Best Practices for Crack Treatments for Asphalt Pavements (2014)

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22 C H A P T E R 4 It is well established that crack sealing and crack filling are cost-effective pavement maintenance techniques. As with any other activity, it is imperative that the work be done with appropriate equipment and in the best manner possible in order to get good performance. Many organizations have maintenance manuals that include Best Practices for crack sealing and crack filling. Examples can be found in References 3, 4, 5, 7, 14, 16, 22, 24, 25, 43, 44, 49, 53, 82, and SS-3. Based on review of the State-of-the-Art and State-of-the-Practice, this chapter synthesizes the Best Practice requirements to achieve a long-lasting crack treatment. General Issues/Project Selection FHWA describes the steps in a crack treatment program as follows: 1. Obtain and review construction and maintenance records. This includes determination of the pavement age, design, repairs done to date, etc. 2. Perform a pavement crack survey. Record the distress types present, the amount of distress, and the severity of distress. 3. Determine the appropriate type of maintenance for the cracked pavement based on the density and condition of cracks. a. A pavement surface treatment is appropriate for a pave- ment with high density of cracks that have moderate to no crack edge deterioration. b. A crack treatment is proper for a pavement with moder- ate density of cracks that have moderate to no crack edge deterioration. c. A crack repair is necessary for pavements with moder- ate density of cracks that have a high level of crack edge deterioration. 4. For crack treatment, determine whether cracks should be sealed or filled. a. Cracks with significant annual horizontal movement (“working” cracks) should have a crack sealing treatment. b. Cracks with little annual horizontal movement (“non- working” cracks) should have a crack filling treatment. 5. Select materials and procedures for the crack treatment operation based on environmental, equipment, personnel, and cost-effectiveness considerations. 6. Acquire materials and equipment to perform the work. 7. Conduct and inspect the crack treatment operation. 8. Periodically evaluate treatment performance. (53) The first three steps are contained within a typical pavement management system. The remaining steps will be discussed in the following sections. The definitions for crack sealing and crack filling presented in Chapter 2 are considered as the Best Practice for evaluation of pavement cracking. It is widely accepted that crack seal- ing is for “working” cracks with an opening greater than 1⁄8″ (3 mm) in the summer and with minimal crack edge deterio- ration. The opening will be much greater in the winter. The cracks will often be uniformly spaced along the pavement and have limited edge deterioration. Often these cracks are routed prior to sealant installation. Crack filling is applicable for “non-working” cracks that show little movement over time and have low to moderate crack edge deterioration. “Non-working” cracks are not typically routed. These definitions generally lead to transverse cracks receiving a crack seal treatment and longitudinal cracks receiving a crack filling treatment. Both crack sealing and crack filling can be per- formed at the same time in different areas of a given project. It is noted that crack sealing techniques and products can be effectively used for both “working” and “non-working” cracks. Michigan DOT (16) recommends the evaluation of crack density as shown in Table 4-1. These recommendations roughly translate into the require- ment of two or three full-width transverse cracks in the 328 ft Best Practices for Crack Treatments

