Asphalt pavement is a mixture of graded stone aggregate and asphalt. The asphalt is the binder or glue that holds the pavement together. If left unprotected, asphalt is subject to degradation from oxidation and water penetration. Ultraviolet rays from the sun begin to break down the asphalt binder, changing the pavement surface color from black to gray. Gas, oil and other petrochemicals will dissolve the asphalt binder, causing holes and raveling.
As the asphalt binder is further broken down from the sun's rays, water begins to penetrate the surface. Water begins to erode the binder between the individual stones in the pavement. If cracks are present, water will begin to erode the base beneath the asphalt, causing the cracks to enlarge and eventually causing base failure in the form of potholes.
In the northern climates, pavement is subject to further damage from normal freeze thaw cycles. Water, in the form of melted snow and ice, enters the pores and cracks in the pavement. When temperatures fall below 32 degrees the water freezes, expanding and causing additional surface erosion and widening of cracks.
Pavement sealers are emulsion (water-based) coatings designed to extend the life of asphalt from damage caused by UV degradation, gas/oil, road salt, and prevent water from entering into the pavement which causes the freeze/thaw cycle damage. Re-paving is very expensive and with routine maintenance, you could delay the expense of repaving.
This product has been used successfully and safely for over the past 60 years.
The refined tar product that pavement sealer is made from makes up approximately 33% by weight in the production of concentrated pavement sealer (that is, sealer that is sold to the contractor and is not ready for application). The other main ingredients in concentrated pavement sealer are water (50%), clay (17%) and emulsifier. During application, the concentrated pavement sealer is further diluted 10 to 40% depending upon mix design and other additives used. Because of this dilution, refined tar may make up only 20-25% by weight of the finished pavement sealer (that is, sealer that is ready to be applied).
One frequently asked question is asked is have refined tar-based pavement sealants been declared a carcinogen by EPA or OSHA? The answer is no.
FAA Engineering Brief No. 44A-Coal-Tar Sealer/Rejuvenator Specification
Typically refined tar-based pavement sealer has a life of around 3-5 years, depending upon traffic and environmental conditions. The typical asphalt-based sealer has a life of 1-3 years, depending upon traffic and environmental conditions. It has been reported that asphalt-based sealers fail in some harsher environments in one year or less.
Attached are two photographs showing test strips of polymer modified asphalt-based pavement sealer and refined tar-based pavement sealer when first applied in early 2007. The second photo shows the same test strips three years later.
-Test strips of polymer modified asphalt-based pavement sealer and refined tar-based pavement sealer applied winter 2006/Spring 2007.
- Test strips of polymer modified asphalt-based pavement sealer and refined tar-based pavement sealer February 2010. Note that the refined tar-based sealer is still present while the asphalt based product had almost completely worn off.