Extending Asphalt Pavement Life Using Thin Whitetopping
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Extending Asphalt Pavement Life Using Thin Whitetopping

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The thin white topping (TWT) can be a cost-effective measure that extends the life of existing asphalt pavements. This project is aimed at calibrating the TWT design method developed by the Colorado ...

The thin white topping (TWT) can be a cost-effective measure that extends the life of existing asphalt pavements. This project is aimed at calibrating the TWT design method developed by the Colorado Department of Transportation using data from an experiment conducted under the accelerated pavement testing (APT) program at Kansas State University.

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  • Tensile stress increases about 160% for the change in interface condition from fully bonded to completely unbonded. TWT thickness has a more pronounced effect on an unbonded interface condition than a bonded condition.
  • As interface bonding condition plays a major role on the behavior of TWT, partial bonding between the interfaces is also considered in this study. For this purpose, frictional coefficients other than 1 (for bonded condition) were assumed at the interface. This resulted in a considerable drop in transverse tensile stress for an unpaved shoulder condition but did not show any significant effect for the paved shoulder condition.
  • Tensile stress significantly decreases with an increase in TWT thickness. For unbonded TWT and an unpaved shoulder, the effect of TWT thickness is more pronounced than other conditions.
  • As higher AC thickness enhances the underlying support to TWT, PCC stress decreases with the increase of AC thickness, .
  • Existing AC modulus is representative of existing AC pavement condition. With the increase in AC modulus, PCC stress decreases. The AC modulus has less effect on unbonded PCC stress than the bonded one.
  • A paved shoulder provides lateral support to pavement. Thus, the addition of a paved shoulder decreases the transverse tensile stress of TWT.

