WO2017000075A1 - Carbonated fly ash as a cement replacement - Google Patents

Abstract

A process for producing a blended binder material containing high calcium fly ash, in particular ASTM Class C fly ash, is provided. The process comprises: (i) carbonating the fly ash with carbon dioxide; and (ii) combining the carbonated fly ash with a cement binder such as Portland cement. The carbonation process improves the performance of the high calcium fly ash and thus allows for higher amounts of the fly ash to be used with the cement binder in cement mix compositions such as concrete. The results presented herein demonstrate the benefits of the carbonation process on the rate of cement hydration, and on the compressive strength and the dimensional stability of the resulting cement products.

Description

CARBONATED FLY ASH AS A CEMENT REPLACEMENT

CROSS-REFERENCE

[0001] This application claims the benefit of U.S. Provisional Application No. 62/187,002, filed June 30, 2015 [Attorney Docket No. 44131-710.102], which application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] Fly ash is one of the residues generated in combustion and comprises the fine particles that rise with the flue gases. Ash which does not rise is termed bottom ash. In an industrial context, fly ash usually refers to ash produced during combustion of coal. There are two types of fly ashes in the U.S. - ASTM class C and ASTM class F. The distinction is based upon the chemical composition of the fly ash. Class F ashes are widely used, e.g., to replace a portion of Portland cement in concrete to improve durability and reduce the cost of binder given that fly ash is considerably less expensive in comparison to Portland cement. Class C ashes have a higher calcium content and are generally more reactive than Class F ashes. However, many class C ashes do not perform to the full potential in many applications (e.g. much lower replacement levels are used). The drawback is that many class C ashes disrupt the hydration of Portland cement in such a way that the development of mechanical properties (e.g. set and early strength) is severely retarded. Therefore, many high calcium fly ashes cannot be used as a cement replacement, except for relatively low levels of cement replacement. Class F Fly ash is conventionally used to mitigate ASR (alkali silicate reaction). Class C ash is potentially useable to control ASR but requires approximately 40- 60% cement replacement. Class C ash is seldom if ever used to control ASR because of the undesirable effects on the set time and strength development that accompany such high cement replacement levels. It would be advantageous to be able to use high calcium fly ash as a cement replacement.

INCORPORATION BY REFERENCE

[0003] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

[0005] FIGURE 1 shows the power curve for a mortar mix containing Portland cement and either no fly ash (middle curve at 6 hours), 20% uncarbonated Class C fly ash (lower curve at 6 hours), or 20% class C fly ash carbonated at 1.36% carbon dioxide uptake per weight of ash (upper curve at 6 hours).

[0006] FIGURE 2 shows the power curve for a mortar mix containing Portland cement and 40% Class C fly ash, uncarbonated, (upper curve at 10 hours) or carbonated at 0.7% carbon dioxide uptake per weight of ash (second curve from top at 10 hours), 1.38% carbon dioxide uptake per weight of ash (third curve from top at 10 hours), or 1.70% carbon dioxide uptake per weight of ash (bottom curve at 10 hours).

[0007] FIGURE 3 shows the energy curve for a mortar mix containing Portland cement and 40% Class C fly ash, uncarbonated, (middle curve at 10 hours) or carbonated at 0.7% carbon dioxide uptake per weight of ash (top curve at 10 hours), 1.38% carbon dioxide uptake per weight of ash (bottom curve at 10 hours), or 1.70% carbon dioxide uptake per weight of ash (bottom curve at 10 hours— indistinguishable from 1.38%).

[0008] FIGURE 4 shows the power curve for a mortar mix containing Portland cement and 30% Class C fly ash, uncarbonated, (lower curve at 20 hours) or carbonated at 0.7% carbon dioxide uptake per weight of ash (second curve from bottom at 20 hours), 1.38% carbon dioxide uptake per weight of ash (third curve from bottom at 20 hours), or 1.70% carbon dioxide uptake per weight of ash (top curve at 20 hours).

[0009] FIGURE 5 shows the energy curve for a mortar mix containing Portland cement and 30% Class C fly ash, uncarbonated, (middle curve at 9 hours) or carbonated at 0.7% carbon dioxide uptake per weight of ash (top curve at 9 hours), 1.38% carbon dioxide uptake per weight of ash (bottom curve at 9 hours), or 1.70% carbon dioxide uptake per weight of ash (bottom curve at 9 hours— indistinguishable from 1.38%).

[0010] FIGURE 6 shows the power curve for a mortar mix containing Portland cement and 30% Class C fly ash, uncarbonated, (upper curve at 12 hours) or carbonated at 0.6% carbon dioxide uptake per weight of ash (lower curve at 12 hours. [0011] FIGURE 7 shows the energy curve for a mortar mix containing Portland cement and 30% Class C fly ash, uncarbonated, (lower curve at 40 hours) or carbonated at 0.6% carbon dioxide uptake per weight of ash (upper curve at 40 hours).

[0012] FIGURE 8 shows the power curve for a mortar mix containing Portland cement and 40% Class C fly ash, uncarbonated, (upper curve at 12 hours) or carbonated at 0.6% carbon dioxide uptake per weight of ash (lower curve at 12 hours.

[0013] FIGURE 9 shows the energy curve for a mortar mix containing Portland cement and 30% Class C fly ash, uncarbonated, (lower curve at 40 hours) or carbonated at 0.6% carbon dioxide uptake per weight of ash (upper curve at 40 hours).

