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1 © Copyright 2012 Daniel J Edelman Inc. Intelligent Engagement

Materials Engineering & Testing

Best Practices for Asphalt Pavement Rehabilitation

Rocky Mountain Asphalt ConferenceFebruary 19-20, 2020Denver, CO

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Pavement Life Cycle – Costs

• Initial Construction• Material, Labor and Traffic Control

• Routine Maintenance• Crack Sealing, Patching, Surface Treatments

• Rehabilitation• Structural Patching, Milling, Overlays, etc…

• Salvage/Perpetual?• Eliminating structural distresses can lead to perpetual

life

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Time

Cost

Initial Construction

Rehabilitation

Routine Maintenance

Salvage

Pavement Life Cycle – Costs

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PavementCondition

(Ride Quality)

Time (Years)

Good

Poor

Pavement Life Cycle – Ride Quality

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Time

RideQuality

Cost

PerformancePeriod

Analysis Period

RemainingLife

Analysis Period

Pavement Life Cycle –Cost vs. Ride Quality

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PavementCondition

(Ride Quality)

Time (Years)

Good

Poor

Pavement Condition?

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FHWA’s LTPP Distress Identification Manual

• Research-oriented• All pavement types• Distress definitions• Description• Severity levels• How to measure

• Schematic drawings• Photographs• Data collection forms

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Pavement Surface Evaluation and Rating (PASER) Manual

• Transportation Information Center at the University of Wisconsin -Madison

• Manuals for various pavement types

• Asphalt distress types and descriptions

• Provides a simple system to visually rate the pavement condition

• Photographs• Tables and charts of recommended

criteria

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Pavement Condition Rating – PASER

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Identification of Pavement Distresses

• Surface Defects−Raveling, Flushing, Polishing

• Surface Deformation−Rutting/Distortion

• Cracking−Transverse, Reflective, Slippage, Longitudinal,

Block, Alligator• Patches and Potholes

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Identification of Pavement Distresses

• Fundamental pavement performance indicator

• Characterized by:• Type – What is it?

• Severity – How bad is it?

• Cause – What is causing the distress?

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Pavement Condition Rating – PASER

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Pavement Condition Rating – PASER

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Pavement Condition Rating – PASER

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Forensic Investigations

• Identify and/or determine the cause for the distresses that are seen using forensic analyses

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Forensic Investigations

• Project Documentation

• Layer Thicknesses?•Materials & Mixtures?• Traffic Levels?• Performance History?•Maintenance Actions?• Soil & Drainage?

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Framework for Forensic Investigations

• FHWA’s Framework for LTPP Forensic Investigations• Recommendation for

forensic investigation• Development of forensic

investigation plan• Implementation of forensic

investigation plan• Details on the activities to

be performed in each element

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So, where are you on the curve?

Routine Maintenance

Rehabilitation

Reconstruction

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Forensic Investigations

• “Tools in the Toolbox”

• Identified Distresses• Dry Drilling•Wet Coring• Trenching• Deflection Testing• Ground Penetrating Radar

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Asphalt Pavement Rehabilitation

“Measures to improve, strengthen or salvage existing deficient pavements to continue service with only routine maintenance.”

University of California Institute of Transportation Studies (ITS)

“Structural enhancements that extend the service life of an existing pavement and/or improve its load carrying capacity.“

AASHTO Highway Subcommittee on Maintenance

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Rehabilitation – Leveling Courses

• Leveling Course - a thin layer of HMA used in rehabilitation to correct minor variations in the longitudinal and transverse profile of the pavement prior to placement of other pavement layers

• Fills low spots

• Corrects pavement profile

• Improves overlay performance

- Consistent compaction

- Increased smoothness

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Rehabilitation – Structural Patching

• Many distresses that we see on the surface are a result of deep structural issues

• Prior to any surface treatment or asphalt overlay, steps should be taken to address the source of the distress

• Just because we might be able to cover it up, doesn’t mean the problem goes away!

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Rehabilitation – Structural Patching

• With any patching, especially structural patching, be sure to address the pavement area just beyond the distressed area

• Cut back until you find good material and structure!

• Also, from a practical standpoint, think about the equipment needed to do the work.

