Method for increasing co2 fixation amount

Abstract

To provide a method for increasing CO2 fixation amounts, capable of fixing CO2 efficiently without necessitating special equipment.SOLUTION: A fresh cement composition with an air quantity increased more than the regulated air quantity of normal concrete is manufactured, and, without injection of CO2 in the atmosphere to an in-service hardened cement composition, prepared by hardening the fresh cement composition, CO2 is fixed by exposure, thus CO2 fixation amounts is increased.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for increasing the amount of CO2 fixed by fixing CO2 in a cement composition. [Background technology]

[0002] There is a demand for reducing CO2, which is believed to be a cause of global warming. Conventionally, a technique for reducing CO2 has been known in which, for example, cement hydrate and water are placed in a container, and while stirring the mixture of cement hydrate and water, CO2 is blown into the container to fix the CO2 through carbonation (see, for example, Patent Document 1). In addition, a technique for fixing the CO2 through carbonation by curing the concrete in a CO2 gas atmosphere under conditions such as high temperature and high pressure during the hardening process of the concrete is also known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-156508 A Summary of the Invention [Problem to be solved by the invention]

[0004] When CO2 is immobilized by injecting it into a mixture of cement hydrate and water, facilities are required to capture the CO2 and store it after liquefying and solidifying it. In addition, energy is required to liquefy and solidify the CO2, and this process is inefficient because CO2 is emitted due to the energy consumption.

[0005] If CO2 is fixed in concrete by placing it in a high-temperature, high-pressure CO2 gas atmosphere while the concrete is hardening, in addition to equipment for capturing and storing the CO2, curing equipment for the high-temperature, high-pressure CO2 gas atmosphere is required. In some cases, energy is needed to create the high-temperature, high-pressure environment, and CO2 is emitted due to the energy consumption, making it inefficient.

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a method for increasing the amount of CO2 fixed, which can fix CO2 efficiently without requiring special equipment. [Means for solving the problem]

[0007] In order to achieve this object, the method of the present invention for increasing the amount of CO2 fixed is characterized in that a fresh cement composition having an air content increased beyond the specified air content of ordinary concrete is produced, and the amount of CO2 fixed is increased by fixing CO2 through exposure without injecting CO2 from the atmosphere into the hardened cement composition in service after the fresh cement composition has hardened. Other features of the present invention will become apparent from the following detailed description of the present invention and the accompanying drawings. Effect of the Invention

[0008] According to the present invention, it is possible to provide a method for increasing the amount of CO2 fixed, which can fix CO2 efficiently without requiring any special equipment. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a flow chart showing a method for increasing the amount of CO2 fixed according to the present embodiment. [Diagram 2] FIG. 1 is a diagram showing conditions and test results of an example. [Diagram 3] FIG. 1 is a diagram illustrating a method for measuring the amount of CO2 fixed in each test specimen. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] At least the following points will become apparent from the following specification and drawings.

[0011] Aspect 1: A method for increasing the amount of CO2 fixed, comprising producing a fresh cement composition with an air content greater than that specified for normal concrete, and fixing CO2 by exposure to the fresh cement composition without injecting atmospheric CO2 into the hardened cement composition in service.

[0012] According to the method for increasing the amount of CO2 fixed of the first embodiment, the amount of air mixed into the produced fresh cement composition is increased compared to the specified amount of air in normal concrete, so that the fresh cement composition has more fine voids in the hardened cement composition during use after hardening. Therefore, when exposed to the hardened cement composition during use, CO2 can easily penetrate deeper from the surface, and the hardened cement composition during use can fix a larger amount of the penetrated CO2 inside.

[0013] In other words, fresh cement compositions with an increased amount of air can fix more CO2 simply by being exposed to the air after hardening while in service. Therefore, there is no need for special equipment, such as equipment to collect, liquefy, solidify, etc., and store the CO2 to be injected into the mixture of cement hydrate and water, as in the past, or equipment to cure under a high-temperature, high-pressure CO2 gas atmosphere. In addition, no energy is required to liquefy and solidify CO2, so there is no additional energy consumption to fix CO2, and CO2 can be fixed efficiently.

