surface distresses

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Pavement Distress - 1

Surface Distresses

Properly designed and maintained HMA pavements can provide manyyears of satisfactory service. However, like all pavements, HMApavements can be damaged by certain conditions.

This page is intended to:1. Assist in identifying basic HMA pavement damage. HMA pavement

damage that is visible at the surface of the pavement is often called"surface distress".

2. Provide some insight into why particular surface distresses areproblematic.

3. Provide some basic guidance into what kinds of conditions might leadto certain surface distresses.

4. Suggest some basic repair strategies.

Photos of each type of distress are accompanied by a description of thedistress, the reason it is a problem, some of the most likely causes andbasic repair strategy.


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magnitude of loads becomes too great, longitudinal cracks begin to form(usually in the wheelpaths). After repeated loading, these longitudinalcracks connect forming many-sided sharp-angled pieces that developinto 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 inpotholes 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 commonones are:

Decrease in pavement load supporting characteristics

Probably the most common reason is a loss of base, subbase orsubgrade support from things like poor drainage or spring thaw.Water under a pavement will generally cause the underlying

materials to become weak. Stripping on the bottom of the HMA layer. The stripped depth

contributes little to pavement strength so the effective HMAthickness decreases.

Increase in loading (i.e., the pavement is being loaded more heavilythan anticipated in design)

Inadequate structural design (i.e., the pavement was designed toothin for the anticipated loads)

Poor construction (i.e., inadequate compaction)

Repair: A fatigue cracked pavement should be investigated to determinethe root cause of failure. Any investigation should involve digging a pitor coring the pavement to determine the pavement's structural makeupas well as determining whether or not subsurface moisture is acontributing factor. Once the characteristic alligator pattern isapparent, repair by crack sealing is generally ineffective. Fatigue crackrepair generally falls into one of two categories:

Small, localized fatigue cracking indicative of a loss of subgradesupport. Remove the cracked pavement area then dig out andreplace the area of poor subgrade and improve the drainage of thatarea if necessary. Patch over the repaired subgrade.

Large fatigue cracked areas indicative of general structural failure.Place an HMA overlay over the entire pavement surface. This overlaymust be strong enough structurally to carry the anticipated loadingbecause the underlying fatigue cracked pavement most likelycontributes little or no strength (Roberts et. al., 1996).


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Bleeding

Classic bleeding on a newly paved road shows up as a shinyreflecting surface - especially in the wheelpaths where the

aggregate voids are less.

Bleeding on a freshly paved SMA job, most likely the result ofmix design or production problems.


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Description: A film of asphalt binder on the pavement surface. Itusually creates a shiny, glass-like reflecting surface that can becomesticky when dry and slippery when wet.

Problem: Loss of skid resistance when wet, unsightly

Possible Causes: Bleeding occurs when asphalt binder fills the aggregatevoids during hot weather or traffic compaction, and then expands ontothe pavement surface. Since bleeding is not reversible during coldweather or periods of low loading, asphalt binder will accumulate onthe pavement surface over time. Likely causes are:

Excessive asphalt binder in the HMA (either due to a poor mix designor manufacturing problems)

Excessive application of asphalt binder during BST application

Low HMA air void content (e.g., not enough void space for theasphalt to occupy), likely a mix design problem

Repair: The following repair measures may eliminate or reduce theasphalt binder film on the pavement's surface but may not correct theunderlying problem that caused the bleeding:

Minor bleeding can often be corrected by applying coarse sand toblot up the excess asphalt binder.

Major bleeding can be corrected by cutting off excess asphalt with amotor grader or removing it with a heater planer. If the resultingsurface is excessively rough, resurfacing may be necessary (APAI, nodate given).


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Block Cracking

Block cracking in a parking lot near the University ofWashington. Block cracking in parking lots is common becausemany parking lot pavements experience only light traffic (e.g.,

no heavy trucks)

Description: Interconnected cracks that divide the pavement up intorectangular pieces. Blocks range in size from approximately 1 ft2 to 100ft2. Larger blocks are generally classified as longitudinal and transversecracking. Block cracking normally occurs over a large portion ofpavement 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 andcontract with temperature cycles because of:

Asphalt binder aging

Poor choice of asphalt binder in the mix design

Repair: Strategies depend upon the severity and extent of the block

cracking: Low severity cracks (< 1/2 inch wide). Crack seal to prevent (1)

entry of moisture into the subgrade through the cracks and (2)further raveling of the crack edges. HMA can provide years ofsatisfactory service after developing small cracks if they are keptsealed (Roberts et. al., 1996).

