© American Concrete Pavement Association 1998

Rubblizing of Concrete Pavements:A Discussion of its UsePublic agencies have been misusing rubblization and an asphaltoverlay of concrete slabs as a rehabilitation technique for the last 10to 15 years. It has been misused because most of the pavementsthat have been rubblized did not need rubblization. In mostsituations, either concrete pavement restoration (CPR) or a concreteoverlay is a more appropriate and economical rehabilitationprocedure. These procedures directly address why a concretepavement is deteriorating and minimize further deterioration.

Rubblization is a destructive procedure that breaks an existingconcrete slab into small fragments. This destroys the structuralintegrity of the pavement and reduces its load carrying capacity.Unlike CPR or concrete overlays, rubblization does not address thecause of the existing pavement deterioration and sometimes it canexacerbate the problem. For example, many concrete distresses area result of poor support conditions. Rubblizing a pavement destroysthe concrete slab’s natural bridging action, causing the problems tobecome more pronounced. This can and has caused early failure ofthe asphalt overlay.1

The only appropriate time to rubblize an existing concrete pavementis when it has severe material durability problems, such as alkali-silicareactivity (ASR), D-cracking, or freeze-thaw damage. These materialproblems cause the concrete pavement to deteriorate and lose itsstructural integrity.

THE THEORY BEHIND RUBBLIZATION

Rubblization∗ breaks the existing concrete pavement into smallfragments that range from sand size pieces to pieces approximately100 mm (4 in.) to 200 mm (8 in.) in width. It was developed as anattempt to control the reflective cracking that occurs in an asphaltoverlay of concrete. Reflective cracking is the cracking that occursabove a concrete pavement’s joints. It happens because the asphaltoverlay is too weak to withstand the daily and seasonal temperaturemovements of the underlying concrete.

* Rubblization is just one type of fracturing procedure that destroys the concrete pavement.Crack and Seat (C/S) and Break and Seat (B/S) are two other types. C/S is used on JPCP andhas a crack spacing from 300 to 1500 mm (12 to 60 in.). B/S is used on JRCP or CRCP and hasa crack spacing from 150 to 600 mm (6 to 24 in.).

INCLUDES:

Discussion on thetheory for rubblizing apavement’s structure

Performance ofrubblized concreteand asphalt overlay

Alternatives toRubblization

• CPR

• Bonded Overlays

• Unbonded Overlays

Recommendations onwhen to rubblize aconcrete pavement

Improved DesignProcedures forAsphalt Overlays ofRubblized ConcretePavement

Proposed DesignProcedures forConcrete Overlays ofRubblized ConcretePavement

Technical InformationConcrete Pavement Engineering and Research

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When an asphalt overlay is placed onan unrubblized concrete pavement,the concrete remains the mainstructural component of thepavement system. The asphalt layeracts mainly as a riding surface.When the concrete slabs expand andcontract because of temperaturechanges, the joints open and close.However, the asphalt layer is tooweak to withstand these movements.This sets up shear stresses in theasphalt-riding layer and it cracks.

To stop the reflective cracking, twofracturing procedures (Crack & Seatand Break & Seat) were developed todecrease the slab length. It wasbelieved that if the slabs wereshorter, the movements at the jointsand cracks would be reduced andthere would no reflective cracking.However, these initial fracturingprocesses were not successful.Even with the reduced movements ofthe smaller slabs, cracks eventuallyreflected through the asphalt overlay.

Rubblization is the reduction of theslab length to the extreme. It

completely destroys the concrete’sslab action by breaking it down intocrushed-stone sized fragments. It isan attempt to turn the existingpavement into base course.However, there is one notableshortcoming to this analogy: arubblized pavement has no gradationor density control. Specifications forbase courses require both gradationand density control.2

In conclusion, rubblization (as well asCrack & Seat and Break & Seat) andan asphalt overlay does not addresswhy an asphalt overlay cracks.Instead, these procedures destroythe concrete slabs so that the asphaltdoes not crack. However, this alsodestroys the main structuralcomponent of the pavement systemand reduces its load carryingcapacity.