[0014] Aspect 2: The method for increasing the amount of CO2 fixation according to Aspect 1, wherein the air content of the fresh cement composition is greater than 6% and less than or equal to 80%.

[0015] According to the method for increasing the amount of CO2 fixation of aspect 2, the air content of the fresh cement composition to be produced is set to be greater than the maximum air content specified for ordinary concrete, which is 6%, but not greater than 80%, thereby ensuring that the amount of air mixed in is greater than that of ordinary concrete and enabling the concrete to be formed into a stable shape.

[0016] Aspect 3: The method for increasing the amount of CO2 fixed according to Aspect 1 or Aspect 2, characterized in that the water-cement ratio of the fresh cement composition is 20% or more and 70% or less.

[0017] According to the method for increasing the amount of CO2 fixation of the third embodiment, the fresh cement composition can be easily mixed, and the properties of the fresh cement composition can be ensured.

[0018] Aspect 4: The method for increasing a CO2 fixation amount according to any one of Aspects 1 to 3, wherein the hardened cement composition is a non-structural object.

[0019] According to the method for increasing the amount of CO2 fixed of the fourth aspect, it is possible to provide a non-structural object capable of efficiently fixing a larger amount of CO2.

[0020] ===About this embodiment=== <<About concrete and carbon dioxide>> Concrete is mainly composed of cement, water, aggregates (fine aggregate, coarse aggregate), admixtures, etc., and is produced by the hydration reaction between water and cement. During the production of concrete components, particularly cement, large amounts of carbon dioxide (CO2), a greenhouse gas, are emitted. As an increase in carbon dioxide concentration causes global warming, there is a demand to reduce carbon dioxide emissions.

[0021] In this embodiment, a fresh cement composition having an increased amount of air mixed in compared to normal concrete is used. More specifically, a foaming agent for air mortar is used as a foaming agent in the solution to be mixed with cement so that the amount of air mixed in is greater than the air content of normal concrete (ready mixed concrete) 4.5±1.5% as specified by the Japanese Industrial Standards (JIS). Examples of foaming agents for air mortar include, but are not limited to, Sanko Neosol (trade name, manufactured by Sanko Colloid Chemical Co., Ltd.).

[0022] <<Method for increasing CO2 fixation amount according to this embodiment>> FIG. 1 is a flow chart showing the method for increasing the amount of CO2 fixed according to this embodiment. As shown in FIG. 1, the method for increasing the amount of CO2 fixation according to the present embodiment first produces a fresh cement composition having a larger amount of air mixed therein than in normal concrete (Step 1: S1).

[0023] The production of a fresh cement composition with an increased amount of air mixed in is carried out by first mixing water and a foaming agent for air mortar to produce a solution, then mixing and stirring the produced solution with cement and aggregates, etc., and carrying out a hydration reaction to produce a fresh cement composition. At this time, by using a foaming agent for air mortar as a foaming agent, it is possible to mix air in an amount greater than the specified air amount (3% to 6%) of normal concrete, and by setting the amount of air mixed in to 80% or less, it is possible to produce a concrete structure with a stable shape. In addition, by setting the water-cement ratio of the fresh cement composition to 20% or more and 70% or less, it is possible to easily mix and ensure the properties of concrete. It is more preferable that the water-cement ratio of the fresh cement composition is 35% or more and 65% or less.

[0024] Next, the produced fresh cement composition is poured into a desired formwork, cured, and after a predetermined period of time, demolded to produce a concrete member (hardened cement composition) (Step 2: S2). At this time, the produced concrete structure contains a larger amount of air than normal concrete, so it may be used as a non-structural member such as a finishing material, interior material, or paving material.

