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Crack Sealing

Introduction

Roads endure enormous stress and strain. Vehicle tires continually push and pull at pg7.gif (72608 bytes)paved surfaces. The faster or heavier the vehicle, the more the pavement is compressed and then tensioned. Temperature changes, even those within a 24-hour day, expand and contract the pavement sheet. Traffic and temperature create small surface cracks. Water seeps through the cracks to the base materials and weakens the roadway. More cracks form and become wider if not repaired. Untreated roads deteriorate much faster than treated roads.

Crack sealing is an inexpensive routine maintenance treatment that will significantly delay roadway deterioration. Local road crews need to apply sealing material directly into cracks before cracks become too large or before the roadway is subject to the freeze-thaw cycles of New England winters. Flexible rubberized asphalt sealants bond to crack walls and move with the pavement, preventing water from entering the road base. The life of the road is extended and maintenance costs greatly reduced over time.

Methods and Equipment

For the sealing process to be successful, crews must be trained and furnished with the proper equipment and materials. For the sealant to work, crews must remove all dirt, debris, and water out of the cracks. The bonding material will not stick to dirty or wet surfaces. Using compressed air and a blow pipe is an effective method for removing the unwanted, loose material. If wet, compact dirt or other materials are in the crack, crews must dig them out.

Crack sealing performs better and costs less when highway crews rout cracks. The 4 ½ year SHRP H-106 study examined the four crack sealing configurations shown in the sidebar. Researchers concluded that traffic increasingly wore away overbanded sealant materials leaving an insufficient amount of sealant in the unrouted cracks. The simple band-aid and reservoir-and-flush configurations (A and D) performed poorly, making them the least effective treatment methods. The most effective method was the standard recessed band-aid (Configuration B).

Crews should rout the cracks in two steps. They first loosen left over debris and widen narrow cracks. It is very important to only widen the crack and not deepen it. Widening cracks allows for a reservoir of sealant in the pavement. When the pavement expands, the reservoir holds enough sealant to stretch with the road. If narrow cracks expand further than the bonding material can stretch, water will seep into the pavement, and soon into the base.

After crews break up debris and widen cracks, they must clean the cracks again. A hot-air lance is the recommended method. The device generates compressed air as hot as 2,000oF and blows the crack clean of debris while drying it. Crews should apply sealant material immediately after the crack is clean and in moderate amounts.

Materials

Pavement cracks can be repaired with either cold or hot sealants. Cold applied materials include liquid asphalt and polymer-modified liquid asphalt. Hot applied materials include asphalt cement, mineral-filled asphalt cement, fiberized asphalt, asphalt rubber, rubberized asphalt, and low-modulus rubberized asphalt.

To effectively seal a crack, the material must move with the road surface and remain adhered to crack walls. Mixtures of asphalt and rubber are long-wearing and can move with pavement during weather changes. One such mixture, commonly called "asphalt-rubber," is a special mixture of asphalt cement and used car tires. Asphalt-rubber is especially effective on roads subject to high traffic volume and heavy loads.

Other mixtures are effective for wide (high severity) cracks. These include polymer-modified liquid asphalt, rubberized asphalt, and low-modulus rubberized asphalt. Polymer-modified liquid asphalt is a mixture of natural and synthetic compounds with liquid asphalt. Rubberized asphalt and low-modulus rubberized asphalt are made by adding rubber to asphalt for flexibility. The choice of material depends on the type and amount of rubber in the mixture, and the type of the asphalt used.

Some materials, although often used because they are inexpensive, have little flexibility. These include asphalt cement, liquid asphalt, mineral-filled asphalt cement, and fiberized asphalt.

Conclusion

Sealants reduce deterioration of lightly damaged roads by minimizing the affects of traffic, weather, and temperature changes. Crack sealing is most cost effective when applied to longitudinal and transverse cracks. If the extent of cracking is high, a chip seal or thin overlay after sealing large cracks is the most cost effective treatment. If the surface has fatigue – so called "alligator" – cracks, the road base is failing and crack sealing is seldom cost effective.

In addition to saving road maintenance dollars, crack sealing saves money for motorists. It provides a smoother, safer road and reduces vehicle repairs.

The UNH T² Center has additional information on crack sealing. Also, sealant equipment and material suppliers can provide information about treatments for particular pavement and climate conditions.

Sources

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Return to UNH T2 Center, 33 College Road, Durham NH 03824 603-862-2826 Fax 603-862-2364