Perpetual Pavement Design

1. Perpetual Pavement Design Perpetual Pavement Open House Ashton, Iowa October 5, 2005

2. Overview • Pavement design background • Layered elastic theory • Perpetual pavement design philosophy • Design basics

3. Goal of Perpetual Pavement Design • Design the structure such that there are no deep structural distresses • Bottom up fatigue cracking • Structural rutting • All distresses can be quickly remedied from surface • Result in a structure with ‘Perpetual’ or ‘Long Life’

4. Surface Distresses Only Top Down Cracking Non-Structural Rutting

5. Materials

6. 1 2 3 After Loading - Same Size as Before Loading Before Loading During Loading Figure 1. How an Elastic Material Behaves.

7. D DD/2 s Dl l el = Dl/l E = s/e et = DD/D m = el/et Figure 1. Definitions of E and m.

8. Dynamic Modulus Test

9. Witczak Equation for E* • cum. % retained on 19-mm sieve • cum. % retained on 9.5-mm sieve • cum. % retained on 4.76-mm sieve • % passing the 0.075-mm sieve • bitumen viscosity (dynamic shear rheometer) • loading frequency • air voids • effective bitumen content

10. HMA Modulus VersusTemperature

11. Soil Modulus Testing

12. Dynamic Cone Penetration Mass Rod Reference

13. Effect of Moisture Content

14. FWD Testing

15. Backcalculation E = f(Load, Pressure, Deflection, Distance)

16. Traffic

17. Single Tire Dual Tire Tandem Tridem

18. Tire has a total load P, spread over a circular area with a radius of a, resulting in a contact pressure of p. Pavement Reactions Deflection (d) Layer 1 HMA E1 No horizontal boundary, assume layers extend infinitely. h1 Tensile Strain (et) Layer 2 Granular Base E2 h2 Layer 3 Subgrade Soil E3 Compressive Strain (ev) No bottom boundary, assume soil goes on infinitely. Figure 2. Layered Elastic Model Representation of a Pavement.

19. 400 Test Section 21 Mn/ROAD Measurements 300 me 200 TransverseStrain, Layered Elastic Results 100 0 20 30 40 50 60 Wheel Load, kN Figure 4. A Comparison of Measured Strains and Computed Strains at Mn/ROAD. (After Timm et al., 1998, Development of Mechanistic- Empirical Pavement Design, Transportation Research Record No. 1629, Transportation Research Board, Washington, DC.)

20. Layer 1 HMA E1 h1 Tensile Strain (et) Thickness vs. Tensile Strain HMA Tensile Strain HMA Thickness

21. Layer 1 HMA E1 h1 Tensile Strain (et) Modulus vs. Tensile Strain HMA Tensile Strain HMA Modulus

22. E1 h1 E2 h2 Subgrade Compressive Strain Compressive Strain (ev) E3 HMA Thickness Thickness vs. Compressive Strain

23. Log e Log N Traditional M-E Design

24. Log e Threshold Strain Log N No Damage Accumulation Perpetual Pavement Design

26. Transfer Functions et ev

27. Miner’s Hypothesis • Provides the ability to sum damage for a specific distress type • D =  ni/Ni  1.0 where ni = actual number of loads during condition i Ni = allowable number of loads during condition i

28. 1200 1200 1200 Normal Range for Region of Damage Accumulation 1000 1000 1000 Fatigue Testing No Damage Accumulation 800 800 800 Strain, (10E-06) Strain, (10E-06) Strain, (10E-06) 600 600 600 400 400 400 Endurance Limit Endurance Limit Endurance Limit 200 200 200 0 0 0 1000 1000 1000 100000 100000 100000 10000000 10000000 10000000 1.1E+08 1.1E+08 1.1E+08 Number of Loads to Failure Number of Loads to Failure Number of Loads to Failure

29. f f Axle Weight Thickness f Monte Carlo Random Sampling Mechanistic Model Material Properties % Below Threshold f % Above Threshold Pavement Response Probabilistic Design – Monte Carlo Simulation

30. How much ‘damage’ does this area correspond to? % Below Threshold • Design should have high % below threshold f % Below Threshold Pavement Response

31. ‘Damage Computation’ • For responses exceeding threshold, compute N using transfer function • User defined • Calculate damage accumulation rate • Damage / MESAL f % Below Threshold Damage MESAL Pavement Response

32. Low Volume Traffic 10 - 20/wk 3 - 5/wk 10 - 20/wk Estimated Long Life • Convert damage rate into an estimated life • Use traffic volume and growth • Calculate when damage = 0.1 • Use for Low Vol. Roads (t ~30 yrs.)

33. PerRoad 2.4 • Sponsored by APA • Developed at Auburn University / NCAT • M-E Perpetual Pavement Design and Analysis Tool • Help File is the Users Manual • Press F1 at Any Time for Help File

38. Deterministic Output

39. Probabilistic Output

40. Design Criteria Recommendations

41. PerRoad is available for freeatwww.AsphaltAlliance.com

42. P.S. • TxDOT intends to incorporate PerRoad in its next generation design procedure. • One-day workshop is available at the request of Iowa Asphalt Paving Association - Work out the dates with Mike.