EP2536669A2

EP2536669A2 - Modification of pozzolanic chemistry at production plant

Info

Publication number: EP2536669A2
Application number: EP11745283A
Authority: EP
Inventors: Andrew S. Hansen; John M. Guynn
Original assignee: Sybre Ltd
Current assignee: Sybre Ltd
Priority date: 2010-02-17
Filing date: 2011-02-17
Publication date: 2012-12-26
Also published as: WO2011103371A2; EP2536669A4; WO2011103371A3

Abstract

Modified pozzolans and methods for making modified pozzolans that have desired chemical characteristics. The desired chemical characteristics are achieved by introducing one or more supplementary materials into the production plant that produces the pozzolans (e.g., usually as a waste material such as fly ash or slag). The supplementary material is incorporated into the pozzolan during its formation in the production plant and becomes an integral chemical constituent of the pozzolan. By forming the pozzolan with the desired characteristics in the production plant, the pozzolan can have optimal performance when blended with Portland cement for use in concrete.

Description

MODIFICATION OF POZZOLANIC CHEMISTRY AT PRODUCTION PLANT

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to pozzolans used in making blended cements and concrete. 2. Relevant Technology

[0002] In modern concrete, pozzolans such as fly ash and volcanic ash are often used to replace a portion of Portland cement. Replacing a portion of Portland cement with pozzolan yields improved concrete with higher durability, lower chloride permeability, reduced creep, increased resistance to chemical attack, lower cost, and reduced environmental impact. Pozzolans react with excess calcium hydroxide released during hydration of Portland cement and therefore help prevent carbonation. However, there is a limit to how much Portland cement can be replaced with pozzolan because pozzolans generally retard strength development.

[0003] Pozzolans are usually defined as materials that contain constituents which will combine with free lime at ordinary temperatures in the presence of water to form stable insoluble CSH compounds possessing cementing properties. Pozzolans can be divided into two groups: natural and artificial. Natural pozzolans are generally materials of volcanic origin, but include diatomaceous earths. Artificial pozzolans are mainly products obtained by heat treatment of natural materials such as clay, shale and certain siliceous rocks, and pulverized fuel ash (e.g., fly ash).

[0004] Two classes of fly ash are defined by ASTM C-618: Class F and Class C. The chief difference between these classes is the amount of calcium, silica, alumina, and iron content in the ash. Class F fly ash typically contains less than 10% lime (CaO); Class C fly ash generally contains more than 20% lime (CaO). The chemical properties of fly ash are largely influenced by the chemical content of the coal burned (i.e., anthracite, bituminous, or lignite). SUMMARY

[0005] Disclosed herein are pozzolans and methods for making pozzolans that have desired chemical characteristics. The desired chemical characteristics are achieved by introducing one or more supplementary materials into the production plant that produces the pozzolans (e.g., usually as a waste material such as fly ash or slag). The supplementary material is incorporated into the pozzolan during its formation in the production plant and becomes an integral chemical constituent of the pozzolan. By forming the pozzolan with the desired characteristics in the production plant, the pozzolan can have optimal performance when blended with Portland cement for use in concrete.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a flow diagram of a method for modifying a pozzolan in a production plant according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Except as otherwise specified, percentages are to be understood in terms of weight percent. It will be appreciated, however, that where there is a significant disparity between the density of the hydraulic cement and that of the pozzolan, adjustments can be made so that an equivalent volume of pozzolan is added in place of a similar volume of hydraulic cement being replaced. For example, the correct weight of pozzolan replacement may be determined by multiplying the weight of cement reduction by the ratio of the pozzolan density to the cement density.

[0008] With reference to Figure 1, in one embodiment a method for producing a pozzolan having a desired chemical composition for use with Portland cement includes (i) combusting a hydrocarbon fuel in a burner of a power plant, where the hydrocarbon fuel and the power plant are configured to produce fly ash; (ii) introducing a supplemental calcium bearing material (e.g., limestone, quicklime, or slaked lime) into the burner of a power plant to produce a modified fly ash having a desired calcium oxide content, where the desired calcium oxide content is greater than the calcium oxide content of fly ash produced by combusting the hydrocarbon fuel in the power plant in the absence of the supplemental calcium bearing material; (iii) recovering the modified fly ash from the power plant; and (iv) providing the modified fly ash to a user for use in concrete (e.g., for blending with Portland cement).

