Pavement Distress
Properly designed and maintained HMA pavements can provide many years of satisfactory service. However, like all pavements, HMA pavements can be damaged by certain conditions. This page is intended to:
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Assist in identifying basic HMA pavement damage. HMA pavement damage that is visible at the surface of the pavement is often called "surface distress".
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Provide some insight into why particular surface distresses are problematic.
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Provide some basic guidance into what kinds of conditions might lead to certain surface distresses.
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Suggest some basic repair strategies.
This section is organized alphabetically by type of surface distress. If you are looking for a specific type, scroll down and look at the thumbnails to see which picture most closely matches the condition you are investigating. Photos of each type of distress are accompanied by a description of the distress, the reason it is a problem, some of the most likely causes and basic repair strategy.
HAPI Pavement Note on Pavement Distress |
The most common pavement distresses in Hawai'i are low to moderate severity alligator (fatigue) cracking and raveling. Mix stability problems like rutting, corrugation and shoving are less common. |
Alligator (Fatigue) Cracking | |||
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Description: A series of interconnected cracks caused by fatigue failure of the HMA surface under repeated traffic loading. As the number and magnitude of loads becomes too great, longitudinal cracks begin to form (usually in the wheelpaths). After repeated loading, these longitudinal cracks connect forming many-sided sharp-angled pieces that develop into a pattern resembling the back of an alligator or crocodile. Problem: Roughness, indicator of structural failure, cracks allow moisture infiltration into the base and subgrade, eventually results in potholes and pavement disintegration if not treated. Possible Causes: Inadequate structural support for the given loading, which can be caused by a myriad of things. A few of the more common ones are:
Repair: A fatigue cracked pavement should be investigated to determine the root cause of failure. Any investigation should involve digging a pit or coring the pavement to determine the pavement's structural makeup as well as determining whether or not subsurface moisture is a contributing factor. Once the characteristic alligator pattern is apparent, repair by crack sealing is generally ineffective. Fatigue crack repair generally falls into one of two categories:
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Bleeding | |||
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Description: A film of asphalt binder on the pavement surface. It usually creates a shiny, glass-like reflecting surface that can become sticky when dry and slippery when wet. Problem: Loss of skid resistance when wet, unsightly Possible Causes: Bleeding occurs when asphalt binder fills the aggregate voids during hot weather or traffic compaction, and then expands onto the pavement surface. Since bleeding is not reversible during cold weather or periods of low loading, asphalt binder will accumulate on the pavement surface over time. Likely causes are:
Repair: The following repair measures may eliminate or reduce the asphalt binder film on the pavement's surface but may not correct the underlying problem that caused the bleeding:
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Block Cracking | |||
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Description: Interconnected cracks that divide the pavement up into rectangular pieces. Blocks range in size from approximately 1 ft2 to 100 ft2. Larger blocks are generally classified as longitudinal and transverse cracking. Block cracking normally occurs over a large portion of pavement area but sometimes will occur only in non-traffic areas. Problem: Allows moisture infiltration, roughness Possible Causes: HMA shrinkage and daily temperature cycling. Typically caused by an inability of asphalt binder to expand and contract with temperature cycles because of:
Repair: Strategies depend upon the severity and extent of the block cracking:
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Corrugation and Shoving | |||
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Description: A form of plastic movement typified by ripples
(corrugation) or an abrupt wave (shoving) across the pavement
surface. The distortion is perpendicular to the traffic
direction. Usually occurs at points where traffic starts
and stops (corrugation) or areas where HMA abuts a rigid
object (shoving).
Problem: Roughness Possible Causes: Usually caused by traffic action (starting and stopping) combined with:
Repair: A heavily corrugated or shoved pavement should be investigated to determine the root cause of failure. Repair strategies generally fall into one of two categories:
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Depression | |||
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Description: Localized pavement surface areas with slightly
lower elevations than the surrounding pavement. Depressions
are very noticeable after a rain when they fill with water.
Problem: Roughness, depressions filled with substantial water can cause vehicle hydroplaning Possible Causes: Subgrade settlement resulting from inadequate compaction during construction. Repair: By
definition, depressions are small localized areas. A
pavement depression should be investigated
to determine the root cause of failure. Depressions
should be repaired by removing the affected pavement
then digging out and
replacing
the area of poor subgrade. Patch over the repaired
subgrade. |
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Joint Reflection Cracking | |||
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Description: Cracks in a flexible overlay of a rigid
pavement. The cracks occur directly over the underlying
rigid pavement joints. Joint reflection cracking does not
include reflection cracks that occur away from an underlying
joint or from any other type of base (e.g., cement or lime
stabilized).
Problem: Allows moisture infiltration, roughness Possible Causes: Movement of the rigid pavement slab beneath the HMA surface because of thermal and moisture changes. Generally not load initiated, however loading can hasten deterioration. Repair: Strategies depend upon the severity and extent of the cracking:
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Longitudinal Cracking | |||
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Description: Cracks parallel to the pavement's centerline
or laydown direction. Usually a type of fatigue cracking.
Problem: Allows moisture infiltration, roughness, indicates possible onset of fatigue cracking and structural failure. Possible Causes:
Repair: Strategies depend upon the severity and extent of the cracking:
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Patching | |||
Description: 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.
