Chip seal

Chipseal (also 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, chipseals 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 chipsealing 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".

Chipsealing 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, chipsealing is used in conjunction with new road construction to make the road bed more durable and longer-lasting.

Chipseals 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 chipseal'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. New methods also utilize cross linking styrene acrylic polymers which also provide quality water resistance. Chips precoated with about one percent bitumen have been used successfully to minimize aggregate loss and to give the surface a black look.

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.

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