Pavement Failure Identification A-1

Appendix A

Pavement FailureIdentification

IDENTIFYING AND CORRECTINGPAVEMENT FAILURES

The key to proper maintenance of asphaltpavements is to understand the causes offailures and the action(s) needed for correctionbefore any repair work is done. To make themost of maintenance budgets, proven methodsmust be used to correct failures and to preventtheir recurrence.

The following section provides basic infor-mation on the most common types of pave-ment failures, including their probable causeand the measures recommended for theircorrection. Personnel involved in asphaltmaintenance operations must be well advised,trained, and properly equipped. With diligentapplication, the following section can assist inhelping them achieve an efficient, effective,and consistent asphalt pavement maintenancesystem.

Types of Pavement FailuresThe following photographs illustrate the

types of pavement failures most commonlyencountered in asphalt pavements. Next toeach photograph is a description of the failuretype, probable cause of the failure, andrecommended correction.

Bleeding or FlushingThis distress is caused by excess asphalt in

the surface layer. Contributing factors includeinsufficient or excess covering stone, lack ofproper rolling during placement, or failure toprotect a newly constructed surface fromtraffic until the asphalt has cured sufficiently.

Minor bleeding can often be corrected byapplying coarse sand or stone screenings toblot up excess asphalt.

Major bleeding can be corrected by cuttingoff excess asphalt with a motor grader orremoving it with a Òheater planer.Ó If theresulting surface is excessively rough, resur-facing may be necessary.

Corrugations and ShovingCorrugations and shoving are caused by

instability in the asphalt layers caused by amixture that is too rich in asphalt, has too highof a proportion of fine aggregate, has coarse orfine aggregate that is too rounded or toosmooth-textured, or has asphalt cement that istoo soft. Corrugations and shoving may also becaused by excessive moisture, contaminationcaused by oil spillage, or lack of curing timebetween placing seal treatments. This type ofdistress frequently occurs at grade inter-sections as a result of braking forces imposedby stopping vehicles.

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To repair corrugations in an aggregate baseoverlain with a thin surface treatment, scarifythe pavement, add aggregate as needed, mixwell, re-compact, prime, and then resurface.Where the surface has 2 inches or more ofasphalt plant mix, corrugations can beremoved with a ÔÕheater planer.ÕÕ After removalof corrugations, cover with a new surfacetreatment or new asphalt overlay. To repairshoved areas, remove surface and base asnecessary and replace with a more stablematerial to prevent a recurrence. For out-of-season inclement weather repairs, smoothshoved areas with patching if the surfaceunevenness is hazardous to traffic.

Cracking, AlligatorInterconnected cracks forming a series of

small polygons resembling an alligatorÕs skinare called alligator cracks. There are numerouskinds of alligator cracks, some of which areillustrated and discussed below.

In situ investigations must be performed todetermine the most probable of several causesof alligator cracking. If poor drainage isimplicated, corrections should be made asquickly as possible. Should the pavement beproperly drained, then the base is probablyinadequate, and the pavement will requirereconstruction or a heavy resurfacing. Majorresurfacing will also be required if crackingresults from the fatigue effect of repetitiveheavy truck loads. If the cause of distress

cannot be corrected soon (rebuilding of thepavement may be several years in the future),temporary repairs may be required.

Alligator Cracking without Surface Distortion

Skin patching should be applied whenweather permits. This is often a temporarymeasure and should not be considered apermanent correction of a major problem.Alligator cracking generally requires removalof the cracked pavement and an asphalt patchof at least 4 inches in depth.

Alligator Cracking with Distortion of IntactSurfaces

Where distortion is 1 inch or less and theexisting surface is intact, a skin patch shouldbe applied. Where distortion is more than 1inch and the existing surface is intact, a tackcoat should be applied followed by an AsphaltConcrete overlay.

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Alligator Cracking with Broken Surfaces

Where the existing surface is badly crackedand loose (regardless of amount of distortion),remove old surface, tack area, and repair usingAsphalt Concrete. Sound judgment should beused to determine when the existing surface isconsidered firm and should remain in place orwhen it is considered loose and should beremoved before placing the Asphalt Concreteoverlay.

Alligator Cracking with Surface Distortionand Pumping

There are several causes of this type ofdistress. Often poor drainage resulting in a wetbase and/or subgrade is responsible. If thepavement is properly drained, then water isgetting to the base and/or subgrade fromcracks or holes in the surface or from moisturecoming up through the subgrade.

This distress should be repaired as follows:

1. Cut out pavement and wet material.2. If the base or surface is wet from

underneath, install necessary underdrainsto prevent future saturation.

3. Prime area.4. Replace with a minimum of 4 inches of

Asphalt Concrete.5. Compact Asphalt Concrete.

For out-of-season inclement weather repair,keep the area filled with either cold patchmaterial or treated aggregate base.