Problem: Roughness Possible Causes:
Repair: Patches are themselves a repair action. The
only way they can be removed from a pavement's
surface is
by either a structural or non-structural
overlay. |
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Polished Aggregate | |||
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Description: Areas of HMA pavement where the portion
of aggregate extending above the asphalt
binder is either
very small or there are no rough or angular aggregate particles.
Problem: Decreased skid resistance Possible Causes: Repeated traffic applications. Generally, as a pavement ages the protruding rough, angular particles become polished. This can occur quicker if the aggregate is susceptible to abrasion. Repair: Apply
a skid-resistant slurry
seal, BST or non-structural
overlay. |
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Potholes | |||
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Description: Small, bowl-shaped depressions in the pavement
surface that penetrate all the way through the HMA layer
down to the base
course. They generally have sharp edges
and vertical sides near the top of the hole. Potholes are
most likely to occur on roads with thin HMA surfaces (1
to 2 inches) and seldom occur on roads with 4 inch or deeper
HMA surfaces (Roberts et al., 1996).
Problem: Roughness (serious vehicular damage can result from driving across potholes at higher speeds), moisture infiltration Possible Causes: Generally, potholes are the end result of fatigue cracking. As fatigue cracking becomes severe, the interconnected cracks create small chunks of pavement, which can be dislodged as vehicles drive over them. The remaining hole after the pavement chunk is dislodged is called a pothole. Repair: In accordance with patching
techniques. |
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Raveling | |||
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Description: The progressive disintegration of an HMA
layer from the surface downward as a result of the dislodgement
of aggregate particles.
Problem: Loose debris on the pavement, roughness, water collecting in the raveled locations resulting in vehicle hydroplaning, loss of skid resistance Possible Causes:
Repair: A raveled pavement should be investigated to determine the root cause of failure. Repair strategies generally fall into one of two categories:
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Rutting | |||
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Description: Surface depression in the wheelpath. Pavement
uplift (shearing) may occur along the sides of the rut.
Ruts are particularly evident after a rain when they are
filled with water. There are two basic types of rutting:
mix rutting and subgrade rutting. Mix rutting occurs when
the subgrade does not rut yet the pavement surface exhibits
wheelpath depressions as a result of compaction/mix
design problems. Subgrade rutting occurs when the subgrade exhibits
wheelpath depressions due to loading. In this case, the
pavement settles into the subgrade ruts causing surface
depressions in the wheelpath.
Problem: Ruts filled with water can cause vehicle hydroplaning, can be hazardous because ruts tend to pull a vehicle towards the rut path as it is steered across the rut. Possible Causes: Permanent deformation in any of a pavement's layers or subgrade usually caused by consolidation or lateral movement of the materials due to traffic loading. Specific causes of rutting can be:
Repair: A heavily rutted pavement should be investigated
to determine the root cause of failure (e.g. insufficient
compaction, subgrade rutting, poor mix design or studded
tire wear). Slight ruts (< 1/3 inch deep) can generally
be left untreated. Pavement with deeper ruts should be leveled and overlayed. |
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Slippage Cracking | |||
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Description: Crescent or half-moon shaped cracks generally
having two ends pointed into the direction of traffic.
Problem: Allows moisture infiltration, roughness Possible Causes: Braking or turning wheels cause the pavement surface to slide and deform. The resulting sliding and deformation is caused by a low-strength surface mix or poor bonding between the surface HMA layer and the next underlying layer in the pavement structure. Repair: Removal and replacement of affected area. |
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Stripping | |||
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Description: The loss of bond between aggregates and asphalt binder that typically begins at the bottom of the
HMA layer and progresses upward. When stripping begins
at the surface and progresses downward it is usually called raveling.
Problem: Decreased structural support, rutting, shoving/corrugations, raveling, or cracking (fatigue and longitudinal) Possible Causes: Bottom-up stripping is very difficult to recognize because it manifests itself on the pavement surface as other forms of distress including rutting, shoving/corrugations, raveling, or cracking. Typically, a core must be taken to positively identify stripping as a pavement distress. Stripping is typically caused by:
Repair: A stripped pavement should be investigated
to determine the root cause of failure (i.e.,
how did the
moisture get in?). Generally, the stripped pavement
needs to be removed and replaced after correction
of any subsurface
drainage issues. |
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Transverse (Thermal) Cracking | |||
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Description: Cracks perpendicular to the pavement's centerline
or laydown direction. Usually a type of thermal cracking.
Problem: Allows moisture infiltration, roughness Possible Causes:
Repair: Strategies depend upon the severity and extent of the cracking:
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Water Bleeding and Pumping | |||
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Description: Water bleeding occurs
when water seeps out of joints or cracks or through an
excessively porous HMA layer. Pumping occurs when water
and fine material is ejected from underlying layers through
cracks in the HMA layer or out the sides
of the HMA layer under moving loads.
Problem: Decreased skid resistance, an indication of high pavement porosity (water bleeding), decreased structural support (pumping) Possible Causes:
Repair: Water bleeding or pumping
should be investigated to determine the root cause.
If the problem is a high
water table or poor drainage, subgrade drainage should
be improved. If the problem is a porous mix (in the
case of water bleeding) a fog
seal or slurry
seal may
be applied
to limit water infiltration. |