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 Beam FWD

Pavement Roughness Roughometer Profilometer

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 Cracking Distortion Disintegration Loss of Skid Resistance

Cracking Cracks occur from a variety of causes including: Stress from traffic axle loads Temperature changes in HMA layers Moisture 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 loads Heavy traffic loads Inadequate drainage Poor subgrade

Types of Cracking Fatigue or Alligator Cracking (leads to potholes) Repairs: Removal and replacement Overlay 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 temperature Use of asphalts with high susceptibility to temperature Use 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 temperature Asphalt with low tensile strength Oxidization High voids Heavy loads Earth movement

Types of Cracking Longitudinal Cracking (Individual cracks that run parallel to pavement centerline) Repairs: Sealing at early stage Removal and replacement at later stage

Types of Cracking Block Cracking (When HMA cracks transversely and longitudinally in approximately squared shape) Causes: High voids Oxidization Low 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 pavement Types: 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 pavement Types: Rutting Repairs overlay

Distortion Permanent change in the shape of the pavement Types: Shoving and Corrugation Causes Shear flow between layers Slippage between layers

Distortion Permanent change in the shape of the pavement Types: 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 dust Segregation Low 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: Cracking Disintegration

Disintegration Types Pothole: As a result of cracking and disintegration. Repairs: Patching at early stage Overlay

Disintegration Types Polishing: As a result of traffic over use, aggregates susceptible to Abrasion. Repairs: Seal coat with good aggregates Milling and Overlay

Stripping Due to Excessive Moisture and an covered aggregates with asphalt

Bleeding Excessive Asphalt and Low void (Excessive compaction)