Method for curing rock wool composition

Abstract

The objective is to provide a technology for fixing carbon dioxide from the atmosphere in a short period of time. More specifically, the present invention provides a technology that can fix more carbon dioxide in a shorter period of time than rock wool compositions produced using conventional sprayed rock wool, etc. [Means] The above problem can be solved by adding carbon dioxide to a rock wool composition formed under specific conditions, mainly consisting of rock wool, cement, and water, after taking measures to suppress the drying of the rock wool composition. Preferably, the measure to suppress the drying of the rock wool composition is to humidify the rock wool composition. Furthermore, it is preferable that the addition of carbon dioxide to the rock wool composition is done in a way that allows the carbon dioxide to penetrate the rock wool composition.

Description

[Technical Field]

[0001] The present invention relates to a method for curing rock wool compositions. In particular, it relates to a method for curing rock wool compositions that promotes carbonation of rock wool compositions formed mainly of cement and water, that is, a method for curing rock wool compositions that promotes carbonation (CO2 fixation) of rock wool compositions containing cement and rock wool. [Background technology]

[0002] In Japan, the goal is to achieve carbon neutrality by 2050, and technologies to contribute to carbon neutrality are being considered in various industries. Cement, a major material in the construction industry, is known to emit a large amount of carbon dioxide (CO2) during its manufacture. Concrete, which uses cement as its main raw material, reacts with CO2 in the air and fixes it within the concrete. However, concrete used in general reinforced concrete structures is dense, making it difficult for CO2 from the atmosphere to penetrate. It takes several decades for it to penetrate to about 20 mm from the surface, and the amount of CO2 fixed in the concrete during the service life of the structure is not very large. Therefore, technologies have been proposed to create carbon dioxide-fixing concrete structures equipped with a carbon dioxide-fixing molded body that fixes CO2 from the air in the surface layer (for example, Patent Document 1). In addition, methods have been proposed such as covering cement-hardened bodies such as precast concrete members with an airtight curing sheet and blowing a gas containing carbon dioxide into the curing sheet (for example, Patent Document 2).

[0003] Incidentally, sprayed rock wool, used as a fire-resistant coating, heat insulation, and sound-absorbing material, is formed by mixing cement, rock wool, and water to create a rock wool composition. The inventors of this invention evaluated the CO2 fixation performance of a rock wool composition consisting of a mixture of cement slurry (a mixture of cement and water) and rock wool, and confirmed that it could fix a large amount of CO2 in a very short period of time compared to ordinary concrete that has undergone general construction and curing, and that it has excellent CO2 fixation performance (for example, Non-Patent Document 1). However, the inventors of this invention believed that there was a need for a technology that could fix more carbon dioxide in a shorter period of time than a rock wool composition produced by conventional sprayed rock wool. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2008-075391 [Patent Document 2] Japanese Patent Publication No. 2023-168775 [Non-patent literature]

[0005] [Non-Patent Document 1] Ikumi Otomochi, et al., "A Study on the CO2 Sequestration Performance of Sprayed Rock Wool," November 2023, Monthly Concrete Techno, Cement Newspaper, November 2023 issue, Vol. 42, No. 11, pp. 56-61. [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a technology for fixing carbon dioxide from the atmosphere in a short period of time. More specifically, the present invention aims to provide a technology that can fix more carbon dioxide in a shorter period of time than rock wool compositions produced using conventional sprayed rock wool, etc. [Means for solving the problem]

[0007] As a result of intensive studies by the present inventors to solve the above problems, the present invention has been completed. That is, the present invention is a curing method for a rock wool composition represented by the following (1) to (3). (1) A curing method for a rock wool composition, characterized in that the rock wool composition formed with rock wool, cement and water as main components is subjected to measures to suppress drying of the rock wool composition without directly adding liquid water to the rock wool composition, and then carbon dioxide gas is added to the rock wool composition. (2) The curing method for a rock wool composition according to the above (1), wherein the measure for suppressing drying of the rock wool composition is humidifying the rock wool composition. (3) The curing method for a rock wool composition according to the above (1) or (2), wherein the addition of carbon dioxide gas to the rock wool composition is bringing the rock wool composition into a state that allows carbon dioxide gas to enter the rock wool composition.

Effects of the Invention

[0008] According to the present invention, carbon dioxide in the atmosphere can be immobilized in a short period of time. According to the present invention, there is obtained a curing method for a rock wool composition that can immobilize more carbon dioxide in a shorter period of time than a rock wool composition produced with ordinary sprayed rock wool. Further, according to the present invention, there is obtained a rock wool composition in which more carbon dioxide is immobilized in a shorter period of time than a rock wool composition produced with ordinary sprayed rock wool.