PERFORMANCE AND COST

The performance of rubblization andasphalt overlay has varied from goodto very poor. The key to goodperformance is properly assessingthe conditions under the concrete

slabs and theuniformity of therubblized layer.However, this is verydifficult, if notimpossible, to do. Assuch, many asphaltoverlays are severelyunder designed.

One example of this isInterstate 85 (I-85)near Greenville, SouthCarolina.1 Thisoverlay was built in1998 and designed asa 200 mm (8 in.)asphalt overlay on arubblized concretepavement. During

Rubblized concrete pavement.Note the lack of uniformity in the rubblized material.16

construction, normal traffic causedsevere rutting problems in the asphaltoverlay. Upon investigation, it wasfound that the underlying soils weremuch weaker than determined beforerubblization (before rubblization, theconcrete was bridging over the weaksoil).

To strengthen the pavement, thestate needed to add 100-mm (4.0-in.)of asphalt to the 200-mm (8.0 in.)design. This supplemental asphaltadded approximately $2.5 milliondollars to a $15 million dollarcontract.1

The state of Michigan has also hadless than desired performance oftheir rubblized and asphalt overlaidpavements. The accompanying chartis from the Michigan PavementManagement System. It shows the5-year distress index (DI) for 65.8 Km(40.9 miles) of rubblized and asphaltoverlaid pavements. Note: a higherDI means poorer performance. 3

The state requires that asphaltpavements with DI greater than eightbe rehabilitated. Using this criteria,between 47-67% of the 5-year-oldasphalt overlays on rubblizedconcrete pavements need

rehabilitation. For concretepavements, the state requires thatthey be restored when the DI isgreater than four. If that criterionwere used, then between 67-87% ofthe rubblized projects would needrehabilitation. Finally, it is importantto note that approximately 28% of allthe 5-year-old rubblized overlayprojects have a DI greater than 15,indicating substantial distress.

In addition to poor performance,Michigan has seen that the costs ofrubblization and asphalt overlays canbe higher than concrete overlays. Anexample is a set of rehabilitationprojects constructed on I-96.4

The first project, in Clinton County, isa 190-mm (7.5 in.) concrete overlaybuilt in 1991. The second project, inIngham County, is a 152-mm (6 in.)asphalt overlay on rubblized concretedone in 1992. The cost of theconcrete overlay was $1,034,000 permile. The cost for the rubblizationand asphalt overlay was $1,437,500per mile. This is 39% difference inthe initial costs of the projects.

Even with the most controlledexperiments, rubblized concrete andasphalt overlays have had poor

performance. The photos onthe next page are from arubblization project in theStrategic Highway ResearchProgram (SHRP) constructedin 1992.

The project is in thesouthbound lanes of I-35 inKay County, OK. The firstphoto shows a 100-mm (4-in.)asphalt overlay on a rubblized228-mm (9-in.) jointedreinforced concrete pavement.The second photo shows an 8-inch asphalt overlay on thesame pavement.

0

5

10

15

20

25

30

Distress Index

Distress index distribution for rubblized concretepavements and asphalt overlays in Michigan

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4

CPR

Age or Traffic

Min. Acceptable Rating

Pav

emen

t C

on

dit

ion

Bonded Concrete Overlay

Unbonded Concrete Overlay

Reconstruction

Life Cycle diagram showing appropriate pavementrehabilitation strategies and where they relate topavement condition

A 1994 report5 stated that both theseprojects were controlling thereflective cracking. However, sincethat time, both have developed aconsiderable amount of longitudinaland fatigue cracking in thewheelpaths. Though the 200-mm (8-in.) overlay is outperforming the 100-mm (4-in.) overlay, it still has aconsiderable amount of distressconsidering it has only been inservice for 6 years.

Overall, the performance and costdata shows that an asphalt overlay ofa rubblized concrete pavement is ashort-term solution that lasts between8 and 12 years. Because of its shortlife, a rubblized concrete pavementwith an asphalt overlay requires morerepairs and is more costly whencompared to other concretepavement rehabilitation options.

ALTERNATIVES TO

RUBBLIZING AND ASPHALT

OVERLAY

Concrete pavement restoration(CPR) and concrete overlays areprocedures that keep and use theintact structural integrity of anexisting concrete slab. Unlikerubblization, CPR and concreteoverlays directly address the cause ofthe problems in the pavement.

