WO2018147360A1 - 石炭灰の改質方法およびコンクリート混和材用のフライアッシュの製造方法 - Google Patents
石炭灰の改質方法およびコンクリート混和材用のフライアッシュの製造方法 Download PDFInfo
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- WO2018147360A1 WO2018147360A1 PCT/JP2018/004375 JP2018004375W WO2018147360A1 WO 2018147360 A1 WO2018147360 A1 WO 2018147360A1 JP 2018004375 W JP2018004375 W JP 2018004375W WO 2018147360 A1 WO2018147360 A1 WO 2018147360A1
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- sieve residue
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
- B07B7/00—Selective separation of solid materials carried by, or dispersed in, gas currents
- B07B7/08—Selective separation of solid materials carried by, or dispersed in, gas currents using centrifugal force
- B07B7/083—Selective separation of solid materials carried by, or dispersed in, gas currents using centrifugal force generated by rotating vanes, discs, drums, or brushes
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B18/04—Waste materials; Refuse
- C04B18/06—Combustion residues, e.g. purification products of smoke, fumes or exhaust gases
- C04B18/08—Flue dust, i.e. fly ash
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B18/04—Waste materials; Refuse
- C04B18/06—Combustion residues, e.g. purification products of smoke, fumes or exhaust gases
- C04B18/10—Burned or pyrolised refuse
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/10—Compositions or ingredients thereof characterised by the absence or the very low content of a specific material
- C04B2111/1087—Carbon free or very low carbon content fly ashes; Fly ashes treated to reduce their carbon content or the effect thereof
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
Definitions
- the present invention relates to a method for modifying coal ash and a method for producing fly ash for a concrete admixture.
- coal ash also called fly ash
- the fly ash for concrete admixture is defined in Japanese Industrial Standard JIS A 6201 (Fly Ash for Concrete).
- Coal ash generated in a coal-fired thermal power plant or a fluidized bed combustion furnace is usually classified by a classifier and then used as fly ash for a concrete admixture.
- Patent Document 1 describes a method using a low-pressure classifier or a multistage cyclone (free vortex centrifugal classifier) as a method for classifying coal ash.
- Patent Document 2 discloses a method of modifying fly ash by combining preliminary classification and pulverization.
- coal ash generally contains unburned carbon, and this unburned carbon may adsorb the chemical admixture of concrete. For this reason, when coal ash with a large amount of unburned carbon is used as an admixture for concrete, it may be necessary to increase the amount of other chemical admixtures or the fluidity of the concrete may fluctuate. In addition, black spots due to unburned carbon occur on the surface of the concrete, and the appearance of the hardened concrete may be deteriorated. For this reason, in order to use coal ash as fly ash for concrete admixture, it is necessary to reduce the amount of unburned carbon in coal ash. In JIS A 6201 (concrete fly ash), ignition loss (ig.loss) including the amount of unburned carbon is limited.
- the present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a coal ash reforming method capable of efficiently reducing the amount of unburned carbon in coal ash. Another object of the present invention is to provide a method capable of efficiently producing fly ash for concrete admixture from coal ash.
- a method for reforming coal ash uses a forced vortex centrifugal classifier to classify coal ash having a 45 ⁇ m sieve residue of 10% by mass or more.
- the classification is performed under the condition that the 45 ⁇ m sieve residue of the coal ash after classification is in the range of 1% by mass to 8% by mass.
- the coal ash after classification (after reforming) has a 45 ⁇ m sieve residue of 1% by mass to 8% by mass. Range and less.
- unburned carbon in coal ash adheres to the coal ash particles and has a high ratio of forming aggregated particles having a particle diameter of 45 ⁇ m or more. Therefore, the coal ash obtained by the coal ash reforming method according to one embodiment of the present invention has a low content of unburned carbon, and when this is used as a concrete admixture, black spots are less likely to occur.
- the obtained coal ash has the fine coal ash particle
- the coal ash having a 45 ⁇ m sieve residue of 10% by mass or more is classified into 45 ⁇ m of the coal ash after the classification using a forced vortex centrifugal classifier. Since the classification is performed under the condition that the sieve residue is 1% by mass or more, as is clear from the results of Examples described later, the recovery rate of coal ash with reduced unburned carbon content is high, and coal ash The amount of unburned carbon can be efficiently reduced.
