laboratory evaluation of fiber-reinforced polymer dowel bars for
TRANSCRIPT
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Yi BianErwin KohlerJohn Harvey
Laboratory Evaluation of Fiber-Reinforced Polymer Dowel Bars for Jointed Concrete
Pavements
TRB Annual Meeting, Washington D.C.January 24th, 2007
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Introduction• LTE controls ride quality and structural life • LTE by aggregate interlock or dowel bars• Aggregate interlock reduced by
– abrasion & shrinkage– slabs thermal contraction
• Steel dowel bars are susceptible to corrosion• Low LTE cracking & faulting
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UCPRC Project on Dowel Bar Retrofit
• General objective: Evaluate DBR and best options for implementation
• Work components1. APT testing2. Lab testing
– steel dowel corrosion– FRP
3. Field Live Traffic Testing 4. …Modeling (FEM, LCCA)
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APT Testing
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HVS testing, Ukiah
Results: – No damage to any of the DBR
joints, or loss of LTE– Greater increase in deflections at
non-DBR joints
Epoxy-coated steel dowels
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HVS testing, Palmdale
Results: – No damage to any of the DBR
joints, or loss of LTE– Fatigue cracking of the slab
1. Epoxy-coated steel2. Hollow stainless steel dowels3. Fiber-reinforced polymer (FRP)
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500 1 2 3 5 6 7 8 9 10 11 1213 14 15 16 17 184 19 20 21 22 23 24 4647 4849454443424140393837363534
333231
302926 282725
554 LT554 HVS553 HVS 555 LT553 LT555 HVS
7 8 9 10
15 16 17
Ukiah DBR
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Epoxy
Epoxy
32 33 34
Epoxy
Hollow
Epoxy
Epoxy
35 36
Epoxy (3)
Epoxy (3)38 39
Epoxy
Epoxy
Epoxy
Epoxy
559 HVS
32 33 34 35 36 37 38 39 40 41 42 43 44 45
557 HVS 558 HVS556 HVS
Epoxy
EpoxyEpoxy
Hollow Epoxy
Epoxy
Epoxy (3)Epoxy (3)
Epoxy
Epoxy
Epoxy
Epoxy Epoxy FRP
FRP
FRP
Palmdale DBR
41 42 43
FRP
FRP
FRP
FRP
Epoxy
Epoxy
Epoxy FRP
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Dowel types in Palmdale DBR1. Epoxy-coated
steel
2. Hollow stainless steel dowel
3. Fiber-reinforced polymer(FRP)
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Lab: Corrosion of steel dowels
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Lab testing: corrosion1. bare carbon steel2. stainless steel clad3. grout-filled hollow stainless steel4. microcomposite steel5. carbon steel coated with flexible epoxy (green)6. carbon steel coated with non-flexible epoxies (purple)7. carbon steel coated with non-flexible epoxies (gray)
Results: 1. Recommend that uncoated carbon steel
dowels not be used2. Epoxy dowels present risk of corrosion at
scrapes and the ends3. Recommend use of stainless steel clad,
hollow stainless steel, or micro-composite for locations with risk of high chloride exposure
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Regular steel dowels
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Epoxy-coated steel
• Defects are inevitable – pinholes, voids and mechanical scrapes & scratches
(macroscopic and microscopic)
• Localized corrosion initiated at the defects accumulated oxide will further lift the coat
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Problems at joints w/corroded bars
• Corrosion products expand and lock the joints – Expansive products Fe(OH)2), (Fe3O4) and (Fe2O3)
Volume 6 times greater
• Decreased LTE due to volume reduction after the corrosion products are washed away
• Cracking concreteCorrosion spalling & transverse cracking
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Lab: FRP Evaluation
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FRP
• High strength-to-weight ratio • Excellent resistance to electrochemical
corrosion• Used extensively to repair and strengthen
reinforced concrete beams and columns
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Caltrans’ Questions
• Are the mechanical properties of FRP dowels adequate to perform acceptably (compared to steel dowels)?
• Are the FRP mechanical characteristics negatively affected by environmental factors?
