Admixture, manufacturing method of admixture, concrete, manufacturing method of concrete, and manufacturing method of material containing calcium

Abstract

To provide an admixture for concrete not needing a special facility for fixing carbon dioxide and a manufacturing method thereof, concrete containing the admixture, and a manufacturing method thereof.SOLUTION: An admixture is manufactured by reacting a by-product obtained in a step of manufacturing quick lime with water and carbon dioxide and contains calcium of 35 mass% or under. A manufacturing method of the admixture employs the by-product obtained in the step of manufacturing quick lime as a raw material and includes a first step of reacting the raw material with water and a second step of reacting a product material obtained by the first step with carbon dioxide.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an admixture for concrete and a method for producing the same, concrete containing the admixture and a method for producing the same, and a method for producing a calcium-containing substance. [Background technology]

[0002] Carbon dioxide (CO2), one of the causes of global warming, is generated during the production of cement. Cement is a powder that hardens by reacting with water and is used to produce mortar and concrete. In order to reduce the amount of CO2 generated, it has been proposed to use blast furnace slag or fly ash instead of cement to produce concrete.

[0003] Furthermore, concrete that uses calcium carbonate (CaCO3) or biochar as a material that fixes CO2 and reduces the amount of CO2 generated during the manufacturing process to virtually zero or less is also known (see, for example, Patent Document 1).

[0004] Concrete containing CaCO3 has been researched for a long time and can be produced using existing technology. However, a large amount of energy is required to burn limestone in the production of CaCO3, and although CO2 is fixed in the process of converting quicklime (CaO) produced by burning into CaCO3, CO2 is generated during the burning process.

[0005] For this reason, it has been proposed to use CaCO3 produced not by burning limestone but by supplying carbon dioxide to calcium contained in concrete sludge generated in ready-mixed concrete factories and the like (see, for example, Patent Documents 2 and 3).It has also been proposed to use CaCO3 produced by supplying factory waste gas or atmospheric CO2 to waste seawater containing calcium after producing magnesium hydroxide from seawater (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-160056 [Patent Document 2] Japanese Patent Application Publication No. 2023-96668 [Patent Document 3] Japanese Patent Application Publication No. 2023-127648 Summary of the Invention [Problem to be solved by the invention]

[0007] The calcium sources described in Patent Documents 2 and 3 above are derived from waste materials, but have the problem of requiring dedicated facilities for fixing CO2 in specific factories such as ready-mixed concrete factories and magnesium manufacturing factories. [Means for solving the problem]

[0008] The present invention has been made in view of the above-mentioned problems, and provides an admixture for concrete, which is produced by reacting a by-product obtained in a process for producing quicklime with water and carbon dioxide, and which contains 5% by mass or more and 37% by mass or less of calcium.

[0009] Also provided is a method for producing an admixture for concrete containing 5% to 37% by mass of calcium, the method comprising a first step of reacting a by-product obtained in a step of producing quicklime with water as a raw material, and a second step of reacting the product obtained in the first step with carbon dioxide. [Effects of the Invention]

[0010] According to the present invention, there is no need for dedicated facilities for fixing CO2. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a process for producing quicklime. [Figure 2] A diagram showing product CaO powder and calcination dust. [Figure 3]1 is a diagram showing an example of the configuration of an apparatus for producing calcium carbonate from quicklime. [Figure 4] FIG. 1 is a diagram showing an example of a manufacturing flow of a concrete admixture. [Figure 5] FIG. 1 is a graph showing the relationship between sieve openings and passing mass percentage. [Figure 6] FIG. 1 is a diagram showing an example of a concrete manufacturing flow. DETAILED DESCRIPTION OF THE INVENTION

[0012] Quicklime (calcium oxide: CaO) is obtained by burning limestone and is used in steel production, soil improvement, as a desiccant, and as a raw material for building materials. Limestone is primarily composed of calcium carbonate (CaCO3), which decomposes at approximately 900°C, releasing carbon dioxide (CO2) and producing CaO.

[0013] The manufacturing process of CaO will be described with reference to Figure 1. In step 100, limestone mined from a mountain or the like is crushed into small pieces by a crusher. In step 101, the crushed limestone is classified using a sieve. In step 102, the classified limestone is placed in a furnace and fired at 900 to 1000°C. When the limestone is fired, the reaction shown in formula (1) below occurs, producing quicklime. CaCO3 → CaO + CO2(1)

[0014] The composition and crystalline structure of quicklime vary depending on where it is mined. The calcination method also affects the degree of shrinkage (consolidation), which in turn affects its reactivity and properties. The calcination method also depends on the type of furnace used to calcine the limestone. The type of furnace is determined by the method of heat exchange between the limestone and combustion gases produced by burning fuel such as heavy oil, and includes vertical furnaces such as the Maerz furnace and Beckenbach furnace, and horizontal furnaces such as the rotary kiln.

[0015] A Mertz furnace consists of two furnace tubes connected by a passage at the bottom. Limestone is alternately charged into each of the two furnace tubes from the top, and while one furnace tube is firing, the other furnace tube is preheating. The limestone passes through a cooling zone below and is discharged from the bottom of the furnace as quicklime.

[0016] The Beckenbach kiln consists of an outer casing and an inner casing inserted inside it. Limestone is charged into the space between the inner and outer casings from the top of the furnace, passes through a preheating zone, a calcination zone, and a cooling zone, and is discharged from the bottom of the furnace as quicklime.

