Laboratory Evaluation of Fiber-Reinforced Polymer Dowel Bars for Jointed Concrete Pavements

Transcription

1 Laboratory Evaluation of Fiber-Reinforced Polymer Dowel Bars for Jointed Concrete Pavements Yi Bian Erwin Kohler John Harvey TRB Annual Meeting, Washington D.C. January 24 th, 2007

2 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

3 UCPRC Project on Dowel Bar Retrofit General objective: Evaluate DBR and best options for implementation Work components 1. APT testing 2. Lab testing steel dowel corrosion FRP 3. Field Live Traffic Testing 4. Modeling (FEM, LCCA)

4 APT Testing

5 HVS testing, Ukiah Epoxy-coated steel dowels Results: No damage to any of the DBR joints, or loss of LTE Greater increase in deflections at non-dbr joints

6 HVS testing, Palmdale Results: 1. Epoxy-coated steel 2. Hollow stainless steel dowels 3. Fiber-reinforced polymer (FRP) No damage to any of the DBR joints, or loss of LTE Fatigue cracking of the slab

7 Ukiah DBR 553 HVS 554 HVS 554 LT 555 HVS 553 LT 555 LT

8 Palmdale DBR 559 HVS 557 HVS 556 HVS 558 HVS EpoxyHollow Epoxy Epoxy Epoxy Epoxy Epoxy FRP FRP EpoxyEpoxy Epoxy (3) Epoxy Epoxy Epoxy Epoxy FRP FRP (3) Epoxy FRP FRP Epoxy FRP FRP Epoxy Hollow Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy (3) Epoxy Epoxy Epoxy Epoxy (3)

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10 Dowel types in Palmdale DBR 1. Epoxy-coated steel 2. Hollow stainless steel dowel 3. Fiberreinforced polymer (FRP)

11 Lab: Corrosion of steel dowels

12 Lab testing: corrosion 1. bare carbon steel 2. stainless steel clad 3. grout-filled hollow stainless steel 4. microcomposite steel 5. 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 used 2. Epoxy dowels present risk of corrosion at scrapes and the ends 3. Recommend use of stainless steel clad, hollow stainless steel, or micro-composite for locations with risk of high chloride exposure

13 Regular steel dowels

14 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

15 Problems at joints w/corroded bars Corrosion products expand and lock the joints Expansive products Fe(OH) 2 ), (Fe 3 O 4 ) and (Fe 2 O 3 ) Volume 6 times greater Decreased LTE due to volume reduction after the corrosion products are washed away Cracking concrete Corrosion spalling & transverse cracking

16 Lab: FRP Evaluation

17 FRP High strength-to-weight ratio Excellent resistance to electrochemical corrosion Used extensively to repair and strengthen reinforced concrete beams and columns

18 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?

19 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

20 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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22 Conditioning 1. Alkaline solution 2. Water 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 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)

23 Results outline Flexural Tests Flexural Stiffness Flexural Strength Flexural Fatigue Shear Tests Shear Strength Shear Fatigue Direct shear strength

24 Flexural Stiffness Stiffness (GPa) Control Alkali conditioned Water conditioned UV conditioned 5.3x10 6 psi 6.4x10 6 psi 0 Type A Type B 1. Type B is 20% stiffer than Type A bars 2. Type A bars unaffected by conditioning processes 3. 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%

25 Effect of loading frequency, temperature, and conditioning Stiffness (GPa) Stiffness (GPa) Test at 5 C 2 Hz 6 Hz 10 Hz Test at 20 C Loading Frequency Type B Type A 2 Hz 6 Hz 10 Hz Loading Frequency Type B Type A C 40 C 20 C Stiffness (GPa) Test at 40 C 2 Hz 6 Hz 10 Hz 1. Type B is stiffer than Type A bars 2. Frequency (2 to 10 Hz) had no effect on dowel stiffness 3. Temperature effect Type B Type A Control Alkali Water UV

26 Stiffness versus temperature 50 Control Alkali Stiffness (GPa) Type B Water UV At 40 C bars are softer than at 20 C. 9 % for Type A 15%for Type B Type A Temperature (C) Should not significantly impair the pavement s performance: FEM max concrete stress is mostly unaffected when dowel stiffness changes 10 20%

27 Flexural Strength Flexural stregth (MPa) Control Alkali conditioned Water conditioned UV conditioned 72x10 3 psi Type A 130x10 3 psi Type B 1. Type B strength is 80% greater than Type A 2. 1% < COV < 4%, except for one (two replicates). 3. Type B alkali conditioned bars: COV =19% (four replicates) More on that

28 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

29 Flexural Fatigue 100,000,000 10,000,000 Flexural fatigue Life, n (cycles) 1,000, ,000 10,000 1,000 Type A - control Type B - control Type A - alkali Type B - alkali 100 Type A - water Type B - water Type A - UV Type B - UV 10 Type A regression Type B regression Combined Types A & B Stress ratio, S n = 10 ( S), R 2 =

30 Stiffness during flexural fatigue Elastic Modlulus (GPa) Type A - control, S=0.54 Type A - control, S=0.58 Type A - alkali, S=0.49 Type A - water, S=0.57 Type A - UV, S=0.56 Type B - control, S=0.45 Type B - control, S=0.50 Type B - alkali, S=0.49 Type B - water, S=0.48 Type B - UV, S= Load cycle (millions) All tested specimens tend to fail when the stiffness drop to GPa

31 Shear strength Shear Strength (MPa) Control Alkali conditioned Water conditioned UV conditioned Type A Type B

32 Shear fatigue life 1,000,000, ,000,000 Shear fatigue life, n (cycles). 10,000,000 1,000, ,000 10,000 1, Type A - control Type A - alkali Type A - water Type A - UV Type A regression Type B - control Type B - alkali Type B - water Type B - UV Type B regression Stress ratio, S Type A > Type B bars in shear fatigue life

33 Direct shear

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35 Direct shear strength Direct shear strength (MPa) Control Alkali conditioned Water conditioned UV conditioned 0 Type A Type B

36 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 bars Type A bars are ~30% stronger than steel

37 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

38 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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41 Thanks Erwin Kohler University of California Pavement Research Center Project Scientist, PhD Civil and Environmental Engineering, UC-Davis