Flexible Pavement Failure

Table of content 1. 2. 3. 4. 5. 6.

Flexible Pavement Layer of Flexible Pavement Failure In Flexible Pavement Typical Failure Pattern Conclusion Conclusion And Discussion Reference

Table of content 1. 2. 3. 4. 5. 6.

Flexible Pavement Layer of Flexible Pavement Failure In Flexible Pavement Typical Failure Pattern Conclusion Conclusion And Discussion Reference

Flexible Pavement

Low or negligible f lexural strength Flexible in their in structural action under load Transmits ransmits stress stress to lower layer by grain to grain transfer Generally Last Las t for 5- 20 yrs Low initial cost cost Easy to upgrade Bituminous roads – DBSD, Asphalt Concrete , Otta seal , DBM etc

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Typical Flexibl Flexiblee Pavement Pavement Lay L ayer er 1. 2. 3. 4.

Soil sub grade Sub- Base Course Base Course Surface Course 2

Typical Flexible Pavement X section

Typical Flexible Pavement

Typical Flexible Pavement according to material quality 

Loading pattern

F exi e Pavement Fai ure

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 According to Highway Research Board, 1970 cited by Pavement Interactive, 2010, pavement distress is "any indication of poor or unfavorable pavement performance or signs of impending failure; any unsatisfactory performance of a pavement short of  failure" To maintain the stability of the pavement structure as a  whole each layer should be stable within itself.

Pavement Failure External Failure

Internal Failure

Over loading Petroleum spillage Sink holes Flooding, seepage, climate Other unforeseen –Earthquake etc..

Lack of Pavement Mixtures Poor materials Poor Construction

One of major cause of pavement failure

Water is enemy of pavement and can worsen cracked pavement problems .Freezing and thawing action makes pavement weak.

Pavement Failure Failure in sub grade Excessive deformation in sub-grade soil due to insufficient bearing capacity or a shear failure in sub-grade soil. 

Inadequate Stability  

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inherent weakness of soil itself, excessive moisture improper compaction

Excessive application of  Stress –consolidation deformation Plastic deformation

Failure in Sub Base –Base Course 

Inadequate Stability  

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Loss of Binding action  

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Repeated stress Application Internal movement of aggregate in base or sub base

Loss of Bearing Course Materials 

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Poor mix proportion , in adequate stability, poor ingradient

 When Wearing course materials worn out

Inadequate Wearing Course Use of inferior materials Lack of lateral confinement of granular base course

Failure of wearing course      

Improper mix design Poor quality control Volatilization and oxidation of binder Improper gradation of aggregates Inadequate binder content Inferior type of binder etc.

Typical Flexible Pavement Failures 1. Surface 2. Surface Deformation Defects

3. Cracking's

1. 2. 3. 4.

1. Fatigue /alligator 1. Patch crack detoritio 2. Block Cracking n 3. Longitudnal 2. Potholes Cracking 4. Transverse(ther mal ) Cracking 5. Edge Cracking /Edge Break /Edge drop offs 6. Crescent shape /slippage cracks

Shoving 1. Bleeding Corrugation Flushing Rutting 2. Ravelling Depression 3. Polishing 4. Surface lifting / Seal Break /Upheaval 5. Water bleeding and pumping

4. Patching and Potholes

Surface Deformation

1.1 Shoving :

Formation of waves across a pavement, Occur at severe horizontal stresses like intersection

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Possible Causes Excess asphalt too much fine aggregate; rounded aggregate; Low modulus of base course , thin wearing course High stress due to braking and acceleration Probable Treatment Partial or full depth patch Reconstruction of base Bituminous overlay   

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1.2Corrugations : Transverse ridges and valleys (or ripples) occurring at regular Intervals,

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Usually occurs at points where traffic starts and stops

Possible Causes Inadequate stability of bituminous surface Heavy traffic on steep downgrade or upgrade Inadequate stability of base course Compaction of base in wave form Probable Treatment Base reconstruction Mill off the corrugated surface and replace with the stiffer mix or use hot mix asphalt 

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1.3Rutting : Surface/channelized depressions in the wheel-tracks , evident after a rain when they are filled with water

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Possible Causes Inadequate pavement thickness Unsuitable bituminous mixes consolidation or lateral movement of any layer due to traffic loading Insufficient compaction Probable Treatment Strengthening overlay or reconstruction Base or sub base strengthening   

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1.4 Depression (birds baths): Surface areas with slightly lower elevations than the surrounding pavement Usually on left lane and shoulder •

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Possible Causes Differential settlement of sub grade or base materials  Volume change of subgrade due to environmental inf luences settlement due to instability of  embankment Probable Treatment  Applying a thin surface patch Base or subgrade reconstruction Embankment stabalization and drainage improvement 

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2.Surface Defects 2.1 Bleeding/ Flushing: shiny, glass-like reflecting surface , thin sticky bitumen layer Loss of skid resistance when wet

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Possible Causes Excessive asphalt in the surface layer Lack of proper rolling during placement Probable Treatment  Applying coarse sand cutting off excess asphalt with a motor grader or removing it  with a heater planer Resurfacing the asphalt 

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2.2Ravelling(very porous asphalt): Separation of aggregate particles in a pavement from the surface downward or from the edges inward more common in the northern regions(snow belt) •

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Possible Causes Insufficient bitumen content Inadequate compaction or construction during wet  weather Poor adhesion of bitumen binder Probable Treatment Thin bituminous overlay   

