By: James R. Rosenmerkel, P.E.
Recycling is certainly not a new idea. Most people are used to separating cans from glass; newspapers from cardboard; and the regular pick up by the municipal service provider. They also are used to paying “environmental” fees for disposal of tires and drain oil. There is a much larger material recycling initiative soon to be brought forth by a coalition of major public agencies, producers and industry associations.
The lead agency in the effort is the U.S Environmental Protection Agency (EPA). Others are the Federal Highway Administration (FHWA), the U.S Department of Energy (DOE), the American Coal Ash Association (ACAA) and several other organizations. The thrust of the initiative is to encourage owners, engineers, architects and contractors on very large projects to incorporate the use of byproducts of U.S. industry in those projects. Byproducts are such things as fly ash, bottom ash and slag produced by coal-burning power plants along with foundry sand and slag produced by various manufactured metal products. A description of actual byproduct applications in recent Wisconsin construction projects appears later in this article.
The first goal of the coalition task force was to develop a list of 20 of the largest highway, bridge and building projects in the country. The entire list should be complete soon and will include contact persons for each project. When it is complete, EPA will communicate with the primary contact for each project to describe the initiative and encourage active promotion of reuse of industrial byproducts.
One project on the list is the reconstruction of the Marquette Interchange in Milwaukee. It is a four- to five-year project with an estimated cost of $810 million. Wisconsin DOT Secretary Frank Busalacchi has tentatively committed to working with EPA to incorporate industrial byproducts in the Marquette Interchange. The real focus of the initiative is to get design and construction professionals to consider these materials for use as the primary components in these important, highly visible projects.
Green with promise
The ACAA, a member of the task force, is working with a number of associations representing producers and managers of foundry sands, slag, paper and forestry products and other industrial byproducts. Together, they are developing initiatives to incorporate a broad variety of recycled materials in construction to create more sustainable projects. One such activity is referred to as “green highways.”
The effort may result in a system of acknowledgements and benefits much like the Leadership in Energy and Environmental Design (LEED) program in the building industry. Major architectural projects qualify for LEED credits in many areas of the country. Owners are constantly in search of these credits.
ACAA, along with its partners, will promote and assist in developing new applications for the entire range of coal-ash products (fly ash, bottom ash, boiler slag, etc.), foundry sands, slag and other byproducts for use in construction of transportation systems. This effort will be in concert with the Coal Combustion Products Partnership (C2P2) program and supports broader EPA goals for conservation and resource recovery. As planning proceeds, ACAA will seek and welcome additional partners in the effort.
Last year coal-burning power plants across the nation produced roughly 70 million tons of fly ash and 18 million tons of bottom ash. And while the majority of fly ash, primarily Class C ash, is used as a cement replacement in concrete, hundreds of thousands of tons are utilized in geotechnical applications, primarily stabilizing soft soils in pavement construction and cold in-place recycling (CIR) of hot-mix asphalt (HMA) pavement.
Clearly, fly ash applications can have a major impact on the highway industry since the nation’s roads are constantly in need of reconstruction, renewal and rehabilitation at all levels of traffic service, everything from interstate highways to local roads. The supply of natural materials (crushed stone, gravel, sand) is finite and the reuse of existing materials is becoming much more sensible. Furthermore, sites for disposal of huge volumes of old road materials are rapidly disappearing.
It makes little sense to dispose of materials the public has already paid for. Fly ash used to strengthen failed subgrades and to recycle old hot-mix asphalt (HMA) pavements becomes a very attractive alternative. Bottom ash, used alone or in combination with fly ash and other existing materials, can provide great strength enhancements in highway pavement rehabilitation and reconstruction efforts. The use of crushed, recycled concrete along with foundry sands and some slag products also is effective when combined with certain fly ash mixtures. In addition to pavement components, fly ash is being used in developing manufactured topsoil products, one a combination of fly ash and biosolid waste. It is clear that there are a number of new opportunities to assign bonuses for use of coal-ash products in the green highway program. All that remains is to get the interested parties (engineers, contractors, pavers, power producers, trade associations and consumer groups) together to develop the parameters.