[0009] It will be understood that fly ash can be further modified by adding additional supplemental materials to modify a different chemical aspect of the fly ash so as to be useful when used to replace a portion of Portland cement in concrete (e.g., aluminate, iron oxide, magnesium oxide, alkali oxide, sulfate, and the like). In addition, other pozzolanic materials can be modified in similar manner by introducing a supplemental material into the production plant, such as by adding a calcium bearing or other supplemental material to a blast furnace or basic oxygen furnace that produces slag as a waste product or a heater used to calcine metakaoline or other natural pozzolan.

[0010] The hydrocarbon to be combusted can be any hydrocarbon that has a mineral component that when combusted in a burner of a power plant will produce a finely divided mineral component such as, but not limited to, fly ash and/or bottom ash. For example, the hydrocarbon fuel may be coal or a biomass such as rice husk hulls, corn husks, wood chips, or refuse. The minerals provided by the hydrocarbon fuel may be primarily silica and can include other constituents such as calcium, aluminum, iron, sulfates, alkali, and the like. The present invention relates to producing a modified pozzolan by adding other mineral components that change the content and ratios of the minerals naturally occurring in the pozzolan produced only from the hydrocarbon fuel (e.g., coal), from ore (e.g., GGBFS from iron ore), or from refining crude reduced metal (e.g., slag from refining pig iron).

[0011] The modified pozzolan may be produced by selecting a desired calcium oxide or other mineral content and introducing the calcium bearing and/or other supplemental material in quantities that will produce a pozzolan with the desired calcium or other mineral content. In many cases, the particular calcium content in the modified pozzolan can be critical to the performance of the modified pozzolan when blended with Portland cement and/or used in concrete. The calcium oxide content alone or in combination with other mineral constituents in the Portland cement can affect set times, heats of hydration, sulfate resistance, early and long term strength, and other properties important to performance of blended cements and concrete. By modifying the calcium oxide and/or other mineral content in the production plant (e.g., coal fired burner, blast furnace, basic oxygen furnace, or calciner), a pozzolan material with desired properties for use with Portland cement can be achieved.

[0012] To modify the calcium content, a calcium bearing mineral or other material is introduced into the burner of a power plant. The calcium bearing material may be any material that can melt and/or decompose in the burner and/or flue gas and combine with melted minerals from the hydrocarbon fuel to produce a pozzolanic material. The calcium producing mineral may be, for example, limestone or burnt lime, which are generally readily available and economical. Another material that can be used if an economical source is available is slaked lime.

[0013] The calcium bearing material (or other additive mineral as described below) is incorporated into the pozzolan at the production plant (e.g., the coal fired burner, blast furnace, basic oxygen furnace, or calciner). This method is in contrast to existing technology that modifies the fly ash after it has been recovered from the power plant (i.e., after the electrostatic separator). By modifying the chemical composition of the pozzolan in the production plant, the pozzolan particles can have a more homogenous chemistry as compared to other treatments carried out on the solidified particles. Moreover, handling costs may be significantly reduced by modifying the chemistry in the production plant because no additional handling or drying is required.

[0014] The process flow for a hydrocarbon fuel such as coal typically begins with preparation of the feed material (e.g., comminution), introduction of the prepared feed into the burner with oxygen to produce a combusted exhaust or flue gas, heating water in a boiler using the combustion gases, and then processing the flue gas to remove particulates such as fly ash. The pozzolan (e.g., fly ash) can be obtained using an electrostatic precipitator or other suitable means for separating fine particles from flue gas. GGBFS and steel slag are alternatively obtained by appropriately cooling and solidifying the hot slag to maintain pozzolanic activity and grinding the solidified slag. [0015] The calcium bearing material may be introduced into the power plant with the feed material, in the hydrocarbon burner, or in the flue gas after the burner. The particular location will depend on where the modified pozzolan is generated. For example, where calcium oxide is desired in the bottom ash, it may be desirable to add the calcium oxide or other additive mineral to the feed. Where the calcium oxide or other mineral is desired in the fly ash, the mineral may be added after the boiler, but before the electrostatic separator.

