Method for manufacturing cement concrete, method for manufacturing carbonated cement concrete

Abstract

The objective is to provide a method for manufacturing cement concrete that can produce cement concrete with high CO2 sequestration capacity with minimal labor. [Solution] A method for producing cement concrete, comprising mixing an admixture containing γ-C2S and β-C2S with water to form an admixture slurry, and then mixing the admixture slurry with cement material.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing cement concrete and a method for manufacturing carbonated cement concrete.

Background Art

[0002] Since a large amount of cement is used as a raw material for concrete, it is regarded as a material with a large CO2 emission. This is mainly due to the fact that in the production process of cement, in addition to using a large amount of fossil fuel to obtain the combustion energy of the furnace, the decarbonation reaction of limestone (CaCO3 → CaO + CO2) occurs. Reducing the CO2 emission as concrete has become an important theme as part of the measures to combat global warming.

[0003] In order to reduce the total amount of CO2 emitted when manufacturing concrete products, it is effective to reduce the amount of cement used by blending a large amount of special admixtures and industrial by-products (such as blast furnace slag fine powder, fly ash, etc.) as cement substitutes, and various studies are being carried out.

[0004] On the other hand, there is a known technique for obtaining a highly durable concrete product in which CO2 is absorbed and the surface layer is densified by forcibly carbonating (salting) and curing concrete blended with a non-hydraulic compound such as γ-C2S (γ-2CaO·SiO2; also called the γ-phase of belite) as an admixture (for example, Patent Document 1). γ-C2S does not undergo a hydration reaction and reacts with CO2 to form a gel rich in CaCO3 and SiO2. These products fill the voids in the cement matrix, and the durability of the surface layer of the concrete product is dramatically improved. In this case, the total CO2 emission in obtaining the concrete product is reduced by the amount of CO2 absorbed by the concrete during carbonation (salting) curing.

[0005] Furthermore, Patent Document 2 proposes a concrete mixture containing one or two types of γ-C2S and steelmaking slag powder as powder components, along with Portland cement, where the total amount of γ-C2S and steelmaking slag powder in the total content is 25-95% by mass, and the water-cement ratio (W / C) is 80-250% by mass. It is described that by reducing CO2 emissions through the reduction of cement usage and by utilizing CO2 absorption through carbonation (salting) curing, it has become possible to realize precast concrete products with significantly reduced total CO2 emissions compared to conventional concrete. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-182583 [Patent Document 2] Japanese Patent Publication No. 2011-168436 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, since powder materials are usually packaged in paper bags, lifting them into the mixer is required during on-site construction, thus reducing the workload is desirable. [Means for solving the problem]

[0008] The inventors of the present invention conducted intensive research to solve the above-mentioned problems and found that the problems can be solved by a method for producing cement concrete in which an admixture containing γ-C2S and β-C2S is mixed with water to form an admixture slurry, and this admixture slurry is mixed with cement material. This led to the present invention. In other words, the present invention is as follows.

[0009] [1] A method for producing cement concrete, comprising mixing an admixture containing γ-C2S and β-C2S with water to form an admixture slurry, and mixing the admixture slurry with cement material. [2] The method for producing cement concrete according to [1] above, wherein the admixture contains 40% by mass or more of γ-C2S and 3% by mass or more of β-C2S. [3] The method for producing cement concrete according to [2] above, wherein the C2AS content in the admixture is 2% by mass or more. [4] A method for producing cement concrete according to any one of [1] to [3] above, wherein the water content in the admixture slurry is 30 to 70% by mass. [5] A method for producing carbonated cement concrete, wherein cement concrete produced by any one of the methods for producing cement concrete described in [1] to [4] above is subjected to carbonation curing. [6] A method for producing carbonated cement concrete as described in [5] above, wherein carbonation curing is performed in an atmosphere with a temperature of 10 to 50°C, a humidity of 50 to 80% RH, and a CO2 concentration of 5% or more. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for manufacturing cement concrete that can produce cement concrete with high CO2 sequestration capacity with minimal labor. [Modes for carrying out the invention]

[0011] One embodiment of the present invention will be described in detail below, but the present invention is not limited to this embodiment. In this specification, "%" and "parts" refer to mass unless otherwise specified. In the present invention, "cement concrete" refers collectively to cement paste, mortar, and concrete.

[0012] [Method of manufacturing cement concrete] The method for producing cement concrete according to this embodiment involves mixing an admixture containing γ-C2S and β-C2S with water to form an admixture slurry, and then mixing the admixture slurry with cement material. This method for producing cement concrete allows for the production of cement concrete with high CO2 sequestration capacity with minimal labor by mixing an admixture slurry containing γ-C2S and β-C2S with cement material.