[0014] FIGURE 10 shows isothermal calorimetry power curves for mortars prepared with 100% OPC, 60% OPC + 40% unground C Fly Ash; 60% OPC + 40% ground C Fly Ash; 60% OPC + 40% unground C Fly Ash + S0₃ addition; 60% OPC + 40% unground C Fly Ash + SO₃ addition

[0015] FIGURE 11 shows energy curves for mortars prepared with 100% OPC, 60% OPC + 40% unground C Fly Ash; 60% OPC + 40% ground C Fly Ash; 60% OPC + 40% unground C Fly Ash + S0₃ addition; 60% OPC + 40% unground C Fly Ash + S0₃ addition

[0016] FIGURE 12 shows Day 1 compressive strengths for mortars prepared with 60% OPC + 40% unground C Fly Ash; 60% OPC + 40% ground C Fly Ash; 60% OPC + 40% unground C Fly Ash + S0₃ addition; 60% OPC + 40% unground C Fly Ash + S0₃ addition

[0017] FIGURE 13 shows power vs. time for isothermal calorimetry of mortar prepared with 100% OPC; mortar prepared with 50% OPC + 50% untreated Class C Fly Ash; mortar prepared with 70% OPC + 30% untreated Class C Fly Ash; and mortar prepared with 50% OPC + 50% beneficiated Class C Fly Ash. Beneficiation was as described in Example 4

[0018] FIGURE 14 shows compressive strength development at 1, 8, and 28 days, in binary mortar systems that contain 100% OPC (control); 50% OPC + 50% beneficiated C fly ash; 70% OPC + 30% untreated C fly ash; 70% OPC + 30% slag; 70% OPC + 30% F fly ash; 50% OPC + 50% untreated C fly ash; 50% OPC + 50% slag; or 50% OPC + 50% F fly ash.

[0019] FIGURE 15 shows compressive strength development at 1, 8, and 28 days, in binary and ternary mortar systems that contain 100% OPC (control); 50% OPC + 50% untreated C fly ash; 50% OPC + 50% beneficiated C fly ash; 50% OPC + 50% slag; 50% OPC + 15% slag + 35% beneficiated C ash; 50% OPC + 30% slag + 20% beneficiated C ash; 50% OPC + 50% F ash; 50% OPC + 15% F ash + 35% beneficiated C ash; 50% OPC + 30% F ash + 20% beneficiated C ash. [0020] FIGURE 16 shows expansion after 75 days for mortars prepared with 50% OPC + 15% slag + 35% beneficiated C fly ash; 50% OPC + 50% slag; 50% OPC + 30% slag + 20% beneficiated C fly ash; 50% OPC + 50% untreated C fly ash; 50% OPC + 50% beneficiated C fly ash; 50% OPC + 50% F fly ash; 50% OPC + 15% F ash + 35% beneficiated C fly ash; and 50% OPC + 30% F ash + 20% beneficiated C fly ash.

[0021] FIGURE 17 shows power vs. time for isothermal calorimetry of mortar prepared with 100% OPC; 50% OPC + 50% untreated C ash; 50% OPC + 50% beneficiated C ash, unground; 50% OPC + 50% beneficiated C ash; 50% OPC + 50% beneficiated C ash + C02 dose 1; 50% OPC + 50% beneficiated C ash + C02 dose 2; 50% OPC + 50% beneficiated C ash + C02 dose 3; 50% OPC + 50% beneficiated C ash + C02 dose 4 (doses as described in Example 6).

[0022] FIGURE 18 shows Day 1 compressive strength of mortar prepared with 100% OPC; 50% OPC + 50% untreated C ash; 50% OPC + 50% beneficiated C ash, unground; 50% OPC + 50% beneficiated C ash; 50% OPC + 50% beneficiated C ash + C02 dose 1; 50% OPC + 50% beneficiated C ash + C02 dose 2; 50% OPC + 50% beneficiated C ash + C02 dose 3; 50% OPC + 50% beneficiated C ash + C02 dose 4 (doses as described in Example 6).

DETAILED DESCRIPTION OF THE INVENTION

[0023] There are several stages in the beneficiation process, each one of them having merit while not every high calcium fly ash will benefit from each and every stage:

[0024] Grinding of a supplementary cementitious material, such as high calcium fly ash, in the presence of a sulfate carrier, to allow for proper hydration control of the reactive aluminate compounds in high calcium fly ash. Said sulfate carrier must have some solubility in water such as an alkali sulfate or an alkali metal sulfate. In the preferred method the fly ash is ground to a Blaine fineness of minimum 100, 150, 200, 250, 300, 350, 400, 450, or 500 m²/kg with a soluble SO₃ content of 1-10% by weight of the CaO content of the ash, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% of the weight of the CaO content of the ash. Alternatively, the sulfate may be added to increase the sulfate (S03) content of the ash to any suitable level, up to the maximum allowable level, which is typically 5%, see ASTM C618. Thus, the sulfate may be increased to at least 0.5, 1, 2, 3, 4, or 4.5% and/or no more than 1, 2, 3, 4, 4.5, or 5%. Exemplary sulfate carriers include calcium sulfate, e.g., monohydrate or dihydrate. In addition, or alternatively, the high calcium fly ash may be interground with a carbonate, such as calcium carbonate. Any suitable level of calcium carbonate may be used, such as those shown in the Examples, for example, in terms of total fly ash SCM, at least 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9% and/or no more than 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10%. Thus, for example, a high calcium fly ash may be interground with a suitable sulfate, such as a calcium sulfate monohydrate (hemihydrate) or dehydrate, and calcium carbonate. In certain embodiments the fly ash may be further treated with carbon dioxide, as described further herein.

[0025] Grinding or blending of high calcium fly ash in presence of moisture and C0₂, such that the moisture content is sufficient to facilitate C0₂ uptake by the high calcium ash, without causing the ash to become sticky, such that the ash can be transported using compressed air or similar methods after treatment.

[0026] Grinding or blending of high calcium ash in presence of one or several carriers of silica, alumina, calcium and carbonates, such as but not limited to: low calcium fly ash, blast furnace slag, volcanic ash, natural pozzolanic materials, calcium carbonate, magnesium carbonate, steel stags, portland cement, silica fume, red mud, and the like

[0027] Grinding or blending of high calcium ash in presence of chemical admixtures intended for hydration control, such as but not limited to: Citric acid, citrates, sodium gluconate, com syrup, fructose, and the like.