- the 45 ⁇ m sieve residue is 10% by mass or more (that is, the coal ash before classification) has the 45 ⁇ m sieve residue.
- 40% by mass or less the degree of compression is 40% or less, the lightness index L value in the Hunter Lab color system is 54.0 or more, and the ignition loss is 5.0% by mass or less. Is preferred.
- the coal ash before classification has a 45 ⁇ m sieve residue of 40% by mass or less and a compressibility of 40% or less, so the recovery rate of coal ash with reduced unburned carbon content is high, The amount of unburned carbon in the coal ash can be reduced efficiently.
- the lightness index L value in the Hunter Lab color system is 54.0 or more and the ignition loss is 5.0% by mass or less, the amount of unburned carbon in the obtained coal ash is further reduced. Therefore, it can be advantageously used as an admixture for concrete.
- the classification accuracy index is set as high as 0.6 or more, the coal ash after classification has a narrow particle size distribution and a uniform particle size, and segregates during storage and mixing with other concrete materials. Is less likely to occur.
- the classification accuracy index is set to 0.7 or less, the recovery rate of coal ash after classification is increased, and the amount of unburned carbon in the coal ash can be more efficiently reduced.
- the obtained coal ash has an ignition loss that is reduced by 8.0% or more compared to the coal ash before classification.
- the obtained coal ash can be advantageously used as an admixture for concrete because the amount of unburned carbon is reliably reduced.
- the method for producing fly ash for concrete admixtures has a 45 ⁇ m sieve residue in a range of 10% by mass to 40% by mass, a compressibility of 40% or less, and a Hunter Lab table.
- the coal ash having a lightness index L value in the color system of 54.0 or more and an ignition loss of 5.0% by mass or less is classified using a forced vortex centrifugal classifier.
- the 45 ⁇ m sieve residue is classified under the condition of 1 mass% or more and 8 mass% or less.
- the obtained coal ash (fly ash) has a small amount of unburned carbon and a particle diameter of 45 ⁇ m or less. Therefore, when this is used as an admixture for concrete, the occurrence of black spots is small and the activity index is high. Furthermore, since a forced vortex centrifugal classification device is used as the classification device, the coal ash recovery rate after classification is high. Therefore, according to the method for producing fly ash for concrete admixture which is one embodiment of the present invention, coal ash (fly ash) useful as a concrete admixture can be efficiently produced.
- coal ash reforming method capable of efficiently reducing the amount of unburned carbon in coal ash.
- the method which can manufacture efficiently the fly ash for concrete admixtures from coal ash can be provided.
- the coal ash used in the present embodiment is ash generated by burning coal used as fuel for thermal power generation or fluidized bed combustion furnace.
- Coal ash obtained by the reforming method of this embodiment can be advantageously used as an admixture for concrete, for example.
- a predetermined coal ash is sieved using a forced vortex centrifugal classifier and the coal ash after classification is sieved by 45 ⁇ m. Classification is performed under the condition that the remainder is in the range of 1 to 8% by mass.
- the coal ash before classification used in the present embodiment has a 45 ⁇ m sieve residue of 10% by mass or more.
- the coal ash before classification is preferably in the range of 10% by mass to 40% by mass, the compression degree is 40% or less, and the lightness index L value in the Hunter Lab color system is 54.0 or more. And the loss on ignition is 5% or less.
- the 45 ⁇ m sieve residue is the residue remaining on the sieve when classified using a standard sieve having an opening of 45 ⁇ m, and is the content of particles having a particle size of 45 ⁇ m or more.
- the particles having a particle size of 45 ⁇ m or more contained in the coal ash are agglomerated particles mainly formed by unburned carbon in the coal ash adhering to the coal ash particles and agglomerating, and usually 10 mass in the coal ash. More than% is included. If the 45 ⁇ m sieve residue exceeds 40% by mass, the amount of 45 ⁇ m sieve residue removed by classification increases, and the recovery rate of coal ash after classification described later may be reduced.
- the 45-micrometer sieve residue is set as the range of 10 mass% or more and 40 mass% or less.
