Carbonation-promoting cement composition, carbonation-promoting mortar concrete, and hardened body

Abstract

To provide a carbonation-promoting cement composition capable of promoting short-term CO2 fixation and enabling carbonation to proceed into interior regions of a hardened body.SOLUTION: The carbonation-promoting cement composition comprises cement and a calcium carbonate-containing powder, and the content of calcium carbonate is 5 to 50 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbonation-accelerated cement composition, a carbonation-accelerated mortar concrete, and a hardened body thereof. [Background technology]

[0002] Concrete is considered a material with a large amount of CO2 emissions because it uses a large amount of cement as a raw material. This is mainly due to the large amount of fossil fuels used to obtain combustion energy for the furnace during the cement production process, as well as the occurrence of a decarbonation reaction of limestone (CaCO3 → CaO + CO2). Reducing CO2 emissions from concrete is an important theme as part of 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 incorporating large amounts of special additives or industrial by-products (ground granulated blast furnace slag, fly ash, etc.) as cement substitutes, and various research projects are being conducted in this area.

[0004] Meanwhile, a technology is known in which concrete containing a non-hydraulic compound such as γ-C2S (γ-2CaO·SiO2; also known as the belite γ phase) as an admixture is subjected to forced carbonate (salt) curing, which causes CO2 absorption and densifies the surface layer, resulting in a highly durable concrete product (see, for example, Patent Document 1). γ-C2S does not undergo a hydration reaction, but reacts with CO2 to form a gel rich in CaCO3 and SiO2. These products fill voids in the cement matrix, dramatically improving the durability of the surface layer of the concrete product. In this case, the total CO2 emissions required to obtain the concrete product are reduced by the amount of CO2 absorbed by the concrete during carbonate (salt) curing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-182583 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when products containing cement or γ-C2S are carbonated, the surface layer becomes dense, and CO2 absorption into the interior may be insufficient. Also, from the perspective of productivity, there is a demand for materials that can sufficiently fix CO2 even if the carbonation curing period is shortened. [Means for solving the problem]

[0007] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the problems can be solved by a carbonation-accelerated cement composition that contains cement and a calcium carbonate-containing powder, and that contains calcium carbonate in a specific ratio, and have arrived at the present invention. That is, the present invention is as follows.

[0008] [1] A carbonation-accelerated cement composition comprising cement and a calcium carbonate-containing powder, the calcium carbonate content being 5 to 50 mass %. [2] The carbonation-accelerated cement composition according to [1] above, wherein the calcium carbonate content of the calcium carbonate-containing powder is 5% by mass or more. [3] The carbonation-accelerated cement composition according to [1] or [2] above, which contains 0.1 to 5 mass % of MgO as a chemical component. [4] The carbonation-accelerated cement composition according to any one of [1] to [3] above, which has a CO2 fixation capacity of 0.15 to 0.60. [5] A carbonation-accelerated mortar concrete comprising the carbonation-accelerated cement composition according to any one of [1] to [4] above and aggregate. [6] The total mass of the cement and the calcium carbonate-containing powder is 20 to 50 kg / m 3 The carbonation-accelerated mortar concrete according to [5] above. [7] A hardened body obtained by hardening the carbonation-accelerated mortar concrete described in [5] or [6] above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a carbonation-accelerated cement composition that can promote short-term CO2 fixation and carbonate the interior of the hardened body. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, one embodiment of the present invention (the present embodiment) will be described in detail, but the present invention is not limited to this embodiment. In this specification, "%" and "parts" are based on mass unless otherwise specified.

[0011] [Carbonation-accelerated cement composition] The carbonation-accelerated cement composition according to this embodiment contains cement and a calcium carbonate-containing powder, and the calcium carbonate content is 5 to 50 mass %. The carbonation-accelerated cement composition contains cement and a calcium carbonate-containing powder, and by containing calcium carbonate in a specific ratio, it is possible to promote short-term CO2 fixation and carbonation to the interior of the hardened body.

[0012] The carbonation-accelerated cement composition of the present invention contains cement. The type of cement is not particularly limited, and examples include various Portland cements, such as normal, early-strength, ultra-early-strength, 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 (ecocements) produced from municipal waste incineration ash or sewage sludge incineration ash; commercially available fine-grain cements; white cements; and filler cements containing limestone fine powder. Various cements can also be used in their finely powdered form. Other examples include geopolymer cements, sulfoaluminate cements, limestone-calcined clay cements (LC3), and carbonated cements that harden by immobilizing CO2, which emit less CO2 than conventional cements. Modified cements can also be used by increasing or decreasing the amount of components typically used in cements (e.g., gypsum). Furthermore, combinations of two or more of these can also be used.