[0028] Each of the above steps may be carried out alone or in combination with each other. The optimum process may be selected by hydrating the beneficiated product in water or in presence of Portland cement and monitoring its hydration performance using calorimetry. The main criteria for selecting a preferable treatment is by minimizing the heat evolution in the so-called dormant period within 20-120 minutes after mixing, while maximizing the heat evolution in presence of Portland cement from 120 minutes and onwards.

[0029] A carbonation process can treat combustion ash, such as fly ash, e.g., a high calcium fly ash such as class C fly ash and improve its performance and thereby allow for higher replacement levels, or change an unusable ash into a usable one.

Methods

[0030] Combustion ash, e.g., fly ash is treated with carbon dioxide; without being bound by theory, it is thought that the reactive calcium components in the fly ash react with C0₂ to form carbonate reaction products with less adverse impact on the cement hydration. In certain embodiments the fly ash comprises a high calcium fly ash, e.g., ASTM Class C fly ash, per 2015 ASTM standards. In certain embodiments, the high calcium fly ash contains at least 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, or 30% CaO by weight fly ash, for example, at least 5, 10, 12, 15, 17, 20, 25, or 30% CaO, or more than 10, 12, 15, or 20% CaO. The carbonated fly ash thus produced may be used in combination with cement binder, such as Portland cement, as a supplemental cementitious material (SCM) that displaces a certain portion of the cement binder in the final blended binder composition. In certain embodiments, the carbonated fly ash displaces at least 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or 60% of the cement binder, e.g., Portland cement. In certain embodiments, more of the carbonated fly ash, e.g., a high calcium fly ash such as a Class C fly ash or a fly ash of minimum CaO content as described herein, may be used in the final blended binder composition, than could be used if the fly ash were not carbonated, e.g., at least 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 150, or 200% more, while still maintaining adequate characteristics for the intended use, such as strength development at one or more times. In certain cases, the carbonation process allows for the use of a fly ash in a blended binder composition that could not have been used if the fly ash were not carbonated.

[0031] The carbon dioxide used in the invention may be of any purity and/or form suitable for contact with cement, e.g., hydraulic cement during mixing to form reaction products. The carbon dioxide is at least above the concentration of atmospheric carbon dioxide. For example, the carbon dioxide may be liquid, gaseous, solid, or supercritical, or any combination thereof. In certain embodiments, the carbon dioxide is gaseous when contacted with the combustion ash, e.g., fly ash, though it may be stored prior to contact in any convenient form, e.g., in liquid form. In alternative embodiments, some or all of the carbon dioxide may be in liquid form and delivered to the combustion ash, e.g., fly ash e.g., in such a manner as to form a mixture of gaseous and solid carbon dioxide; the stream of liquid carbon dioxide can be adjusted by, e.g., flow rate and/or orifice selection so as to achieve a desired ratio of gaseous to solid carbon dioxide, such as ratio of approximately 1 : 1, or within a range of ratios.

[0032] The carbon dioxide may also be of any suitable purity for contact with the cement or cement mix (concrete), e.g., hydraulic cement during mixing under the specified contact conditions to form reaction products. In certain embodiments the carbon dioxide is more than 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, or 99% pure. In certain embodiments, the carbon dioxide is more than 95% pure. In certain embodiments, the carbon dioxide is more than 99% pure. In certain embodiments, the carbon dioxide is 20-100% pure, or 30-100% pure, or 40-100% pure, or 50-100% pure, or 60-100% pure, or 70-100% pure, or 80-100% pure, or 90-100% pure, or 95-100% pure, or 98-100% pure, or 99-100% pure. In certain embodiments, the carbon dioxide is 70-100% pure. In certain embodiment, the carbon dioxide is 90-100% pure. In certain embodiment, the carbon dioxide is 95-100% pure. In certain cases, the gas does not contain SOx, and/or NOx, and/or mercury, and/or VOCs. The impurities in the carbon dioxide may be any impurities that do not substantially interfere with the reaction of the carbon dioxide with the wet cement mix, e.g., hydraulic cement mix. Commercial sources of carbon dioxide of suitable purity are well-known. The gas may be commercially supplied high purity carbon dioxide that is substantially free of impurities. In this case, the commercial gas may be sourced from a supplier that processes spent flue gasses or other waste carbon dioxide so that sequestering the carbon dioxide in the cement mix, e.g., hydraulic cement mix sequesters carbon dioxide that would otherwise be a greenhouse gas emission. In certain embodiments, some or all of the C0₂ used in the process may be the result of calcination in a cement production facility, for example, at least 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, or 99% of the C0₂, or 100% of the C0₂, for carbonated fly ash production is derived from calcination in a cement production facility. In certain

embodiments, some or all of the C0₂ used in the process may be the result of fuel combustion at a power plant, such as the combustion of coal at a coal-fired power plant, for example, at least 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, or 99% of the C0₂, or 100% of the C0₂, for carbonated fly ash production is derived from flue gas produced by combustion of fuel at a power plant, e.g., the combustion of coal at a coal-fired power plant. In the latter embodiment, some or all of the fly ash that is carbonated may be fly ash produced by the same power plant from which some or all of the C0₂ is derived.

[0033] In certain embodiments, carbonation is by means of carbon dioxide addition only, without addition of bicarbonate or carbonate materials.

