http://www.flyash.info/2011/
In an earlier report, now accessible on the West Virginia Coal Association's web site via the link:
US Government Coal Ash Cement Stronger than Portland Cement | Research & Development; concerning: "United States Patent 4,256,504 - Fly Ash-based Cement; 1981; Inventor: Edwin Dunstan, Jr.; Assignee: The United States of America (as represented by the Secretary of the Interior); Abstract: A cement composition comprising a high calcium-content fly ash and calcium sulfate, and mortar and concrete compositions containing the cement;
we documented that an award-winning US Bureau of Reclamation scientist, Ed Dunstan, had developed a high-performance substitute for conventional Portland cement that was based on Coal Fly Ash as one of the primary raw materials.
Please keep in mind as we go along that Coal Fly Ash can be used in cement and concrete in a couple of different ways:
First, some Coal Utilization Byproducts can be consumed as one of the raw materials, replacing some of the natural raw materials, that go into the making of the cement itself during calcination, as seen, for one instance, in:
Pittsburgh Makes Coal Flue Gas Gypsum for Fly Ash Cement | Research & Development; concerning: "United States Patent 5,312,609 - Sulfur Dioxide Removal from Gaseous Streams with Gypsum Product Formation; 1994; Dravo Lime Company, Pittsburgh; Abstract: A method is provided for removing sulfur dioxide from a hot gaseous stream while directly producing .alpha.-hemihydrate gypsum from a scrubber effluent";
and, in which report it's more fully explained how and why gypsum is employed in the cement-making process.
Second, Fly Ash can be utilized as an aggregate, a substitute for some of the sand and gravel, which can be added to the cement as its being blended and poured, to make concrete.
An example of the latter use for Coal Ash can be seen in our report of:
US EPA Headquarters Housed in Coal Ash | Research & Development' wherein we're told, among other things, that: "fly ash has been used in concrete since the 1930’s. Most notably, it has been used in several construction projects and prominent buildings, including the Ronald Reagan Government Office building, home to the Environmental Protection Agency (EPA) in Washington, D.C.".
Further, though, adding finely-ground Fly Ash to cement, after it has been made by the calcination process, and in particle sizes too small to serve as structural concrete aggregate, takes advantage of the Fly Ash in its role as what's known as a "Pozzolan".
We've explained what pozzolan's are before, but we'll reintroduce them via additional references, such as:
Pozzolan - Wikipedia, the free encyclopedia; which tells us, as part of a lengthy exposition worth reading for anyone truly interested, that:
"A pozzolan is a material which, when combined with calcium hydroxide, exhibits cementitious properties. Pozzolans are commonly used as an addition (the technical term is "cement extender") to Portland cement concrete mixtures to increase the long-term strength and other material properties of Portland cement concrete, and in some cases reduce the material cost of concrete. Pozzolans are primarily vitreous siliceous materials which react with calcium hydroxide to form calcium silicates"; and:
Pozzolans for Concrete and alternative cements; wherein we're told that the "term 'pozzolan' is derived from the name of the town Pozzuoli, Italy. It is situated near Mt. Vesuvius and is the place where the Romans more than 2,000 years ago mined the ashes deposited by the occasional eruptions of this volcano. Adding these ashes at a ratio of 2:1 to aged lime putty (aged 2+ years) they were able to construct those sturdy buildings we still admire today. Given this mineral origin, some purists consider only volcanic ashes, pumice, tuffs, etc. as 'pozzolans'. But as the ashes of organic origin, like 'pulverized fuel ashes' (PFA, mostly coal ashes) ... also show enhancing properties when mixed with cement or lime, most of the times the origin is irrelevant. What counts are the properties, primarily particle size and purity (absence of carbon), and the results!"
In the above reference, note the importance of making certain that no residual "carbon" remains in the Coal Ash; and, recall our earlier report of:
Virginia Converts Coal Ash to Cash | Research & Development; which includes, among other information, excerpts relating, that:
"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".
As we will further address in coming reports, there are established and economical ways to accomplish the "Burn Out", as above, of residual Carbon in Coal Ash, and thereby make the Ash very suitable for use as a additive in, a component of, Portland cement and concrete.