[0013] From the viewpoint of manufacturing cost and strength development, cement is required to have a Blaine specific surface area (also called Blaine value) of 2,500 to 7,000 cm 2 / g, and 2,750 to 6,000 cm 2 / g, and more preferably 3,000 to 4,500 cm 2 In the present invention, the Blaine specific surface area is determined in accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement."

[0014] The carbonation-accelerated cement composition of the present invention contains a calcium carbonate-containing powder. The calcium carbonate-containing powder in the present invention is a powder containing calcium carbonate in each particle, and examples thereof include commercially available limestone fine powder and synthetic calcium carbonate, artificial calcium carbonate obtained from raw materials such as concrete sludge, waste concrete, and paper sludge, and calcium carbonate obtained by processing waste materials containing calcium carbonate as a main component, such as eggshells and seashells.

[0015] The calcium carbonate content of the calcium carbonate-containing powder is preferably 5% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, and even more preferably 80% by mass or more. There is no particular upper limit, but it may be 100% by mass. When the calcium carbonate content is within the above range, better strength development can be achieved. The calcium carbonate content of the calcium carbonate-containing powder can be measured by powder X-ray diffraction (powder X-ray diffractometer: "SmartLab" manufactured by Rigaku Corporation).

[0016] The calcium carbonate powder has a Blaine specific surface area of ​​2,000 to 7,000 cm 2 / g, and 2,750 to 6,000 cm 2 / g, and more preferably 3,000 to 4,500 cm 2 / g is more preferred.

[0017] The calcium carbonate-containing powder is preferably contained in the carbonation-accelerated cement composition at 5 to 50 mass %, more preferably 8 to 40 mass %, and even more preferably 10 to 30 mass %. When the content of the calcium carbonate-containing powder is within the above range, carbonation is facilitated to the interior, and strength development is also good.

[0018] The carbonation-accelerated cement composition according to this embodiment has a calcium carbonate content of 5 to 50% by mass. If the calcium carbonate content is less than 5% by mass or more than 50% by mass, short-term CO2 fixation cannot be promoted, carbonation may not be achieved to the inside, and strength development may be poor. The calcium carbonate content is preferably 8 to 40% by mass, and more preferably 10 to 30% by mass. When the calcium carbonate content is within the above range, short-term CO2 fixation is further promoted and carbonation is more easily achieved to the inside. The calcium carbonate content can be measured by powder X-ray diffraction or the coulometric drip method described below.

[0019] The carbonation-accelerated cement composition preferably contains 0.1 to 5 mass% of MgO as a chemical component, more preferably 0.3 to 3 mass%, and even more preferably 0.5 to 2 mass%. The MgO content in the carbonation-accelerated cement composition can be measured in accordance with the method specified in JIS R 5202:2015 "Methods for chemical analysis of cement."

[0020] The carbonation-accelerating cement composition of the present invention can contain one or more of the following known additives and admixtures used in ordinary cement materials, such as water reducing agents, air-entraining water reducing agents, high-performance water reducing agents, superplasticizers, antifoaming agents, thickeners, rust inhibitors, antifreeze agents, polymer dispersions for cement admixtures, shrinkage reducing agents, admixtures such as granulated blast furnace slag, slowly cooled blast furnace slag, sewage sludge incineration ash and its molten slag, municipal waste incineration ash and its molten slag, and pulp sludge incineration ash; fibrous materials such as polymers, vinylon fibers, acrylic fibers, and carbon fibers; set modifiers; clay minerals such as bentonite; and anion exchangers such as hydrotalcite, within a range that does not adversely affect performance and does not substantially impair the objects of the present invention.

[0021] The carbonation-accelerated cement composition of the present invention can be produced by mixing cement and calcium carbonate-containing powder. The respective materials may be mixed at the time of construction, or some or all of them may be mixed in advance. Any existing mixer can be used, such as a tilting mixer, an omni mixer, a Henschel mixer, a V-type mixer, or a Nauta mixer.

[0022] [Carbonation Accelerated Mortar Concrete] The carbonation-accelerated mortar concrete according to this embodiment contains the carbonation-accelerated cement composition of the present invention and aggregate. The aggregate is not particularly limited, and fine aggregates such as river sand, mountain sand, sea sand, lime sand, and silica sand, and coarse aggregates such as river gravel, mountain gravel, and lime gravel can be used.