[0016] The amount of calcium bearing material introduced into the power plant will depend on the amount of calcium oxide desired in the modified pozzolan. The desired calcium oxide content can be in a range from 2%-60%. In some embodiments, the calcium bearing material is added in sufficient quantities to produce a modified pozzolan with at least 5%, 10%, 15%, 20%>, 35%, 45% calcium oxide by mass. The calcium oxide content may also be below 60%, 50%, 45%, 35%, 20%, 15%, 10% or any combination of ranges from the foregoing lower and upper limits of calcium oxide content.

[0017] The particular desired amount of calcium oxide will depend on many different factors, including the amount of calcium oxide and other minerals already in the hydrocarbon fuel, the cost of the calcium producing mineral, heat requirements of the burner, furnace or calciner, and the particular cement, aggregates, and admixtures that the pozzolan will be blended with in making blended cement and/or concrete. Preferably the calcium content in the modified pozzolan is selected for a desired performance with a particular Portland cement fraction.

[0018] The increase in the calcium oxide content can be at least 2%, 5%, 10%, 15%, 25%, 35%, or 45% and optionally less than 60%, 50%, 45%, 35%, 20%, 15%, or 10% relative to the unmodified pozzolan produced in the absence of supplemental calcium.

[0019] In one embodiment, the modified pozzolan can have at least 20% calcium oxide and/or be a Class C pozzolan according to ASTM C618-03 and where, without introducing the calcium producing mineral, the hydrocarbon fuel when combusted would produce a pozzolan with less than 10% calcium oxide and/or qualify as a Class F fly ash under ASTM C618-03. [0020] In one embodiment, the calcium bearing material and/or other supplemental material is selectively metered into power plant burner, furnace, or calciner on a continuous or semi-continuous basis according to the amount needed to achieve the desired calcium oxide and/or other mineral content of the modified pozzolan and/or a blended cement made therefrom. To determine the amount of calcium bearing material to be added, the mass flow of the pozzolanic material may be calculated, the amount of endogenous calcium oxide may also be determined, and an appropriate amount of calcium bearing material is added to achieve the desired calcium oxide content.

[0021] The mass flow can be determined using any technique suitable for calculating the rate at which pozzolan will be produced. The mass flow can be determined from the feed, the amount of pozzolan in the flue gas, and/or the amount of pozzolan being collected at the electrostatic separator, for example. The amount of native calcium already in the pozzolan from the feed material can be determined by performing a chemical analysis of the feed material or the pozzolan (while adding no additional calcium oxide or subtracting the amount of calcium oxide added). Examples of suitable chemical analyzers include XRF and XRD analyzers.

[0022] Alternatively or in addition to modifying pozzolan to achieve a desired calcium oxide content, the pozzolan can be modified at the production plant to produce a modified pozzolan having one or more chemical characteristics including a desired tricalcium aluminate content, a desired tricalcium silicate content, a desired sulfate content, a desired iron content, a desired alkali content, or a desired ratio of two of these.

[0023] Modification of these alternative chemical characteristics can be carried out by adding an alternative or second supplemental material. This method can be performed in the same manner as described herein with regard to achieving a desired calcium oxide content except that the second supplemental material is selected to modify the content of the alternative or second mineral characteristic. For example, where the chemical characteristic is tricalcium aluminate, the mineral component may be bauxite or an aluminosilicate with a relatively high aluminate content compared to the native pozzolan producing feed material. If the chemical characteristic is sulfate, the supplemental material may be gypsum or other suitable source of sulfate. Where the chemical characteristic is an iron mineral compound, the supplemental material may be iron oxide or other suitable iron compound. Other desired chemical characteristics may be achieved and/or monitored in a similar manner as described above with respect to calcium oxide except that the detection and/or monitoring in the modified pozzolan is carried out with respect to the particular chemical characteristic being modified.

