Carbonated hardened body and method for producing the same

Abstract

To provide a carbonation hardening body capable of largely reducing a total amount of carbon dioxide exhausted and having large strength, by absorbing a large amount of carbon dioxide in an aging process.SOLUTION: A carbonation hardening body obtained by carbonating a hardening body of a hydraulic composition containing (A) a powdery hydraulic material containing C2S and C2AS and containing pulverized calcined material that satisfies the following conditions (1) and (2), (B) water, and (C) an aggregate containing cement hydrate-containing aggregate. (1) When the fired product does not contain C4AF, an amount of C2AS is 10 to 2,000 pts.mass with respect to 100 pts. mass of C2S, and when the fired product contains C4AF, a total amount of C2AS and C4AF with respect to 100 pts.mass of C2S is 10 to 2,000 pts.mass, and a ratio of C4AF in the total 100 mass% of C2AS and C4AF is 70% by mass or less, and (2) the fired product does not contain C3A or contains C3A in an amount of 20 pts.mass or less relative to 100 pts.mass of C2S.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbonated hardened product and a method for producing the same. [Background technology]

[0002] Currently, reducing carbon dioxide emissions is an important issue in order to curb global warming. One method known for reducing carbon dioxide emissions in the production of hardened cementitious materials is to absorb carbon dioxide during the curing process of the hardened cementitious material, thereby reducing the total amount of carbon dioxide emitted up to the time the hardened cementitious material is obtained. For example, Patent Document 1 describes a precast concrete produced by hardening a concrete mixture containing one or both of γ-CS (symbol γ) and steelmaking slag powder (symbol B) and Portland cement (symbol C) as powder components, where the total of γ and B accounts for 25 to 95 mass% of the total content of γ, B, and C, and the water-to-cement ratio W / C is 80 to 250%, and the precast concrete undergoes carbonation curing during the hardening process, forming a carbonated region at a depth of 20 mm or more from the surface (but throughout the entire thickness for sections less than 20 mm thick). By utilizing the carbon dioxide absorption achieved by carbonation curing, this precast concrete can significantly reduce the total amount of carbon dioxide emitted during the production of concrete products.

[0003] Patent Document 2 describes a cementitious hardened body obtained by carbonating a hardened body of a cement mixture containing (A) a powdered cement composition containing Portland cement, a pulverized product of a fired material containing 10 to 200 parts by mass of C2AS per 100 parts by mass of C2S and with a C3A content of 20 parts by mass or less, (B) water, and (C) aggregate. This cementitious hardened body can significantly reduce carbon dioxide emissions by absorbing a large amount of carbon dioxide during the curing process, and, although it contains powdered materials other than Portland cement, can reduce the rate of decrease in compressive strength compared to a case in which all of the powdered materials are Portland cement. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-168436 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-047788 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a carbonated hardened body that contains a powder material other than Portland cement (especially one that emits less carbon dioxide during the production of powder than Portland cement) but that can significantly reduce the total amount of carbon dioxide emitted by absorbing a large amount of carbon dioxide during the curing process, and that has excellent strength. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned objects can be achieved by a carbonated hardened body obtained by carbonating a hardened body of a hydraulic composition including: (A) a powdered hydraulic material containing C2S and C2AS and a pulverized product of a burned material that contains the above-mentioned C2S and C2AS and satisfies the following conditions (1) and (2); (B) water; and (C) an aggregate that contains a cement hydrate-containing aggregate that contains at least one of a cement clinker mineral and a hydrate thereof, and have completed the present invention. (1) If the fired product does not contain C4AF, the amount of C2AS per 100 parts by mass of C2S is 10 to 2,000 parts by mass. If the fired product contains C4AF, the total amount of C2AS and C4AF per 100 parts by mass of C2S is 10 to 2,000 parts by mass, and the proportion of C4AF in the total of 100% by mass of C2AS and C4AF is 70% by mass or less. (2) The fired product does not contain C3A or contains C3A in an amount of 20 parts by mass or less per 100 parts by mass of C2S. That is, the present invention provides the following [1] to

[10] .

[0007] [1] A carbonated hardened body obtained by carbonating a hardened body of a hydraulic composition including: (A) a powdered hydraulic material containing C2S and C2AS and a pulverized product of a fired material that satisfies the following conditions (1) to (2); (B) water; and (C) an aggregate containing a cement hydrate-containing aggregate that contains at least one of a cement clinker mineral and a hydrate thereof. (1) When the fired product does not contain C4AF, the amount of the C2AS is 10 to 2,000 parts by mass relative to 100 parts by mass of the C2S. When the fired product contains C4AF, the total amount of the C2AS and the C4AF is 10 to 2,000 parts by mass relative to 100 parts by mass of the C2S, and the proportion of the C4AF in the total of 100% by mass of the C2AS and the C4AF is 70% by mass or less. (2) The fired product does not contain C3A or contains C3A in an amount of 20 parts by mass or less per 100 parts by mass of the C2S. [2] The carbonated hardened body according to [1], wherein the proportion of the cement hydrate-containing aggregate in the aggregate (C) is 20 mass % or more. [3] The carbonated hardened body according to [1] or [2], wherein the proportion of the total amount of the cement clinker mineral and its hydrate in the total amount of the cement hydrate-containing aggregate contained in the (C) aggregate is 2 mass% or more. [4] The carbonated hardened body according to any one of [1] to [3], wherein the cement hydrate-containing aggregate is recycled aggregate obtained from waste concrete, and the proportion of the area where a coating layer containing at least one of cement clinker minerals and their hydrates is present in the total surface area of ​​the recycled aggregate is 20% or more. [5] The carbonated hardened material according to any one of [1] to [3], wherein the cement hydrate-containing aggregate is solidified concrete sludge.

