PUBLIC WORKS News Service -Chemical stabilization additives such as Portland cement and fly ash have long been the preferred materials for full-depth reclamation projects, but a third option-lime kiln dust-is becoming an increasingly attractive and affordable alternative that generally makes the reconstructed road as strong as roads reconstructed with cement additives.
"Consider lime if you're going deep down into the sub-materials," says Larry Cole, technical marketing manager of construction for Carmeuse Lime and Stone Company.
Lime kiln dust is captured during the manufacturing of quick lime. The limestone is heated to 1,300 degrees in kilns and converted into lime; those fumes are vented and processed in a baghouse, which captures the particulate matter. The combination of lime (calcium and magnesium oxide) and alumina and silica oxide (basically a combination of lime and fly ash) is attractive because the pozzolanic reaction of the materials stabilizes the base materials to prepare it for compaction-making lime kiln dust an effective stabilizer for deep reclamation projects that reclaim up to 20 inches of material.
And it's affordable, too.
In a residential full-depth reclamation project in Xenia, Ohio, in 2007 the use of lime kiln dust at $6.35/square yard was half of what it would have cost the contractor to remove 13 inches of the existing asphalt and replace it with a new granular base.
In 2006 The Ohio State University partnered with the state's fastest growing county, Delaware, to test the durability of lime kiln dust in FDR projects.
A 4.1-mile stretch of county road was reconstructed using a variety of materials, including a half-mile section using 5% lime kiln dust and 5% fly ash for an 8-inch stabilization. After two years the test section had held up as well as the section reconstructed with cement.
But Cole encourages road departments to consult with their engineers before deciding to use lime or Portland cement. Lime is an effective stabilizer for silt soils, while Portland cement performs better in clay soils. "It's an engineering decision to use lime kiln dust, but local experience and contractor capabilities also should weigh in on the decision to use it," he says.
American Public Works Association Congress & Exposition
Session: Full-Depth Reclamation with Lime Kiln Dust - Case Studies
Mon., Sept. 14, 2009
Lawrence Cole, Technical Marketing Manager - Construction (larry.cole@carmeusena.com)
Carmeuse Lime and Stone Company
Pittsburgh, Penn.