[0034] In certain embodiments, some water may be added to the fly ash to facilitate the carbonation reaction. In certain embodiments, water is added to the fly ash but in an amount less than 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% water added by weight of fly ash, for example, less than 10%, and/or greater than 0.001, 0.01, or 0.1%, in certain embodiments. The gas can be hydrated to supply the necessary water. In certain cases, the fly ash is mixed with water and C0₂, as gas, liquid, and/or solid, is added, in sufficient amount to provide a desired degree of carbonation of the fly ash. In these embodiments, the amount of water may be, e.g., 0.1-50% by weight of fly ash, or 0.1-40, 0.1-30, 0.1-20, 0.1-10, 0.1-5%, 1-50 1-40, 1-30, 1-20, 1-10, 1-5, 2-40, 2-30, 2-20, 2-10, 2-5, 5-40, 5-30, 5-20, 5-10, or 5-9%, for example, 5-30%. In certain embodiments, the carbon dioxide uptake, that is, the mass of carbon dioxide converted to stable form (e.g., carbonate) per mass of fly ash, is at least 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50%. In certain cases, the degree of carbonation, that is, the percentage of calcium-containing compounds in the fly ash that is carbonated in the process, is at least 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, or 95%. The method may be carried out in such a manner, e.g., by use of control mechanisms as described below, to achieve a desired efficiency of carbonation, defined as the amount of added carbon dioxide that is present in the carbonated fly ash as a stable carbonate, such as calcium carbonate, per total amount of carbon dioxide added during carbonation The efficiency of the method may be at least 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 98, 99, or 99.5%; in certain embodiments, the efficiency is at least 50%; in certain embodiments, the efficiency is at least 70%.

[0035] The carbonated fly ash is then added to a cement binder, e.g., Portland cement. The carbonated ash used in conjunction with a cement, e.g., Portland cement, to produce a blended binder, may perform better (stronger and faster setting) than a system using an uncarbonated fly ash (see Example 1, below). This improvement allows for higher amounts of fly ash to be used with the cement than would otherwise be possible, while retaining acceptable characteristics for the intended use, e.g., strength at one or more times after concrete mixing. An increase in fly ash usage thereby allows for less cement to be used. Additionally, the treatment can allow new types of fly ash to be used, that is, fly ash that is not suitable for combination with cement, e.g., Portland cement, in its uncarbonated form, can become suitable due to the carbonation processes described herein.

[0036] As an environmental consideration, increasing the fly ash fraction in a concrete mix reduces the cement fraction and thereby results in avoided C0₂ emissions. Additionally, a carbonation treated ash contains sequestered C0₂ that will be contained within the concrete product. The use of carbonated fly ash produced in the process in a blended binder can result in decreased carbon dioxide in the atmosphere compared to if non-carbonated fly ash were used in the blended binder; the decreased carbon dioxide may result from increased avoided carbon dioxide (due to displacement of a greater amount of Portland cement than would be possible without carbonation of the fly ash) and/or from directly sequestered carbon dioxide (due to the carbonation of the fly ash used in the blended binder). For example, in certain embodiments, the decrease of carbon dioxide in the atmosphere due to avoided carbon dioxide may be at least 5, 10, 15, 20, 30, 40, 50, 60, or 70% compared to the same blended binder without carbonated fly ash (i.e., due to the increased amount of fly ash use, and thus decreased use of Portland cement, because of carbonation of the fly ash). In certain embodiments, the sequestered carbon dioxide (i.e., due to uptake of carbon dioxide by the fly ash in the carbonation process) may be at least 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 40, or 50%. For example, if an uncarbonated fly ash possessed properties such that no more than 20% could be used in a given blended cement, and the same fly ash if carbonated could be used at 40%, then the avoided carbon dioxide would be 40-20% = 20%. If the carbonated fly ash had a C0₂ uptake of 10%, the blended binder would be 4% C0₂ by mass of binder, and thus have a direct carbon dioxide sequestration of 4%.

[0037] The carbonation of the fly ash may occur at any suitable location, as described below for apparatus.

[0038] Additionally, or alternatively, the fly ash may be treated with a sulfate, e.g., a calcium sulfate, such as a calcium sulfate monohydrate or dehydrate, and/or with a calcium carbonate. This may be done by intergrinding the sulfate and/or carbonate with the fly ash; without being bound by theory, intergrinding increases the surface area of the sulfate and/or carbonate and increases its availability to chemically react with components of the fly ash and/or the cement mixture to which the fly ash is added. Thus, the method may produce a fly ash composition with a Blaine fineness of minimum 100, 150, 200, 250, 300, 350, 400, 450, or 500 m²/kg, comprising added sulfate, e.g., calcium sulfate, and/or added calcium carbonate, as an additional component, or an alternative, to the carbon dioxide described herein. The sulfate may be added so that S03 reaches a soluble SO₃ content of 1-10% by weight of the CaO content of the ash, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% of the weight of the CaO content of the ash. Alternatively, the sulfate may be added to increase the sulfate (S03) content of the ash to any suitable level, up to the maximum allowable level, which is typically 5%, see ASTM C618. Thus, the sulfate may be increased to at least 0.5, 1, 2, 3, 4, or 4.5% and/or no more than 1, 2, 3, 4, 4.5, or 5%. Exemplary sulfate carriers include calcium sulfate, e.g., monohydrate or dihydrate. In addition, or alternatively, the high calcium fly ash may be interground with a carbonate, such as calcium carbonate. Any suitable level of calcium carbonate may be used, such as those shown in the Examples, for example, in terms of total fly ash SCM, at least 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9% and/or no more than 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10%. Thus, for example, a high calcium fly ash may be interground with a suitable sulfate, such as a calcium sulfate monohydrate (hemihydrate) or dehydrate, and calcium carbonate. In certain embodiments the fly ash may be further treated with carbon dioxide, as described further herein.