[0024] In the foregoing embodiments, the calcium bearing material and or the alternative or second supplemental material may be added in any form. However, to ensure rapid incorporation of a desired mineral into the pozzolan formed in the power plant or other production facility, the materials are preferably provided as finely divided powders. In one embodiment, the average particle size of the supplemental materials is less than 200 microns, less than 100 microns, less than 75 microns, or even less than 50 microns.

[0025] In one embodiment, the particle size distribution of the pozzolan fraction can have a distribution similar to distributions typical of fly ash (e.g., 0.1 to 100 microns). In other embodiments, the particle size distribution of the modified pozzolan can be similar to that of the larger particle fractions found in OPC (e.g., 10-45 μιη). According to one embodiment, the dl5, dlO, d5 or dl of the pozzolan particles is at least about 3 μιη, at least about 5 μιη, at least about 10 μιη, at least about 15 μιη, or even at least about 20 μιη. The pozzolan fraction can also have a desired narrow distribution in which the d80, d85, d90, d95, or d99 is less than about 120 μιη, preferably less than about 100 μιη, more preferably less than about 80 μιη, even more preferably less than about 60 μιη, and most preferably less than about 45 μιη.

[0026] The particle size of perfectly spherical particles is measured by the diameter. While fly ash is generally spherical owing to how it is formed, Portland cement and pozzolan particles may be non spherical. Thus, the "particle size" shall be determined according to accepted methods for determining the particle size of ground or other otherwise non spherical materials, such as Portland cement and many pozzolans. The size of particles in a sample can be measured by visual estimation or by the use of a set of sieves. Particle size can be measured individually by optical or electron microscope analysis. The particle size distribution (PSD) can also be determined or estimated by laser diffraction.

[0027] Notwithstanding the foregoing, a small percentage of fine pozzolan particles (e.g. , about 0.1-3 μιη) may be desirable to help disperse the fine cement particles, increase fluidity, increase early concrete strength, and increase concrete density. All things being equal, particles that are more spherical or uniform can reduce water demand, which means that such particles can be smaller on average compared to more jagged particles while providing the same or lower water demand. On the other hand, more jagged particles with higher surface area may be more reactive.

[0028] The present invention also includes methods that can be used alone or in combination with a detector to control the chemical variation in the pozzolan fraction of a blended cement. In this embodiment, the chemical composition of the pozzolan is measured over time to produce a series of measurements that reveal the chemical variation of the pozzolan. Typically, the measurement will be made using an analyzer such as an XRD and/or XRF instrument. In some embodiments, the "effective chemical content" can be approximated or measured. As discussed above, the chemical reactions that occur in the hydration of cement are most directly related to the availability of the chemical constituents (e.g., silicates, aluminates, ferrates, calcium oxide, etc) on the surface of the particles. Thus, particles that have substantially different surface areas may have the same vol% or mass% of a particular chemical constituent yet provide very different "effective chemical content." Similarly, pozzolan and cement materials that have very different vol% or mass% of a particular constituents may perform similarly if they have a similar "effective chemical content" (also referred to herein as "effective chemical concentration"). For purposes of this invention, the term "effective chemical content" refers to a percentage of a chemical constituent in the blended cement or a fraction thereof where the percentage accounts for the surface area of the particles of that fraction. The "effective content" can be a direct measurement of the chemical constituent on the surface of the fraction (e.g., using a microscope) or may be an approximation of the effective amount using the surface area of the fraction to mathematically adjust for the difference in the availability of the chemical constituent (or similar approximation technique). The effective chemical content can be used to determine the proper blending of one or more pozzolan fractions, one or more hydraulic cement fractions, and/or one or more chemical admixtures to make a blended cement with a desired reactivity based on the surface area of chemical constituents available for reaction.