[0008] [6] The carbonated hardened product according to any one of [1] to [5], wherein the powdery hydraulic material (A) contains gypsum powder. [7] The carbonated hardened body according to any one of [1] to [7], wherein the powdery hydraulic material (A) contains cement, and the proportion of the pulverized material in the powdery hydraulic material (A) is 5 to 90 mass % and the proportion of the cement is 10 to 95 mass %. [8] The carbonated hardened body according to [7], wherein the powdered hydraulic material (A) contains 10 to 60% by mass of the pulverized material and 40 to 90% by mass of the cement, and the cement is at least one of ordinary Portland cement and high-early-strength Portland cement. [9] A method for producing a carbonated hardened body according to any one of [1] to [8] above, comprising: a kneaded mixture preparation step of kneading the materials (A) to (C) above to prepare a kneaded mixture of the hydraulic composition; a casting step of casting the kneaded mixture into a formwork; a demolding step of, after the kneaded mixture in the formwork has hardened, releasing from the formwork a hardened body of the hydraulic composition obtained by the hardening of the kneaded mixture; and a carbonation curing step of carbonating the hardened body of the hydraulic composition released from the formwork to obtain a carbonated hardened body.

[10] The method for producing a carbonated hardened body according to [9], further comprising a high-strength curing step for increasing the strength of the hardened body of the hydraulic composition between the demolding step and the carbonation curing step. [Effects of the Invention]

[0009] The carbonated hardened material of the present invention has excellent strength (for example, compressive strength) and can significantly reduce the total amount of carbon dioxide emitted by absorbing a large amount of carbon dioxide during the curing process. DETAILED DESCRIPTION OF THE INVENTION

[0010] The carbonated hardened product of the present invention is obtained by carbonating a hardened product of a hydraulic composition including: (A) a powdered hydraulic material containing C2S (2CaO·SiO2: belite) and C2AS (2CaO·Al2O3·SiO2: gehlenite) and a pulverized fired product satisfying the following conditions (1) and (2); (B) water; and (C) a cement hydrate-containing aggregate (hereinafter sometimes abbreviated as "cement hydrate-containing aggregate") containing at least one of a cement clinker mineral and a hydrate thereof. (1) If the fired product does not contain C4AF (4CaO·Al2O3·Fe2O3: ferrite phase), the amount of C2AS per 100 parts by mass of C2S is 10 to 2,000 parts by mass. If the fired product contains C4AF, the total amount of C2AS and C4AF per 100 parts by mass of C2S is 10 to 2,000 parts by mass, and the proportion of C4AF in the total of C2AS and C4AF (100% by mass) is 70% by mass or less. (2) The fired product does not contain C3A (3CaO·Al2O3: aluminate phase) or contains C3A in an amount of 20 parts by mass or less per 100 parts by mass of C2S. Here, "carbonation" refers to the reaction of an alkaline component in the set hydraulic composition with carbon dioxide to lower the pH of the alkaline component. The present invention will be described in detail below.

[0011] [(A) Powdered hydraulic material] The powdered hydraulic material contains C2S and C2AS, and also contains a pulverized product of the fired material that satisfies the above conditions (1) and (2). Regarding the above condition (1), when the calcined product does not contain C4AF, the amount of C2AS per 100 parts by mass of C2S is 10 to 2,000 parts by mass, preferably 15 to 1,000 parts by mass, more preferably 20 to 500 parts by mass, even more preferably 23 to 100 parts by mass, and particularly preferably 25 to 50 parts by mass. If the amount is less than 10 parts by mass, the amount of free lime (unreacted CaO) is not reduced even when the calcination temperature is increased, making calcination difficult. If the amount exceeds 2,000 parts by mass, the amount of melt generated at high temperatures during production of the calcined product increases, narrowing the calcination temperature range. Furthermore, the relatively small amount of C2S reduces the strength of the cured product when demolded in the demolding step described below.

