Field Manual For Crack Sealing In Asphalt Pavements (0 .
3208 Red RiverAustin, TX 78705Research Project 0-4061-P3Comparison of Hot-Poured Crack Sealant to Emulsified Asphalt Crack SealantField Manual for Crack Sealing inAsphalt PavementsYetkin Yildirim, Ahmed Qatan, and Jorge ProzziJanuary 2006
Field Manual for Crack Sealingin Asphalt PavementsDr. Yetkin Yildirim, P.E.DirectorTexas Pavement Preservation CenterThe University of Texas at Austin3208 Red River, CTR 318Austin, TX 78705Phone: 512 / 232-3083Fax: 512 / 232-3070http://www.utexas.edu/research/tppcAhmed QatanGraduate Research AssistantThe University of Texas at AustinECJ 6.100 Mail Code: C1761Austin, TX 78712Phone: 512 / 475-7912Fax: 512 / 475-8744andJorge Prozzi, Ph.D.Assistant ProfessorThe University of Texas at AustinECJ 6.100 Mail Code: C1761Austin, TX 78712Phone: 512 / 232-3488Fax: 512 / 475-8744Research Project 0-4061Comparison of Hot-Poured Crack Sealant to Emulsified Asphalt Crack SealantProduct Number 3
DisclaimersAuthors' Disclaimer: The contents of this report reflect the views of the authors, whoare responsible for the facts and the accuracy of the data presented herein. The contentsdo not necessarily reflect the official view or policies of the Federal Highway Administration or the Texas Department of Transportation. This report does not constitute a standard,specification, or regulation.Patent Disclaimer: There was no invention or discovery conceived or first actually reduced to practice in the course of or under this contract, including any art, method, process,machine manufacture, design or composition of matter, or any new useful improvementthereof, or any variety of plant, which is or may be patentable under the patent laws of theUnited States of America or any foreign country.Engineering DisclaimerNOT INTENDED FOR CONSTRUCTION, BIDDING, OR PERMIT PURPOSES.Dr. Yetkin Yildirim, P.E. (Texas No. 92787)AcknowledgmentsThis project has been initiated and sponsored by the Texas Department of Transportation (TxDOT). The financial support of TxDOT is greatly appreciated. The authors wouldlike to thank TxDOT Project Director John Bohuslav for his guidance. The assistance of theparticipating district maintenance personnel through the advisory committee, as well asother districts, is greatly appreciated.Performing Organization:Center for Transportation Research,The University of Texas at Austin3208 Red River, Suite 200Austin, Texas 78705-2650Sponsoring Organization:Texas Department of Transportation,Research and Technology Implementation OfficeP.O. Box 5080Austin, Texas 78763-5080Project conducted in cooperation with the the Federal Highway Administration and theTexas Department of Transportation.Keywords:Hot Poured Crack Sealants, Cold Poured Crack Sealants, Emulsified Crack Sealants,Asphalt PavementsNo. ofPages:16
Table of ContentsINTRODUCTION. 1TERMINOLOGY. 1PAVEMENT SELECTION. 1Preventative Maintenance. 1CONSIDERATIONS FOR CRACK SEALING. 2Time of Year and Temperature. 2Safety. 2Traffic Control. 2Crack Cleaning and Drying. 3Backer Rod. 3Blotting. 4METHOD SELECTION. 4Crack Sealing. 5Crack Sealing with Routing. 5Material Placement. 5MATERIAL SELECTION. 6Cold Pour. 6Hot Pour. 7APPENDIX A: QUALITY CONTROL CHECKLIST. 9REFERENCES. 12
INTRODUCTIONThis field manual was developed as aproduct of research project 4061 “Comparison of Hot Poured Crack Sealant to Emulsified Asphalt Crack Sealant” conducted byThe University of Texas at Austin Center forTransportation Research (CTR). Organization of this field manual accompanies thatof the “Crack Sealing in Asphalt Pavements”training video also developed by CTR.Pavement cracking is an inevitablephenomenon that maintenance engineershave to accustom themselves to. It is impossible to construct a pavement that doesnot develop cracks after a certain amountof service time. Cracking is one of the twomain concerns considered in the pavementdesign process (the other being rutting); itis the primary mode of deterioration in asphalt cement pavement. Cracking occurs ina variety of forms: transverse, longitudinal,block, and alligator shape. Cracks needto be treated promptly because they create openings for moisture to penetrate thepavement layers. Moisture or water cancause severe damage when trapped in thecrack. Neglecting pavement cracking usually leads to accelerated deterioration of thepavement, resulting in significant problemssuch as potholes or base failures, whichcause the serviceability of the pavement todecline.Cracking, since it is such a major formof pavement deterioration, is usually the deciding factor in determining the proper timefor rehabilitation and the appropriate method to be applied. When cracks develop onthe surface of the pavement, it is a sign ofreduction in pavement integrity and serviceability. Regular repair of pavement