pavement faults what they are and why they · pdf filepavement faults what they are and why...
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Pavement Faults
What they are and why they happen
Andy Simms Jacobs Laboratories
Failures in Road Surfacing and why they happen
Some background / engineering principlesRuttingCrackingFrettingJointsPotholes
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Modern Road Requirements
Heavier Loads
Safe interface for traffic
Ride quality
Good load spreading
Waterproof / Weather Resistant
Quiet
Crack and Deformation Resistant
Flexible
Flexible Composite
Rigid
Rigid Composite
4 Types of Road Pavement
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Road Pavement Terminology (Flexible or Flexible Composite)
Surf ace CourseBinder Course
Base
Sub Base
Capping Lay er
Sub grade
Fou
ndat
ion
Surf acing
Formation Lev el
Pav ement
Road Surf ace
Load Spreading in Road Pavements
Weak Pavement Strong........
Poor Load Spreading
Good LoadSpreading
Compressive stress on subgrade
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Critical Stresses and Strains in a Flexible Pavement
Forces in a Flexible Pavement
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Traffic Loading
Commercial Vehicle – Supersingle Tyres
Traffic Loading
Commercial Vehicle – Twin Wheel axle
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Traffic Loading
Thickness of bound layers depends on traffic loading
Heavier axles have greater effect on pavement life
AASHTO Road Test - 1950s
6 vehicle types
Pavement damage = axle load to the power n (usually taken as 4)
Fourth Power Law
Traffic LoadingConversion of Axle Load to Equiva lent Standard Ax les
0.001
0.010
0.100
1.000
10.000
100.000
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Axle Load ( Kg)
Equi
vale
nt S
tand
ard
Axle
s
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•Covered in DMRB HD24/06
•Can simplify further using NRSWA Road Categories
Traffic Loading
One standard axle taken as 8160kg (18000lb)
In UK we use 8000kg (=80kN)
SA has damaging effect of unity
5000 passe s of 1T axle = equivalent damage
One 18 Tonne axle does 23 times the damage
Modern truck su spensions affect 4th power law
Number of Commercial vehicles per day
Vehicle damaging factor
− Buses, OGV1, OGV2 etc
Anticipated growth in CVs
Rutting
Structural RuttingLayer Deformation (Rutting)
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Structural Rutting
Deep SeatedPavement Design – load spreading and design lifeResults from Overstressing of Foundation LayerWater Damage accelerates deterioration− Drainage maintenance is vital
Deformation in Foundation is transmitted though overlying bound layersWheelpath deformation has no shoulders
Forces in a Flexible Pavement
Vertical Compressive stress and vertical compressive strain
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Structural Rutting
BaseBase
SubgradeSubgrade
Structural Rutting
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Layer Deformation - Rutting
Shallow - often surface course (and binder course)− Isothermal penetration
Wheelpath deformation has shoulders (pushing)Results from material selection / mix designEnvironmental Issues
Layer Deformation – M25 Case study
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Layer Deformation – M25 Case study
Layer Deformation – M25 Case study
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Layer Deformation – Loading times
Factors affecting Layer Deformation
AggregateBinderMixtureSite conditions
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Layer Deformation - Aggregate Factors
Surface texture / roughnessMechanical Interlock− Particle
Shape− Particle
size− Grading
Layer Deformation - Binder Factors
Binder StiffnessRecovered Penetration (dmm)− The low er the better
Binder Type (PMB)− Not all polymers
have same effectPlastomericElastomeric
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Layer Deformation - Mixture Factors
Mixture Type− HRA / DBM / NTS
Binder ContentAir Voids Content% VMA (= Binder Volume + Air Voids)WheeltrackingMixture Stiffness
Time
Stress
Load on Load off
σ = constant
Strain
Elastic + Plastic
Elastic
Visco-elastic
Permanent (Viscous + Plastic)Time
Bituminous Mixtures - Viscoelastic – plastic behaviour
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Layer Deformation –Wheeltracking : mixture types
HRA Design Mix S/C Tested 60oC HRA Design Mix S/C Tested 45oC
HRA Binder Course Tested 60oC NTS Tested 60oC
Layer Deformation - Site Factors
Traffic VolumeLoading time / speedVehicle typeAspect − South facing− uphill
ChannelisationGlobal warming
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Cracking
Fatigue Cracking− Flexible and flexible composite pavements
Thermal / Reflective Cracking− Flexible Composite Pavements
Thermal / Reflective Cracking− Rigid Pavements
Fatigue Cracking in Flexible Pavements
Affected by Pavement Design− Asphalt thickness− Mixture stiffness
Prevalent on undesignedpavementsBottom up or top down?Number of load cyclesAxle loads /configurationWheelpaths?