Therefore, they are much moreappropriate and viable solutions.

Concrete PavementRestorationCPR is a series of engineeredtechniques that repairs isolated areasof deterioration in a concretepavement. Appropriate and timelyCPR maintains the pavement in asmooth, safe, and quiet condition andextends its service life on average by9-10 years. This is about the samelife expected of an asphalt overlay ofa rubblized concrete pavement.Some CPR projects have performedfor more than 17 years.6

100-mm asphalt overlay on rubblized JRCP 200-mm asphalt overlay on rubblized JRCP

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Table 1: Concrete Pavement Restoration Techniques

Concrete PavementRestoration Technique Used to:

Full-Depth Repairs Repair cracked slabs and joint deterioration

Partial-Depth Repairs Repair joint and crack deterioration and surface distress

Diamond Grinding Extend serviceability; improve ride and skid resistance;reduce noise

Dowel-Bar Retrofit Restore load transfer at joints and cracks

Joint and Crack Resealing Minimize infiltration of water and incompressible material intojoint system

Slab Stabilization Fill small voids underneath the concrete slab

Cross-Stitching Repair low and medium severity longitudinal cracks

Grooving Reduce wet weather accidents and prevent hydroplaning

Retrofitting Edge Drains Add a longitudinal drainage system

Retrofitting Concrete Shoulder Decrease pavement edge stresses and corner deflections

Table 1 shows the CPR techniques.Each technique is specificallydesigned to repair or prevent therecurrence of a certain distress or acombination of distresses. Whileeach technique can be usedindividually, they are more effectivewhen several are used together. Insome cases more than one CPRtechnique may be applicable.However, one technique is usuallymore suitable than the other becauseof the condition of the pavement.

CPR has several advantages overrubblizing. First, it repairs theisolated areas of distress that needrepaired without destroying thestructural integrity of the slab. Thisfundamental difference makes CPRmore effective and less costly thanrubblization and asphalt overlays.

In addition, CPR does not limit futurepavement rehabilitations options.Once a pavement has beenrubblized, it can only be overlaid.After CPR, all overlay, CPR, andrecycling options are still availablewhen the pavement needs its nextrehabilitation.

Diamond Grinding of an old concretepavement to restore smoothness

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Finally, CPR does not have to beplaced over the entire pavementwidth, as does an asphalt overlay.This maintains the existing grade ofthe pavement and means featuressuch as curbs and gutters, bridgeclearances, and roadsideappurtenances do not needadjustment. These advantagesmakes CPR quicker and cause lesstraffic disruption than rubblization andan asphalt overlay. For moreinformation on CPR, see references6-11.

Concrete OverlayAlternatives -Concrete overlays provide twoimportant functions. First, theyimprove the surface characteristic ofthe pavement (rideability, safety, skidresistance, cross-section and surfacedefects, etc.). Secondly, theyincrease the structural capacity of apavement. There are two basic typesconcrete overlays for existingconcrete pavements: bondedconcrete overlay and unbondedconcrete overlay. Each overlaytechnique has its own uniquecharacteristics.

Bonded OverlaysBonded concrete overlays consists ofa thin concrete layer (usually 100 mmor less) bonded to the top of anexisting concrete surface. They areused on pavements that are in goodcondition with little deterioration inorder to increase their structuralcapacity. The bond causes theoverlay and existing pavement to actas one thick slab. A good candidatefor a bonded overlay is a pavementthat has little deterioration, but is toothin due to increased truck volumes(i.e., it is only 150 mm (6.0 in.) whenit should actually be 230 mm (9.0 in)).

In order to ensure that bonddevelops, specific steps are taken toprepare the surface of the existingpavement. This is done with eithershotblasting and milling. Withshotblasting, steel shot are hurled atthe pavement surface to removeabout 3 mm (0.125 in.) from thepavement surface. This creates arough and extremely porous surfacethat increases the mechanicalinterlock and provides a strong bond.Milling is primarily used where deeperremoval is desired. It typicallyremoves between 6 and 25 mm (0.25and 1.0 in). Afterwards, a secondarycleaning is required, which is typicallyshotblasting.