Brief Description of the Drawings

[0009] [Figure 1] Figure 1 shows the change over time in the degree of carbonation when the rock wool composition is cured in a constant humidity tank under specific conditions up to a material age of 12 weeks.

Modes for Carrying Out the Invention

[0010] The present invention provides a method for curing a rock wool composition, characterized in that, without directly adding liquid water to the rock wool composition, a rock wool composition formed mainly from rock wool, cement, and water is prepared by taking measures to suppress the drying of the rock wool composition, and then adding carbon dioxide to the rock wool composition.

[0011] The rock wool composition in this invention is formed mainly from rock wool, cement, and water. Here, rock wool refers to a material obtained by melting raw materials mainly composed of natural rocks such as basalt or metal oxides such as blast furnace slag and then fiberizing them. In this invention, rock wool also includes slag wool. As cement, any hydraulic cement is acceptable, such as ordinary, rapid-hardening, ultra-rapid-hardening, low-heat, and moderate-heat Portland cements, white cement, eco-cement, and various mixed cements obtained by mixing these Portland cements, white cements, or eco-cement with fly ash, blast furnace slag, silica fume, or limestone powder. Two or more of these may be used in combination. In addition to rock wool, cement, and water, one or more cement admixtures may be used in the rock wool composition in this invention, as long as they do not substantially impair the effects of this invention. Examples of admixtures include cement dispersants, expansives, waterproofing agents, cement polymers, rust inhibitors, shrinkage reducers, pigments, fibers, water repellents, efflorescence inhibitors, rapid setting agents, rapid hardening agents, setting retarders, thickeners, foaming agents, defoaming agents, gypsum, blast furnace slag powder, pozzolanic substances, and surface hardening agents.

[0012] In the present invention, a "strategy to suppress drying of the rock wool composition without directly adding liquid water to the rock wool composition" is a preferred strategy that involves humidifying the rock wool composition and suppressing the evaporation of moisture within the rock wool composition without directly adding liquid water to the rock wool composition. When liquid water (e.g., water, aqueous solution, O / W type emulsion) is directly added to a rock wool composition, if the hydration of the cement contained in the rock wool composition has not progressed, the strength of the rock wool composition tends to decrease, the strength development (degree of strength increase over time) tends to worsen, and / or the self-weight of the rock wool composition increases due to the addition of excessive water, which may cause the rock wool composition to fall or peel off if it is placed on the surface of a wall, column, or ceiling.

[0013] Suitable methods for humidifying a rock wool composition without directly adding liquid water include humidifying the area around the rock wool composition with a humidifier, placing a water-absorbing material (hereinafter sometimes referred to as a "water vapor supply material") such as a sponge, superabsorbent polymer, or cloth around the rock wool composition after it has absorbed water, and placing a container filled with water that can supply water vapor around the rock wool composition. Here, the water vapor supply material may be placed in direct contact with the rock wool composition or at a distance from it.

[0014] The rock wool composition in this invention has an absolute dry bulk density of 0.08 to 1.5 g / cm³. 3 This type is preferred because it fixes carbon dioxide in a shorter time and maintains its shape, and more preferably has an oven-dry bulk density of 0.12 to 1.0 g / cm³. 3 The oven-dry bulk density of the rock wool composition is set to 0.08 to 1.5 g / cm³. 3To achieve this, the ratio of the mass of cement to the mass of rock wool (C / RW) is set to 0.10 to 2.0. In addition, the absolute dry bulk density of the rock wool composition is set to 0.12 to 1.0 g / cm 3 To achieve this, C / RW is set to 0.20 to 1.7. Here, the absolute dry bulk density refers to the bulk density when the rock wool composition is dried in a drying oven at 105°C until it reaches a constant mass (W DRY ) and volume (V DRY ), which is determined by the following formula (1) (ρ DRY ). If the difference between the volume (V DRY ) of the rock wool composition when dried in a drying oven at 105°C until it reaches a constant mass and the volume (V WET ) before drying is negligible, the bulk density (ρ DRY ) may be determined by the following formula (2). ρ DRY =W DRY ÷V DRY ······ (1) ρ DRY =W DRY ÷V WET ······ (2)