Put to use
Among the innovative applications of a variety of coal ash products in Wisconsin, there are two of note: a highway reconstruction project on STH 32 in Ozaukee County and an airport CIR project in Merrill.
STH 32
The reconstruction of STH 32 in Ozaukee County was let to contract in late 2002. It was for complete reconstruction of a multilane facility along the shore of Lake Michigan. Plans called for removing the existing pavement, crushing and recycling it for reuse as base course, excavating the subgrade by 12 in., replacing the excavation with a granular sub-base course and following with a new dense and open-graded crushed aggregate base course. This is a common approach when field investigation indicates the existing subgrade materials are not capable of performing adequately.
Before the actual construction commenced, the excavation contractor, Edgerton Contractors of Oak Creek, Wis., submitted a cost reduction incentive (CRI) proposal to the Wisconsin DOT District 2 Waukesha office recommending removing the old pavement and base and stabilizing the subgrade with Class C fly ash as an alternative to the plan concept.
The proposal predicted a cost saving of several hundred thousand dollars and a significant reduction in construction time. Based on the details of the proposal, additional sampling and testing of the proposed mixes in the lab, the proposal was accepted.
The recommended soil/fly ash blend was approximately 12% fly ash, 9-12% total moisture and a stabilized depth of 12 in. Soil types varied from mostly heavy clays and silty clays to granular. As work commenced, two pulverizers were employed, both equipped with direct water injection systems and the typical vibratory padfoot rollers along with grading and finishing equipment. Fly ash was spread in the process with specially constructed and equipped hopper trucks known as vane feeders to control both ash concentration and fugitive dust.
Testing on the ash-stabilized subgrade exhibited an increase in CBRs from 4-6 to as high as 65. Unconfined compressive strengths increased 100% in many cases.
Merrill Airport
In fall 2003, the HMA runway at the Merrill Airport was extended. Repair of the badly deteriorated aprons in the hanger area was considered as a change order, but proposals were unreasonably high. The apron repair became the focus of a primary letting in early 2004.
Alternative bids were considered. The primary option was CIR, with a more traditional undercut, waste and replace alternative. The CIR option bids were returned at approximately one-half of the cost of the more traditional option. The cost saving was attractive to both the Wisconsin DOT’s Bureau of Aeronautics (BOA) and the local manager. Contracts were awarded, and the work commenced in fall.
The existing pavement was badly failed and cracked; drainage was very poor; access to the work area was limited; and the airport manager was concerned about access to the hanger buildings. Engineers recommended adding 5-7 in. of crushed-aggregate base course (CABC) on top of the existing 3-in. pavement, pulverizing through the CABC and pavement, regrading to drain, stabilizing with Class C fly ash and repaving.
New CABC was spread over 5,000 sq yd of pavement and the prepulverizing was completed on day one. Fly ash was delivered, spread at approximately 120 lb/sq yd and blended with the pulverizer the next day. Moisture for the mixture was added through direct injection into the mixing chamber. Total moisture was approximately 9%. Initial compaction was provided immediately with a vibratory padfoot roller (three passes were usually sufficient). Final grading was completed, and the surface was rolled and sealed with a smooth drum roller in static mode.
The new surface was firm, smooth, able to shed water in the event of rain and ready for the new 4-in. HMA pavement. Paving and landscape finishing followed, and the airport was back in business. The airport manager indicated he was very happy with the final product and the short time of completion. And to further confirm the efficacy of the CIR project, the BOA received an innovation award from the Wisconsin Asphalt Pavement Association.
About The Author: Rosenmerkel is president of Rosenmerkel Engineering and a consultant to Lafarge North America. He can be reached at [email protected].