cracksis one of the main methods of preventivemaintenance, since failure to repair cracksin a timely fashion can lead to accelerateddeterioration of the pavement in the formof crack growth, spalls, secondary cracks,and potholes. The main causes of pavementcracks are thermal movements and fatiguedue to excessive loading. Cracking is an inevitable problem given the network of morethan two million miles of asphalt surfacedResearch Product 0-4061-P3roads in the United States. It is important tofind effective solutions to minimize its effectand to extend the service life of our roads.TERMINOLOGYCrack repair consists of crack sealingand crack filling. Usually, crack sealing refers to routing cracks and placing materialon the routed channel. Crack filling, on theother hand, refers to the placement of material in/on an uncut crack. For the purposes ofthis manual, crack sealing will refer to bothcrack filling and sealing. Specifically, whatis usually referred to as crack sealing will bereferred to as crack sealing with routing.PAVEMENT SELECTIONPreventative MaintenanceTxDOT employs crack sealing extensively as a cost effective technique inpreventive maintenance. Preventive maintenance is characterized by its ability to preserve and extend the life of pavement. Sincecracks on the pavement surface allow waterand incompressible materials such as sand,dirt, and other debris to enter the pavementstructure, the presence of these cracks candramatically accelerate deterioration andweakening. Sealing cracks prevents furtherdeterioration of the pavement and, whenproperly executed, can extend the life ofthe pavement anywhere from 6 months to 4years. In many cases, when roads are selected for a full width seal coat (or chip seal)or hot mix asphalt concrete overlay, cracksthat are 1/16 inch or greater in width willrequire crack sealing prior to the seal coator overlay. If crack sealing is required priorto a seal coat or overlay, such crack sealing should be completed 6 to 12 monthsbefore the seal coat or overlay to minimizethe potential for bleeding of the sealant thruthe subsequent surface layer. Selecting theproper pavements for crack sealing is criticalto ensure the preservation and extension ofthe life of the pavement.Since crack sealing is a preventive
Figure 1. Fatigue Crackingmaintenance technique that adds no structural capacity to pavement, ideal pavementcandidates for this technique exhibit minorpavement distress and have sufficient structural capacity to meet present and futurestructural needs. Pavements with transverseand longitudinal cracks are good candidates for crack sealing, but pavements withfatigue and alligator cracking, as displayedin Figure 1, should not be subjected to thismaintenance technique. Fatigue and alligator cracking indicates pavement structurefailure, and crack sealing will not extendthe life cycle of this type of pavement condition. In addition to pavement selection,other considerations have to be taken intoaccount for crack sealing, as discussed inthe following section.CONSIDERATIONS FOR CRACKSEALINGTime of Year and TemperatureFactors affecting crack sealing includethe time of the year and the ambient temperature in which the treatment is applied.Crack sealing should generally be doneduring the winter months when the cracks are open; and thus, sealant can more easilypenetrate the crack. The ambient temperature should be between 45 and 65 degreesFahrenheit.SafetyDuring the sealing procedure, thematerials and the equipment involved canpresent safety hazards to both workers andthe traveling public. All safety precautionsregarding material handling and the operation of the equipment should be strictly adhered to. Additionally, construction workers should wear safety apparel such as longsleeved shirts, leather gloves, steel toedboots, hard hats, and adequate eye protection. Since hot pour crack sealants are applied at approximately 350 degrees Fahrenheit or more, special caution should beexercised during this operation.Traffic ControlPerhaps the most important consideration for a crack sealing procedure is traffic control. In order to ensure the safety ofall workers and the traffic traveling near thework area, proper traffic control devicesshould be installed. The Texas Manual ofUniform Traffic Control Devices (MUTCD)Research Product 0-4061-P3
