CHAPTER 5

Summary of Findings

There is a current unmet need for guidance on maintaining wide transverse cracks and wide longitudinal cracks and joints in asphalt pavements. There are well-documented guidelines on crack filling and sealing, but those actions are directed toward the sealing of cracks less than 1-inch wide. The maintenance of wide cracks that develop in asphalt pavements, whether that is relatively early or later in the life of the pavement, is challenging.

The objective of this synthesis was to document practices used by state DOTs for flexible and composite pavement maintenance for wide transverse and longitudinal cracks and joints. Information gathered in the development of this synthesis was intended to address the following:

• Products and methods used;
• Cost data for different treatment methods and materials;
• Crack widths above which traditional sealing methods and materials are not advisable;
• Written policies, definitions, specifications, decision processes, and guidelines related to treatments of wide cracks and joints;
• Use of cost-effectiveness analyses to select treatment methods;
• Application records, such as age of pavement, pavement type, climatic zone, traffic, and pavement condition;
• Impact of different applications and treatments on pavement service life, and performance measures such as overall condition, ride quality, noise, and skid resistance;
• Written procedures for acceptance and quality assurance of new or current maintenance materials (e.g., testing, inspection, or traceability); and
• Performance records of related pavement maintenance products and techniques for wide cracks.

Based on the results of a literature review, a survey of state practices, and case examples, this report identifies current practices related to maintenance of wide cracks. Key findings are summarized here, concluding with knowledge gaps and suggestions for future research. A focus of this synthesis is on DOT use of, and experience with, mastic materials for wide crack repairs. Mastics are a blend of polymer-modified asphalt binder and aggregate, which have good flexibility and durability, bond well to pavement surfaces, and can be placed wider and deeper than conventional crack fillers and sealers. Standard practice prior to the introduction of mastic repairs was to use other patching materials. The use of mastics for wide crack maintenance is a comparatively recent practice.

Key Findings from the Literature

• Wide crack repair is accomplished using a variety of approaches. These range from the use of crack sealing and filling to mill and replace with AC and sealing with slurry or micro surface, either with or without milling. The use of mastic repair materials for wide crack repairs is a

• comparatively recent practice; these have been available for perhaps 20 years. The proprietary mastic materials available conform to the ASTM D8260 specification, which identifies three material types based on the temperature extremes to which the material will be exposed. Other materials used for wide crack repair include milling and patching with asphalt, patching with micro surface, and cold and hot mix asphalt patching.
• There are limited studies of mastic performance in the literature, especially of materials commonly used in the past 6 years.

Key Findings from the Survey

• Fifteen of the 46 responses (32.6%) indicated that their DOT did not distinguish between narrow and wide cracks for crack maintenance treatments.
• Sixteen of 30 (53.3%) responses indicated a wide transverse crack is defined as either 1- to 1.5-inches wide or 1.5- to 2-inches wide, while 8 of 30 (26.7%) responses identified a wide crack as being between ¾ and 1 inch.
• Responses for longitudinal cracks were similar: 16 of 29 responses (55.2%) indicated a wide longitudinal crack was either 1- to 1.5-inches wide or 1.5- to 2-inches wide.
• In most cases no upper limit is set on crack widths for maintenance.
• Wide crack identification is accomplished by visual assessment and review of images from DCVs.
• Several different materials and procedures are being used for wide crack maintenance. In addition to mastic sealers, crack fillers or sealers, mill and replace with AC, slurry or micro surface patching with or without milling, and localized patching are also used. For wide longitudinal crack maintenance in particular, mill and replace or micro surfacing have faster placement rates than mastic patching.
• Traffic volumes and roadway classification were generally not considered in determining crack width repair limits or repair materials.
• Preparation of the crack prior to mastic repair is very similar to the steps used for crack sealing and filling. The most commonly used techniques were crack cleaning with compressed air (33 of 38 responses, or 86.8%) and drying with a hot air lance (24 of 38 responses, or 63.2%).
• Performance of wide crack maintenance repairs was varied, especially for mastic repairs. However, experience with mastic repairs was comparatively new, ranging from about 20 years to fewer than 4 years.
• The effect of wide crack repairs on pavement performance was also varied. Of the 36 responses to a question about the effect of those repairs on roughness, friction, and noise, “unknown” was given by 61.1%, 83.3%, and 63.9%, respectively. Specifically for roughness, of the 14 responses indicating some effect, 35.7% said it made the pavement smoother and 50% said it made the pavement rougher. For noise, of the 13 responses indicating some effect, 61.5% said repairs increase noise and 23.1% said it decreased noise. The remaining responses for both roughness and noise identified no impact. Other factors affect wide crack repair performance, including the overall condition of the pavement when the repair is constructed and the quality of the repair.

