Each year Columbia Public Works uses a variety of proven approaches to pave, patch or preserve our City streets.
“Our goal is to extend the life of our roadways in the most cost effective and least disruptive manner possible,” Engineering Manager Richard Stone said. “The approach for each street is based on our resources such as budget and manpower and the condition of each road.”
Roadways are rated on a 10-point scale with a rating of 10 indicating “new/excellent” condition. Roadways with a rating of 1 have “totally failed” and require reconstruction (very expensive). Typically, an asphalt roadway with a rating of 6-7, or “good shape,” is the best candidate for a chip seal. The objective is to preserve the underlying roadway structure at a relatively low cost.
How cost-effective is it?
The chip seal process typically costs $1-$2 per square yard. By comparison, milling off the road surface and putting down a new overlay of asphalt costs between $7 and $10 per square yard. This means that a typical 1,000-foot residential street would cost $5,000 to chip seal but more than $25,000 to mill and overlay. (Total reconstruction, on the other hand, could range between $200,000 to $350,000 for that same street.)
What is chip seal?
Chip sealing uses the same ingredients as asphalt concrete paving, but rather than milling the road and laying down new pavement, a thin film of heated asphalt liquid is sprayed on the road surface, followed by the placement of small “chips” or stones. Rollers then go over the chips to compact and adhere them to the existing asphalt. The excess stone is swept from the surface after a period of time to allow the chips to dry and settle.
What does it do?
The chip seal process is a crucial element of the City’s pavement preservation process. It prevents deterioration by sealing up cracks and providing a pliable long-term wearing surface that can typically last 5-7 years (longer if followed up by a fog seal or other treatment).
With the passage of time and vehicles over the roadway, chip seal tends to self heal the cracks in the street and protect the pavement from water intrusion (which is the enemy). Excess chips are swept up by Street Sweepers as soon as the chip seal dries but may need to be addressed several more times after that.
“We have recently been using more fog seal treatments to help better lock those chips in place,” Stone said. “People have been responding positively to that approach.”
During chip seal operations, and several days afterwards, drivers are advised to drive more cautiously. Please avoid speeding, turning too sharply and spinning tires.
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