coefficient of thermal expansion of concrete pavements - kohler.pdf · erwin kohler ramon alvarado...

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

Importance of CTE for pavements

• Joint opening LTE• Thermal curling cracking• Joint sealant perf. spalling• Even potential for

catastrophic failures such as blow ups

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)

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

CTE in ME-PDG

• Transverse crack predictions highly dependent on the assumed CTE value

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

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)

Testing Procedure

AASHTO TP60 + recommendations by Texas DOT

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

Steps to test CTE (cont’d)

Steps to test CTE (cont’d)

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

Software’s screen capture

5.11

5.12

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.

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

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

) .

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

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

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 )

Effect of concrete saturation

• 1 oven-dried core, saturated for 4 days• 2 oven-dried cores, immediate test

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)

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)

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

50 rigid pavement sites, 56 composite pavement sites (ac overlay)

• 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.

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

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

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

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

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

Thanks

Erwin KohlerUniversity of California Pavement Research Center

Project Scientist, PhDCivil and Environmental Engineering, UC-Davis

530-754-8699

ekohler@ucdavis.edu