Chip seal (BST)

A Chip seal or bituminous surface treatment (BST), also known as a seal coat or chip seal, is a thin protective wearing surface that is applied to a pavement or base course. BSTs can provide all of the following:

:: A waterproof layer to protect the underlying pavement.

:: Increased skid resistance.

:: A filler for existing cracks or raveled surfaces.

:: An anti-glare surface during wet weather and an increased reflective surface for night driving.

Historically, BSTs have been in use since the 1920s, primarily on low volume gravel roads. BSTs are increasingly in use as a preventative maintenance procedure on flexible pavements of good structure.



A BST offers preventive maintenance from the effects of sun and water, both of which may deteriorate the pavement structure. BSTs create a new wearing course, as well as a waterproof covering for the existing pavement. A BST makes it more difficult for water to enter the base material, and preventing freeze thaw damage for those locations with below freezing temperatures.

BSTs also increase the surface friction of the pavement, due to the addition of the cover aggregate. This combats the effects of raveling, which can make the pavement slippery and stopping difficult. A BST gives good, gripping texture to the pavement surface.

BSTs should be applied to a distress-free to moderately distressed pavement surface. A two to four year service life is common, while five year service lives are achievable.



BSTs are created using two main materials: asphalt and a cover aggregate.



Design of BSTs must take into consideration all of the points mentioned in the Asphalt and Aggregate sections of this article. Material must be of good quality and the correct properties.

The design must also take into consideration the amount of binder and cover aggregate to apply. In order to prevent excessive chip loss, about 70 percent of the aggregate (and a minimum of 50 percent) must be embedded in the residual asphalt – the asphalt left after the water or cutback has evaporated. With an asphalt emulsion, the binder must rise near to the top of the aggregate, otherwise the residual asphalt will be insufficient to properly embed the aggregate. The goal is to have the binder at about 70% of the chip height after the binder has cured.

 BS group is ready to provide suitable asphalt emulsion, additive, equipment and give you advice to have best mix design then help you for doing quality tests during the project; at the result , we help you to achieve best performance.