[0013] The present invention provides a method for producing cement concrete using admixtures containing γ-C2S and β-C2S. C2S is known to have crystalline layers in the low-temperature phase γ-C2S and the high-temperature phases α-C2S, α'-C2S, and β-C2S. Although all of these are represented as 2CaO·SiO2, their crystalline structures and true densities differ. β-C2S is a hydraulic compound, while γ-2CaO·SiO2 is a non-hydraulic compound, but it has the property of hardening by absorbing carbon dioxide from the atmosphere, i.e., it is air-hardened.

[0014] The γ-C2S content in the admixture is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. There is no particular upper limit, but it may be 90% by mass or less. When the γ-C2S content in the admixture is within the above range, the strength development of the cement concrete produced can be improved.

[0015] The β-C2S content in the admixture is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more. There is no particular upper limit, but it may be 35% by mass or less. When the β-C2S content in the admixture is within the above range, the strength development of the cement concrete produced can be improved.

[0016] The mass ratio of the content of β-C2S to the content of γ-C2S in the admixture is preferably 1:2 to 1:9, and more preferably 1:3 to 1:4. When the ratio of the content of β-C2S to the content of γ-C2S is within the above range, the CO2 fixation ability and strength development can be made better.

[0017] The admixture preferably further contains C2AS. C2AS is a non-hydraulic compound represented by 2CaO·Al2O3·SiO2. When the admixture contains C2AS, the CO2 fixation ability and strength development can be made better.

[0018] In the admixture, the content of C2AS is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more. The upper limit is not particularly limited, but it may be 10% by mass or less. When the content of C2AS in the admixture is within the above range, the CO2 fixation ability and strength development can be made better.

[0019] In the admixture, the content of 12CaO·7Al2O3 is preferably less than 25% by mass, and more preferably less than 15%. It may also be 0% by mass. When the content of 12CaO·7Al2O3 in the admixture is within the above range, the CO2 fixation ability and strength development can be made better.

[0020] In addition to the above compounds, the admixture can contain, for example, 3CaO·2SiO2, α-CaO·SiO2, 3CaO·MgO·2SiO2 (C3MS2), 3CaO·3Al2O3·CaSO4, 4CaO·Al2O3·Fe2O3, 3CaO·Al2O3, and among them, it is preferable to contain 3CaO·2SiO2 and α-CaO·SiO2.

[0021] The admixture used in the present invention can be obtained, for example, by blending CaO raw material, SiO2 raw material, Al2O3 raw material, etc. in a predetermined molar ratio and subjecting them to heat treatment by a rotary kiln, an electric furnace, or the like. The heat treatment temperature is usually carried out in the range of about 1,000 to 1,800 °C. Examples of the CaO raw material include calcium carbonate such as limestone, calcium hydroxide such as slaked lime, by-product slaked lime such as acetylene by-product slaked lime, fine powder generated from waste concrete blocks, concrete sludge (dehydrated cake) generated in ready-mixed concrete plants and concrete product plants, incineration ash (coal ash, woody biomass, municipal solid waste incineration ash, sewage sludge incineration ash, paper sludge, etc.), steel slag (converter slag, electric furnace slag, etc.). Examples of the SiO2 raw material include quartz, clay, and various silica dusts generated as industrial by-products represented by silica fume and fly ash. Examples of the Al2O3 raw material include bauxite. Further, the contents of γ-C2S and β-C2S can be adjusted according to the cooling rate after heat treatment. When the cooling rate is slowed down, the content of γ-C2S can be increased, and when it is speeded up, the content of β-C2S can be increased.

[0022] In the admixture, the content of MgO is preferably 5% by mass or less, and more preferably substantially not contained. Note that "substantially not contained" means that the content of MgO is below the detection limit, and it means that MgO raw material and raw materials containing MgO are not actively added during the production of the admixture. When the content of MgO in the admixture is within the above range, the CO2 fixation ability and strength development property can be made better. The content of MgO in the admixture can be measured, for example, by fluorescent X-ray analysis.

[0023] Furthermore, even if the raw materials contain other impurities, this is not particularly problematic as long as it does not hinder the effects of the present invention. Specific examples of impurities include, for example, Fe2O3, TiO2, MnO, Na2O, K2O, S, P2O5, F, B2O3, and chlorine. Other coexisting compounds include free calcium oxide, calcium hydroxide, calcium aluminate, calcium aluminosilicate, calcium ferrite and calcium aluminoferrite, calcium phosphate, calcium borate, magnesium silicate, leucite (K2O·Al2O3·4SiO2), magnetite (Fe3O4), and sulfur compounds such as CaS, A12S3, and CaC2·CaS.

