United States Patent: 5624491

We've begun to document the plain fact that the mineral residues resulting from our varied and productive uses of Coal represent a store of value that hasn't yet been widely recognized or acknowledged.

"Fly Ash", and the less-often mentioned "Bottom Ash", can be considered, for instance, as concentrated ores of various metal silicates from which the diluting "dross", i.e., Coal, has been removed; with the metals thus made more available for extraction.

One example of our reportage concerning those potentials can be accessed via the link:

Iowa Mines Metals from Coal Ash for the USDOE | Research & Development; concerning: "United States Patent 4,386,057 - Recovery of Iron Oxide from Coal Fly Ash", and, the closely related: "United States Patent 4,397,822 - Process for the Recovery of Alumina from Fly Ash".

However, much of the unsung work that has been directed toward the profitable employment of our Coal-use residuals seems to be focused on the unique composition of Coal Ash relative to it's employment in the actual making of Portland-type cement, for concrete construction, and mortar, for bonding blocks and bricks.

But, keep in mind all of that is aside from the use of Coal ash as a rather unique filler, or "aggregate", which is added to the cement once it is made, in addition to or instead of traditional sand and gravel, thus serving to help transform the cement into structural concrete.

We've previously documented such use of Coal ash in at least one application that reeks of irony, as in:

US EPA Headquarters Housed in Coal Ash | Research & Development; wherein the CertainTeed Corporation tells us 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.".

We've also documented that the US Federal Highways Administration actually recommends the use of Coal ash in concrete employed for road construction, as in:

Federal Highway Administration Recommends Fly Ash Concrete | Research & Development; wherein we learn of two independent engineering organizations' specifications for the use of Coal Fly Ash as a "mineral admixture in concrete", and are told that our "FHWA has", unbeknownst to us mere mortals "been encouraging the use of fly ash in concrete. When the price of fly ash concrete is equal to, or less than, the price of mixes with only portland cement, fly ash concretes are given preference if technically appropriate under FHWA guidelines."

One reason that "fly ash concretes are given preference" is because they can actually have improved physical properties relative to conventional concretes.

We'll have more to offer on that fact in coming reports.

But, herein, we wanted to affirm that not only can concrete supplemented with Coal Ash, indeed, meet the physical performance specifications, but, they can also offer the added benefit of a "price ... less than ... mixes with only portland cement".

Comment follows excerpts from the initial link in this dispatch to the USDOE-sponsored:

"United States Patent 5,624,491 - Compressive Strength of Concrete and Mortar Containing Fly Ash

Date: April, 1997

Inventors: John Liskowitz, et. al., New Jersey and Thailand

Assignee: New Jersey Institute of Technology, Newark

(We know that the "New Jersey Institute of Technology", NJIT, isn't too well-known in US Coal Country, especially since they haven't sent any teams to the Orange Bowl in recent memory. But, they are a very credible institution of higher learning, more about which can be learned via:

New Jersey Institute of Technology - Wikipedia, the free encyclopedia; which tells us that the: "New Jersey Institute of Technology (NJIT) is a public research university ... . It is often also referred to as Newark College of Engineering which was the official name of the university between 1919–1975. NJIT is New Jersey's science and technology university. The school opened as the Newark Technical School in 1881 with 88 students. Today (fall, 2011), the school has 9,019 students (and, is) home to six colleges including: Newark College of Engineering, the College of Architecture and Design, the School of Management, the Albert Dorman Honors College, the College of Science and Liberal Arts, and the College of Computing Sciences";

and, via:

About • NJIT; which tells us that: "NJIT offers 92 undergraduate and graduate degree programs in six specialized schools".

Thus, even though you might not have heard them mentioned on "College Game Day", they ain't the Dogpatch School of Beekeeping and Pottery Throwing; and, they likely know a little bit about engineering. So much so, in fact, that our own United States Department of Energy, as you will see, paid them to figure out some of the specifics of using Coal Ash in structural concrete.)

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.

Government Interests: The research leading to the present invention was conducted with Government support under Contract No. DE-FG22-90PC90299 awarded by the Department of Energy. The Government has certain rights in this invention.