[0017] A rotary kiln has a preheating section, a calcining section, and a cooling section. After preheating to the temperature at which thermal decomposition begins in the preheating section, the material is burned while moving in the calcining section due to a gentle incline and rotation, becoming quicklime. The quicklime is then discharged from the furnace through the cooling section.

[0018] The main component of limestone is calcium carbonate, but it also contains other components such as aluminum oxide (Al2O3), iron oxide (Fe2O3), and silica (SiO2).

[0019] In the process of calcining limestone in the production of quicklime, by-products are generated in the production of the finished quicklime. The by-products are, for example, calcination dust, which is fine particles floating in the furnace, and are collected by a dust collector such as a bag filter. The calcination dust is powdered by the introduction of limestone into the furnace or by friction with the furnace, and is then calcined, containing fine CaO particles generated according to the above formula (1).

[0020] For example, in Beckenbach kilns, limestone and lump coke are mixed and fed into the furnace to reduce fuel costs. The limestone is then calcined by burning the coke. Coke contains ash, such as Al2O3, Fe2O3, SiO2, CaO, and magnesium oxide (MgO), which remains after combustion. The ash adheres to the CaO produced during calcination, adheres to the CaO particles that make up the retained dust, disperses in the exhaust gas, remains in the furnace, or is discharged from the bottom of the furnace. These are generally addressed by surface treatment and sorting (Reference 1: Michitaka Fujio, "Establishment of Operating Technology for Beckenbach Lime Kilns," Journal of the Society of Inorganic Materials, Japan, 7, 220-226 (2000)). These constitute the by-products or calcination dust obtained during the limestone production process.

[0021] Since calcination dust is a powder containing CaO particles as well as ash, it can be brown, gray, black, or other colors, whereas the finished CaO is white. The color varies depending on the type of furnace and the composition of the fuel, and includes colors such as sand, chalk, off-white, ivory, silver gray, brown gray, gray, Rikyu gray, lead, gray, soot bamboo, dark brown, ink, black, iron black, silver, ivory, sky gray, pearl gray, silver gray, ash gray, rose gray, gray, steel gray, straight gray, charcoal gray, lamp black, and black, as specified in Appendix 1 of the Japanese Industrial Standards (JIS) Z 8102:2001 (Color Names of Object Colors).

[0022] In addition, JIS Z 8102:2001 allows the addition of modifiers to the above conventional colors using the terms specified in 7.2 Table 3 and 7.3 Table 4 of the same specification, and includes colors modified by any of the above conventional color names with "bright," "strong," "dark," "light," "soft," "dull," "dark," "very light," "light grayish," "grayish," "dark grayish," "very dark," and "medium" as specified in JIS Z 8102:2001.7.2 Table 3 and 7.3 Table 4 (JIS Z 8102:2001.11.2 and 7.2 Table 3, 7.3 Table 4).

[0023] Figure 2 shows the color of the CaO product and the color of the calcined dust. Figure 2(a) shows the CaO powder product, which is white, and Figure 2(b) shows the calcined dust, which is gray.

[0024] Calcination dust contains CaO, but the content is small and it does not have a consistent color, so it is a waste Ca content containing CaO and is usually discarded.

[0025] The results of X-ray fluorescence analysis and particle size distribution measurement of the calcined dust obtained by calcining limestone in a Beckenbach furnace are shown below. The X-ray fluorescence analysis was performed using an X-ray fluorescence analyzer ZSX Primus II (manufactured by Rigaku Corporation).

[0026] The results of X-ray fluorescence analysis showed that the main components were 48.2% by mass of oxygen, 29.9% by mass of calcium, 10.4% by mass of carbon, 4.8% by mass of silicon (silica), and 4.1% by mass of aluminum. Other components of the calcined dust included 0.9% by mass of sulfur, 0.6% by mass of iron, 0.3% by mass of magnesium, 0.2% by mass of titanium, and 0.2% by mass of sodium.

[0027] Particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer (Beckman Coulter, Inc. LS 13 320XR: Universal Liquid Module / Wet Measurement Unit; Dispersion Medium / Ion-exchanged Water: Particle Size / Volume). The cumulative percentage of volume-based particle sizes below a certain value was then calculated. The cumulative percentage of volume-based particle sizes measured using the laser diffraction / scattering method was 99.0% for particle sizes below 600 μm, 79.3% for particle sizes below 150 μm, and 60.8% for particle sizes below 75 μm.

[0028] The by-product or calcined dust obtained in the process for producing quicklime of the present invention may have a cumulative fraction of particles with a volumetric particle size of 600 μm or less as measured by a laser diffraction / scattering method of 70% or more, and preferably 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 97% or more.

[0029] The cumulative fraction of particles having a volumetric particle size of 150 μm or less as measured by a laser diffraction / scattering method may be 50% or more, or may be 55% or more, 60% or more, 65% or more, 70% or more, or 75% or more. The upper limit may be 95% or less, 90% or less, or 85% or less.

[0030] Furthermore, the cumulative fraction of particle diameters of 75 μm or less on a volume basis measured by a laser diffraction / scattering method may be 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, or 55% or more. The upper limit may be 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, or 65% or less.

