session 3-6 hma overlays. learning objectives describe the characteristics of typical hot-mix...
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Session 3-6Session 3-6
HMA OverlaysHMA Overlays
Learning ObjectivesLearning Objectives
Describe the characteristics of typical Describe the characteristics of typical Hot-Mix Asphalt (HMA) overlaysHot-Mix Asphalt (HMA) overlays
Identify best applications Identify best applications
Describe preoverlay repair need and Describe preoverlay repair need and feasibilityfeasibility
Describe thickness design approachDescribe thickness design approach
Describe key construction issuesDescribe key construction issues
IntroductionIntroduction Most popular methodMost popular method
Relatively fast and cost-effective means Relatively fast and cost-effective means for:for: Correcting deficienciesCorrecting deficiencies Restoring user satisfactionRestoring user satisfaction Adding structural capacityAdding structural capacity
Poor performance is NOT uncommonPoor performance is NOT uncommon
DefinitionsDefinitions Functional performance - Ability to Functional performance - Ability to
provide a safe, smooth riding surfaceprovide a safe, smooth riding surface
Structural performance - Ability to carry Structural performance - Ability to carry traffic without distresstraffic without distress
Empirical - Design based on past Empirical - Design based on past experience or observationexperience or observation
Mechanistic - Design based upon Mechanistic - Design based upon engineering mechanicsengineering mechanics
Improve functional and/or structural Improve functional and/or structural characteristicscharacteristics
Wide range of applicationsWide range of applications Road surface categoriesRoad surface categories Climate and support conditionsClimate and support conditions
Purpose and ApplicationsPurpose and Applications
Characteristics of Typical Characteristics of Typical HMA OverlayHMA Overlay
Dense graded HMADense graded HMA
Flexible or rigid surfaceFlexible or rigid surface
25 to 200 mm (1 to 8 in) thickness25 to 200 mm (1 to 8 in) thickness
Mill and FillMill and Fill
Best ApplicationsBest Applications
What is the best What is the best application for HMA application for HMA
overlays?overlays?
Limitations and Limitations and EffectivenessEffectiveness
Why do we have premature failures?Why do we have premature failures?
Improper selectionImproper selection
Wrong typeWrong type
Inadequate designInadequate design
Insufficient preoverlay repairInsufficient preoverlay repair
Lack of consideration of reflection Lack of consideration of reflection crackingcracking
Limitations and Limitations and EffectivenessEffectiveness
What limits the effectiveness of HMA What limits the effectiveness of HMA overlays?overlays?
Distress exhibited in HMADistress exhibited in HMA
Intended design life of the overlayIntended design life of the overlay
Availability of quality materialsAvailability of quality materials
Limitations and Limitations and EffectivenessEffectiveness
How can we improve our overlays?How can we improve our overlays?
Preoverlay treatmentsPreoverlay treatments
Better materials and practicesBetter materials and practices
Sound engineering judgmentSound engineering judgment
Thin Overlay Thick Overlay
Surface Defects Structural Defects
Overlay Selection to Overlay Selection to Correct DeficienciesCorrect Deficiencies
What Are Considerations What Are Considerations in Overlay Selection?in Overlay Selection?
Construction feasibilityConstruction feasibility Traffic controlTraffic control ConstructibilityConstructibility Vertical clearancesVertical clearances UtilitiesUtilities
Performance periodPerformance period
FundingFunding
Preoverlay Treatment and Preoverlay Treatment and RepairRepair
Dependent upon:Dependent upon: Type of overlayType of overlay Structural adequacy of existing Structural adequacy of existing
pavementpavement Existing types of distressExisting types of distress Future trafficFuture traffic Physical constraintsPhysical constraints CostCost
To Repair or Not to To Repair or Not to Repair?Repair?