Surface preparation and cleanlinessis the key to long-term bonddevelopment and overlayperformance. If the surface isproperly cleaned, and the existingpavement is not too deteriorated,bonded concrete overlays can last forover 15 years without any, or verylittle maintenance work. However,when they are placed on a pavementin poor condition, they do not performwell.12 For more information onBonded Concrete overlays, seereference 13.

Shotblasting the surface in preparationfor a bonded concrete overlay.

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Unbonded OverlaysAn unbonded concrete overlayconsists of thicker concrete layer(125 mm or greater) on top of anexisting concrete pavement. It usesa thin asphalt separation (stressrelief) layer, placed between the newand existing concrete, to separate thetwo layers so that they actindependently of each other.Because the two concrete layers areindependent, unbonded overlaysreact structurally as if built on astrong, non-erodable base course.For this reason, unbonded concreteoverlays are a much better option fordeteriorated concrete pavementsthan rubblization and an asphaltoverlay.

One of the concerns with unbondedconcrete overlays is that thedistresses from the lower concretelayer will reflect into the new overlay.Fortunately, the separation interlayeracts as a cushioning layer thatprevents distresses from theunderlying concrete from reflectinginto the overlay. Additionally,because the pavement is on a strong,non-erodable foundation, loadinduced distresses such as loss ofsupport, pumping, faulting and cornerbreaks are minimized. Overall, thestructural capacity of the overlay isenhanced because of the existing

intact pavement.

Another advantage of unbondedoverlays over rubblization andasphalt overlays is that they do notrequire that the existing slab bebroken. Therefore, traffic can bemaintained on adjacent lanes andshoulders during construction. Thisis a critical issue in constricted andcongested areas.

The performance of an unbondedoverlay has been very good. Studiesdone by the National CooperativeHighway Research Program(NCHRP) have shown that unbondedoverlays have performed well for over20 years.12 Where there has beenpoor performance, it has usuallybeen caused by an inadequateseparation interlayer. The separationinterlayer must isolate the overlayfrom distress and horizontalmovement in the existing pavement.For more information on UnbondedConcrete overlays, see reference 14.

WHEN TO RUBBLIZE AN

EXISTING CONCRETE

PAVEMENT

Rubblization should never be used ona pavement that is structurally sound.Destroying a structurally soundpavement in order to minimizereflective cracking is poor practiceand a waste of resources. It is muchbetter to save and use the structureof the existing pavement.

Furthermore, rubblizing a structurallysound pavement eliminates all othercurrent and future pavementrehabilitation options. Once apavement is rubblized, the only thingthat an agency can do with it isoverlay it. Later, this could causeproblems with elevated crowns andraised grades for futurerehabilitations. Keeping the

Ultra-thinUnbonded Overlays –An Untested Alternate.

One of the problemswith traditionalunbonded overlays isthat they are usuallyfairly thick (150 to 250mm (6 to 10 in.),depending on trafficand sight conditions).A recent development,used on existingasphalt pavements, isUltra-ThinWhitetopping (UTW).

One of the reasonsthat UTW’s work isbecause of their shortjoint spacing. Theshort joint spacingallows the pavement toact like a cast-in-placeblock system. It hasbeen reasoned that athin unbonded overlay,with short joint spacing,may behave in muchthe same way andprovide 8 to 15 years ofservice.

The Pennsylvania DOTbuilt a 3.5 inch ultra-thin unbonded overlayon a ramp in Hershey,PA in 1995. Though ithas not had long-termmonitoring, earlyinvestigations showthat it is performingwell and should beconsidered as analternative for millingand overlaying with HotMix Asphalt.

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Schematic of an unbonded overlay.Note how the Asphalt layer separatesthe two concrete layers so that they actindependently.

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pavement intact keeps all optionsopen for future rehabilitations.

Rubblization is an appropriatesolution when the existing concreteslab exhibits material problems suchas alkali-silica reactivity (ASR), D-cracking, or freeze-thaw damage.These material problems cause theconcrete pavement to deteriorate andlose its structural integrity.