[0023] The aggregate content is 1,200 to 2,200 kg / m3 It is preferable that the density is 1,500 to 2,000 kg / m 3 More preferably, it is 1,600 to 1,800 kg / m 3 When the content of the aggregate is within the above range, the fluidity retention and early strength development can be improved.

[0024] The carbonation-accelerated mortar concrete of the present invention can be produced by kneading with water. The amount of water used is preferably 10 to 70 parts by mass, more preferably 15 to 65 parts by mass, and even more preferably 20 to 60 parts by mass, per 100 parts by mass of the total mass of the cement and calcium carbonate-containing powder in the carbonation-accelerated mortar concrete. The mixing apparatus used can be any of the above-mentioned mixing apparatuses. The water is not particularly limited, and examples of water that can be used include tap water, groundwater, recycled water from ready-mixed concrete plants, and water containing CO2.

[0025] <Cured body> The hardened body according to this embodiment is obtained by hardening the carbonation-accelerated mortar concrete of the present invention.

[0026] The hardened body of the present invention can be obtained by filling (casting) the carbonation-accelerated mortar concrete of the present invention into a formwork, then generally demolding it and subjecting it to carbonation curing. The carbonation-accelerated mortar concrete of the present invention can be demolded about one day after casting.

[0027] The carbonation curing is preferably carried out in an environment with a temperature of 15 to 60°C, a humidity of 20 to 80% RH, and a CO2 concentration of 1 to 95%, and more preferably in an environment with a temperature of 18 to 50°C, a humidity of 40 to 75% RH, and a CO2 concentration of 3 to 95%. The atmosphere may be atmospheric pressure, but may also be pressurized as necessary.

[0028] The amount of CO2 fixed in the hardened body by carbonation curing (CO2 fixation amount) is calculated from the CO2 amounts measured by coulometric titration using a coulometer on the hardened body after carbonation curing and on the carbonation-accelerated mortar concrete before carbonation curing. The amount of CO2 was measured by crushing the hardened body or carbonation-accelerated cement composition, placing it in an Erlenmeyer flask, adding hydrochloric acid (3 mol / L), stirring with a stirrer, and introducing the generated CO2 gas into an absorption solution using nitrogen. The amount of carbon was measured from the amount of electricity required to maintain a constant transmittance of the absorption solution, which was then converted into CO2 content. The amount of CO2 fixation can then be calculated from the difference between the CO2 content of the hardened body and the CO2 content of the carbonation-accelerated mortar concrete. Alternatively, the amount of CO2 fixation can be measured by taking a portion of the hardened body and measuring only the surface or a portion of the interior of the hardened body.

[0029] The amount of CO2 fixed at 20-25mm from the surface of the hardened concrete after 28 days (including 27 days of carbonation curing), with the time of pouring being considered as day 0, is 30kg / m 3 It is preferable that the saturation is 40 kg / m or more. 3 More preferably, it is 50 kg / m or more. 3 More preferably, it is equal to or greater than this.

[0030] The CO2 fixation rate of the hardened body can be calculated using the following formula: The CO2 fixation rate can be calculated from the amount of CO2 fixed described above and the CO2 fixation capacity and content of the carbonation-accelerated cement composition described below. (CO2 fixation rate)=(CO2 fixation amount) / {(CO2 fixation ability)×(carbonation-promoting cement composition content)}×100

[0031] The CO2 fixation capacity of a carbonation-accelerated cement composition is a parameter value calculated by the following formula. (CO2 fixation ability)=0.785(CaO-0.56CaCO3-0.7SO3)+1.091MgO+1.42Na2O+0.935K2O In the above formula, the contents of components other than CaCO3 in the carbonation-accelerated cement composition can be measured in accordance with JIS R 5202:2015 "Methods for chemical analysis of cement," and the CaCO3 content can be calculated from the CO2 content of the carbonation-accelerated cement composition in the above-mentioned measurement of the fixed CO2 amount as follows: (CaCO3 content) = (CO2 content) / (molecular weight of CO2) × (molecular weight of CaCO3). Alternatively, in the case of simple measurement, calculation may be performed using the following formula. (CO2 fixation ability)=0.785CaO

[0032] The CO2 fixation capacity of the carbonation-accelerated cement composition is preferably 0.15 to 0.60, more preferably 0.20 to 0.50, and even more preferably 0.22 to 0.48. When the CO2 fixation capacity of the carbonation-accelerated cement composition is within the above range, short-term CO2 fixation is further promoted, and carbonation easily extends to the interior of the hardened body. [Example]

[0033] The present invention will be further explained below based on experimental examples, but the present invention is not limited to these.