[0029] After detecting the variation, the variation can be mitigated by adding a calcium bearing material and/or other supplemental material as described above. In one embodiment, the difference in variation of the calcium content, effective calcium content, and/or calcium reactivity of a modified pozzolan fraction and/or a blended cement produced using any of the methods described herein is less by at least 1% in over a period of 1 month, more preferably over a period of 1 week, and most preferably over a period of 1 day. More preferably the difference in variation of the calcium content and/or effective calcium content, and/or chemical reactivity of the calcium is less by at least 2%, 3%, 4%, or 5% over a period of 1 month, 1 week, or 1 day as compared to not chemically modifying the pozzolan fraction and/or blended cement. The decrease in variation can also be measured according to the maximum variation in the pozzolan fraction or blended cement. In one embodiment, the maximum variation in the calcium content or effective calcium content, and/or in a one month period (more preferably a one week period, or even a one day period) is less than 10%, 5%, 4%, 3%, 2%, or 1% by volume, weight, or unit of reactivity.

[0030] In some embodiment, the amounts and ratios of the different pozzolans, different cements, and/or chemical agents to be added or combined are controlled in part using a computer module running computer executable instructions. The computer module receives a series of measurements from the chemical analyzer and detects variation in the pozzolan fraction and/or blended cement by comparing the readings to a concentration parameter. The concentration parameter can be a fixed numerical value for a particular chemical constituent (e.g., CaO, sulfate, aluminate, tricalcium silicate, iron oxide, or the like). The computer module can then calculate the ratios and/or amounts of pozzolan, cement, and/or chemical agents to be mixed to achieve a desired concentration, desired effective concentration, and/or desired chemical reactivity based on the deviation of an actual measurement from the concentration parameter.

[0031] The control module can manipulate the pozzolan fraction and/or blended cement upstream from the chemical analyzer and/or downstream from the chemical analyzer. If the control module modifies the pozzolan fraction and/or blended cement upstream from the chemical analyzer, the control module can continue making an adjustment until the actual chemical reading by the analyzers shows that the chemical composition is within a desired range of the concentration parameter. Alternatively or in addition, the modification can occur downstream from the control module.

[0032] The control module can be configured to operate conveyors, injectors, fans, feed hoppers, comminution equipment, blenders, and the like to achieve the desired modification in the content, effective content, and/or chemical reactivity of a chemical constituent of the pozzolan fraction and/or blended cement (described below), thereby reducing the chemical variability thereof.

Blended Cements

[0033] The present invention also includes methods for making a blended cement from the modified pozzolan and a hydraulic cement fraction. The blended cements can take the place of ordinary Portland cement (e.g., Type I, II, III, IV and V cements) used in both common and high end construction.

[0034] The inventive pozzolan cement blends include a desired composition and/or particle size distribution for achieving an optimized blended cement. Examples of methods for optimizing cement can be found in Applicant's U.S. Provisional Patent Application Number 61/305,423, filed February 17, 2010, U.S. Provisional Patent Application Number 61/324,741 , filed April 15, 2010, U.S. Provisional Patent Application Number 61/365,064, filed July 16, 2010, U.S. Provisional Patent Application Number 61/413,966, filed November 15, 2010, U.S. Provisional Patent Application Number 61/418,264, filed November 30, 2010, and U.S. Provisional Patent Application Number 61/429, 138, filed January 1 , 201 1 , the disclosures of which are incorporated herein by reference. [0035] For example, the cement fraction can be highly reactive and include unique distribution of pozzolan and hydraulic cement particles in which the larger sized particles comprise mostly or exclusively pozzolan and the smaller sized particles comprise mostly or exclusively hydraulic cement. The cement fraction can also be made to be highly reactive by increasing the C₃S content (e.g., greater than 57% or 59%>) and/or C₃A content (e.g., greater than 5% or 8%) of the hydraulic cement fraction as compared to traditional hydraulic cements. The pozzolan fraction can be manufactured in the production plant to have a desired chemical composition for optimal performance with a particular cement fraction. Using the techniques described above, the calcium oxide content, the aluminate content, iron content and/or sulfate content can be adjusted in the pozzolan production plant to ensure desired properties such as early strength, heat of hydration, set time, and/or color when blended with the Portland cement fraction and/or used in concrete.

