Crack Treatments for Asphalt Pavements - Best Practices

by Airton Kohls (Source: NCHRP Report 784 - Best Practices for Crack Treatments for Asphalt Pavements)

This NCHRP Report released in 2014 points to the pavement maintenance techniques known as crack sealing and crack filling. Crack sealing is generally performed on "working" cracks, e.g., cracks that are more than 1/8" in the summer and significantly larger in the winter. However, crack sealing can be used for any crack treatment operation. Crack filling is generally performed on cracks that do not open and close due to environmental conditions. Treating cracks in asphalt pavements is a major part of every maintenance engineer's work. The objective of any crack treatment is to minimize the intrusion of water into underlying layers of the pavement structure. Such water infiltrates the base layers of the pavement and may lead to pavement structural failures.

FHWA describes the following steps in a crack treatment program:

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.
   1. A pavement surface treatment is appropriate for a pavement with high density of cracks that have moderate to no crack edge deterioration.
   2. A crack treatment is proper for a pavement with moderate density of cracks that have moderate to no crack edge deterioration.
   3. A crack repair is necessary for pavements with moderate density of cracks that have a high level of crack edge deterioration.
4. For crack treatment, determine whether cracks should be sealed or filled.
   1. Cracks with significant annual horizontal movement ("working" cracks) should have a crack sealing treatment.
   2. Cracks with little annual horizontal movement ("nonworking" cracks) should have a crack filling treatment.
   Select materials and procedures for the crack treatment operation based on environmental, equipment, personnel, and cost-effectiveness considerations.
5. Acquire materials and equipment to perform the work.
6. Conduct and inspect the crack treatment operation.
7. Periodically evaluate treatment performance.

The NCHRP Report 784 presents a discussion on best practices for crack treatments in Chapter 4 and details important issues like climatic conditions during sealant applications, crack configurations, crack preparation, crack cleaning, material preparation, sealant installation and safety.

Climatic Conditions
The environmental conditions at the time of sealant placement have a significant impact on the performance of the sealant. Typically the temperature should be between 40°F and 70°F for both crack sealing and crack filling. The following weather considerations should also be observed:

• 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 treatment operation. If an unexpected shower occurs, any crack that has been cleaned and dried must be re-evaluated for proper conditions.

  Seasonal Impact on Sealing Operations
  When sealing in the winter, the crack will be at its maximum width, as shown in the first row of the graphic below. In the other seasons, the crack reduces in size and squeezes the sealer out of the reservoir. The center image of the middle row below illustrates sealing in the spring/autumn. The crack is at a "middle" size and will have less deformation of the sealant during cold and hot temperatures. The bottom images demonstrate that if the crack is filled in the summer when the crack is at its smallest size, extreme stresses will be induced on the sealant during the winter, potentially leading to cohesive failure.

  Troubleshooting Crack Treatment Issues
  For most construction operations, inspection of the work performed is an integral part of the construction process. Inspection of the crack treatment installation is important regardless of the personnel performing the work (contracted out or in-house personnel). Montana DOT published the Crack Treatment Troubleshooting guide.

  For additional information on "Best Practices for Crack Treatments for Asphalt Pavements" go to: https://www.nap.edu/catalog/22314/best-practices-for-cracktreatments-for-asphalt-pavements

  
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