- the 45 ⁇ m sieve residue is more preferably in the range of 10% by mass to 20% by mass, but is not limited thereto.
- the degree of compression is a value defined by the following equation.
- Compressibility (%) ⁇ (Fixed apparent specific gravity ⁇ Loose apparent specific gravity) / Folded apparent specific gravity ⁇ ⁇ 100
- the loose apparent specific gravity is the specific gravity of coal ash (coal ash weight / capacity of container) when a predetermined capacity of container is filled with coal ash by free fall.
- the solid apparent specific gravity is a specific gravity (weight of coal ash / compressed coal ash volume) when coal ash filled in a container by free fall is compressed by tapping.
- the degree of compression tends to correlate with the fluidity of the powder. If the degree of compression exceeds 40%, the fluidity of the coal ash becomes low, and the recovery rate of coal ash after classification described later may be reduced. For this reason, in this embodiment, the degree of compression is set to 40% or less. The degree of compression is preferably in the range of 30% to 40%.
- the lightness index L value in the Hunter Lab color system represents lightness, and the larger the L value, the closer to white, that is, the smaller the amount of black material such as unburned carbon mixed.
- the brightness index L value in the Hunter Lab color system is set to 54.0 or more.
- the lightness index L value is preferably in the range of 54.0 to 70.0.
- the ignition loss is an index of the amount of unburned carbon contained in coal ash.
- the ignition loss exceeds 5.0% by mass, if the coal ash after classification described later is added to concrete as an admixture, black spots may easily occur in the obtained concrete.
- the ignition loss is set to 5.0 mass% or less.
- the ignition loss is preferably in the range of 1.0% by mass or more and 5.0% by mass or less.
- the ignition loss is more preferably in the range of 1.0% by mass or more and 3.0% by mass or less, but is not limited thereto.
- the coal ash is classified using a forced vortex centrifugal classifier.
- a centrifugal classifying device that classifies using the centrifugal force of particles and an inertia type classifying device that classifies using the inertial force of particles are known.
- a centrifugal classifier is known to be a forced vortex type, a semi-free vortex type, and a free vortex type.
- the forced vortex classifier is a classifier in which a rotating body (also referred to as a classification rotor) is provided inside the apparatus, and the rotator is rotated at high speed to forcibly form a vortex.
- the semi-free vortex classifier is a classifier provided with a guide plate (also referred to as a slit) for generating a vortex inside the apparatus instead of a rotating body.
- the free vortex classifier is a classifier that generates vortices by blowing a gas in a tangential direction inside the apparatus, as represented by a cyclone.
- the particle size of the powder after classification can be accurately adjusted by adjusting the rotational speed of the rotating body. For this reason, in this embodiment, a forced vortex centrifugal classifier is used.
- the forced vortex centrifugal classifier is used, and classification is performed under the condition that the 45 ⁇ m sieve residue of the coal ash after classification is in the range of 1% by mass to 8% by mass. If the 45 ⁇ m sieve residue is set to a high value exceeding 8% by mass, the removal efficiency of unburned carbon may be lowered. On the other hand, if the 45 ⁇ m sieve residue is set to a low value of less than 1% by mass, the coal ash recovery rate after classification may be excessively reduced. For this reason, in this embodiment, the classification condition is set to a condition in which the 45 ⁇ m sieve residue of the coal ash after classification is in the range of 1% by mass to 8% by mass. The 45 ⁇ m sieve residue of coal ash after classification is preferably in the range of 1% by mass to 5% by mass, but is not limited thereto.
- classification by a forced vortex centrifugal classifier is performed under the condition that the classification accuracy index excellent is 0.6 or more and 0.7 or less.
- the classification accuracy index ⁇ is closer to 1, it means that the particle size distribution is narrower and the particle sizes are uniform.
- the classified coal ash preferably has a narrow particle size distribution and a uniform particle size because segregation hardly occurs during storage or mixing with other concrete materials. Accordingly, the classification accuracy index ⁇ is preferably close to 1, but if the classification accuracy index ⁇ is too close to 1, the coal ash recovery rate after classification is too low. For this reason, in this embodiment, the classification condition is set as a condition in which the classification accuracy index ITA is 0.6 or more and 0.7 or less.