[0039] In certain embodiments, the invention provides composition comprising a fly ash that is at least 5, 10, 15, 20, or 25% CaO by weight, a sulfate, such as a calcium sulfate, that has been added the to the fly ash in an amount as described herein. The composition may further comprise calcium carbonate, that has been added to the composition in an amount described herein. The composition may be any fineness as described herein. In certain embodiment, the composition may also comprise calcium carbonate formed by carbonation of the fly ash; such calcium carbonate can be distinguished from calcium carbonate that is exogenously added by the size of the crystals of calcium carbonate; the calcium carbonate formed by carbonation of the fly ash is less than 1 micron, or less than 900, 800, 700, 600, 500 400, 300, 200, or 100 nanometers, in longest dimension of crystals, on average, and can be present, for example, in an amount of at least 0.01, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, or 3.0% by weight of the fly ash composition, and/or no more than 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, or 4.0% by weight of the fly ash composition. The invention also provides a concrete that contains the fly ash composition of the invention, as well as a hydraulic cement, such as Ordinary Portland Cement (OPC) and, in certain embodiments, additionally comprising a second supplementary cementitious material besides the fly ash composition, such as another fly ash, e.g., a fly ash of lower CaO content (for example, the fly ash composition may be made from Class C fly ash and the other fly ash may be a Class F fly ash), or slag, or a combination thereof. In certain embodiments, the composition is no more than 40, 50, 55, 60, 65, 70, or 75% OPC and/or no less than 45, 50, 55, 60, 65, 70, 75, or 80% OPC. In certain embodiments, the composition comprises the fly ash composition of the invention in an amount of at least 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50%, and/or no more than 10, 15, 20, 25, 30, 35, 40, 45, or 55%. In certain embodiments in which a second SCM is present, the second SCM, such as another fly ash or slag, may be present in an amount of at least 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50%, and/or no more than 10, 15, 20, 25, 30, 35, 40, 45, or 55%.

Apparatus

[0040] The invention also provides various embodiments of apparatus for carbonating fly ash. The fly ash may be carbonated at any suitable location, such as at a concrete plant, or at a fly ash producer, such as a power plant, e.g., a coal-fired power plant.

Apparatus at a concrete plant

[0041] In an existing silo (such as at a concrete plant) the aeration system can be used to inject measured amounts of C0₂ within the compressed air stream. The system is normally used to promote dispensing of the powdered contents. The gas can be hydrated.

[0042] Alternately, a small batch mixing silo can be installed wherein the fly ash for each batch is carbonated immediately before dispensing into the mixer or truck. In this case, rapid carbonation is needed as time is important but efficient mixing and high concentration C0₂ and water can be employed.

[0043] Altemately, the material can be carbonated as it is moving from the storage silo to the batch section while the material is moved by an auger (in some embodiments requires the addition of injection ports where C0₂ and water are added as the material moves to the batch section of the plant from the silo).

Apparatus at a fly ash producer

[0044] The fly ash may be carbonated by use of the mixing silo or pressure mixing silo wherein compressed air is typically used in a specifically configured silo which, in operation, fluidizes the cement and promotes movement and mixing. In this case inject C0₂ is also injected into the compressed air stream

[0045] Altemately, the pugmill can be used so that batches are carbonated then moved to the storage silo. This requires sufficiently stable properties after carbonation such that existing material handling is possible. Post-carbonation drying and milling may be required.

[0046] Altemately, integration into the existing process is possible.

[0047] Altemately, if material is moved on a fluidized bed under its own weight by gravity down a slope then C0₂ may be integrated into the compressed air stream to facilitate carbonation.

[0048] Since fly ash is produced by coal fired power plants, in certain embodiments some or all of the source of C0₂ for fly ash production locations might preferably be from the power plant. For example, in certain embodiments, at least 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, or 99% of the C0₂, or 100% of the C0₂, for carbonated fly ash production using fly ash from a power plant comes from a power plant, e.g., from the same power plant that produces the fly ash. The C0₂ may be any suitable purity, as described elsewhere. In certain embodiment the C0₂ contains impurities, so long as the impurities do not substantially interfere with the carbonation process and so long as any impurities released to the atmosphere in the process comply with applicable environmental standards in terms of type, amount, and so on. In certain embodiments, the C0₂ contains one or more impurities from the burning of coal, such as one or more of SOx, NOx, or volatile organic compounds (VOCs). Sensors and control

[0049] Lab testing data (target carbonation level) can be attained by using temperature and/or injected C0₂ content with limits on loss determined using C0₂ sensors at exits. In the case of silos the sensors are, e.g., at the exhaust. In a pressure vessel they can be metered in. In a batch carbonation a carbon dioxide and feedback system as described in U.S. Patent

Publication No. 20140373755. Control systems using a variety of types of feedback are described in that patent application for use in carbonation of mixing cement and any suitable type of sensor and feedback as described therein may also be used in a fly ash carbonation process.

EXAMPLES

Example 1

[0050] This Example below demonstrates the beneficial effect of carbonating a class C ash prior to adding it to a cementitious mix.

[0051] Class C fly ash (Joliet Fly Ash, a high calcium fly ash) was carbonated at three different levels of carbon dioxide dosage. Mortar mix was then prepared using either no fly ash or fly ash in one of three different proportions, 20%, 30%, or 40%; the fly ash was either uncarbonated or carbonated at one of the three carbon dioxide doses.

[0052] More specifically:

[0053] A mixture of high calcium fly ash (Joliet), water and sand was prepared as per the following mix design:

535 g high calcium fly ash

267.5 g water

1350 g sand

[0054] This mixture was then subjected to carbonation in a sealed vessel under the following conditions:

25 psi C02, 6 RPS mixing, 15 minutes total mixing

C0₂ introduced for either 3, 7.5 or all 15 minutes of the mixing

[0055] The high calcium fly ash mixture was then blended into a mortar containing type GU cement. Mortar was prepared using following mix design:

535 g type GU cement

267.5 g water

1350 g sand

High calcium fly ash was blended with the standard mortar as per the following: 20% fly ash cementitious mixture

2152g mortar

538g fly ash mixture

30% fly ash cementitious mixture

lOOOg mortar

428.6 g fly ash mixture

40% fly ash cementitious fraction

lOOOg mortar

666.6 g fly ash mixture

[0056] The blended mixture was mixed for 3 minutes in a paddle-type stand mixer.