[0031] Incidentally, the quality of commercially available industrial lime (CaO) is specified in the Japanese Industrial Standards (JIS) R9001:2006. According to JIS R9001:2006, special grade lime must contain 93% or more by mass of CaO, grade 1 lime must contain 90% or more by mass of CaO, and grade 2 lime must contain 80% or more by mass. Even if the CaO content is 80% or more by mass, the Ca content exceeds 57% by mass.

[0032] Furthermore, when producing Grade 1 quicklime, it is necessary to produce quicklime with a CaO content of 90% by mass or more and a Ca content exceeding 64% by mass, and when producing Special Grade quicklime, it is necessary to produce quicklime with a CaO content of 93% by mass or more and a Ca content exceeding 66% by mass. Therefore, to produce quicklime that meets both grades, it is necessary to produce quicklime with a CaO content of 93% by mass or more and a Ca content exceeding 66% by mass.

[0033] In contrast, the by-product or calcined dust obtained in the process of producing quicklime may have a Ca content of 57% by mass or less as determined by X-ray fluorescence analysis. Furthermore, the by-product or calcined dust obtained for the purpose of producing Grade 1 quicklime may have a Ca content of 64% by mass or less. Furthermore, the by-product or calcined dust obtained for the purpose of producing Special Grade quicklime may have a Ca content of 66% by mass or less. For this reason, the by-product or calcined dust may not have a CaO content of 93% by mass or more, or a Ca content of 66% by mass, which meets the requirements for either grade.

[0034] Furthermore, the Ca content of the by-product or calcined dust obtained in the process for producing quicklime of the present invention, as determined by X-ray fluorescence analysis, may be 66% by mass or less, 64% by mass or less, 62% by mass or less, 60% by mass or less, 59% by mass or less, 57% by mass or less, less than 57% by mass, 56% by mass or less, 55% by mass or less, 50% by mass or less, 48% by mass or less, 45% by mass or less, 40% by mass or less, or 35% by mass or less. The lower limit is preferably 5% by mass or more, 10% by mass or more, or 15% by mass or more, more preferably 20% by mass or more, or 25% by mass or more.

[0035] In addition, commercially available industrial lime (CaO) has a sieve permeability of 100% when passing through a sieve with 600 μm openings, and a sieve permeability of 95% or more when passing through a sieve with 150 μm openings.

[0036] For this reason, the Ca content of the by-product, calcination dust, is less than that of commercially available industrial lime (CaO).

[0037] Concrete is produced by measuring cement, water, aggregate, etc. in a predetermined ratio, pouring them into a concrete mixer, and kneading them. When producing concrete, admixtures such as water-reducing agents and quick-setting agents are added as needed.

[0038] Cement is produced by placing raw materials such as limestone, clay, silica, and iron in a kiln such as a rotary kiln, firing them at a temperature of approximately 1500°C, and then rapidly cooling them to create a clinker, which is then mixed with gypsum and crushed.

[0039] During the firing process to produce clinker, CO2 is generated as shown in equation (1) above. A large amount of fuel is burned to raise the firing temperature to approximately 1500°C, generating a large amount of CO2. CO2 is one of the greenhouse gases that causes global warming, and there is a need to reduce emissions. To solve this problem, CO2 absorbing concrete, which absorbs CO2 into concrete and hardens it, is attracting attention. Using this technology, it is possible to achieve so-called carbon negative, where the amount of CO2 absorbed exceeds the amount of CO2 emitted.

[0040] To achieve carbon negativity, it is necessary to use materials that can adsorb or absorb CO2, such as materials containing CaO.

[0041] The absorption of CO2 is realized by a hydration reaction in which CO2 reacts with water according to the following formula (2), and a carbonation reaction in which CO2 reacts with carbon dioxide according to the following formula (3). CaO + H2O → Ca(OH)2(2) Ca(OH)2+CO2→CaCO3+H2O (3)

[0042] Conventionally, concrete sludge generated at ready-mix concrete plants and waste seawater remaining after producing magnesium hydroxide from seawater have been used as materials containing CaO, and CO2 has been supplied to produce CaCO3, which is then used to produce concrete.

[0043] However, there is a problem in that specific factories, such as ready-mix concrete plants and magnesium manufacturing plants, require dedicated facilities to fix CO2.

[0044] In the production of concrete, calcium carbonate, an admixture primarily composed of CaCO3, is used. One example of calcium carbonate used as an admixture for concrete is Calfinder (https: / / www.omi-mining.co.jp / business / calcium-carbonate / calfinder / ), manufactured by Omi Mining Co., Ltd., which contains over 90% CaCO3 by mass. Calculating the Ca content of this 90% CaCO3 content yields a Ca content of 36% by mass. This CaCO3 is described as calcium carbonate produced by crushing limestone (CaCO3), and is known as "heavy calcium carbonate." Because heavy calcium carbonate is calcium carbonate produced by crushing limestone (CaCO3), its manufacturing process does not involve a reaction with CO2, and therefore does not have the effect of fixing atmospheric CO2.

[0045] One product that can be used as an admixture for concrete is Ecotancal (registered trademark) (https: / / www.ncic.co.jp / products / environment / ecocaco3.html) manufactured by Nippon Concrete Industries Co., Ltd., which has a CaCO3 purity of 97-99% and high whiteness. This CaCO3 is calcium carbonate known as "light calcium carbonate (also known as "precipitated calcium carbonate")." This CaCO3 is produced by reacting with CO2. This light calcium carbonate (precipitated calcium carbonate) has a CaCO3 content of 95% by mass or more and a Ca content of 38% by mass or more.