- the coal ash after classification (after reforming) has a 45 ⁇ m sieve residue in the range of 1% by mass to 8% by mass. And less.
- the obtained coal ash is usually reduced by 8.0% or more in terms of loss on ignition compared to the coal ash before classification. Therefore, since the coal ash obtained by the coal ash reforming method of the present embodiment has a low content of unburned carbon, when this is used as an admixture for concrete, black spots are less likely to occur.
- the obtained coal ash preferably has a loss on ignition of 10.0% or more compared with the coal ash before classification, but is not limited thereto.
- the obtained coal ash is mainly composed of fine coal ash particles having a particle size of 45 ⁇ m or less, the activity index becomes high when this is used as an admixture for concrete.
- the coal ash obtained by this embodiment usually has a quality equivalent to that of fly ash type II defined by JIS A 6201 (fly ash for concrete).
- the classification is performed under the condition that the 45 ⁇ m sieve residue of the coal ash after classification is in the range of 1% by mass to 8% by mass using a forced vortex centrifugal classifier.
- the recovery rate of coal ash with reduced content of fuel carbon is high, and the amount of unburned carbon in coal ash can be reduced efficiently.
- the coal ash before classification has a 45 ⁇ m sieve residue of 40% by mass or less and a compressibility of 40% or less, recovery of coal ash with reduced unburned carbon content The rate is high, and the amount of unburned carbon in the coal ash can be efficiently reduced.
- the coal ash before classification has a brightness index L value in the Hunter Lab color system of 54.0 or more and an ignition loss of 5.0% by mass or less. Since the amount of carbon is further reduced, it can be advantageously used as an admixture for concrete.
- the coal ash after classification may be used for applications other than the admixture for concrete.
- the coal ash before classification has a 45 ⁇ m sieve residue in the range of 10% by mass to 40% by mass, the degree of compression is 40% or less, and the lightness index L value in the Hunter Lab color system. Is 54.0 or more, and it is not necessary that the loss on ignition is 5.0% by mass or less.
- the coal ash before classification is required to have a 45 ⁇ m sieve residue of 10% by mass or more.
- the 45-micrometer sieve residue and ignition loss were measured by the method based on the method described in JIS A6201 (fly ash for concrete).
- the degree of compression was calculated from the above equation by measuring the loose apparent specific gravity and the hard apparent specific gravity using a powder tester (manufactured by Hosokawa Micron Corporation).
- a classification device of the following classification method was prepared.
- Forced vortex centrifugal classifier Turbo classifier, manufactured by Nissin Engineering Co., Ltd.
- Semi-free vortex centrifugal classifier Micro classifier, manufactured by Seishin Corporation Free vortex centrifugal classifier: Cyclone, Mitsubishi Inertia classifier manufactured by Material Co., Ltd .: Elbow Jet, Matsubo Co., Ltd.
- the above-mentioned coal ash raw material was classified using the classification system classification device, and the classified coal ash was recovered.
- the classification conditions were such that the 45 ⁇ m sieve residue of the classified coal ash was 1% by mass or more and 8% by mass or less.
- Recovery rate (mass%) weight of recovered coal ash / weight of coal ash charged into the classification device ⁇ 100
- the particle size distribution (under the sieve) of the coal ash after classification was measured with a laser diffraction particle size distribution meter (Microtrack particle size distribution meter manufactured by Nikkiso Co., Ltd., model: MT3000II).
- the obtained particle size distribution was divided into several particle size intervals, the partial classification efficiency was determined from the recovery rate for each particle size interval, and a partial classification efficiency curve was created.
- the ratio of d25: 25% classification diameter and d75: 75% classification diameter (d25 / d75) was used as the classification accuracy index.
- the lightness index L value was measured using a colorimetric color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., model: ZE2000).
- the above coal ash DH is classified using a forced vortex centrifugal classifier (turbo classifier, manufactured by Nissin Engineering Co., Ltd.), and the classified coal ash is recovered. did.