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Fatigue Cracking –Structural failure
Wheelpath crackingThin PavementOften Consistent along length
Interconnected Wheelpath Cracking –structural failure
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Fatigue Cracking
Map / alligator crackingThin PavementLocalised areas
Reflective Cracking
Thermal / Reflective Cracking− Flexible Composite Pavements
Cement Bound Base / Lean Concrete − Cracks into bays
Thermal expansion and contraction− Cracks tend to be transverse / regularly spaced
Loss of structural strength at jointRelative vertical movementDeterioration of asphaltWater ingress / sub base deterioration
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Reflective Cracking in Flexible Composite Pavement
Reflective Cracking in Flexible Composite Pavement
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Reflective Cracking in Flexible Composite Pavement
Reflective Cracking in Flexible Composite Pavement
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Reflective Cracking in Flexible Composite Pavement
Cracking extending from CBM
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Flexible Composite Pavement- Mud Pumping
Flexible Composite Pavement- Mud Pumping
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Flexible Composite Pavement- Mud Pumping
Flexible Composite Pavement- Mud Pumping
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Reflective Cracking –Overlaid Rigid Pavements
Thermal / Reflective Cracking− Rigid Pavements− Overlaid Pavement Quality Concrete− Expansion and contraction joints− Thermal movement reflects through thin overlay− Poor Ride Quality
Thin Overlay to Rigid Pavement
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Thin Overlay to Rigid Pavement
Thin Overlay to Rigid Pavement
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Rigid Construction Joints
Fretting
Definition: Progressive loss of interstitial fines from the road surface ( Shell Bitumen Handbook)− Traffic stresses exceed breaking strength of asphalt− More Likely at low temperatures / short loading times
Factors− Bitumen Content
High Binder content minimises fretting− Compaction− Age Hardening (not always)
Removal of fines permits ingress of water
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Fretting in High Stone Content Asphalt
Fretting
Fretting along longitudinal joint
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Fretting
Fatigue fretting on line of old sewer trench reinstatement
Fretting
Fretting on patch repair − cold load− Fatigue fretting
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Fretting outside Industrial Access
High Turning StressesSlow speed
Fretting in Asphalt Concrete on sharp bend
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Fretting in Centre Line Joint – New TSCS
Occurred within a few weeks of layingCold WeatherJoint under compacted
Fretting in Centre Line Joint – New TSCSFull layer thicknessOne side of joint onlyTransverse profile
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Fretting in New TSCS - Layer ThicknessOccurred within a few months of layingThinCracking in substrate
HFS Adhesion Failure
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HFS Adhesion Failure
HFS Adhesion Failure
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Colour Matching!
HFS Adhesion Failure
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Adhesion failure of thin patch overlay
Inappropriate layer thickness for aggregate size− Less than 2.5 x
stone sizePoor bondCracking
Pothole in High Stone Content Asphalt
Can result from severe frettingCan take place along edges of unconfined pavementsProgressive – start where layer is thin / highly stressedFatigue damageDelaminationUnder compactionLoad ends
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Development of Potholes
Summary
Must know construction type before considering treatmentNeed to understand the failure mechanism and reason for it before spending moneySite conditionsCost effectiveness of treatment
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Site Conditions
BEST PRACTICE GUIDELINES FOR SPECIFICATION OF MODERN NEGATIVE TEXTURE SURFACES (NTS) ON LOCAL AUTHORITY HIGHWAYSContains useful MethodologyFound at http://www.roadscodes.org
Best Practice Guidelines –The Right Material for the Right Site
The evaluation of an existing site comprises the use of a checklist and four decision charts A to D inclusive.Collate all of the available data relating to the site and to undertake a walk through inspection by experienced personnel. The walk through inspection will enable collection of all of thecondition information necessary to use the decision charts. A checklist comprises:− Geometry and layout− Traff ic− Road function− Condition− Road surface− Data availability.
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Checklist - Geometry and layout
Road type Dual, single.Situation Urban, rural.Junctions or crossings Frequency , type, etcExposed site Yes/NoGradient Flat, level, gentle, steep.Direction facing North, south, east or westBend Yes/NoRoundabout Yes/NoRoad closure possible Yes/No
Checklist - Traffic
Speed limit 20, 30, 40, 50, 60, 70 mphBraking area Yes/NoAccelerating area Yes/NoTurning - Bends Gentle, acute, etcTurning - Roundabout Radius: tight/int./gentle.Commercial vehicles High, medium, lowReduced spray required Yes/NoReduced noise required Yes(+40mph)/No
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Checklist - Road functional Hierarchy
CoP function category 1, 2, 3a, 3b, 4a, 4b
Checklist - Conditions
Surface drainage Good/fair, falls, gullies, etcHighway drainage Ditch, filter drain, etcSite prone to flooding Yes/NoEdge restraint Good (kerb/strip)/PoorRestriction on overlay. Thresholds, access, etcRestriction on inlay Practicality, etc
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Checklist - Road Surface
Walk through inspection Yes(date)/No(reason)Surface material HRA, DBM, NTS,etcOxidised Yes/NoFretting Yes (severity)/ NoCracking - longitudinal Yes (severity)/ NoCracking – map (craze) Yes (severity)/ NoCracking - transverse Yes (severity)/ NoTexture Good, average, poorRutting Yes (severity)/ NoDelamination Yes/NoDamp or wet areas Yes/NoSubsidence areas Yes/No
Checklist - Condition Data availability
CVI Yes/NoDVI Yes/NoCore records Yes/NoExploratory pit records Yes/NoDeflectograph survey Yes/NoFWD survey Yes/NoGround penetrating radar Yes/No