[0024] The present invention relates to a method for producing cement concrete, which includes the step of mixing the above-mentioned admixture with water to form an admixture slurry. The water is not particularly limited, and for example, tap water, groundwater, recovered water from a ready-mix concrete plant, or water containing CO2 can be used.

[0025] The water content in the admixture slurry is preferably 30 to 70% by mass, more preferably 40 to 60% by mass, and even more preferably 50 to 55% by mass. When the water content in the admixture slurry is within the above range, cement concrete can be manufactured with less labor, and the strength development of the manufactured cement concrete can be improved.

[0026] The present invention's method for producing cement concrete includes the step of mixing the above-mentioned admixture slurry with cement material. In this invention, the cement material refers to a hydraulic material containing cement. The cement is not particularly limited and includes various types of Portland cement such as ordinary, rapid-hardening, ultra-rapid-hardening, low-heat, and moderate-heat cements; various blended cements obtained by mixing these Portland cements with blast furnace slag, fly ash, silica, silica fume, metakaolin, allophane, etc.; environmentally friendly cements (eco-cements) manufactured using municipal solid waste incineration ash and sewage sludge incineration ash as raw materials; commercially available fine-particle cements; white cements; filler cements obtained by mixing limestone fine powder, etc. It is also possible to use various types of cement after they have been pulverized. In addition, geopolymer cements, sulfoaluminate cements, and limestone calcined clay cements (LC3), which have lower CO2 emissions compared to conventional cements, are also mentioned. Furthermore, cements that have been adjusted by increasing or decreasing the amount of components normally used in cement (e.g., gypsum) can also be used. Moreover, combinations of two or more of these can also be used.

[0027] From the perspective of manufacturing cost and strength development, cement has a Blaine specific surface area of ​​2,500 to 7,000 cm². 2 It is preferable that the amount is / g, and the range is 2,750 to 6,000 cm³. 2 It is more preferable that the amount is / g, and the range is 3,000 to 4,500 cm 2 It is even more preferable that the value is / g. The Blaine specific surface area can be measured based on the specific surface area test specified in JIS R 5201:2015 "Physical Testing Methods for Cement".

[0028] Cement materials may contain aggregates. The aggregates are not particularly limited and can include fine aggregates such as river sand, mountain sand, sea sand, lime sand, and silica sand, as well as coarse aggregates such as river gravel, mountain gravel, and lime gravel.

[0029] The aggregate content is preferably 40 to 600 parts by mass, more preferably 50 to 500 parts by mass, and even more preferably 60 to 450 parts by mass, per 100 parts by mass of cement in the cement material. Having the aggregate content within the above range allows for better strength development.

[0030] In addition to the materials mentioned above, the cement material may also use one or more known additives and admixtures commonly used in cement materials, to the extent that they do not adversely affect performance, such as water-reducing agents, AE water-reducing agents, high-performance water-reducing agents, fluidizers, defoamers, thickeners, rust inhibitors, antifreezes, polymer dispersions for cement admixture, shrinkage reducing agents, admixtures such as granulated blast furnace slag powder, slowly cooled blast furnace slag powder, sewage sludge incineration ash and its molten slag, municipal solid waste incineration ash and its molten slag, and pulp sludge incineration ash, as well as fibrous materials such as polymers, vinylon fibers, acrylic fibers, and carbon fibers, setting regulators, viscosity minerals such as bentonite, and anion exchangers such as hydrotalcite, to the extent that they do not substantially hinder the objectives of the present invention.

[0031] In the method for manufacturing cement concrete of the present invention, each material may be mixed during construction, or some or all of them may be mixed in advance. Conventional mixing equipment can be used as the mixing device, such as a tilting drum mixer, a forced twin-shaft mixer, an omni mixer, a Henschel mixer, a V-type mixer, and a Nauta mixer.

[0032] [Manufacturing method for carbonated cement concrete] The method for producing carbonated cement concrete according to this embodiment is a method of carbonicating and curing cement concrete produced by the cement concrete production method of the present invention. Carbonation curing is a curing method in which the produced cement concrete is cured in a gas containing carbon dioxide, thereby forcibly carbonating the cement concrete.

[0033] In this invention, the carbonation curing is preferably carried out in an atmosphere with a temperature of 10 to 50°C, a humidity of 50 to 80% RH, and a CO2 concentration of 5% or higher, and more preferably in an atmosphere with a temperature of 20 to 40°C, a humidity of 60 to 70% RH, and a CO2 concentration of 5 to 20%. The atmosphere may also be at atmospheric pressure, but may be pressurized as needed.