[0046] Furthermore, Reference 2 (Haruki Sato and Kazuyoshi Ozone, "Distinguishing Natural and Artificial Calcium Carbonates," Bulletin of the Central Customs Analysis Laboratory, No. 59, pp. 101-112) reports that numerous commercially available calcium carbonates were analyzed using X-ray fluorescence and found to have "C, O, and Ca" values ​​of 97% by mass or higher. Therefore, calcium carbonate with a CaCO3 content of less than 90% by mass, i.e., a material with a Ca content of less than 36% by mass, has not been used as an admixture to manufacture concrete. Furthermore, only materials with high whiteness have been used as concrete admixtures until now. In particular, calcium carbonate produced by reacting with CO2 (light calcium carbonate (precipitated calcium carbonate)) has a CaCO3 content of 95% by mass or higher and a Ca content of 38% by mass or higher.

[0047] Furthermore, the commercially available tungsten carbonate used as an admixture for concrete has a sieve permeability of 100% for passing through a sieve with 600 μm openings, a sieve permeability of 90% or more for passing through a sieve with 150 μm openings, and a sieve permeability of 70% or more for passing through a sieve with 75 μm openings.

[0048] Calcined dust has a Ca content of approximately 30% by mass, and is either 66% by mass or less, or 57% by mass or less. Even if calcined dust is hydrated and carbonated according to the above formulas (2) and (3), only a Ca content of less than 38% by mass or less than 36% by mass is produced. Incidentally, when calcined dust with a Ca content of approximately 30% by mass is hydrated and carbonated according to the above formulas (2) and (3), a Ca content of approximately 22% by mass is produced. Furthermore, it is expected that calcined dust will not be white. For these reasons, calcined dust has not been used in the production of concrete.

[0049] The inventors of the present invention have been studying raw materials for producing an admixture whose main component is CaCO3 without using dedicated facilities for fixing CO2 in a specific factory. They have produced concrete using materials produced from calcined dust, which is normally discarded, and have found that the compressive strength (N / mm) at 7 and 28 days after concrete ageing is significantly higher than that of concrete produced from calcined dust. 2The results of measuring the porosity of slag from the calcined dust were better than those of commercially available calcium carbonate and ground granulated blast furnace slag, and it was found that the material produced from the calcined dust can be used as an admixture. The present invention was made based on this finding.

[0050] The above measurements were conducted in accordance with JIS A 1108:2018, with the case using only ordinary Portland cement as the binder being considered a normal mix and a water / binder mass ratio (W / B) of 50%. The case using high-early-strength Portland cement and blast furnace slag was considered a slag mix, with the high-early-strength Portland cement and blast furnace slag in a mass ratio of 1:9 and a W / B of 47%. The case using commercially available calcium carbonate was considered a calcium carbonate mix, with the same amounts of high-early-strength Portland cement, blast furnace slag, and water as the slag mix, with the high-early-strength Portland cement and blast furnace slag in a mass ratio of 3:2 and a W / B of 47%. The case where material made from calcined dust was used was designated the calcined dust manufacturing material mix, and material made from calcined dust was used instead of calcined tank in the calcined tank mix, with the same high-early-strength Portland cement and material made from blast furnace slag and calcined dust in a mass ratio of 3:2, with a W / B of 47%.The material made from calcined dust is a material whose main component is CaCO3, produced by reacting calcined dust with water and fixing CO2 through adsorption, absorption, and reaction, as explained below.

[0051] The test specimens were poured into the formwork and removed the next day, and then subjected to standard curing (underwater curing at 20°C). The measurement results showed that the compressive strength of the normal mix at 7 days was 39 N / mm 2 , the compressive strength at 28 days is 51N / mm 2 The compressive strength of the slag mixture at 7 days is 21N / mm 2 , the compressive strength at 28 days is 26N / mm 2 In the case of the Calcium carbonate mixture, the compressive strength at 7 days is 42N / mm 2 , the compressive strength at 28 days is 56N / mm 2 In contrast, the compressive strength of the burnt dust manufacturing material mixture at 7 days was 53N / mm 2, the compressive strength at 28 days is 64N / mm 2 The compressive strength exceeded that of the normal mix, slag mix, and calcium carbonate mix. This demonstrates that the material made from calcined dust can be fully utilized as an admixture for concrete.

[0052] Calcination dust is a by-product obtained from the limestone calcination process and is a waste calcium component containing CaO. Therefore, it can be reacted with water to produce slaked lime (Ca(OH)2) as shown in the above formula (2). Then, CO2 can be adsorbed, absorbed, and reacted with it to fix it as shown in the above formula (3), producing an admixture for concrete (main component: CaCO3).

[0053] By using the resulting admixture in the production of concrete, it is possible to fix and store CO2 from the atmosphere, exhaust gases, etc. Note that because the main component of limestone is CaCO3, using limestone as an admixture does not result in fixing and storing CO2, but by using the calcination dust, it is possible to fix and store CO2.

[0054] Calcination dust, a by-product obtained from the process of calcining limestone, contains CaO, and known hydration and carbonation processes can be used to produce CaCO3, the main component of concrete admixtures, from CaO.

