We've documented from time to time that the addition of Coal Ash to Portland Cement, PC, as a component of the mix that comprises Portland Cement Concrete, PCC, can result in a final concrete composite product that has physical properties markedly superior to those of conventional PCC.
One of our reports outlining some of the benefits of using Coal Ash as a component of PCC can be accessed via;
West Virginia Coal Association | Ohio State Says Coal Ash Extends Service Life of Concrete | Research & Development; and concerns: "'Prevention of Corrosion in Concrete Using Fly Ash Concrete Mixes'; ISG Resources, Inc., Toledo, Ohio (and) The Ohio State University, Columbus; This paper reviews the benefits of using high-volume fly ash in resisting corrosion damage in concrete structures. It considers the usefulness of current fly ash concrete technology and prevention techniques, and advances a new approach for making concrete resist the deleterious effects of corrosion. ... Recent research has indicated the benefit of using fly ash in preventing corrosion damage in concrete. Reduced permeability, lower water/cement ratio, decreased drying shrinkage/cracking, and increased durability are all benefits of fly ash concrete".
The superior physical properties of PCC that incorporates a significant amount of Coal Ash in the mix evolve from reactions between metal oxides, like Calcium Oxide, that are components of the concrete mix, and added metal oxides and hydroxides, such as Sodium Hydroxide, "Lye", and the silica in the Coal Ash. And, the compounds, or composites, resulting from those Coal Ash reactions are so unique, even in some ways resembling plastics, that some have begun to label them as "Geopolymers":
Geopolymer - Wikipedia, the free encyclopedia; "Geopolymers are new materials for fire- and heat-resistant coatings and adhesives, medicinal applications, high-temperature ceramics, new binders for fire-resistant fiber composites, toxic and radioactive waste encapsulation and new cements for concrete".
There are, as a read of the Wikipedia overview will reveal, a number of mineral, and industrial byproduct, substances that can be used in the formulation of Geopolymers. However, they specifically cite the United States Patent we enclose herein as being one of the seminal expositions of the technology for utilizing Coal Ash, likely the most abundant and readily-available of the optional materials, in Geopolymer compositions.
And, since there have been some more recent developments in the technology for compounding Coal Ash Geopolymers, as an additive to or full replacement for PC and PCC, we wanted to make certain we had recorded for you one of the basic technical foundations of those developments.
As in excerpts from the initial link in this dispatch to:
"United States Patent 5,601,643 - Fly Ash Cementitious Material and Method of Making a Product
Fly ash cementitious material and method of making a product - Drexel University
Date: February 11, 1997
Inventor: Thomas Silverstrim, et. al., PA
Assignees: Drexel University, Philadelphia, and By-Products Development Company, PA
(Note that we have cited Drexel University's achievements in the productive utilization of Coal combustion byproducts previously, as in our report of:
West Virginia Coal Association | Drexel University Recycles CO2 and Cogenerates H2 | Research & Development; concerning: "United States Patent Application 20090305091 - Production and Uses of Carbon Suboxides; 2009; Inventors: Alexander Fridman, et. al., NJ; Assignee: Drexel University, Philadelphia; Abstract: Methods for the reduction of gaseous carbon dioxide emissions from combustion or oxidation reactions are provided. The various methods involve the formation of carbon suboxides and/or polymerized carbon suboxides (PCS), preferentially over gaseous carbon oxides to thereby reduce gaseous carbon dioxide emissions. The various methods can be employed for efficient generation of energy and/or hydrogen. In addition, various methods for the use of polymerized carbon suboxide are disclosed";
and, which US Patent Application, though we didn't make separate report of it, did evolve into:
"United States Patent: 7829051 - Production and Uses of Carbon Suboxides".)
