http://www.nrmca.org/research/
Aside from the potentials for actually using the solid byproducts of Coal combustion as raw materials for making of Portland-type Cement, as demonstrated, for just one example, in our report of:
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; Dravo Lime Company, Pittsburgh; Cement is produced (from) a moist mixture of a flue gas desulfurization process waste product (and) aluminum, iron, silica and carbon, ... wherein said source of aluminum and iron comprises fly ash";
we've also seen that Coal Ash can be added to Portland cement, once the cement has been made from whatever raw materials, as a reactive aggregate, in place of some of some or all of the sand, wherein, acting as what is known as a "pozzolan", or, more plainly and as more commonly labeled, a "Supplemental Cementitious Material", or "SCM", Coal Ash reacts with the cement to help form a stronger and more durable concrete.
An example of our reportage documenting that fact can be accessed via:
West Virginia Coal Association | Coal Ash Concrete More Durable, Resists Chemical Attack | Research & Development; concerning: "United States Patent 5,772,752 - Sulfate and Acid Resistant Concrete and Mortar; 1998; Assignee: New Jersey Institute of Technology; The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction and other applications, which hardenable mixtures demonstrate significant levels of acid and sulfate resistance".
Much of that is, in fact, known by the cement and concrete industries; even if we producers of Coal, and, as a somewhat indirect consequence, of Coal Ash, seem oddly to prefer to remain stubbornly unaware of it.
First, by way of preface, we introduce you to:
NRMCA | About NRMCA; "Founded in 1930, the National Ready Mixed Concrete Association is the leading industry advocate. Our mission is to provide exceptional value for our members by responsibly representing and serving the entire ready mixed concrete industry through leadership, promotion, education and partnering to ensure ready mixed concrete is the building material of choice".
And, the NRMCA is quite serious about the "leadership" and "education" parts of their mission statement.
For instance, they aren't shy, as we miners of Coal seem to be, about openly discussing and promoting the use of Coal Ash in Portland Cement Concrete, as seen in an article from their own trade magazine, as excerpted from the initial link in this dispatch to:
"'Specifying Fly Ash for Use in Concrete'; Concrete In Focus; Spring, 2008; Karthik H. Obla, Ph.D., P.E.
Managing Director, Research & Materials Engineering, NRMCA
(NRMCA Research & Engineering Department; Karthik Obla; Vice President, Technical Services.)
Over the past several decades, the use of fly ash in concrete has had a successful track record.
The performance benefits fly ash provides to mechanical and durability properties of concrete have been well researched and documented in actual structures.
Currently, fly ash is used in more than 50% of all ready mixed concrete placed in the United States, yet many design professionals continue to remain overly restrictive when it comes to using fly ash in concrete.
This article addresses some optimal ways of specifying fly ash for use in concrete while ensuring that the desired concrete performance is achieved. Most of these recommendations form part of a larger NRMCA publication that should be released later in 2008. Project specifications for most commercial work in the United States are typically written as per American Institute of Architects MasterSpec format. Any cementitious material is typically addressed under Section 2.5 (Concrete Materials) of that format as follows. Cementitious materials: Use materials meeting the following requirements: Hydraulic Cement: ASTM C150 or ASTM C1157 or ASTM C595; Pozzolan or Fly Ash: ASTM C618; Slag: ASTM C989.
The above format clearly states that fly ash has to meet ASTM C618, which is the standard specification for coal fly ash and raw or calcined natural pozzolan for use in concrete. This by itself is adequate for specifying fly ash in concrete.
Frequently, design professionals make it more complicated and too restrictive. Some of these restrictions, the possible rationale behind them and issues related to not having these restrictions are discussed below.
Limitations on quantity of fly ash: This is perhaps the most frequently applied restriction governing the use of fly ash in a concrete specification. When fly ash was originally used in concrete in the 1970s, there was some basis for restricting its use. However, after extensive research and several decades of successful utilization of fly ash, there is no basis for a restriction on the quantity of fly ash that should be permitted to be used in concrete.
(As seen in our report of:
West Virginia Coal Association | State Governments Specify Use of Coal Ash | Research & Development; concerning: "Engineering and Environmental Specifications of State Agencies for Utilization and Disposal of Coal Combustion Products: Volume 1 – DOT Specifications; 2005;
even in the hearts of US Coal Country, with the shining exception of Pennsylvania, the amount of Coal Ash which can be used in state-contracted Cement and Concrete mixes, sadly, and inexplicably, is limited by just such unwarranted "restriction on the quantity of fly ash ... permitted to be used in concrete".)
The primary reason for these limits in the Building Code is to minimize the potential for deicer-related surface scaling that can subsequently compromise the concrete cover over reinforcement and initiate corrosion
earlier than expected. There is no technical reason to extend this maximum 25% limit for other applications. It is seen that for adequate resistance to alkali silica reaction (ASR) with some types of aggregate and for sulfate resistance, more than 25% of fly ash frequently is required.
(In other words, more Fly Ash than is allowed by some specifications would result in better performance of the concrete, insofar, at least, as greater "resistance to alkali silica reaction" is concerned.)
Prescriptive limits on fly ash amounts do not help concrete performance in any way and may actually limit the improvement in concrete durability.
Also, with greater quantities of fly ash, the durability of concrete related to resistance to ASR, sulfate attack
and chloride-induced corrosion is further enhanced. Further, the use of fly ash in concrete supports sustainable construction.