[0055] For example, dry methods can be used for hydration and carbonation. Reference 3 (Kiyoji Itaya et al., "Preparation of Granular Hydrated Lime by Hydration of Quicklime," Gypsum & Lime No. 234, pp. 306-314 (1991)) describes a dry production method in which deionized water is sprayed onto CaO powder from above, the mixture is stirred with a scrubber, and CaO is hydrated to produce Ca(OH)2. Reference 4 ("On the Slake of Limestone," Inorganic Materials Society, Gypsum and Lime, Vol. 1957, No. 29, pp. 1434-1335 (1957)) describes a method adopted by most small and medium-sized Japanese industries in which CaO is piled on the floor or in a container and hydrated by pouring water over it. Reference 4 describes dry mechanical methods for hydrating CaO by adding water, such as the Anker automatic hydrator and the Schnlthess automatic hydrator. It also mentions that CaO naturally hydrates when exposed to moisture in the air. It naturally absorbs moisture from the air to produce Ca(OH)2, which then absorbs CO2 from the air to produce CaCO3. Therefore, natural weathering can be used to achieve the hydration and carbonation reaction. Reference 5 (Yasue, Nin, et al., "Research Trends in Lime," Inorganic Materials, Vol. 1, No. 252, pp. 370-381 (1994)) also mentions that extensive research has been conducted on carbonation. Thus, dry methods for hydration and carbonation are widely used, and known dry hydration and carbonation methods can be used to produce CaCO3, the main component of concrete admixtures, from CaO.

[0056] The hydration and carbonation method may be a dry method or a wet method. Figure 3 is a diagram showing an example of a known wet hydration and carbonation process. In the hydration and carbonation process shown in Figure 3, a known manufacturing apparatus for hydrating and carbonating CaO to produce CaCO3 is used. Since the calcination dust contains CaO, it is possible to use an apparatus and method similar to the conventional apparatus and method for hydrating and carbonating CaO to produce CaCO3.

[0057] The CaCO3 manufacturing apparatus 10 includes a digester 11, a dissolution tank 12, a filter 13, a reaction tank 14, an aging tank 15, a washer 16, a dehydrator / dryer 17, and a filler 18. Calcination dust, which is waste Ca containing CaO, and water are fed into the digester 11. In the digester 11, the CaO in the calcination dust reacts with water as shown in the above formula (2) to produce Ca(OH)2.

[0058] The reaction vessel 14 is supplied with CO2, which reacts with CO2 as shown in the above formula (3) to produce CaCO3.

[0059] The dehydrator / dryer 17 dehydrates and dries the CaCO3. The filling machine 18 packages the dried CaCO3. The packaged CaCO3 is shipped as a product.

[0060] The admixture, whose main component is CaCO3 and is produced by hydrating and carbonating calcined dust as a raw material, has a Ca content of 37% by mass or less, or 35% by mass or less, unlike commercially available calcium carbonate, which has a Ca content of 36% by mass or more, and in particular commercially available light calcium carbonate (precipitated calcium carbonate), which has a Ca content of 38% by mass or more.Since the admixture contains CaCO3, it contains Ca, and it is desirable that the Ca content be 5% by mass or more.

[0061] Therefore, the concrete admixture is produced by reacting a by-product obtained in the CaO production process with water and CO2, and contains 37% by mass or less of Ca. The preferred lower limit of the Ca content of the concrete admixture is 5% by mass, as described above, with 10% by mass being more preferred and 15% by mass being even more preferred. The lower limit is preferably 17% by mass rather than 15% by mass, with 20% by mass being more preferred. The upper limit of the Ca content of the concrete admixture is 37% by mass, as described above, but may also be 36% by mass or less, 35% by mass or less, 34% by mass or less, 33% by mass or less, 32% by mass or less, 30% by mass or less, 28% by mass or less, or 25% by mass or less.

[0062] The by-product may be, but is not limited to, calcination dust obtained in the step of calcining limestone in the step of producing CaO. The by-product has a Ca content of 66% by mass or less, and may also have a Ca content of 57% by mass or less.

[0063] Concrete admixtures can be manufactured using conventional methods. Figure 4 shows the manufacturing flow of concrete admixtures. The following description assumes the use of a known dry hydration and carbonation method. In step 200, concrete admixtures are made using by-products obtained in the CaO manufacturing process. Water is sprayed onto the raw materials to cause a reaction. In step 201, the raw materials are reacted with water, and the resulting product is placed in a rotating cylindrical container and aerated with air to react with CO2 in the air. This reaction produces CaCO3, and a material containing the resulting CaCO3 as its main component is used as the admixture. Thus, the reaction with water can be carried out outside of solution, and the subsequent reaction with CO2 can also be carried out outside of solution. Similarly, the reaction of the by-products obtained in the CaO manufacturing process with water can also be carried out outside of solution, and the subsequent reaction with CO2 can also be carried out outside of solution. In addition, the step of reacting the by-product content obtained in the step of producing CaO with water may be a reaction in solution, and the reaction with CO2 after the reaction with water may be a reaction in solution.

[0064] A sieving test was conducted on the admixture produced in this way, and the passing mass percentage was measured. Particle size measurements were made using a stainless steel sieve with a frame diameter of 200 mm manufactured by Nonaka Rikagakuki Seisakusho Co., Ltd., which conforms to JIS Z 8801-1. The relationship between sieve openings and passing mass percentage (%) is as follows: 75 μm: 62.0%, 106 μm: 68.4%, 250 μm: 87.3%, 425 μm: 96.4%, 850 μm: 99.8%, 2 mm: 99.9%, 4.75 mm: 100%.