[0034] The CO2 content of carbonated cement concrete can be calculated by dividing the CO2 content of the manufactured carbonated cement concrete by its mass. The CO2 content of carbonated cement concrete can be measured, for example, by differential thermogravimetric analysis or coulometric titration using a coulometer, and the mass of the carbonated cement concrete is the value obtained by subtracting the loss on ignition at 1,000°C.

[0035] In differential thermogravimetric analysis, a differential thermogravimetric analyzer (TG-DTA) is used, and the temperature is raised to 1,000°C at a heating rate of 10°C / min under a nitrogen atmosphere (gas flow rate of 70 ml / min). Based on the obtained TG-DTA curve, the mass loss in the range of 550°C to 850°C can be used to determine the CO2 content of carbonated cement concrete.

[0036] In the electroporative drip method, carbonated cement concrete is crushed and placed in a flask, perchloric acid (2 mol / L) is added, and the mixture is stirred with a stirrer. The resulting CO2 gas is then introduced into the absorbent solution using nitrogen, and the amount of carbon calculated from the amount of electricity required to maintain a constant permeability of the absorbent solution can be converted into the CO2 content.

[0037] The CO2 fixation rate of carbonated cement concrete one day after the start of carbonation curing is preferably 5% or more, more preferably 8% or more, and even more preferably 10% or more. [Examples]

[0038] The present invention will be further described below based on experimental examples, but the present invention is not limited thereto.

[0039] <Experimental Example 1> Admixtures with the compositions listed in Table 1 below were mixed in predetermined proportions with by-product slaked lime (Ca(OH)2 content 95%, Al2O3 content 1%, median diameter 45 μm) and silica powder (SiO2 content 96%, Al2O3 content 3%, median diameter 15 μm) and heat-treated to prepare an admixture. The prepared admixture and water were then mixed to the water content ratios listed in Table 1 to prepare an admixture slurry. Mortar was prepared by mixing 100 parts by mass of the prepared admixture slurry, 150 parts by mass of cement (equivalent to blast furnace type B cement), and 500 parts by mass of fine aggregate (standard sand for cement strength testing). After the prepared mortar was cast into a formwork (40 × 40 × 160 mm), it was demolded after 1 day and subjected to carbonation curing in an environment of 40°C, 60% RH relative humidity, and 20% CO2 concentration to obtain carbonated mortar. Various measurements were performed on the manufactured carbonated mortar. The results are shown in Table 1.

[0040] (Measurement items) Compressive strength: Compressive strength was measured at 4 hours and 1 day of age, from the start of carbonation curing, in accordance with the method specified in JIS R 5201:2015 "Physical Testing Methods for Cement".

[0041] Bending strength: Bending strength was measured from the start of carbonation curing, at 4 hours and 1 day of age, in accordance with the method specified in JIS R 5201:2015 "Physical Testing Methods for Cement".

[0042] Carbonation depth: In accordance with the method specified in JIS A 1152:2018 "Method for measuring the carbonation depth of concrete," the carbonation depth was measured from the start of carbonation curing, at 4 hours and 1 day of age.

[0043] CO2 content: Using a differential thermogravimetric analyzer (NETZSCH), the temperature was raised to 1,000°C at a heating rate of 10°C / min under a nitrogen atmosphere (gas flow rate 70 ml / min). Based on the obtained TG-DTA curve, the mass loss in the range of 550°C to 850°C was defined as the CO2 content of the carbonated mortar, and the mass loss up to 1,000°C was subtracted from the mass before analysis to determine the mass of the carbonated mortar. The CO2 content was then measured from the start of carbonation curing, at 4 hours, and at 1 day of age.

[0044] [Table 1] [Industrial applicability]

[0045] The present invention's method for producing cement concrete is particularly useful as a method for producing cement concrete used in civil engineering, construction, and other fields, and can produce cement concrete with high CO2 sequestration capacity.

Claims

1. γ-C ２ S and β-C ２ A method for producing cement concrete, comprising mixing an admixture containing sulfur with water to form an admixture slurry, and then mixing the admixture slurry with cement material.

2. γ-C in the aforementioned admixture ２ The S content should be 40% by mass or more, and β-C ２ A method for producing cement concrete according to claim 1, wherein the sulfur content is 3% by mass or more.

3. C in the aforementioned admixture ２ A method for producing cement concrete according to claim 2, wherein the AS content is 2% by mass or more.

4. A method for producing cement concrete according to any one of claims 1 to 3, wherein the water content in the admixture slurry is 30 to 70% by mass.

5. A method for producing carbonated cement concrete, comprising carbonizing and curing cement concrete produced by the cement concrete production method described in any one of claims 1 to 3.

6. Temperature 10-50℃, humidity 50-80%RH, CO ２ A method for producing carbonated cement concrete according to claim 5, wherein the carbonation curing is performed in an atmosphere with a concentration of 5% or more.

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