United States Patent: 5681384
Among our many reports documenting the now-plain fact that Coal Ash can be productively consumed in the manufacture of Portland-type Cement and Portland-type Cement Concrete that are better-performing and more environmentally-friendly than those products made from traditional raw materials, are two focused on technologies developed, with United States Government funding, by the highly-regarded New Jersey Institute of Technology, as now accessible via:
West Virginia Coal Association | Coal Ash Can Reduce Construction Costs | Research & Development; concerning: "US Patent 5,624,491 - Compressive Strength of Concrete and Mortar Containing Fly Ash; 1997; Inventors: John Liskowitz, et. al.; Assignee: New Jersey Institute of Technology; Abstract: The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction. Such materials can ... significantly reduce construction costs. 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"; and:
West Virginia Coal Association | Coal Ash Concrete More Durable, Resists Chemical Attack | Research & Development; concerning: "US Patent 5,772,752 - Sulfate and Acid Resistant Concrete and Mortar; 1998; Inventors: John Liskowitz, et. al.; Assignee: New Jersey Institute of Technology; Abstract: 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 while maintaining acceptable compressive strength properties. 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".
In other of our reports concerning similar issues, such as:
West Virginia Coal Association | Coal Ash Used in More Than 50% of Ready Mixed Concrete | Research & Development; concerning: "'Specifying Fly Ash for Use in Concrete'; Concrete In Focus; Spring, 2008; National Ready Mix Concrete Association";
it has been noted, that, even though Concrete made with Coal Ash, upon curing, is stronger and more durable than traditional Concrete, generally speaking: "concrete containing fly ash has a slower rate of strength development", even though it "results in a higher later-age strength than with portland cement concrete".
In other words, Concrete made by incorporating a certain amount of Coal Ash is ultimately stronger and otherwise better than traditional Portland Cement Concrete, but, it does take a little longer to cure and to achieve it's final, superior properties.
That fact can be a sticking point in some applications, where the scheduling of construction activities is most often structured around long-established Portland Cement Concrete 28-day strength gain guidelines.
By way of explanation for our readers not really familiar with the chemistry of Cement and Concrete, even though Concrete seems to "set", or "harden" fairly quickly, it remains "green" for quite some extended period of time, as, even though the mass seems "solid", fairly slow chemical reactions continue within the mass, during it's "cure", that result in a gradual progression towards it's ultimate strength.
In theory, those reactions, and strength gain, go on forever at a rate that grows slower and slower; and, by convention, 28 days has been established as the time frame in which Concrete should, for all practical purposes, have achieved it's design strength for the specific application in which it's being used.
That convention allows for standardized scheduling and contracting of construction activities; and, thus, the slower strength gain of Fly Ash concrete, even though the strength it gains is ultimately higher, has led to the disqualification of it in applications where it otherwise could, and should, be used.
Herein, we learn that New Jersey Institute of Technology scientist John Liskowitz, lead named inventor of United States Patents "5,624,491 - Compressive Strength of Concrete and Mortar Containing Fly Ash" and "5,772,752 - Sulfate and Acid Resistant Concrete and Mortar", has devised a treatment to overcome that slower strength gain in Fly Ash-based Concrete, thus making it more acceptable for specification in construction designs.
As seen in excerpts from the initial link in this dispatch, with comment appended, to:
"US Patent 5,681,384 - Method for Increasing the Rate of Compressive Strength Gain in Hardenable Mixtures Containing Fly Ash
(Method for increasing the rate of compressive strength gain in hardenable mixtures containing fly ash - New Jersey Institute o)
Date: October, 1997
Inventors: John Liskowitz, et. al., New Jersey and Thailand
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 provides a method for increasing the rate of strength gain of a hardenable mixture containing fly ash by exposing the fly ash to an aqueous slurry of calcium oxide (lime) prior to its incorporation into the hardenable mixture. The invention further relates to such hardenable mixtures, e.g., concrete and mortar, that contain fly ash pre-reacted with calcium oxide. In particular, the fly ash is added to a slurry of calcium oxide in water, prior to incorporating the fly ash in a hardenable mixture. The hardenable mixture may be concrete or mortar. In a specific embodiment, mortar containing fly ash treated by exposure to an aqueous lime slurry are prepared and tested for compressive strength at early time points.
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.
(We'll interrupt here to note that the technology, or technique, being disclosed, is in no way "revolutionary"; and, we are, in fact, puzzled that it was deemed innovative enough to be awarded patent protection. It is, as you will see, and as we will attempt to explain, simple and straightforward, and, it requires nothing that isn't already being used in the Concrete blending process.)
Claims: A method for increasing the early rate of strength gain of a hardenable mixture containing fly ash comprising exposing fly ash to an aqueous slurry of an alkaline material prior to incorporation of the fly ash in a hardenable mixture, wherein the fly ash is characterized by at least 99% of the particles having a particle size (as specified and detailed).
The method ... wherein the alkaline material coats the fly ash.
