Fly Ash Facts for Highway Engineers - Recycling - Pavements - FHWA
First, we apologize in advance for the complex, and no doubt confusing, structure of the report we bring to you herein. We note that there will be some seeming repetition within it, resulting from our attempt to reproduce for you the critical facts concerning the productive and beneficial use of Coal Ash in road and highway construction, as presented by the Federal Highways Administration, FHWA, as faithfully, though succinctly, as was possible for us.
Our report contains a lot of links to separate chapters and associated information that are all part of the core document accessible via the initial link above.
We hope that all of the links will transmit with their functionality intact. If not, then, if any one of them do, the FHWA web site it will take you to should provide you with facilities to access the other information.
That said, we remind you that we earlier made report of a continuing education course for highway and civil construction engineers, as accessible via:
West Virginia Coal Association | FHWA Instructs on the Use of Coal Ash in Road Construction | Research & Development; concerning:
"Fly Ash Facts for Highway Engineers; Course No: T06-003; Continuing Education and Development, Inc.; Stony Point, NY 10980; (Reference): Report No. FHWA-IF-03-019; Title: Fly Ash Facts for Highway Engineers; 2003; American Coal Ash Association; Contract No. DTHF61-02-X-00044; Sponsoring Agency: Federal Highway Administration. Coal fly ash is a coal combustion product that has numerous applications in highway construction. Since the first edition of Fly Ash Facts for Highway Engineers in 1986, the use of fly ash in highway construction has increased and new applications have been developed. Fly ash has been used in roadways and interstate highways since the early 1950s. In 1974, the Federal Highway Administration encouraged the use of fly ash in concrete pavement with Notice N5080.4, which urged states to allow partial substitution of fly ash for cement whenever feasible."
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The course itself, as we demonstrated in that report, presents a lot of details about the various road construction applications in which Coal Ash can be utilized; and, herein, we wanted to provide you with the source US Government document itself, and it's supporting components, upon which that course was based.
It's purpose is summed up by an advance excerpt taken from the report's introductory abstracts:
"Coal fly ash is a coal combustion product that has numerous applications in highway construction.
Since the first edition of "Fly Ash Facts for Highway Engineers" in 1986, the use of fly ash in highway construction has increased and new applications have been developed. This document provides basic technical information about the various uses of fly ash in highway construction that advance its use in ways that are technically sound, commercially competitive, and environmentally safe."
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More complete information can be accessed via the initial link in this dispatch, as represented by the following, and relatively brief, excerpts from that link, which excerpts include additional links as present in the full report to specific chapters and topics:
"Fly Ash Facts for Highway Engineers
American Coal Ash Association; DTFH61-02-X-00044; (for the) Federal Highway Administration
Report Number: FHWA-IF-03-019; June 13, 2003
Environmental benefits:
Fly ash utilization, especially in concrete, has significant environmental benefits including:
(1) increasing the life of concrete roads and structures by improving concrete durability,
(2) net reduction in energy use and greenhouse gas and other adverse air emissions when fly ash is used to replace or displace manufactured cement,
(3) reduction in amount of coal combustion products that must be disposed in landfills, and
(4) conservation of other natural resources and materials
Preface: Coal fly ash is a coal combustion product that has numerous applications in highway construction. Since the first edition of Fly Ash Facts for Highway Engineers in 1986, the use of fly ash in highway construction has increased and new applications have been developed. This document provides basic technical information about the various uses of fly ash in highway construction.
Fly ash has been used in roadways and interstate highways since the early 1950s. In 1974, the Federal Highway Administration encouraged the use of fly ash in concrete pavement with Notice N 5080.4, which urged states to allow partial substitution of fly ash for cement whenever feasible. In addition, in January 1983, the Environmental Protection Agency published federal comprehensive procurement guidelines for cement and concrete containing fly ash to encourage the utilization of fly ash and establish compliance deadlines.
This document is sponsored by the U.S. Department of Transportation, through the Federal Highway Administration, in cooperation with the American Coal Ash Association and the United States Environmental Protection Agency.
The United States Environmental Protection Agency supports the beneficial use of coal combustion products as an important priority and endorses efforts by the Federal Highway Administration as described in this document.
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Fly Ash: An Engineering Material; Chapter 1: Currently, over 20 million metric tons (22 million tons) of fly ash are used annually in a variety of engineering applications. Typical highway engineering applications include: portland cement concrete (PCC), soil and road base stabilization, flowable fills, grouts, structural fill and asphalt filler.
