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Road Management & Engineering Journal
Copyright © 1997 by TranSafety, Inc.
April 1, 1997
TranSafety, Inc.
(360) 683-6276
Fax: (360) 335-6402
transafety@live.com

Pothole Was Repaired after Louisiana Parish Notified of Hazard; Parish Not Liable Without Knowledge of Recurrence
Article Outlines Six Steps to Patching Potholes
Automated Pothole Patching--Better Patches for Less Money


















Sealing Cracks Extends Life of Asphalt Pavement

Since 94 percent of U.S. paved roads are asphalt, extending the life of asphalt roadways can save money and time for the local government agencies who are responsible for 70 percent of them. An article in Louisiana State University's Technology Exchange (October, November, December 1995) dealt with methods of treating asphalt cracking problems. The article's title was "To Seal or Not to Seal? Crack Treatment in Asphalt Pavements."

The Strategic Highway Research Program (SHRP) has experimented with methods and materials for treating cracks in asphalt paving. SHRP's research results helped answer questions roadway maintenance agencies face when deciding whether to seal cracks and how to go about sealing them.

What Cracks Should be Sealed or Filled?

Pavement cracking can create problems and should be repaired. Cracks allow water to get into the roadway base and subgrade, resulting in pavement breakup and potholes. Most cracks are good candidates for filling or sealing. The only exceptions mentioned in this article were: (1) where there is a failure in the subsurface or (2) where cracking was not caused by water problems (i.e., the subgrade is sandy soil).

According to the article, the decision on whether to seal or fill a crack would depend on the amount of horizontal movement:

Cracks with widths between 0.2 to 0.75 inches should be sealed. Likewise, cracks showing greater than or equal to 0.1 inch movement should be sealed. Pavements that have failed because of extensive alligator or block cracking may not be candidates for crack sealing methods. In such cases, other methods of repair, such as surface seals or partial depth patching may be more appropriate.

What Materials and Methods Should Crews Use?

Rubberized asphalts are flexible enough to adjust as cracks open and close. The article mentioned three categories:

  • cold-applied thermoplastic materials (emulsions, cutbacks, polymer modified liquid asphalts)
  • hot-applied thermoplastic materials (asphalt cements, fiberized asphalt, asphalt rubber, etc.)
  • chemically-cured thermosetting materials such as self-leveling silicon.

The final decision about what material to use will depend on the specific properties needed for the intended purpose and on logistical considerations such as preparation time, workability, and cure time. In a 32-month test, SHRP experiments showed that rubberized asphalt and asphalt rubber sealants fail only about 10 percent of the time and silicon sealants fail about 11 percent of the time.

Crews should follow several steps when treating cracks. The article suggested the most important are "cleaning and drying and material preparation and application." When repaired cracks will experience great ranges in temperature, the article pointed out that "crack cutting (routing or sawing), material finishing/shaping, and blotting are also employed as part of the procedure."

Cold temperatures, dirt, and moisture can prevent proper adhesion between the sides of the crack and the sealing material. Therefore, "using hot compressed air followed by a heat lance is recommended."

What Time of Year Should Crews Repair Cracks?

Temperatures affect the timing of crack sealing or filling. Fall or spring temperatures are generally best. Temperatures of 35 to 50 degrees Fahrenheit (2 to 13 degrees Celsius) allow crack channels to stand partially open and at the middle of the working range, thus minimizing the amount of expansion and contraction the seal or fill must tolerate.

Copyright © 1997 by TranSafety, Inc.


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