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)