[0012] When the fired product contains C4AF, the total amount of C2AS and C4AF per 100 parts by mass of C2S is 10 to 2,000 parts by mass, preferably 15 to 1,000 parts by mass, more preferably 20 to 500 parts by mass, particularly preferably 23 to 100 parts by mass, and particularly preferably 25 to 50 parts by mass. If the amount is less than 10 parts by mass, the amount of free lime (unreacted CaO) is unlikely to decrease even when the firing temperature is increased, making firing difficult. If the amount exceeds 2,000 parts by mass, the amount of melt generated at high temperatures during production of the fired product increases, narrowing the firing temperature range. Furthermore, the relatively small amount of C2S reduces the strength of the hardened body when demolding in the demolding step described below, or it takes a long time to demold. Furthermore, the proportion of C4AF in the total of 100% by mass of C2AS and C4AF is 70% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. If the proportion exceeds 70% by mass, the amount of C2AS decreases relatively, so that even if the firing temperature is increased during firing, the amount of free lime (amount of unreacted CaO) is difficult to decrease, making firing difficult.

[0013] Regarding the above condition (2), when the fired product contains C3A, the amount of C3A relative to 100 parts by mass of C2S is 20 parts by mass or less, preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less. If the amount exceeds 20 parts by mass, the fluidity of the hydraulic composition before hardening decreases.

[0014] The mineral composition of the fired product (the proportions of C2S, C2AS, C4AF, and C3A: mass %) can be calculated from the proportions (mass %) of CaO, SiO2, Al2O3, and Fe2O3 in the raw materials for the fired product or in the fired product using the following formula. C2S=1.02×CaO+0.95×SiO2-1.69×Al2O3-0.36×Fe2O3 C2AS=-1.63×CaO+3.04×SiO2+2.69×Al2O3+0.57×Fe2O3 C4AF=3.04×Fe2O3 C3A = 1.61 x CaO - 3.00 x SiO2 - 2.26 x Fe2O3 (However, if the value is negative, it is considered to be "0.")

[0015] As raw materials for the burned product, common raw materials used in the production of cement clinker can be used, such as calcium-containing raw materials (CaO sources) such as limestone, quicklime, slaked lime, etc., silicon-containing raw materials (SiO sources) such as silica stone and clay, aluminum-containing raw materials (AlO sources) such as clay, iron-containing raw materials (FeO sources) such as iron slag and iron cake, etc. In addition to the above-mentioned raw materials, one or more selected from industrial waste, general waste, and construction waste soil can also be used. After the above-mentioned raw materials are appropriately mixed, the resulting mixture is preferably fired at a firing temperature of 1,000 to 1,450°C (more preferably 1,150 to 1,400°C), thereby obtaining the above-mentioned fired product. The method for mixing the raw materials is not particularly limited, and examples thereof include methods using conventional equipment. Furthermore, the equipment used for calcination is also not particularly limited, and for example, a rotary kiln can be used. When calcination is performed using a rotary kiln, waste oil, waste tires, waste plastics, and the like may be used as fuel substitute waste materials.

[0016] The form of the C2S mineral in the fired product is not particularly limited and may be any of α-, β-, and γ-types. However, from the viewpoint of increasing the strength of the hardened body when demolding is performed or performing demolding earlier in the demolding step described below, it is preferable that the fired product contains at least one of α- and β-types. The morphology of a mineral can be measured using powder X-ray diffraction, electron backscatter diffraction (EBSD), or the like.

[0017] The proportion of C2S in the fired product is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more, from the viewpoint of increasing the strength of the carbonated hardened body. Furthermore, the proportion of C2AS in the fired product is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, and particularly preferably 15 to 30% by mass. If the proportion is 5% by mass or more, the amount of free lime (unreacted CaO) is less likely to remain when the firing temperature is increased during firing, making firing easier. In addition, the effect of reducing carbon dioxide emissions is greater. If the proportion is 50% by mass or less, the amount of melt generated at high temperatures during production of the fired product is reduced, broadening the range of possible firing temperatures. In addition, the strength of the carbonated hardened body is greater.

[0018] The proportion of free lime in the burned product is preferably 2% by mass or less, and more preferably 0.2 to 1.5% by mass, from the viewpoint of strength development in the carbonation curing step. The fired product may contain other minerals in addition to the above-mentioned minerals such as C2S, such as mullite, anorthite, amorphous phase, quartz, cristobalite, rankinite, and wollastonite, etc. These may be contained alone or in combination of two or more. The total content of ingredients other than the above-mentioned C2S, C2AS, C4AF, and C3A in the fired product is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

[0019] The Blaine specific surface area of ​​the pulverized product obtained by pulverizing the fired product is preferably 2,500 to 10,000 cm 2 / g, more preferably 3,000 to 9,000 cm 2 / g. The Blaine specific surface area is 2,500 cm 2 / g or more, the effect of reducing carbon dioxide emissions is large. In addition, the strength of the resulting carbonated hardened body is high. 2 If the pulverization rate is 1 / g or less, the energy required for pulverization can be kept low, and the production cost can be reduced.