High severity cracks (> 1/2 inch wide and cracks with raveled edges).Remove and replace the cracked pavement layer with an overlay.


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Corrugation and Shoving

Corrugation on the uphill side of a street. Corrugations wereprobably caused by vehicles starting on the uphill grade

Shoving at a busy intersection. Conditions are bad enough here

that the shoving occurs not only near rigid objects but acrossthe pavement in general

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 atpoints where traffic starts and stops (corrugation) or areas where HMAabuts a rigid object (shoving).


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Problem: Roughness

Possible Causes: Usually caused by traffic action (starting and stopping)combined with:

An unstable (i.e. low stiffness) HMA layer (caused by mix

contamination, poor mix design, poor HMA manufacturing, or lack ofaeration of liquid asphalt emulsions)

Excessive moisture in the subgrade

Repair: A heavily corrugated or shoved pavement should be investigatedto determine the root cause of failure. Repair strategies generally fallinto one of two categories:

Small, localized areas of corrugation or shoving. Remove thedistorted pavement and patch.

Large corrugated or shoved areas indicative of general HMA failure.

Remove the damaged pavement and overlay.


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Depression

Depression in an access roadway probably caused by subgradesettlement. Note that the pavement has fatigue cracked

significantly as it has settled

Depression in parking lot probably caused by subgradesettlement. Again, the pavement has a considerable amount of

fatigue cracking where it has settled


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Description: Localized pavement surface areas with slightly lowerelevations than the surrounding pavement. Depressions are verynoticeable after a rain when they fill with water.

Problem: Roughness, depressions filled with substantial water can causevehicle hydroplaning

Possible Causes: Frost heave or subgrade settlement resulting frominadequate compaction during construction.

Repair: By definition, depressions are small localized areas. Apavement depression should be investigated to determine the rootcause of failure (i.e., subgrade settlement or frost heave). Depressionsshould be repaired by removing the affected pavement then digging outand replacing the area of poor subgrade. Patch over the repairedsubgrade.


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Joint Reflection Cracking

Joint reflective cracking on a low-use industrial road. Thispavement has been cracked for many years and will probablynot get much worse. Notice the grass growing in the cracks.

Joint reflective cracking on an urban arterial. Some jointreflective cracks on this pavement are crack sealed but theseare probably too advanced and too wide to be crack sealed.

Description: Cracks in a flexible overlay of a rigid pavement. The cracksoccur directly over the underlying rigid pavement joints. Joint


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reflection cracking does not include reflection cracks that occur awayfrom an underlying joint or from any other type of base (e.g., cement orlime stabilized).


Possible Causes: Movement of the rigid pavement slab beneath the HMAsurface because of thermal and moisture changes. Generally not loadinitiated, however loading can hasten deterioration.

Repair: Strategies depend upon the severity and extent of the cracking:

Low severity cracks (< 1/2 inch wide and infrequent cracks). Crackseal to prevent (1) entry of moisture into the subgrade through thecracks and (2) further raveling of the crack edges. In general, rigidpavement joints will eventually reflect through an HMA overlaywithout proper surface preparation.

High severity cracks (> 1/2 inch wide and numerous cracks). Removeand replace the cracked pavement layer with an overlay.


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Longitudinal Cracking

Longitudinal cracking on a city arterial. Its location in thewheelpath indicates that is probably the onset of fatigue

cracking


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Longitudinal cracking on a rural county road. Its location in thewheelpath indicates that is probably the onset of fatigue

cracking possibly caused by a thin pavement structure.

Description: Cracks parallel to the pavement's centerline or laydowndirection. Usually a type of fatigue cracking.

Problem: Allows moisture infiltration, roughness, indicates possibleonset of fatigue cracking and structural failure.

Possible Causes:

Poor joint construction or location. Joints are generally the least

dense areas of a pavement. Therefore, they should be constructedoutside of the wheelpath so that they are only infrequently loaded.Joints in the wheelpath like those shown in third through fifth figuresabove, will general fail prematurely.

A reflective crack from an underlying layer (not including jointreflection cracking)

HMA fatigue (indicates the onset of future fatigue cracking)

top-down cracking


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Low severity cracks (< 1/2 inch wide and infrequent cracks). Crackseal to prevent (1) entry of moisture into the subgrade through thecracks and (2) further raveling of the crack edges. HMA can provideyears of satisfactory service after developing small cracks if they are

kept sealed (Roberts et. al., 1996). High severity cracks (> 1/2 inch wide and numerous cracks). Remove

and replace the cracked pavement layer with an overlay.


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Patching

Two patches on an urban arterial placed after utilitycuts.

A patch on an urban arterial used to repair a spalledjoint reflective crack.


