http://circainfo.ca/pdf/K.%20Bargaheiser%20-%20Corrosion%20Paper.pdf
We've many times documented that Coal Ash can be productively consumed in the making of cement and concrete that are superior in many ways to what are officially known as "Ordinary Portland Cement", "OPC", and Ordinary Portland Cement Concrete.
There is, in fact, a rather vast body of scientific literature "out there" demonstrating the truth of the matter; but, due both to technical expositions of the chemistry involved that are beyond our limited capacities to fully understand and accurately summarize for you, and, to legal constraints involving copyright laws, there is much about the value of Coal Ash we must leave unsaid.
As an example of the latter difficulties, we refer you, in passing, to the report:
http://www.americancoalcouncil.org/associations/10586/files/ACC_2010_CCP_ECON_ASSESSMENT.pdf; concerning: "The Value of Coal Combustion Products: An Economic Assessment of CCP Utilization for the US Economy; 2010; Prepared by John Ward, Inc. (for the) American Coal Council, Washington, DC; Executive Summary: Coal Combustion Products (CCP's) - including fly ash, bottom ash, and flue gas desulfurization (FGD) materials - represent a strategic resource for the United States that has been steadily growing in utilization since the 1950's".
The Coal Council prefaces that report with a warning against reproduction or transmission of any or all of it's contents so stringent we thought that maybe we should hide our copy of it under the mattress - - even though the information it contains about the current and potential use of Coal Ash is so positive that we would have thought a pro-Coal industry group would want copies of it scattered about like confetti.
But, it is freely accessible via the link, and does contain a good deal of information concerning the utilization of Coal Combustion Products that should be of interest to any Coal Country journalist who actually does have at least a little concern for the vital core industry of his or her home state, rare as unicorns such scribes now appear to us to be; most, it seems, having been lobotomized in the shale gas chambers.
In any case, we have previously reported that Cement and Concrete made from Coal Ash can be formulated so as to provide a level of resistance to chemical corrosion notably superior to that which can be obtained by OPC concrete.
Among our reports documenting that fact is:
West Virginia Coal Association | Texas Fly Ash Concrete Resists Chemical Corrosion | Research & Development; concerning: "US Patent 5,578,122 - Concretes Containing Class C Fly Ash that are Stable in Sulphate Environments; 1996; Assignee: The University of Texas System; Abstract: Methods for combining Class C fly ash into cementitious mixtures for producing concretes that are resistant to sulfate-containing environments. In one method, Class C fly ash is intergound with portland cement clinker and gypsum to produce a cementitions mixture, which, when combined with water and an aggregate produces a hardened concrete that is resistant to sulfate environments".
So effective is a cement compounded out of Coal Ash in resisting chemical attack, that, as seen in:
West Virginia Coal Association | Louisiana Coal Ash Protects Concrete from Corrosion | Research & Development; concerning: United States Patent Application 20120156381 - Geopolymer Mortar and Method; 2012; (Presumed Assignee: Louisiana Tech University); Abstract: A geopolymer mortar formed by mixing about 35% to about 45% by weight pozzolanic material, about 35% to about 45% by weight silicon oxide source, about 15% to about 20% by weight alkaline activator solution, and about 0.3% to about 2.5% by weight copper ion source. The pozzolanic material may be fly ash ... . The geopolymer mortar may be applied as a protective coating on a surface of a structure";
such Coal Ash cement compositions can be utilized as protective coatings for OPC concrete structures.
And, herein we see that Ohio State University, and a now-notable corporate partner, confirm the assertions of it's southern state higher education institutional colleagues, via excerpts, with comment appended, from the initial link in this dispatch to:
"'Prevention of Corrosion in Concrete Using Fly Ash Concrete Mixes'
Keith Bargaheiser (and) Tarunjit S. Butalia;
ISG Resources, Inc., Toledo, Ohio (and) The Ohio State University, Columbus, Ohio
(Note, according to information accessible via:
Headwaters Resources, Inc.: Private Company Information - Businessweek;
"ISG Resources" became, or is now a part of, the perhaps better-known "Headwaters Resources, Inc.".