Note: If you follow the photographs onrandom surface cracks and alligator cracking,you can see how surface distress can progressfrom undesirable to intolerable because of lackof proper drainage. This is not to imply thatpoor drainage is the only cause of surface crack-ing. However, it is often a major contributor.

Cracking, EdgeThe following items discussing edge cracks

concern those pavement surfaces underlain bybase material and not areas where the surfacehas been gradually widened over the yearsuntil its edge is inadequately supported by abase layer.

Cracking without surface distortion isusually caused by lack of shoulder (lateral)support. When the surface is distorted,possible causes are more diverse. In somecases, the base layer may be of insufficientquality or thickness to support the trafficloads. Poor drainage is also a frequent cause. Iswater getting in from the top, sides, or bottom?Is base failure causing distortion and allowingwater to wet the base and/or subgrade? Is aclogged ditch line causing water to seepthrough porous shoulder material and saturatethe base and subgrade? Corrective measuresshould be undertaken as soon as possible.

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Edge Cracks without Surface Distortion

The first step is to correct the problem of lackof lateral support if necessary. For cracks lessthan 1/4 inch in width, no maintenance isrequired. A skin patch is sufficient for largercracks.

Edge Cracks with Distortion of IntactSurfaces

Where distortion is 1 inch or less and theexisting surface is intact, a skin patch shouldbe applied. Where distortion is more than 1inch and existing surface is intact, tack areaand build up with Asphalt Concrete.

Edge Cracks with Broken Surfaces

Where the existing surface is badly crackedand loose, regardless of distortion, the oldsurface must be removed. Prior to replacingthe surface, consideration should be given tothe necessity of first replacing the basematerial if it has been pushed up and out intothe shoulder. This action will have reduced theamount of base material that remains in placeand thus will have reduced the strength of thepavement. If this condition exists, it should becorrected by either replacing the base materialor by building up the depressed area withAsphalt Concrete.

Sound judgment should be used todetermine whether the existing surface isconsidered firm and should remain in place orif it is considered loose and should be removedand replaced. When Asphalt Concrete is usedto replace the base material, it should be ofequal or greater strength than the material itreplaces.

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Edge Cracks with Surface Distortion andPumping

To repair such distress, take the followingsteps:

1. Remove unsuitable material. 2. Install any necessary underdrains. 3. Replace base with a well-graded aggregate. 4. Compact aggregate. 5. Prime area. 6. Replace surface using Asphalt Concrete.

When inclement weather prohibits properrepair, try to keep the distressed area filledwith cold patch material.

Cracking, JointJoint cracks occur where the shoulder or

paved wedge separates from the mainlinepavement or along weak seams of adjoiningpavement spreads in the surface layers.

Joint Crack at Pavement Edge

This distress is caused by wetting or dryingaction beneath the shoulder surface caused byconditions that trap water and allow it to standalong and seep through the joint between theshoulder and the mainline surface.

If the cracking is less than 1/4 inch in width,no maintenance is required. Otherwise, a crackshould be filled with a cutback or emulsifiedasphalt.

Joint Crack at Lane Joints

Distress is caused by a weak seam betweenadjoining spreads in the courses of thepavement.

If the cracking is less than 1/4 inch in width,no maintenance is required. Otherwise, thecrack should be filled with a cutback oremulsified asphalt.

Cracking, RandomThe causes of random cracking are

numerous and, in its early stages, difficult todetermine. Consequences range from severe,such as deep foundation settlement, to slight,such as a construction error or mishap.

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Narrow Cracks

For cracking less than 1/4 inch in width,take no action. If associated distress of anothertype exists, the cracking will progress, andremedial action will ultimately be required.

Wide Cracks

When random cracks reach 1/4 inch or morein width, remedial action is often required.However, the appropriate action may bedifficult to determine. On some pavements,cracking will not progress significantly fromyear to year. Previous experience and/or thetraffic volume and type of pavement mayindicate that it is not necessary to takeimmediate action. Sound judgment should beused when deciding if action should be takenin this case. In most cases, the crack shouldeither be covered with a skin patch or be filledwith a cutback or emulsified asphalt andcovered with sand.

Note: Both methods are acceptable, andgood judgment should be used to determinewhich method is best according to theparticular distress, materials available, andprevious experience.

Cracking, ReflectionReflection cracking is caused by vertical and

horizontal movements in the pavementbeneath overlays that result from expansionand contraction with temperature or moisturechanges. Reflection cracking is very apparentwhere plant mix has been placed over PortlandCement Concrete pavement or where oldalligator cracks have propagated up throughan overlay or patch.

If reflection cracks are no more than 1/4 inchin width, no maintenance is required. Largercracks should be filled with a cutback or anemulsified asphalt and covered with sand.

Such treatment is seldom permanent whenapplied to overlays over old Portland CementConcrete pavement. Continual expansion andcontraction of the concrete causes convention-ally repaired cracks to reappear quickly. Asingle course surface treatment over theexisting pavement immediately preceding theoverlay is a good crack relief measure thatminimizes reflective cracking.

