Professional Engineers Of North Carolina

SUM 2014

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7 Summer 2014 the Professional Engineer UNC Charlotte's entry in the U.S. Department of Energy's Solar Decathlon Competition in Irvine, Calif., last fall. UNC Charlotte was one of 20 universities in the event, which requires competi- tors to design and construct a house that only uses solar power. UNC Charlotte's house incorpo- rated structural members built entirely of CFA and additives that engendered geopolymer reactions. Te entry won the People's Choice Award, and it tied for frst place among U.S. institutions in the engineering category. Stanford University was a close second. CFA also can be mixed with soils to decrease plasticity and increase workability. Such needs are common with soils in North Carolina's Piedmont, although CFA is generally underuti- lized in the state; lime or cement are used more often for subgrade stabilization. A more common use of CFA in North Carolina, and the second largest use nationally, is structural flls or embankments. Examples are the structural fll built with CFA at the Asheville Regional Airport and the one proposed for the Charlotte Douglas International Airport. It also can be used as fll material for bridge abutments, retaining walls, roadways and parking lots. Other uses include mining applications, waste stabilization, roofng material and agricultural applications. CFA is an attractive fll material because of its low unit weight, high shear strength and ease of compaction. Less weight means less settlement in a given application. Still, concerns have been raised regarding CFA structural flls in North Carolina. For example, Te Charlotte Observer reported that across the state there are 77 structural flls, all unlined and only one regularly monitored for groundwater impact. Some argue that unlined structural flls pose the same risk as unlined ash ponds. Draft legislation in North Carolina proposes limiting the size of structural flls to 5,000 cubic yards, given that larger flls have resulted in groundwater contamination. And yet numerous projects have been completed in many states without any reported problems. For example, the Federal Highway Administra- tion summarized data from 21 construction projects involving 2 million or more cubic yards of CFA. Structural flls remain a good re-use option, but as with any project, they need to be properly designed and built. Concrete/concrete products/grout 11,779,021 Structural flls/embankments 3,083,441 Blended cement/raw feed for clinker 2,281,211 Waste stabilization/solidifcation 2,187,514 Mining applications 2,086,074 Soil modifcation/stabilization 303,354 Flowable fll 141,081 Road base/sub-base 193,711 Agriculture 26,312 Blasting grit/roofng granules 11,678 Miscellaneous/other 543,035 Amount of CFA used in product categories (2012) Source: American Coal Ash Association Amount of CFA used (short tons) Coal Combustion Product Category Pollutants regulatory requirements and CFA leachate concentrations Comparison between North Carolina structural fll regulatory requirements and typical CFA leachate concentrations. Arsenic 5 0.33 Barium 100 0.64 Cadmium 1 < 0.01 Chromium 5 0.06 Lead 5 0.04 Mercury 0.2 <0.0002 Selenium 1 0.22 Silver 5 < 0.02 33 Parameter Regulatory TCLP Limit (mg/L) Typical CFA TCLP concentration (mg/L)

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