http://www.flyash.info/2005/
In a recent dispatch, now accessible on the West Virginia Coal Association's web site, via the link:
we made report of:
"Specifying Fly Ash for Use in Concrete; Concrete In Focus; Spring, 2008; National Ready Mix Concrete Association (NRMCA)";
which is what it's title implies: a general guide for, and overview of, designing and specifying concrete mixes that incorporate Coal Ash, in order to achieve generally better physical properties of the cured concrete, and, to improve the economics of concrete manufacture and placement.
The author, Karthik Obla, now Vice-President, Technical Services, for the NRMCA, in the course of his dissertation, made note of the improved performance of concrete containing Coal Ash in marine environments, given the superior chemical resistance of Coal Ash concrete; and, we noted that the United States Navy had, in separate studies, confirmed that superior marine environment performance.
Herein, via the initial and two following links in this dispatch, we document both the US Navy's findings that properly-specified Coal Ash Concrete can, indeed, be better, in terms of chemical resistance, specifically in marine environment exposure, than conventional Portland Cement Concrete; and, the subsequent recommendation, by a team of Navy, and contracted university, scientists, that, wherever possible, more Coal Ash be used in concrete, for construction projects related to US Navy, and other Department of Defense, installations, even at levels above what might now be specified or permitted in existing guidelines.
But, a caveat:
Our above summary is a coarse, very coarse, generalization of the US Navy's findings; and, it could be construed as a misinterpretation of them. The Navy, in point of fact, performed very detailed analyses of the chemical content of various Coal Ashes from various sources; and, then correlated their chemical makeup with their actual performance, at various levels of loading, in Portland Cement Concrete mixtures; which mixtures also contained various other aggregates with their own levels of reactivity.
The gist is, that, the Navy developed data which can be used by knowledgeable parties to design Portland Cement Concrete mixes that contain more, and more optimum, amounts of either/or Class C and Class F Coal Ash, amounts in excess of those currently permitted by some specifications.
Comments, and two additional links and excerpts, follow highly-abbreviated, due to the authors' heavy reliance on graphical presentation of data, excerpts from the initial link in this dispatch to:
"Minimum Fly Ash Cement Replacement to Mitigate Alkali Silica Reaction
World of Coal Ash; April, 2005
L.J. Malvar, US Navy (and) L.R. Lenke, University of New Mexico
Abstract: Alkali Silica Reaction (ASR) in concrete results in deleterious expansion and deterioration.
While a recent specification already addresses ASR prevention using recycled products, such as fly ashes for cement replacement, the restrictions on fly ashes may be too conservative and prevent further savings during the replacement process by preventing use of local ashes that do not meet current requirements.
Data from previous research studies were used to assess the effectiveness of fly ashes in preventing ASR, based on their chemical composition, the compositions of the cement and the reactivity of the aggregates.
A chemical index was derived based on the fly ash (or cement) constituents (which) should allow for the safe use of many additional ashes while further reducing concrete costs."
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Again, our necessarily-brief excerpts don't do justice to the work; but, really, you would need an expert in cement chemistry who's also a polymath statistician to decipher the graphics Malvar and Lenke present, and, then, to explain in more accessible terms how an increased use of Coal Ash, in combination with Portland-type Cement, in concrete mixtures can lead to an increase in the resulting concrete's durability; and, concurrently, make the process of producing cement and concrete more economical.
A somewhat later presentation by Malvar and Lenke sums it all up a bit more clearly, in terms of both technology and economy, as can be seen in:
"Efficiency Of Fly Ash In Mitigating Alkali Silica Reaction Based On Chemical Composition
ACI Materials Journal, Vol. 103, No. 5, September-October 2006
L. J. Malvar and L. R. Lenke; U.S. Navy, Naval Facilities Engineering Service Center (and) University of New Mexico
Abstract: While recent specifications address alkali silica reaction (ASR) prevention using recycled products, such as fly ashes, as cement replacement, the restrictions on the ashes may be too conservative. Data from previous research studies were used to assess the effectiveness of fly ashes in preventing ASR based on their chemical composition, the composition of the cement, and the reactivity of the aggregates. A chemical index was derived to characterize the fly ash and cement based on their chemical constituents. For the fly ashes, this index correlated well with the ASTM C 618 and CSA A3001 classifications. This index was also used to assess the efficiency of ashes that did not meet either specification. For a given ash, cement, and aggregate reactivity, it was possible to derive the minimum cement replacement that is needed to insure with 90% reliability that the 14-day ASTM C 1260 (modified, or C 1567) expansion would remain below 0.08%.