Key Findings from the Case Examples

• Common wide crack repair techniques include mill and patch with AC, slurry and micro surface patching, spray injection patching, and patching with cold or hot mix AC.
• DOT experience with the use of mastics for wide crack maintenance ranges from as many as 20 years to as few as 4 years. Demonstration projects and specialized training on the materials and equipment have helped to spur the use of mastics for wide crack repairs.

• DOTs experiencing temperature extremes (e.g., ADOT, MnDOT) use mastics to address their extensive wide crack concerns. ARDOT does not experience extensive wide cracking, and its crack maintenance strategies focus on crack filling and sealing.
• DOTs reported on the use of mastics for problems other than wide crack repair of asphalt pavements. These included repair of raised pavement markers (MDSHA, WSDOT), asphalt pavement patching (ADOT, ARDOT, and MDSHA), fatigue cracks (ADOT, ARDOT), filling rumble strips (MDSHA), and spall repairs in concrete pavements (ARDOT, WSDOT).
• Both in-house maintenance crews and contractors carry out wide crack maintenance. If the DOT is repairing wide cracks with mastics, they typically lease the equipment.
• Timing of mastic applications varies. Wide crack repairs are used both on pavements that are in fair to good condition as well as on pavements at the end of their serviceable life.
• Guidance on where to use mastics is varied. MDSHA, MnDOT, PennDOT, and WSDOT have developed their own guidelines on wide crack maintenance using mastics and other procedures. The project-level memo issued by MDSHA’s Pavement and Geotechnical Division and PennDOT’s HPM guidance are specific examples of guidance available to maintenance crews and contractors prior to the initiation of crack repair work.
• Some guidelines call for deep mastic repairs to be constructed in multiple lifts. Deep repairs are a concern because of the quantity of material that may be used, the difficulty in cleaning deep cracks, and the potential for the repair material to sag in a deep and wide crack.
• Production (placement) rates for mastic applications are limited by the size of the melter/applicators.

Knowledge Gaps and Suggestions for Future Research

The need to maintain wide cracks in asphalt pavements is not new. Approaches such as crack sealing and filling, patching with cold mix or hot mix AC or by spray patching, and milling and patching with AC, slurry, or micro surface have been used to repair wide cracks for years. In the past 4 to 6 years, the use of mastics for such repairs has increased. No other new techniques were identified. As a relatively new strategy, there are opportunities to improve the general understanding of when and how to use mastics as well as the other available strategies for wide crack maintenance.

• The performance limitations of crack sealants and fillers in wide cracks are well-documented (Smith and Romine 1999; Caltrans 2009; Decker 2014). Such materials placed in cracks wider than 1 inch, and especially cracks that open and close, do not perform well. There is no accepted definition of a wide crack, which creates an opportunity to better define that width. This would improve project selection and help define associated material performance limitations.
• The limitations of mastic repair materials are not well-documented. From the survey responses and case examples it is suggested that performance limitations might be based on traffic levels, secondary distresses, crack widths, and crack depths.
• Little information is available on the effect of wide crack maintenance repairs on various indicators of pavement performance. The availability of such guidance would help DOTs make treatment selections based on the condition of the pavement and project the impact of selected treatments on performance indicators such as distress, roughness, friction, and noise.
• Guidance on reasonable pavement maintenance or rehabilitation strategies after mastic use on wide cracks is also needed to answer questions such as what treatments can be placed over mastics and whether pavements with mastic materials can be recycled. Studies to explore these limitations would help to further refine available guidance on wide crack maintenance.
• Available wide crack maintenance strategies include sealing with mastics, mill and replace with asphalt, sealing with micro surface, spray patching, and other patching. Further guidance on when to use these materials/procedures for transverse and longitudinal cracks is needed.

• This guidance could include production rates, costs, and treatment life. The differences between wide transverse cracks and wide longitudinal cracks warrant separate studies of materials and procedures.
• Many DOTs have only started using mastics to seal wide cracks in the past 4 to 6 years. There have been limited studies of the long-term performance of these materials, especially under the range of conditions in which they might be used (e.g., environment, traffic volumes). Better long-term performance data will contribute to better cost-effectiveness analyses. Such performance data will also help define where mastic crack repairs fit in the overall pavement maintenance cycle.
• Wide cracks in asphalt pavements appear comparatively early in the pavement life for some DOTs and much later for others. For the latter case, DOTs are using mastics at the end of a pavement’s life to extend pavement life for several years before major rehabilitation or reconstruction. Guidance on wide crack repairs distinguishing between end-of-life maintenance activity and more proactive maintenance would be useful for those DOTs undertaking wide crack repairs.
• Information that is already available regarding different strategies for the maintenance of wide transverse and longitudinal cracks could be assembled into training materials to help DOTs with project and material selection and placement, including implementation tools and pocket guides.