BUILDING A BETTER PERPETUAL PAVEMENT

Richard Willis

Maryland Quality Initiative

January 25, 2017

Baltimore, Maryland

OVERVIEW

Introduction

Perpetual Pavements

Perpetual Pavement Design

Examples

Environmental Performance

3

Introduction

• Layers are necessary to provide economy while

protecting ‘weak’ materials

Courtesy of David Timm

4

Introduction

Courtesy of David Timm

HOW A FLEXIBLE

PAVEMENTWORKS

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

Evolution of Pavement

Design

Courtesy of David Timm

Pre 1950’s

Experience

1960’s

Development of

Empirical Methods

1980’s

Initial

Mechanistic-

Empirical

Methods

http://www.pcgerms.com/wp-content/uploads/2012/08/Evolution-of-technology-e1344530962564.jpg

1990’s

NCRHP 1-37A

M-E Design

2000’s

Implementation

of M-E Methods

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, 2002

8

The Misconception

• More = better

• Just keep adding thickness

• Truth vs. Practicality

• 1993 AASHTO Design Guide

9

Washington Study (Mahoney)

• Long-lasting pavements thinner than many other

pavements built

–Fatigue resistance

–Right materials in the right places

10

Changing Times

11

M-E Pavement Design

12

Limitation #1

Vertical Compression

• Critical Location: Top of

Subgrade

• Distress: Subgrade or

structural rutting

• Thicker or stiffer

pavements disperse

stress

13

Limitation #2

Horizontal Strain

• Critical Location: Bottom

of Asphalt Pavement

• Distress: Fatigue

Cracking

• Pulling pavement apart

14

The Perpetual Pavement Diet

15

A Word of Warning

16

Getting in Shape

17

Perpetual Pavement Structure

Rut Resistant Surface Layer

Newcomb et al.Newcomb et al.

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?

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

20

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

21

Step #2 – High Modulus Layer

• High modulus = stiff

• The Good

–Reduce overall necessary thickness or

–Reduce tensile strains of equivalent thickness

22

Step #2 – High Modulus Layer

• The Bad:

–Cracking?

–Hamstring pull

–Know where to place

them

–Minimal strains near

center of pavement

structure

23

Strength Training

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 . . .

25

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

10

100

1000

1 10 100 1000

log cycles

log

mic

rostr

ain

26

Translation

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

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

29

Fatigue Endurance Limits

Mixture Description Fatigue Endurance Limit (FEL), microstrainS9-3 Control 92

N10-3 50% RAP - HMA 100N11-3 50% RAP - WMA 134S10-3 WMA – Foam 99S11-3 WMA – Additive 84N5-4 Thiopave 109N7-3 Kraton 241S12-3 TLA 137

30

So What??

• How does this impact

me?

• AASHTOWare Pavement

M-E

• States have own tools

and systems

• PerRoad 4.2

31

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35

36

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

38

• 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

39

• 1964 – 1 in overlay

• 1973 – 4 in overlay

–Heavier plans

• 1987 – 3 in mill and fill

• 2002 – 95% of base

HMA still in service

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

Environmental Product Declarations

www.AsphaltPavement.org/EPDs

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/epdEnvironmental Product

Declarations

Thank you