[0020] The powdered hydraulic material includes a pulverized product obtained by pulverizing the above-mentioned fired product. The method for pulverizing the fired product is not particularly limited, and examples thereof include a method using a conventional device such as a ball mill. The powdered hydraulic material may contain gypsum powder from the viewpoint of the fluidity and workability of the hydraulic composition before hardening. The gypsum is not particularly limited, and examples thereof include natural gypsum dihydrate, flue gas desulfurization gypsum, phosphate gypsum, titanic gypsum, and hydrofluoric gypsum. Examples of the form of gypsum include gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum. These may be used alone or in combination of two or more. The powdered hydraulic material may be produced by mixing gypsum powder obtained by crushing a calcined material with a crushed material obtained by crushing a calcined material, or by crushing the calcined material and gypsum simultaneously. The proportion of gypsum powder in the powdered hydraulic material is preferably 5.0 mass% or less, more preferably 1.0 to 4.0 mass% in terms of SO3. If the proportion is 5.0 mass% or less, the fluidity of the hydraulic composition before hardening is further improved. Note that when the powdered hydraulic material contains cement (described below), the proportion of gypsum powder includes the gypsum powder contained in the cement.

[0021] The powdered hydraulic material may contain cement from the viewpoint of strength development and the like. The cement is not particularly limited, and examples thereof include various types of Portland cement such as ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement, as well as ecocement, rapid-hardening cement, and ultra-rapid-hardening cement. These may be used alone or in combination of two or more. Among these, at least one of ordinary Portland cement and high-early-strength Portland cement is preferred from the viewpoint of strength development and cost.

[0022] The proportion of the pulverized material in the powdered hydraulic material is preferably 5 to 90% by mass, more preferably 10 to 85% by mass, even more preferably 15 to 80% by mass, even more preferably 20 to 70% by mass, even more preferably 30 to 60% by mass, even more preferably 35 to 55% by mass, and particularly preferably 40 to 50% by mass. If the proportion is 5% by mass or more, the effect of reducing carbon dioxide emissions is greater. In addition, the strength of the resulting carbonated hardened body is increased. If the proportion is 90% by mass or less, the strength of the hardened body when demolded is greater or the demolding time is earlier, improving the production efficiency of products made from the carbonated hardened body. Furthermore, when the powdered hydraulic material contains cement, the proportion of cement in the powdered hydraulic material is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, even more preferably 15 to 85% by mass, even more preferably 20 to 80% by mass, even more preferably 30 to 70% by mass, even more preferably 35 to 65% by mass, and particularly preferably 40 to 60% by mass. If the proportion is 5% by mass or more, the time for demolding can be accelerated, improving the production efficiency of products made from carbonated hardened bodies. If the proportion is 95% by mass or less, the effect of reducing carbon dioxide emissions can be increased. Furthermore, the strength of the resulting carbonated hardened body can be increased.

[0023] The content of free lime in the powdered hydraulic material is preferably 2% by mass or less, and more preferably 0.2 to 1.5% by mass, from the viewpoint of strength development in the carbonation curing step. The powdered hydraulic material may contain amines. Amines are known to react with carbon dioxide to promote the production of carbonate ions, and the inclusion of amines can efficiently promote the carbonation of calcium components. Amines are compounds that have an amino group and a hydroxyl group in the molecule. Examples of amines include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diglycolamine (DGA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), and triisopropanolamine (TIPA). These amines are known as grinding aids. Furthermore, used amines obtained from a carbon dioxide recovery unit may be used as the amines. In an amine-based carbon dioxide recovery unit for recovering carbon dioxide from exhaust gases from factories, etc., a liquid containing deteriorated amines is usually discarded. However, in the present invention, the waste liquid can be effectively utilized. The amines may be used as grinding aids. The amount of amines is preferably 0.002 to 1 part by mass, more preferably 0.01 to 0.1 part by mass, per 100 parts by mass of the powdery hydraulic material, from the viewpoint of accelerating the carbonation of the hardened body and enhancing the strength development in the carbonation curing step.

[0024] [(B)Water] In the hydraulic composition, the mass ratio of water to powdered hydraulic material (water / powdered hydraulic material) is preferably 0.3 to 1.0, more preferably 0.4 to 0.7. When the ratio is 0.3 or more, the effect of reducing carbon dioxide emissions is greater. In addition, the workability of the kneaded product of the hydraulic composition is improved. When the ratio is 1.0 or less, the strength of the carbonated hardened body is greater.

[0025] [(C) Cement hydrate-containing aggregate containing at least one of cement clinker minerals and their hydrates] The aggregate used in the present invention includes a cement hydrate-containing aggregate containing at least one of a cement clinker mineral and a hydrate thereof. Cement clinker minerals include C3S (3CaO·SiO2: alite), C2S (2CaO·SiO2: belite), C3A (3CaO·Al2O3: aluminate phase), and C4AF (4CaO·Al2O3·Fe2O3: ferrite phase). Hydrates of cement clinker minerals include CSH (calcium silicate hydrate), CASH (calcium silicate hydrate with aluminum as a solid solution), portlandite, ettringite, monosulfate, and monocarbonate. The aggregate may contain one of these materials alone, or two or more of these materials may be contained.

