Long Life Pavement Fundamentals

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2 Long Life Pavement Fundamentals Dr. David Timm, PE North Dakota Asphalt Conference Bismarck, ND - April

3 Global Roadway Infrastructure Nearly 40 million miles of roads on Earth (2013) Enough roads to circle Earth 1,600 times

4 Global Roadway Mileage Top 5 Countries

5 U.S. Roadway Infrastructure 2,674,821 miles paved 1,417,901 miles unpaved

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7 U.S. Road Report Card (2013)

8 Dakota Report Cards (2013)

9 Road Construction Economics Estimates according to ARTBA Construct new 2-lane undivided road $2-$3 million per mile in rural areas $3-$5 million in urban areas Construct a new 4-lane highway $4-$6 million per mile in rural and suburban areas $8-$10 million per mile in urban areas Construct a new 6-lane Interstate highway $7 million per mile in rural areas $11 million or more per mile in urban areas Expand an Interstate Highway from 4 lanes to 6 lanes about $4 million per mile Mill and resurface a 4-lane road about $1.25 million per mile

10 Evolution of Pavement Thickness Design Pre 1950 s Experience 1960 s Development of Empirical Methods 1980 s Initial Mechanistic- Empirical Methods 1990 s NCRHP 1-37A M-E Design 2000 s Implementation of M-E Methods

11 Flexible Pavement Design in the U.S. - State of the Practice Pierce and McGovern, 2013 NCHRP Project 20-05, Topic 44-06

12 AASHTO Empirical Flexible Pavement Design Method log W Z S 9.36 log SN PSI log SN log 18 R 0 R M 8.07

13 Empirical Method Based on AASHO Road Test HRB, 1962 HRB, 1962

14 Specific Traffic and Climate HRB, 1962 HRB, 1962

15 Flexible Pavement Design Curves HRB, 1962

16 Mechanistic- Empirical Pavement Design H 1 E 1 H 2 E 2 H 3 E 3 H 4 E 4 H 5 E 5

17 AASHTO M-E Design Software

18 Major Limitations of M-E Design Pavement performance prediction Evaluation Calibration Verification Pavements are still designed to fail

19 Long-Life (Perpetual) Pavements 35+ Year Service Minimal Improvements No deep distress Problems only at surface

20 Perpetual Pavements Avoid Deep Structural Problems

21 Perpetual Pavement Cross-Section

22 Mechanistic-Empirical Perpetual Pavement Design P Log e Contact Area D 1 E 1 D 2 E 2 e t D 3 D 4 E 3 E 4 Threshold Strain e v E 5 Log N No Damage Accumulation

23 What is the endurance limit for asphalt concrete? 1972 Monismith estimates about 70 me 2001 I-710 designed at 70 me me used by APA 2007 NCHRP 9-38 Lab Study 100 me for unmodified binders 250 me for modified binders Lab conditions more severe than field 2007 MEPDG uses 100 to 250 me 2008 Measurements at NCAT Test Track show higher strains

24 Measured Strains & Endurance Limit Lab-measured endurance limit

25 Strain Distributions NCAT Test Track 100% 90% No Fatigue Percentile 80% 70% 60% 50% 40% 30% 20% 10% 0% Microstrain Fatigue N N N N N N N N N N N N N N S S

26 Further Evaluation of Criteria Perpetual Pavement Award Winners

27 Perpetual Pavement Metrics

28 Further Evaluation Results Fatigue Cracking

29 Further Valuation Results Rutting

30 Example Designs with New Criteria

31 Design Comparison M-E vs Perpetual Minneapolis 6 30 ksi Agg Base 5 ksi Soil

32 Need for Distribution-Based Design Pavements experience wide range of loading and environmental conditions Results in wide range of strain responses Traditional M-E design uses transfer functions and Miner s Hypothesis to sum damage over time Fatigue transfer functions difficult to develop and may not provide sufficient accuracy Transfer functions not needed with perpetual pavement design Designing with a strain distribution will limit fatigue cracking and avoid transfer functions Also arrive at reasonable perpetual (maximum) pavement thicknesses

33 Long-Life Pavement Design Software Software

34 Cold Central Plant Recycled Perpetual Pavements RAP usage common 81.8 million tons used in 2016 Majority used as HMA or WMA Opportunity to use RAP with cold recycling techniques Fewer virgin materials Less fuel consumption Fewer emissions Faster construction time Cold RAP usage in 2016 = 0.2 million tons

35 Cold Central Plant Recycling Milling Fractionation CCPR Mixing (RAP+recycling agents) Conventional Paving

36 Virginia DOT CCPR Experience 2011: I-81 CIR, FDR & CCPR 6000 trucks/day 2012: NCAT Test Track CCPR and Stabilized Base Sections 10 million ESALs/test cycle 2016: I-64 CCPR and Stabilized Base

37 VDOT Sections at the NCAT Test Track

38 VDOT Test Sections N3-6 AC N4-4 AC S12-4 AC SB CCPR-100% RAP with 2% Foamed and 1% Type II Cement 6 Crushed granite aggregate base and 2 subgrade stabilized in-place with 4% Type II cement

39 Cracking Performance after 20 Million ESALs N3-6 AC N4-4 AC S12-4 AC SB

40 Rutting Performance After 20 Million ESALs

41 Ride Quality after 20 Million ESALs

42 In-Place AC 68F

43 Tensile 68F

44 Perpetual Pavement Analysis

45 Additional Perpetual Analysis

46 Stabilized Base? Use Caution!

47 VDOT Implementation I-64 Williamsburg, VA 7.08 miles 200,000 tons of RAP $10,000,000 savings $88/yd 2 $42/yd 2

48 Future Challenges SMA RAP RAS pg GTR WMA CIR

49 U.S. Asphalt Concrete Industry WMA RAS RAP

50 Concluding Remarks Pavement thickness design in transition From empirical to mechanistic-empirical M-E design much more robust Better traffic/climate/materials/performance characterization Capable of adapting to new conditions Perpetual pavements are key to sustainable future Incorporation of sustainable materials is critical Innovative materials can achieve long-life

51 Thank you! Reach me at

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