Introduction: A recent state-of-the-art review resulted in the development of guidelines to prevent ASR, which are now used by the Tri-Services (U.S. Navy, Air Force, and Army) for airfield pavements, and are being exported into Department of Defense (DOD) unified facilities guide specifications dealing with concrete in general. However, these guidelines are somewhat conservative, allowing only the use of ASTM C 618 Class F fly ashes with additional restrictions. Hence, many ashes very close to, but not meeting that specification cannot be used, in some cases increasing concrete costs by requiring the transportation of other ashes from far away. The objective of this paper is to refine the fly ash requirements using their chemical composition, and to provide an alternate classification to ASTM C 618 that would allow ash assessment, as well as the usage of ashes currently not meeting that specification.
(Note, please, that, so eager are our armed services to benefit from the improved performance of concrete that is made with Coal Ash "for airfield pavements", that they appear willing to arrange for "the transportation of" approved Coal "ashes from far away" to the places where the airfields are being constructed.)
Significance: Public Law 106-398 (2001) directs the Secretary of Defense to explore available technologies to prevent, treat, or mitigate ASR. To date 32 DOD airfields have reported ASR problems. The costs are staggering: as an example, the Air National Guard Channel Islands Site concrete apron was built in 1989 and replaced in 2003 at a cost of $16 million. While recent specifications now address ASR prevention using recycled products such as fly ash as cement replacement, the restrictions on the ashes may be too conservative, preventing further savings.
Alkali silica reaction (ASR) is the reaction between the alkali hydroxide in Portland cement and certain siliceous rocks and minerals present in the aggregates, such as opal, chert, chalcedony, tridymite, cristobalite, strained quartz, etc. The products of this reaction often result in significant concrete expansion and cracking, and ultimately failure of the concrete structure, including significant potential for foreign object damage to aircraft. Alkali aggregate reaction (AAR) is the reaction between the cement hydroxides and mineral phases in the aggregates, usually of siliceous origin. In this paper no distinction is made between AAR and ASR. ASR needs several components to occur: alkali (supplied by the cement, although external sources can exist), water (or high moisture content or humidity), and a reactive aggregate.
There are 3 characteristics of a fly ash that determine its efficiency in preventing ASR:
- Fineness: Finer pozzolans are more efficient in reducing ASR expansion ... .
- Mineralogy: While ashes can be characterized by their basic chemical components, these components can be bound differently and react differently from ash to ash ... .
- Chemistry: In general, for a given ash, the chemical composition is easily obtained, but not the fineness (except for its compliance with ASTM C 618), or its mineralogy.
Data were gathered from five previous research studies addressing the use of fly ash in mitigating ASR. A correlation was sought between the chemical composition of the ash and the cement, and the 14-day expansion per ASTM C 1260 (also called the accelerated mortar bar test, or AMBT). The fly ash content of calcium oxide (or lime) has been shown to have the most effect on the efficiency of the ash in mitigating ASR. Current DOD guidelines for pavements do not allow Class C fly ash and limit the CaO content of Class F fly ash to 10%. The New Mexico State Highway and Transportation Department (2000) places a 10% restriction as well.
Silicon dioxide shows pozzolanic activity, i.e., forms a cementitious product by reaction with calcium hydroxide. Increased contents of SiO2 have proven to increase the ash effectiveness, and lower the expansion.
Alumina can contribute to the pozzolanic effect of silica ... .
Constituents Promoting Expansion: Calcium Oxide has been recognized as having one of the most deleterious effects on expansion, and ASR expansion has often been correlated to CaO, or CaO/SiO2.
Constituents Reducing Expansion: SiO2 is typically considered the most beneficial constituent in preventing expansion."
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Thus, a high silica, "SiO2", Fly Ash would be "most beneficial ... in preventing expansion" of a Portland Cement Concrete into which it was blended.
And, as can be learned from our US Geological Survey, via:
http://pubs.usgs.gov/bul/1528/
Coal Ash from our Appalachian fields will have an average silica content of, roughly, 40 to 50%.
Finally, as we will likely further document in future reports, our US Navy found the blending of Coal Ash into Portland Cement Concrete so effective at increasing the concrete's durability and resistance to deterioration, it even, more recently, recommended that such Coal Ash-enhanced concrete start being used in applications where such durability and resistance to deterioration can be seen as being absolutely critical, as in:
http://www.airporttech.tc.faa.