Claims: A high early strength concrete consisting essentially of about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, about 1 to about 5 parts by weight coarse aggregate, and ...  wherein the cementitious materials comprise from about 10% to about 35% by weight fly ash and about 65% to about 90% by weight cement, wherein the fly ash (is of particle sizes specified).

The concrete ... wherein the fine aggregate comprises sand and fly ash, wherein a ratio by weight of sand to fly ash (can be) about 1:1.

The concrete ... further comprising silica fume.

A high early strength mortar consisting essentially of about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate ... wherein the cementitious materials comprise from about 10% to about 35% by weight fly ash and about 65% to about 90% by weight cement ... .

The mortar ... wherein the fly ash is wet bottom boiler fly ash (as specified).

(Thus, again, not only can we productively use the more-commonly objected-to Fly Ash, but the, "bottom boiler ash", i.e., slag, as well, as long as we run it through a common roller or ball mill and reduce it's particle size to those sizes specified by the NJIT in their full Disclosure.)

Background and Field: 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.

(There, again, the improved ultimate physical properties of concrete made using Coal Ash are noted.)

Fly ash, a by-product of coal burning power plant, is produced worldwide in large quantities each year.

It is generally more beneficial for a utility to sell its ash, even at low or subsidized prices, rather than to dispose of it in a landfill, since this will avoid the disposal cost. In the 1960's and 70's the cost of ash disposal was typically less than $1.00 per ton. However, due to the more stringent environmental regulations starting in the late 1970's, the cost of ash disposal has rapidly increased to from $2.00 to $5.00 per ton and is still rising higher. The shortage of landfill due to environmental concerns has further escalated the disposal cost.

The Environmental Protection Agency (EPA) estimated in 1987 that the total cost of waste disposal at coal fired power plants ranged from $11.00 to $20.00 per ton for fly ash and bottom ash. This increasing trend of disposal cost has caused many concerns and researchers are urgently seeking means for better utilization of fly ash. One potential outlet for fly ash is incorporation in concrete or mortar mixtures. 

Fly ash is used in concrete in two distinct ways, one as a replacement for cement and the other as a filler.

The first use takes advantage of the pozzolan properties of fly ash, which, when it reacts with lime or calcium hydroxide, can enhance the strength of cementitious composites.

Incorporation of fly ash in concrete improves workability and thereby reduces the water requirement with respect to the conventional concrete. This is most beneficial where concrete is pumped into place. Among numerous other beneficial effects are reduced bleeding, reduced segregation, reduced permeability, increased plasticity (and) lowered heat of hydration.

(Sounds better and better, don't it? However, NJIT does go on to explain, that, even though Fly Ash concrete is very good, it takes a longer time for Fly Ash concrete to develop it's full, superior structural properties. It takes a longer time to fully "cure", in other words, than plain, Portland Cement-based concrete; which can be a drawback in some construction applications.)

(But) for fly ash to be used as a replacement for cement, it must be comparable to cement in terms of strength contribution at a point useful in construction. As a practical matter, this means that the fly ash concrete must reach an acceptable compressive strength within about 2 weeks.

(Yes, even conventional Concrete does take quiet a long time to cure into it's final, high-strength form. There are actually specifications for it's curing wherein measurements are made at the 28 day mark.)

Many factors affect the size or average diameter of fly ash, including storage conditions, ash collection processes, and combustion conditions. Combustion conditions are perhaps most important, because these determine whether carbon remains in the ash or if combustion is complete.

(We've touched on the issue of Carbon remaining in the Fly Ash previously, as seen in:

Virginia Converts Coal Ash to Cash | Research & Development; concerning, in part: "South Carolina Electric and Gas Successful Application of Carbon Burn-Out (CBO) at the Wateree Station; CBO combusts residual carbon in fly-ash, producing a very consistent, low-carbon, high-quality pozzolan";

and, we will address it further in reports to follow. It is something that can readily be dealt with.)

It is critically important in construction to have concrete or mortar that predictably achieves required performance characteristics, e.g., a minimum compressive strength within 14 days. A corollary is that a construction or civil engineer must be able to predict the compressive strength of a concrete or mortar mixture after a given period of time. However, the prior art concrete or mortar mixtures that contain fly ash lack predictability with respect to compressive strength ... (and) there is a need in the art for a method of quantitatively determining the rate of strength gain of a concrete or mortar containing fly ash. 