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Rehabilitation – Milling

• Cold Milling - removal of pavement surface using drum-mounted carbide steel cutting bits

• Diamond Grinding• Restore ride-remove bumps• Improve friction• Not to remove material

• Grooving – hydroplaning

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Milling – Purpose and Application

• Primary use on asphalt pavements

• Overlays• Recycling• Reconstruction

• Full lane to partial lane width

• Partial depth to full depth removal

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Milling – Advantages on Asphalt Pavements

• Removal of rutting

• Restoration of curb line

• Restoration of cross slope

• Restoration of surface friction

• Mass removal of asphalt

• Roughened surface for improved bond between layers

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Rehabilitation – Milling/Inlay

• Selectively remove top few inches of existing pavement,and replace with new HMA

• Advantages:– Even if existing pavement appears

to be “distress free”, it has aged and oxidized depending on how long it has been in service

– Ability to improve/revise profilethrough partial removal and replacement

– Generate material suitable for recycling

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Rehabilitation – Overlays

• Historically, has been the most common method, however, recent increases in material costs have forced agencies to re-evaluate.

• Relatively fast and cost-effective means for:• Correcting deficiencies

• Restoring user satisfaction

• Adding structural capacity

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Rehabilitation – Overlays

• Purpose and Applications• Improve functional and/or structural characteristics

• Wide range of applications

• Road surface categories• Climate and support conditions

• Characteristics of Typical AC Overlay• Dense-graded asphalt concrete

• Flexible or rigid surface

• 25 to 100 mm (1 to 4 in) thickness

• Mill and Inlay

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Rehabilitation – Overlays

• Functional performance• Ability to provide a safe, smooth

riding surface

• Structural performance• Ability to carry traffic without

distress

• Empirical Design• Based on past experience or

observation

• Mechanistic Design• Based upon engineering mechanics

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Rehabilitation – Overlays

• Lift Thickness/NMAS Recommendations to promote good compaction which directly relates to good performance

Mix DesignationNMAS

PavementLayer

MinimumThickness(3 x NMAS)

MaximumThickness(5 x NMAS)

4.75 mm Surface 3/4” 1-1/4”

9.5 mm Surface 1” 2”

12.5 mm Surface 1-1/2” 2-1/2”

19.0 mm Binder 2-1/4” 3-3/4”

25.0 mm Binder/Base 3” 5”

37.5 mm Base 4-1/2” 7-1/2”

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Rehabilitation – Overlays

Stone Matrix Asphalt

• Premium Mix/Preferred Choice

• High rut resistance combined with increased durability

• Ability to provide increased performance with typical layer thicknesses

• However, SMA is not a “magic bullet” for ignoring deep structural problems

SMA Dense-Graded

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Rehabilitation – Multiple Lifts

“Obviously, if we had a single 2” overlay on a road, the most we could expect to improve the ride would be by 50%. If on the other hand we were able to put down mix in two lifts we could improve the ride by 75% (50% improvement with each opportunity).”

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Rehabilitation – Mill/Inlay

“If the surface can be milled out, we have not only conserved a valuable resource, but if no adjacent lane has to be matched this mill-and-fill may give us two opportunities for smoothness.” Roadtec Technical Paper T-123

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Summary

• Proper pavement rehabilitation starts with identifying distresses and knowing where you are on the life cycle curve

• Be sure to evaluate and address any deep structural problems, whether confined to small areas or throughout project

• Leveling is a fundamental best practice that can lead to smoother, better performing overlays

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Summary

• Cold milling provides an opportunity to remove distresses, recycle materials, correct profiles, and leads to smoother, better performing overlays

• Remember your “best practices” when both selecting mixture sizes and lift thicknesses for new overlays

• Don’t forget your fundamentals when utilizing premium mixtures and other pavement performance enhancements

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• Transportation Information Center at the University of Wisconsin – Madison. Pavement Surface Evaluation and Rating (PASER) Manual

• https://www.michigan.gov/documents/tamc/asphaltpaser_602531_7.pdf

Key References

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• FHWA Publication: Distress Identification Manual for the Long-Term Pavement Performance Program FHWA-HRT-13-092 Rev. May 2014

• https://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/13092/13092.pdf

Key References

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Key References

• FHWA Publication. Framework for LTPP Forensic Investigations -April 2004

• https://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/framework/

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Questions?

Michael H. Huner, P.E.Huner Consulting, LLC

www.hunerconsulting.commike@hunerconsulting.com

(615) 477-5079 CELL

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