BUILDING A BETTER PERPETUAL PAVEMENT

Transcription

1 BUILDING A BETTER PERPETUAL PAVEMENT Richard Willis Maryland Quality Initiative January 25, 2017 Baltimore, Maryland

2 Introduction Perpetual Pavements OVERVIEW Perpetual Pavement Design Examples Environmental Performance

3 Courtesy of David Timm Introduction Layers are necessary to provide economy while protecting weak materials 3

4 Courtesy of David Timm Introduction 4

5 HOW A FLEXIBLE PAVEMENT WORKS Courtesy of David Timm Two functions Provide sufficient total pavement thickness above any material to prevent permanent deformation Provide enough surface thickness to prevent fatigue cracking Layered approach to distribute load over weaker materials

6 Courtesy of David Timm Evolution of Pavement 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 6

7 Perpetual Pavements an asphalt pavement designed and built to last longer than 50 years without requiring major structural rehabilitation or reconstruction, and needing only periodic surface renewal in response to distresses confined to the top of the pavement APA,

8 The Misconception More = better Just keep adding thickness Truth vs. Practicality 1993 AASHTO Design Guide 8

9 Washington Study (Mahoney) Long-lasting pavements thinner than many other pavements built Fatigue resistance Right materials in the right places 9

10 Changing Times 10

11 M-E Pavement Design 11

12 Limitation #1 Vertical Compression Critical Location: Top of Subgrade Distress: Subgrade or structural rutting Thicker or stiffer pavements disperse stress 12

13 Limitation #2 Horizontal Strain Critical Location: Bottom of Asphalt Pavement Distress: Fatigue Cracking Pulling pavement apart 13

14 The Perpetual Pavement Diet 14

15 A Word of Warning 15

16 Getting in Shape 16

17 Newcomb et al. Perpetual Pavement Structure Rut Resistant Surface Layer 17

18 Step 1: Rut Resistant Surface Designed to protect the other pavement layers Without this, the other layers can t do their job Design ideas? 18

19 Options for Surface Mixtures Good dense-graded mix Stone-matrix asphalt RAP and RAS? Choose appropriate binder grade Balancing rutting and cracking Too stiff vs. too soft 19

20 Change Your Mind Sometimes called a sacrificial layer In years, milled and replaced This must be a high quality mixture Performance test based? APA, Hamburg, Flow Number 20

21 Step #2 High Modulus Layer High modulus = stiff The Good Reduce overall necessary thickness or Reduce tensile strains of equivalent thickness 21

22 Step #2 High Modulus Layer The Bad: Cracking? Hamstring pull Know where to place them Minimal strains near center of pavement structure 22

23 Strength Training 23

24 Step #3 Get Flexible Fatigue resistant base layer to prevent fatigue cracking High strain tolerance Need will depend on structure Stiffer structure = reduced strain If stiff enough or thick enough, FRBL not necessary But we want thinner, so... 24

25 log microstrain Fatigue Endurance Limits The horizontal asymptote of the relationship between the applied stress or strain and the number of load repetitions, such that a lower stress or strain will result in an infinite number of load repetitions (Von Quintus, 2001) με log cycles 25

26 Translation 26

27 Fatigue Life Use a softer binder Allows mix to stretch without cracking Use more binder Most common method Rich-bottom layer Bump AC or design for lower air voids (2-3%) Better compaction Improves fatigue resistance Does not influence rutting Reduces moisture susceptibility 27

28 Fatigue Resistance of Mixtures Numerous technologies can be used for mixtures Must appropriately select materials for structure Can use recycled materials; however, must understand structure of pavement 28

29 Fatigue Endurance Limits Mixture Description Fatigue Endurance Limit (FEL), microstrain S9-3 Control 92 N % RAP - HMA 100 N % RAP - WMA 134 S10-3 WMA Foam 99 S11-3 WMA Additive 84 N5-4 Thiopave 109 N7-3 Kraton 241 S12-3 TLA

30 So What?? How does this impact me? AASHTOWare Pavement M-E States have own tools and systems PerRoad

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37 Are Perpetual Pavements Real? Asphalt Pavement Alliance Award Minimum 35 years of service life No more than 4 inches of added structure Average minimum 13 years between rehabs 37

38 Two main 10,000 ft runways; 7,000 ft runway, taxiways, and ramps Built in in gravel sub-base 10 in bank gravel HMA 1.5 in stone HMA Ensured subgrade compaction during process 38

39 in overlay in overlay Heavier plans in mill and fill % of base HMA still in service 39

40 The state of Maryland is extremely proud of the men and women who have built and maintained Baltimore/Washington International Airport over the last 52 years. BWI has grown into the busiest airport in the Washington region and the durability of its airfield has provided a strong foundation for that success. Paul J. Wiedefeld, Executive Director of Maryland Aviation Administration 40

41 Environmental Product Declarations

42 An EPD Program for Asphalt Mixtures Program created and overseen by industry Web tool to aid contractors to receive EPDs Fast to get EPDs Easy to use Saves money Launches at NAPA Annual Meeting Environmental Product Declarations

43 Thank you