Types of Asphalt Cracks and How to Repair-Part 2

This type of cracking resembles an alligator skin.

This is part 2 of our series on Asphalt Cracks and How to Repair. Another great article from our Northern California Technical Director of the Asphalt Pavement Association of California.

Technical Corner
by Rita B Leahy, APACA Technical Director

Crack Treatment ? Seal or Fill?

Crack treatment involves two types of action: crack sealing and crack filling. Crack treatment is the placement of specialized materials into the cracks of pavement surfaces to prevent the intrusion of water and foreign objects that may damage the pavement structure. So, the obvious question is “to seal or fill?” To answer that question, a bit more background on cracking is needed. First, recognize that cracks may open and close horizontally with temperature and moisture changes and may undergo vertical movements as the result of load applications. Second, to decide upon the appropriate crack treatment, one must ascertain its employment status: Is it a “working” crack or “non-working” crack?

The Federal Highway Administration (FHWA) identifies the distinct difference between crack filling and crack sealing.

Crack sealing is “the placement of specialized treatment materials above or into working cracks using unique configurations to prevent the intrusion of water and incompressibles into the crack.” A working crack is defined as having movement in excess of ? inch. Caltrans definition of a working crack is ≥¼ inch. Transverse cracks, cracks perpendicular to the direction of traffic, are typically considered to be working cracks and are often targeted for crack sealing.

Crack filling is defined as “the placement of ordinary treatment materials into nonworking cracks to reduce infiltration of water and to reinforce the adjacent pavement.” Non-working cracks are defined by the FHWA as “cracks where little movement occurs between crack edges.” Most longitudinal cracks, ie, cracks parallel to the direction of traffic, are typically considered non-working cracks and are often targeted for crack filling.

The FHWA criteria for deciding whether to seal or fill a crack are shown below:

Note that because many projects contain both working and non-working cracks, Caltrans treats all cracks as working cracks and uses only crack sealing materials.

WHEN to do Crack Treatment

Ideally, crack-sealing treatments should be applied during relatively cool weather when the crack width is at its midpoint to widest, usually in the spring, fall, or winter. Fall is generally a good season for application in most parts of California, as air temperatures are typically between 45 to 65°F. Weather conditions during installation need to be appropriate for the material used, not too cold or wet. Since non-working cracks do not change in width significantly with temperature, application of crack filling treatments can proceed at any time of the year when weather conditions are appropriate. Traffic passing over a hot applied sealed or filled crack is usually not an issue. However, traffic control during the application of the treatment should be in force long enough to allow for adequate curing of the product and prevent tracking.

Next week – materials and placement methods.

References:
1) K.L. Smith and A.R. Romine, Materials and Procedures for Sealing and Filling Cracks in Asphalt-Surfaced Pavements, Manual of Practice, FHWA-RD-99-147.
2) Caltrans, Maintenance Technical Advisory Guide, Volume I, Flexible Pavement Preservation, Second Edition, 2008.
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