[0057] Strength cubes and calorimetry samples were then prepared and the effect of carbonation on the properties of the high calcium fly as a supplementary cementitious material were followed. Control fly ash samples were subjected to the same mixing procedure described above without exposure to C0₂.. Isothermal calorimetry monitored the early hydration.

[0058] As expected, carbon dioxide uptake increased with increasing treatment time. In addition, compressive strength was greater than control (mortar mix using untreated ash) in 5 of 6 cases. See Table 1 :

TABLE 1

Carbon dioxide uptake and strength effects of various doses of carbon dioxide applied to fly ash

30% high calcium fly 40% high calcium fly ash

C0₂ uptake in

C0₂ Exposure ash substitution substitution

ash (% by

Time (minutes)

weight) 24 hr Compressive Strength (% of Control)

3.0 0.73 109% 141%

7.5 1.38 97% 122%

15.0 1.70 103% 128% [0059] When carbonated fly ash was added to the mortar at 20% (1.36% carbon dioxide uptake by weight of ash), there was an acceleration in hydration compared to uncarbonated fly ash control. See Figure 1. The power curve represents the rate of cement hydration in each mixture. Figure 1 shows either no fly ash (middle curve at 6 hours), 20% uncarbonated Class C fly ash (lower curve at 6 hours), or 20% class C fly ash carbonated at 1.36 carbon dioxide uptake per weight of ash (upper curve at 6 hours), and indicates that adding uncarbonated fly ash to the mix showed a slight retarding effect, while carbonating the fly ash before using it in the mix removed the retarding effect and showed a slight acceleration over the plain (no fly ash) control.

[0060] When ash carbonated at 3 different levels was added to the mortar at 40%, calorimetry indicated that the samples with carbonated fly ash were more actively hydrating than the untreated fly ash control. See Figures 2 and 3. The power curve represents the rate of cement hydration in each mixture, while the Energy curve represents the degree of cement hydration, which is approximately proportional to the rate of strength development. In particular, the lowest level of carbonation shifted the calorimetry curve to lower times, indicating an accelerating effect and all levels of carbonation resulted in more heat being released during early hydration, indicating greater strength development; i.e., calorimetry indicated that samples with carbonated fly ash were more actively hydrating than the one with untreated fly ash.

[0061] When ash carbonated at 3 different levels was added to the mortar at 30%, similar effects of carbonation to those at 40% were seen. See Figures 4 and 5.

[0062] This Example demonstrates the beneficial effects of carbonation of a high calcium fly ash before addition to a cement blend.

Example 2

[0063] In this Example, a different type of Class C fly ash was used, Headwaters II Fly ash. The fly ash was carbonated as in Example 1, for one exposure time (7.5 min), producing a carbon dioxide uptake by weight fly ash of 0.59% (rounded to 0.6% in Figures). Mortar containing the fly ash was prepared as in Example 1.

[0064] 24 hour compressive strength measurements showed improvement in both samples that were prepared using carbonated high calcium fly ash at 24 hours. See Table 2. TABLE 2

24 hour compressive strength of 30% and 40% fly ash mortar, carbonated, compared to uncarbonated

30% high calcium fly ash 40% high calcium fly

C0₂ Exposure CO₂ uptake in ash substitution ash substitution

Time (minutes) (% by weight)

24 hr Compressive Strength (% of Control)

7.5 0.59 105% 113%

[0065] At both 30% (Figures 6 and 7) and 40% (Figures 8 and 9) addition levels for the fly ash, the carbonation of the ash slightly improved the overall heat released during the calorimetry scan.

[0066] This Example also demonstrates the beneficial effects of carbonating high calcium fly ash before addition to a cement blend.

Example 3

[0067] In this Example, the effects of soluble sulfate addition to Class C Fly Ash, with and without additional grinding, were examined.

[0068] Mortar was prepared by combining the following into a bench top paddle mixer: 1350 g sand, 214 g cement, 231 g fly ash, Class C fly ash from the Parish, TX generating station operated by NRG, 241 g water. Some samples also contained sodium sulfate decahydrate. This form of sulfate was used because it is highly soluble, removing the variable of increased solubility due to increased grinding. In addition, some samples were ground further by combining ingredients in a ball mill and grounding for approximately 40 min. Mixing of mortar proceeded as follows: Combine sand, water and mix for 30 seconds, Add fly ash, cement, sodium sulfate decahydrate (if used) and mix for 30 seconds. Scrape down walls of bowl, mix additional 2 minutes and cast samples

[0069] The results are shown in Figures 10-12 and in Tables 3 and 4. Figure 10 shows isothermal calorimetry power curves for mortars prepared with 100% OPC, 60% OPC + 40% unground C Fly Ash; 60% OPC + 40% ground C Fly Ash; 60% OPC + 40% unground C Fly Ash + S0₃ addition; 60% OPC + 40% unground C Fly Ash + S0₃ addition; Figure 11 shows energy curves for the same samples; and Tables 3 and 4 show isothermal calorimetry, cumulative energy normalized to total cementitious content, and isothermal calorimetry, cumulative energy normalized to total cement content, respectively. Finally, Figure 12 shows compressive strength at 1 day for the samples with Fly Ash.

[0070] The results demonstrate a clear change in hydration kinetics and compressive strength in Class C (high CaO) fly ash containing mixtures when applying a chemical treatment. There is a shift in onset and intensity of calorimetry power and energy curve features to earlier ages (see Figures 10 and 11 and Tables 3 and 4), as well as an increase in compressive strength after one day of curing when using chemical (sulfate) treatment. In contrast, there was a limited change in either calorimetry or compressive strength development due to grinding.

