|FHWA Instructs on the Use of Coal Ash in Road Construction|
|Friday - December 16, 2011|
We've documented more than once that the United States Federal Highways Administration recommends the use of Coal-fired power plant Fly Ash in certain road construction applications.
An example of our reportage on such issues can be accessed via:
Federal Highway Administration Recommends Fly Ash Concrete | Research & Development; concerning the FHWA's "Infrastructure Materials Group: Fly Ash"; and, wherein we're told, in part, that
"Fly ashes are finely divided residue resulting from the combustion of ground or powdered coal. They are generally finer than cement and consist mainly of glassy-spherical particles as well as residues of hematite and magnetite, char, and some crystalline phases formed during cooling. Use of fly ash in concrete started in the United States in the early 1930's. The first comprehensive study was that described in 1937, by R. E. Davis at the University of California. The major breakthrough in using fly ash in concrete was the construction of Hungry Horse Dam in 1948, utilizing 120,000 metric tons of fly ash. This decision by the U.S. Bureau of Reclamation paved the way for using fly ash in concrete constructions.
In addition to economic and ecological benefits, the use of fly ash in concrete improves its workability, reduces segregation, bleeding, heat evolution and permeability, inhibits alkali-aggregate reaction, and enhances sulfate resistance."
The "ecological benefits" noted above by the FHWA have actually led to active support from the United States Environmental Protection Agency for the use of Coal Fly Ash, in those road construction applications for Fly Ash specified by the FHWA.
The document we enclose herein is, in fact, an accredited continuing education course for professional highway engineers that was co-sponsored and co-developed, through a professional education contractor, but with the help of the American Coal Ash Association, who composed the original report upon which the course is based, by both the Environmental Protection Agency and the Federal Highways Administration.
And, it centers on the appropriate use, wherever possible, of Coal Fly Ash in road construction.
Comment follows, and is inserted within, excerpts from the initial link in this dispatch to:
"Fly Ash Facts for Highway Engineers
Course No: T06-003; Continuing Education and Development, Inc.; Stony Point, NY 10980
(By way of introduction, see:
CED Engineering - Continuing Education Course Online - Engineering Courses - Online PDH Courses; wherein we learn, that: "CEDengineering.com was created with the vision to share with engineering colleagues, technical industries, and professional societies new engineering ideas and advanced technological concepts for the benefit of all fellow engineers. Our primary goal is to reinforce the need for lifelong learning in order to stay current with changing technology and established standards (and, to)
provide professional online continuing education to Licensed Professional Engineers to enhance their engineering knowledge and competence as well as to assist them in fulfilling the Continuing Professional Competency (CPC) requirements required by their respective State Licensing Boards.
CEDengineering.com is the official website for Continuing Education & Development, Inc. which was incorporated on June 26, 2006 in the State of New York. The company is an approved sponsor of continuing education by the State Licensing Boards of Florida, Louisiana, New York and North Carolina.")
(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.
(Note that statement: "Coal fly ash ... has numerous applications". Far past time other people, besides professional highway engineers exposed to this course found that out, ain't it?)
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 N5080.4, which urged states to allow partial substitution of fly ash for cement whenever feasible.
(See, for instance, our earlier report of:
Scientists Convert Coal Ash to Cement | Research & Development; concerning, in part: "Role of Fly Ash In Reducing Greenhouse Gas Emissions During The Manufacturing Of Portland Cement; Natural Resources Canada; Abstract: This paper gives a global review of portland cement production and greenhouse gas emissions during its manufacturing. It is emphasized in the paper that fly ash is and will remain the major supplementary cementing materials for decades to come";
with quite a few more, similar, to follow.)
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.
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.
(Topics and Applications covered include:)
Fly Ash in Portland Cement Concrete
Fly Ash in Stabilized Base Course
Fly Ash in Flowable Fill
Fly Ash in Structural Fills/Embankments
Fly Ash in Soil Improvements
Fly Ash in Asphalt Pavements
Fly Ash in Grouts for Pavement Subsealing
(We've previously documented a number of the above Fly Ash applications, and will more fully document them, and others, in reports to follow.)
Fly ash is most commonly used as a pozzolan in Portland Cement Concrete 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.
Fly ash is typically finer than portland cement and lime. Fly ash consists of silt-sized particles which are generally spherical, typically ranging in size between 10 and 100 micron. These small glass spheres improve the fluidity and workability of fresh concrete. Fineness is one of the important properties contributing to the pozzolanic reactivity of fly ash.
Quality requirements for fly ash vary depending on the intended use. Fly ash quality is affected by fuel characteristics (coal), cofiring of fuels (bituminous and sub-bituminous coals), and various aspects of the combustion and flue gas cleaning/collection processes. The four most relevant characteristics of fly ash for use in concrete are loss on ignition (LOI), fineness, chemical composition and uniformity.
LOI is a measurement of unburned carbon (coal) remaining in the ash and is a critical characteristic of fly ash, especially for concrete applications. High carbon levels, the type of carbon (i.e., activated), the interaction of soluble ions in fly ash, and the variability of carbon content can result in significant air entrainment problems in fresh concrete and can adversely affect the durability of concrete. AASHTO and ASTM specify limits for LOI. However, some state transportation departments will specify a lower level for LOI. Carbon can also be removed from fly ash.