Abstract: Rapid curing, high strength cementitious binder mixtures are provided containing fly ash and an alkali metal or alkaline earth metal silicate binder that has a weight ratio of Silicon Dioxide (SiO2:M2O of about 0.20:1 to about 0.75:1 wherein M is selected from the group consisting of Li (Lithium), Na (Sodium), (and) K (Potassium), 1/2Ca (Calcium) and 1/2Mg (Magnesium). The cementitious binder mixtures can be mixed with aggregates to provide mortar and concrete mixtures. Any of the binder, mortar and concrete mixtures can be cured under elevated temperatures to yield high strength products.
Claims: A high strength cementitious binder mixture comprising fly ash and an alkali metal or alkaline earth metal silicate binder, the silicate binder comprising an alkali metal or alkaline earth metal silicate component and an alkali metal or alkaline earth metal hydroxide component (as specified) and, further, wherein sufficient silicate binder is present to provide said cementitious binder mixture with a compressive strength after curing of at least about 2000 psi.
The cementitious binder mixture ... wherein M is Na and the alkali silicate component comprises an aqueous sodium silicate solution containing about 38% to about 55% sodium silicate solids content, a SiO2 :Na2O ratio of about 2:1 to about 3.22:1, and about 45% to about 62% water based on the weight of the aqueous sodium silicate solution, and the hydroxide component comprises about 25% to about 100% sodium hydroxide and up to about 75% water based on the weight of the hydroxide component.
The cementitious binder mixture ... wherein the fly ash is selected from the group consisting of Class C fly ash and Class F fly ash.
The cementitious binder mixture ... wherein the fly ash is Class F fly ash (and) wherein the Class F fly ash is present in an amount of from about 15% to about 90% based on weight of the binder mixture.
(Class F Fly Ash, as we get from burning our eastern bituminous Coal, seems preferred in this process; although, as will be seen, some Class C Fly Ash, from burning lignite Coal, is permissible as well.)
The cementitious binder mixture ... wherein the Class F fly ash is present in an amount of about 60% to about 80%, and wherein the Class F fly ash has a carbon content of less than about 6%.
(This binder can consist primarily of "Class F fly ash" from bituminous Coal; but, note that there are limits on the content of unburned Carbon. If needed, any Fly Ash with an excessive residual Carbon content could be treated via a process like that explained in our report of:
West Virginia Coal Association | Virginia Converts Coal Ash to Cash | Research & Development; concerning, in part, the news article: "Dominion Recycling Center Turns Ash to Cash;The Virginia Pilot; November, 2006; It looks like a really big igloo, or maybe an indoor skating rink. But Dominion Virginia Power says the new, domed structure next to its Chesapeake power station will make money, create jobs and help the environment. The waterfront facility, on the Elizabeth River just south of the Gilmerton Bridge, is an ash recycling center - the first of its kind in Virginia, and just the fourth in the nation. The facility acts like a big oven. It bakes black, carbon-laden fly ash into a kinder, gentler and paler byproduct that can be sold and made into concrete, roof tiling and construction blocks, among other alternative uses";
wherein Fly Ash is further oxidized, in a way which can generate useful amounts of heat energy, to reduce its content of unburned Carbon, and thereby make it more suitable for use in "concrete", etc.)
The cementitious binder mixture ... wherein the silicate component comprises about 2% to about 20% by weight of the cementitious binder mixture and the hydroxide component comprises about 2% to about 20% by weight of the cementitious binder mixture.
The cementitious binder mixture ... further comprising Portland cement in an amount of up to about 15% by weight of the binder mixture.
A cementitious mortar mixture comprising the cementitious binder mixture ... and fine aggregate (and, a) cementitious concrete mixture comprising the cementitious mortar mixture ... and a reinforcement selected from the group consisting of coarse aggregate and fibers (thus comprising a) cementitious concrete mixture (which is comprised of) about 10% to about 90% Class F Fly Ash, about 1% to about 20% sodium hydroxide component, about 1% to about 20% sodium silicate component, up to about 10% additional water, about 18 to about 85% coarse aggregate, and about 1% up to about 85% fine aggregate based on the weight of the concrete mixture.
