Despite the apparent benefits and widespread use of emulsion-based chip seals with emulsified asphalt binders and natural mineral aggregate chips, as a preservation treatment, some state departments of transportation (DOTs) have been reluctant to adopt the technology because of limited familiarity with chip seal practices.
North Carolina DOT therefore sponsored a series of research projects at North Carolina State University (NCSU) to evaluate and improve the various aspects of chip seal design and construction.
The program of research on surface treatments has produced obvious benefits. Better performing, longer-life chip seal is now in use. Although several years of operation are needed to quantify these benefits, positive improvements have occurred.
The use of lightweight aggregate has reduced tort claims for windshield damage. In one division, the annual tort claims associated with the preservation program have dropped from approximately 20 per season to none since the implementation of lightweight aggregate.
Adopting polymerized emulsions has improved aggregate retention; chip loss was reduced by 30 percent. The surface treatments are now being used on higher volume roadways. Although polymer-modified chip seals cost about 20 percent more than unmodified chip seals, other preservation treatment options for higher-volume roads—such as thin (1.25-inch) hot-mix asphalt overlays—cost nearly three times as much as the unmodified chip seals.
Although each road treatment is a relatively low-cost activity, North Carolina DOT’s annual budget for chip seal was $63.2 million in 2010 and approximately $75 million in 2011.
The cost savings accrued from the increased service life, improved performance, and increased public satisfaction, reduced tort liability, and increased safety will allow for the preservation of more roadways with the same budget, compounding the benefits year after year.