Asphalt Pavement Distresses
February 12, 2024 2024-04-27 14:00Asphalt Pavement Distresses
Asphalt Pavement Distresses
Team of Writers :
Team of Writers:
Mehran Hatami
Dr.Zia Alavi
Rozhin Falahati
پریسا شیخ معماری
introduction
Asphalt pavements, while providing a smooth and durable surface for our roads, are not immune to wear and tear. Over time, various factors can lead to the development of distresses, compromising the pavement’s performance and safety. Recognizing and understanding these distresses is crucial for timely maintenance and ensuring smooth riding.
These distresses manifest in various ways, generally falling into five major categories:
- Cracking: These are the most prevalent, appearing as linear separations in the asphalt surface. Different types of cracks exist, like fatigue cracks (alligator cracks) caused by repeated traffic loading, thermal cracks akibat temperature fluctuations, and block cracks indicating underlying structural issues.
- Distortion: This category encompasses issues affecting the overall shape of the pavement. Rutting, characterized by sunken wheel paths, occurs due to repeated traffic load and weak pavement structure. Shoving, on the other hand, involves lateral movement of asphalt material, creating ridges and bumps.
- Disintegration:This refers to the breakdown of the asphalt itself, leading to surface material loss. Raveling involves the loosening and loss of aggregate stones, while potholes are deeper depressions formed by the combined effects of traffic, water, and weather.
- Skidding Hazards: These distresses affect the pavement’s texture and friction, impacting vehicle safety. Polished aggregate, where smooth stones lose their grip, and bleeding, where excess asphalt rises to the surface, are two common examples.
- Surface Treatment Distresses: Over time, sealants and overlays used to protect the asphalt surface can also deteriorate. Examples include stripping, where the bond between the asphalt and the treatment fails, and cracking within the treatment layer itself.
Table of Contents
Fatigue (Alligator) Cracking
Unit of Measure
Area (m^2)
Description
Fatigue cracking is a type of structural failure in asphalt pavements. It is primarily caused by repeated loading. Fatigue cracking, often referred to as alligator cracking due to its resemblance to an alligator’s skin, is a series of interconnected cracks that form in the asphalt layer of pavement. With repeated loading cycles, these cracks begin to propagate, slowly growing in size and number.
POSSIBLE CAUSES
- Repeated Traffic Loading
- Weak or Inadequate Base or Subgrade Layer
- Insufficient Pavement Thickness
- Excess or deficient fines
- Poor drainage
Repair
LOW
Small, isolated areas of cracking with cracks less than 1/2 inch wide. The cracks are not spalled.
MEDIUM
More extensive areas of cracking, with cracks wider than 1/2 inch but pavement still intact.
HIGH
Large areas of interconnected cracking with pieces of asphalt dislodged and accompanied by rutting and settlement.
Rutting (Distortion)
Unit of Measure
Rut Depth (mm)
Description
Rutting is a type of structural failure in asphalt pavements, primarily caused by loading. Rutting refers to the longitudinal depressions formed in the wheel path of a road. It’s a common distress in asphalt pavements, often resulting from the consolidation of asphalt layers or subgrade under traffic load. Over time, continuous load can cause deformation in the asphalt layer, leading to the formation of ruts.
POSSIBLE CAUSES
- Inadequate compaction
- Insufficient pavement thickness
- Poor mix design
- Overloading
- Extreme temperature fluctuations, excessive moisture
Repair
LOW
Shallow ruts limited to the surface layer.1/4 to 1/2 in (6 to 13 mm). Minor depressions in the wheel path, not significantly affecting the ride quality.
MEDIUM
Deeper ruts affecting multiple layers, accompanied by minor cracking. 1/2 to 1 in (> 13 to 25 mm). Noticeable depressions causing water accumulation and slightly affecting the ride quality.
HIGH
Extensive ruts, significant cracking, and potential base failure. 1 in (> 25 mm). Deep depressions causing significant water accumulation and severely affecting the ride quality.
Transverse (Thermal) Cracking
Unit of Measure
- Crack Width (mm)
- Crack Length (mm)
- Crack Depth (mm)
- Number
Description
Transverse (thermal) cracking falls under the functional distress category, signifying its primary impact on ride quality and surface smoothness rather than compromising the structural integrity of the pavement. These cracks typically manifest as linear separations perpendicular to the direction of traffic flow and are primarily triggered by environmental changes rather than traffic loading. In simpler terms, as temperatures decrease, asphalt contracts, causing internal stresses that can manifest as thin cracks across the pavement surface, negatively impacting the driving experience.
POSSIBLE CAUSES
- Low Temperatures
- Extreme Temperature Fluctuations
- Insufficient Pavement Thickness
- Improper Mix Design (Insufficient flexibility)
Repair
LOW
Isolated, short cracks limited to the surface layer of the pavement.
MEDIUM
Interconnected network of shallow cracks affecting multiple pavement layers.
HIGH
A combination of crack sealing and a thin asphalt overlay application is employed to bridge the existing cracks and enhance ride quality.
Block Cracking
Unit of Measure
- Crack Width (mm)
- Area (m^2)
Description
Block cracking manifests as a series of rectangular or square-shaped cracks on the asphalt surface, disrupting the pavement's visual uniformity and potentially compromising its serviceability. While generally considered a functional distress, its occurrence often indicates underlying weaknesses that could progress into structural failures if left unaddressed. Causes of block cracking are typically a combination of environmental changes and limitations within the pavement system itself.