(See, for instance, our report of:
Virginia Converts Coal Ash to Cash | Research & Development; which contains separate information concerning: "South Carolina Electric and Gas Successful Application of Carbon Burn-Out (CBO) at the Wateree Station; 1999 International Ash Utilization Symposium; Center for Applied Energy Research, University of Kentucky; South Carolina Electric and Gas Company; Progress Materials, Inc.; and, Southeastern Ash Co., Inc.; CBO combusts residual carbon in fly-ash, producing a very consistent, low-carbon, high-quality pozzolan";
with more reports to follow concerning how residual Carbon can be efficiently removed from Coal Ash, to make it more acceptable for use as an aggregate in concrete applications.)
Chemical composition of fly ash relates directly to the mineral chemistry of the parent coal and any additional fuels or additives used in the combustion or post-combustion processes. The pollution control technology that is used can also affect the chemical composition of the fly ash.
(See, for instance, our report of:
Wisconsin Cleans Ammonia from Coal Ash | Research & Development; concerning: ""United States Patent 6,755,901 - Ammonia Removal from Fly Ash; 2004; Wisconsin Electric Power Company, Milwaukee; Abstract: A method and apparatus for the application of beat to remove ammonia compounds from fly ash, thereby making the fly ash a marketable product is disclosed";
wherein Fly Ash contaminated with Ammonia by some types of mandated air pollution control scrubbers can be treated for the removal of residual Ammonia, thereby making the contaminated "fly ash a marketable product".)
Fly Ash In Portland Cement Concrete (PCC): 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.
The many benefits of incorporating fly ash into a PCC 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 (include):
The use of fly ash in portland cement concrete (PCC) has many benefits and improves concrete performance in both the fresh and hardened state. Fly ash use in concrete improves the workability of plastic concrete, and the strength and durability of hardened concrete. Fly ash use is also cost effective. When fly ash is added to concrete, the amount of portland cement may be reduced.
(The above, as we've earlier reported, could be seen as an important feature, since the making of Portland cement, through the calcination of limestone, generates copious quantities of Carbon Dioxide, via the reaction: CaCO3 + Heat = CaCO + CO2.
So, any Portland cement we could displace with Fly Ash would result in a net reduction of total combined Carbon Dioxide emissions from the Cement-making and Power-generating industries taken in total.
But, of course, since, as seen in:
USDOE Converts CO2 to Gasoline | Research & Development; about: "US Patent 4,197,421 - Synthetic Carbonaceous Fuels and Feedstocks; 1980; Assignee: The United States of America; Abstract: This invention relates to the use of a three compartment electrolytic cell in the production of synthetic carbonaceous fuels and chemical feedstocks such as gasoline, methane and methanol by electrolyzing an aqueous sodium carbonate/bicarbonate solution, obtained from scrubbing atmospheric carbon dioxide with an aqueous sodium hydroxide solution";
we can convert Carbon Dioxide into Gasoline, who cares?
However, it does take a large amount of energy to calcine limestone, to make Portland cement, so any amount of cement we could displace with Coal Fly Ash would result in significant energy economies.)
Generally, fly ash benefits fresh concrete by reducing the mixing water requirement and improving the paste flow behavior.
Fly ash is used to lower the cost and to improve the performance of Portland Cement Concrete.
Typically, 15 percent to 30 percent of the portland cement is replaced with fly ash, with even higher percentages used for mass concrete placements."
We'll close our excerpts there, even though the course, "Fly Ash Facts for Highway Engineers", does go on at great, commendable length about the other potential uses for Coal Ash in road construction, such as "Stabilized Base Course", etc.
We will, in fact, be treating most of those other potential applications, as documented from other sources, in separate reports we have in progress based on information from those other sources.
But, the point of it all will be the same as the point herein:
The Ash that is co-produced from our essential use of Coal as a fuel for the generation of electrical power, like the co-product Carbon Dioxide, is a valuable raw material resource, that, if properly utilized, could result in rather immense benefits, a few of which include:
Improved road durability and highway pavement performance - a special blessing in West Virginia.
Reduced energy costs in making Portland cement.
Reduced total, combined emissions of CO2.
Avoided costs for Fly Ash disposal.
Increased employment and tax revenue for US Coal Country.
In closing, we wanted to ask, to voice, a few questions:
Since professional engineers are required to maintain their certifications through specified amounts of ongoing education, and, since the course we treat herein presents itself as being approved for such ongoing education for professional engineers, is it required, or even being offered, to the state road engineers employed by the various state highway departments in US Coal Country?
And, since Coal Fly Ash can offer equivalent, in some cases better, performance, in certain road construction applications, such as "Stabilized Base Course", "Flowable Fill", and "Structural Fills", is Coal Fly Ash specified for such applications in road construction contracts designed and let by the various state highway departments in US Coal Country?
If not, why not?
And, what can we do to change the situation?