Best treatment methods
By Jeff Winke
Pavement cracks. For anyone involved in asphalt paving, pavement cracks are serious stuff. They rarely foretell romance, hope, or initiative. Pop artist Annie Lennox captures it in her song “Pavement Cracks:”
The city streets are wet again with rain
But I’m walkin’ just the same
Skies turn to the usual grey
When you turn to face the day
And love don’t show up in the pavement cracks
For contractors, the questions they grapple with are how do cracks initially form, what are the ramifications if not addressed quickly, and what are the best ways to seal cracks?
“In most cases, asphalt is installed over the top of a base layer that is constructed of rock, sand, and clay fines,” stated Ben Thielbar director of sales, Cimline, Inc., Plymouth, Minnesota. “The base layer is formulated in such a way that those ingredients when compacted work together to lock in as a structure that can support the weight of an asphalt layer, still be somewhat flexible, allow weight distribution from traffic above it, and provide a median for water to flow away from the asphalt mat structure.”
When asphalt pavements is first placed, it is most resistant to cracking because it is at its most flexible.
“Over time the asphalt concrete mix becomes less flexible and cracks can form,” said Chris M. Vacca, senior marketing manager, Crafco, Inc., Chandler, Arizona. “Cracks can form due to:
- Thermal Movement – Expansion and contraction due to temperature changes. Is a single-day temperature can change as much as 100 degrees in some areas.
- Traffic Loads – Cars and trucks pound the pavement—any weakness in the structure of the pavement fracture or crack.
- Age and Oxidation – As pavement ages, it loses flexibility and cohesion within the pavement structure, making it more susceptible to the first two causes of cracking.
Vacca continued: “Cracks in the pavement if left untreated can lead to premature wear of that pavement’s life. The longer one waits the damage can affect the pavement’s integrity if water is permitted to continually trickle in. When properly sealed, only 1% of cracks form into potholes within three years. Without proper sealing, 75% of cracks form into potholes within the same time frame.”
Cracks in an asphalt pavement surface begin to form when traffic weight and temperature variations cause the asphalt surface to move and flex above the base layer eventually pulling the surface apart forming cracks that ultimately lead to water ingression into the base layer.
“Once water seeps through the asphalt mat it not only deteriorates the asphalt but the sub-structure base below it,” stated Thielbar. “This will cause cracks to grow, cracks to spread, and potholes to be made as the base and asphalt combination are no longer fit to handle the stress load of traffic and climate. Water ingression commonly occurs in low spots, rumble strips, and where asphalt mats meet each other on a road or paving project.
“Initial failures can come from the suns UV rays deteriorating the black asphalt component in a pavement resulting in a more brittle less flexible asphalt. This allows less movement due in changing weather conditions and traffic weight along with movement of the asphalt creates cracks in this condition.”
In hot arid climates, heat can cause asphalt to expand and contract daily. This can cause it to heave then separate as it cools.
What are the ramifications if pavement cracks are not addressed quickly?
In short, more cracks, more potholes, more deterioration and a greater cost of restoration or replacement. Not addressing the problem early can cost the contractor more when finally addressed.
When water is allowed to permeate the asphalt surface, that water will erode the base layer, moving the sand and clay fines away that are holding the base layer together in a compacted state. When the smaller particles are removed, the larger rocks in the base fall into that void and cause a “pocket” to open up between the base layer and the asphalt sheet above it. The asphalt mat then begins to break apart without its base support under the stress of traffic weight and the asphalt begins forming a pothole as it falls into the void space below.
In some arid and consistently warm climates cracks can go longer without seeing much base erosion. However, over time, due to weathering and the sun’s UV rays, all asphalt will begin to show distress. Eventually increased separation will be seen as cracking allows greater movement of the asphalt. With this additional movement more cracks spread from the initial crack and soon with the assistance of traffic and weight load the asphalt will continue to deteriorate the pavement.
Thielbar stated and described the three primary categories of seal crack sealant methods being sold on the market today: Cold Pour, Direct Fire and Oil Jacketed sealants.
Oil Jacketed hot-applied crack sealants are considered by many to be the most cost effective in the long term for any commercial or road application.
Direct Fire and Cold Pour can be a solution for home owners, but do not have the longevity for over-the-road usage or larger parking lot areas.
Crack Sealing (routed, cleaned, sealed) is the best method in this area, but Crack Filling (cleaned with high power air, and sealed) is the most bang for the buck when it comes to lane miles and production.
Cold pour sealants are simple to use, completely safe to apply and can be installed by a homeowner with household tools. But do not expect these sealants to last more than a year or two and they should not be used in high traffic or high load conditions.
Direct fire sealants and melters are commonly available at asphalt sealant manufacturers and some hardware stores. Direct fire melters are more difficult to operate as they require constant attention to the heating and temperature levels that the sealant is being subjected to. These units are hand operated and generally are wheeled melter applicators that are rolled around a parking lot. Overheating of the crack sealant can be an issue with direct fire units so the operator must understand temperature specifications of the sealant and safe application procedures.
Oil jacketed melters are considerably safer to operate and much simpler to use. Many of the units being sold today are completely automated, with simplified user controls that reduce the startup and operation to a single switch and observable temperature indicators and controllers. These units are generally available in a variety of sizes from 60-gallon material tanks up to 400 plus gallon tanks with conveyer belt automated material loading. The sealant is delivered to the ground using a sealant pump, an ergonomically designed application wand and electrically heated hose that is both safer to handle and comfortable for an operator to use on a day-long shift. Oil jacketed melters will give the most production of any method and also maintain the crack sealant so that it is applied at the proper temperature, agitated, not over heated in the kettle, and provides the longest life span when applied.
Mastic Applicators that are oil jacketed are also a great resource for wide cracks, distressed areas with cracks close together, and shallow potholes.
Understanding the dynamics of the stresses that asphalt pavement experience over its life will help when addressing the cracks that emerge and how best to treat them.