- the classification conditions are as follows. In Examples 4 to 7 of the present invention and Comparative Examples 14, 17, and 19, the 45 ⁇ m sieve residue of the coal ash after classification is in the range of 1% by mass to 8% by mass, and the classification accuracy index is The conditions were in the range of 0.6 to 0.7. In Comparative Examples 10, 12, and 16, the 45 ⁇ m sieve residue of the classified coal ash exceeded 8 mass%, and the classification accuracy index was in the range of 0.6 to 0.7. In Comparative Examples 11, 13, 15, and 18, the 45 ⁇ m sieve residue of the coal ash after classification was less than 1% by mass, and the classification accuracy index was in the range of 0.6 to 0.7.
- a mortar specimen was prepared by a method based on the method described in JIS R 5201 (Cement physical test method). Observe the presence or absence of a black substance that floats on the surface of the mortar specimen prepared, and mark “A” when no black spots occur, and “B” when any black spots occur. did.
- the activity index was measured based on the method described in JIS A 6201 (fly ash for concrete).
- An activity index having an activity index of 7 days of age is 70% or more, an activity index of 28 days of age is 80% or more, and an activity index of 91 days of age is 90% or more.
- B Activity index of coal ash after classification
- the 45 ⁇ m sieve residue, the degree of compression, the lightness index L value, and the coal ash whose ignition loss is within the scope of the present invention are adjusted to the condition that the 45 ⁇ m sieve residue of the classified coal ash exceeds 8% by mass.
- the coal ash after classification had a large 45 ⁇ m sieve residue, and the ignition loss was not reduced.
- the activity index was low and it was inadequate to use as a concrete admixture.
- Comparative Examples 14, 15, and 16 using coal ash having a lightness index L value lower than the range of the present invention black spots were generated on the mortar specimen. Furthermore, in the comparative example 16 which classified on the conditions that the 45 micrometer sieve residue of the coal ash after classification exceeds 8 mass%, the coal ash after classification had a high ignition loss, and the activity index became low.
- Comparative Example 17 using coal ash whose ignition loss was higher than the range of the present invention the coal ash after classification had a high ignition loss and a low activity index.