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2.3Polishing: •

surface consisting of rough exposed aggregates

Possible Causes Inadequate resistance to polishing of surface aggregates Use of naturally smooth uncrushed aggregates Repeated traffic on an aging pavement system. Probable Treatment The bituminous overlay of use of stiffer mix 

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2.4 Surface lifting /Seal Break/Upheaveal: •

Upward movement in a pavement

Possible Causes Inadequate cleaning or inadequate tack cot before placement of upper layers  Adhesion of surface binder to  vehicle tyres Seepage of water through asphalt swelling of the subgrade Inadequate cleaning or inadequate tack coat before placement of upper layers Probable Treatment Reconstruction of weak layer Thin bituminous overlay  

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2.5 Water Bleeding and pumping :  Water seeps out of joints or cracks or through an excessively porous  Water and fine material is ejected from underlying layers through cracks •

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Decreased skid resistance , decreased structural support

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Possible Causes High water table Poor drainage Poor mix design and compaction Probable Treatment slurry seal to limit water infiltration Lower water table and good drainage  

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3.Cracking Cracks 3.1 Fatigue /Alligator /Crocodile crack: load associated structural failure cracks allow moisture infiltration, roughness, may further deteriorate to a pothole Repeated loading, the longitudinal cracks connect forming many-sided sharp-angled piece like crocodile Possible Causes •

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Inadequate pavement thickness Increase in loading Brittle base and wearing course Poor base drainage and inadequate structural design

Probable Treatment 

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Strengthen the pavement or reconstruction Base recycling or reconstruction

3.2 Block Cracking : Large interconnected rectangles (roughly) is not load-associated, but generally caused by shrinkage of the asphalt pavement •

Possible Causes  Joints in underlying layer Shrinkage and fatigue of  underlying cemented materials Shrinkage cracks (due to bitumen hardening) in bituminous surfacing Probable Treatment Crushed aggregate overlay  Replace underlying cemented materials Cut and patch or crushed aggregate overlay   

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3.3 Longitudnal Cracking : Cracks that are parallel to the pavements centerline

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Possible Causes Reflection of shrinkage cracks Displacement of joints at pavement widening Differential settlement between cut and fill  

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Probable Treatment   

Cut and patch Replace bituminous surfacing Crushed aggregate overlay or reconstruction of joints.

3.4Transverse or thermal Cracking : Perpendicular to the pavement's centerline or laydown direction Induced by daily temperature cycles, and poor construction

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Possible Causes Reflection of shrinkage cracks Construction joint in bituminous surfacing Shrinkage crack bituminous surfacing Reflection of joints in the underlying base Probable Treatment  

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Cut and patch Crack sealant

3.5Edge Cracks /Edge Breaks /Edge Drop off : Edge Cracks travel along the inside edge of a pavement surface  within one or two feet •

Possible Causes Poor drainage conditions and lack of  support at the pavement edge Excessive traffic loading at the pavement edge Inadequate pavement width Insufficient bearing support Edge drop-off  Heavy vegetation along the pavement Probable Treatment  Widen the pavement or strengthen the pavement edge 

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Improve drainage and shoulder

3.6Crescent /Parabolic /Slippage /Shear cracks : Slippage cracks are crescent-shaped cracks or tears in the surface layer(s) of asphalt where the new material has slipped over the underlying course Possible Causes Lack of bond between wearing course and the underlying layer Thin wearing course High stress due to braking and acceleration movements •

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By dirt, oil, or other contaminants preventing adhesion Probable Treatment 

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Partial or full depth patch Reconstruction of base Bituminous overlay 

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4.1Patch deterioration :  An area of pavement that has been replaced with new material to repair the existing pavement.  A patch is considered a defect no matter how well it performs. Possible Causes •

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Inadequate cleaning or inadequate tack cot before placement of upper layers  Weak, loose layer immediately  underlying seal Break the bond between surface and lower layers

Probable Treatment   

Reconstruction of weak layers Mill off and re-lay upper layers Replace wearing course or thin bituminous overlay 

4.2Pot Holes: Small, bowl-shaped depressions in the pavement surface that penetrate all the way through the asphalt layer down to the base course •

Possible Causes Loss of surface course Moisture entry to base course through a cracked pavement surface Load associated disintegration of  base Probable Treatment  

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Patching Cut and patch Base reconstruction

Conclusion and Discussion 

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Flexible pavement failures are affected by various factors such as sub grade soil , drainage , climate ,traffic and environmental condition etc. There is not just one type of road failure, and there is not just one reason for each type of failure, this attempt is made to give guidance and supply some information Localized settlement of any component layer of flexible pavement structure could be strong enough to cause pavement failure. Timely maintenance reduce operation cost and life of pavement The aging and oxidization of bituminous films lead to the deteriorations of bituminous pavement.  A proper drainage system or good protection measure on moisture elongates pavement life.

References  

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Highway Engineering –Book by Dr S.K Khanna and Dr C E G Justo Highway specification and maintenance pdf  – . http://ww.pavementinteractive .org Proceeding of Malaysian Universities Transportation Research Forum and Conferences 2010 (MUTRFC2010), University Tenaga Nasional ,21 December 2010 Vehicles of today and motor ways in Myanmar (4). Retrieved on 16  August 2010 from http://www.mrtv3.net.mm/open6/230909for1.html  http :// www.uotechnology.edu.iq Data Collection Strategies in Malaysia, Public Work Department  Malaysia ,Zakaria, S. & Hasan, M. Z. (2005).