BUILDING A BETTER PERPETUAL PAVEMENT Richard Willis Maryland Quality Initiative January 25, 2017 Baltimore, Maryland
Introduction Perpetual Pavements OVERVIEW Perpetual Pavement Design Examples Environmental Performance
Courtesy of David Timm Introduction Layers are necessary to provide economy while protecting weak materials 3
Courtesy of David Timm Introduction 4
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
Courtesy of David Timm Evolution of Pavement Design http://www.pcgerms.com/wp-content/uploads/2012/08/evolution-of-technology-e1344530962564.jpg 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
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, 2002 7
The Misconception More = better Just keep adding thickness Truth vs. Practicality 1993 AASHTO Design Guide 8
Washington Study (Mahoney) Long-lasting pavements thinner than many other pavements built Fatigue resistance Right materials in the right places 9
Changing Times 10
M-E Pavement Design 11
Limitation #1 Vertical Compression Critical Location: Top of Subgrade Distress: Subgrade or structural rutting Thicker or stiffer pavements disperse stress 12
Limitation #2 Horizontal Strain Critical Location: Bottom of Asphalt Pavement Distress: Fatigue Cracking Pulling pavement apart 13
The Perpetual Pavement Diet 14
A Word of Warning 15
Getting in Shape 16
Newcomb et al. Perpetual Pavement Structure Rut Resistant Surface Layer 17
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
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
Change Your Mind Sometimes called a sacrificial layer In 15-20 years, milled and replaced This must be a high quality mixture Performance test based? APA, Hamburg, Flow Number 20
Step #2 High Modulus Layer High modulus = stiff The Good Reduce overall necessary thickness or Reduce tensile strains of equivalent thickness 21
Step #2 High Modulus Layer The Bad: Cracking? Hamstring pull Know where to place them Minimal strains near center of pavement structure 22
Strength Training 23
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
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) 60-100με 1000 100 10 1 10 100 1000 log cycles 25
Translation 26
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
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
Fatigue Endurance Limits Mixture Description Fatigue Endurance Limit (FEL), microstrain S9-3 Control 92 N10-3 50% RAP - HMA 100 N11-3 50% RAP - WMA 134 S10-3 WMA Foam 99 S11-3 WMA Additive 84 N5-4 Thiopave 109 N7-3 Kraton 241 S12-3 TLA 137 29
So What?? How does this impact me? AASHTOWare Pavement M-E States have own tools and systems PerRoad 4.2 30
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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
Two main 10,000 ft runways; 7,000 ft runway, taxiways, and ramps Built in 1949 12 in gravel sub-base 10 in bank gravel HMA 1.5 in stone HMA Ensured subgrade compaction during process 38
1964 1 in overlay 1973 4 in overlay Heavier plans 1987 3 in mill and fill 2002 95% of base HMA still in service 39
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
www.asphaltpavement.org/epds Environmental Product Declarations
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 www.asphaltpavement.org/epd Environmental Product Declarations
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