Types of Preoverlay Types of Preoverlay TreatmentsTreatments
Localized repair (patching)Localized repair (patching)
Surface levelingSurface leveling
Controlling reflection crackingControlling reflection cracking
Drainage improvementsDrainage improvements
% Area repaired
Repaircost
Overlaycost
Localized Repair Localized Repair
% of Area Repaired
Total Cost
Minimum Total CostOptimum
Localized Repair Localized Repair
Surface Leveling Surface Leveling PurposePurpose
Rut fillingRut filling Restore cross slopeRestore cross slope Improve longitudinal profileImprove longitudinal profile
MethodMethod Cold millingCold milling Leveling course Leveling course
Controlling Reflection Controlling Reflection Cracking Cracking
What do you use to control reflective What do you use to control reflective cracking?cracking?
Geotextiles or fabrics Geotextiles or fabrics
Stress relieving or stress absorbing Stress relieving or stress absorbing membrane interlayersmembrane interlayers
““Band aid” type crack sealantsBand aid” type crack sealants
Reflective Crack Reflective Crack Treatments Treatments
Geotextile: varied results on its Geotextile: varied results on its effectivenesseffectiveness
SAMI: varied results alsoSAMI: varied results also
Aggregate Interlayers: effective when Aggregate Interlayers: effective when designed correctlydesigned correctly
Route and seal: does not prevent but Route and seal: does not prevent but effective at limiting deteriorationeffective at limiting deterioration
Drainage Corrections Drainage Corrections Drainage surveyDrainage survey
Identify moisture / drainage related Identify moisture / drainage related distressesdistresses
Develop solutions that address moisture Develop solutions that address moisture problemsproblems
Two Aspects of Two Aspects of Overlay DesignOverlay Design
Asphalt mixtureAsphalt mixture Fatigue crackingFatigue cracking Permanent Permanent
deformationdeformation Thermal Thermal
crackingcracking Moisture Moisture
susceptibilitysusceptibility
Overlay ThicknessOverlay Thickness Engineering Engineering
judgmentjudgment Deflection Deflection
approachapproach Structural Structural
deficiencydeficiency Mechanistic Mechanistic
approachapproach
Mix DesignMix DesignSuperpaveSuperpave
Goal – integrate mixture/structural designGoal – integrate mixture/structural design Performance Graded (PG) asphalt Performance Graded (PG) asphalt
cementscements Mix designMix design
MaterialsMaterials Aggregate structureAggregate structure Binder contentBinder content Moisture susceptibilityMoisture susceptibility
50 100 150 2000 250
0.0
0.4
0.8
1.2
1.6
2.0
Overlay Thickness, THov (mm)
Def
lect
ion
,
(
mm
)
Limiting
Deflection
Original SurfaceDeflection
HMA Overlay
HMA Layer
Granular Layer
Natural Soil
Simulated 80-kN Axle Load
THov
150 mm
75 mm
Structural DesignStructural DesignDeflection ApproachDeflection Approach
TrafficTraffic
PSIPSI
2.52.5
1.51.5
OverlayOverlay
SCSC
SCSC
SCSC
SCSC
effeff
ooLL
ff
Structural Design Structural Design Structural Deficiency Structural Deficiency
SCSCOL OL = SC= SCf f – SC– SCeffeff
Problem: Determining SCProblem: Determining SCeffeff
Distress surveyDistress survey Remaining lifeRemaining life Deflection testingDeflection testing
Structural DesignStructural DesignAASHTO ApproachAASHTO Approach
Natural Soil
Subbase
Base
OriginalHMA SurfaceLayer
HMA OverlayTH
TH
TH
TH
E
E
E
E
1
2
3
4
1
2
3
4
Thickness Young’s Modulus
ov
HMA
SimulatedDesign Axle Load
σV
Structural Design Structural Design Mechanistic-EmpiricalMechanistic-Empirical
Critical Stress or Strain
AllowableTraffic
RuttingFatigue
Structural Design Structural Design Mechanistic-Empirical Mechanistic-Empirical
HMA Overlay Thickness, THov (mm)
Allo
wab
le A
xle
Load
App
licat
ions
(8
0 -
kN E
SA
Ls,
mill
ions
)Simulated 80 - kN Axle Load