See:
Fly Ash; "Operating coast to coast, Headwaters Resources is the leader in supplying materials derived from coal combustion products. From ready mixed concrete construction to precast concrete fabrication ... to soil stabilization technologies, Headwaters Resources supplies materials that make building products perform better. Fly ash use improves concrete performance, making it stronger, more durable, and more resistant to chemical attack. Fly ash use also creates significant benefits for our environment.")
This paper reviews the benefits of using high-volume fly ash in resisting corrosion damage in concrete structures. It considers the usefulness of current fly ash concrete technology and prevention techniques, and advances a new approach for making concrete resist the deleterious effects of corrosion.
Nationally, the use of coal combustion products (CCPs) has increased more than 50 percent in the past decade. In 2000, more than 32 million tons of coal combustion products were recycled for beneficial uses. This is more than seven times the volume of aluminum that is recycled. But even though consumption has increased rapidly, only a third of all CCPs generated in the United States are currently being used in beneficial applications. This leaves more than 76 million tons of CCPs to be disposed of annually.
The United States has recognized that its infrastructure of concrete bridges and highways is facing structural distress due to increased traffic volumes, increased axle loads and due to corrosion. In a landmark study conducted by Battelle Memorial Institute for the National Bureau of Standards, it is estimated that corrosion damage in the United States is 4.2 percent of the Gross National Product (GNP). Projecting this percentage out to recent GNP information, this amounts to about $350 billion of corrosion damage annually.
Battelle estimates that over $139 billion (40%) of these costs could be avoided through application with existing technologies and best-known practices.
(See our report of:
West Virginia Coal Association | Coal Ash in Concrete Saves $100 Billion | Research & Development; concerning: "The Economic Impacts of Prohibiting Coal Fly Ash Use in Transportation Infrastructure Construction; 2011; American Road & Transportation Builders Association";
for another take on the rather large economic rewards of using Coal Ash, with it's inherent corrosion resistance and other performance benefits, in road and highway construction. We'll search for the Battelle report mentioned, and bring it to you when and if we find it.)
Corrosion of concrete takes place when carbon dioxide (CO2) and chlorides penetrate concrete. As the chlorides and CO2 penetrate concrete, the pH level of the concrete begins to drop from 12-13 to about a value of 9. In concrete construction, the 1.5 to 2 inches of concrete cover over the rebar acts as protective layer from the chlorides/CO2 reaching the rebar. Once the threshold is reached, the concrete cover is compromised and the pH of the concrete surrounding the rebar allows for corrosion. This weakens the concrete and reduces its service life. This subsequently increases costly maintenance on repair and restoration projects for the damaged concrete structure.
Recent research has indicated the benefit of using fly ash in preventing corrosion damage in concrete. Reduced permeability, lower water/cement ratio, decreased drying shrinkage/cracking, and increased durability are all benefits of fly ash concrete.
Introduction: Corrosion of reinforcing steel in concrete bridges and highways has become a considerable
economic and social burden (and) premature deterioration has led to an inadequate design life of the infrastructure within the United States.
The aging infrastructure is at the top of the list for the most serious problems facing the Federal Highway Administration (FHWA). The adoption of corrosion protection measures in new concrete construction has become a major focus.
The direct cost today of repairing or replacing all deteriorated concrete structures is estimated to be more than $276 billion annually or 3.1 percent of the nation’s Gross National Product (GNP) (but, today, only) $121 billion per year is spent on mitigating corrosion, leaving a growing deficit of $155 billion a year.
Further facing FHWA and the concrete construction industry is the continued environmental emphasis from the federal government and environmentalists. Concrete is an environmentally friendly and versatile material for the construction of infrastructure. Unfortunately, Portland cement, the critical component of concrete, may not be as environmentally friendly.