[0026] Specific examples of cement hydrate-containing aggregates include recycled aggregate obtained from waste concrete, solidified concrete sludge, and crushed demolished concrete or demolished mortar. Among these, aggregate obtained from solidified concrete sludge is preferred from the viewpoint of further increasing the amount of carbon dioxide absorbed in the carbonated hardened body and further reducing carbon dioxide emissions. These aggregates can be obtained by known methods. Examples of recycled aggregate and its manufacturing method include recycled aggregate H for concrete and its manufacturing method specified in "JIS A 5021:2018 (Recycled aggregate H for concrete)", recycled aggregate M for concrete and its manufacturing method specified in Appendix A of "JIS A 5022:2018 Recycled aggregate concrete M", and compatible recycled aggregate L for concrete and its manufacturing method specified in Appendix A of "JIS A 5023:2018 (Recycled aggregate concrete L)". Among the recycled aggregates, recycled aggregate for concrete M and recycled aggregate for concrete L are preferred from the viewpoint of having a larger content of cement clinker minerals and their hydrates. Furthermore, the crushed material of demolished concrete or demolished mortar can be obtained by crushing waste concrete blocks or waste mortar blocks and adjusting the particle size. Furthermore, the type and material of the raw aggregate (e.g., aggregate originally contained in the waste concrete, etc.) contained in recycled aggregate obtained from waste concrete, aggregate obtained from solidified concrete sludge, or crushed demolished concrete or demolished mortar is not particularly limited, but limestone or dolomite (e.g., crushed limestone sand, crushed limestone stone, crushed dolomite sand, crushed dolomite stone, and recycled aggregates thereof) are preferred. When aggregate containing limestone or dolomite is used, the amount of shrinkage of the hardened body during carbonation curing and during service life can be reduced, and dimensional stability can be further improved.

[0027] When only aggregate obtained from solidified concrete sludge is used as aggregate, the carbonated hardened product of the present invention can be recovered after use and used entirely as a cement clinker raw material. In this case, cement clinker can be produced by simply adding a small amount of new raw material. The aggregate obtained from solidified concrete sludge is preferably a dehydrated cake of concrete sludge, from the viewpoint of not disintegrating when kneaded with the hydraulic composition and increasing the strength of the carbonated hardened body, and more preferably, the dehydrated cake is one that has been left for at least 3 days (preferably at least 7 days) since it was collected. In addition, aggregate obtained from solidified concrete sludge can be obtained by crushing the solidified concrete sludge to a desired particle size. Alternatively, aggregate obtained from solidified concrete sludge may be produced by molding and solidifying pre-solidified concrete sludge (dewatered cake).

[0028] The surface of the above-mentioned cement hydrate-containing aggregate is coated with cement clinker minerals or hydrates thereof. Therefore, when the cement clinker minerals or hydrates thereof are carbonated from the coated portions, the total amount of carbon dioxide absorbed into the hardened body of the hydraulic composition can be increased, and the strength of the carbonated hardened body obtained after carbonation curing can be further increased. The cement hydrate-containing aggregate may be contained in the fine aggregate, or in at least one of the fine aggregate and the coarse aggregate when the hydraulic composition contains coarse aggregate, but it is preferable that it be contained in the fine aggregate from the viewpoint of increasing the total amount of carbon dioxide absorbed in the hardened body of the hydraulic composition.

[0029] The proportion of the cement hydrate-containing aggregate in the total amount of aggregate contained in the hydraulic composition is preferably 20% by mass or more, more preferably 25% by mass or more, and particularly preferably 30% by mass or more. When the proportion is 20% by mass or more, the total amount of carbon dioxide that the carbonated hardened body can absorb can be increased and the strength of the carbonated hardened body can be increased compared to when general aggregate is used. When the cement hydrate-containing aggregate is a fine aggregate, the proportion of recycled aggregate in the total amount of fine aggregate is preferably 20% by mass or more, more preferably 25% by mass or more, and particularly preferably 30% by mass or more. When the proportion is 20% by mass or more, the total amount of carbon dioxide that can be absorbed by the carbonated hardened body can be increased and the strength of the carbonated hardened body can be increased compared to when ordinary aggregate is used.

[0030] The proportion of the total amount of cement clinker minerals and their hydrates in the total amount of cement hydrate-containing aggregate is preferably 2 mass % or more, more preferably 5 mass % or more, and even more preferably 10 mass % or more. The method for measuring the above ratio is not particularly limited, but examples thereof include powder X-ray diffraction, thermogravimetric analysis, acid dissolution method, and image analysis using an electron microscope. When the cement hydrate-containing aggregate is recycled aggregate obtained from waste concrete, aggregate obtained from solidified concrete sludge, or crushed concrete or mortar, it may be difficult to measure the above ratio using powder X-ray diffraction. In this case, the amount of dissolved cement hydrate can be measured using the acid dissolution method. When the raw aggregate used in the recycled aggregate is limestone or dolomite, it is preferable to use thermogravimetric analysis to calculate the mass loss from 100°C to 550°C.