[0065] From the above passing mass percentage (%), a particle size accumulation curve was created, with the passing mass percentage (%) on the vertical axis and the particle size on a logarithmic scale on the horizontal axis. The created particle size accumulation curve is shown in Figure 5. When the passing mass percentage (%) values ​​for particle diameters of 600 μm, 150 μm, and 75 μm were read from the particle size accumulation curve shown in Figure 5, the passing mass percentage value for a particle diameter of 600 μm was 99%, the passing mass percentage value for a particle diameter of 150 μm was 76%, and the passing mass percentage value for a particle diameter of 75 μm was 62%.

[0066] The passing mass percentage value for particle diameter 600 μm obtained in this manner is 70% or more, the passing mass percentage value for particle diameter 150 μm is 45% or more, and the passing mass percentage value for particle diameter 75 μm is 30% or more. The passing mass percentage value for particle diameter 600 μm of the admixture obtained in this manner is preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. The passing mass percentage value for particle diameter 600 μm is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more.

[0067] The mass percentage of the admixture passing through a particle diameter of 150 μm determined as described above is 50% or more, preferably 55% or more, more preferably 60% or more, and even more preferably 65% ​​or more. The mass percentage of the admixture passing through a particle diameter of 150 μm is preferably 70% or more, more preferably 75% or more, than 65% or more. The upper limit of the mass percentage of the admixture passing through a particle diameter of 150 μm can be 95%, 90%, or 85%.

[0068] The mass percentage of the admixture passing through a particle diameter of 75 μm determined as described above is preferably 35% or more, more preferably 40% or more, and even more preferably 45% or more. The mass percentage of the admixture passing through a particle diameter of 75 μm is preferably 50% or more, more preferably 55% or more, rather than 45% or more. The upper limit of the mass percentage of the admixture passing through a particle diameter of 75 μm can be 95%, 90%, 85%, 80%, 75%, or 70%.

[0069] Furthermore, a portion of the admixture produced as described above was analyzed using an energy dispersive X-ray fluorescence analyzer manufactured by Rigaku Corporation (model number: EDXL300, measurement conditions: FP (fundamental parameter) method), and the Ca content was found to be 33% by mass. Even if the Ca content of the admixture were 35% by mass, the Ca content of the calcined dust used as the raw material would be 56.9% by mass, which is 57% by mass or less. Furthermore, if the Ca content of the admixture were 37% by mass, the Ca content of the calcined dust used as the raw material would be around 60% by mass (approximately 62% by mass), which is 66% by mass or less.

[0070] The admixture produced by hydration and carbonation was gray, similar to the calcined dust in Figure 2(b). The admixture produced was not white, but rather brown, gray, black, and other colors. These colors are specified in Appendix 1 of the Japanese Industrial Standard (JIS) Z 8102:2001 (Color Names of Object Colors), including sand, chalk, off-white, ivory, silver gray, brown gray, gray, Rikyu gray, lead gray, gray, bamboo green, dark brown, ink, black, iron black, silver, ivory, sky gray, pearl gray, silver gray, ash gray, rose gray, gray, steel gray, straight gray, charcoal gray, lamp black, and black. In addition, JIS Z 8102:2001 allows the addition of modifiers to the above conventional colors using the terms specified in 7.2 Table 3 and 7.3 Table 4 of the same standard, and includes colors modified by any of the above conventional color names with "light," "strong," "dark," "light," "soft," "dull," "dark," "very light," "light gray," "gray," "dark gray," "very dark," and "medium" as specified in JIS Z 8102:2001.11.2 and 7.2 Table 3, 7.3 Table 4. Admixtures are materials that have the above particle sizes, or materials that have the above colors, or both.

[0071] In addition, the whiteness W (L) of admixtures (calcium-containing materials) manufactured by hydration and carbonation according to the Lab color space established by the International Commission on Illumination (CIE) * a *b * ) may be less than 95, 90 or less, 85 or less, 80 or less, 75 or less, 70 or less, 65 or less, 60 or less, 55 or less, 50 or less, 45 or less, or 40 or less. Furthermore, the lightness index L according to the Lab color space established by the CIE for admixtures (calcium-containing materials) manufactured by hydration and carbonation may be * may be measured as less than 95, 90 or less, 85 or less, 80 or less, 75 or less, 70 or less, 65 or less, 60 or less, 55 or less, 50 or less, 45 or less, or 40 or less.

[0072] The whiteness W(L * a * b * ) and the measured value L * , a * , b * The relationship between L and L is as shown in (4) below. * is the lightness index in the Lab color space, and a * , b * are color coordinates in the Lab color space. W(L * a * b * )=100-[(100-L * ) 2 +(a * ) 2 +(b * ) 2 ] 1 / 2 (4)

[0073] The by-products generated in the calcination process for producing quicklime (CaO) are made from dust and other raw materials, and therefore have a whiter W (L) value in the Lab color space established by CLE than general light calcium carbonate (precipitated calcium carbonate). * a * b * ) tends to be low. Similarly, the lightness index L in the Lab color space established by CLE * also tends to be low.

