Cracking in asphalt pavements.pdf

7/30/2019 Cracking in asphalt pavements.pdf

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op c:op c:CRACKING IN ASPHALTCRACKING IN ASPHALT

PAVEMENTSPAVEMENTS

Dec 2010Dec 2010


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IntroductionIntroduction

Cracks occur from a variety of causes includingstresses from axle loads, temperature changes in

e ayer, or mo s ure an empera urechanges in an underlying layer.

t s mportant to accurate y ent y t e type o

cracking which a pavement exhibits in order to

subsequently the proper repair techniques.

fatigue, low temperature, longitudinal, block,


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Types, causes and repair of crackingTypes, causes and repair of cracking

Fatigue Cracking

Low temperature Cracking

Longitudinal Cracking

Reflection Cracking Slippage Cracking


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Fatigue CrackingFatigue Cracking

pavementinteractive.org

this closely spaced crack pattern is similar to the pattern

on an alligators back.


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www8.dotd.louisiana.gov

has been stressed to the limit of its fatigue life byrepetitive axle load applications.


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Causes of Fatigue cracking:

too heavy loads

more repetitions of a given load than provided for in design. repetitive passes with overweight trucks and/or

inadequate pavement thickness due to improper design orpoor quality control during construction

development of potholes when the individual pieces of HMAphysically separate from the adjacent material and are

s o ge rom e pavemen sur ace y e ac on o ra c


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Investigation:

needed prior to repair of a pavement with fatigue cracking

determines the cause of the problem so that a propersolution can be selected

pavement layers

Sam les of the la ers can be obtained


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Repair strategies for fatigue cracking: typicallyinvolve

Removal & replacement

If the cracking is localized the damaged areas can

be removed and replaced prior to overlay Another option is to place a thick overlay over the

area that is fatigue cracked


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Low temperature CrackingLow temperature Cracking

http://whrpnews.orghttp://www.fhwa.dot.gov/hfl/partnerships/

Low temperature cracks: transverse cracks whichgenerally run perpendicular to the roadway centerline andare o en approx ma e y equa y space


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Occur: when the temperature at the surface dropssufficiently to produce a thermally induced shrinkages ress n e ayer a excee s e ens e s reng

of the asphalt mixture


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Usually initiate at the top of the HMA and propagatedownward through the mixtures.


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Controlling the occurrence of thermal cracking:

select a PG graded asphalt that has desirable low

Repair:

yp ca y sea e w a qu asp a or o er ype o sea ngmaterial (ASTM D5078 and D3405)

When the sides of the crack are at different elevationsgrinding has been performed to minimize the bump at thecrack, thereby improving the ride quality

crac ng ecomes oo severe, e pavemen may ave o

be overlaid with adequate thickness of HMA to resistreflective cracking


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Longitudinal CrackingLongitudinal Cracking

Longitudinal cracks are individual cracks that basically run

http://www.asphaltinstitute.org

parallel to the centerline of the roadway


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often occur at the joint between adjacent lanes of asphalt


mixture or at the edges of the wheel paths on high traffic

volume roads


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These cracks allow water to penetrate into the underlying


ayers, so en ng ayers a ave no een s a ze w

asphalt or other materials and accelerating thedevelopment of fatigue cracks


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Sometimes longitudinal cracks develop in the mat as a


resu o mproper p acemen an compac on ur ng

construction


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The longitudinal cracks between adjacent lanes can be


nc u e y ow empera ure, s nce e ens y a e o n

between paving lanes is lower than the remainder of themat, resulting in low tensile strength at the joint


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Poor adhesion between the asphalt and the aggregate can


aggrava e e pro em a acen o ong u na crac ng

and cause more rapid deterioration


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Longitudinal cracks at the edges of the wheel path are


mos o en cause y eavy oa s or g re pressures

applied in the wheel path


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Repair:

During early stages, these cracks are most oftenrepaired by sealing

After raveling begins to develop, the repair is more. ,

overlay is usually the best solution if the amount of

raveling is extensive


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Block CrackingBlock Cracking

http://training.ce.washington.edu/

Block cracking: when a HMA layer cracks both

. .

shapes


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Typically, these cracks are caused by the same factors

. .


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The block cracking pattern most often develops on

. .


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Repair: can be very expensive

Often the old surface is removed by milling andoverlaid with a new or recycled HMA material

Cutting out the damaged material at the cracks and

the pavement shrinks and cracks in the old pavement

material with the next cycle of cold temperatures.

Less costly repair strategies are usually used until theentire surface can be replaced

Either a thick overlay is placed on the existing surface,some type of method to reduce reflective cracking is

,a new HMA surface


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Reflection CrackingReflection Cracking

training.ce.washington.edu

Reflection cracks are caused by discontinuities inthe underlying layers which propagate through


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Reflection cracks may be caused by:

Cracks or joints in an underlying concrete pavement

Low temperature cracks in the old HMA surface Block cracks induced by the old HMA surface or those

included by subgrade soil cracking due to shrinkagewhether stabilized or not

Longitu ina crac s in t e o sur ace; or

Fatigue cracks in the old surface


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One technique that has been successfully used toprevent the recurrence of these cracks is rubblizing

Another process that has been used to treat reflective

the HMA overlay directly over the existing joints in the

concrete. These cuts are made shortly after construction and

before the reflection cracks develop.

This technique cannot be applied to random cracks inthe concrete pavement


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Slippage CrackingSlippage Cracking


Slippage cracks typically occur as a result of poor bondbetween the HMA surface and the underlying layer

hese cracks most often show up first in areas where

vehicles brake, turn, or accelerate


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Slippage CrackingSlippage Cracking

Repair:

The only repair for areas with slippage cracks isremoval and replacement of the material in the slipped

area, -> ensure that a proper bond between the oldsurface and the new HMA material is obtained.

Removal of the existing slipped material with a milling

machine results in a rough surface texture -> thatshould help provide good bond when overlaid.

The material must be removed to a depth slightly

e ow e po n a w c s ppage as occurre .


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Cracking in asphalt pavements.pdf