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 Non-Structural Rutting Top Down Cracking

5. Materials

6. 123 Before Loading During Loading After Loading - Same Size as Before Loading Figure 1. How an Elastic Material Behaves.

7. Figure 1. Definitions of E and . D  D/2  l ll  l =  l/l  t =  D/D E =   =  l /  t

8. Dynamic Modulus Test

9. Witczak Equation for E* bitumen viscosity (dynamic shear rheometer) loading frequency air voids effective bitumen content 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

10. HMA Modulus Versus Temperature

11. Soil Modulus Testing

12. Dynamic Cone Penetration Rod Reference Mass

13. Effect of Moisture Content

14. FWD Testing

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

16. Traffic

17. Single Tire Dual Tire TandemTridem

18. Layer 1 HMA E 1 Layer 2 Granular Base E 2 Layer 2 Granular Base E 2 Layer 3 Subgrade Soil E 3 h1h1 h2h2 No bottom boundary, assume soil goes on infinitely. No horizontal boundary, assume layers extend infinitely. 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 (  ) Tensile Strain (  t ) Compressive Strain (  v ) Figure 2. Layered Elastic Model Representation of a Pavement.

19. 0 100 200 300 400 2030405060 Wheel Load, kN Transverse Strain,  Test Section 21 Layered Elastic Results Mn/ROAD Measurements 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. HMA Thickness HMA Tensile Strain Layer 1 HMA E 1 h1h1 Tensile Strain (  t ) Thickness vs. Tensile Strain

21. HMA Modulus HMA Tensile Strain Layer 1 HMA E 1 h1h1 Tensile Strain (  t ) Modulus vs. Tensile Strain

22. HMA Thickness Subgrade Compressive Strain E1E1 E2E2E2E2 E2E2E2E2 E3E3 h1h1 h2h2 Compressive Strain (  v ) Thickness vs. Compressive Strain

23. Traditional M-E Design Log N Log 

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

26. tt vv Transfer Functions

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

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

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

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

32. 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.) 10 - 20/wk 3 - 5/wk 10 - 20/wk Low Volume Traffic

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

39. Deterministic Output

40. Probabilistic Output

41. Design Criteria Recommendations

42. PerRoad is available for free at www.AsphaltAlliance.com

43. 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.