Production method of cement composition

Abstract

To attempt reduction of a material cost and a CO2 discharge amount.SOLUTION: A CO2 mixed cement composition production method has a washing water acquisition step to acquire washing water for a residual cement composition left in a cement composition supply system, a recycled water acquisition step to acquire recycled water with aggregates of a particle diameter of 75 μm or more removed from the washing water, and a CO2 mixed cement composition production step to produce a CO2 mixed cement composition using solution that mixes CO2 into the recycled water as kneading water.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing a cement composition. [Background technology]

[0002] As a method for reducing carbon dioxide (CO2) emissions during the production of concrete (an example of a cement composition), a technique has been proposed in which carbon dioxide is immobilized by absorbing or mixing it into concrete. For example, in Patent Document 1, calcium hydroxide is added in advance to water (mixing water), which is a concrete material, and then carbon dioxide (gaseous carbon dioxide) is injected to incorporate the carbon dioxide. By using carbon dioxide separated and recovered from the exhaust gas during concrete production, it is possible to reduce CO2 emissions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent application 2022-201204 Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of Patent Document 1, calcium hydroxide is added to the mixing water, which may increase the material cost for the calcium hydroxide and the CO2 emissions associated with production.

[0005] During the production of ready-mixed concrete, a large amount of sludge water (recovered water) consisting mainly of cement is generated during the cleaning process of factory equipment and truck agitator vehicles, and its treatment has become an issue.

[0006] The present invention has been made in view of the above problems, and its object is to effectively utilize sludge water to reduce material costs and CO2 emissions. [Means for solving the problem]

[0007] The main invention for achieving the above object is a method for producing a CO2-mixed cement composition, comprising: a washing water obtaining step of obtaining washing water for washing a residual cement composition left in a cement composition supply facility; a recovered water obtaining step of obtaining recovered water by removing aggregate having a particle size of 75 μm or more from the washing water; and a CO2-mixed cement composition producing step of producing a CO2-mixed cement composition by using a solution obtained by mixing the recovered water with CO2 as mixing water.

[0008] Other features of the present invention will become apparent from the description of this specification and the accompanying drawings. [Effects of the Invention]

[0009] According to the present invention, it is possible to reduce material costs and CO2 emissions. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a flow chart showing a concrete manufacturing method according to a reference example, broken down by material. [Figure 2] FIG. 1 is a flow diagram showing a method for producing concrete according to an embodiment of the present invention. [Figure 3] FIG. 1 is a flow chart showing a concrete manufacturing method according to an embodiment of the present invention, broken down by material. [Figure 4] FIG. 2 is a diagram showing the blending conditions of the specimen in this example. [Figure 5] FIG. 10 is a diagram showing test results of fresh properties. [Figure 6] FIG. 10 is a diagram showing the relationship between W / P and 0-stroke flow. [Figure 7] FIG. 10 is a diagram showing the test results of compressive strength. [Figure 8] This is a graph showing the compressive strength of materials at 3 and 7 days of age, for each level (type of mixing water). [Figure 9] Graph showing the relationship between W / P and compressive strength (N / mm2) [Figure 10]Figure 1 shows the test results for CO2 fixation amount DETAILED DESCRIPTION OF THE INVENTION

[0011] At least the following matters will become clear from the description of this specification and the accompanying drawings.

[0012] (Aspect 1) A method for producing a CO2-mixed cement composition, comprising: a washing water obtaining step of obtaining washing water for washing a residual cement composition left in a cement composition supply facility; a recovered water obtaining step of obtaining recovered water by removing aggregates with a particle size of 75 μm or more from the washing water; and a CO2-mixed cement composition producing step of producing a CO2-mixed cement composition by using a solution obtained by mixing the recovered water with CO2 as mixing water.

[0013] According to the method for producing a CO2-mixed cement composition of the first aspect, the CO2-mixed cement composition can be produced using recovered water (sludge water), which reduces the amount of calcium hydroxide used, thereby reducing material costs and CO2 emissions.

[0014] (Aspect 2) In the method for producing a CO2-mixed cement composition according to the first aspect, the amount of CO2 mixed with the recovered water is preferably 88.0 g / L of water or less.

[0015] According to the method for producing a CO2-mixed cement composition of the second embodiment, CO2 can be reacted with a calcium source in the recovered water.

[0016] (Aspect 3) The method for producing a CO2-mixed cement composition according to the first or second aspect may further include a slaked lime mixing step of mixing slaked lime with the recovered water.

[0017] According to the method for producing a CO2-mixed cement composition of the third aspect, the calcium concentration of the recovered water can be adjusted.

[0018] (Aspect 4) In the method for producing a CO2-mixed cement composition according to the third aspect, the amount of slaked lime mixed with the recovered water is preferably 38.0 g / L of water or less.