[0034] <Experimental Example 1> A carbonation-accelerated cement composition was prepared by mixing the materials listed below in the proportions listed in Table 1. The carbonation-accelerated cement composition and fine aggregate were mixed so that 300 parts by mass of fine aggregate was used per 100 parts by mass of cement and calcium carbonate-containing powder. Water was added at a ratio of 50 parts by mass per 100 parts by mass of cement and calcium carbonate-containing powder, and the mixture was kneaded to prepare a carbonation-accelerated mortar concrete. The carbonation-accelerated mortar concrete was poured into a formwork (4 × 4 × 16 cm) and demolded after one day. All but one side (4 × 4 cm) of the demolded hardened body was sealed with aluminum tape and subjected to carbonation curing for 28 days under an environment of 20°C, 60% relative humidity, and 5% CO2 concentration, yielding a hardened body. The results of the following measurements are shown in Table 1.

[0035] (Materials used) Cement: Ordinary Portland cement (commercially available), Blaine specific surface area 3,300 cm 2 / g, specific gravity 3.15g / cm 3 . Calcium carbonate-containing powder: limestone fine powder (commercially available), calcium carbonate content 95%, Blaine specific surface area 3,200 cm 2 / g. Water: Tap water. Fine aggregate: sand from the Himekawa River system in Itoigawa City, Niigata Prefecture, maximum size 5 mm or less, density 2.62 g / cm 3 .

[0036] (Measurement items) Compressive strength: In accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement," the compressive strength was measured at 3 days, 7 days, and 28 days, with the time of casting being considered as 0 days.

[0037] CO2 fixation amount: For the carbonation-accelerated mortar concrete and the hardened concrete, a coulometer (2000S-CAT model, manufactured by Nippon Ansu Co., Ltd.) was used to crush the hardened concrete or carbonation-accelerated mortar concrete and place it in an Erlenmeyer flask. Hydrochloric acid (3 mol / L) was added and stirred with a stirrer. The generated CO2 gas was introduced into the absorption solution using nitrogen. The amount of carbon was measured from the amount of electricity required to maintain the transmittance of the absorption solution at a constant level, and converted to CO2 content. The amount of CO2 fixation was calculated from the difference between the CO2 content of the hardened concrete and that of the carbonation-accelerated mortar concrete. The amount of CO2 fixation was measured for each of the hardened concrete surfaces (0-5 mm), the interior (10-15 mm, and 20-25 mm), depending on the vertical distance from the unsealed surface.

[0038] CO2 fixation rate: The CO2 fixation capacity, expressed by the following formula, was measured in accordance with JIS R 5202:2015 "Methods for chemical analysis of cement" to determine the contents of components other than CaCO3 in the carbonation-accelerated cement composition. The CaCO3 content was calculated from the CO2 content of the carbonation-accelerated cement composition in the above-mentioned measurement of the CO2 fixation amount, as follows: (CaCO3 content) = (CO2 content) / (molecular weight of CO2) × (molecular weight of CaCO3). CO2 fixation ability=0.785(CaO-0.56CaCO3-0.7SO3)+1.091MgO+1.42Na2O+0.935K2O Using the calculated CO2 fixation capacity, the CO2 fixation rate of the hardened body was calculated using the following formula. (CO2 fixation rate)=(CO2 fixation amount) / {(CO2 fixation ability)×(carbonation-promoting cement composition content)}×100

[0039] [Table 1] [Industrial Applicability]

[0040] The carbonation-accelerated cement composition of the present invention can be suitably used particularly in the fields of civil engineering and construction.

Claims

1. A carbonation-accelerated cement composition comprising cement and a calcium carbonate-containing powder, the calcium carbonate content being 5 to 50 mass %.

2. 2. The carbonation-accelerated cement composition according to claim 1, wherein the calcium carbonate content of the calcium carbonate-containing powder is 5% by mass or more.

3. 3. The carbonation-accelerated cement composition according to claim 1, which contains 0.1 to 5 mass % of MgO as a chemical component.

4. CO ２ 3. The carbonation-accelerated cement composition of claim 1, wherein the fixing capacity is from 0.15 to 0.

60.

5. A carbonation-accelerated mortar concrete comprising the carbonation-accelerated cement composition according to claim 1 or 2 and aggregate.

6. The total mass of the cement and the calcium carbonate-containing powder is 20 to 50 kg / m ３ The carbonation-accelerated mortar concrete according to claim 5,

7. A hardened body obtained by hardening the carbonation-accelerated mortar concrete according to claim 5.

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