POSSIBLE CAUSES
- Age-Related Hardening of Asphalt Binder
- Thermal Fluctuations
- Inadequate Pavement Thickness or Structural Deficiencies
- Excessive Moisture Intrusion
Repair
LOW
Initial isolated cracks, typically confined to the surface layer of the pavement.
MEDIUM
Interconnected network of cracks affecting multiple pavement layers with signs of minor surface raveling or material loss.
HIGH
Extensive network of deep, wide cracks exhibiting significant surface raveling, potentially accompanied by other distresses such as rutting or deformation.
Longitudinal cracking
Unit of Measure
- Crack Width (mm)
- Crack Length (m)
Description
Longitudinal cracking manifests as cracks running parallel to the centerline or direction of traffic in asphalt pavements. This type of distress can fall into either the functional or structural failure category depending on its root cause, which may be attributed to traffic loading, environmental changes, or a combination thereof. Longitudinal cracks often form at points of weakness within the pavement structure or may arise from stresses induced by repeated vehicular traffic or fluctuations in temperature.
POSSIBLE CAUSES
- Inadequate Pavement Structure
- Thermal Fluctuations
- Heavy Traffic Loads
- Reflective Cracking
- Poorly Constructed Pavement Joints
Repair
LOW
Initial isolated cracks, typically confined to the surface layer of the pavement.
MEDIUM
Interconnected cracks potentially extending through multiple pavement layers with signs of minor surface raveling.
HIGH
Extensive cracks with widening, potentially accompanied by surface deformation or signs of underlying structural failure.
Shoving (Distortion)
Unit of Measure
- Area (m^2)
- Number
Description
Shoving manifests as a localized distortion in the asphalt surface, characterized by an upward and sideways displacement of the pavement. It falls under the category of functional distress, primarily affecting ride quality and surface smoothness, but can also suggest underlying structural weaknesses. Shoving is typically attributed to traffic loading acting on an unstable asphalt mix, often exacerbated by environmental conditions.shoving results from forces exceeding the internal resistance of the asphalt mix, leading to permanent deformation.
POSSIBLE CAUSES
- Insufficient Stability of Asphalt Mix
- Heavy and Slow-Moving Traffic
- Elevated Temperatures
- Moisture Infiltration
Repair
LOW
Localized shoving with minor height variation and surface distortion, often confined to a specific area.
MEDIUM
Moderate shoving with noticeable height variation and surface distortion, potentially affecting a larger area.
HIGH
Extensive shoving with significant height variation, surface cracking, and potential disruption of drainage.
Raveling (Disintegration)
Unit of Measure
Area (m^2)
Description
Raveling refers to the progressive disintegration of the asphalt pavement surface. It is primarily considered a functional distress, impacting ride quality and visual appearance but can also indicate underlying structural weaknesses. Raveling can be caused by a combination of environmental changes and deficiencies in the asphalt mixture itself, rather than direct traffic loading. Raveling results from the dislodgement of individual aggregates, creating a rough texture and leaving voids.
POSSIBLE CAUSES
- Insufficient Asphalt Binder Content
- Poor Quality or Degradation of Asphalt Binder
- Moisture Infiltration
- Freeze-Thaw Cycles
- Traffic Abrasion
Repair
LOW
Minor dislodgement of fine aggregates, exposing coarse aggregates and creating a rougher surface texture.
MEDIUM
Increased aggregate loss with visible voids and rough surface texture, potentially extending into the upper layers of the asphalt.
HIGH
Extensive aggregate loss extending into deeper layers, potentially accompanied by cracking and surface deformation.
Bleeding (Skidding Hazards)
Unit of Measure
Area (m^2)
Description
Bleeding refers to the upward migration of excess asphalt binder to the pavement surface, resulting in a shiny, black, and often sticky film. It falls under the category of functional distress since it primarily compromises surface texture and skid resistance. Bleeding arises from issues in the internal composition of the asphalt mix combined with the impact of environmental changes.Bleeding create a potential safety hazard for both vehicles and pedestrians.
POSSIBLE CAUSES
- Excessive Asphalt Binder Content
- Poor Compaction
- High Temperatures
- Segregation of Asphalt Mix
Repair
LOW
Initial presence of a thin, shiny film on the pavement surface.
MEDIUM
Thicker, sticky film with noticeable aggregate embedment, causing decreased skid resistance.
HIGH
Extensive bleeding, forming a thick, smooth surface with severe loss of skid resistance and potential for rutting and deformation.
Potholes (Disintegration)
Unit of Measure
- Number
- Area (m^2)
Description
Potholes are bowl-shaped depressions in the asphalt surface, penetrating through the entire pavement structure and exposing the underlying layers. They primarily fall under the category of functional distress, compromising ride quality and potentially causing vehicle damage. However, extensive potholing can progress into a structural failure if left unaddressed. potholes form due to a complex interplay of environmental factors and traffic loading, ultimately leading to the disintegration of the asphalt layers.
POSSIBLE CAUSES
- Fatigue Cracking
- Moisture Infiltration
- Inadequate Drainage
- Heavy Traffic Loads
- Thermal Fluctuations
Repair
LOW
Small, isolated potholes with a depth of less than 2.5 cm (1 inch) and a diameter of less than 30 cm (12 inches).
MEDIUM
Larger potholes with a depth of 2.5-7.5 cm (1-3 inches) and a diameter of 30-60 cm (12-24 inches), potentially with some loose aggregate around the edges.
HIGH
Extensive and deep potholes exceeding 7.5 cm (3 inches) in depth and 60 cm (24 inches) in diameter, often with fractured edges, raveling, and potential underlying structural damage.
