concrete saturation
• 1 oven-dried core, saturated for 4 days• 2 oven-dried cores, immediate test
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CTE at high saturation levels
85%
90%
95%
100%
105%
0 24 48 72 96 120 144 168 192 216 240 264 288
Time (hours)
Satu
ratio
n (%
) .
3
4
5
6
7
8
9
97% 98% 99% 100% 101%
Saturation (%)
CTE
(mic
rost
rain
/°F)
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Oven-dried cores, immediate test
3
4
5
6
7
8
9
0 10 20 30 40 50
CTE
(mic
rost
rain
/°F)
RisingFalling
3
4
5
6
7
8
9
0 10 20 30 40 50
Time (hours)
CTE
(mic
rost
rain
/°F)
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Comparison With Results From Other Laboratories
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
TX-1 FHWA-1 FHWA-2 FHWA-3 FHWA-4 TX-2
CTE
(mic
rost
rain
/F)
UCPRCTX or FHWA
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50 rigid pavement sites, 56 composite pavement sites (ac overlay)
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• Mechanistic inputs being collected– thickness, joint spacing, accumulated traffic, subgrade
type, solar reflectivity, etc.
• Data will be used to verify the effect of CTE and other factors on concrete pavements.
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Histograms of CTE values
0
2
4
6
8
10
12
14
4.5 5 5.5 6 6.5 7
District 4n=42
0
2
4
6
8
10
12
14
4.5 5 5.5 6 6.5 7
Num
ber o
f cor
es
District 2n=9
0
2
4
6
8
10
12
14
4.5 5 5.5 6 6.5 7
CTE (microstrain/F)
District 11n=4
0
2
4
6
8
10
12
14
4.5 5 5.5 6 6.5 7
Num
ber o
f cor
esAll
data
0
2
4
6
8
10
12
14
4.5 5 5.5 6 6.5 7
CTE (microstrain/F)
Num
ber o
f cor
es
District 10n=19
across the state: 4.5 to 6.7 microstrain/°F.
District 2 : 6.3District 4 : 5.2 District 10: 6.4 District 11: 5.5
Geographical Variability
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Aggregate types in CA
• District 2:–alluvial or glacial deposits. A mix of
sedimentary (sandstone) and volcanic (basalt) rocks
• Districts 4 and 10:–sedimentary (predominantly sandstone), more
angular and probably quarried. • District 11:
–predominantly granitic and probably quarried
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CTE spatial variability
3.03.54.0
4.55.05.56.0
6.57.0
13.0 13.5 14.0 14.5 15.0 15.5
Postmile
CTE
(mic
rost
rain
/°F) Northbound
Southbound
Site 4-SCL-85
3.03.54.0
4.55.05.56.0
6.57.0
4.0 6.0 8.0 10.0 12.0
Postmile
CTE
(mic
rost
rain
/°F)
Eastbound
Westbound
Site 10-SJ-580
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CTE spatial variability
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
15.0 20.0 25.0 30.0 35.0 40.0 45.0
Postmile
CTE
(mic
rost
rain
/°F) .
Eastbound
Site 4-SOL-80
3.03.54.0
4.55.05.56.0
6.57.0
50.0 50.5 51.0 51.5 52.0 52.5 53.0 53.5
CTE
(mic
rost
rain
/°F) Northbound
Southbound
Site 4-SON-101
3.03.54.0
4.55.05.56.0
6.57.0
25.0 30.0 35.0 40.0 45.0
Postmile
CTE
(mic
rost
rain
/°F)
Northbound
Southbound
Site 2-SHA-5
3.03.54.0
4.55.05.56.0
6.57.0
20.0 25.0 30.0 35.0 40.0
CTE
(mic
rost
rain
/°F) Southbound
Site 11-IMP-86
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Summary and Conclusions
• CTE being evaluated from in-service pavements in California
• Involves thermal cycles in a waterbath• Range is 4.5 to 6.7 microstrain/°F• 3-cycle testing is good practice:
–Better regressions –Reduction in difference between ramps–(Lower CTE)
• Continue work
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Thanks
Erwin KohlerUniversity of California Pavement Research Center
Project Scientist, PhDCivil and Environmental Engineering, UC-Davis
530-754-8699