ASR reduces the durability ofconcrete by creating a gel that mayabsorb water, expand, and crack theconcrete. Once cracked, theconcrete loses it strength anddeteriorates. D-cracking occurswhen certain aggregates in aconcrete mixture become saturated,freeze, and expand. This expansioncauses the surrounding concrete tocrack.

Freeze-thaw damage occurs inconcrete that has a poor entrained-airsystem. Entrained air is a system ofmicroscopic air bubbles in theconcrete that protects it as it freezes.If the volume and spacing of the airbubbles is not adequate, the concretecracks when it freezes. All three ofthese material problems typicallytakes several years to occur and thedegree of deterioration depends uponthe amount of poor materials in theconcrete.

The RubblizationProcedureThere are two pieces of machineryused to rubblize concrete pavement:the resonant breaker and themultihead breaker (MHB). Thoughboth machines break the slab intosmaller pieces, neither one breaksthe concrete into the uniform highquality base course that they claim.Instead, rubblization produces abroken concrete that ranges from

sand size particles to fragments thatare approximately 150 to 200 mm (6to 8 in.) in width, with no gradation ordensity control.

The resonant breaker has a 150-mm(6-in.) wide head that vibrates at alow amplitude and high frequency.As it vibrates, it impacts and shattersthe slab. However, this small headcan only break a small, longitudinalstrip at a time. Thus, it requiresabout 50 passes to completely breaka 7.3 m (24 foot) wide pavement.

The multihead breaker (MHB)pulverizes an entire lane in a singlepass. However, it uses highamplitude drop hammers that impactthe concrete and crushes or breaks itin flexure. As such, it is notrubblization, it is pulverization.

Besides not providing a uniformbase, both pieces of equipment candamage and introduce variability intothe subgrade support. With theresonant breaker, the subgrade canbe damaged because two of itswheels, which are around 20,000 lbs.each, must ride on the brokenconcrete, which can push the brokenconcrete into the underlying subbaseor subgrade.15 The MHB damagesthe subgrade when its forcefulcrushing procedure impacts theconcrete and pushes it into thesubbase or subgrade.16

Once the subgrade and subbase isdamaged, it no longer providesuniform support. This must be takeninto account in the design procedureor it must be removed and repairedduring the construction procedure.

The importance ofsubgrade support.

Eventually, thesubgrade carries theload of any pavement.Therefore, it is veryimportant that it becharacterized correctly.

The main deficiencywith rubblization is thatit is difficult to predictthe subgradeconditions until afterrubblization.

Testing on top of theintact concrete doesnot guarantee correctcharacterization of thesubgrade. In manycases, the concrete’snatural bridging actionwill cover up a weaksubgrade and masksits true strength.

A good rule for judginghow a rubblizedpavement will performis to look at theperformance of theexisting concrete. Ifthe existing concrete isdeteriorating due topoor support, thenrubblization will alsohave problems due topoor support.

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DESIGNING AN OVERLAY

ON A RUBBLIZED

CONCRETE PAVEMENT

Once it has been determined that apavement has a materials problemand is good candidate forrubblization, the pavement engineersmust properly select the overlaythickness. Though most overlayshave been asphalt, it is possible toplace a concrete overlay on therubblized concrete pavement. Ineither case, the most importantaspect of the design procedure is thecharacterization of the rubblizedconcrete layer.

Asphalt OverlayThe most recognized designprocedure for asphalt overlays ofrubblized concrete is the AASHTOOverlay Design of Fractured slabs.17

This procedure uses the concept ofstructural numbers (SN) and layercoefficients (a) to determine thethickness of the overlay. The basicequation to determine the asphaltoverlay thickness is:

tasph = SNreq-(arub conc*trub conc+abase*tbase)

aasphalt

WhereSNreq = required structural

number to carry the futuretraffic

ai = structural coefficient of theasphalt, rubblized concrete, orbase course

ti = thickness of the asphalt,rubblized concrete, or basecourse

The key to the AASHTO designprocedure is correctly quantifying thecontribution of the rubblized layer.However, because rubblization is not

done until construction, this is adifficult procedure.