[0036] The cement fraction of a blended cement can be manufactured in conjunction with producing a pozzolan with a desired chemical composition in a production plant. The Portland cement fraction can be configured for use with a modified fly ash by comminuting, classifying, and/or modifying the chemistry of the hydraulic cement fraction to have a desired particle size distribution, desired chemical composition, and/or a desired consistency in chemical properties and/or particle size for use with the modified pozzolan.

[0037] The modified hydraulic cement fraction and the pozzolan fraction are blended together to produce a blended pozzolan cement having a desired particle size distribution and strength developing properties.

[0038] "Portland cement" commonly refers to a ground particulate material that contains tricalcium silicate ("C₃S") ("alite"), dicalcium silicate ("C₂S") ("belite"), tricalcium aluminate ("C₃A") and tetracalcium aluminoferrite "(C₄AF") ("celite") in specified quantities established by standards such as ASTM C-150 and EN 197. The term "hydraulic cement", as used herein, shall refer to Portland cement and related hydraulically settable materials that contain one or more of the four clinker materials (i.e., C₂S, C₃S, C₃A and C₄AF), including cement compositions which have a high content of tricalcium silicate, cements that are chemically similar or analogous to ordinary Portland cement, and cements that fall within ASTM specification C- 150-00.

[0039] In general, hydraulic cements are materials that, when mixed with water and allowed to set, are resistant to degradation by water. The cement can be a Portland cement, modified Portland cement, or masonry cement. "Portland cement", as used in the trade, means a hydraulic cement produced by pulverizing cement clinker particles (or nodules), comprising hydraulic calcium silicates, calcium aluminates, and calcium aluminoferrites, and usually containing one or more forms of calcium sulfate as an interground addition. Portland cements are classified in ASTM C-150 as Type I II, III, IV, and V. Other hydraulically settable materials include ground granulated blast-furnace slag, hydraulic hydrated lime, white cement, calcium aluminate cement, silicate cement, phosphate cement, high-alumina cement, magnesium oxychloride cement, oil well cements (e.g., Type VI, VII and VIII), and combinations of these and other similar materials. In a preferred embodiment, the Portland cement has a chemical composition according to ASTM C-150 for Type I, II, III, or V cements, which tend to have beneficial properties for the ready mix industry.

[0040] Portland cement is typically manufactured by grinding cement clinker into fine powder. Various types of cement grinders are currently used to grind clinker. In a typical grinding process, the clinker is ground until a desired fineness is achieved. The cement is also typically classified to remove particles greater than about 45 μιη in diameter, which are typically returned to the grinder for further grinding. Portland cements are typically ground to have a desired fineness and particle size distribution between 0.1-100 um, preferably 0.1 -45 μιη. The generally accepted method for determining the "fineness" of a Portland cement powder is the "Blaine permeability test", which is performed by blowing air through an amount of cement powder and determining the air permeability of the cement. This gives an approximation of the total specific surface area of the cement particles and also a rough approximation of the particle size distribution, which is related to the specific surface area. [0041] In one embodiment the d85, d90, d95 or d99 of the hydraulic cement particles may be less than about 30 μιη, or less than about 25 μιη, or less than about 20 μιη, or less than about 15 μιη, or less than about 10 μιη, or less than about 7.5 μιη, or even less than about 5 μιη. In one embodiment, the d5, dlO, dl5, or d20 of the hydraulic cement may be greater than 0.6 micron, greater than 1 micron, or even greater than 2 microns.

[0042] In one embodiment, the tricalcium silicate content of the hydraulic cement may be greater than about 50%, preferably greater than about 57%, more preferably greater than about 60%, and most preferably greater than about 65%. The hydraulic cement may advantageously include a higher concentration of tricalcium silicates as compared to OPC because excess lime released therefrom does not remain as interstitial portlandite (Ca(OH)₂), as in concrete made using 100% OPC, but reacts with pozzolan to form calcium-silicate-hydrate ("CSH"). The increased tricalcium silicate content can be used to offset the lack of tricalcium silicates in the pozzolan fraction of the blended cements. The increase in tricalcium silicate may depend in part on the percentage of pozzolan in the blend. For example increased concentrations of tricalcium silicate in the hydraulic cement fraction can be used when percentages of pozzolan are greater than about 20%, preferably greater than about 30%, more preferably greater than about 40%, about 50%, or even about 60%>.

