SUMMARY

Wide Cracks and Joints in Flexible and Composite Pavements: State DOT Maintenance Practices

The repair of transverse cracks and longitudinal paving joints and cracks in asphalt and asphalt-surfaced pavements is a common maintenance activity for state departments of transportation (DOTs). One of the limitations of crack sealing and filling, however, is the width of the crack for which these repairs are successful. Cracks that are good candidates for sealing and filling are relatively narrow and experience limited movement (both horizontal opening and closing and vertical movement). There is limited guidance available on maintenance practices for cracks that are not good candidates for sealing and filling. These include wider and deeper cracks for which crack sealing and filling may not be appropriate treatments. The objective of this synthesis is to document practices used by state DOTs for flexible and composite pavement maintenance for wide transverse and longitudinal cracks and joints.

A literature review, survey of DOT practices, and development of case examples were used to meet the project objective. The literature review indicated that several different patching and sealing techniques have been used to maintain wide cracks and joints in asphalt-surfaced pavements. The introduction of asphalt mastics as a crack maintenance strategy is fairly recent and to date, there have not been studies of mastic practices or performance.

A survey of practice on wide transverse crack and wide longitudinal joint and crack maintenance was distributed to 50 state DOTs, the District of Columbia DOT, and the Puerto Rico Highway Authority DOT. Responses were received from 46 of the 52 DOTs, representing a survey response rate of over 88%. Almost 33% (15 responses) of the 46 respondents indicated that they do not distinguish between narrow and wide cracks in determining crack maintenance treatments. Of the 30 DOTs that did make this distinction for wide transverse cracks, 53% (16 responses) identified the width at which a crack becomes too wide for crack filling or sealing as between 1 and 2 inches, while 55% (16 responses) of the 29 DOTs identified that same width as too wide for longitudinal cracks.

DOTs use multiple materials for wide crack maintenance, including mastics, crack fillers and sealers, spray patching, milling and patching with asphalt, patching with micro surfacing, and cold and hot mix asphalt patching. Performance data for mastics in particular are limited because there has not been much experience using them. Furthermore, wide crack repairs are done on both pavements in good condition and pavements toward the end of their lives. This makes it difficult to summarize the effect of these repairs on pavement or treatment life.

Based on the survey responses, the following DOTs were asked and agreed to participate in more in-depth interviews to develop case examples of their experiences maintaining wide cracks:

• Arizona DOT.
• Arkansas DOT.

• Maryland DOT.
• Minnesota DOT.
• Nevada DOT.
• Pennsylvania DOT.
• Washington State DOT.

The experiences of these case example DOTs include both new and long-time users of mastics and cover a range of techniques for wide crack repair. Specific documentation on the use of mastics for wide crack repair, including guidelines and specifications, are provided by five of the seven case example DOTs.

The following are key findings from the study:

• There is a limit to the effectiveness of conventional crack sealants and fillers to seal wide cracks.
• There is no consensus on the definition of a wide crack, but conventional sealants and fillers reportedly do not perform well when used to seal cracks wider than 1 to 1.5 inches.
• Wide cracks are often also deep cracks. The repair of wide and deep cracks with mastics calls for the placement of the mastic material in multiple lifts.
• Materials and procedures used to maintain or repair wide transverse and longitudinal cracks include mastic sealers, mill and patch with asphalt, patching with cold or hot mix asphalt, spray patching, and patching with slurry or micro surface.
• As the use of mastic sealers expands, DOTs are developing internal guidance and sponsoring training on wide crack repairs using mastics.

The following knowledge gaps and suggestions for future research are suggested based on the literature review, survey results, and case examples:

• Given the acknowledged limitations of conventional crack sealants and fillers, especially for the maintenance of wide cracks, there is a need for expanded guidance on materials and procedures for that activity.
• Available wide crack maintenance strategies include sealing with mastics, mill and patch with asphalt, sealing with micro surface, spray patching, and other patching. Further guidance is needed on when each of these materials/procedures is appropriate for wide transverse and longitudinal crack maintenance. This guidance could include production rates, costs, and performance.
• Mastic repair material limitations are not well understood or documented. Performance limitations might be based on traffic levels, pavement and crack conditions, and crack widths and depths, among other factors, but these have yet to be studied.
• 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 would contribute to better cost-effectiveness analyses.
• Guidance on maintenance and rehabilitation strategies after mastic use on wide cracks is also needed to answer questions such as what treatments can be placed over mastics and if pavements with mastic materials can be recycled. Studies to explore these limitations would help refine available guidance on wide crack maintenance.