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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