The cementitious concrete mixture ... wherein said fiber is selected from the group consisting of steel, glass, polypropylene, carbon, and high density polyethylene.
A method of manufacture of a high strength cured cementitious product ... (wherein the) cured cementitious product (contains) sufficient silicate binder ... to provide a compressive strength in the cured cementitious product of at least about 2000 psi.
The method ... wherein the fly ash is selected from the group consisting of Class C fly ash and Class F fly ash (and) wherein the Class F fly ash is present in the composition in an amount of from about 10% to about 90% based on weight of the mixture.
A high pressure strength cementitious material comprising a heat cured reaction product of a mixture of fly ash selected from the group consisting of Class F fly ash and Class C fly ash, and an alkali metal or alkaline earth metal silicate binder wherein the silicate binder ... comprises sodium silicate and sodium hydroxide.
Background and Field: The invention generally relates to cementitious materials. More particularly, the invention relates to chemically-activated fly ash cementitious materials.
Portland cement concrete, although useful in building construction, is limited in its application due to its long curing time to attain a high compressive strength. Chemical additives, such as superplasticizers and curing accelerators added to Portland cement produce high early compressive strength but are expensive.
Fly ash which is landfilled or stored in surface impoundments presents environmental concerns associated with potential soil and ground water pollution. The art has attempted to address these concerns by admixing fly ash with Portland cement during production of concrete as a means to dispose of the fly ash.
Setting time of fly ash Portland cement blends, however, can be shortened by alkali silicates (but, a need) continues for cementitious materials which can rapidly achieve high compressive strength in shortened time periods.
Summary and Description: The invention provides rapid curing, high strength cementitious mixtures comprising fly ash and alkali metal or alkaline earth metal silicate binder, hereafter referred to as CAFA binder mixture.
Preferably, the fly ash is Class F or Class C fly ash, more preferably Class F fly ash. Preferably, the silicate binder comprises a sodium silicate component and a sodium hydroxide component (as specified).
The CAFA binder mixtures can be admixed with fine aggregates to provide CAFA mortar mixtures. The CAFA mortar mixtures can be combined with coarse aggregates, optionally with fibers, to provide CAFA concrete mixtures. Any of the CAFA binder, mortar and concrete mixtures can be cured at elevated temperatures of about 40 C to about 120 C to yield high strength products.
(The hydration reaction in curing cement/concrete mixtures, which would be occurring here if, as specified, the blend contained "Portland cement in an amount of up to about 15% by weight of the binder mixture", is exothermic; and, curing concrete can get pretty hot. Whether such would be sufficient to provide for the specified temperatures herein, with the relatively low "Portland cement" content, is unclear. Expositions of related technologies do suggest the application of steam heat, or similar. If so, application of this specific Geopolymer could well be limited to manufacturing facilities; or, outdoor construction with it would be limited to the warmest months. Such supplemental heating is indicated further on in the full Disclosure.)
The invention provides novel cementitious materials comprising fly ash mixed with alkali metal or alkaline earth metal silicate binder. The resultant CAFA binder mixture can be used alone. Alternatively, the CAFA binder mixture can be admixed with fine aggregates to provide CAFA mortar mixtures. Similarly, the CAFA mortar mixtures can be used alone, or further admixed with coarse aggregate as well as optional fibers to provide CAFA concrete mixtures. The CAFA binder mixtures, as well as the CAFA mortar mixtures and CAFA concrete mixtures, are hereinafter collectively referred to as CAFA compositions.
The CAFA compositions of the invention may employ any type of fly ash such as particulates separated from coal combustion flue gases ... . Preferably, low carbon content fly ash, that is, fly ash which has less than about 6% carbon, is employed in the CAFA compositions. More preferably, at least one of Class C fly ash and Class F fly ash, most preferably Class F fly ash, is employed ... . Class F fly ash can be obtained from combustion of bituminous and anthracite coals. Class C fly ash can be obtained from combustion of sub-bituminous and lignite coals.