The method ... wherein exposing the fly ash to the alkaline material comprises adding fly ash to a slurry of alkaline material in water, thereby forming a fly ash-alkaline material water slurry.
The method ... comprising incorporating the fly ash in a hardenable mixture by mixing the fly ash-alkaline material water slurry with cement and fine aggregate, whereby mortar is formed.
The method ... comprising incorporating the fly ash in a hardenable mixture by mixing the fly ash-alkaline material water slurry with cement, fine aggregate and coarse aggregate, whereby concrete is formed.
The method ... further comprising incorporating the fly ash exposed to alkaline material with cement in a hardenable mixture, wherein the fly ash and alkaline material is about 5% to about 60%, by weight, of cementitious materials of the hardenable mixture, wherein the cementitious materials comprise cement and fly ash.
The method ... wherein the amount of alkaline material present in the hardenable mixture is about 5% to about 50% of the amount of fly ash in the hardenable mixture, by weight.
The method ... wherein the alkaline material is calcium oxide.
A hardenable mixture comprising cement and a preformed slurry of fly ash, alkaline material and water, wherein the fly ash and alkaline material together are about 5% to about 60% by weight of cementitious materials in the hardenable mixture, wherein the cementitious materials comprise cement and fly ash ... .
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 provides a method for increasing the rate of strength gain of a hardenable mixture containing fly ash by exposing the fly ash to calcium oxide slurry or other alkaline material slurry prior to its incorporation into the hardenable mixture. The invention further relates to such hardenable mixtures, e.g., concrete and mortar, that contain fly ash pre-reacted with an alkaline material, e.g., calcium oxide (lime) slurry.
Fly ash, a by-product of coal burning power plants, 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. (And) due to the more stringent environmental regulations starting in the late 1970's, the cost of ash disposal has rapidly increased ... .
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. However, fly ash is relatively inert and the increase in compressive strength can take up to 90 days to materialize.
Also, since fly ash is just a by-product from the power industry, the quality of fly ash has always been a major concern to the end users in the concrete industry.
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, lowered heat of hydration, and increases setting times ... .
However, the use of fly ash in concrete has many drawbacks. For example, addition of fly ash to concrete results in a product with low air entrainment and low early strength development.
As noted above, a critical drawback of the use of fly ash in concrete is that initially the fly ash significantly reduces the compressive strength of the concrete. (The) compressive strength(s) of fly ash concrete at early ages are lower than those for the control concrete, which is a general property of concrete or mortar when fly ash is added. Most of the reported studies tend to show a lower concrete strength due to the presence of fly ash; none has yet suggested a solution to actually enhance the property of concrete economically. Yet, 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.
(Again, to emphasize the point: Even though Fly Ash Concrete will, ultimately, be as strong as or stronger than conventional Portland Cement Concrete, it takes too long to achieve that strength for it to be specified, on a practical basis, in many construction applications.)
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. However, the prior art concrete or mortar mixtures that contain fly ash and cement generally have lower compressive strength than concrete or mortar mixtures that lack fly ash. Therefore, there has been a disincentive to use fly ash in such hardenable mixtures.
Accordingly, there is a need in the art for a method for increasing the early rate of compressive strength gain of hardenable mixtures containing fly ash.
There is a further need in the art for such hardenable mixtures that demonstrate an early rate of compressive strength gain.
There is yet a further need in the art for the utilization of fly ash generated during coal combustion.
Summary: It has now been discovered that the rate of strength gain of a hardenable mixture comprising fly ash can be increased. Accordingly, the invention provides a method for increasing the early rate of compressive strength gain of a hardenable mixture containing fly ash comprising exposing the fly ash to an aqueous slurry of alkaline material, e.g., calcium oxide (CaO), prior to adding the slurry to cement and other components of the hardenable mixture. In particular, the fly ash is added to a slurry of calcium oxide in water, prior to incorporating the fly ash in a hardenable mixture.
The present invention further relates to such hardenable mixtures comprising cement and a preformed slurry of fly ash, alkaline material such as calcium oxide, and water, wherein the fly ash and alkaline material together are about 5% to about 60%, preferably about 10% to about 50%, and more preferably about 30%, by weight of cementitious materials in the hardenable mixture, and cement is about 95% to about 40% by weight of cementitious materials in the hardenable mixture, and wherein the percentage of alkaline material by weight of alkaline material and fly ash ranges from about 5% to about 50%. In a specific embodiment, the hardenable mixture is concrete; in another specific embodiment, the hardenable mixture is mortar. Preferably, the alkaline material is calcium oxide.
Fly ash treated by exposure to a lime slurry demonstrates increased pozzolanic properties compared to untreated fly ash, as detected by the increased early rate of compressive strength gain of hardenable mixtures containing treated fly ash. This modification of the early rate of compressive strength gain is evidence that the treated fly ash is chemically distinct from the untreated fly ash.