[0074] Similarly to the above, some of the admixtures (calcium-containing materials) produced by hydration and carbonation were measured using the following measuring equipment and conditions as admixture A and admixture B. The measurement results are shown in Table 1. Measurement equipment: Spectrophotometer SE7700 manufactured by Nippon Denshoku Industries Co., Ltd. Measurement conditions: Reflection, light source / field of view = C / 2, filled into a φ58mm round cell and measured

[0075] [Table 1]

[0076] From the results in Table 1 above, the whiteness W (L * a * b * ) is a low value of 36, and the brightness index L * However, admixtures A and B had low values ​​of 36.03 and 35.90.

[0077] Since the admixture contains CaCO3, it is a calcium-containing material, and the manufacturing flow shown in Figure 4 is a manufacturing flow for an admixture for concrete, as well as one of the manufacturing flows for calcium-containing materials.

[0078] Fig. 6 shows a concrete manufacturing flow. In step 300, a by-product obtained in the CaO manufacturing process is reacted with water and CO2 to produce a mineral admixture containing 35 mass% or less of Ca. Specifically, the mineral admixture is manufactured by the manufacturing process shown in Fig. 4.

[0079] Once the admixture is produced, in step 301, Portland cement, aggregate, water, and admixture are weighed out according to a predetermined ratio. High-early-strength Portland cement can be used as the Portland cement, but ordinary Portland cement is also acceptable. The aggregate includes fine aggregate and coarse aggregate. Fine aggregate is aggregate in which all particles are 10 mm or less, of which 85% by mass or more are 5 mm or less. In contrast, coarse aggregate is aggregate in which particles 5 mm or larger account for 85% by mass or more. The volume ratio of fine aggregate to total aggregate in concrete (s / a) can be, for example, in the range of 35 to 55% when expressed as a percentage. Furthermore, the mass ratio of water to Portland cement can be, for example, 100:5 to 100:25. Furthermore, the mass of the admixture can be 5 to 10 times the mass of the Portland cement.

[0080] In step 302, the measured Portland cement, aggregate, water, and admixture are poured into a concrete mixer. Then, in step 303, the mixture is mixed using the mixing blades in the concrete mixer to produce fresh concrete (ready-mixed concrete), which is concrete that has not yet hardened.

[0081] The ready-mixed concrete is transported to the construction site in a vehicle such as a mixer truck, where it is poured into formwork. After pouring, it is cured for a specified period of time, and the formwork is removed, after which the concrete structure is constructed.

[0082] When producing concrete, Portland cement, aggregate, water, admixtures derived from by-products produced during the CaO production process, as well as admixtures such as water-reducing agents can be used.In addition to the admixtures derived from the by-products and Portland cement, at least one of ground blast furnace slag, fly ash, silica fume, expansive agents, and waterproofing materials can also be mixed and used.

[0083] As a result of the above, no CO2 is generated during production because the by-product obtained from the limestone burning process is used. The admixture is a negative material because it is produced simply by reacting the by-product with CO2. In addition, because it uses a by-product, the admixture can be provided at a low cost.

[0084] The by-product is a solid Ca-containing material, and because it can be used anywhere to fix CO2, large-scale dedicated facilities are not required when producing the admixture. Furthermore, since the Ca-containing material produced by the above manufacturing method contains CaCO3, it can be used as a fertilizer for growing plants, a soil conditioner, a plant growth agent, and an agricultural material, just like CaCO3 (calcium carbonate), which is widely sold as a fertilizer and soil conditioner. It can also be used as a raw material for manufacturing these.

[0085] The admixture, the method for manufacturing an admixture, the concrete, the method for manufacturing a concrete, and the method for manufacturing a calcium-containing material of the present invention have been described in detail with reference to the embodiments shown in the drawings. However, the present invention is not limited to the above-described embodiments, and can be modified within the scope of what a person skilled in the art can conceive, such as other embodiments, additions, changes, deletions, etc., and any embodiment is within the scope of the present invention as long as it exhibits the functions and effects of the present invention. [Explanation of symbols]

[0086] 10…Manufacturing equipment 11...Digestion tank 12...Dissolution tank 13...Filter 14...Reaction tank 15...Aging tank 16...Washing machine 17…Dehydrator / dryer 18...Filling machine

Claims

1. A concrete admixture produced by reacting a by-product obtained in the process of manufacturing quicklime with water and carbon dioxide, containing 5% to 37% by mass of calcium and free of silica fume.

2. The concrete admixture according to claim 1, wherein the by-product is calcination dust obtained in the step of calcining limestone in the step of producing quicklime.

3. The admixture is Powders with a whiteness W (L*a*b*) of less than 95 in the L*a*b* color space established by the International Commission on Illumination (CIE) or Powders with a lightness index L* in the L*a*b* color space, as defined by the International Commission on Illumination (CIE), have a lightness index L* of less than 95. The concrete admixture according to claim 1 or 2.

4. The concrete admixture according to claim 2, which is produced by reacting the calcined dust with the water, and then reacting it with carbon dioxide.

5. The concrete admixture according to claim 1 or 2, wherein the by-product has a cumulative fraction of 70% or more of particles with a volume-based particle size of 600 μm or less, measured by laser diffraction and scattering, a cumulative fraction of 50% or more of particles with a particle size of 150 μm or less, and a cumulative fraction of 30% or more of particles with a particle size of 75 μm or less.

