Types of Seal Coating for a New Driveway
- Asphalt consists of stones, gravel and sand that are bound together by asphalt cement, a liquid petroleum product that heats up during the mixing process and gradually hardens as it cools. The stones, gravel and sand feed into a conveyor belt where they are flame-dried, then combined with asphalt cement. The finished product pours out of the conveyor belt and proceeds to be used for paving. The hardened product is what you see in an asphalt driveway.
- Asphalt fades from black to gray due to oxidation.Jupiterimages/Comstock/Getty Images
A freshly paved asphalt driveway looks very black at first. Oxidation causes the black color to fade to gray over time. Oxidation occurs when oxygen combines with certain elements while losing electrons, resulting in corrosion. It manifests as rust on metal and as brittleness and grayness on a once-dark asphalt pavement. Nature's elements -- sun, rain, sleet, wind and snow -- cause oxidation. Also, leakage of other petroleum products into asphalt pavement causes damage by weakening the adhesive that holds it together. Seal coatings, correctly applied, guard against this damage. - Seal coating mixtures exist in two main categories: refined coal tar and asphalt. The coal tar type comes from the coking process, which involves the distillation of coal. Made up of thousands of chemicals, refined coal tar sealers are characterized by stability of molecular structure. This stability makes coal tar sealers very efficient in protecting asphalt against chemicals and weather, as these things cannot alter the properties of refined coal tar. Another name for these sealers is coal tar pitch emulsions, or CTPE. Due to mineral fillers, these sealers flex with pavement movements, making them less likely to crack.
- Asphalt seal coating performs as well as refined coal tar mixtures, except in the area of fading. Asphalt possesses an affinity for petrochemicals because it is itself a petroleum byproduct. Thus, fading happens when the asphalt is dissolved by substances containing petrochemicals. Advantages of asphalt seal coatings have to do with the fact that they are almost odorless and do not burn or irritate the skin.
