Aggregates are a mix of crushed stone, gravel, and sand. Aggregates make up about 95% of hot mix asphalt pavement. Aggregates act as the skeleton, providing skid resistance, stability and workability. Aggregate is primarily responsible for the load-supporting capacity of a pavement. Aggregate types are natural or uncrushed (smooth and round)—or crushed with single or multiple crushed faces. Rough textured, crushed and angular aggregate is needed to carry heavy loads without rutting or deformation. Particle size and surface texture also change the workability, strength characteristics and compactability of an asphalt mix. Maximum particle size and gradation are also key aggregate properties. Aggregate gradation is the distribution of the various particle sizes. The maximum particle size is important because it controls the appropriate lift thickness of the mixture placement. For good paving results, the lift thickness of a dense-graded asphalt mix should be 2½ to 3 times the maximum aggregate size or 3 to 4 times the nominal aggregate size in the mix.
Bitumen is the black or dark viscous material that holds the aggregates together and is composed of polycyclic hydrocarbons (a petroleum byproduct). The asphalt binder, which is the glue that binds the aggregate, provides waterproofing, flexibility and durability.
- Sealcoating–All asphalt types require proper maintenance and proactive repair to retain their appearance and overall condition. Due to the nature of asphalt ingredients, driveways should be sealed every two to three years to prevent oxidation, loss of flexibility, cracking, and crumbling. Recommended is the use of coal tar sealer which protects the bitumen from oxidizing, becoming brittle, and cracking. It is easy to apply with either a spray system or a squeegee and dries quickly in three to four hours.
- With all types of asphalt, a certain amount of cracking is inevitable. The secret is to fill the cracks before they expand and turn into potholes or larger areas of crumbling pavement. There are two types of crack filler that can be used on any asphalt or concrete surface. Cold liquid pour asphalt crack fill is high effective in sealing cracks up to ½” in width. The product is easy to use and keeps cracks on all types of asphalt sealed for several years.
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