[0043] While increased calcium content can be beneficial for particle size optimized blended cements as described herein, increased tricalcium silicate content is not required. Moreover, the increased tricalcium silicate concentrations may be advantageously used with traditional particle size distributions of Portland cement and pozzolan (e.g., pozzolans and hydraulic cements where both distributions are substantially overlapping and/or have a majority of particles ranging from 1-45 microns, particularly for blended cements with between 25% and 60%> pozzolan, more preferably between 30%> and 50%> pozzolan).

[0044] In an embodiment of invention, a pozzolan cement composition is provided that includes at least about 30%> pozzolan and less than about 70%> hydraulic cement (e.g., 55- 70% hydraulic cement by volume and 30-45% pozzolan by volume). In another embodiment, a pozzolan cement composition is provided that includes at least about 40% pozzolan and less than about 60% hydraulic cement. In another embodiment, a pozzolan cement composition is provided that includes at least about 45% pozzolan and less than about 55% hydraulic cement. In yet another embodiment, a pozzolan cement composition is provided that includes at least about 55% pozzolan and less than about 45% hydraulic cement. In still another embodiment, a pozzolan cement composition is provided that includes at least about 60% pozzolan and less than about 40% hydraulic cement. And in another embodiment, a pozzolan cement composition is provided that includes at least about 70% pozzolan and less than about 30% hydraulic cement.

[0045] The pozzolan-hydraulic cement compositions (i.e., blended cements) according to the invention typically include a distribution of particles spread across a wide range of particle sizes (e.g., over a range of about 0.1-120 μιη, or about 0.1-100 μιη, or about 0.1- 80 μιη, or about 0.1-60 μιη, or about 0.1-45 μιη).

[0046] In one embodiment, at least about 50%, 65%, 75%, 85%, 90%, or 95% of the combined pozzolan and hydraulic cement particles larger than about 20 μιη, 15 μιη, 10 μιη, 7.5 μιη, or 5 μιη comprise pozzolan and less than about 50%>, 35%, 25%, 15%, 10%, or 5% comprise hydraulic cement. Similarly, at least about 75%, 85%, 90%, or 95% of the combined pozzolan and hydraulic cement particles smaller than about 25 μτη, 20 μτη, 15 μτη, 10 μτη, 7.5 μτη, or 5 μιη comprise hydraulic cement and less than about 25%, 15%), 10%), or 5% comprise pozzolan.

[0047] The inventive pozzolan cement compositions can be used to make concrete, mortar, grout, molding compositions, or other cementitious compositions. In general, "concrete" refers to cementitious compositions that include a hydraulic cement binder and aggregate, such as fine and coarse aggregates (e.g., sand and rock). "Mortar" typically includes cement, sand and lime and can be sufficiently stiff to support the weight of a brick or concrete block. "Grout" is used to fill in spaces, such as cracks or crevices in concrete structures, spaces between structural objects, and spaces between tiles. "Molding compositions" are used to manufacture molded or cast objects, such as pots, troughs, posts, fountains, ornamental stone, and the like. [0048] Water is both a reactant and rheology modifier that permits fresh concrete, mortar or grout to flow or be molded into a desired configuration. The hydraulic cement binder reacts with water, is what binds the other solid components together, and is responsible for strength development. Cementitious compositions within the scope of the present invention will typically include hydraulic cement (e.g., Portland cement), pozzolan (e.g., fly ash), water, and aggregate (e.g., sand and/or rock). Other components that can be added include water and optional admixtures, including but not limited to accelerating agents, retarding agents, plasticizers, water reducers, water binders, and the like.

[0049] It will be appreciated that the inventive pozzolan cement compositions can be manufactured (i.e., blended) prior to incorporation into a cementitious composition or they may be prepared in situ. For example, some or all of the hydraulic cement and pozzolan particles can be mixed together when making a cementitious composition. In the case where supplemental lime is desired in order to increase the speed and/or extent of pozzolan hydration, at least some of the supplemental lime or other base may be added to the cementitious composition directly.