[0031] When the cement hydrate-containing aggregate is recycled aggregate obtained from waste concrete or crushed concrete or mortar, the cement paste contained in the cement hydrate-containing aggregate contains cement clinker minerals and their hydrates. The strength of the carbonated hardened body is further improved by the hydration or carbonation of the cement clinker minerals and their hydrates. Therefore, the proportion (coverage rate) of the region (area) where a coating layer (a layer made of cement paste) containing at least one of the cement clinker minerals and their hydrates exists relative to the total surface area of ​​the cement hydrate-containing aggregate is important. The coverage can be determined by image analysis of the cross section of the aggregate particle. The method for obtaining the image used for image analysis is not particularly limited, and can be changed depending on the particle size of the aggregate to be analyzed. For example, for coarse aggregate, images can be taken using a general digital camera. For fine aggregate with a particle size of 0.3 mm or more, images can be taken using a stereo microscope. For fine aggregate with a particle size of less than 0.3 mm, images can be taken as backscattered electron images using an electron microscope in addition to the stereo microscope. When using a digital camera or a stereo microscope, the cross section of the aggregate is the subject of image acquisition. When using an electron microscope, a polished sample of the cross section is the subject of image acquisition. By using image analysis software, the area of ​​the total surface area of ​​the cement hydrate-containing aggregate that is covered with a coating layer containing at least one of cement clinker minerals and their hydrates can be identified by color tone in the case of an image obtained with a digital camera or a stereo microscope, or by brightness in the case of a backscattered electron image (composition image) obtained with an electron microscope.

[0032] The coverage rate can be calculated from the total length of the periphery of the aggregate particle and the length of the area covered by the identified cement clinker minerals and their hydrates (the length of the area covered by the cement clinker minerals and their hydrates in the total length of the periphery) using the following formula. Coverage rate (%) = Length of area covered by cement clinker minerals and their hydrates (mm) / Total circumference of aggregate particle (mm) × 100 The coverage rate of the aggregate is preferably calculated by calculating the coverage rate of each of a plurality of aggregate particles (preferably 100 or more), and then taking the average value as the coverage rate of the entire aggregate. The coverage rate of the cement hydrate-containing aggregate is preferably 20% or more, more preferably 30% or more, and even more preferably 50% or more, from the viewpoint of improving the strength of the carbonated hardened body.

[0033] The cement hydrate-containing aggregate may be pre-absorbed or dried. It may also be pre-heated in the range of 100 to 1,000°C. Heating at a temperature above 1,000°C is not preferable from the viewpoint of energy costs and reducing carbon dioxide emissions. The cement hydrate-containing aggregate may be wetted from the viewpoint of improving the fluidity of the hydraulic composition during kneading. The fine particle content of the cement hydrate-containing aggregate used as the fine aggregate is preferably 15% by mass or less, more preferably 2 to 10% by mass, from the viewpoint of the fluidity of the hydraulic composition before hardening. The amount of fine particles in the entire fine aggregate is preferably 10% by mass or less, more preferably 1 to 8% by mass, from the viewpoint of the fluidity of the hydraulic composition before hardening.

[0034] The aggregate may include aggregate other than cement hydrate-containing aggregate. Examples of fine aggregates other than cement hydrate-containing aggregates include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag, lightweight fine aggregate, and mixtures thereof. Examples of coarse aggregates other than cement hydrate-containing aggregates include river gravel, mountain gravel, land gravel, crushed stone, slag, lightweight coarse aggregate, and mixtures thereof. Furthermore, from the viewpoint of reducing the amount of shrinkage during carbonation curing and during the service life and further improving dimensional stability, it is preferable that the material of the aggregate other than the cement hydrate-containing aggregate is limestone or dolomite (specifically, crushed limestone sand, crushed limestone stone, crushed dolomite sand, crushed dolomite stone, and recycled aggregates thereof). Furthermore, if the material of the aggregate other than the cement hydrate-containing aggregate is limestone or dolomite, it can be recovered after use of the carbonated hardened body and used in its entirety as a cement clinker raw material. In this case, cement clinker can be produced by simply adding a small amount of new raw material.

[0035] When the hydraulic composition contains coarse aggregate, the fine aggregate ratio is preferably 5 to 60%. If the fine aggregate ratio is within the above range, the workability and ease of molding of the kneaded product are improved. The amount of aggregate (the total amount when fine aggregate and coarse aggregate are used in combination) is preferably 200 to 700 parts by mass, more preferably 200 to 600 parts by mass, per 100 parts by mass of the powdered hydraulic material. If the amount is within the above range, the strength of the carbonated hardened body will be increased and the shrinkage rate of the carbonated hardened body will be reduced. The coarseness ratio when the fine aggregate and the coarse aggregate are combined is preferably 1.0 to 7.0, and more preferably 1.5 to 6.5.