THov
THhma
THbg
ov HMA overlay
BaseNatural soil
Design HMAOverlay Thickness
25 50 75 125100 150 175
1
2
3
4
Design 80-kN ESALS, W
Original HMA layer (fatigued)
80
Structural DesignStructural DesignMechanistic-EmpiricalMechanistic-Empirical
1
2
3
Distance Along Roadway
Des
ign
Ove
rlay
Th
ickn
ess
Structural Requirement Structural Requirement Varies Along RoadwayVaries Along Roadway
Key Construction IssuesKey Construction Issues
Lift ThicknessLift Thickness Old – 2X maximum aggregate sizeOld – 2X maximum aggregate size
New – 3X nominal maximum aggregate New – 3X nominal maximum aggregate sizesize
Lift thickness versus mix designLift thickness versus mix design
CompactionCompaction
ConsequencesConsequences Rutting Rutting RavelingRaveling OxidationOxidation StrippingStripping
KeysKeys Proper Proper
equipmentequipment Roller Roller
immediately immediately behind paverbehind paver
Newer mixes more difficult to achieve densityNewer mixes more difficult to achieve density
Ride QualityRide Quality Public’s No. 1 issuePublic’s No. 1 issue Ride specificationRide specification
Method of measurementMethod of measurement Incentive/disincentiveIncentive/disincentive
Increased pavement Increased pavement performanceperformance
Key – continuous, steady Key – continuous, steady operationoperation
ReviewReview What are the characteristics of an HMA What are the characteristics of an HMA
overlay?overlay?
Where are HMA overlays applicable? Where are HMA overlays applicable?
What types of pre-overlay repair should What types of pre-overlay repair should be considered?be considered?
Name three structural design Name three structural design approaches?approaches?
What are some of the key construction What are some of the key construction issues?issues?
Key ReferencesKey References Daleiden, J. F., A. Simpson, and J. B. Rahut. Daleiden, J. F., A. Simpson, and J. B. Rahut.
1998. 1998. Rehabilitation Performance Trends: Rehabilitation Performance Trends: Early Observation from Long-Term Pavement Early Observation from Long-Term Pavement Performance (LTPP) Specific Pavement Performance (LTPP) Specific Pavement Studies (SPS). Studies (SPS). FHWA-RD-97-099. Federal FHWA-RD-97-099. Federal Highway Administration, Washington, DC.Highway Administration, Washington, DC.
Brown, E. R. 1997. Brown, E. R. 1997. Superpave Construction Superpave Construction Guidelines. Guidelines. Special Report 180. National Special Report 180. National Asphalt Pavement Association, Lanham, MD.Asphalt Pavement Association, Lanham, MD.
Key References Key References (continued)(continued)
Huber, G. A. 1999. Huber, G. A. 1999. Methods to Achieve Rut-Methods to Achieve Rut-Resistant Durable Pavements.Resistant Durable Pavements. Synthesis of Synthesis of Highway Practice 274. Transportation Highway Practice 274. Transportation Research Board, Washington, DC.Research Board, Washington, DC.
Collura, J., T. El-Korchi, K. Black, M. Chase, Collura, J., T. El-Korchi, K. Black, M. Chase, and L. Jin. 1997. and L. Jin. 1997. Guidelines for Ride Quality Guidelines for Ride Quality Acceptance of Pavements Final Report. Acceptance of Pavements Final Report. New New England Transportation Consortium, University England Transportation Consortium, University of Connecticut, Storrs, CT.of Connecticut, Storrs, CT.
Key References Key References (continued)(continued)
American Association of State Highway and American Association of State Highway and Transportation Officials (AASHTO). 1993a. Transportation Officials (AASHTO). 1993a. AASHTO Guide for Design of Pavement AASHTO Guide for Design of Pavement StructuresStructures. American Association of State . American Association of State Highway and Transportation Officials, Highway and Transportation Officials, Washington, DC.Washington, DC.