Hot Mix Asphalt Types
Widely used for its convenience, hot mix asphalt, is the most common used flexible pavement in the US. It is also known as blacktop or bitumen, and sometimes just hot mix. Hot mix pavements are classified mainly as dense-graded mixes, stone matrix mixes and open-graded hot mix asphalt.
There are also other types of asphalt but are limited to maintenance and rehabilitation works.
Hot Mix Asphalt: Dense-Graded Mixes
This hot asphalt mix is the most common mix used. Its great impermeable characteristics allow water to run away from surface area. The name comes from the aggregate size used while mixing the raw materials to produce the asphaltic composition. It can also be subdivide as fine-graded or coarse-graded, depending on the majority of the aggregates in the final product.
This type of asphalt is ideally for all traffic conditions, and has great performance under structural conditions, friction, and for surfacing and repairing needs.
Hot Mix Asphalt: Stone Matrix Asphalt
This mix, created in Europe, has the goal to create contact between the stones that are part of the bituminous mix. It was developed to maximize rutting resistance and to have great durability. Due to the process of production, this asphalt mix is more expensive than regular dense-graded mixes. Its design is based upon higher asphalt content, modified asphalt binder and fibers. Stone matrix asphalt has been used in the US since 1988, and can be used depending on the conditions that will be exerted upon it.
Due to its high costs, it is recommended to be used on high volume interstate highways to get benefits from its durability and endurance. It will also increase driver’s safety due to the impressive friction capabilities with tires; it will also reduce tire noise and will reduce reflective cracking.
Mineral fillers and additives are used to minimize asphalt binder drain-down during construction, increase the amount of asphalt binder used in the mix and to improve mix durability.
Hot Mix Asphalt: Open-Graded Mixes
The difference from the first two with the open-graded mixes is the permeability characteristic. This hot mix asphalt is designed only with crushed stone and a small amount of sands in the mix. The most common types are:
- Open-graded friction course- Air voids minimum requirement is 15%, and no maximum air void percentage is specified. This mix is only used for surface courses. It has a smoother surface finish than the dense-graded. It’s low cost of placement counteracts the high cost of producing it. Caution: Clogging or sealing the pores will dramatically reduce and will degrade asphalt performance and stability.
- Asphalt treated permeable bases - It is used only under dense-graded, stone mix or portland cement concrete for drainage. It is used for drainage purposes below dense-graded, stone mix, or portland cement concrete.