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Description: An area of pavement that has been replaced with newmaterial to repair the existing pavement. A patch is considered adefect no matter how well it performs.

Problem: Roughness

Possible Causes: Previous localized pavement deterioration that has been removed

and patched

Utility cuts

Repair: Patches are themselves a repair action. The only way they canbe removed from a pavement's surface is by either a structural or non-structural overlay.


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Polished Aggregate

Two adjacent SMA pavements at the NCAT Test Track near Auburn, AL. Thepavement on the right uses river rock, which is more susceptible to abrasion,

as its aggregate and is showing some signs of aggregate polishing.

This close-up picture of a road surface shows aggregate wear after about 5years of wear. Washington generally has high quality aggregate that rarelysuffers from excessive polishing. Notice the aggregate still appears rough.


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Description: Areas of HMA pavement where the portion of aggregateextending above the asphalt binder is either very small or there are norough or angular aggregate particles.

Problem: Decreased skid resistance

Possible Causes: Repeated traffic applications. Generally, as apavement ages the protruding rough, angular particles become polished.This can occur quicker if the aggregate is susceptible to abrasion orsubject to excessive studded tire wear.

Repair: Apply a skid-resistant slurry seal or BST or overlay.


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Potholes

A pothole in the surface course of an urban arterial.This pothole may have come about from fatigue

cracking that started in an excessively raveled area.Left untreated it may eventually spread to the

underlying pavement layers


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A pothole beginning to form from an area of excessivefatigue cracking. Notice how just a few chunks of

pavement are missing forming the genesis of apothole. Left untreated, adjacent pavement chunks

will be dislodged by traffic making the pothole larger.Additionally, the pothole makes it easier for water to

get into the underlying subgrade, further weakening it,and speeding up the deterioration process

Description: Small, bowl-shaped depressions in the pavement surfacethat penetrate all the way through the HMA layer down to the base

course. They generally have sharp edges and vertical sides near the topof the hole. Potholes are most likely to occur on roads with thin HMAsurfaces (1 to 2 inches) and seldom occur on roads with 4 inch or deeperHMA surfaces (Roberts et al., 1996).

Problem: Roughness (serious vehicular damage can result from drivingacross potholes at higher speeds), moisture infiltration


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Possible Causes: Generally, potholes are the end result of fatiguecracking. As fatigue cracking becomes severe, the interconnectedcracks create small chunks of pavement, which can be dislodged asvehicles drive over them. The remaining hole after the pavement chunkis dislodged is called a pothole.

Repair: In accordance with patching techniques.


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Raveling

Raveling possibly resulting from segregation,temperature differentials or inadequate compaction

Raveling that is likely the result of segregation and/orconstruction-related temperature differentials

Description: The progressive disintegration of an HMA layer from thesurface downward as a result of the dislodgement of aggregateparticles.


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Problem: Loose debris on the pavement, roughness, water collecting inthe raveled locations resulting in vehicle hydroplaning, loss of skidresistance

Possible Causes:Loss of bond between aggregate particles and the asphalt binder as a

result of: A dust coating on the aggregate particles that forces the asphalt

binder to bond with the dust rather than the aggregate

Aggregate segregation. If fine particles are missing from theaggregate matrix, then the asphalt binder is only able to bind theremaining coarse particles at their relatively few contact points.

Inadequate compaction during construction. High density is requiredto develop sufficient cohesion within the HMA.

Mechanical dislodging by certain types of traffic (studded tires,snowplow blades or tracked vehicles).

Repair: A raveled pavement should be investigated to determine theroot cause of failure. Repair strategies generally fall into one of twocategories:

Small, localized areas of raveling. Remove the raveled pavementand patch.

Large raveled areas indicative of general HMA failure. Remove thedamaged pavement and overlay.


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Rutting

Rutting in a busy arterial in the Greenwood area of Seattle. Ruts can even be seenin the two-way left turn lane indicating that the rutting is not due to heavy traffic

Rutting in the parking lane. Likely, an overlay of the main road was extendedbeyond the original roadway out to the curb . Extra HMA was used to make up thedifference in height but was not adequately compacted because the roller bridgedover the rut area (one side of the drum on the original pavement and the other on

the new mix nearest the curb). Subsequently, a large load or two (i.e., a bus) droveover the poorly compacted area and caused a large rut.


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Description: Surface depression in the wheelpath. Pavement uplift(shearing) may occur along the sides of the rut. Ruts are particularlyevident after a rain when they are filled with water. There are twobasic types of rutting: mix rutting and subgrade rutting. Mix ruttingoccurs when the subgrade does not rut yet the pavement surfaceexhibits wheelpath depressions as a result of compaction/mix design

problems. Subgrade rutting occurs when the subgrade exhibitswheelpath depressions due to loading. In this case, the pavementsettles into the subgrade ruts causing surface depressions in thewheelpath.