Pozzolan, as defined by ASTM C 593 (1990, ASTM C 593-89, Annual Book of ASTM Standards, Vol. 04.02), is 'a siliceous or alumino-siliceous material that in itself possesses little or no cementitious value but that in finely divided form and in the presence of moisture will chemically react with alkali and alkaline earth hydroxides at ordinary temperatures to form or assist in forming compounds possessing cementitious properties.'
As used herein, the term 'fly ash' refers to a solid material having a chemical composition similar to or the same as the composition of the material that is produced during the combustion of powdered coal."
-----------------------
Look, all they're doing here, before actually adding it to the Concrete, is mixing the Fly Ash with lime water, i.e., "calcium oxide, and water"; the "calcium oxide", CaO, being the primary component of Portland Cement in the first place.
They are, in a way, pre-treating, or pre-reacting, Fly Ash with a little highly-diluted Cement mixture.
Then, they're mixing the diluted mixture in with more, less-hydrated, Cement mixture, with the ultimate ratios of Water and Cement pre-calculated so that appropriate final ratios for the designed Concrete mix are achieved; and, that's all there is to it.
It falls into the general category of what, among it's various labels, is known as "Fly Ash Activation", which is itself a component of a broader technical area generically called "Fly Ash Beneficiation"; all of which are just ways to process or pre-process raw material Fly Ash so that it works better in specific applications where it's use adds value.
Another example, of different Fly Ash beneficiation technology, is introduced in our report of:
West Virginia Coal Association | Virginia Converts Coal Ash to Cash | Research & Development; concerning: "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".
And, there are quite a few others related, variously, to both the chemical activation of Fly Ash, as demonstrated by the process of our subject herein, "US Patent 5,681,384 - Method for Increasing the Rate of Compressive Strength Gain in Hardenable Mixtures Containing Fly Ash"; and, as in the "Carbon Burn-Out" technology, the removal or chemical "passivation", or neutralization, of undesirable contaminants in Fly Ash.
None of it should be seen as revolutionary; it might only seem that way to some of our readers since, in spite of all the negative press concerning Coal and the byproducts resulting from it's essential use in the generation of genuinely economical electrical power, no one in the Coal Country public press seems at all interested in educating anyone about the true, overarching value of Coal.
Nobody, even those we would have a right to expect to, cares.
But, people whom we've been led to believe are "out to get us", do care.
As we've documented on many occasions, the United States Environmental Protection Agency has studied and reported on numerous technologies for the improved and broader, more efficient and more beneficial, use of our strategic Coal resource, including the documentation of the ways in which Coal can be converted into liquid hydrocarbon fuels and technologies whereby Carbon Dioxide could be productively utilized.
And, they were, at least at one time, dedicated to helping us find ways to better use our Coal Ash; their dedication including the financing of a project to better define and improve the general process of our subject herein, as can be learned via:
Construction Material from Chemically Activated Fly Ash | Research Project Database | NCER | ORD | US EPA;
"Construction Material from Chemically Activated Fly Ash
EPA Contract Number 68D50099; September 1, 1995, through March 1, 1996
Investigators: Rostami Hossein; By-Products Research, Inc.
Description: Out of 50 million tons of fly ash generated each year in the United States, only 27% is reused or recycled. The remaining 73% is landfilled which presents potential environmental problems in the future. This projects main objective is to develop a new class of construction material from the Chemically Activated Fly Ash (CAFA) in conjunction with fine and coarse aggregates, and determine pertinent mechanical and environmental properties of the final product. The information in this investigation will provide information needed to create a production process most suitable both technically and economically. Preliminary results reveal that is material reaches compressive strength of 6,000 psi after 2 hours and an ultimate strength of 13,000 psi after one day. Typically portland cement concrete requires 28 days to reach the same strength level that CAFA material achieves after 2 hours. Economic analysis of this material indicated that the cost of this material is significantly less than comparable strength portland cement material on the market."
----------------------
Now, whatever the EPA-contracted company in the above study was using to activate their Fly Ash seems to work a tad better than the plain old Lime, Calcium Oxide, bath used by the New Jersey Institute of Technology in the subject of our report herein, "US Patent 5,681,384 - Method for Increasing the Rate of Compressive Strength Gain in Hardenable Mixtures Containing Fly Ash".
We haven't, yet, been able to acquire a copy of the full, final report of "EPA Contract Number 68D50099", although we will keep trying; an endeavor made difficult by our disability-enforced inabilities to, simply, either use the telephone with any effectiveness or to pay the long distance charges.
It's pretty clear now that the Coal Country press has little or no real interest in the Coal industry or in Coal people - - they're all still in the back room sniffing Shale Gas and making themselves giddy with the induced hallucinations about the coming Shale Gas riches, we reckon - - so we're not expecting any help from them, joyous though we would be if it unexpectedly should come.
So, we'll keep plugging along in our tedious way; and, hopefully, a few old Coal mining souls will hang in there with us. We just might, purely by accident, one of these days, fiddle around and get something positive and good, and of genuine worth, perhaps, as herein, of "concrete" value, accomplished for all of us.