The production of one ton of Portland cement releases about one ton of carbon dioxide (CO2) emissions into the atmosphere.
(That "one ton" of CO2, as we've illustrated in a number of previous reports, comes from heating the limestone to make cement, according to the formula: CaCO3 + Heat = CaO + CO2. It doesn't really take into account CO2 that might be being generated by fuel combustion to generate the needed heat.)
The current U.S. production of Portland cement contributes about 750 million tons of CO2 to the greenhouse gases (GHG) in the earth’s atmosphere annually. Governmental regulations on these GHG emissions are stimulating the cement industry to look at supplementary cementing materials that could be used to produce lower CO2 emissions.
The increased interest in sustainable design and construction has created a renewed interest in Coal Combustion Products (CCPs). This trend has been accelerated by the emergence of agencies like the U.S. Green Building Council (USGBC), Leadership in Energy and Environmental Design (LEED), Coal Combustion Products Partnership (C2P2) of the USEPA, along with President Bush’s Clear Skies Initiative. Their primary goal is environmentally and socially focused towards overall sustainable development. Secondarily, CCPs have been found to provide the catalyst for these groups to reach their individual goals and objectives.
According to the United States Geological Survey, CCPs rank third as the most abundant nonfuel mineral resource in the United States, its annual production is just below crushed stone, and sand and gravel. Portland cement ranks just below that of CCPs. Concrete is said to be only second to water as the world’s most consumed product. In order to produce concrete, it is necessary to use some Portland cement as a binder. The challenge is that for every ton of cement produced; about a ton of CO2 is released into the atmosphere. By replacing one ton of cement with fly ash, an equal amount of CO2 release into the atmosphere can be prevented.
(As we have said before, and tried to emphasize: Coal Ash is a "mineral resource", not a valueless, or harmful, waste; and, we should all begin thinking of, and treating, it that way. - JtM)
The increased use of Portland cement is expected to continue to grow in the U.S. as in the rest of
the world. Thus, we can expect increasing CO2 emissions into the atmosphere from cement manufacturers. The agencies listed above, have brought economical and environmental pressures onto these manufacturers of cement. At this point in time, it is important to manufacture cement as environmentally friendly as possible. Furthermore, the manufacturers of cement are very much aware that for the commission of any new cement plant, the industry must show increased stewardship. One such responsible measure is the increased use and promotion of supplementary cementing materials in the production of cement and concrete.
Seventy percent of all the energy in the United States is produced by the approximately 720 coalfired power plants in about 45 states. When burning coal at these power plants, two main types
of ashes are produced, coal fly ash and bottom ash. Fly ash is the very fine material carried in the flue gas, collected typically by an ESP or a baghouse, and stored in silos for use in concrete.
Bottom ash is the larger/heavier particles that fall to the bottom of the boiler after combustion.
An additional solid byproduct of clean coal technology processes is produced from coal containing sulfur. When this coal is burned, sulfur dioxide is produced. Scrubbers are used to collect the sulfur dioxide (by injecting a sorbent) and Flue Gas Desulfurization (FGD) material is generated. In this study, we will limit our focus to coal fly ash.
(Although, remember, as in, for just two examples, our reports of:
West Virginia Coal Association | Pittsburgh Makes Coal Flue Gas Gypsum for Fly Ash Cement | Research & Development; concerning: "US Patent 5,312,609 - Sulfur Dioxide Removal from Gaseous Streams with Gypsum Product Formation; 1994; Assignee: Dravo Lime Company, Pittsburgh"; and:
West Virginia Coal Association | Pittsburgh Converts Coal Ash and Flue Gas into Cement | Research & Development; concerning: "United States Patent 5,766,339 - Producing Cement from a Flue Gas Desulfurization Waste; 1998; Assignee: Dravo Lime Company, Pittsburgh; Abstract: Cement is produced by forming a moist mixture of a flue gas desulfurization process waste product (and fly ash, and subsequent specified treatment)";
"Flue Gas Desulfurization (FGD) material" also has value, with Fly Ash, in the making of cement; or, in and of itself, in the making of "Gypsum Board", aka "Wallboard" and "Drywall".)