[0025] It is then used as a concrete component and the CO2 is fixed inside through exposure (Step 3: S3). There are many fine voids in concrete in service as a concrete member. Therefore, when exposed to sunlight, CO2 can easily penetrate deeper into the concrete from the surface. This allows the CO2 to react with calcium hydroxide in the concrete to produce calcium carbonate, which can fix more CO2 inside the concrete. In other words, by simply putting the fresh cement composition with an increased air content into service in an exposed state after it has hardened, it is possible to fix more CO2 than when it is made from normal concrete.

[0026] For this reason, the manufactured concrete members can capture more CO2 from the atmosphere in the environment in which they are placed while in service, and there is no need for special equipment, such as equipment to capture, liquefy, solidify, and store the CO2 to be injected into the mixture of cement hydrate and water, as was previously required, or equipment to cure under a high-temperature, high-pressure CO2 gas atmosphere.In addition, there is no need for energy to liquefy CO2 or to create a high-temperature, high-pressure environment, so there is no additional energy consumption to fix CO2, and it is possible to fix CO2 efficiently.

[0027] <<Example>> FIG. 2 is a diagram showing the conditions and test results in the examples. In this example, the amount of fixed CO2 was measured using the air content and water-cement ratio of fresh cement paste (mixed with water and cement) as parameters (see Figure 2).

[0028] The amount of fixed CO2 was measured by TG-DTA thermal analysis. In TG-DTA thermal analysis, the amount of carbon dioxide released, i.e. the amount of carbon dioxide contained in the test specimen, is measured by the mass reduction caused by the decarbonation reaction of calcium carbonate contained in the test specimen as the temperature is raised to 1000°C. The specific implementation procedure will now be described.

[0029] <Manufacture of Fresh Cement Composition (Cement Paste) with Increased Air Content> First, cement is put into a solution obtained by mixing water and a foaming agent for air mortar, and kneaded for about 1 minute and 30 seconds to produce a cement paste. The cement paste is produced at various water-cement ratios and fresh air contents as shown in Figure 2.

[0030] Next, each produced cement paste is driven into a mold for specimens, demolded after one day has passed, and various specimens are manufactured. As shown in Figure 3, each specimen 1 has a cylindrical shape with a diameter of 50 mm and a height of 100 mm.

[0031] <Curing Method> Each manufactured specimen 1 is cured for 7 days in an atmosphere with a temperature of 20°C, a humidity of 60%, and a CO2 concentration of 5%. The 7-day curing in the above atmosphere is considered to be equivalent to a period 167 times that of outdoor exposure in the atmosphere in the accelerated carbonation test in the "Guidelines (Draft) for the Design and Construction of High-Durability Reinforced Concrete Structures and Explanation Thereof" (edited by the Japan Architectural Society, a general incorporated association), so it is equivalent to being exposed and cured in the atmosphere for about 3 years.

[0032] Also, each cylindrical specimen is covered with an aluminum seal after demolding so that only the bottom surface (lower surface) 1a is exposed and the driving surface (upper surface) and side surfaces are not exposed. During curing, the bottom surface (lower surface) is oriented upward.

[0033] <Measurement of CO2 Fixation Amount> ==Analysis Sample== Figure 3 is a diagram for explaining the method of measuring the CO2 fixation amount of each specimen. After curing, each specimen 1 first has its cement hydration reaction stopped immediately after curing, as shown in Figure 3. Specifically, the process of immersing each specimen 1 in acetone for 30 minutes and then drying it is repeated twice.

[0034] Each test specimen 1 after the hydration reaction has been stopped is cut into sliced ​​layers at intervals of 5 mm in the height direction from the above-mentioned surface 1a to produce analytical samples 2. As a result, analytical samples 2 are formed in layers of different depths at 5 mm intervals from the surface 1a in each test specimen 1.