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To repair slippage cracks, neatly remove theunbonded section of the surface, apply a suit-able tack, and replace the surface with a highquality Asphalt Concrete. During inclementweather, keep the exposed area filled with coldmix material if it is likely to be a traffic hazard.

Cracking, TransverseA transverse crack follows a course approxi-

mately at right angles to the pavement centerline, usually extending across the full pave-ment width. In Iowa, transverse cracks aremost often the result of reflection cracking.However, they can also result from stressesinduced by low-temperature contraction of thepavement, especially if the asphalt is hard andbrittle.

Repair procedures for transverse crackingare similar to those for reflection cracking.

Polished AggregateAlthough uncrushed gravels often have

surfaces that are initially smooth andpotentially hazardous, crushed rock initiallyhas a rough, skid-resistant texture. Under theaction of traffic, however, some aggregates Ðincluding many limestones Ð become polishedand slick, especially when wet. The likelihoodof aggregate becoming polished increases withthe volume of traffic. Because polishedaggregate results in a loss of skid resistance, itis potentially hazardous. The most economicalrepair is to apply a skid-resistant surfacetreatment.

PotholesPotholes occur most frequently during the

winter months when it is difficult to make themost desirable repairs. Consequently, it isoften necessary to repair potholes in ways thatare less than permanent. General patchingshould not be done during inclement weatherexcept to correct hazardous conditions. Soundjudgment must be exercised when makingrepairs during poor weather conditions.

Potholes are caused by water penetrat-ing the surface and causing the base and/or subgrade to become wet and unstable. They also may be caused by a surface that is too thin or that lacks

Cracking, ShrinkageShrinkage cracking appears on the pave-

ment surface as interconnected cracks forminga series of polygons, usually having sharpangles at the corners. Unlike alligator cracking,which is associated primarily with trafficloading, shrinkage cracking is caused byvolume change within the Asphalt Concrete,the aggregate base, and/or the subgradelayers.

If the shrinkage cracking is severe and hasseriously weakened the pavement structure, astructural overlay will be necessary to restoreit. Most likely, however, the cracking will notbe progressive, and a surface treatment Ðpreceded by filling the larger cracks with acutback or emulsified asphalt Ð will suffice forsurface restoration.

Cracking, SlippageSlippage cracks are crescent-shaped cracks

that usually point in the direction of trafficmovement. They result from insufficient bondbetween the surface and underlaying courses,caused by dust, oil, rubber, dirt, water, or notack coat between the two courses.

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sufficient asphalt content, lacks sufficient base, or has too many or too few fines. Did youand/or your personnel fail to performmaintenance that would have preventedpothole formation? If water is the culprit, it iscaused by a cracked surface, high shoulders orpavement depressions ponding water on thepavement, porous or open surface, or cloggedside ditches? Correct the cause of the problemas soon as possible.

Potholes in Surface Treatments overAggregate Base

To repair potholes in surface treatments,take the following actions:

1. Clean out hole. 2. Remove any wet base. 3. Shape hole so that it has vertical sides. 4. Prime hole. 5. Fill hole with Asphalt Concrete.

Potholes in Asphalt Concrete

To repair potholes in Asphalt Concrete, takethe following actions:

1. Clean out hole.2. Remove any wet base.3. Square up pothole so that it has neat lines

both perpendicular and parallel to thecenter line and has vertical sides.

4. Prime the pothole.5. Fill the pothole with Asphalt Concrete.

RavelingRaveling is caused by a dry brittle surface;

dirty, dusty, or soft aggregate; patching beyondbase material; lack of compaction of surfaceduring construction; too little asphalt in mix;or excessive heating during mixing.

When a small percentage of the pavement israveling, repair with a skin patch (this includesedge raveling). When a large percentage of thepavement shows raveling, the pavementshould be resurfaced.

Note: If the raveling is not a part of thepaved surface, no action should be taken. Inother words, donÕt patch beyond the edge ofthe pavement.

Channels or RuttingChannels are caused by heavy loads and high

tire pressures, subgrade settlement caused bysaturation, poor construction methods, orasphalt mixtures of inadequate strength.

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Intact Surface

Where the depression is 1 inch or less andthe surface is cracked but still largely intact,skin patch the area. Where the depression ismore than 1 inch and the surface is cracked butstill largely intact, repair with asphalt concrete.

Disintegrated Surface

Where the surface is badly cracked and loose(regardless of amount of depression), removethe old surface. If the area shows signs of mudbeing pumped to the surface, remove all wetmaterial, replace base material, compact,prime, and build up with Asphalt Concrete.

Upheaval or Frost BoilUpheaval is caused by expansion of freezing

moisture in the lower courses of the pavementor subgrade or by the swelling effect ofmoisture in expansive soils.

When this distress occurs, repair byinstalling combination drains as necessary andreplacing base and surface.