RALEIGH During this past summer, you may have noticed crews out paving local roads near you. Much of that work is called preservation, which is intended to keeps roads in good condition to avoid costly repairs later.
Once they're finished, that familiar "ting" of tiny rocks tapping your car's undercarriage is a sign of a treatment type called chip seal. It gets its name from the crushed, or chipped, pieces of rocks that are sealed on the road surface with a thin layer of asphalt. Until these chips are compacted by traffic or swept off completely, you may notice that "ting" while driving.
"This is not the old tar and gravel' process people are used to," said Emily McGraw, state maintenance operations engineer. "NCDOT has worked with North Carolina State University for more than 10 years to improve and refine this type of paving technique. It's not only preserving our roads, but it's cost effective for tax payers."
Why does NCDOT use the chip seal technique?
With 80,000 miles of road throughout North Carolina, the equivalent of driving from Wilmington to Barstow, California 31 times, North Carolina Department of Transportation has to spend limited funds throughout many projects. The chip seal technique allows crews to make minor improvements to good roads regularly, delaying or even preventing major road repairs that are much more costly, time-consuming and disruptive to motorists. It repairs cracked or weathered pavement, extending the life of the roads, reducing further maintenance needs and increasing motorist comfort and mobility. Additionally, chip seal is only about 25 percent of the cost of traditional asphalt.
Other benefits of chip seal include:
- Keeps water from seeping into the pavement
- Fills and seals cracks and crumpling surfaces of old pavement
- Provides drivers an anti-glare surface during wet weather and a more reflective surface for night driving
- Provides a highly skid-resistant surface, particularly on wet pavements
- Seals the pavement surface, minimizing the effects of aging
What is the chip seal process?
- First, liquid asphalt is mixed with about 30 percent water and an emulsifier. This mixture is then applied to the road using a special spray truck. As soon as the liquid asphalt meets the road surface, the water starts to evaporate.
- Immediately after spraying this asphalt, a layer of crushed rock (or chips) is applied by a spreader.
- Next, the gravel is compacted and embedded into the asphalt by rubber-tired rollers. However, even with the high pressure rolling, not all of the gravel will embed in the asphalt. This is why you have the familiar "ting" tapping your car's undercarriage.
- The new chip-seal surface can require up to two days to cure properly. Summer's hot, dry weather helps speed up this process in which all of the remaining water in the emulsion evaporates and the asphalt hardens. Traffic can pass over this surface at reduced speeds during the curing process.
- After curing, the loose chips are swept off the surface. This may take several sweepings.
NCDOT uses several types of pavement treatment and determines which one is best for a particular section of road by considering several factors, including the amount of traffic that uses that road and the condition of the existing pavement. Chip seal is just one of the many ways NCDOT preserves pavement to keep our roads safe and smooth.