Extending Asphalt Pavement Life Using Thin Whitetopping Presentation Transcript

  • 1. Extending Asphalt Pavement Life Using Thin Whitetopping Mustaque Hossain, Ph.D., P.E. Department of Civil Engineering Kansas State University
  • 2. Disclaimer The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presentedherein. This document is disseminated under thesponsorship of the Department of Transportation University Transportation Centers Program, in the interest of information exchange. The U.S.Government assumes no liability for the contents or use thereof.
  • 3. Acknowledgements Sharmin SultanaUniversity of Texas, Austin Slide design © 2009, Mid-America Transportation Center. All rights reserved.
  • 4. Outline Background Objective Modeling of Thin Whitetopping Pavement Results Conclusions Recommendations
  • 5. Background Whitetopping is the process of rehabilitating asphalt concrete (AC) pavements using a concrete overlay There are three types of whitetopping:  Conventional: thickness > 8 in.  Thin: thickness = 4-8 in.  Ultra-thin: thickness < 4 in.
  • 6. Thin Whitetopping Pavement (US 287, Lamar, Colorado)
  • 7. Thin Whitetopping Construction (I-70, Salina, Kansas)
  • 8. Thin Whitetopping Pavement (I-70, Salina, Kansas)
  • 9. Background Whitetopping Interface Bonding Condition:  Bonded  Unbonded (After Rasmussen and Rozycki 2004)
  • 10. Background Cases where whitetopping is feasible:  Existing AC pavements highly deteriorated (rutted and cracked)  Adequate vertical clearance  No AC layer settlement issues
  • 11. Background Existing design procedures for whitetopping:  AASHTO*  Colorado*  New Jersey  PCA/ACPA  Modified ACPA  Illinois  Texas* * Thin whitetopping only
  • 12. Objectives To assess the behavior of thin whitetopping (TWT) with respect to:  Thin whitetopping thickness (5 in., 6 in., and 7.5 in.)  Existing AC thickness (5 in., 7 in., and 9 in.)  Interface bonding conditions (Bonded and Unbonded)  Existing AC modulus (250 ksi and 350 ksi)  Shoulder (Unpaved or Paved)  Temperature gradient To estimate the service life
  • 13. Finite Element Modeling Structure: Thin whitetopping (TWT) on existing AC pavement FE software: SolidWorks Pavement model: A three-layer pavement system:  TWT  Existing HMA/AC layer  Subgrade layer (After McGhee 1994)
  • 14. Finite Element Modeling Layer materials: Isotropic and linear elastic Mesh: High quality Symmetry: Both geometry and loading Pavement segment : 3-ft. wide & 30-in. in depth Joint spacing: 6 ft.
  • 15. Finite Element ModelsWith Tied and Paved Shoulder No Tied or Paved Shoulder
  • 16. Model Loading• Loading: 20,000 lbs on a single axle with dual tires (legal load in Kansas)• Loaded area: Rectangular, normal, uniform, and equal to the tire inflation pressure• Self weight: Considered for all layers
  • 17. Model LoadingNo Paved Shoulder Paved Shoulder (After Dumitru 2006)
  • 18. Analysis Results• The critical response, maximum transverse tensile stress, was found at the bottom of the thin whitetopping (TWT) layer• It varied from 75 psi for bonded 7.5-in. TWT to as much as 442 psi for unbonded 5-in. TWT
  • 19. Effect of Interface Condition 500 450 400 350 PCC Stress (psi) 300 5 in.TWT 250 6 in. TWT 200 7.5 in.TWT 150 100 50 0 Bonded Unbonded Interface Condition
  • 20. Effect of Interface Condition 450 400 400 350 350 300 300 250 250PCC Stress (psi) PCC Stress (psi) AC Modulus 200 AC Modulus 200 250 ksi 250 ksi AC Modulus AC Modulus 350 ksi 150 350 ksi 150 100 100 50 50 0 0 Bonded 0.75 0.5 0.25 0 Bonded 0.75 0.5 0.25 0 Frictional Coefficiant Frictional Coefficiant Unpaved Shoulder Paved Shoulder
  • 21. Effect of TWT Thickness PCC Stress vs. Bonded Unpaved TWT Thickness PCC Stress vs. Unbonded Unpaved TWT Thickness (AC Modulus 250 ksi) (AC Modulus 250 ksi) 500 500 450 450 400 400 350 350 300 300PCC Stress (psi) 5 in.AC 5 in.AC PCC Stress (psi) 250 7 in. AC 250 7 in. AC 200 9 in.AC 9 in.AC 200 150 150 100 100 50 50 0 0 5 6 7.5 5 6 7.5 TWT Thickness (in.) TWT Thickness (in.) Bonded TWT with Paved Shoulder Unbonded TWT with No Shoulder
  • 22. Effect of AC Thickness 180 160 140 120PCC Stress (psi) 100 5 in.TWT 80 6 in. TWT 7.5 in.TWT 60 40 20 0 5 7 9 AC Thickness (in.)
  • 23. Effect of Existing AC Modulus 180 160 140 PCC Stress (psi) 120 100 5 in.AC 80 7 in. AC 9 in.AC 60 40 20 0 250 350 AC Modulus (ksi)
  • 24. Effect of Paved Shoulder 180 160 140PCC Stress (psi) 120 100 5 in.AC 80 7 in. AC 9 in.AC 60 40 20 0 Unpaved Paved Shoulder Condition
  • 25. Effect of Temperature Gradient 250 200Curling Stress (psi) 150 Bonded Unbonded 100 50 0 5 6 7.5 TWT Thickness (in)
  • 26. Computation of Service Life• In PCA method, allowable load repetitions are calculated based on the stress ratio (= calculated tensile stress/ modulus of rupture)• If the stress ratio is less than 0.45, the pavement can take unlimited load repetitions
  • 27. PCA model• For S.R. > 0.55 0.97187 − SR log 10 ( N ) = 0.0828 3.268• For 0.45 ≤ S.R. ≤ 0.55 N =   4.2577   SR − .43248  0• For SR < 0.45 N=UnlimitedS.R. = ration of flexural stress to modulus of raptureN = number of allowable load repetitions
  • 28. Service Life (full bonding) (for various ADTT level) 12 10Service Life (yrs) 8 ≤200 300 6 400 500 4 2 0 5 6 7.5 TWT Thickness (in.)
  • 29. Service Life (unbonded TWT & 5” AC) (250 ksi AC Modulus and Unpaved Shoulder) (350 ksi AC Modulus and Unpaved Shoulder) 12 12 10 10 Service Life (yrs) 8 Service Life (yrs) ≤200 8 ≤200 300 6 300 400 6 400 4 500 500 4 2 2 0 5 6 7.5 0 5 6 7.5 TWT Thickness (in.) TWT Thickness (in.) (AC, 250 ksi AC Modulus and Paved Shoulder) (AC, 350 ksi AC Modulus and Paved Shoulder) 12 12 10 10 Service Life (yrs) 8Service Life (yrs) 8 ≤200 ≤200 300 300 6 6 400 400 500 4 500 4 2 2 0 0 5 6 7.5 5 6 7.5 TWT Thickness (in.) TWT Thickness (in.)
  • 30. Service Life (unbonded TWT & 7” AC) (250 ksi AC Modulus and Unpaved Shoulder) (350 ksi AC Modulus and Unpaved Shoulder) 12 12 10 10Service Life (yrs) Service Life (yrs) 8 8 ≤200 ≤200 300 300 6 6 400 400 500 500 4 4 2 2 0 0 5 6 7.5 5 6 7.5 TWT Thickness (in.) TWT Thickness (in.) (250 ksi AC Modulus and Paved Shoulder) (350 ksi AC Modulus and Paved Shoulder) 12 12 10 10 Service Life (yrs) Service Life (yrs) 8 8 ≤200 ≤200 300 300 6 6 400 400 500 500 4 4 2 2 0 0 5 6 7.5 5 6 7.5 TWT Thickness (in.) TWT Thickness (in.)
  • 31. Service Life (unbonded TWT and 9” AC) 12 10Service Life (yrs) 8 ≤200 300 6 400 500 4 2 0 5 6 7.5 TWT Thickness (in.)
  • 32. Conclusions• Interface bonding is the most important factor that affects the longevity of thin whitetopping• Bonding has a more pronounced effect on transverse tensile stress for the unpaved shoulder condition than that of the tied and paved shoulder condition• Thin whitetopping thickness has a more pronounced effect for the unbonded interface condition than the bonded condition
  • 33. Conclusions (cont.)• Tied, paved PCC shoulder decreases stresses in thin whitetopping• Tied, paved PCC shoulder is particularly useful for unbonded thin whitetopping with low truck traffic
  • 34. Recommendations• Field experimentation to investigate actual behavior of thin whitetopping• The effect of environment, subgrade soil types, and different joint spacing can be investigated
  • 35. Recommendations (cont.)• Pavement response under moving loads would give a better approximation of the actual scenario• Partial bonding at the interface should be investigated as it is very difficult to achieve full bonding in the field
  • 36. Thank You!