Better Roads Staff
“We paved a project with the ultra-thin friction course this past year and it seems to be performing very well,” says Blight. “We put it down in the spring, and so far so good. We’ll see how it goes through the winter.”
Blight says New Jersey did not place any HPTO in 2011. “Right now we’re looking at HPTO, the Ultra-thin and the SMA, and we’re evaluating all three of them for performance and cost-effectiveness,” he says.
Blight estimates that in 2011 the DOT placed on the order of 10 thin overlay projects with the 9.5-mm SMA mix. “A lot of them are mill-and-inlay jobs where we place a 1.5-inch surface course,” he says.
HMA Ultra-Thin in Michigan
In Michigan, the DOT uses an HMA ultra-thin surface treatment that is typically placed at 83 pounds per square yard, or approximately 3/4-inch thick, says Kevin Kennedy, a preventive maintenance engineer with the Michigan DOT.
Kennedy says an agency needs to take care in selecting roads for a thin overlay. “The existing pavement should exhibit a good base condition and a uniform cross-section,” he says. “The visible surface distress may include slight raveling, minor surface irregularities and a slightly polished surface. The cross-sections should be free of ruts or distortions.”
Michigan’s HMA ultra-thin surface treatment protects the remaining pavement structure, slows the rate of deterioration, corrects minor surface irregularities, improves skid resistance and improves ride quality, Kennedy says.
Michigan does impose a crushed aggregate requirement for the HMA ultra-thin overlays. For high-volume roads, the minimum crushed content is 95 percent; for medium-volume roads, the requirement is 75 percent; and for low-volume roads, it is 50 percent. The top-size aggregate is 3/8 inch. Similarly, the binder grades vary, depending on traffic volumes. For low-volume roads, Michigan specifies a PG 64-22; for medium volumes, it’s PG 64-28P; and for high-volume roads, the requirement is PG 70-22P.
Thin overlays are succeeding in this country because they work and they’re cost-effective. A road manager just needs to take care in selecting which roads get thin overlays, and choose a well-proven mix design.
The economics of recycling roof shingles into asphalt pavement
Everyone wants to be green until they see red, meaning we all want to recycle until it costs us money,” says Phil Hutchens, chairman of Missouri-based Hutchens Construction. “Recycling with roofing shingles in asphalt saves in two ways – it saves a product that would otherwise go to a landfill and it saves money.”
Since shingle recycling for pavements got started in the late 1990s, asphalt producers have increased the amount of recycled shingles to about a million tons per year, according to estimates by the National Asphalt Pavement Association. That’s the good news. The not-so-good news is that we still send 10 million tons of roofing shingles to landfills every year. A ton of shingles contains approximately 25-percent liquid asphalt. If you do the math, that means we waste 100,000 transport loads of asphalt binder every year.
When the costs of processing and handling shingles are considered, it often turns out that the liquid asphalt cement (AC) in those shingles is a bargain. Recycling a ton of shingles costs Hutchens’ company about $30. That covers handling, asbestos testing, grinding and so forth. It takes about four tons of shingles to make one ton of liquid AC. So if you multiply four tons times $30, you can acquire liquid AC for just $120 per ton. (That is an operating cost only.) Virgin AC can cost $500 a ton. “Plus you get 3 tons of sand from the shingles,” says Hutchens.
“Really our driving force when we started was more of an environmental effort than it was economic.”
– Phil Hutchens, Chairman
“We started running shingles about five years ago, in 2006,” Hutchens says. “We first started thinking about it in about 1996; that was around the time NAPA wrote its first publication on shingle recycling. At that time it was not very feasible, because there was no one available in this area to grind shingles.
MORE FROM In the Magazine
- Rand Paul introduces bill to fund emergency transportation projects475 Views
- Sydney uses water curtains to alert drivers to stop (VIDEO)475 Views
- Tesla Model S earns top ratings from Consumer Reports428 Views
- Big four cellphone companies jointly launch anti-texting campaign261 Views
- Acceptance of connected vehicles depends on cost, LaHood says256 Views