Figure 2: Hot Air Lanceprovides guidelines on traffic control devices for the TxDOT. The traffic control planmay need to consider the traffic volume andthe curing time (or time between placementof sealant and removal of the traffic controldevices) of the sealant selected for a worklocation.Crack Cleaning and DryingBefore placing sealant, all cracks mustbe thoroughly cleaned to ensure a clean,dry crack channel and to optimize adhesion between the sealant and the pavementsurface. Crack cleaning is an essential stepin crack sealing since most failures occur asa result of loss of adhesion. To effectivelyclean the crack, high-pressure air blasting,which uses compressors to produce a jetstream of air, is used to remove dust, debrisor loose pavement fragments. The cracksshould be cleaned to a depth of at leasttwice the crack width. Airflow should befree of oil and moisture and the compressedair should have a minimum pressure of 100lb/in2 and minimum blast flow of 150 ft3/min. These blasting operations should always be directed away from passing traffic. Although this method is very effectivein cleaning the crack, it is not effective fordrying it. For proper crack sealing the crackmust be free of moisture. For drying, a hotair lance (Figure 2) can be used. Sealantshould be placed immediately after crackcleaning.Research Product 0-4061-P3If crack sealing with routing is the selected method, additional considerationsmust be taken into account. Crack routinginvolves cutting through the crack to providea uniform rectangular reservoir in which thesealant is to be placed. This procedure creates uniform and smooth edges, thus allowing the sealant material to adhere better withthe asphalt pavement.Backer RodWhen sealing large cracks, it is important that the sealant does not drain to thebottom of the crack. To prevent this, sandor backer rods may be placed in the cracksbefore the placement of the sealant. As seenin Figure 3, using a backer rod when appro- Figure 3. Backer Rod
Figure 4. Blottingpriate will prevent the sealant from drainingto the bottom of the crack.BlottingWhen crack sealing wide areas, aggregate should be placed on the fresh sealant tomaintain the skid resistance. All traffic mustbe kept off the sealant until it has cured.If traffic is inevitable before the sealant iscured, the seal can be blotted. Blotting isthe application of fine aggregate or sand tothe non-cured sealant to prevent tracking.The fine aggregate or sand must be appliedimmediately after the sealant material isplaced so that it adheres to the sealant andcan serve its purpose. Figure 4 shows theblotting process in progress.METHOD SELECTIONTo ensure an effective, long-lastingcrack seal, the proper method must be selected. This selection will depend on themovement and physical characteristics ofthe crack. The main consideration in cracksealing method is the annual movement ofthe crack. Another important considerationused in method selection includes crackedge deterioration. Table 1 presents recom-Table 1. Recommendations for Crack SealingCrack Characteristics Crack Treatment MethodCrack Sealing w/RoutingCrack SealingWidth (in.)0.2 to 0.750.2 to 1.0Edge DeteriorationMinimal to none 25% of crack lengthModerate to none 50% of crack lengthAnnual HorizontalMovement (in.) 0.1 0.1Type of CrackTransverse ThermalTransverse ReflectiveLongitudinal ReflectiveLongitudinal Cold-JointLongitudinal ReflectiveLongitudinal Cold-JointLongitudinal EdgeDistantly Spaced BlockResearch Product 0-4061-P3
mendations to follow when deciding between crack sealing and crack sealing withrouting.Crack SealingAppropriate candidates for crack sealing are non-working cracks—cracks thathave horizontal or vertical movementsless than 1/10 inch. These types of cracksare usually diagonal, longitudinal, or blockcracks. Additionally, crack sealing shouldbe considered for cracks that have moderate or no edge deterioration. These types ofcracks do not require a routing process andthe sealant is placed directly in the crack asseen in Figure 5. volves cutting along the crack to providea uniform rectangular reservoir in whichthe sealant is to be placed. This procedurecreates uniform and smooth edges, thus allowing the sealant material to adhere betterwith the asphalt pavement. Not only that,but crack routing also allows the sealantlevel to remain below the surface of thepavement. This protects the sealant materialfrom traffic and snowplow contact.If crack sealing with routing is the selected method, additional considerationsmust be taken into account. Special preparation should be done to the crack if there islimited crack edge deterioration. The preparation consists of routing the crack in orderto place the sealant in the routed crack, orreservoir, as discussed earlier. In the cracksealing with routing procedure the mostcommonly used configurations are the reservoir and combination, as presented in Figure 7. Figure 8 displays the routing equipment used in the crack routing procedure. Figure 5. Crack SealingThe most common configurations usedwith the crack sealing method are the flushfill and the overband, as shown in Figure 6. Figure 6. Crack Sealing CommonConfigurationsCrack Sealing with RoutingWorking cracks, which are cracks thathave horizontal or vertical movementsgreater than 1/10 