1. DARWIN AC/AC Overlay Design

2. Course Materials Tables and Design Procedures for this manual

3. Why have a Pavement Course? Pavements are among the most complex structures that an engineer can design!

4. Overlay Designs Minor Overlay (Final elevation is maintained) Mill 2”/Overlay 2” Mill 4”/Overlay 4” Major Overlay Overlay adds structure to the pavement Mill 2”/Overlay 4”

5. Overlay Thickness

6. Effective Structural Number, SN eff The existing pavement structure is based on adjustments based on: Visual Distress Observations FWD Deflections Analysis

7. Layer Coefficients, a i Materialaiai Polymer Modified HMA0.5 HMA (surface and stabilized base)0.44 Granular Base0.14 Granular Subbase0.10

9. FWD Analysis

10. FWD

11. Sensor Spacing SensorD1D2D3D4D5D6D7D8D9 9-Sensor Configuration 0-128122436486072 7-Sensor Configuration 0-121224364872n/a

12. 8” 12” 24” 36” 48” 72” - 12” Sensor Spacing

13. Loads HeightTarget Load Seating9,000 lbs 16,500 lbs 29,000 lbs 312,000 lbs 416,000 lbs

14. FWD Test Spacing Project Size (miles)Test Spacing (feet) Minimum Number of Tests < 0.550-10025 0.5 – 1.0100-15030 1.0 – 3.0150-25040 > 3.025060

15. Subgrade Resilient Modulus, M R C=0.33, convert backcalculated modulus to estimate of lab modulus P = applied load, lbs d r = deflection at r inches from center of the load plate r = distance from the center of the load plate use deflection at r = 60 or 72 inch

16. Effective Modulus of Pavement, E p

17. d o = deflection at center of the load plate, inch p = load plate pressure applied load, lbs (applied load/load plate area) a = load plate radius, inch D = total thickness of pavement above subgrade M R = subgrade resilient modulus, psi E P = Effective modulus of pavement layers above subgrade, psi Effective Modulus of Pavement, Ep

18. dodo EPEP EPEP dodo 5,000d o 5,000 … 100,000d o 100,000 d o from FWD EPEP

19. Temperature Adjustment of E P (mid-depth of AC layers) Darwin adjusts E P to 68 degrees, F o

20. SN eff From FWD Analysis D = Total thickness of the pavement layers above the subgrade, inch E P adj = Temperature Adjusted Effective modulus of pavement layers above the subgrade, psi

21. SN eff From FWD Analysis * E P Adjusted

22. DARWIN EXAMPLE

24. 7 “ HMA = 6” after milling 12 “ DGABC Subgrade Mill 1 “ MR=11,880

25. DARWIN EXAMPLE

26. Traffic Requirements

27. Traffic Mix

28. DARWIN EXAMPLE F1 for Help

29. DARWIN EXAMPLE

32. After milling

33. DARWIN EXAMPLE >1 inch

34. DARWIN EXAMPLE

38. > 1 “

39. DARWIN EXAMPLE

40.       Data Limits (AASHO Road Test) CurrentDesigns >100 million <2 million AXLE LOAD REPETITIONS PAVEMENT THICKNESS Projection A Projection C Projection B Current design traffic is far beyond AASHO road test limits Dilemma – How to project traffic beyond AASHO limits?

41. Input Requirements 1993 AASHTO Design Guide 5 flexible inputs 10 rigid inputs M-E Design Guide (200X) 100+ Total Inputs 35+ Flexible 25+ PCC