Asphalt Deterioration & Raveling
Posted by Jesse Willoughby on Wed, Feb 11, 2009 @ 12:32 PM
Deterioration is any break-down in the pavement surface allowing more serious problems, such as raveling, to occur. The chemical structure of asphalt inherently allows many destructive elements - such as weather elements (rain, snow); salts; oils; and other materials - to break it down. As these destructive elements break down the pavement surface, much of the original benefits are lost (i.e., weather proofing) and the color visually changes from rich, black to brownish gray. This deterioration, if left unattended, inevitably leads to more serious problems such as raveling and/or cracking.
Raveling is loss of pavement material from the surface downward and is caused by the loss of asphalt binder (deterioration), ultraviolet exposure, traffic frequency, weather conditions, asphalt mix design, and compaction of the asphalt during construction. As the asphalt binder in the pavement wears away, the appearance starts to turn grayish from the fresh, black look of new asphalt. Also, as the binder wears away, aggregate particles begin to
break away. This begins with fine aggregate particles breaking away and, consequently, exposing the coarse aggregate.
As the raveling begins to become more prevalent, the dislodged particles lead to a severely rough surface and pitted areas forming where aggregate particles have been completely removed.
Deterioration - Oil spots
These areas of serious oil spots have led to deterioration and corrosion of the pavement surface and will eventually lead to pavement failure in these areas.
Raveling
The fine aggregate particles have worn away and coarse
aggregate particles are becoming exposed.
Remedy
To avoid the ill effects of deterioration, seal coat provides a protective ayer for the pavement that is not vulnerable to the destructive elements such as weather conditions and ultraviolet rays.
Furthermore, the sealcoat provides a uniform surface for areas where he asphalt binder has worn away completely.
The procedure includes:
1. The area is power cleaned and oil stains are chemically treated.
2. Coats of coal tar emulsion (exceeding Government
specification RP-355E) with a latex additive and four to six pounds of silica sand for improved durability. Application
coverage rate is 0.3 gallons per square yard.