Fly ash is most commonly used as a pozzolan in PCC applications. Pozzolans are siliceous or siliceous and aluminous materials, which in a finely divided form and in the presence of water, react with calcium hydroxide at ordinary temperatures to produce cementitious compounds.
The unique spherical shape and particle size distribution of fly ash make it a good mineral filler in hot mix asphalt (HMA) applications and improves the fluidity of flowable fill and grout. The consistency and abundance of fly ash in many areas present unique opportunities for use in structural fills and other highway applications.
Environmental benefits. Fly ash utilization, especially in concrete, has significant environmental benefits including:
(1) increasing the life of concrete roads and structures by improving concrete durability,
(2) net reduction in energy use and greenhouse gas and other adverse air emissions when fly ash is used to replace or displace manufactured cement,
(3) reduction in amount of coal combustion products that must be disposed in landfills, and
(4) conservation of other natural resources and materials.
Highway Applications; Chapter 2 - Highway Applications:
Chapter 2 - Fly Ash Facts for Highway Engineers - Recycling - Pavements - FHWA;
Fly Ash in Portland Cement Concrete
Overview. Fly ash is used in concrete admixtures to enhance the performance of concrete. Portland cement contains about 65 percent lime. Some of this lime becomes free and available during the hydration process. When fly ash is present with free lime, it reacts chemically to form additional cementitious materials, improving many of the properties of the concrete.
Benefits. The many benefits of incorporating fly ash into a Portland Cement Concrete have been demonstrated through extensive research and countless highway and bridge construction projects. Benefits to concrete vary depending on the type of fly ash, proportion used, other mix ingredients, mixing procedure, field conditions and placement. Some of the benefits of fly ash in concrete:
Higher ultimate strength
Improved workability
Reduced bleeding
Reduced heat of hydration
Reduced permeability
Increased resistance to sulfate attack
Increased resistance to alkali-silica reactivity (ASR)
Lowered costs
Reduced shrinkage
Increased durability
See Chapter 3 for additional information.
Fly Ash in Stabilized Base Course
Overview. Fly ash and lime can be combined with aggregate to produce a quality stabilized base course. These road bases are referred to as pozzolanic-stabilized mixtures (PSMs). Typical fly ash contents may vary from 12 to 14 percent with corresponding lime contents of three to five percent. Portland cement may also be used in lieu of lime to increase early age strengths. The resulting material is produced, placed, and looks like cement-stabilized aggregate base
Benefits. PSM bases have advantages over other base materials:
Use of locally available materials
Provides a strong, durable mixture
Lower costs
Autogenous healing
Increased energy efficiency
Suitable for using recycled base materials
Can be placed with conventional equipment
Chapter 4 provides a more thorough discussion of stabilized base course.
Fly Ash in Flowable Fill
Overview. Flowable fill is a mixture of coal fly ash, water, and portland cement that flows like a liquid, sets up like a solid, is self-leveling, and requires no compaction or vibration to achieve maximum density. In addition to these benefits, a properly designed flowable fill may be excavated later. For some mixes, an optional filler material such as sand, bottom ash, or quarry fines, is added. Flowable fill is also referred to as controlled low-strength material, flowable mortar, or controlled density fill. It is designed to function in the place of conventional backfill materials such as soil, sand, or gravel and to alleviate problems and restrictions generally associated with the placement of these materials.
Chapter 5 includes a detailed discussion of flowable fill applications.
Fly Ash in Structural Fills/Embankments
Fly ash can be used as a borrow material to construct fills and embankments. When fly ash is compacted in lifts, a structural fill is constructed that is capable of supporting highway buildings or other structures. Fly ash has been used in the construction of structural fills/embankments that range from small fills for road shoulders to large fills for interstate highway embankments.
Chapter 6 provides additional information.
Fly Ash in Soil Improvements
Overview. Fly ash is an effective agent for chemical and/or mechanical stabilization of soils. Soil density, water content, plasticity, and strength performance of soils. Typical applications include: soil stabilization, soil drying, and control of shrink-swell.
Benefits. Fly ash provides the following benefits when used to improve soil conditions:
Eliminates need for expensive borrow materials
Expedites construction by improving excessively wet or unstable subgrade
By improving subgrade conditions, promotes cost savings through reduction in the required pavement thickness
Can reduce or eliminate the need for more expensive natural aggregates in the pavement cross-section
Soil improvement is discussed more thoroughly in Chapter 7.
