Sealcoating is one of the most important elements of a pavement management plan. Air, sunlight, and moisture are a major cause of surface deterioration. Progressive weakening, erosion, oxidation, and unravelling due to water and weather damage can reduce pavement thickness by as much as 50%! If not kept in check, costly repairs or resurfacing may be necessary.
A Closer Look at Seal Coating
Asphalt is a very complex mixture of chemicals with very little saturation in their molecular structure.
The structure is considered “open chain” or “asphaltic” which provides easy access to weather, salts, and chemicals which in turn disintegrate the asphalt itself. This will result in loss of its original properties such as binding and waterproofing. Typically, the first visual sign of this loss is the “graying” of the asphalt from its original rich black look.
Asphalt is derived from the petroleum distillation process and when additional byproducts meet, such as oils, fats, grease, mineral spirits, etc. they have a natural affinity to join together. So when automotive oil or gasoline, both petroleum distillates, leak onto the pavement, they work to easily dissolve the similar chemicals in asphalt. These problems are associated primarily with off-street areas, such as, parking lots, minor roads, airport aprons or runways, service stations and home driveways.
These all have low levels of traffic flow. Highways and major streets have the advantage of continuous rolling raffic which creates a kneaded oxidation effect back into the pavement, therefore, creating a longer visual and strength advantage. Eventually all asphalt life is exhausted and the aggregate begin to unravel, evolving into minor cracks which widen and deepen with time. If water seeps into the cracks it allows the load capacity to falter. This then results into rutting, shifting, and serious alligatoring of the pavement.
Offstreet pavements do not have the advantage of the kneading action. The surface layers of off-road pavements are under continuous attack from the weather and other destructive elements, eventually developing minor surface cracks. It is logical to conclude that off-street pavements can be preserved by a protective sealcoating that resists the attack of elements that destroy the asphalt anyway.
Currently, there are 2 types of sealcoating materials – those made from refined coal tar and those made from asphalt. Blackjack Paving recommends a refined coal tar sealcoat. Refined coal tar molecules have a closed ring or aromatic structure with a minor degree of un-saturation. This molecular structure doesn’t allow the elements of weather to affect the property of coal tar.
They act as a tough barrier for asphalt surfaces. The asphalt emulsions do not provide the resistance to color fading, salts, and petrochemicals such as, oils, fats, grease, and solvents such as the refined coal tar.