Table 3

Isothermal calorimetry, cumulative energy normalized to total cementitious content, for mortars with various chemical treatments

12 15.4 34.2 15.0 34.8 65.0

13 17.6 39.6 17.3 40.1 73.3

14 20.2 45.3 19.8 45.8 81.6

15 23.0 51.5 22.7 51.9 89.9

16 26.1 58.3 25.9 58.6 98.4

17 29.4 65.5 29.3 65.7 106.9

18 33.0 73.4 32.8 73.6 115.1

19 36.9 82.4 36.6 82.5 123.1

20 41.0 93.1 40.7 93.3 130.8

21 45.3 104.7 45.0 105.7 138.0

22 49.9 115.2 49.5 117.0 144.8

23 55.1 124.5 54.5 127.0 151.1

24 61.4 132.8 60.6 135.9 156.9

Table 4

Isothermal calorimetry, cumulative energy normalized to total cement content, for mortars with various chemical treatments

8 22.2 42.5 21.5 43.1 32.5

9 25.7 53.9 24.9 54.9 40.3

10 29.5 66.2 28.6 67.5 48.4

11 33.7 79.0 32.8 80.6 56.7

12 38.5 92.5 37.6 94.0 65.0

13 44.1 107.0 43.2 108.4 73.3

14 50.4 122.4 49.6 123.8 81.6

15 57.5 139.2 56.8 140.3 89.9

16 65.3 157.4 64.7 158.3 98.4

17 73.6 177.0 73.2 177.7 106.9

18 82.5 198.4 82.1 198.9 115.1

19 92.2 222.6 91.6 222.9 123.1

20 102.5 251.5 101.8 252.1 130.8

21 113.4 283.0 112.6 285.6 138.0

22 124.8 311.3 123.9 316.2 144.8

23 137.7 336.5 136.3 343.2 151.1

24 153.5 358.9 151.6 367.2 156.9

[0071] This example demonstrates that intergrinding alone has little effect on set time and hydration kinetics, while intergrinding of chemicals can significantly impact the system. Without being bound by theory, it is thought that this occurs because grinding will expose more surface area for less soluble chemicals than the sodium sulfate used in this Example, such as CaSC>4 and CaCC .

Example 4

[0072] In this Example, the effects of intergrinding CaSC>4 and CaCCb with a high-calcium fly ash (Class C), on energy kinetics and compressive strength development were investigated.

[0073] Mortar was prepared by combining sand, cementitious material and water in a 5.6:2.2: 1 ratio in a paddle mixer. Mixing proceeded as follows: Combine sand, water and mix for 60 seconds. Add fly ash, cement and other additives (if necessary) and mix for 30 seconds. Scrape down walls of bowl, mix additional 4.5 minutes and cast samples. [0074] Class C fly ash was beneficiated by combining ash, calcium carbonate and calcium sulfate hemihydrate in a ball mill and intergrinding, as described in Example 3. The additives and fly ash composition were: 5% CaC0₃, 5.6% CaS0₄ . H₂0, 89.4% C ash. Mortars were prepared with differing binder compositions: 100% OPC; binary systems where cement was combined with one SCM: C ash, beneficiated C ash, F ash or slag, each of which was introduced at a cement replacement level of 30% or 50%; and ternary binder combinations, which were mixes where beneficiated C ash was combined with cement one other SCM for assessment of both strength development and resistance to expansion.

[0075] Results for binary systems with Class C Fly Ash as the SCM are shown in Tables 5 and 6 (isothermal calorimetry, cumulative energy normalized to total cementitious content, and isothermal calorimetry, cumulative energy normalized to total cement content, respectively, for mortar prepared with 100% OPC; mortar prepared with 50% OPC + 50% untreated Class C Fly Ash; mortar prepared with 70% OPC + 30% untreated Class C Fly Ash; and mortar prepared with 50% OPC + 50% beneficiated Class C Fly Ash) and Figure 13, which shows power vs. time for isothermal calorimetry of mortar prepared with 100% OPC; mortar prepared with 50% OPC + 50% untreated Class C Fly Ash; mortar prepared with 70% OPC + 30% untreated Class C Fly Ash; and mortar prepared with 50% OPC + 50% beneficiated Class C Fly Ash. It can be seen from calorimetry that the beneficiation treatments improve the hydration kinetics of C ash and cement mixtures. In this case the onset and intensity of features in the power curve show that both 50% and 30% additions of untreated C ash cause a shift of features to later times, consistent with set retardation, whereas intergrinding of additives (calcium carbonate and calcium sulfate, in amounts described above) into the C ash allows a mixture with 50% beneficiated C ash to demonstrate the same hydration kinetics as a mixture with 30% untreated C ash. This indicates that a greater amount of the beneficiated high calcium fly ash could be used in a concrete composition, with the same or even better results for early set and compressive strength than with a lower amount of untreated fly ash.

[0076] Table 5

Cumulative energy normalized to total cementitious content

[0077] Table 6

Cumulative energy normalized to total cement content

[0078] Figure 14 shows compressive strength development at 1, 8, and 28 days, in binary mortar systems that contain 100% OPC (control); 50% OPC + 50% beneficiated C fly ash; 70% OPC + 30% untreated C fly ash; 70% OPC + 30% slag; 70% OPC + 30% F fly ash; 50% OPC + 50% untreated C fly ash; 50% OPC + 50% slag; or 50% OPC + 50% F fly ash. Figure 15 shows compressive strength development at 1, 8, and 28 days, in binary and ternary mortar systems that contain 100% OPC (control); 50% OPC + 50% untreated C fly ash; 50% OPC + 50% beneficiated C fly ash; 50% OPC + 50% slag; 50% OPC + 15% slag + 35% beneficiated C ash; 50% OPC + 30% slag + 20% beneficiated C ash; 50% OPC + 50% F ash; 50% OPC + 15% F ash + 35% beneficiated C ash; 50% OPC + 30% F ash + 20% beneficiated C ash.

