Chip seal is a pavement surface treatment that combines one or more layer(s) of asphalt with one or more layer(s) of fine aggregate. In the United States, chip seals are typically used on rural roads carrying lower traffic volumes, and the process is often referred to as "asphaltic surface treatment". In Australia and New Zealand, chip sealing is referred to as a "sprayed seal" or "tarseal" and is used on a larger percentage of roads, both rural and urban. This type of surface has a variety of other names including "tar and chip", "sprayed seal" or "surface dressing".
Chip sealing is cheaper than resurfacing an asphalt concrete or a Portland cement concrete pavement, but not as long-lasting. In some states of the United States, chip sealing is used in conjunction with new road construction to make the road bed more durable and longer lasting.
Chip seals are constructed by evenly distributing a thin base of hot bitumen or asphalt onto an existing pavement and then embedding finely graded aggregate into it. The aggregate is evenly distributed over the seal spray, then rolled into a smooth pavement surface. A chip-seal-surfaced pavement can optionally be sealed with a top layer, which is referred to as a fog seal or enrichment.
The introduction of polymer-modified bitumen and emulsion binder has increased chip seal's ability to prevent crack reflection and improve stone retention by improving the properties of the bitumen binder. Newer techniques use asphalt emulsion (a mixture of liquid asphalt, surfactant, and water) instead of asphalt. This has been shown to help reduce aggregate loss and reduce cost of installation, but can increase stripping. It reduces emissions of volatile organic compounds (VOCs) due to the lower solvent content.
It can keep good pavement in good condition by sealing out water, but provides no structural strength and will repair only minor cracks. While the small stones used as surface yield a relatively even surface without the edges of patches, it also results in a very rough surface that leads to louder rolling noise from automobile wheels.
Although chip seal is an effective low-cost way to repair road, it has some drawbacks. Loose crushed stone is often left on the surface, owing to underapplication of bitumen or overapplication of stone. If not removed, this can cause safety and environmental problems such as cracked windshields, loss-of-control crashes (especially for motorcyclists, bicyclists and small trucks), and deposition of foreign material into drainage courses. Therefore, it is very important to sweep the road after the emulsion sets. Overapplication of emulsion can lead to bleeding, a condition where the excess asphalt rises to the surface, creating a very smooth surface that is very slippery when wet.
Asphalt (or bitumen as it is known outside the United States and Canada), is the binder used in chip-seal applications.
Noise and vibration effects
The rough wearing surface of the chipseal generates more roadway noise at any operating speed than does typical asphalt or concrete surfaces. This typically is not a major concern at very low operating speeds, moreover, chipseals are typically used on low volume rural and urban roadways. These sound intensities increase with higher vehicle speeds. There is a considerable range in acoustical intensities produced depending upon the specific tire tread design and its interaction with the roadway surface type.
The rough surface causes noticeable increases in vibration and rolling resistance for bicyclists, and increased tire wear in all types of tires.
Vehicle speed can affect the set up time with chipseal. Shortly after construction (depending on weather conditions) the set speed for chip seal is 10–15 miles per hour (16–24 km/h) for the first 24–48 hours after construction.
- "Sprayed Seal". Local Government & Municipal Knowledge Base. Retrieved January 29, 2010.
- Sprayed Seal, Local Government & Municipal Knowledge Base, accessed January 29, 2010
- Gransberg, Douglas D.; James, David M. B. (2005). Chip Seal Best Practices. National Cooperative Highway. Transportation Research Board. pp. 13–20. ISBN 9780309097444.
- Hogan, C. Michael (September 1973). "Analysis of highway noise". Journal of Water, Air, & Soil Pollution (Springer Verlag, Netherlands) 2 (3): 387–392. ISSN 0049-6979.