Hall County considering fly ash for road projects

(The Independent 6-2-2012) Fly ash -- a very light, talcum-powder-like tan dust left over from burning coal in a power plant -- may be the next best thing for Hall County roads. Hall County Public Works Director Casey Sherlock and county engineer Steve Riehle are looking at ways to upgrade gravel and failing asphalt county roads with fly ash.  "When you mix it with sand, road dirt materials, ground up asphalt -- fly ash becomes a binder and you wet it down and it turns into cement," Sherlock said. "It basically turns a road into a concrete road if you work it in."
 
Hall County has long been plagued with the costs of maintaining its 813 miles of county roads -- 629 of which are gravel and 184 that are asphalt.
 
The $300,000 a mile cost to construct a new asphalt road is so high the county has abandoned the idea of any new paving. Even the $100,000 a mile cost to put down a new two-inch overlay on failing asphalt roads is so expensive that the county has reverted to grinding up some asphalt and returning it to gravel. Many of the ground-up roads are at the former Cornhusker Army Ammunition Plant, the old ordnance production plant west of Grand Island.
 
"It is really cheap to maintain gravel roads," Riehle said.
 
But traffic counts on some roads are such that gravel simply doesn't hold up well. It becomes rutted, grooved and swaled from the constant flow of vehicles.
 
East Stolley Park Road is like that. So is Webb Road north of Abbott Road on the way to 1-R School.
 
That's why Hall County is prepping for a June 18 trial project to use fly ash to "pave" a 500-foot stretch of Webb Road between Abbott Road and a county bridge.
 
With the use of fly ash, Riehle said, it's likely the county will be able to take "an asphalt road beyond repair and turn it into a really good base to pave or a really good gravel road."
 
It could literally give new life to old roads at a much more affordable cost.
 
"We could potentially make a concrete road out of some gravel roads that are high-traffic roads that should be paved," Sherlock said. "Some of these roads at the ordnance plant that we are grinding up, we could mix some in with those and stabilize them into a hard-surface road again."
 
Fly ash is readily available in Grand Island.
 
Grand Island's Platte Generating Station produces about 16,000 to 18,000 tons of fly ash a year, said Utilities Director Tim Luchsinger.
 
Fly ash has long been a commodity for the city, which sells it to vendors, but the value is rising to the point the city is getting more money than ever before for the coal-burning product.
 
Riehle said fly ash makes a great binder in Portland cement concrete in order to reduce the amount of Portland cement needed in the mix.
 
The Nebraska Department of Roads uses fly ash in some of its projects, including a joint project with the county on Alda Road south of Interstate 80, Riehle said. The fly ash is mixed in with the subgrade soil to stabilize the ground and make a nice firm foundation for new paving on top.
 
Hall County could save money by using fly ash to stabilize and strengthen the subgrade for new construction. A fly ash subgrade could allow the county to reduce its pavement thickness by 1 to 1.5 inches, which translates into a savings of $35,000 to $55,000 a mile, Riehle said.
 
Mixing it with ground asphalt at the Cornhusker Plant may make a solid enough surface to simply seal with armor coat or chip sealing for a permanent hard-surfaced road, he said.
 
But most promising, and what the county will be testing in two weeks, is upgrading ragged gravel roads by tilling through the top seven to eight inches, mixing in fly ash and adding water to harden the fresh surface.
 
Riehle estimated the fly ash alone will cost about $23,000 a mile. That's calculated at a $20 per ton purchase price.
 
"We don't want to go put fly ash in it and have it bust up in five years," Sherlock said. "That would be a waste of money, so that's why we need the demo to see how it holds up under high traffic."
 
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