[0036] [Other ingredients] The hydraulic composition may contain other materials as needed within the scope of not impairing the object of the present invention. Examples of other materials that may be added as needed include various additives such as water-reducing agents, antifoaming agents, and shrinkage-reducing agents, and various admixtures such as fly ash, silica fume, ground granulated blast furnace slag, and ground limestone. The proportion of the other materials in the hydraulic composition varies depending on the type of the other materials, but is, for example, 20% by mass or less, preferably 10% by mass or less.

[0037] [Method of manufacturing carbonated hardened body] An example of the method for producing a carbonated hardened product of the present invention includes a kneaded product preparation step of kneading the aggregate materials including (A) the powdery hydraulic material, (B) water, and (C) cement hydrate-containing aggregate (aggregate containing at least one of cement clinker minerals and hydrates thereof) described above to prepare a kneaded product of a hydraulic composition; a casting step of casting the kneaded product into a formwork; a demolding step of releasing the hardened product of the hydraulic composition obtained by hardening the kneaded product in the formwork from the formwork after the kneaded product in the formwork has hardened; and a carbonation curing step of carbonating the hardened product of the hydraulic composition released from the formwork to obtain a carbonated hardened product. Each step will be explained in detail below.

[0038] [Kneaded material preparation process] This step is a step of kneading the above-mentioned (A) powdered hydraulic material, (B) water, and (C) aggregate materials including cement hydrate-containing aggregate to prepare a kneaded hydraulic composition. The method for kneading the materials is not particularly limited, and the device used for kneading is also not particularly limited, and for example, a conventional mixer such as an omni mixer, a pan mixer, a twin-screw mixer, or a tilting mixer can be used. In this step, the components (A) to (C) may be kneaded with the amines. [Pouring process] This step is a step of casting the kneaded material obtained in the previous step into a formwork. The casting method is not particularly limited, and a conventional method such as pouring can be used. The curing method used after the kneaded material is poured into the formwork and before it is removed from the formwork is not particularly limited, and general curing methods such as air curing, moist air curing, underwater curing, and steam curing can be used. [Demolding process] This step is a step in which, after the kneaded material in the formwork has hardened, the hardened hydraulic composition obtained by the hardening of the kneaded material is removed from the formwork.

[0039] [High strength curing process] This step is optionally performed between the demolding step and the carbonation curing step, and is a step for increasing the strength of the hardened product of the hydraulic composition. In this step, the hardened hydraulic composition removed from the formwork is subjected to a compressive strength of preferably 3 N / mm 2 More than 5N / mm 2 More than 10 N / mm 2 By curing until the above temperature is reached, the strength of the carbonated hardened body after carbonation curing (for example, the compressive strength of mortar and the compressive strength of concrete) can be increased. The curing method is not particularly limited, and general curing methods such as air curing, moist air curing, underwater curing, and steam curing can be used. Note that the "curing" in the high-strength curing step does not include carbonation curing.

[0040] [Carbonation curing process] This step is a step of carbonating and curing the hardened hydraulic composition released from the formwork to obtain a carbonated hardened body by carbonating the hardened hydraulic composition. The concentration of carbon dioxide gas used for carbonation curing in this step is preferably 1% by volume or more, more preferably 3% by volume or more, even more preferably 10% by volume or more, even more preferably 50% by volume or more, and particularly preferably 60% by volume or more. If the concentration is 1% by volume or more, the amount of carbon dioxide absorbed in the carbonation curing step can be increased. The upper limit of the carbon dioxide gas concentration is not particularly limited, and the higher the carbon dioxide gas concentration, the more carbon dioxide absorption can be achieved. However, from the viewpoint of reducing costs for curing equipment and the like, the upper limit is preferably 90% by volume or less, more preferably 70% by volume or less, and particularly preferably 50% by volume or less.

[0041] The temperature in the carbonation curing step is not particularly limited, but is preferably 5 to 100°C, more preferably 10 to 50°C, and particularly preferably 15 to 35°C. If the temperature during carbonation curing is within the above range, the productivity of products made from the carbonated hardened body can be improved, and the strength of the carbonated hardened body can be increased. Furthermore, the carbonated hardened product of the present invention is highly effective in reducing carbon dioxide emissions even when carbonation curing is carried out at a relatively low temperature (for example, 5 to 30°C). The relative humidity in this step is not particularly limited, but is preferably 20 to 90%, more preferably 30 to 80%, and particularly preferably 40 to 70%. If the relative humidity is 20% or higher, the productivity of the carbonated hardened body will be improved and the strength of the carbonated hardened body will be greater. It is difficult to increase the relative humidity above 90%, and the cost of equipment, etc. will be excessive.