6. A method for producing a concrete admixture containing 5% by mass or more and 37% by mass or less calcium, comprising a first step of reacting a byproduct obtained in the process of producing quicklime with water, and a second step of reacting the product obtained in the first step with carbon dioxide.

7. The method for producing a concrete admixture according to claim 6, wherein the by-product is calcined dust obtained in the step of calcining limestone in the step of producing quicklime.

8. The method for producing a concrete admixture according to claim 6 or 7, wherein the by-product has a cumulative fraction of 70% or more of particles with a volume-based particle diameter of 600 μm or less, measured by laser diffraction and scattering, a cumulative fraction of 50% or more of particles with a particle diameter of 150 μm or less, and a cumulative fraction of 30% or more of particles with a particle diameter of 75 μm or less.

9. Concrete containing an admixture that contains 5% by mass or more and 37% by mass or less of calcium, and does not contain silica fume, The aforementioned admixture is concrete produced by reacting a by-product obtained in the process of producing quicklime with water and carbon dioxide.

10. The concrete according to claim 9, wherein the by-product is calcined dust obtained in the step of calcining limestone in the step of producing quicklime.

11. The concrete according to claim 10, which is produced by reacting the calcined dust with the water, and then reacting it with carbon dioxide.

12. The concrete according to any one of claims 9 to 11, wherein the by-product has a cumulative fraction of 70% or more of particles with a volume-based particle diameter of 600 μm or less, measured by laser diffraction and scattering, a cumulative fraction of 50% or more of particles with a particle diameter of 150 μm or less, and a cumulative fraction of 30% or more of particles with a particle diameter of 75 μm or less.

13. The aforementioned admixture is 1 m ３ The concrete according to any one of claims 9 to 11, wherein it contains 400 kg or less of the concrete.

14. The concrete comprises Portland cement, aggregate, water, and the admixture. The concrete according to any one of claims 9 to 11, wherein the mass of the admixture is in the range of 5 to 10 times the mass of the Portland cement.

15. A method for manufacturing concrete, A process of reacting by-products obtained in the process of manufacturing quicklime with water and carbon dioxide to produce an admixture containing 5% by mass or more and 37% by mass or less of calcium, A process of producing concrete by mixing the manufactured admixture, aggregate, and water. A method for manufacturing concrete, including [the specified element].

16. The method for producing concrete according to claim 15, wherein the by-product is calcined dust obtained in the step of calcining limestone in the step of producing quicklime.

17. The method for producing concrete according to claim 15 or 16, wherein the step of producing the admixture includes a first step of reacting the byproduct with water, and a second step of reacting the product obtained in the first step with carbon dioxide.

18. The method for producing concrete according to claim 15 or 16, wherein the by-product has a cumulative fraction value of 70% or more for particle diameters of 600 μm or less on a volume basis, measured by laser diffraction and scattering, a cumulative fraction value of 50% or more for particle diameters of 150 μm or less, and a cumulative fraction value of 30% or more for particle diameters of 75 μm or less.

19. The aforementioned admixture is 1 m ３ A method for producing concrete according to claim 15 or 16, wherein the amount of the substance is 400 kg or less relative to the concrete.

20. The aforementioned concrete comprises Portland cement, aggregate, water, and admixture. The method for producing concrete according to claim 15 or 16, wherein the mass of the admixture is in the range of 5 to 10 times the mass of the Portland cement.

21. A method for producing a calcium-containing substance, comprising a first step of reacting a by-product obtained in the calcination process of producing quicklime with water, and a second step of reacting the product obtained in the first step with carbon dioxide, wherein the whiteness W (L*a*b*) in the L*a*b* color space established by the International Commission on Illumination (CIE) is 55 or less.

22. A method for producing a calcium-containing substance, comprising: a first step of reacting a by-product obtained in a calcination process for producing quicklime with water, wherein the reaction between the raw material and the water does not occur in a solution; and a second step of reacting the product obtained in the first step with carbon dioxide.

23. A method for producing a calcium-containing substance, comprising: a first step of reacting a by-product obtained in a calcination process for producing quicklime with water; and a second step of reacting the product obtained in the first step with carbon dioxide, wherein the reaction between the product obtained in the first step and the carbon dioxide does not take place in solution.

24. A method for producing a calcium-containing substance having a calcium content of 37% by mass or less, comprising: a first step of reacting a by-product obtained in the calcination process for producing quicklime with water; and a second step of reacting the product obtained in the first step with carbon dioxide.

25. A method for producing a calcium-containing substance according to any one of claims 21 to 24, wherein the by-product has a cumulative fraction value of 70% or more for particle diameters of 600 μm or less on a volume basis, measured by laser diffraction and scattering, a cumulative fraction value of 50% or more for particle diameters of 150 μm or less, and a cumulative fraction value of 30% or more for particle diameters of 75 μm or less.

26. The method for producing a calcium-containing substance according to any one of claims 21 to 24, wherein the by-product is calcined dust obtained in the step of calcining limestone in the step of producing quicklime.

27. ​​The calcium-containing substance has a whiteness W (L*a*b*) of less than 95 in the L*a*b* color space established by the International Commission on Illumination (CIE). or The lightness index L* in the L*a*b* color space, as defined by the International Commission on Illumination (CIE), is less than 95. A method for producing a calcium-containing substance according to any one of claims 22 to 24, wherein the substance is a powder.

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