23 evaluation section for crack treatment to be justified (16). These guidelines of course require good engineering judg- ment to ensure appropriate work is performed. In order to differentiate between a “working” and “non- working” crack, an owner must evaluate the pavement over a period of time to determine the extent of the crack move- ment. Unfortunately, proper evaluation of pavement crack- ing condition is often not performed prior to crack treatment operations. As a generality, crack sealing is typically performed in cold weather climates and crack filling is performed in warm weather climates. As noted in Chapter 3, many agencies do not differentiate between crack sealing and crack filling. This likely precipitates some of the performance issues experi- enced by some agencies. Contracting Procedures The manner in which an owner specifies and pays for crack treatment services is not the primary determinant for the per- formance of the treatment. The work may be done in-house or by contract personnel. Whether a low bid, lump sum, cost plus, indefinite delivery/indefinite quantity, or warranty contracting approach is used is not the key crack treatment performance predictor. Any of these approaches have the possibility of pro- ducing a crack treatment with good performance. Consider- ation must be given to what works best for a specific owner, what works best for the project, and what fits within the eco- nomic and political environment of the project. The deciding factors, as Jim Sorenson said, are using the right materials at the right time for the right conditions. This author adds that these activities must be coupled with the right people with the right training to perform the work. Materials The materials used for crack treatments vary in differ- ent regions of the country. States with extensive freeze/thaw activity need sealants with more ductility, while warmer areas require sealants with less flow in hot weather (23). The materials used for crack sealing are generally polymer modified asphalt based materials and are applied at high temperature (hot-poured sealants). The materials used for crack filling can be either hot-poured or cold-applied materials and are often asphalt emulsions. It has been shown that cold-applied materials, while easily penetrating into the crack, do not perform nearly as well as hot-poured sealants. However, the emulsion products are typically significantly less expensive. The materials used for any crack treatment project must be decided by the project engineer. This report makes no attempt to recommend or evaluate specific commercially available products. There are many products available with each hav- ing advantages and disadvantages. The purchaser of the seal- ant must make the product determination based on local experience and knowledge. It is noted that NTPEP is a good resource for materials evaluation information. In addition, many agencies have an Approved Products List. Sealants are selected in a given region based on the manu- facturer’s test results for the product. A prudent owner should verify the manufacturer’s results. The Federal Highway Admin- istration’s (FHWA) LTPP Bind software provides guidance to the user for determination of pavement temperatures for a specific sealant grade. ASTM D977 (Standard Specification for Emulsified Asphalt [TM-12]) and D2397 (Standard Specification for Cationic Emulsified Asphalt [TM-13]) are used to evaluate cold-applied emulsion products. The emulsion specifications are focused on the emulsion product and not on the crack fill application. ASTM D6690 (TM-11) is used to evaluate hot-poured materials. These ASTM sealant specifications have been in use for many years. A new SG system has been developed to better address environmental variables that impact the per- formance of hot-poured materials, as discussed in Chapter 2. It is expected that sealant purchasers and manufacturers will adopt the SG system at some time in the future. Construction This section of the Best Practices will discuss the following issues: • Climatic conditions • Crack configurations • Crack preparation • Crack cleaning • Material preparation • Sealant installation • Safety Climatic Conditions The environmental conditions at the time of sealant place- ment have a significant impact on the performance of the sealant. Typically the temperature should be between 40°F Linear Crack Length per 100m (328ft) pavement section Density Definition < 10 m (33ft) Low 10m (33ft) to 135m (443ft) Moderate >135m (443ft) High Table 4-1. Evaluation of crack density (16).

24 and 70°F for both crack sealing and crack filling. Al-Qadi et al. (84) recommend a range of 40–80°F. Montana DOT (5) has requirements for the following weather considerations: • Temperature of the roadway surface should be 35°F and rising. • Humidity should be 50% or lower. High humidity may reduce adhesion of the sealant to the crack edges. Excess moisture can be observed as small bubbles forming in the sealant. • Wind may be a friend or a foe. A gentle wind can help to cool the sealant more quickly, minimizing sealant tracking issues. However, wind can also cause problems when cleaning the cracks, with the potential for flying debris. Cold winds will increase the melter heating time. • Rain is cause for immediate shutdown of the crack treat- ment operation. If an unexpected shower occurs, any crack that has been cleaned and dried must be re-evaluated for proper conditions. Crack Configurations From the survey, there was no single crack treatment con- figuration that was overwhelmingly favored. Rather, different applications call for different treatment configurations. Res- ervoir configurations are commonly used when crack sealing will occur. The reservoir provides a mechanism for expansion and contraction during which adhesion of the sealant to the crack edges remains intact. Reservoirs are not typically used for crack filling operations. Each of the configurations has advan- tages and disadvantages. A discussion of each configuration follows. Recessed Crack Treatment Configuration The recessed crack treatment configuration (Graphic 4-1) is often used when an overlay is to be placed. The recess mini- mizes the potential for a bump to form in the overlay, which can occur when the hot overlay comes in contact with the sealant. A recess depth of approximately 3⁄8″ is commonly used. The sealant should be placed 6–12 months prior to the overlay to minimize potential for bumps. Survey results indi- cated that the recessed crack treatment configuration is not commonly used (35% usage). Flush Fill Crack Treatment Configurations Approximately 50% of the survey respondents use flush fill configurations all the time. The configuration can be used with either a routed (Graphic 4-2[left]) or non-routed approach (Graphic 4-2[right]). The flush fill is commonly used when a chip seal or microsurfacing is to be applied on the pavement. Because of the lower temperature of the sur- face treatment, there should be no concern about bump for- mation. The non-routed flush fill is commonly utilized with crack filling using an emulsion. The emulsion will readily flow into the crack. Photographs 4-1 illustrate squeegee operations to smooth the surface of the treated crack. The type of squeegee is deter- mined by the sealant used. A hot sealant uses the all-metal squeegee shown on the left, while cold-poured materials have a rubber-faced squeegee as shown on the right. Overband Crack Treatment Configurations Overband crack treatment configurations (Graphic 4-3) are used when traffic will be on the treatment soon after place- ment. Low-traffic roadways are good candidates for this type of treatment. Care must be taken to avoid excess sealant on the surface from a traffic safety perspective and from a sealant Recess Depth Reservoir Width Reservoir Depth Graphic 4-1. Recessed crack treatment configuration. Reservoir Width Reservoir Depth Routed Crack Non-Routed Crack Graphic 4-2. Flush fill crack treatment configurations.