[0042] In the carbonation curing step, it is preferable to carry out carbonation curing so that the carbonation depth from the surface of the carbonated hardened body is preferably 2 mm or more, more preferably 3 mm or more, even more preferably 4 mm or more, and particularly preferably 5 mm or more. By carrying out carbonation curing so that the carbonation depth is 2 mm or more, a larger amount of carbon dioxide can be absorbed into the carbonated hardened body. Specifically, the carbonation depth can be made 2 mm or more by appropriately adjusting the carbon dioxide gas concentration, temperature, and relative humidity values, as well as the curing time, in the carbonation curing step described above. From the viewpoint of absorbing carbon dioxide in a short time, it is preferable to carry out carbonation curing so that the carbonation depth is 2 mm or more, preferably at an age of 1 day, more preferably at an age of 3 days. The "carbonation depth from the surface of the carbonated hardened body" can be measured in accordance with "JIS A 1152:2018 (Method for measuring the carbonation depth of concrete)". The obtained carbonated hardened material can be used as a roadbed material, interlocking blocks, etc. Furthermore, even after being installed as a roadbed material, etc., it can continue to absorb and fix carbon dioxide.

[0043] In addition, from the viewpoint of increasing the efficiency of carbonation, the cement hydrate-containing aggregate may be subjected to a carbonation treatment before the kneaded product preparation step. In this case, if carbonation is carried out excessively until no cement clinker minerals and their hydrates remain in the cement hydrate-containing aggregate, the improvement in strength of the carbonated hardened body after carbonation curing, which is one of the effects of the present invention, cannot be obtained.

[0044] In the present invention, the carbonated hardened material obtained by the above production method preferably has a reduction in the amount of carbon dioxide emitted during production of the carbonated hardened material of 15% or more (more preferably 20% or more, even more preferably 30% or more, and particularly preferably 40% or more) compared to when the same Portland cement as that contained in the powdered cement composition is used instead of the pulverized calcined material, and the reduction in strength (e.g., compressive strength) of the carbonated hardened material is preferably 50% or less (more preferably 40% or less).

Claims

1. (A) C ２ S and C ２ The present invention relates to a hydraulic composition, which is obtained by carbonating a hardened body of a hydraulic composition including: a powdered hydraulic material containing AS and a pulverized product of a fired material that satisfies the following conditions (1) and (2); (B) water; and (C) an aggregate containing a cement hydrate-containing aggregate that contains at least one of a cement clinker mineral and a hydrate thereof, The cement hydrate-containing aggregate is a fine aggregate, or a fine aggregate and a coarse aggregate, The cement hydrate-containing aggregate is a recycled aggregate obtained from waste concrete, or a crushed material of demolished concrete or demolished mortar, The proportion of a region where a coating layer containing at least one of a cement clinker mineral and a hydrate thereof is present in the total surface area of ​​the cement hydrate-containing aggregate is 50% or more, The proportion of the cement hydrate-containing aggregate in the (C) aggregate is 30% by mass or more, A carbonated hardened body, characterized in that the total amount of the cement clinker mineral and its hydrate in the cement hydrate-containing aggregate is 10 mass% or more. (1) The above-mentioned fired product is C ４ If AF is not included, the above C ２ The above C relative to 100 parts by mass of S ２ The amount of AS is 10 to 2,000 parts by mass, and the fired product is C ４ If AF is included, the above C ２ The above C relative to 100 parts by mass of S ２ The total amount of AS and the C4AF is 10 to 2,000 parts by mass, and ２ The above C in a total of 100% by mass of AS and the above C4AF ４ The AF ratio is 70% by mass or less (2) The fired product is C ３ Does not contain A or C ３ A to the above C ２ The content is 20 parts by mass or less per 100 parts by mass of S.

2. A carbonated hardened body as described in Claim 1, wherein the recycled aggregate obtained from the waste concrete, or the raw aggregate contained in the crushed material of the demolished concrete or the demolished mortar, is limestone or dolomite.

3. The carbonated hardened body according to claim 1 or 2, wherein the powdery hydraulic material (A) contains gypsum powder.

4. The carbonated hardened body according to any one of claims 1 to 3, wherein the powdery hydraulic material (A) contains cement, and the proportion of the pulverized material in the powdery hydraulic material (A) is 5 to 90 mass% and the proportion of the cement is 10 to 95 mass%.

5. In the (A) powdery hydraulic material, the proportion of the pulverized material is 10 to 60 mass % and the proportion of the cement is 40 to 90 mass %, 5. The carbonated hardened product according to claim 4, wherein the cement is at least one of ordinary Portland cement and high-early-strength Portland cement.

6. A method for producing the carbonated hardened body according to any one of claims 1 to 5, comprising: a kneaded mixture preparation step of kneading the materials (A) to (C) to prepare a kneaded mixture of the hydraulic composition; A casting step of casting the kneaded material into a formwork; a demolding step of demolding a hardened body of the hydraulic composition obtained by hardening the kneaded material in the formwork after the kneaded material in the formwork has hardened; a carbonation curing step of carbonating the set body of the hydraulic composition released from the form to obtain a carbonated set body of the hydraulic composition; A method for producing a carbonated hardened body, comprising:

7. The method for producing a carbonated hardened body according to claim 6, further comprising a high-strength curing step for increasing strength of the hardened body of the hydraulic composition between the demolding step and the carbonation curing step.

8. A process provided before the kneaded product preparation process, The method for producing a carbonated hardened product according to claim 6 or 7, further comprising an aggregate carbonation treatment step of carbonating the cement hydrate-containing aggregate.