There is a further need in the art for high strength concrete and mortar containing fly ash. 

There is yet a further need in the art for the utilization of fly ash generated during coal combustion.

Summary: In a first aspect, the present invention provides a method for predicting the compressive strength of a hardenable mixture containing cement and fly ash of a defined fineness comprising determining the contribution to compressive strength ... contributed by the cement over a given period of time, which is a function of the concentration of cement; and ... the compressive strength contributed by the fly ash of a defined fineness over a given period of time, wherein the fineness is either a distribution of fly ash particle sizes or a distribution of fly ash particle volumes. 

According to the invention, the compressive strength contributed by the fly ash of a defined fineness is a function of the fineness of the fly ash, the concentration of fly ash in the mixture, and the age of the hardenable mixture in days. 

A particular advantage of the present invention is that in a preferred aspect it provides a highly quantitative measure of fineness of fly ash, which measure can be used to accurately predict the compressive strength of a hardenable mixture at a given time. 

In a specific embodiment, the compressive strength of the hardenable mixture is determined as a percentage compressive strength of the hardenable mixture compared to a control hardenable mixture that does not contain fly ash.

In specific embodiments, the fly ash is either wet bottom boiler fly ash or dry bottom boiler fly ash, and 

In other embodiments, the fly ash content of the hardenable mixture is between about 10% to about 50% by weight of cementitious materials in the mixture, and 

In a preferred aspect of the invention, the fly ash is wet bottom boiler fly ash or dry bottom boiler fly ash, the fly ash content of the hardenable mixture is between about 10% and about 50%, and 

The hardenable mixtures of the invention advantageously have predictable compressive strengths. Preferably, the hardenable mixtures of the invention have the same or greater performance characteristics, such as compressive strength after 7 to 14 days of hardening, as a comparable hardenable mixture that does not include fly ash.

Hardenable mixtures according to the invention include, but are not limited to, concrete and mortar."

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There is, God bless 'em, even quite a lot more to it.

But, the main point is, that:

If Coal Ash is used in "concrete and mortar", according to the specifications of this "United States Patent 5,624,491", then, the resulting product will, after specified periods of time, offer at least "the same", and, perhaps, even "greater performance characteristics" than such "concrete and mortar" made only with conventional Portland-type cement and standard aggregates.

The NJIT specifies size ranges for the Coal Ash, and, some crushing/grinding and other prep would likely be required. But, as noted in our interjected comments, there are standard types of industrial equipment, various "mills", that are used for crushing stone, and we doubt that reducing poorly-consolidated chinks of Coal ash to appropriate size would add that much to the cost.

We also note, without citing our prior references, since we will be addressing the topics again specifically in the future, that, such use of Coal Ash, as a replacement for some of the typical constituents of Portland-type cement and concrete, entails further, direct and indirect, economies relative to energy consumption and Carbon Dioxide emission.

And, thus, even the solid by-products arising from our varied and productive uses of Coal represent a material resource of potentially great value that we have available to us in United States Coal Country.

They aren't, as we've been beaten into believing, a somehow noxious, or "toxic", waste we must somehow, at great expense to the Coal industry, and to the consumers of Coal-based electric power, find some way to satisfactorily dispose of.

As with the now irrefutable potentials we have documented for you concerning the facts that Coal can, cleanly and efficiently, be converted into anything we now obtain from increasingly-dear natural petroleum; and, that, Carbon Dioxide can, on a practical basis, be reclaimed and converted into similar products, we can either accept the value of the riches that lie, unappreciated and disdained, literally at our feet, and proceed towards a goal of increased prosperity and an improved environment for all of us; or, we can ignore those potentials, and, let the special interests of Big Oil and the Environmental Lobby drive us, and our children and our grandchildren, even deeper into national indebtedness and Coal Country impoverishment.

We have a lot of options, and a lot of choices we can make.

We need to get ourselves educated about all of them; and, then, start selecting the right options and making the right choices, which include, as certified to be feasible and practical herein, utilizing our Coal Ash as a major component of structural concrete, a practice that would, among other things, as affirmed by our own United States Department of Energy and their contractors, "significantly reduce construction costs".


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