25 integrity perspective. If the sealant sticks to vehicle tires, it can be pulled out of the crack, resulting in a failure of the crack sealant. This application should not be used if an overlay is planned as the potential for a bump in the overlay is high. The non-routed application is often used for crack filling. The surface may be squeegeed to smooth the overband. Installation of an overband application is shown in Photo- graph 4-2. The overband material may be squeegeed flat or may be left as a “cap.” The overband should be no more than 3″ wide. Photograph 4-3 illustrates the condition of a pave- ment with excessive sealant overband application. Chong (37) recommends overfilling the crack to just cover both edges of the crack and to allow for shrinkage during cooling. This approach minimizes snowplow damage for routed cracks. Photographs 4-1. Squeegee for sealant (hot-poured sealant on left, cold-poured sealant on right) (21). Overband Width Reservoir Depth Routed Non-Routed Overband Width Reservoir Width Graphic 4-3. Overband crack treatment configurations. Photograph 4-2. Overbanding (22). Photograph 4-3. Excessive overbanding (22).

26 Crack Preparation A controversial subject is whether to cut the crack prior to the treatment. Crack cutting can be performed either by a diamond saw or a rotary impact router, shown in Photographs 4-4 and 4-5, respectively. Table 4-2 provides an overview of the advantages and disadvantages of the saw and router. As a result of the productivity advantage and the ability to follow the crack more closely, the router is the most commonly used cutting procedure. However, less than half of respondents in the survey routinely rout cracks (recessed routed 35%, flush routed 48%, and over- band routed 43%). Routing is a process that should be evaluated by agencies in more detail—it is a good tool for the toolbox. Filice (72) provides recommendations for routing selection: Do Rout: • crack opening 3 mm to 12 mm (1⁄8″ to ½″) • cracks 12 mm to 20 mm (½″ to ¾″) shall be evaluated to determine appropriateness • cracks greater than 19 mm (¾″) shall be cleaned and filled Photographs 4-4. Diamond saw crack cutting (16). Photographs 4-5. Router head (left: courtesy Crafco) and machine (right: courtesy Marathon Mfg.).