[0035] ==Calculation of CO2 fixation mass%== Each analytical sample 2 is crushed in a mortar, and a TG-DTA thermal analysis is performed for each analytical sample. This allows the amount of CO2 fixed in each analytical sample 2 to be measured, and the mass % of CO2 (fixed mass %) is calculated from the measurement results. This allows the mass % of CO2 fixed in layers at different depths from the surface 1a of each specimen 2 to be calculated.

[0036] As a result of the calculation, it was confirmed that the mass % of CO2 fixed was greater on the surface 1a side and decreased the deeper from the surface 1a, and that the test specimen 1 containing a greater amount of air fixed more CO2.

[0037] ==Calculation of the amount of CO2 fixed in concrete== For each test piece 1, the product of the depth from the surface 1a is used to determine the thickness of the concrete. 2 The amount of CO2 fixed in cement paste per unit is calculated.

[0038] As mentioned above, the amount of CO2 fixed in the concrete is greater in test specimen 1, which contains a greater amount of air. In test specimen 1 that has fixed more CO2, the CO2 is fixed deeper from the surface 1a.

[0039] Therefore, 1m of general concrete mix 2 In the concrete of each test piece 1, the CO2 fixed by mass% of the analysis sample 2 constituting the corresponding layer of the test piece 1 is fixed in the layer at the same depth as each layer of the test piece 1. 2 The amount of CO2 fixed in each layer of concrete is calculated.

[0040] For example, 1 m of a typical concrete mix 2 The amount of CO2 fixed in a layer 5 mm from a surface of the concrete (hereinafter referred to as the calculation target layer) is calculated by multiplying the mass% of CO2 fixed in the analysis sample 2 that forms a layer 5 mm from the surface 1a of the test piece 1 by the mass of the calculation target layer. 2 The amount of CO2 fixed in each layer of concrete was calculated using the mass% of CO2 fixed in analytical sample 2 at the same depth in test piece 1, and the sum of these was calculated to obtain the total amount of CO2 fixed in 1 m of a general concrete mix. 2 Calculate the amount of CO2 fixed in the entire concrete.

[0041] At this time, the general concrete mix is -Unit water volume 175kg / m 3 - Unit cement amount (ordinary Portland cement) 389kg / m 3 and cement paste 564 kg / m 3 The calculated CO2 fixation mass percentage is multiplied by the product of the calculated CO2 fixation mass percentage. Specifically, the calculation is performed using (Equation 1). 1m 2 CO2 fixation per unit (kg / m 2 ) =Σ(564kg / m 3 × thickness 5 mm × CO2 fixed mass%) (Equation 1) The amount of CO2 fixed in concrete calculated using Equation 1 is shown in Figure 2.

[0042] The above-mentioned embodiment is intended to facilitate understanding of the present invention, and is not intended to limit the present invention. The present invention can be modified or improved without departing from the spirit of the present invention, and it goes without saying that the present invention includes equivalents thereof. [Explanation of symbols]

[0043] 1. Test specimen 1a surface 2. Analytical Samples

Claims

【Request 1】 A fresh cement composition having an increased air content compared to the standard air content of normal concrete is produced, and the fresh cement composition is hardened and the hardened cement composition is subjected to CO2 absorption in the atmosphere. ２ Without injection of CO ２ By immobilizing CO ２ CO ２ Methods for increasing fixation amount. 【Request 2】 The CO according to claim 1 ２ A method for increasing the amount of fixation, comprising the steps of: The fresh cement composition has an air content of more than 6% and not more than 80%. ２ Methods for increasing fixation amount. 【Request 3】 The CO according to claim 1 or 2 ２ A method for increasing the amount of fixation, comprising the steps of: The water-cement ratio of the fresh cement composition is 20% or more and 70% or less. ２ Methods for increasing fixation amount. 【Request 4】 The CO according to claim 1 or 2 ２ A method for increasing the amount of fixation, comprising the steps of: The hardened cement composition is a non-structural material. ２ Methods for increasing fixation amount.

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