Types and Applications of Asphalt Pavement Surfaces
Asphalt pavement surfaces come in various types, each with unique characteristics and suitable applications. Selecting the right type of asphalt pavement surface can significantly enhance road performance and longevity.
1. Asphalt Concrete: Comprising asphalt, coarse aggregate, fine aggregate, and fillers, asphalt concrete offers easy construction, low maintenance, low permeability, good water stability, and high strength. However, it requires strong bases and stability at high and low temperatures, with initial construction costs being high. It is suitable for highways and major urban roads with heavy traffic, having a lifespan of about 20 years.
2. Hot Mix Asphalt (HMA): This type is made by mixing asphalt with various sizes of crushed stone aggregate and fine fillers like stone dust or cement. HMA provides good high-temperature stability, rough texture beneficial for high-speed travel, and low cost due to less asphalt usage. Its major drawback is the large voids in the aggregate, leading to water infiltration and faster aging. It is ideal for tertiary and quaternary roads and as a base or leveling layer under asphalt concrete surfaces.
3. Emulsified Asphalt Aggregate Mix: Utilizing emulsified asphalt as a binder, mixed with various sizes of aggregate, this mixture is applied to the road surface and compacted to form a stable structure. It offers good bonding, water resistance, elasticity, and can be constructed over a wide temperature range with low equipment requirements. Proper control of emulsified asphalt spraying and aggregate distribution is necessary. It is suitable for tertiary and quaternary roads, maintenance overlays for secondary roads, and as a leveling and flexible base layer.
4. Penetration Macadam: At ambient temperatures, asphalt is uniformly spread over a prepared base layer, followed by successive layers of crushed stone and asphalt, compacted to form a dense structure. This method provides high stability, good load-bearing capacity, and low maintenance costs. However, it has more voids and lower durability compared to asphalt concrete. It is used for tertiary and quaternary roads and as a transition or bonding layer between asphalt concrete layers.
5. Surface Dressing: In this method, asphalt (bitumen, coal tar, or emulsified asphalt) is sprayed on the road surface, followed by a layer of fine aggregate such as stone chips or sand. The process is simple, with low construction and maintenance costs, and can quickly improve road conditions. However, it has limited load-bearing capacity and lower durability under heavy traffic or adverse weather, requiring a strong base. It is ideal for low-traffic roads, road renovations, tertiary and lower-grade roads, temporary roads, or short-term surface improvements.
6. Stone Mastic Asphalt (SMA): Known for its high durability, SMA is made using a special mixing and paving process with specific equipment. It offers superior skid resistance, wear resistance, density, durability, fatigue resistance, rutting resistance at high temperatures, and reduced cracking at low temperatures, resulting in a longer lifespan compared to traditional asphalt concrete. However, it demands high-quality materials and construction techniques with higher initial costs. It is suitable for high-load traffic, high-wear conditions on highways, primary roads, and other critical road surfaces.