LOI is a measure of unburnt carbon in fly ash. Certain forms of unburnt carbon can absorb air-entraining admixtures and affect air entrainment of concrete. So, some may argue that by restricting LOI contents,
the air-entrainment problems due to fly ash can be reduced. However, that is inaccurate.
The issue is not the LOI but rather the variability of carbon content and type at a given source.
(As can be learned in our reports of:
West Virginia Coal Association | Virginia Converts Coal Ash to Cash | Research & Development; which concerns, in part: "South Carolina Electric and Gas Successful Application of Carbon Burn-Out (CBO) at the Wateree Station; 1999; South Carolina Electric and Gas Company; CBO combusts residual carbon in fly ash, producing a very consistent, low-carbon, high-quality pozzolan";
and, as we will document in more reports to follow, there exist effective technologies for the economical removal of any objectionable "unburnt carbon" in Coal fly ash)
In general, concrete containing fly ash has a slower rate of strength development and often results in a higher later-age strength than with portland cement concrete.
In some projects, there may not be a need for a 28-day strength requirement for members or classes of concrete that will not have anticipated construction or service loads applied at 28 days. For example, specifying 8,000-psi compressive strength to be achieved at 56 instead of 28 days for columns will result in highly optimized mixtures. A later-age strength requirement when feasible will permit a higher quantity of supplementary cementitious materials, reduce the total cementitious content (paste volume) and therefore reduce the potential for cracking while improving long-term concrete durability.
(The "28-day strength requirement" is a standard measure of concrete performance, and construction projects are scheduled around it. Adding another 28 days to it would, we imagine, cause some difficulties in some projects, especially in northern areas of the country, where the seasons dictate the time periods actually available for construction; and, in applications where time limitations on traffic and utility must be kept to a minimum. However, since Coal Ash concrete actually performs better and lasts longer, it would seem conceivable that, in most cases, it would be worth whatever extra effort is needed to accommodate such a "later-age strength requirement". The real issue here might be re-education of the design and specifying engineers; coupled, perhaps, with formalized requirements for use of recycled materials.)
For concrete exposed to chlorides (deicing chemicals, marine exposure), it is well known that fly ash, silica fume and slag can increase resistance to deterioration related to the corrosion of reinforcing steel by reducing chloride ion penetrability of concrete, with increasing levels typically leading to improved performance."
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Actually, we wondered if the United States Navy were aware that Coal Ash used at "increasing levels" in concrete subject to "marine exposure" leads "to improved performance"; and, if so, if they were specifying their construction projects accordingly. That, especially, again, since "increasing levels" of Coal Ash in the concrete "typically" does lead "to improved performance".
As it happens, some US Navy scientists are well aware of the fact, and, as we will document in a report or two to follow, are actively promoting changes in what they see as overly-conservative restrictions on the use of Coal Ash in concrete, as might be embodied in the above-noted "ASTM C150 or ASTM C1157 or ASTM C595; Pozzolan or Fly Ash: ASTM C618; Slag: ASTM C989" specifications.
At least two Navy research facilities have confirmed that increased levels of Coal Ash in concrete do lead to improved performance, and have begun lobbying to be allowed to use more of it, again as we will document in a future report or two.
In any case, Karthik Obla; Vice President, Technical Services, of the National Ready Mixed Concrete Association, herein confirms, that, the blending of Coal Utilization Byproducts into Portland Cement Concrete mixes can improve the concrete's overall performance, with some caveats concerning the time it takes for concrete incorporating Coal Ash to fully set and achieve design strength.
He states, that "fly ash is used in more than 50% of all ready mixed concrete placed in the United States, yet many design professionals continue to remain overly restrictive when it comes to using fly ash in concrete", and, it should be both pleasing to Coal Country partisans to learn that so much Coal Ash is being used, but, since such use of Coal Ash can lead to "improved performance" of the resulting concrete, and, since we keep hearing public broadcast news about the dangers, and proposed laws penalizing our Coal-use industries, and by consequence their customers, for the production of Coal Ash, maybe we Coal Country partisans need to start thinking about getting off our cans and kicking the cans of our Coal Country press and Coal Country politicians, to make certain the news of the true value of Coal Ash gets out there.
A commendable start has been made, as seen in:
Coal Residuals Reuse and Management Act (H.R. 2273) - GovTrack.us; "H.R. 2273: Coal Residuals Reuse and Management Act; 112th Congress, 2011–2012; To amend subtitle D of the Solid Waste Disposal Act to facilitate recovery and beneficial use, and provide for the proper management and disposal, of materials generated by the combustion of coal and other fossil fuels. Sponsor: Rep. David McKinley [R-WV1]; Status: Passed House"; and, in:
McKinley coal ash bill added to transportation bill as amendment - Business, Government Legal News from throughout WV; "McKinley coal ash bill added to transportation bill as amendment. With its bill delegating the regulation of coal ash to the states stalled in the Senate, the House of Representatives added it on April 18 as an amendment to the Surface Transportation Extension Act".
But, we're willing to bet that a great majority of the Coal Country public remains unaware of it; and, we need to do more. We all need to do a lot more.
Coal Ash might, as the National Ready Mixed Concrete Association herein states, now be utilized in something more than 50% of the concrete currently being produced in the United States of America.
Our goal should be 100%.