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Experimental Set Up • The study consisted of evaluating the flexural and shear
properties of glass FRP dowel bars• 1.5-in diameter and 18-in long, from 2 manufacturers
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Properties of the FRP dowel bars
Type A Type B
Glass fiber content 70% Min. 65%, typical 72-73%
Glass type E-type glass E-type glass
Matrix type Polyester resin Epoxy Vinyl Ester resin
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Conditioning
1. Alkaline solution • glass FRP could be highly sensitive to alkaline attack • specimens submerged in alkali solution for 3 months • pH level for the alkali solution was 13.5
2. Water• Simulate high moisture content• submerged in water for 3 months in plastic tanks
3. Ultraviolet radiation• bond dissociation between fiber and matrix• bars exposed to direct sunshine for 2 months (July and August)
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Results outline
• Flexural Tests–Flexural Stiffness–Flexural Strength–Flexural Fatigue
• Shear Tests–Shear Strength–Shear Fatigue
• Direct shear strength
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Flexural Stiffness
1. Type B is 20% stiffer than Type A bars2. Type A bars unaffected by conditioning
processes3. Stiffness in conditioned Type B bars decreased:
- 4% for water conditioned - 6% for UV conditioned specimens
- 20°C - Avg loading freq. of 2, 6, and 10 Hz - Two replicates- COV <2%
0
5
10
15
20
25
30
35
40
45
50
Type A Type B
Stiff
ness
(GPa
)
Control Alkali conditioned Water conditioned UV conditioned
5.3x106 psi 6.4x106 psi
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Effect of loading frequency, temperature, and conditioning
1. Type B is stiffer than Type A bars
2. Frequency (2 to 10 Hz) had no effect on dowel stiffness
3. Temperature effect
25
30
3540
45
50
2 Hz 6 Hz 10 HzLoading Frequency
Stif
fnes
s (G
Pa) Test at 5°C
Type B
Type A
253035404550
2 Hz 6 Hz 10 Hz
Loading Frequency
Stif
fnes
s (G
Pa) Test at 20°C
Type B
Type A
253035404550
2 Hz 6 Hz 10 Hz
Stif
fnes
s (G
Pa) Control
AlkaliWaterUV
Test at 40°C
Type B
Type A
5°C 40°C
20°C
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Stiffness versus temperature
25
30
35
40
45
50
0 5 10 15 20 25 30 35 40 45Temperature (C)
Stiff
ness
(GPa
)
Control Alkali
Water UV
Type B
Type A
At 40°C bars are softer than at 20°C.
9 % for Type A 15%for Type B
Should not significantly impair the pavement’s performance:
FEM max concrete stress is mostly unaffected when dowel stiffness changes 10 – 20%
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Flexural Strength
0
100
200
300
400
500
600
700
800
900
1000
Type A Type B
Flex
ural
stre
gth
(MPa
)Control Alkali conditioned Water conditioned UV conditioned
1. Type B strength is 80% greater than Type A2. 1% < COV < 4%, except for one (two replicates).3. Type B alkali conditioned bars:
• COV =19% (four replicates)• More on that
72x103 psi 130x103 psi
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Damage on Type B bars after exposure to alkaline solution
• Visible cracks on one or both ends of the dowel• Cracks could be observed before any load application • Only on alkali conditioned specimens
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Flexural Fatigue
1
10
100
1,000
10,000
100,000
1,000,000
10,000,000
100,000,000
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Stress ratio, S
Flex
ural
fatig
ue L
ife, n
(cyc
les)
Type A - control Type B - controlType A - alkali Type B - alkaliType A - water Type B - waterType A - UV Type B - UVType A regression Type B regressionCombined Types A & B
n = 10(12.75 – 12.74×S), R2 = 0.9475
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Stiffness during flexural fatigue
0
5
10
15
20
25
30
35
40
45
0 1 2 3 4 5 6Load cycle (millions)
Elas
tic M
odlu
lus (
GPa
)
Type A - control, S=0.54 Type B - control, S=0.45Type A - control, S=0.58 Type B - control, S=0.50Type A - alkali, S=0.49 Type B - alkali, S=0.49Type A - water, S=0.57 Type B - water, S=0.48Type A - UV, S=0.56 Type B - UV, S=0.49
All tested specimens tend to fail when the stiffness drop to 15 – 20 GPa
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Shear strength
0
100
200
300
400
500
600
700
800
900
1000
Type A Type B
Shea
r Stre
ngth
(MPa
) .
Control Alkali conditioned Water conditioned UV conditioned
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Shear fatigue life
1
10
100
1,000
10,000
100,000
1,000,000
10,000,000
100,000,000
1,000,000,000
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Stress ratio, S
Shea
r fat
igue
life
, n (c
ycle
s) .
Type A - control Type B - controlType A - alkali Type B - alkaliType A - water Type B - waterType A - UV Type B - UVType A regression Type B regression
Type A > Type B bars in shear fatigue life
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Direct shear
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0
50
100
150
200
250
300
350
400
450
500
Type A Type B
Dire
ct s
hear
stre
ngth
(MP
a) .
ControlAlkali conditionedWater conditionedUV conditioned
Direct shear strength
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Summary and conclusions
1. Stiffness for FRP bars:• It’s not influenced by loading frequency
(in the range of 2 to 10 Hz)
• It is affected by testing temperature (<20% at 40°C)2. Type B bars are ~20% stiffer, 80% stronger in
bending, and 100% stronger in shear than Type A bars
In bending, Type B are two times stronger than typical steel barsType A bars are ~30% stronger than steel
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Summary and conclusions
3. Strength of Type B bars might be reduced by the high pH environment within the concrete slabs
– Type A bars were not affected by any of the three conditioning types
– Water and UV conditioning had no effect in either Type A or B bars
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Summary and conclusions
4. Fatigue– both types of bars offer similar flexural
fatigue performance – greater number of shear cycles can be
expected from Type A bars – At low stress ratio (0.3 to 0.4), both types of
FRP bars will likely survive more than 100 millions wheel load repetitions
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Thanks
Erwin KohlerUniversity of California Pavement Research Center
Project Scientist, PhDCivil and Environmental Engineering, UC-Davis
530-754-8699