- Comparative Example 19 using coal ash having a lightness index L value lower than the range of the present invention and an ignition loss higher than the range of the present invention black spots are generated on the mortar specimen, and the activity index is lowered. It was.
- the amount of unburned carbon in the coal ash can be efficiently reduced.
- the fly ash for concrete admixtures can be efficiently manufactured from coal ash.
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Abstract
Description
本願は、2017年2月10日に、日本に出願された特願2017-023389号に基づき優先権を主張し、その内容をここに援用する。
この場合、分級前の石炭灰は、45μmふるい残分が40質量%以下で、圧縮度が40%以下とされているので、未燃カーボンの含有量が低減した石炭灰の回収率が高く、石炭灰中の未燃カーボン量を効率よく低減させることができる。また、ハンターLab表色系における明度指数L値が54.0以上であり、かつ強熱減量が5.0質量%以下とされているので、得られる石炭灰の未燃カーボン量がより低減されるので、コンクリート用の混和材として有利に使用することができる。
この場合、分級精度指数が0.6以上と高く設定されているので、分級後の石炭灰は、粒度分布が狭く、粒径が揃っていて、保存時や他のコンクリート材料との混合時に偏析が起こりにくくなる。また、分級精度指数が0.7以下と設定されているので、分級後の石炭灰の回収率が高くなり、石炭灰中の未燃カーボン量をより効率よく低減させることができる。
この場合、得られる石炭灰は、未燃カーボン量が確実に低減されているので、コンクリート用の混和材として有利に使用することができる。
本実施形態で用いる石炭灰は、火力発電や流動床燃焼炉の燃料として使用された石炭が燃焼して生成した灰である。本実施形態の改質方法で得られる石炭灰は、例えば、コンクリートの混和材として有利に利用することができる。
本実施形態で用いる分級前の石炭灰は、45μmふるい残分が10質量%以上とされている。上記の分級前の石炭灰は、好ましくは10質量%以上40質量%以下の範囲にあって、圧縮度が40%以下であって、ハンターLab表色系における明度指数L値が54.0以上であり、かつ強熱減量が5%以下とされている。以下、本実施形態において、石炭灰の物性を上記のように設定した理由を説明する。
このため、本実施形態では、45μmふるい残分を10質量%以上40質量%以下の範囲と設定している。前記45μmふるい残分は、10質量%以上20質量%以下の範囲とすることがより好ましいが、これに限定されることはない。
圧縮度(%)={(固め見掛け比重-ゆるみ見掛け比重)/固め見掛け比重}×100
このため、本実施形態では、圧縮度を40%以下と設定している。圧縮度は30%以上40%以下の範囲にあることが好ましい。
このため、本実施形態では、ハンターLab表色系における明度指数L値を54.0以上と設定している。なお、明度指数L値は、54.0以上70.0以下の範囲にあることが好ましい。
このため、本実施形態では、強熱減量を5.0質量%以下と設定している。なお、強熱減量は、1.0質量%以上5.0質量%以下の範囲にあることが好ましい。前記強熱減量は、1.0質量%以上3.0質量%以下の範囲にあることがより好ましいが、これに限定されることはない。
分級装置としては、粒子の遠心力を利用して分級する遠心方式の分級装置と、粒子の慣性力を利用して分級する慣性方式の分級装置とが知られている。さらに、遠心方式の分級装置は、強制渦式と、半自由渦式と、自由渦式とが知られている。強制渦式の分級装置は、装置内部に回転体(分級ロータともいう)が備えられていて、その回転体を高速で回転させることで強制的に渦を形成する分級装置である。半自由渦式の分級装置は、回転体の代わりに、装置内部に渦を生成させる案内板(スリットともいう)が備えられている分級装置である。自由渦式の分級装置は、サイクロンに代表されるように、装置内部の接線方向に気体を吹き込んで渦を生成させる分級装置である。
45μmふるい残分が8質量%を超える高い値に設定すると、未燃カーボンの除去効率が低下するおそれがある。一方、45μmふるい残分を1質量%未満の低い値に設定すると、分級後の石炭灰の回収率が過度に低下するおそれがある。
このため、本実施形態では、分級条件を、分級後の石炭灰の45μmふるい残分が1質量%以上8質量%以下の範囲となる条件と設定している。分級後の石炭灰の45μmふるい残分は、1質量%以上5質量%以下の範囲が好ましいが、これに限定されることはない。
к=d25/d75
分級後の石炭灰は、粒度分布が狭く、粒径が揃っている方が、保存時や他のコンクリートの材料との混合時に偏析が起こりにくくなるので好ましい。従って、分級精度指数κは1に近い方が好ましいが、一方、分級精度指数κを1に近づけすぎると、分級後の石炭灰の回収率が低くなりすぎる。
このため、本実施形態では、分級条件を分級精度指数кが、0.6以上0.7以下となる条件と設定している。