inch, are recommendedfor routing. In general, this type of crack istransverse in orientation. Crack routing inResearch Product 0-4061-P3 Figure 7. Crack Sealing with RoutingCommon ConfigurationsMaterial PlacementThe material should be applied to theinside of the cracks. Excess sealant shouldbe removed before hardening occurs. Anoverband should be formed during, or immediately after, sealant application. Theoverband should not be more than 3 incheswide and no more than 1/8 inch above thepavement surface. For hot-pour applications, the sealant should be poured at themanufacturer’s recommended temperature.The sealant should be circulated in the hosewhen the installation train is idle. Thereshould be no bubbles due to moisture present in the crack. For cold-pour applications,adequate sealant should be placed to sealup to the surface of the crack, since cold
Figure 8. Crack Routing Procedurepour tends to flow deep into a crack.MATERIAL SELECTIONCracks should be carefully examined todetermine the most suitable material for theproject. The two commonly used materialsfor crack sealing procedures are cold pourand hot pour sealants. The test sections inTxDOT research study 4061 indicated thatfor crack sealing without routing cold pourhas a typical life cycle of 1-2 years, whilehot pour has a typical life cycle of 3-5 years.Specific procedures must be followed foreach particular sealant material.Cold PourCold pour sealants are those that areapplied at ambient temperatures and therefore do not require heating. This type of material is more appropriate for cracks of 3/16inch or less in width. Emulsified asphalt isthe most commonly used cold pour sealant.It is a dispersion of asphalt particles in waterwith the presence of an emulsifying agentthat sets due to the evaporation of waterwhen exposed to air. The main advantageof asphalt emulsions is safety, since it typically does not require heating. Additionally, they can be applied during times of highhumidity or when cracks are moist or damp.However, such humid conditions result in a significant extension in the curing time.Ideal conditions for cold pour sealantapplication are when the air temperature isabove 40oF and rising. Cold pour sealantshould not be applied if the air temperatureis below 50oF and falling. This temperatureshould be based on a reading taken in theshade and away from any form of artificialheat. Due to the low viscosity of cold poursealant, the material will penetrate intothe crack easily without any need for routing procedures. It is critical that the vertical surface of the crack be clean to insurethat the cold pour will adhere to the crack.The sealant should be applied using a barrel pump or pressurizing system to providean uninterrupted flow of cold pour sealantFigure 9. Rubber Finishing Squeegee for Usewith Cold Pour SealantResearch Product 0-4061-P3
through the hose to the wand. The wand applicator should have an appropriate nozzlefor applying the material in the crack. Thesqueegee, shown in Figure 9, should bekept over the center of the crack channel.Depending on the humidity and temperature, curing time can vary from 30 minutesto several hoursHot PourHot pour sealants are sealants thatmust be heated to high temperatures inpreparation for application. As the materialcools, the hot thermoplastics harden. Thistype of material generally consists of asphaltcement with or without the addition of amodifier. The simplest and most commontype of modifier added to asphalt cement isrubber. Additions of such a modifier givethe asphalt desirable properties such ashigh elasticity and high melting point. Unlike cold pour sealants, hot pour materialsshould not be applied when the cracks andpavement surface are moist and damp. Allmanufacturers’ recommendations to determine an acceptable ai
Crack repair consists of crack sealing and crack filling. Usually, crack sealing re-fers to routing cracks and placing material on the routed channel. Crack filling, on the other hand, refers to the placement of mate-rial in/on an uncut crack. For the purposes of this manual, crack sealing will refer to both crack filling and sealing.
crack growth as a mutual competition between intrinsic mechanisms of crack advance ahead of the crack tip (e.g., alternating crack-tip blunting and resharpening), which promote crack growth, and extrinsic mechanisms of crack-tip shielding behind the tip (e.g., crack closure and bridging), which impede it. The widely differing
Crack filling is the placement of materials into nonworking or low movement cracks to reduce infiltration of water and incompressible materials into the crack. Filling typically involves less crack preparation than sealing and performance requirements may be lower for the filler materials. Filling is
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