[0079] The beneficiated C ash displayed the best compressive strength development over 1, 8, and 28 days after mixing compared to the next best alternatives at 30% and 50% replacement levels. Ternary blends of beneficiated C ash and other SCMS had improved 28 day strength compared to the binary mixtures with potential for improved durability.

[0080] This Example demonstrates that intergrinding high calcium (Class C) fly ash with

CaC03 and CaS0₄ . H₂0 greatly improves early set development as well as early

compressive strength development, both in binary systems and in temary systems, in concrete prepared with the fly ash.

Example 5

[0081] In this Example, the effect of beneficiated C fly ash, treated as described in Example 4 with intergrinding of calcium sulfate and calcium carbonate, on expansion of mortars containing fly ash or other SCM was demonstrated.

[0082] Mortars were prepared as described in Example 4, except that ground pyrex glass used in place of sand, and sodium hydroxide added to bring Na₂0 equivalent up to 0.90%. Mortars were prepared with 50% OPC + 15% slag + 35% beneficiated C fly ash; 50% OPC + 50% slag; 50% OPC + 30% slag + 20% beneficiated C fly ash; 50% OPC + 50% untreated C fly ash; 50% OPC + 50% beneficiated C fly ash; 50% OPC + 50% F fly ash; 50% OPC + 15% F ash + 35% beneficiated C fly ash; and 50% OPC + 30% F ash + 20% beneficiated C fly ash. Test procedures followed ASTM C441 and ASTM C227.

[0083] Results (Figure 16) showed incremental improvements in durability when using beneficiated C ash combined with F ash. Thus, the use of calcium carbonate with calcium sulfate interground with the class C (high CaO) fly ash led to a decrease in expansion of the mortars produced, compared to untreated fly ash, indicating again that the process results in a fly ash that may be used in greater quantities than untreated fly ash, with no decrease in function.

[0084] Demonstrates the ability to optimizes ash properties in terms of set, strength and durability, through the intergrinding of chemical additives Example 6

[0085] In this Example, the effects of beneficiation of class C fly ash (as described in Examples 4 and 5, intergrinding with calcium carbonate and calcium sulfate), with or with additional carbonation of the fly ash, was demonstrated.

[0086] Mortars were prepared, with and without class C ash, beneficiation additives and grinding. Ash was sourced from Parish, TX. Additives were calcium sulfate and calcium carbonate, as described in Example 4. Intergrinding was accomplished in a ball mill, as described in Example 3. A series of samples containing beneficiated C ash were also subjected to carbonation treatment C0₂ doses of 0.05 (dose 1), 015 (dose 2), 0.30 (dose 3) and 1.5% (dose 4) by weight of total cementitious material corresponding to C02-1 to C02-4 respectively, were used. Mortar was prepared by combining the following into a bench top paddle mixer: 1350 g sand, 535g cementitious material, 241 g water. Mixing proceeded as follows: combine sand, water and mix for 30 seconds, add fly ash, cement, additives (if necessary) and mix for 30 seconds; scrape down walls of bowl, mix additional 2 minutes and carbonate (if necessary); cast samples

[0087] Figure 17 and Tables 7 and 8 show isothermal calorimetry for the various samples used: 100% OPC; 50% OPC + 50% untreated C ash; 50% OPC + 50% beneficiated C ash, unground; 50% OPC + 50% beneficiated C ash; 50% OPC + 50% beneficiated C ash + C02 dose 1; 50% OPC + 50% beneficiated C ash + C02 dose 2; 50% OPC + 50% beneficiated C ash + C02 dose 3; 50% OPC + 50% beneficiated C ash + C02 dose 4. Figure 18 shows compressive strength at Day lfor the various samples.

[0088]

[0089]

Table 7

Cumulative energy normalized to total cementitious content

[0090]

Table 8

Cumulative energy normalized to total cement content

179.5 201.7 228.3 203.0 205.8 222.2 216.1 201.4

184.6 208.5 236.2 217.0 220.1 236.8 230.2 214.8

189.4 215.1 243.3 231.0 234.0 249.6 242.4 228.7

194.0 221.4 250.1 243.2 245.5 259.9 252.1 240.6

[0092] The onset and intensity of features in the power curves along with the 1 day compressive strength show that the untreated class C fly ash causes significant set retardation, while the addition of the beneficiation additives helped reverse the retardation; intergrinding the beneficiation additives further reversed the set retardation and increased hydration kinetics. The exposure of the mortar to increasing doses of carbon dioxide further helped reverse set retardation and increase the hydration kinetics.

[0093] While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A method of producing a blended binder material comprising

(i) carbonating a combustion ash, wherein the carbonation comprises contacting an aqueous combustion ash slurry with carbon dioxide, wherein the slurry comprises less than 10% water, to produce a carbonated combustion ash;

(ii) combining the carbonated ash with a cement binder to produce a blended binder.

2. The method of claim 1 wherein the combustion ash comprises fly ash.

3. The method of claim 2 wherein the fly ash is ASTM Class C fly ash.

4. The method of claim 1 wherein the cement binder comprises Portland cement.

5. A method of producing a blended binder material comprising

(i) carbonating a combustion ash with carbon dioxide under conditions sufficient to achieve an uptake of carbon dioxide of at least 2% by weight of the combustion ash;

(ii) combining the carbonated combustion ash with cement binder to produce a blended binder.

6. The method of claim 5 wherein the blended binder contains at least 10% more combustion ash than the maximum percentage of combustion ash achievable with uncarbonated combustion ash.

7. The method of claim 5 wherein the combustion ash comprises fly ash.

8. The method of claim 7 wherein the fly ash is ASTM Class C fly ash.

9. The method of claim 5 wherein the cement binder comprises Portland cement.