Asphalt parking lots and roads need to be maintained. There is no question about that. And often, asphalt maintenance can be more cost effective than removing and replacing asphalt. And when done properly, maintenance can directly extend a pavement's life.
Cracksealing and crack filling are two of many pavement preservation strategies, and often they are used in conjunction with other strategies such as sealcoating or slurry seal. There are two types of cracks - working and non-working. Working cracks have a considerable amount of horizontal or vertical movement - greater than or equal to 3 mm - because of temperature change or amount of traffic, according to the Materials and Procedures for Sealing and Filling Cracks in Asphalt-Surfaced Pavement - Manual of Practice. Non-working cracks typically have "little movement between crack edges."
The Manual defines cracksealing as placing "specialized treatment materials above or into working cracks to prevent the intrusion of water." Crack filling is the "placement of ordinary treatment materials into non-working cracks to reduce infiltration of water and to reinforce the adjacent pavement."
But before contractors crackseal or crack fill, they should understand why and how cracks occur.
Asphalt expands and contracts in different temperature environments. If not all of the asphalt is moving in a uniform way, it will become weak at the joints, says James B. Curtis, president of Chec Management Systems Inc. in Redding, CA. "Cracks are usually wider when it's cold and narrower in warmer temperatures," he says.
Left untreated, cracks in asphalt enable water to penetrate beneath the pavement surface, weakening the base and subbase, leading to raveling or failure of the pavement and to more extensive, costly repairs. So repairing cracks is a relatively inexpensive preventive maintenance technique that can help property managers extend the life of their parking lot.
Preparation is Key
"Good prep will give you the best performance for your crack filler or sealer," Curtis says. Before crack filling or sealing, be sure to properly clean and dry the crack. This can be done with wirebrushing, airblasting or sandblasting. Proper cleaning helps to minimize the potential for adhesion failures resulting from dirty or moist cracks.
Cracks can be airblasted using backpack or walk-behind blowers or high-pressure air compressors. Another option is hot airblasting done with a hot compressed-air lance or a heat lance. Contractors choosing this method need to be careful not to burn the asphalt and cause further damage. A heat lance can also allow a contractor to fill or seal cracks in colder or damp conditions because it will heat and dry the asphalt.
Another approach, recommended by various studies as the way to ensure the most successful crack repair, is to cut or route the crack prior to sealing or filling. Routing widens cracks to create a clean reservoir to better contain the sealer. Curtis suggests routing if a crack is at least 3/4 of an inch wide and has at least 1/2 to 3/4 inches of movement. Contractors need to be cautious so the cutting does not increase or create further damage to the asphalt.
Material Options Available
Curtis says installation of crack filler or sealer must be done right after cleaning the crack to ensure the crack stays dry and free of debris prior to material application and minimize the chance for failures. Contractors have an array of sealing and filling material options to choose from.
Emulsified crack filler contains both oil and water. If using emulsified filler, make sure it is fully cured before sealcoating over it. A deeper crack will take longer for the emulsion to cure. If the emulsion isn't fully cured the water in it will be kept in the asphalt, possibly causing the crack filler to fail and the asphalt to ravel, Curtis says. Depending on the material and job requirements, emulsions can be applied partially heated or unheated.