27 Diamond Saw Rotary Impact Router Operation Small wide-diameter blade Multiple impacting cutting heads Cut Description Smooth-walled reservoir Rougher surface Reservoir Description More rectangular Higher % aggregate surface area More maneuverable Follows cracks more closely Production Low 1.2 to 2.1 m/min High 3.6 to 4.6 m/min Maintenance Faster blade wear Table 4-2. Sawing versus routing (16). Graphic 4-4. Installation of backer rod (shown as an ellipse). Photograph 4-6. Pavement sweeping (photo by Dale Decker). • types of cracks for consideration – longitudinal cracks – transverse cracks – edge cracks Do Not Rout: • crack opening less than 3 mm (1⁄8″) • fatigue cracks • pavements with high-density cracking • pavements being considered for rehabilitation The router or saw width must touch both sides of the crack for proper cutting. It is recommended that the router remove 1⁄8″ from each side of the crack and cut back to sound pave- ment. The minimum and maximum widths of the cut are recommended as ½″ and 1-½″, respectively, with a recom- mended cut depth of ¾″. The pavement should not spall dur- ing the routing in order to obtain the best adhesion of the sealant to the crack edges (78). When treating large cracks, backer rod is used to eliminate drainage of the sealant to the bottom of the crack. This allows better expansion and contraction of the sealant during cool- ing and heating and reduces the amount of sealant required, as shown in Graphic 4-4. If the sealant is placed too deep in the crack, the potential for cohesive failure is high. Almost 50% of the participants in the survey indicated that cohesive failure was frequently observed. Crack Cleaning The crack must be clean and dry prior to the placement of any sealant material. If this is not completed correctly, the sealant will not adhere to the sides of the crack and perfor- mance will be poor (adhesive failure). Lack of bond was the most common source of failure identified in the State-of- the-Practice Survey. Best Practice suggests that the pavement should be swept to remove dirt and debris prior to starting crack treatment operations. A power sweeper or vacuum cleaner should be used, as shown in Photograph 4-6. High-pressure air blasting should be used to remove dust, debris, and loose pavement fragments for both crack sealing and crack filling operations, as shown in Photo- graph 4-7. To accomplish this the compressor should have a minimum pressure of 100psi and a minimum blast flow

28 of 150cfm (16, 21, 22). The compressed air must be free of oil and moisture to ensure that the sealant will adhere to the crack edges. A backpack blower (leaf blower) should not be used for crack cleaning. Almost 90% of the survey par- ticipants indicated that compressed air was used for crack cleaning. The compressed air cleaning should be directed away from passing traffic and should not blow debris into an already cleaned crack. Crack vacuuming can also be performed to clean the crack. Photograph 4-8 shows a vacuum system cleaning the crack. For crack filling, use of compressed air and/or vacuum- ing may be adequate, particularly if a cold-poured asphalt emulsion is to be used as the sealant. However, if crack seal- ing is to be done or if a hot-poured product is to be used for crack filling, the crack must be dried prior to sealant placement. Hot air lances are used to dry the crack, as shown in Photo- graphs 4-9. Not only does the hot air lance dry the pavement, but it also warms the surface of the crack to enhance bonding of the sealant. A significant challenge for the hot air lance oper- ator is to avoid overheating the asphalt mixture. Overheating can damage the asphalt binder and potentially weaken the crack edge. There is no agreement in the technical literature regarding the temperature and velocity of the hot air lance, as are shown in Table 4-3. Temperatures range from about 1,000°F to 2,500°F, and velocities range from approximately 2,000 fps to 3,000 fps. While there is disagreement about the specific operational characteristics, there is no disagreement that the hot air lance Photograph 4-7. Compressed air cleaning of crack (courtesy Crafco). Photograph 4-8. Crack vacuum (courtesy Crafco). Photographs 4-9. Hot air lances (left: courtesy Crafco, right: courtesy Lab Mfg.).

29 is a valuable tool for crack sealing and should be used cau- tiously to avoid damage to the existing pavement. Appropri- ate safety gear should always be used. Sandblasting has also been used to clean cracks. However, clean-up and environmental issues can be problematic. While sandblasting is effective, the cost is usually high so the process is seldom used. Material Preparation The manufacturer of every sealant provides handling and heating recommendations for the specific product. The rec- ommendations must be followed. Issues such as melting rec- ommendations, minimum placement temperature, heating temperatures, and guidelines for length of heating time to avoid overheating will typically be included in the recommendations. Improperly handling the material, particularly overheating, may result in significantly different material properties for some sealants, affecting both application and performance of the material. The user must know and follow the recommenda- tions from the manufacturer. In addition, the manufacturer is required to provide Material Safety Data Sheets (MSDS) for each product. All personnel should be familiar with the MSDS requirements for safe handling. For crack sealing installation to proceed, the sealant must be brought to application temperature. For hot-poured sealant, the material must be heated to proper application temperature. For cold-poured sealant, the sealant will have minimal if any heat applied to the material. It is recommended that the melter for hot-poured applica- tions be a self-contained double boiler device with the trans- mittal of heat through heat transfer oil to the sealant vessel. Direct-fired melters are used in some areas, but with the seal- ants commonly used today, there is a considerable concern for damage to the sealant. Direct-fired melters are not considered Best Practice for polymer modified crack sealants. The melter equipment from three manufacturers is illustrated in Photographs 4-10 to 4-12. The melter must be equipped with an on-board automatic heat-controlling device to achieve and maintain the proper sealant temperature for the proper instal- lation of material. The melter must be capable of safely heating product to 400°F. The temperature control should not allow the heat transfer oil to exceed 525°F. There should be tem- perature readings of the sealant within the melting vessel and Agency Hot Air Lance Temperature, oF Hot Air Lance Air Velocity, fps Michigan DOT (16) 2,500 1,970 Minnesota DOT (43) 1,800 3,000 Canadian Research Council (24) 932 (not specified) Table 4-3. Hot air lance temperature and velocity. Photograph 4-12. Loading Crafco melter (courtesy Crafco). Photograph 4-10. SealMaster melter (courtesy SealMaster). Photograph 4-11. Marathon melter (courtesy Marathon Manufacturing).

