CHAPTER 1

Introduction

Background

The repair of transverse cracks and longitudinal paving joints and cracks in flexible and composite pavements is a common maintenance activity for state departments of transportation (DOTs). Such repairs, most often carried out by crack sealing or filling, have been studied extensively [e.g., Decker 2014; Truschke et al. 2014; Minnesota Local Road Research Board (Mn LRRB) 2023], and effective materials and procedures for sealing cracks in flexible-surfaced pavements are well-documented.

Effective crack sealing and filling programs provide documented benefits to pavement performance, including the following:

• Keeping moisture out of the pavement structure, thereby slowing the weakening of sub-surface layers and further deterioration.
• Slowing the progression of distresses worsened by the presence of moisture, such as pothole formation and asphalt stripping.
• Maintaining a smooth pavement ride and extending pavement life by keeping sealed cracks from progressing to more deteriorated and widespread cracks.

The following are definitions of crack sealing and crack filling:

• Crack sealing consists of placing sealant material in or over cracks that experience movement (also referred to as working cracks). These are typically transverse cracks that open and close due to daily and seasonal temperature changes. Crack sealing is often performed on cracks that are routed and cleaned, using sealing materials that have good adhesion, cohesion, and elasticity characteristics when exposed to repeated crack opening and closing.
• Crack filling consists of placing sealant material in cracks that do not experience movement or non-working cracks. These are typically longitudinal cracks that may only be cleaned before being sealed.

One of the limitations of crack sealing and filling 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). In NCHRP Report 784: Best Practices for Crack Treatments for Asphalt Pavements, for example, survey respondents indicated the following:

• Minimum and maximum widths for crack sealing—0.24 and 1.01 inches.
• Minimum and maximum widths for crack filling—0.42 and 1.66 inches.

A brief review of limits on crack widths for sealing and filling is provided in Table 1; material suppliers place similar limits on crack widths. While there is not unanimous agreement on these widths, they all fall within a narrow, similar range.

Table 1. Limits on crack widths for sealing and filling.

Unfortunately, cracks in flexible pavements do not remain in this narrow range forever. Cracks widen over time because of secondary cracking, additional breakdown or spalling of the crack, and aging and shrinking of the asphalt surface. Transverse thermal cracks will both increase in number and widen over time. While the need to keep the pavements sealed does not change, as cracks widen, they become more difficult to repair, and repair procedures other than conventional crack sealing and filling must be used.

Synthesis Objectives

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. 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.

Synthesis Methodology

The methodology followed to achieve the synthesis objectives broadly consisted of collecting and synthesizing relevant information in three different ways: a literature review, a survey of DOT practices, and case examples of the experiences of seven DOTs. Focusing on publications from the past 15 years, the literature review included information about both the uses and limitations of conventional crack filling and sealing, as well as mastic materials, application methods, and performance. In addition to crack sealing and mastic seals, the following approaches to maintaining wide cracks were also identified:

• Crack filling with a non-proprietary blend of asphalt and aggregate.
• Crack filling with a slurry or micro surface product, either with or without milling (see Figure 5).
• Crack patching with cold mix blends or hot mix asphalt.

• Crack patching with spray injection patchers (see Figure 6).
• Crack patching by milling the crack and repairing it with asphalt (also referred to as slot paving, mill and patch, or mill and replace).

Literature review sources included research reports and DOT reports and specifications.

Based on the findings from the literature review and the synthesis objectives, a questionnaire on practices for maintenance of wide cracks and joints was developed and distributed electronically to 50 state DOTs, the District of Columbia DOT, and the Puerto Rico Highway Authority DOT. The initial distribution of the questionnaire was to the voting members of the AASHTO Committee on Maintenance or their designees. Responses were received from 46 DOTs, representing an 88% response rate. Responding DOTs are shown in Figure 1. In some cases, follow-up phone calls or emails helped clarify responses. When all the completed questionnaires were received, the results were tabulated and analyzed and became the basis for the presentation of DOT current practices.

In the questionnaire, DOTs were asked if they were willing to serve as case examples. From the volunteer DOTs, the following seven were selected to participate in supplementary interviews: Arizona DOT, Arkansas DOT, Maryland DOT, Minnesota DOT, Nevada DOT, Pennsylvania DOT, and Washington State DOT. These states represent a range of environments, geographic regions, and experience with a variety of materials and techniques to maintain wide cracks and joints in asphalt-surfaced pavements.

Synthesis Organization

The remainder of this synthesis is organized in the following manner:

• Chapter 2: A literature review of maintenance strategies for wide cracks and joints.
• Chapter 3: DOTs’ state of the practice for wide crack and joint maintenance.
• Chapter 4: Case examples of seven DOTs.
• Chapter 5: Summary of findings, identification of knowledge gaps, and suggestions for further research.

Supporting information on the questionnaire and case examples can be found in the appendices to this report.