[0015] Preferred methods for adding carbon dioxide to a rock wool composition in the present invention include diffusing carbon dioxide contained in the surrounding air into the rock wool composition, supplying carbon dioxide to the surrounding air to increase the atmospheric carbon dioxide concentration and then diffusing the carbon dioxide contained in the surrounding air into the rock wool composition, arranging a carbon dioxide pathway with pores that can release carbon dioxide or liquid carbon dioxide in and / or on the surface (or interface) of the rock wool composition and supplying carbon dioxide or liquid carbon dioxide to the rock wool composition through these pores, and arranging a water vapor supply material that has absorbed carbonated water around the rock wool composition. It is preferable that the addition of carbon dioxide to the rock wool composition is carried out in a way that allows the carbon dioxide to enter the rock wool composition, and in particular, the method of diffusing carbon dioxide contained in the surrounding air into the rock wool composition is more preferable because it does not require a separate supply of carbon dioxide. In order to diffuse carbon dioxide contained in the surrounding air into the rock wool composition, the oven-dry bulk density of the rock wool composition should be 1.5 g / cm³. 3 Preferably, it is 1.2 g / cm³. 3 The following is more preferable: 1.0 g / cm³ 3 The following is particularly preferable because it facilitates the diffusion of carbon dioxide into the rock wool composition and accelerates the carbonation of the rock wool composition. [Examples]

[0016] [Example 1] Samples of rock wool composition were prepared under the conditions shown in Table 1. The samples were in the shape of 30 × 30 × 30 mm cubes. To minimize variations in mixing ratio and bulk density between samples, a predetermined amount of each material was weighed for each sample, placed in a poly bag, and then mixed within the poly bag to prepare the rock wool composition. The entire amount of the prepared rock wool composition was poured into a mold to produce 30 × 30 × 30 mm cube-shaped samples of rock wool composition. The cement and rock wool used were ordinary Portland cement manufactured by Taiheiyo Cement Corporation and granular rock wool cotton manufactured by Taiheiyo Material Corporation, respectively.

[0017] [Table 1]

[0018] Samples of the prepared rock wool composition were cured for 12 weeks in a constant temperature and humidity chamber at 20°C and the relative humidity shown in Table 2, with only the top surface open. The amount of carbon dioxide fixed and the degree of carbonation were determined, and the results are shown in Table 2 and Figure 1. The amount of carbon dioxide fixed and the degree of carbonation were determined by the following method.

[0019] <Carbon dioxide fixation amount> Thermogravimetric differential thermal analysis (TG-DTA) was used to measure the mass loss between 600°C and 850°C by heating the pulverized sample to 1000°C at a rate of 20°C / min under an N2 gas flow environment. The amount of fixed CO2 (q) was determined using the analysis results and the following equations (3) and (4). CO2 ) was calculated. Here, to exclude other mass losses such as dehydration of free water and crystal water, the calculation was based on the mass at a heating temperature of 1000°C. Furthermore, it was confirmed beforehand that rock wool alone does not change mass when heated up to 1000°C. X CO2 =(W 600 -W 850 )÷W 1000 ... (3) q CO2 =X CO2 ×1000 ··· (4) Here, X CO2 and W T (W 600 , W 850 , W 1000 ) are as follows: X CO2 Fixed CO2 rate W T : Mass (mg) at temperature T (°C) obtained by thermogravimetric analysis (TG) q CO2 CO2 fixation amount per ton of rock wool composition

[0020] <Carbonation level> The degree of carbonation is an indicator of the proportion of CaO in cement that has been converted to CaCO3, and can be calculated using equation (5) assuming that 60% of the cement mass is CaO. Y=(X CO2 / (r C ×0.6 × 44 / 56)) × 100 ··· (5) Here, Y and r c , 0.6, 44, and 56 are as follows: Y: Carbonation level (%) r C Cement content (%) in the analyzed sample 44: Molecular weight of CO2 56: Molecular weight of CaO 0.6: Mass percentage of CaO in cement

[0021] [Table 2]

[0022] From the results in Table 2 and Figure 1, it can be seen that the rock wool composition cured at a higher relative humidity (cured with humidification) carbonated (fixed carbon dioxide) faster and at a higher rate than the rock wool composition cured at 20°C and 45% RH. [Industrial applicability]

[0023] The present invention can be suitably applied to structures and buildings, for example, in which a rock wool composition is coated on the surface of a structural member made of concrete, steel, or wood, for the purpose of providing heat insulation, fire resistance, or sound insulation. It can also be suitably applied to structures and buildings in which a rock wool composition is filled inside the member.

Claims

1. A method for curing a rock wool composition, characterized by adding carbon dioxide to a rock wool composition formed mainly of rock wool, cement, and water, after taking measures to suppress the drying of the rock wool composition, without directly adding liquid water to the rock wool composition.

2. The method for curing a rock wool composition according to claim 1, characterized in that the measure to suppress the drying of the rock wool composition is to humidify the rock wool composition.

3. The method for curing a rock wool composition according to claim 1 or 2, characterized in that the addition of carbon dioxide to the rock wool composition makes it possible for the carbon dioxide to penetrate the rock wool composition.

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