Fly Ash in Asphalt Pavements
Overview. Fly ash can be used as mineral filler in Hot Mix Asphalt paving applications. Mineral fillers increase the stiffness of the asphalt mortar matrix, improving the rutting resistance of pavements, and the durability of the mix.
Benefits. Fly ash will typically meet mineral filler specifications for gradation, organic impurities, and plasticity. The benefits of fly ash include:
Reduced potential for asphalt stripping due to hydrophobic properties of fly ash
Lime in some fly ashes may also reduce stripping
May afford a lower cost than other mineral fillers
Chapter 8 has additional information.
Fly Ash in Grouts for Pavement Subsealing
Fly ash grouts are used for sealing voids beneath pavement slab sections. The unconfined compressive strength requirements for a grout mixture will usually exceed 8,300 kPa (1,200 psi) at 28 days and will range between 4,100 and 5,500 kPa (600 and 800 psi) at 7 days. This strength profile for grouts differentiates them from flowable fill materials inasmuch as the flowable fill definition (or controlled low strength material) sets an unconfined compressive strength limit of 8,300 kPa (1,200 psi) at 28 days. Furthermore, the relatively small size of the void filled with the grout mixture further differentiates this application from the larger voids where the lower strength flowable fills are utilized.
The principal requirements for a slab stabilization material is that it can flow to fill very small voids and still have adequate strength to support the slab. A good stabilization material should remain insoluble, incompressible, and not erode after it has been placed and hardened. It should also have sufficiently low internal friction to flow into very small voids and water channels. If the material is too stiff, it will create a seat below the grout hole and not fill all voids. If it is too wet, it will not have enough strength to support the slab and may have a large amount of shrinkage. Finally, it should have sufficient body to displace free water from under the slab and develop adequate strength and durability."
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Again, our apologies for the awkward formatting. But, the import of it all should be obvious:
A genuinely vast commercial market exists for the solid byproducts arising from our essential use of Coal in the generation of truly economical and affordable electric power; a vast market wherein the use of those Coal byproducts would provide enhanced performance relative to the materials traditionally employed and, ultimately, through that enhanced performance, save us, as a nation, many, many billions of dollars - as we will document in a future report addressing even more of these potentials.
As we recently reported, in:
West Virginia Coal Association | Obama White House Blocked EPA Coal Ash 'Hazardous' Label | Research & Development; concerning: "'EPA Backed Off 'Hazardous' Label for Coal Ash After White House Review'; by Patrick Reis; Greenwire; Published: May 7, 2010; U.S. EPA's proposed regulation of coal ash as a hazardous waste was changed at the White House to give equal standing to an alternative favored by the coal industry and coal-burning electric utilities";
an initiative begun by the US EPA, during the prior White House administration, to have Coal Ash officially labeled as a "Hazardous" waste, which would have effectively prevented the immensely-profitable and environmentally-beneficial uses of Coal Ash catalogued and described herein by the Federal Highways Administration, was blocked by the current US Government executives in charge.
We have been given at least a reprieve; and, we should take that opportunity to get ourselves educated and organized concerning the true value of Coal Ash, as detailed so thoroughly herein by the Federal Highways Administration; and, to get started doing something with that information before, Heaven forbid, the political climate changes once again, and, a different administration attempts to prevent us from establishing a new profit and employment center in US Coal Country, one based on the productive utilization of Coal Ash.
Make no mistake, the applications and markets outlined herein by the FHWA are so vast, that, like the market for the utilization of Coal Ash in the making of Portland-type cement alone, as we once documented, the potential exists for not only the complete utilization of all the Coal Ash we currently produce, but, for the demand to be so big that we will be motivated to mine old accumulations of Coal Ash, from wherever they have been "disposed" of, and, to prepare that disposed-of Ash for market.
So real is that possibility, in fact, that, as we will document in at least one report to follow, technologies and techniques are being developed to do just that: i.e., to mine older accumulations of Coal Ash; to process it for some necessary cleaning and preparation; and, to take it to market.
Coal Ash, as definitively and officially established herein by our own United States Government, via the Federal Highways Administration, is a valuable raw material resource.
We can use Coal Ash to build better, longer-lasting roads and highways; with the result being that we, as a nation, conserve both our wealth and our environment.