[0019] According to the method for producing a CO2-mixed cement composition of the fourth aspect, it is possible to reduce the material cost of slaked lime and the amount of CO2 emissions.

[0020] (Aspect 5) In the method for producing a CO2-mixed cement composition according to any one of the first to fourth aspects, it is preferable that the calcium concentration contained in the recovered water is 2.0 mol / L or less.

[0021] According to the method for producing a CO2-mixed cement composition of the fifth aspect, mixing is possible, and the compressive strength and the amount of CO2 fixed can be increased.

[0022] (Aspect 6) In the method for producing a CO2-mixed cement composition according to any one of Aspects 1 to 5, it is preferable that the CO2 is mixed in a theoretical amount that allows the calcium source contained in the recovered water to completely react.

[0023] According to the method for producing a CO2-mixed cement composition of the sixth aspect, CO2 can be efficiently fixed.

[0024] === Implementation form === <<Cement Composition and Carbon Dioxide>> The production of cement compositions such as concrete and mortar emits large amounts of carbon dioxide (CO2), a greenhouse gas. Since an increase in carbon dioxide concentration contributes to global warming, there is a need to reduce carbon dioxide emissions.

[0025] Below, we will explain a technology that mixes and immobilizes CO2 in concrete as a method for reducing carbon dioxide emissions.

[0026] Before describing this embodiment, a concrete manufacturing method of a reference example will be described first.

[0027] <<Reference example concrete manufacturing method>> FIG. 1 is a flow diagram showing a concrete manufacturing method of the reference example, broken down by material.

[0028] As shown in Figure 1, a calcium hydroxide solution is produced by mixing water and a calcium source (here, calcium hydroxide). By mixing an amount of calcium hydroxide that exceeds the saturation concentration in water, the amount of carbon dioxide fixed can be maximized. Calcium hydroxide (Ca(OH)2) is also called slaked lime.

[0029] Next, carbon dioxide (CO2) is injected into the calcium hydroxide solution. The reaction between calcium hydroxide and CO2 produces a carbonate (here, calcium carbonate), and as a result, a solution containing calcium carbonate (CaCO3) and water (hereinafter also referred to as calcium carbonate solution) is produced. In the reference example, this calcium carbonate solution is used as mixing water.

[0030] Next, cement, calcium carbonate solution (mixing water), aggregate, chemical admixtures (additives), etc. are mixed and stirred to cause a hydration reaction, producing concrete (ready-mixed concrete) as a cement composition. Ready-mixed concrete is concrete at the stage where cement, aggregate, etc. are mixed (but not yet hardened), and is also called ready-mix concrete or ready-mixed concrete.

[0031] In this way, by using calcium carbonate solution (calcium hydroxide solution injected with CO2) as mixing water, the amount of CO2 fixed can be increased. Also, by using CO2 separated and recovered from exhaust gas during concrete production, CO2 emissions can be reduced.

[0032] However, in the method of this reference example, calcium hydroxide (slaked lime) is added to the water used as the mixing water, which increases the material cost of the calcium hydroxide used.

[0033] Furthermore, since CO2 is released during the production of calcium hydroxide, there is a risk that the amount of CO2 emitted during the production of calcium hydroxide will increase.

[0034] Calcium hydroxide (slaked lime) is produced, for example, as follows.

[0035] First, by heating limestone, CO2 is released from its main component, calcium carbonate (CaCO3), which turns into quicklime (CaO: calcium oxide). Furthermore, by adding water (H2O) to quicklime (CaO), slaked lime (Ca(OH)2) is produced. In this way, CO2 is emitted when calcium hydroxide is produced.

[0036] During the production of ready-mixed concrete, a large amount of sludge water, mainly composed of cement, is generated during the cleaning process of factory equipment and truck agitators, and its disposal has become an issue.

[0037] Sludge water is wastewater (hereinafter referred to as wash water) generated in ready-mixed concrete plants and when washing agitator trucks, from which aggregates (specifically, aggregates with a particle size of 75 μm or more) have been removed. In this embodiment, sludge water corresponds to recovered water.

[0038] Sludge water contains fine aggregate particles (aggregate fine particles). As specified in JIS A1103:2003, "fine particles" refers to particles (particles with a particle size of less than 75 μm) that pass through a metal mesh sieve with a nominal mesh size of 75 μm (0.075 mm). Furthermore, the supernatant water is the sludge water from which the sludge solids (hydration products and aggregate fine particles) have been removed.

[0039] In this embodiment, calcium hydroxide (slaked lime) is replaced with sludge water to reduce material costs and CO2 emissions.