Complicating the problem is the factthat the rubblized material is notuniform and difficult to characterize.The AASHTO Guide for Design ofPavement Structures states thatthere is “a wide range ofbackcalculated modulus valuesamong different projects, from100,000 psi (690 MPa) to severalhundred thousand psi, and withinproject coefficient of variation of asmuch as 40 percent.” 17

In a recent research project,Structural Coefficients for FracturedConcrete Slabs,18 an attempt todevelop realistic values wasundertaken. In this research, thestructural coefficients weredeveloped by relating the overlaythicknesses from both the rigid andflexible asphalt overlay models usedin the AASHTO Guide.

The AASHTO Guide uses twomodels to design asphalt overlays ofconcrete. One is used for asphaltoverlays of intact concrete and isbased on rigid pavement modeling.The second is based on flexiblepavement modeling and is used forasphalt overlays of asphaltpavements and fractured slabs.

For a given traffic volume, these twomodels should give the samestructural capacity. Using thispremise, the research related theoverlay thicknesses from both therigid and flexible asphalt overlaymodels and developed the structuralcoefficients so that the structuralcapacity from the two methods wereas close as possible to each other.

Rubblized slab thicknesses from 180to 280 mm (7 to 11 in.) wereinvestigated. It found that no singlevalue for the structural coefficient of a

Structural coefficientsdescribe the strengthof the layer. Thehigher the value, thestronger the layer.

AASHTO recommendsthe following structuralcoefficient values forthe design of anasphalt overlay onrubblized slabs:

New Asphalt Concrete0.20 – 0.44

Rubblized Slab0.14 - 0.30

Base Course0.0 - 0.14

These values arereasonable, except forthe rubblized slab. Anstabilized material hasa structural coefficientvalue of 0.20. Theupper values forrubblized slabs arehigher than for thestabilized materials.This indicates that thebroken slabs arestronger than an intactstabilized material.

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rubblized slab yielded equivalentoverlay designs for the full range ofthe existing slab thicknesses. Thestructural coefficient value variedbased on the expected traffic values.

Overall, the structural coefficientrange was between 0.149 to 0.245,with an average value of 0.197. Thevalues at the low end of this rangeare appropriate for larger futurethickness requirements (high trafficvolumes), while values at the highend are more appropriate for smallerfuture thickness requirements (lowtraffic volumes).

Based on the results of this analysis,ACPA recommends that a range of0.14 to 0.25, with a midrange of 0.20be used in the current AASHTOdesign procedure for asphalt overlaysof rubblized pavements. For highvolumes of traffic, the lower structuralcoefficient values should be used andfor low volumes of traffic, the highervalues should be used.

Rubblizing and ConcreteOverlayThough not used as often, it ispossible to place a concrete overlayon a rubblized concrete pavement.This technique has been extremelysuccessful in both Pennsylvania andIowa. Furthermore, becauseconcrete overlays last 25 years ormore while asphalt overlays typicallylast only 10 to 15 years, the concreteoption is a better long-term solution.

Still, particular care should be used inthe decision to rubblize the existingconcrete pavement because it willreduce the structural capacity andlikely warrant a thicker concreteoverlay. The benefits of improvedload transfer from sleeper-slabaction, and decreased potential for

pumping are lost when the existingstructure is rubblized.

Concrete OverlayThough there is no establishedprocedure to design a concreteoverlay of rubblized pavement, it ispossible to use concepts from theAASHTO new concrete pavementand overlay design procedures todetermine an overlay thickness.

The proposed procedure consists ofdesigning the overlay as a newconcrete pavement on an improvedgranular base with a higher k-value.This is the procedure used withconcrete pavements on basescourses and concrete overlays ofasphalt pavements (whitetopping). Italso characterizes the rubblizedpavement in the same manner as anasphalt overlay of a rubblizedpavement.

Similar to the asphalt overlay, the keyin the design procedure is tocharacterize the rubblized slab withan appropriate k-value. The followingprocedure is recommended:

1. Determine the rubblized slabmodulus value (use the sameprocedure as used in the overlaydesign procedure for an asphaltoverlay of a rubblized pavement).

2. Convert the rubblized slabmodulus value to k-value usingthe procedures outlined inAASHTO Overlay Procedure forConcrete Overlays of AsphaltPavements (whitetopping).