Typically, fly ashes such as Class C fly ash and Class F fly ash can be present in CAFA binder mixtures in amounts of from about 10% to about 90%. Preferably, Class F fly ash is present in an amount of about 60% to about 80% by weight based on the total weight of the CAFA binder mixture. Typically, about 90% of the Class F fly ash has a particle size having a major particle dimension less than about 100 microns.
The alkali silicate component is typically used in the form of an aqueous solution (as described). Sodium silicate solutions having ratios of SiO2 :Na2O within (the specifications) are available from the PQ Corporation, Valley Forge, Pa.
The alkali hydroxide component comprises at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide and the like, preferably sodium hydroxide. The alkali hydroxide component can comprise about 25% to about 100%, preferably about 25% to about 75% sodium hydroxide, and up to about 75%, preferably about 25% to about 75% water based on the weight of the sodium hydroxide component.
CAFA binder mixtures can be made by mixing alkali silicate binder, fly ash and optional additional water. As used hereinafter, additional water is understood to mean water which is added to a CAFA composition in addition to water present in the alkali silicate binder. Special mixing procedures are not required to mix the alkali silicate binder, fly ash and additional water. The amounts of fly ash, additional water, fine aggregate and coarse aggregate, alkali hydroxide component and alkali silicate component employed to produce CAFA binder mixtures, CAFA mortar mixtures, and CAFA concrete mixtures are expressed ... as based on the total weight of those mixtures, respectively. In addition, the amount of alkali silicate component included in those compositions is expressed ... as based on the use of an aqueous alkali silicate component that is an aqueous alkali silicate solution which contains about 38% alkali silicate solids. Also, the amount of alkali hydroxide component in those compositions is ... as based on the use of an alkali hydroxide component that is a 50% aqueous alkali hydroxide solution which has about 50% NaOH solids.
CAFA binder mixtures can be prepared as described above with ... preferably about 60% to about 80% of the Class F fly ash.
Various additives may be included in the CAFA binder mixture to provide desired aesthetic properties as well as to improve strength development. Examples of these additives include but are not limited to coloring agents such as dyes. Additives useful for strength development include fine powders and aqueous solutions of multivalent compounds such as aluminates, ferrites, and calcium. These additives provide multivalent metal cations which function to decrease the solubility of the silicate structures present in the CAFA binder mixture to improve durability and weather resistance. Although slaked lime and calcareous products may be present in the CAFA binder mixture, their presence is not required.
Portland cement may be included in CAFA binder mixtures in amounts of up to about 15% by weight of the CAFA binder mixture. As used herein, Portland cement is understood to mean commercially available compositions of a calcium-based material which hardens through exothermic hydration wherein water reacts with the constituents of the cement.
(More preferably), CAFA mortar mixtures may be prepared by mixing about 45% to about 55% CAFA binder mixture and about 45% to about 55% fine aggregate.
CAFA mortar mixtures thus can be mixed to include a broad range of amounts of fly ash, additional water, alkali silicate component, the alkali hydroxide component, and fine aggregate.
CAFA concrete mixtures can be prepared by mixing a wide range of CAFA mortar mixtures, coarse aggregate and additional water. The amount of coarse aggregate in the CAFA concrete mixture is similar to the amount of coarse aggregate employed in Portland cement concrete. Useful coarse aggregates include common pebbles and stones of sizes comparable to those employed in manufacture of Portland cement concrete. Especially useful coarse aggregates are those which satisfy ASTM C-33.
CAFA concrete mixtures can thus be prepared with a broad range of amounts of fly ash, additional water, alkali silicate component, alkali hydroxide component, fine aggregate, and coarse aggregate (and) may employ fiber reinforcements. ... The type of reinforcing fibers employed depends on the properties desired in the final concrete product. For example, steel fibers can be employed to provide concrete products with increased fracture toughness.
