Asphalt Pavement Crack Repair

Submitted by Ann Johnson, Instructor

Many Minnesota airports include crack sealing as part of their pavement maintenance program. Sealing cracks in asphalt-surfaced taxiways and runways is an effective means of preventing moisture from infiltrating the pavement structure. This moisture can weaken the structural subsurface layers and is a primary cause of pavement deterioration. Crack sealing can greatly reduce the amount of water that enters the structure, thereby prolonging pavement life. Although the benefits of crack sealing may not be immediately apparent, they will be evident several years later when a sealed pavement shows fewer signs of deterioration than a non-sealed pavement.

The following two types of crack treatments are most common:

Crack sealing: a localized treatment method used to prevent water and debris from entering a crack, which might include routing to clean the entire crack and to create a reservoir to hold the sealant. Cracks that are sealed are typically less than 3/4-inch wide.
Crack filling: differs from crack sealing, mainly in the preparation given to the crack prior to treatment and in the type of sealant used. Crack filling is most often reserved for more worn pavements with wider, more random cracking. Cracks are typically wider than 3/4 inch.

Deciding whether to seal or fill

The width and spacing of the targeted crack type is the principal basis for determining whether to seal or fill. Normally, cracks less than 3/4-inch wide, which are spaced uniformly along the pavement and have limited edge deterioration, should be sealed. To effectively seal the cracks, the router or saw width must touch both sides of the crack. Cracks that are greater than 3/4-inch wide and are very numerous are not practical to seal, both because the router or saw will not touch both sides of the crack and because of the number of cracks present.

Sealant or filler selection

Many types of crack treatment materials are available. The principal material families and types are given in Table 1.

Asphalt cement and liquid asphalt possess little flexibility and are very temperature susceptible, so they are limited to use as fillers in non-working cracks. Additives such as mineral fillers and fibers provide minimal elasticity to asphalt and do not significantly affect temperature susceptibility. Mineral-filled and fiberized asphalt are most appropriate for use in crack-filling operations.

Table 1. Recommended Applications for Crack Sealant and Fillers

Material	Mn/DOT Spec.	Recommended Application
Low Modulus Rubberized Asphalt	3720 3725	Crack sealer—The use of a lower-modulus sealant with a 3/4-inch x 3/4-inch reservoir size and less overband has shown to be very effective for rout and seal. Mn/DOT specification 3725, which has slightly higher resiliency properties than 3720, is now the recommended sealant for rout and seal. It is also the recommended sealant for saw and seal. Also note: this sealant is not to be used for longitudinal cracks (those cracks that are parallel to the centerline). For those cracks, use a spec. 3723 or 3719 sealant.
Rubberized Asphalt	3723	Crack filler/crack sealer—This product exhibits good adhesion qualities and has been the common sealer for rout and seal until recently. It can be used for rout and seal in situations where wider reservoir widths are needed, and also for the clean and seal (formerly known as blow and go) method.
Crumb Rubber	3719	Crack filler—Crumb rubber is very effective with the clean and seal method. This process works best in the early spring or late fall when the cracks are open. Crumb rubber will crack in the winter, but will re-heal during warmer weather. A double jacket melter is needed to maintain proper temperature of the product during application.
Asphalt Emulsion	CSS-1 CSS-1 HCRS-2 PHFMS-2	Crack filler—Asphalt emulsion can be used as a crack filler, primarily to coat the crack edges and fill some of the crack. Quantities will shrink with curing. Emulsions are safe and easy to use, but limited to use in warmer seasons.
Asphalt Cement	AC-3	Crack filler—AC-3 is an air-blown asphalt that can be used to coat the edges and fill cracks. This product will get quite brittle in the winter and will track in warmer weather.
Cutback Asphalt	RC MC SC	Crack filler—Cutback asphalt, like emulsions, can be used primarily to coat the edges of cracks. They are not as readily available or safe as emulsions, but can be used in the winter months.

Table 2. Effective Sealing Tips

Technique	Tip
Saw and seal	Place the sealant flush to the pavement surface. The strike-off will create a “slight overband” that provides better adhesion of the sealant to the pavement surface/reservoir edge corner.
Rout and seal	The total width of the overband should be about 2 1/2 inches (3/4-inch rout plus 3/4-inch overband on each side of the reservoir). The overband thickness should be as thin as possible.
Clean and seal(formerly “blow and go”)	Ensure cracks are clean and dry before placing sealant.Perform in late fall or early spring when cracks are open.Take care to not burn pavement with hot air lance.Follow manufacturer’s recommendations for sealant application temperatures.

Bumps in overlays do not have to happen. Perform crack sealing 6 to 12 months prior to an overlay. Proper sealant application procedures and roller operation techniques can eliminate bumps caused by too much sealant or roller slippage.

Additional information about best practices for asphalt pavement management can be found in the Asphalt Pavement Maintenance Handbook and Asphalt Pavement Maintenance Field Guide, available from the AirTAP office or the Center for Transportation Studies.