3. Design the overlay as a newpavement using the improved k-value determined in Step 2.

ACPA recommendedlayer coefficients values:

Rubblized Slab0.14 - 0.25

Value depends on thefuture thickness or trafficrequirements.

Lower values areappropriate for hightraffic volumes, wherethicknesses will begreater.

Higher values areappropriate for low trafficvolumes, wherethicknesses will bethinner.

Degradation or intrusionof fines into base courseshould also be taken intoaccount. If there isdegradation or intrusionof fines, then the lowervalues are appropriate.

Because of the widevariation of the modulusvalue, and because anexact value for a givenproject is impossible todetermine untilconstruction, it isrecommended to use lowvalues (i.e. 100,000 psi)until actual field andperformance dataprovide betterinformation.

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SUMMARY

Rubblization is used to stop reflectivecracking in asphalt overlays ofexisting concrete overlays. Though itis perceived as a rehabilitationtechnique, it is actually a destructiveprocedure that destroys the structureof the existing concrete slab andweakens the entire pavementsystem. Its use has been necessarybecause asphalt overlays are tooweak to withstand the movements ofthe underlying concrete structure,resulting in reflective cracking andquick deterioration of the overlay.

Better alternatives to rubblization andasphalt overlays are concretepavement restoration (CPR) andconcrete overlays. Theseprocedures directly address thecause of the pavement distress andkeep the structural integrity of thepavement system intact.

Still, there are times whenrubblization is an option for anexisting concrete pavement. Thisoccurs when the concrete slabsexhibit material problems such asalkali silica reactivity (ASR), D-cracking, or freeze-thaw damage.These materials problems cause theconcrete pavement to deteriorate andlose its structural integrity.

Once a pavement is rubblized, it isviable to place either a concrete or anasphalt overlay. The advantage ofthe concrete overlay is that it is along-term solution that will not needto be rehabilitated again for many,many years.

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REFERENCES:1. Phone conversations with the South

Carolina DOT, SC I-85 nearGreenville SC.

2. Guide Specifications for HighwayConstruction, American Association ofState Highway and TransportationOfficials, Washington, DC, 1993

3. Michigan PMS data

4. Michigan Cost data

5. Rehabilitation of Jointed PortlandCement Concrete Pavement on I-35(Southbound) in Kay County,Oklahoma, J.F. Daleiden, D.a. Ooten,M.D. Sargernt, TransportationResearch Record 1513, .

6. The Concrete Pavement RestorationGuide: Procedures for PreservingConcrete Pavements, TB020PAmerican Concrete PavementAssociation, Skokie, IL, 1997.

7. Diamond Grinding and CPR 2000,TB008P, American ConcretePavement Association, Skokie, IL,1990.

8. Guidelines for Full-Depth Repair,TB002P, American ConcretePavement Association, Skokie, IL,1995.

9. Guidelines for Partial-Depth Repair,TB003P, American ConcretePavement Association, Skokie, IL,1989.

10. Joint and Crack Sealing and Repairfor Concrete Pavements, TB012P,American Concrete PavementAssociation, Skokie, IL, 1993.

11. Slab Stabilization Guidelines forConcrete Pavements, TB018PAmerican Concrete PavementAssociation, Skokie, IL, 1994.

12. NCHRP 204, Performance ofConcrete Overlays

13. Guidelines for Bonded ConcreteOverlays, TB007P, AmericanConcrete Pavement Association,Skokie, IL, 1990.

14. Guidelines for Unbonded ConcreteOverlays, TB005P, AmericanConcrete Pavement Association,Skokie, IL, 1990.

15. Thompson, M.R., et al. HMA OverlayConstruction with One Pass/lane-Width with PCCP Rubblization,Asphalt Paving Technology, Journalof the Association of Asphalt PavingTechnologist, Vol. 66, 1997.

16. Presentation by Phillip Kirk, RMIgiven a the Southeastern PavementConference, Baton Rouge LA, .June23, 1998

17. “AASHTO Guide for Design ofPavement Structures,” AmericanAssociation of State Highway andTransportation Officials, WashingtonD.C., 1993.

18. Structural Coefficients for FracturedSlabs, Hall, K.T., Proyekta Ingenieria,Ltda. paper prepared for the 1999TRB Annual Meeting.