Asphalt Road Surfacing Materials Information

Asphalt roadAsphalt road surfacing materials include composite materials used to create a smooth surface for roads and airport runways. All asphalt road materials use asphalt—a naturally-occurring viscous liquid or semi-solid form of petroleum also known as bitumen—as a binder. For example, asphalt concrete consists of mineral aggregate mixed with asphalt, which is then deposited onto the ground and compacted to create a smooth road surface. (Asphalt concrete is often simply referred to as "asphalt" or, in North America, "blacktop.") Chip seal, another type of road material that is used for low-traffic areas, is created by depositing a thin layer of stone aggregate onto an asphalt layer, which itself had been deposited on existing pavement.

Types

There are multiple types of asphalt pavement that are used based on the application. The types of asphalt pavement include:

  • mix type
  • perpetual
  • porous
  • quiet

Mix type asphalt is a combination of various aggregates and emulsions that are mixed together to create the road surface. The mixes include hot, warm, and cold, which can either be mixed on site or mixed at a plant and then transported to the site.

Perpetual pavement uses multiple layers of durable asphalt beginning with a strong flexible layer, strong intermediate layer, and a top layer that consists of an asphalt mix. The bottom flexible layer helps prevent cracks in the surface by resisting strain caused by traffic.

Perpetual pavement provides a durable, safe, smooth, and long-lasting roadway without expensive, time-consuming, traffic-disrupting reconstruction or major repair. More information about perpetual pavement can be found on the Asphalt Pavement Alliance's website. When scheduled surface restoration is performed, perpetual pavement can be maintained easily and cost-effectively without removing the road structure for reconstruction, saving time and money while keeping motorists happy.

Porous asphalt provides storm-water management for paved areas by allowing the water to pass through the surface to the soil below. This form of asphalt allows greater storm water management by greatly reducing water run-off. 

Asphalt road surfaces are inherently a large source of noise pollution, specifically on roads with higher traffic speeds. Thus, a need to reduce noise pollution of roadways has been a desire for some time. Continued research for quiet asphalt has shown that a reduction of 3 to 5 dB (A) or more is possible when using stone-matrix asphalt or open-graded friction course mix. 

Specifications

There are four main construction methods that asphalt materials use when constructing road surfaces. They include hot mix, cold constructed, full-depth reclamation, and tack and prime coats.

Hot mix asphalt consists of 95% aggregate and 5% asphalt cement and is used for over 90% of the roads in the United States. A plant heats the aggregate, mixes in the asphalt cement, and is then transported to the location of the paving site. 

Cold constructed asphalt pavement is an asphalt binder mixed with the aggregate that is mixed in a pug mill or at a plant at warm temperatures for use with low to medium volume roads. The benefits include road flexibility to prevent cracking, durability to resist flushing and tracking, and the ability to stockpile until material is needed.

Full-depth reclamation is used for creating a strong, flexible base on site that will resist damage and cracking. It is composed of reclaimed material, new material, and emulsion. The benefits include strong foundation, improved smoothness, and recycled material.

Tack and prime coatings are used to prep and strengthen the bonds between the layers of pavement.

Applications

There are six materials for preserving an original asphalt road surface to aid in the longevity and condition of the surface. The six are chip seal, fog seal, microsurfacing, spray patch, dust control, and crack filling.

Chip seal is a layer of aggregate that is covered with a spray asphalt binder and is designed to protect and prolong pavement. It seals the pavement from moisture and small cracks as well as restores friction to the road surface.

Fog seal is an asphalt emulsion that is lightly applied to a road surface to harden the surface, enrich the asphalt binder, and prolong the pavement life.

Microsurfacing is a surface treatment that uses polymer modified asphalt emulsion consisting of fine aggregates, performance enhancing additives, and water. Also known as slurry seal, this treatment covers cracks, improves skid performance, and reduces water intrusion and oxidation deterioration.

Spray patching is an emulsion used for patching potholes. It helps reduce the continued deterioration of the existing pavement while helping the new material in the repair area.

Dust control is a diluted asphalt emulsion sprayed onto a road surface to control dust for unpaved road surfaces. Benefits of dust control include grading maintenance cost reduction, decreased aggregate loss, and reduction in dust in building and environment.

Crack filling uses an asphalt binder that fills the crack and is designed to adhere to the sides of cracks in the surface and will expand and contract in varying temperature environments. Benefits include reduced water and debris penetration, reduction in pavement deterioration, and reduced crack growth.

Resources

National Asphalt Pavement Association—Types of Asphalt Pavement

Asphalt Facts—Asphalt Facts

Asphalt Materials, Inc.—Process

American Asphalt Materials—Asphalt Mixes

Related Information

CR4 Community—Concrete to Fill Holes in Asphalt

Engineering360—Asphalt Testing Equipment Information

Engineering360—Paving Machines Information

Engineering360—Soil and Asphalt Compactors Information