From Tech Transfer Newsletter, Fall 2005 » printer-friendly

Six Steps To A Better Chip Seal

Chip sealing is a common pavement preservation tactic that prevents water from seeping into an asphalt pavement's base course and subgrade, while improving skid resistance and rehabilitating weathered asphalt surfaces.

If a chip seal ceases to perform these functions, it has failed. Chip seal failures usually occur in two forms: stripping (loss of cover stone) and bleeding (excess asphalt on the road surface). Many in the industry believe chip seals fail because emulsion and aggregate are not well suited to each other. Certain emulsions do work better with certain aggregates, but seldom - if ever - is the degree of compatibility between any emulsion and aggregate so poor that the asphalt will not coat the rocks. Most failures result from issues related to one of the following six aspects of chip seal construction, listed here with easy solutions:

Aggregate and emulsion spread rates.
Spread rates must be tailored to each project.

Construction techniques.
Properly adjusted and maintained equipment, proper timing, and good teamwork ensure quality chip seals.

Weather.
Hot, dry weather is best for proper emulsion setting and curing.

Surface preparation.
Repair and clean the road surface: fill potholes, level ruts, seal large cracks, repair broken edges, and scarify and recompact or stabilize an aggregate base, if necessary. If you chip seal over any of these problems, expect these problems to reappear in short time.

Traffic control.
Keep traffic under 25 mph until after the emulsion sets, the rolling has been done, and the first brooming is completed.

Materials.
Aggregate should be clean and dry, otherwise the emulsion won't adhere.

This information was drawn from the California Chip Seal Association's "Six Steps to a Better Chip Seal."

Download the 35-page document [PDF, right-click to download]