また、得られる石炭灰は、強熱減量が分級前の石炭灰と比較して、通常は8.0%以上低減されている。従って、本実施形態の石炭灰の改質方法によって得られる石炭灰は、未燃カーボンの含有量が少ないので、これをコンクリートの混和材として使用した場合は黒色斑点が発生しにくくなる。得られる石炭灰は、強熱減量が分級前の石炭灰と比較して、10.0%以上低減されていることが好ましいが、これに限定されることはない。さらに、得られる石炭灰は、粒径が45μm以下の微細な石炭灰粒子を主成分とするので、これをコンクリートの混和材として使用した場合は活性度指数が高くなる。本実施形態により得られる石炭灰は、通常は、JIS A 6201(コンクリート用フライアッシュ)で規定されているフライアッシュII種と同等の品質を有する。
例えば、上記の実施形態では、分級後(改質後)の石炭灰を、コンクリートの混和材以外の用途で使用してもよい。この場合は、分級前の石炭灰は、45μmふるい残分が10質量%以上40質量%以下の範囲にあって、圧縮度が40%以下であって、ハンターLab表色系における明度指数L値が54.0以上であり、かつ強熱減量が5.0質量%以下とする必要はない。但し、分級前の石炭灰は、45μmふるい残分が10質量%以上であることは必要である。
石炭灰(分級前)として、下記の石炭灰A~Cを用意した。
石炭灰A:45μmふるい残分:39質量%、圧縮度:35質量%、強熱減量:3.5質量%
石炭灰B:45μmふるい残分:40質量%、圧縮度:40質量%、強熱減量:5.0質量%
石炭灰C:45μmふるい残分:41質量%、圧縮度:41質量%、強熱減量:2.0質量%
圧縮度は、パウダーテスター(ホソカワミクロン株式会社製)を用いて、ゆるみ見掛け比重と固め見掛け比重とを測定し、上述の式より算出した。
強制渦式遠心方式の分級装置:ターボクラシファイアー、日清エンジニアリング株式会社製
半自由渦式遠心方式の分級装置:マイクロクラシファイアー、株式会社セイシン企業製
自由渦式遠心方式の分級装置:サイクロン、三菱マテリアル株式会社製
慣性方式の分級装置:エルボージェット、株式会社マツボー製
回収率(質量%)=回収した石炭灰の重量/分級装置に投入した石炭灰の重量×100
石炭灰(分級前)として、下記の石炭灰D~Hを用意した。
石炭灰D:45μmふるい残分:21質量%、圧縮度:38%、明度指数L値:62.0、強熱減量:2.1質量%
石炭灰E:45μmふるい残分:38質量%、圧縮度:37%、明度指数L値:54.0、強熱減量:5.0質量%
石炭灰F:45μmふるい残分:23質量%、圧縮度:35%、明度指数L値:53.7、強熱減量:4.6質量%
石炭灰G:45μmふるい残分:22質量%、圧縮度:39%、明度指数L値:55.1、強熱減量:5.2質量%
石炭灰H:45μmふるい残分:30質量%、圧縮度:34%、明度指数L値:53.9、強熱減量:5.8質量%
なお、分級条件は、本発明例4~7および比較例14、17、19では、分級後の石炭灰の45μmふるい残分が1質量%以上8質量%以下の範囲で、かつ分級精度指数が0.6以上0.7以下の範囲となる条件とした。比較例10、12、16では、分級後の石炭灰の45μmふるい残分が8質量%を超え、かつ分級精度指数が0.6以上0.7以下の範囲となる条件とした。比較例11、13、15、18では、分級後の石炭灰の45μmふるい残分が1質量%未満で、かつ分級精度指数が0.6以上0.7以下の範囲となる条件とした。
モルタル供試体を、JIS R 5201(セメントの物理試験方法)に記載されている方法に準拠した方法によって作製した。作製したモルタル供試体の表面に浮き出す黒色物質の有無を目視で観察し、黒色の斑点が発生しなかったものを「A」とし、黒色の斑点が一つでも発生したものを「B」とした。
JIS A 6201(コンクリート用フライアッシュ)に記載されている方法に準拠して、活性度指数を測定した。材齢7日の活性度指数が70%以上であって、材齢28日の活性度指数が80%以上であり、そして材齢91日の活性度指数が90%以上であるものを「A」とし、それ以外のものを「B」とした。
Claims (5)
- 45μmふるい残分が10質量%以上である石炭灰を、強制渦式遠心方式の分級装置を用いて、分級後の石炭灰の45μmふるい残分が1質量%以上8質量%以下の範囲となる条件にて分級することを特徴とする石炭灰の改質方法。
- 前記45μmふるい残分が10質量%以上である石炭灰は、前記45μmふるい残分が40質量%以下であって、圧縮度が40%以下であり、ハンターLab表色系における明度指数L値が54.0以上であって、かつ強熱減量が5.0質量%以下であることを特徴とする請求項1に記載の石炭灰の改質方法。
- 前記分級を、分級精度指数(к=d25/d75)が、0.6以上0.7以下となる条件にて実施することを特徴とする請求項1または請求項2に記載の石炭灰の改質方法。
- 得られる石炭灰は、強熱減量が分級前の石炭灰と比較して8.0%以上低減されていることを特徴とする請求項1から請求項3のいずれかの一項に記載の石炭灰の改質方法。
- 45μmふるい残分が10質量%以上40質量%以下の範囲にあって、圧縮度が40%以下であり、ハンターLab表色系における明度指数L値が54.0以上であって、かつ強熱減量が5.0質量%以下である石炭灰を、強制渦式遠心方式の分級装置を用いて、分級後の石炭灰の45μmふるい残分が1質量%以上8質量%以下の範囲となる条件にて分級することを特徴とするコンクリート混和材用のフライアッシュの製造方法。
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