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Why Seal Asphalt?
In spite of its excellent
adhesive and waterproofing properties, asphalt has some serious drawbacks that
relate to its
chemical make-up. Asphalt is a very complex mixture of thousands of chemicals
which are predominately open chain in
structure (aliphatic) with a considerable degree of un-saturation within there
molecule structure. The open chain provides
easy access to weather, salts and chemicals to attack and disintegrate the
asphaltic molecules. As the asphaltic
molecules disintegrate, the asphalt in the pavement loses much of its original
properties, such as binding and waterproofing.
The First visual sign of this phenomenon is the progressive change in color of
asphalt pavement from rich black to brown
to gray. The next step is the development of minor cracks which widen and
deepen with time. If the cracks are not repaired
at this stage water seeps into the base courses and damages the pavements load
bearing capacity. It is evidenced by
rutting, shifting, and serious alligatoring. The pavement must then be
overlaid or completely removed and reinstalled,
depending on the condition.
Furthermore asphalt being a by product of the petroleum distillation process, is easily dissolved by other products that are
derived from petroleum such as oils, fats, grease, mineral spirits etc. So when automobile oil and gasoline leak onto
asphalt pavement, they will work to easily dissolve the similar
chemicals in the asphalt. These problems are associated
primarily with off street pavement such as parking lots, minor
streets, airport aprons or runways, service stations, and
home driveways which carry low levels of traffic.
Sealing Asphalt
Currently there are two
primary types of sealcoating materials on the market. Those made from coal tar
and those made
from asphalt. Refined coal tar - a by-product of the coking process - is a
very complex mixture of thousands of chemicals
and quite different in its molecular structure than asphalt. The coal tar
molecules have a predominantly closed ring structure
with a minor degree of un-saturation. Being stable in molecular structure,
these chemicals do not allow the destructive
elements of weather, gas, oil, fat and chemicals to affect the property of the
coal tar. Coal tar based sealcoating acts as a
barrier coat to protect the asphalt surface. Southern Ohio Sealcoating uses
only 100% coal tar based sealer.
In recent years asphalt emulsion based sealers have been introduced with varying
amounts of success. The asphalt
emulsion based sealers deliver many of the same qualities as the refined coal
tar based coatings with the exception of
resistance to color fading, due to ultraviolet degradation, salts and
petrochemicals. Being a petroleum derivative, asphalt
emulsion has the natural affinity for petrochemicals, so it is easily
dissolved by them. In recent years sealcoat
manufacturers have been quite successful refining the performance of asphalt
emulsion through the use of specialty
chemicals and pigments. But asphalt emulsion's resistance to petrochemicals
and solvents - while improved - has yet
to overcome. In spite of this deficiency sealcoaters have recognized some definite
advantages of asphalt emulsion
over refined coal tar sealers. It is more user friendly " practically odorless
and does not irritate the skin", however
The Federal Aviation Administration specifications accept only coal tar based
sealcoatings for airport projects, because
the refined coal tar based products offer the greatest resistance to jet
fuel.
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