Mixing of CAFA compositions is performed to yield a viscosity which is sufficiently low to permit conveying and casting of the CAFA compositions but high enough to prevent segregation of particulates therein. The viscosity of the CAFA compositions can be controlled by varying the amount and type of fly ash, the amounts of alkali silicate component and alkali hydroxide component in the alkali silicate binder, as well as the temperature of the alkali silicate binder. For example, increasing the amount of alkali silicate binder in the CAFA binder mixture reduces the viscosity of the CAFA binder mixture. Also, increasing the temperature of the alkali silicate binder reduces the viscosity of the CAFA binder mixture.
Any of the CAFA compositions can be cast into a variety of shapes. During casting, the CAFA compositions can be vibrated and tamped to eliminate air bubbles. Any of the cast CAFA compositions then can be heat cured to produce products having superior strength and pleasing aesthetic properties.
(A molding and curing process is described by way of example, as are experimental mixes and measured curing and physical property testing results.)
The cured CAFA compositions of the invention, as identified by X-ray diffraction, differ from unreacted fly ash. While not wishing to be bound by any particular theory, applicants believe that mixing fly ash with alkali silicate binder, and heat curing the resulting material in accordance with the invention, reduces the crystallinity of the quartz, mullite and other crystalline components of the fly ash to provide a new composition.
The foregoing (results show) that the invention provides CAFA mixtures which develop compressive strength much more rapidly than Portland cement materials (and, this) rapid strength development enables substantially increased output of production facilities.
Without wishing to be bound by any theory, the rapid increase in compressive strength during heat curing of the CAFA compositions of the invention is believed due to chemical activation and partial dissolution of fly ash within an aqueous alkali environment, as well as activation of the surface oxides of any aggregate particles present. When a CAFA composition is heat cured, the CAFA composition is believed to create a silicate gel which releases water. The released water is believed to cause polymerization of the silicates in the silicate gel to yield a stone-like matrix in which aggregate particles are integrally bound. The superior compressive strength of cured CAFA compositions is also believed due to the large amounts of aluminosilicate glass. Thus, in contrast to Portland cement, strength development is not believed to rely on slaked lime or calcareous products.
In addition to high compressive strength, the CAFA compositions of the invention also have low permeability. Permeability is an indication of the relative ease with which a material can become saturated with water, as well as the rate at which water can flow through that material.
The CAFA mixtures of the invention may be employed in a variety of applications including cast construction products such as walls, floors, roads, and the like. Other uses include linings and coatings on objects such as pipes, rebar, walls, as well as coatings on electronic components. Other additional uses include, for example, abrasives."
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We regret the lengthy presentation; but, again, the technology disclosed herein forms the basis from which other, perhaps more advanced and more versatile, technologies for the productive use and consumption of Coal Ash in the formulation of Geopolymers have been devised.
That technology disclosed herein is, as we perceive it, intended to be more of a factory-based process, wherein articles, like "pipes" and "rebar" would be made from, or coated with, a Coal Ash-based Geopolymer that would provide greater strength and much improved resistance to chemical attack and corrosion, relative to conventional Portland Cement Concrete. Although, as noted, cast-in-place structures like "floors" and "roads" are specifically named as possible applications.
In any case, as we will see in reports to follow, our subject herein, "United States Patent 5,601,643 - Fly Ash Cementitious Material and Method of Making a Product", defines and discloses a technology for the productive and profitable consumption of Coal Ash, in the formulation of Geopolymers, that laid the foundation for further developments that go well beyond the perhaps more direct use of Coal Ash as a property-enhancing additive to, or fine aggregate for, Portland Cement Concrete, as seen, for one example, in our report of:
West Virginia Coal Association | Coal Ash Concrete More Durable, Resists Chemical Attack | Research & Development; concerning, in part: "US Patent 5,772,752 - Sulfate and Acid Resistant Concrete and Mortar; 1998; 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 acid and sulfate hardenable mixtures of the invention containing fly ash comprise cementitious materials and a fine aggregate. The cementitious materials may comprise fly ash as well as cement. The fine aggregate may comprise fly ash as well as sand".