Chemical asphalt is an open-chain carbon compound with a high degree of unsaturation. The unsaturated carbon compound can bind easily with salts and other elements present in the atmosphere. Also, asphalt, being a petroleum derivative, has great affinity toward other petroleum products, such as fuel, oil and gasoline. These products, leaked on a pavement or car park, immediately make their way toward the asphalt molecules and dissolve them. As a result of these two occurrences, some of the asphalt molecules on the pavement are now not asphalt at all but new entities. And the protection that asphalt offers to the pavement is compromised. Sealcoating provides a protective coating on the asphalt, enabling it to resist the elements and petroleum products that cause damage.
There are two main types of sealcoats available on the market -- coal tar-based and asphalt-based. Coal tar-based sealcoats have been used for a long time. There are complex aromatic carbon compounds with a closed ring structure and a slight degree of unsaturartion. Their closed structure and low unsaturation makes them more resistant to elements and enable them to offer good protection to asphalt. Coal tar sealcoatings are part of the Federal Aviation Administration's specifications for airport projects because they have high resistance to jet fuel. Asphalt-based sealcoatings processed to improve asphalt's petroleum-resistant properties have been introduced more recently. They are getting popular because they are odorless and do not irritate or burn the skin.
On busy streets with continuous traffic movement, there is a rolling action that continuously brings lower layers rich in asphalt to the surface and gently pushes back the oxidized surface layers inside. Busy roads, therefore, do not need sealcoating protection. Sealcoating for asphalt, however, is required for off-street pavements, including car parks, minor streets and home driveways, where the traffic movement is light. Because of low traffic, these pavements do not have the advantage of rolling action, so the top surface is continuously exposed to elements, making the asphalt more vulnerable.
Asphalt pavements without sealcoating are not very safe. The loss of flexibility of asphalt adversely affects the load-carrying capacity. Unsealed asphalt car parks develop cracks and there is deposition of sand, stone and other debris from the aggregate layers. Continuous exposure to sunlight also causes the asphalt to change from black to brown and then gray due to oxidation. This spoils the overall look. Sealcoating ensures that asphalt pavements are in good condition for a longer duration. This obviates the need for constant and expensive repair and maintenance work.