Problem: Ruts filled with water can cause vehicle hydroplaning, can behazardous because ruts tend to pull a vehicle towards the rut path as itis 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 thematerials due to traffic loading. Specific causes of rutting can be:

Insufficient compaction of HMA layers during construction. If it is notcompacted enough initially, HMA pavement may continue to densifyunder traffic loads.

Subgrade rutting (e.g., as a result of inadequate pavement structure)

Improper mix design or manufacture (e.g., excessively high asphaltcontent, excessive mineral filler, insufficient amount of angularaggregate particles)

Ruts caused by studded tire wear present the same problem as the rutsdescribed here, but they are actually a result of mechanical dislodgingdue to wear and not pavement deformation.

Repair: A heavily rutted pavement should be investigated to determinethe root cause of failure (e.g. insufficient compaction, subgrade rutting,poor mix design or studded tire wear). Slight ruts (< 1/3 inch deep) cangenerally be left untreated. Pavement with deeper ruts should beleveled and overlayed.


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Slippage Cracking

Slippage crack at an intersection due to stopping. Thedirection of traffic is from top to bottom. Most likelycaused by poor bonding with the underlying pavement

possibly from a poor tack coat.


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Slippage crack near a bus stop on the University ofWashington Seattle campus. Based on the direction of

traffic flow, it appears to be caused by traffic acceleratingfrom a stop. Since this area of campus suffers from anumber of poor overlay bonding problems, this is mostlikely caused by poor overlay bonding to the underlying

pavement.

Description: Crescent or half-moon shaped cracks generally having twoends pointed into the direction of traffic.


Possible Causes: Braking or turning wheels cause the pavement surfaceto slide and deform. The resulting sliding and deformation is caused bya low-strength surface mix or poor bonding between the surface HMAlayer and the next underlying layer in the pavement structure.

Repair: Removal and replacement of affected area.


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Stripping

A small pavement core showing stripping at the bottom ofthe pavement section

A small pavement core showing stripping at the bottom ofthe pavement section


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Description: The loss of bond between aggregates and asphalt binderthat typically begins at the bottom of the HMA layer and progressesupward. When stripping begins at the surface and progresses downwardit 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 recognizebecause it manifests itself on the pavement surface as other forms ofdistress including rutting, shoving/corrugations, raveling, or cracking.Typically, a core must be taken to positively identify stripping as apavement distress.

Poor aggregate surface chemistry

Water in the HMA causing moisture damage

Repair: A stripped pavement should be investigated to determine theroot cause of failure (i.e., how did the moisture get in?). Generally, thestripped pavement needs to be removed and replaced after correctionof any subsurface drainage issues.


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Transverse (Thermal) Cracking

A large transverse crack caused by the pavements contraction in coldweather. The crack has subsequently been patched as a temporary fix.

Another transverse crack caused by thermal contraction during coldweather. This crack has been sealed.


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Description: Cracks perpendicular to the pavement's centerline orlaydown direction. Usually a type of thermal cracking.


Possible Causes: Shrinkage of the HMA surface due to low temperatures or asphalt

binder hardening.

Reflective crack caused by cracks beneath the surface HMA layer

top-down cracking


Low severity cracks (< 1/2 inch wide and infrequent cracks). Crackseal to prevent (1) entry of moisture into the subgrade through thecracks and (2) further raveling of the crack edges. HMA can provide

years of satisfactory service after developing small cracks if they arekept sealed (Roberts et. al., 1996).

High severity cracks (> 1/2 inch wide and numerous cracks). Removeand replace the cracked pavement layer with an overlay.


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Water Bleeding and Pumping

Water bleeding through a pavement surface on a rural mountainhighway. The subgrade around the pavement is still wet from a

recent rain indicating that the water has come up through aporous pavement.

Similar conditions


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Description: Water bleeding (left two photos) occurs when water seepsout of joints or cracks or through an excessively porous HMA layer.Pumping (right-most photo) occurs when water and fine material isejected from underlying layers through cracks in the HMA layer or outthe sides of the HMA layer under moving loads.

Problem: Decreased skid resistance, an indication of high pavementporosity (water bleeding), decreased structural support (pumping)

Possible Causes:

Porous pavement as a result of inadequate compaction duringconstruction or poor mix design

High water table

Poor drainage

Repair: Water bleeding or pumping should be investigated to determinethe 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 appliedto limit water infiltration.

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