The 720 coal-fired U.S. power plants annually produce about 63 million tons of fly ash. About 31 million tons are disposed of, either onsite or in state-regulated disposal sites. Approximately 12 million tons are recycled and put to beneficial reuse in the concrete industry. Another 20 million tons are used for a range of other applications including, soil stabilization, roller compacted concrete, road base stabilization, etc. In this paper, we will focus on the use of fly ash as a mineral admixture for Portland cement concrete.
Fly Ash As A Supplementary Cementing Material:
The United States consumes over 108 million tons of cement a year, with 75 million tons being domestically produced. Roughly 25% of all cement is imported from all over the world for U.S. consumption. Currently, in the U.S., it is an accepted practice to substitute 15 to 35% cement in concrete with fly ash. The question that needs to be asked is: why are we only consuming 12 million tons of fly ash and allowing 31 million tons of fly ash to go to disposal? The answer lies in the fact that fly ash is really not well understood by specifiers.
The opportunity comes by promoting the features and benefits of fly ash to the specifiers.
Specifically, addressing the engineers needs, according to specific market segment. These market segments include architectural, chemical, civil, electrical, environmental, geotechnical, highway, industrial, mechanical, mining, sanitary, structural, surveying, and transportation.
The use of fly ash (Class C and Class F) in concrete offers several significant advantages. These
include:
- Reduced permeability
- Reduced water/cement ratio
- Reduced concrete segregation
- Reduced bleeding
- Increased workability/ plasticity
- Increased flexural and compressive strength
- Increases pumpability
- Reduced heat of hydration
- Cost savings to the user
- Increased sulfate resistance
- Improved freeze-thaw durability
- Reduced volume changes: dry shrinkage
- Better finishability
- Reduced expansion due to ASR
- Improved hot weather handling characteristics
- Reduced corrosion damage
Currently, concrete designers and specifiers are not designing the same as they did twenty, ten, and even two years ago. Society is demanding concrete structures last fifty, one hundred, five hundred, and even a thousand years. Wacker Drive in Chicago, Illinois was designed to last eighty to one hundred years. The Confederation Bridge located between the Northumberland Strait and Prince Edward Island and mainland Canada has a design life of one hundred years. BAPS Temple in Stafford, Texas was designed to have a service life of one thousand years. This list is growing by the day. What do all these structures have in common?
Fly ash is playing a key role for the designers to build these concrete structures with a service life lasting hundreds of years.
Cost of Corrosion: In 2002 a study was presented to the U.S. Federal Highway Administration (FHWA)6 outlining the cost of corrosion. The study titled “Corrosion Costs and Preventive Strategies in the United
States” focused on identifying the cost of corrosion by specific industry sectors and establishing control methods to minimize the problem.
Results of the study showed the total annual estimated direct cost of corrosion for 1998 to be $276 billion, (i.e,) 3.1% of the nation’s Gross Domestic Product (GDP). Extrapolated into 2003, it is $350 billion. The report revealed that although corrosion management has improved over the past several decades, the U.S. must find better methods to control corrosion.