"Use Of Fly Ash In Concrete Pavements
2007 FAA Worldwide Airport Technology Transfer Conference
April, 2007; Atlantic City, New Jersey
L. Javier Malvar; Naval Facilities Engineering Service Center
Abstract: Recent concrete pavement failures due to alkali-silica reaction (ASR) point to the need to use
supplementary cementitious materials, such as fly ash ... to prevent deleterious expansions. Recent research has shown the effect of fly ash chemical composition on its effectiveness in mitigating ASR, and has allowed the determination of minimum cement replacement values to prevent deleterious expansions. Minimum replacement values are proposed for use even when the aggregate is labeled as innocuous. The potential impact of these observations on Department of Defense specifications is discussed.
A state-of-the-art review resulted in the development of guidelines to prevent alkali silica reaction (ASR) now used by the Tri-Services (U.S. Navy, Air Force, and Army) for airfield pavements, and which are being adapted into Department of Defense (DOD) unified facilities guide specifications (UFGS) dealing with concrete in general. However, these guidelines are somewhat conservative for fly ash, allowing only the use of ASTM C 618 Class F fly ashes with additional restrictions. Hence, many ashes very close to, but not meeting those specifications cannot be used, in some cases increasing concrete costs by requiring transportation of other ashes from far away. Recent research] has shown that those specifications could be relaxed while insuring ASR mitigation. This paper presents a summary of the updated fly ash requirements and the proposed enhancements to the tri-service UFGS for concrete pavements."
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Please note that Malvar and, by extension, the US Navy, are actually lobbying for at least aminimum required use of Coal Ash as an additive for Portland Cement Concrete at allairports, military and civilian, that is, those governed by the Federal Aviation Administration, the "FAA", and, even, "Worldwide".
The extensive tables of data included in the three reports provide the specifics of how such use of Coal Ash can lead to better performance of the Concrete, with the added benefit of "reducing concrete costs"; a benefit corroborated in our earlier report of:
West Virginia Coal Association | Coal Ash Can Reduce Construction Costs | Research & Development; concerning:
"United States Patent 5,624,491 - Compressive Strength of Concrete and Mortar Containing Fly Ash; 1997; Assignee: New Jersey Institute of Technology, Newark; Abstract: The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction. The invention includes a method for predicting the compressive strength of such a hardenable mixture, which is very important for planning a project. The invention also relates to hardenable mixtures comprising cement and fly ash which can achieve greater compressive strength than hardenable mixtures containing only concrete over the time period relevant for construction. In a specific embodiment, a formula is provided that accurately predicts compressive strength of concrete containing fly ash out to 180 days. In other specific examples, concrete and mortar containing about 15% to 25% fly ash as a replacement for cement, which are capable of meeting design specifications required for building and highway construction, are provided. Such materials can thus significantly reduce construction costs".
Moreover, as we have noted several times, and as we will more fully document in the future, the manufacture of Portland Cement, as seen in our report of:
West Virginia Coal Association | Scientists Convert Coal Ash to Cement | Research & Development; which contains, among other references:
"Role of Fly Ash In Reducing Greenhouse Gas Emissions During The Manufacturing Of Portland Cement;V.M. Malhotra, Scientist Emeritus, Advanced Concrete Program, CANMET, Natural Resources Canada; Synopsis: 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, and the concrete industry must concentrate its major efforts for the increased use of fly ash in concrete. Not only is the manufacturing of portland cement highly energy intensive, it also is a significant contributor of the greenhouse gases. The production of one tonne of cement contributes about 1 tonne of CO2 to the atmosphere. (And, about) half of the CO2 emissions are due to the calcination of limestone";
entails the emission of significant amounts of Carbon Dioxide; and, replacing a given weight of Portland Cement, which would have otherwise been made by the calcination of limestone, with Coal Ash, will result in a,reduction of half that weight in the amount of Carbon Dioxide which would have otherwise been emitted by the Cement-making process.
The reduction in Carbon Dioxide emissions, in point of fact, is even greater, since less fuel needs to be combusted, with the consequent generation of additional CO2, in order to generate the heat needed to calcine the limestone, which calcination generates Carbon Dioxide by the equation:
CaCO3 + heat = CaO + CO2.
Our United States Navy, as herein, knows all about the multiple benefits of using Coal Ash in the manufacture of Concrete for use in various, high-performance applications.
Why haven't we landlubbers, out here in the US Coal Country hills, yet been afforded the privilege of even being given an overview of just one or two of those benefits?