30 within the discharge plumbing to provide monitoring of the sealant throughout the operation (81). The unit shall also have a means to vigorously and continu- ously agitate the sealant that meets requirements of ASTM D6690. Extreme caution must be used when charging the seal- ant into the melter to avoid injury to the operator. The sealant should be applied to the pavement under pressure supplied by a gear pump with a direct connecting applicator tip (81). The melters are manufactured with different size melting chambers for use on jobs of different sizes. Some melter mod- els allow two operators to be working at the same time, thereby greatly increasing productivity. Sealant Installation For cold-poured crack filling applications, if the sealant is an emulsion, it can be placed in the crack using a gravity feed system or something as simple as a cone, as shown in Photograph 4-13. Gravity feed systems are used in some areas but are not considered Best Practice. It is difficult to get the sealant into the crack, and a significant amount of sealant is wasted on the surface (82). After installation of the crack treatment, it may be neces- sary to apply a blotter material to minimize tracking by traffic. Sand, toilet paper, and commercial products have all been used as blotting material. Photograph 4-14 (a) illustrates a sand blotter being applied, (b) illustrates use of toilet paper, and (c) illustrates a spray-on application of anti-tracking solution (sprayer on right side of photo). While the sand and paper will serve as a blotter, there is debris created because of the residue generated. There is also a potential for the toilet paper to be mistaken for lane markings on longitudinal cracks. For hot-poured applications, the conditions at the time of installation are critical to the success of the treatment. Graphic 4-5 illustrates the wrong times for crack sealing (SS-1). If sealant is applied in the winter when the crack is wide, the sealant will be squeezed out of the crack in the sum- mer when the crack is narrower, as shown in row one of the graphic. The middle row of the graphic demonstrates that if the crack is sealed in the summer, there is a risk for cohesive failure in the sealant during the winter when the crack width is at its highest value. The final row of the graphic illustrates that spring and fall are optimum times for crack sealing in order to get best performance of the sealant. It is noted that the survey respondents indicated the aver- age crack sealing season is May to August, which for many areas in North America may not be considered optimum tim- ing for crack treatment installation. Since a significant per- centage of crack treatment is done with agency personnel, the decision on timing possibly depends on availability of per- sonnel rather than on performance of the crack treatment. It is not recommended to apply hot-poured sealants over cold patches (22). The sealant may cause failure of the cold patch. Photograph 4-13. Application of emulsion crack treatment (24). Photographs 4-14. Blotter applications: (a) Sand blotter (16), (b) Toilet paper (16), (c) Anti-tracking solution (photo by Dale Decker).