Corrosion experts have spent the last decade focusing on new construction, specifically on materials and design. Today, much of our infrastructure is reaching the end of its design life. The emphasis has shifted to maintaining and extending the service life of these concrete structures. Of the nearly 600,000 bridges, there are roughly 235,000 conventional reinforced concrete bridges, and 108,000 prestressed concrete bridges operating in the U.S. They support nearly 270 million residents and 7 million business establishments. It is estimated that 15% are structurally deficient because of corroded steel and steel reinforcement. The Status of the Nation’s Highway Bridges: Highway Bridge Replacement and Rehabilitation Program and National Bridge Inventory, Thirteenth Report to the United States Congress, estimated that 80,000 bridges on the
federal system and 103,000 bridges of the federal system were deficient in some way. While there was a decrease in the number of bridges in need of repair or replacement, the costs increased by 12% during the same period. Assuming that the total transportation sector is responsible for 21.5% of the corrosion, it can be calculated, that the cost will be about $75,250,000. The direct corrosion cost associated with bridges is 37% or $27,842,500 annually in 2003. The indirect costs or those incurred by users are estimated to be tenfold (example, wear and tear on the automobiles, increased gasoline, delays in product transport, missed
appointments, and other inconveniences that result in lost revenue.) This indirect cost that is due
to corrosion of bridges, burdens our society roughly $278,425,000 annually.
Fly Ash For Corrosion Mitigation: Mineral admixtures can be used to enhance the corrosion-control potential of concrete by reducing permeability. Fly ash is one of the most common admixtures used in concrete but rarely thought of to mitigate corrosion.
Normally, designers focus at maintaining the alkaline pH in concrete to sustain the steel in a non-corrosive environment. Because lower pH fly ash replaces cement, the primary source of the alkalinity in concrete, many designers have avoided its use. (But, because) fly ash improves the density of concrete along with other beneficial factors, it more than compensates for the slightly lower pH.
The Ohio State University is collaborating with ISG Resources in researching the use of high volume fly ash for increased durability and lowered corrosion potential of structural concrete. Two methods are under investigation:
1. Fly ash replacement for cement in conjunction with fly ash addition for fine aggregate.
2. Fly ash replacement for cement.
(A) portion of research at The Ohio State University was stimulated by Washington State’s DOT projects on fly ash overlays as an alternative to silica fume or latex-modified overlays. The interest for this alternative approach was stimulated by the sensitivity of the existing mixes to weather, temperature and pouring schedule. The goal for Washington State DOT was: to provide an air-entrained fly ash mix that could be field placed at an 11/4 to 11/2 thickness, would develop a 3000 psi compressive strength in 4 days and achieve 150 day rapid-chloride permeability of 750 coulombs or less.
Mix proportions were developed by the local ready mix producer who selected 611 pounds of Type II cement and 275 pounds of Class F fly ash as the mix to meet the specifications.
Results showed high volume fly ash mixes could improve the concrete strength and permeability while providing workability superior to that of the original overlay mixers.
(Results also showed that) high-volume fly ash mixes would be the most durable concrete mixes for preventing corrosion in reinforced concrete structures.
Conclusions: Corrosion remediation and prevention in the United States continues to burden the budgets of
state Departments of Transportation, Federal Highway Administration. Government regulations, environmentalists and society further complicate the situation by requiring lower CO2 sustainable design and longer service life of its infrastructure. Fly ash through its synergies with CO2, sustainable design, and natural pozzolanic reaction with cement can provide the benefits necessary to appeal to these groups and the designers.
(Note: "Fly Ash ... can ... appeal to these groups", i.e., "environmentalists and society".)
The pozzolanic reaction of fly ash in concrete ... (leads) to reduced permeability.
With the use of fly ash, the ingress of moisture, oxygen, chlorides, carbon dioxide, and aggressive chemicals are slowed significantly - thus improving durability and serviceability.
The chloride ion permeability of the fly ash concrete mixes are significantly lower than that of no fly ash mixes (and, clearly,) the high-volume fly ash concrete mixes, with low chloride ion permeability values, are desirable in concrete technology to prevent the deleterious effect of corrosion in reinforced concrete structures.
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Just think: If we finally got our heads screwed on straight about Coal Ash, and started using it the way we could and should be using it, maybe the durability of our Coal Country roads, which has been for many decades a destructive inconvenience and a financial drain, would become much less of a source of dark humor and tiresome editorializing.
And, maybe we could generate a few additional, long-term for a change, income streams and employment opportunities for our Coal Country citizens - some real jobs, in other words, that Country Roads improved by Coal Ash could take them to.