[0050] Admixtures typically used with OPC can also be used in the inventive concrete compositions of the invention. Examples of suitable admixtures include, but are not limited to, hydration stabilizers, retarders, accelerantors, and/or water reducers. Additional details regarding cementitious compositions that can be manufactured according to the invention and incorporated into the embodiments disclosed herein can be found in co-pending patent application serial number 12/576,117, filed October 8, 2009, which is hereby incorporated by reference in its entirety.

[051] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

What is claimed is:

Claims

1. A method for producing a pozzolan having a desired chemical composition for use with Portland cement, the method comprising:

combusting a hydrocarbon fuel in a power plant, wherein the hydrocarbon fuel and the power plant are configured to produce fly ash;

introducing a calcium bearing material into the power plant to produce a modified fly ash having a desired calcium oxide content, wherein the desired calcium oxide content is greater than the calcium oxide content of pozzolan produced by combusting the hydrocarbon fuel in the power plant without introducing the calcium bearing material;

recovering the modified pozzolan from the power plant; and providing the modified pozzolan for use in concrete or blending with a hydraulic cement.

2. A method as in claim 1, wherein the modified pozzolan has a calcium oxide content of at least 5%, 10%, 15%, or 20% by mass.

3. A method as in claim 1, wherein the modified pozzolan has a calcium oxide content greater than 20% and without introducing the calcium bearing material the hydrocarbon fuel when combusted would produce a pozzolan with less than 10% calcium oxide.

4. A method as in claim 1 further comprising measuring the calcium oxide content of the modified pozzolan over time and adjusting the amount of calcium bearing material introduced into the power plant to achieve the desired calcium oxide content.

5. A method as in claim 4, wherein the calcium oxide content is measured using a chemical analyzer.

6. A method as in claim 1, wherein the calcium bearing material includes limestone.

7. A method as in claim 1, wherein the calcium bearing material is added to the power plant before the burner.

8. A method as in claim 1, wherein the calcium bearing material is added to the power plant after the burner.

9. A method as in claim 1, wherein the calcium bearing material is selectively metered into power plant on a continuous or semi-continuous basis according to the amount needed to achieve the desired calcium oxide content.

10. A method as in claim 11, further comprising introducing a second supplemental material to the power plant to produce a modified pozzolan having one or more chemical characteristics including a desired tricalcium aluminate content, a desired tricalcium silicate content, a desired sulfate content, a desired iron content, or a desired ratio of two of these.

11. A method as in claim 12, further comprising monitoring over time the tricalcium aluminate content, tricalcium silicate content, sulfate content, iron content, or ratios of two or more of these and adjusting the introduction of the calcium bearing material and/or second supplemental material to keep the tricalcium aluminate content, tricalcium silicate content, sulfate content, iron content, or ratio of two of these within a desired range over time.

12. A method as in claim 12, wherein the second supplemental material is added in an amount in a range from about 0.5% to about 20%, more preferably about 1% to about 15% by weight of the pozzolan, even more preferably about 1.5% to about 10%), by weight of the pozzolan.

13. A method as in claim 12, wherein the calcium bearing material and/or the second supplemental material is added the power plant as a powder.

14. A method as in claim 1 further comprising blending the pozzolan fraction with a Portland cement.

15. A method as in claim 1, further comprising blending the pozzolan fraction with Portland cement, water, and aggregate to make concrete.

16. A method for producing a pozzolan having a desired chemical composition for use with Portland cement, the method comprising:

heating a pozzolan forming material in a burner, furnace or calciner to produce a pozzolan or pozzolan precursor that becomes pozzolanic if ground and/or activated;

introducing a supplemental material into the burner, furnace or calciner to produce a modified pozzolan or modified pozzolan precursor having a desired mineral content, wherein the desired mineral content is different than the mineral content of the pozzolan produced in the absence of the supplemental material;

recovering the modified pozzolan or modified pozzolan precursor from the burner, furnace or calciner;

optionally grinder a modified pozzolan precursor to form the modified pozzolan; and

providing the modified pozzolan for use in concrete or blending with a hydraulic cement.