And, herein, we again cite the award-winning former US Department of Interior scientist, Ed Dunstan, Jr., working subsequent to his career at the US Bureau of Reclamation as a private industry consultant, as he further explains how using Fly Ash as an additive in, or substitute for some of, the Portland cement itself, through it's action as a "pozzolan", improves both the performance and the intrinsic environmental characteristics of that cement.
Comment is inserted within and follows excerpts from the initial link in this dispatch to the recent:
"How Does Pozzolanic Reaction Make Concrete 'Green'?
2011 World of Coal Ash (WOCA) Conference, May, 2011, Denver, CO
Edwin R. Dunstan, Jr., PE; ERD Consultants, LLC, and Construction Materials Engineering Council, FL
When Portland cement is produced, there is a significant amount of CO2 emitted from the calcination of limestone. If the amount of CO2 can be reduced a system can be considered to be more 'green'.
(As we've previously documented, CO2 is emitted from the limestone during calcination via the reaction: CaCO3 + Heat = CaO + CO2. And, that is in addition to the CO2 emitted from whatever fuel might be combusted to generate the needed heat to calcine the CaCO3, i.e., limestone. Thus, any reduction in the amount of limestone utilized in the production of cement and concrete will result in significant reductions in the amount of Carbon Dioxide emitted by the various cement and concrete manufacturing industries.)
Less cement in concrete would (thus) make concrete 'more green'.
One method to reduce the amount of cement in concrete is to use a pozzolan.
Pozzolanic Reaction - Fly Ash: If a concrete mixture contains a pozzolan, less cement is required to obtain a specific strength.
By definition a pozzolan ... is: 'a siliceous or siliceous and aluminous material that in itself possesses little or no cementitious value but that will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds having cementitious properties'.
By definition to form a compound that has cementitious value a pozzolan must react with lime which in concrete comes from cement.
Green Concrete: The National Ready Mix Concrete Association has recently developed a 'Sustainable Concrete Carbon Calculator'.
As expected the primary source of CO2 is Portland cement,
This calculator shows (that) a reduction in cement of 40% reduces carbon (emissions) by 37%.
(However, when) the percentage of fly ash is greater than the optimum, the pozzolanic efficiency will be reduced.
For concretes with percentages greater than optimum, there will not be enough lime to react with the reactive portion of the fly ash."
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We close there since Dunstan's full exposition includes numerous tables, graphs and calculations that would bewilder all but the most astute concrete-savvy Civil engineer.
Those graphics do demonstrate, that, in Dunstan's use of finely-ground Coal Ash as a direct substitute for some of the Portland cement, the optimum substitution level, due to several factors, is about 25%.
However, with certain additives, whose cost we have no way of determining, the level of direct cement replacement, by cementitious Fly Ash, can be raised to 40% without affecting the cured cement or concrete properties.
That actually sounds pretty good, since the process outlined herein by Dunstan does productively utilize and consume at least some of what the powers that be seem to want to view as a hazardous waste, a waste that consumers of Coal-based electricity need to be financially punished for having supported the production of.
And, as we will attempt to document for you in coming reports, it might actually be feasible, on a practical basis, to produce substitutes for Portland cement, and for concrete made from that cement, that are composed in their entirety of Coal Utilization Byproducts, as is, in essence, the case with our above-cited report concerning: "United States Patent 4,256,504 - Fly Ash-based Cement".
The point of it all being that, just like Carbon Dioxide, as seen for one example in our report of:
USDOE Converts 100% of Power Plant CO2 to Methanol | Research & Development; concerning: "The Carnol Process System for CO2 Mitigation and Methanol Production; Brookhaven National Laboratory (USDOE); Abstract - The feasibility of an alternative CO2 mitigation system and a methanol production process is investigated. The Carnol system has three components: (i) a coal-fired power plant supplying flue gas CO2, (ii) the Carnol process which converts the CO2 with H2 from natural gas to methanol, (iii) use of methanol as a fuel component in the automotive sector. For the methanol production process alone, up to 100% CO2 emission reduction can be achieved";
it is reasonable to start thinking in terms of "100%" when it comes to considering how, and how much of, the valuable Coal Utilization Byproducts, arising from our essential consumption of Coal in the generation of electrical power, we can put to profitable, needed, and environmentally-beneficial, use.