31 Safety It is important for all sealant crewmembers to under- stand safety requirements for handling the sealants and the equipment being used. Sealant and equipment manufactur- ers provide recommended safe operating procedures for their products. The following PPE is recommended for application of sealants: • Long pants; • Long-sleeved shirt buttoned at the wrists; • Heat-resistant gloves; • Eye protection (safety glasses or face shield); • Hard-soled work shoes; and • Traffic safety vests and hard hats (when exposed to traffic). Photograph 4-15 illustrates proper protection for work- ers involved in crack treatment applications. Basically, all skin should be covered to prevent a potential burn from skin contact with the hot sealant. If skin contact does occur, cool the affected area with cool water or compounds specifically designed for asphalt removal—do not attempt to remove the material from skin either mechanically or with solvents. Once cool, the sealant will fall off the affected skin in a few days. In addition, good safety practices include the availability of a fire extinguisher, a first aid kit, and burn packs. Quality Control For most construction operations, inspection of the work performed is an integral part of the construction process. The survey responses indicated that inspection is generally not performed during crack sealing operations even though participants reported better performance of the crack treatment if an inspector is present. Inspection of the crack treatment installation is important regardless of the personnel performing the work. In order to optimize performance of the sealant, verification of the quality of the work is critical. Some agencies have used warranty contracts to relieve the owner of inspection responsibility. Since 60% of the survey respondents indicated that crack treatments are performed with in-house personnel, a warranty contract model cannot be used effectively for a substantial portion of the crack treat- ments installed under current practices. Masson et al. (24) discussed an inspection method for evaluating the efficiency of the routing procedure. A metal die was developed (Graphic 4-6) that enables the inspector to measure the rout depth and width. Minnesota DOT (43) uses a square die to inspect routed cracks. Included in the inspector’s duties are verification of: • Proper sealant for the project; • Proper equipment for the project; • Inspection of the equipment to be used; • Proper equipment operation; • Equipment calibration; Graphic 4-5. Not the right time for crack treatment (SS-1). Photograph 4-15. Crack treatment operations (21).

32 Graphic 4-6. Metal die for QC of routing depth and width (24). • Temperature of the melter; • Sample sealant for specification testing; • Proper crack cleaning and routing (if used); • Proper sealant installation; • Usage of proper PPE; and • Safe workzone. In addition, the inspector can maintain a professional diary of project activities. Inspection of the work performed is a critical need for crack treatment operations. Montana DOT published the Troubleshooting guide found in Table 4-4 (5). This guide provides good insight into issues that may be encountered. Problem Encountered Possible Causes Possible Solutions Bubbles in Sealant Damaged backer rod Wrong backer rod Change backer rod installation method or rod diameter Use proper backer rod for hot-poured sealants Moisture in crack Grass or weeds in crack Dry reservoir Bubbles in melter Moisture present Add sealant Reduce agitator speed Slowly heat to evaporate water Air trapped by sealant Fill reservoir from bottom Sealant is deeply sunken in reservoir Crack is underfilled Rod is slipping into crack No rod present Use proper sealant volume Use proper rod diameter Sealant surface is not consistent Operator control is poor Operator movement is uneven Reservoir width/depth is variable Inconsistent material temperature Use nozzle with depth control plate Use wand with shutoff at nozzle Use an experienced operator Sealant not sticking to routed reservoir walls Reservoir walls are not clean Remove all contaminants Moisture on walls from rain, dew, or condensation Wait for pavement to dry Use hot air lance Use compressor with moisture trap Sealant temperature too low Maintain recommended sealant temperature Pavement temperature too low Wait until it warms up Incompatibility of sealant and asphalt mix Use proper formulation Sealant remains tacky after installation Melter is contaminated with heat transfer oil, solvent, or other sealant Empty and clean melter Sealant has been overheated or heated too long Empty melter and replace with fresh sealant Check melter temperature regularly Table 4-4. Troubleshooting crack treatment issues (5).

33 Conclusion The primary focus of crack treatments is to achieve a pave- ment maintenance application that will perform well under a variety of environmental and traffic conditions. As with most pavement construction activities, there are many, many details that must be given attention. Crack treatments are no exception to that statement. The state-of-the-art review highlighted areas in which the state-of-the-practice has not kept up with current technol- ogy. This is all too easy to happen. People applying crack treatments have learned how to do the job mainly by experi- ence. As a result, it is often challenging to implement new technology. Based on the results of this project, areas in which improve- ments in the state-of-the-practice should be considered include: • Evaluation of pavement condition prior to sealant application—i.e., what type of crack is present, how severe is the cracking, and what is the density of the cracking; • Acceptance of the new SG evaluation system; • Proper preparation of the crack prior to sealant application—making sure that the crack is clean, dry, and properly configured for the application; • Training for sealant application personnel—this is an ongo- ing need; • Quality Control testing for sealant products—establishment of uniform sampling and testing protocols; • Inspection of the crack treatment operations—many agen- cies do little if any inspection of the treatment work; and • Evaluation of sealant performance—understanding how the sealant performs enables the owner to make knowl- edgeable decisions about materials and procedures.