performance & distress of flexible pavement serviceability/performance concept
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Performance & Distress of Flexible Pavement
Serviceability/Performance Concept
Pavement Roughness
Surface deviation that produces a response in the suspension system of a vehicle.
It is the pavement property that is most noticeable to the traveling public. It is the primary quantitative measure of public satisfaction with the highway system
Measured by a: Rolling straightedge (Benkelman Beam) Roughometer Profilometer
Pavement Roughness
Benkelman BeamFWD
Pavement Roughness
RoughometerProfilometer
Performance
Is the area under the Serviceability Curve with Time.
Performance of the Pavement decreases with time due to traffic and climate consumption
Once the performance fall bellow a certain level the pavement is becoming impassable and unacceptable by the user.
Distresses in Flexible Pavement
Distress is a condition of the pavement structure that reduces or lead to the reduction in serviceability.
Distresses are expected as the pavement approaches its design life, However distresses are alarming if they occur early in the life of a pavement.
Distresses in pavement can be identified at early stages and preventive measures should be taken before they result in failure.
If preventive measures are not taken, then corrective measure must be performed.
Types of Distresses
CrackingDistortionDisintegrationLoss of Skid Resistance
Cracking
Cracks occur from a variety of causes including:Stress from traffic axle loadsTemperature changes in HMA layersMoisture or temperature changes in
underlying layers
Types of Cracking
It is important to identify exactly the type of cracking in the pavement structure so the cause of cracking is correctly assessed and the right preventive and corrective measures are taken.
Types of Cracking
Fatigue or Alligator Cracking (closely spaced crack pattern)Causes:
Excessive repetition of traffic loadsHeavy traffic loads Inadequate drainagePoor subgrade
Types of Cracking
Fatigue or Alligator Cracking (leads to potholes)Repairs:
Removal and replacementOverlay over the entire surface
Types of Cracking
Low Temperature Thermal Cracking (transverse cracking due to drop in temperature which causes shrinkage stresses that exceeds the tensile strength of HMA )Causes:
Drop in temperatureUse of asphalts with high susceptibility to
temperatureUse of asphalt with high penetration
Types of Cracking
Low Temperature Thermal Cracking (transverse cracking due to drop in temperature which causes shrinkage stresses that exceeds the tensile strength of HMA )Repairs:
Seal with liquid asphalt or any other suitable sealants
Remove and replace
Types of Cracking
Longitudinal Cracking (Individual cracks that run parallel to pavement centerline)Causes:
Low temperatureAsphalt with low tensile strengthOxidizationHigh voidsHeavy loadsEarth movement
Types of Cracking
Longitudinal Cracking (Individual cracks that run parallel to pavement centerline)Repairs:
Sealing at early stageRemoval and replacement at later stage
Types of Cracking
Block Cracking (When HMA cracks transversely and longitudinally in approximately squared shape)Causes:
High voidsOxidizationLow strength HMA
Types of Cracking
Block Cracking (When HMA cracks transversely and longitudinally in approximately squared shape)Repairs:
Removal and replacement
Types of Cracking
Reflection Cracking (propagation of underlying cracking through the surface )Causes:
Cracks in the old HMA underlayer
Types of Cracking
Reflection Cracking (propagation of underlying cracking through the surface )Repairs:
Removal and replacement with milling of the old underlayer
Types of Cracking
Slippage Cracking (Poor bond between the surface layer and the underlayer )Causes:
Poor bond
Types of Cracking
Slippage Cracking (Poor bond between the surface layer and the underlayer )Repairs:
Removal an replace with stronger bonds between the layers
Distortion
Permanent change in the shape of the pavementTypes:
Rutting Causes
Load and high tire pressure Continuous densification Improper mix design (High AC content, Excessive
fillers)
Distortion
Permanent change in the shape of the pavementTypes:
Rutting Repairs
overlay
Distortion
Permanent change in the shape of the pavementTypes:
Shoving and Corrugation Causes
Shear flow between layers Slippage between layers
Distortion
Permanent change in the shape of the pavementTypes:
Shoving and Corrugation Repair
Overlay
Disintegration
Is the break up of the pavement structure (loss of individual pieces or the separation of individual pieces)
Disintegration Types
Raveling: the lose of bond between the aggregates and asphalt and therefore between aggregates. The disintegration starts from the surface of HMA layer and moves downward.Causes:
Aggregates cover with dustSegregationLow in-place density
Disintegration Types
Raveling: the lose of bond between the aggregates and asphalt and therefore between aggregates. The disintegration starts from the surface of HMA layer and moves downward.Repairs:
Removal and replacement
Disintegration Types
Pothole: As a result of cracking and disintegration.Causes:
CrackingDisintegration
Disintegration Types
Pothole: As a result of cracking and disintegration.Repairs:
Patching at early stageOverlay
Disintegration Types
Polishing: As a result of traffic over use, aggregates susceptible to Abrasion.Repairs:
Seal coat with good aggregatesMilling and Overlay
Stripping
Stripping
Due to Excessive Moisture and an covered aggregates with asphalt
Bleeding
Bleeding
Excessive Asphalt and Low void (Excessive compaction)
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