[0040] <<Present Embodiment>> Fig. 2 is a flow diagram showing the concrete manufacturing method of this embodiment. Fig. 3 is a flow diagram showing the concrete manufacturing method of this embodiment divided by material. The concrete manufactured in this embodiment corresponds to a CO2-mixed cement composition.

[0041] First, washing water for residual concrete (corresponding to residual cement composition) left in a cement composition supply facility (for example, a ready-mixed concrete manufacturing plant or a truck agitator vehicle) is obtained (S1).

[0042] Next, aggregates with a particle size of 75 μm or more are removed from the obtained wash water to obtain sludge water (recovered water) (S2). The method for removing aggregates with a particle size of 75 μm or more is not particularly limited, and examples thereof include classification treatment (filtration treatment) and precipitation treatment.

[0043] Next, carbon dioxide (CO2) is injected (mixed) into the sludge water to produce a calcium carbonate solution (corresponding to a solution) containing calcium carbonate (CaCO3) (S3). There are no restrictions on the method of CO2 injection; for example, CO2 may be supplied to the liquid surface while the sludge water is being stirred, or a nozzle with multiple fine openings, such as a diffuser, may be placed in the sludge water and CO2 may be bubbled through these openings. Alternatively, dry ice may be added to the sludge water, or CO2 may be injected using a commercially available carbonated water maker. There are also no restrictions on the CO2 supply source; for example, CO2 injected into a cylinder (pure CO2 gas) may be used, or CO2 obtained by separating and recovering it from exhaust gases from factories, etc.

[0044] The reaction between calcium hydroxide (Ca(OH)2) contained in sludge water (specifically cement) and carbon dioxide is shown in equation (1). Ca(OH)2+CO2→CaCO3+H2O ·····(1)

[0045] In this case, 1 mol (=44 g) of CO2 is required for the above reaction per 1 mol of calcium hydroxide (Ca(OH)2). In other words, the amount of CO2 (theoretical amount) that can be absorbed (fixed) by 1 mol / L of Ca(OH)2 is 44 g / L of water.

[0046] The calcium concentration contained in the sludge water is preferably 2.0 mol / L or less (exceeding the saturated concentration) (see Examples below).

[0047] It is also desirable to mix CO2 in the theoretical amount that will completely react with the calcium source in the sludge water (recovered water). This allows for efficient mixing of CO2. For example, if the calcium concentration is 2.0 mol / L, the theoretical amount of CO2 is 88 g / L of water.

[0048] If necessary, slaked lime (Ca(OH)2) may be further added (see Figure 3). The process of adding slaked lime to the sludge water corresponds to the slaked lime mixing process. This allows the calcium concentration to be adjusted.

[0049] The calcium carbonate solution produced in step S3 is then used as mixing water and mixed with cement, aggregate, chemical admixtures, etc. to produce concrete (S4).

[0050] There are no restrictions on the type (composition) of cement, and it is possible to use, for example, Portland cement (such as ordinary Portland cement) as specified in JIS R 5210 or blast furnace slag cement as specified in JIS R 5211. Research cement is used in the examples described below.

[0051] Examples of chemical admixtures include air-entraining agents (air bubble dispersants) that prevent freezing and increase air entrainment, superplasticizers that increase fluidity, thickeners that increase viscosity (also called separation-reducing agents or non-segregation admixtures), quick-setting agents that promote hardening, and water-reducing agents (also called air-entraining water reducers or high-performance air-entraining water reducers) that improve fluidity by dispersing cement.

[0052] Furthermore, although the present embodiment has been described with reference to the case of producing concrete, the present invention is not limited to concrete, and may be applied to any hydration product in which the hydrate produced by the reaction (hydration reaction) between cement and water hardens and loses fluidity. For example, the present invention may be applied to mortar, which is a cement hydrate containing gravel (fine aggregate), or cement paste, which does not contain aggregate. In other words, by using sludge water as mixing water when producing mortar, cement paste, etc., it is possible to reduce material costs and CO2 emissions.

[0053] <<Example>> In this example, simulated sludge water was used to prepare and evaluate cement paste specimens. Laboratory cement (CaO content in cement: 64.23%) was used as the cement. As comparative examples, samples using ion-exchanged water and the aforementioned reference examples were also evaluated.

[0054] <About the composition of the test specimen> FIG. 4 is a diagram showing the blending conditions of the specimens in this example.

[0055] Ion-exchanged water was used as the mixing water in Comparative Examples 1 to 3. Note that Comparative Example 3 uses the mixing water of the above-mentioned Reference Example (a mixture of water, slaked lime, and CO2).

[0056] In Comparative Example 4, simulated sludge water was used as the mixing water, but CO2 was not injected.

[0057] In Examples 1 to 4, simulated sludge water was used as the mixing water, and CO2 was further injected.

[0058] In Example 2, slaked lime was also added (mixed). However, the amount of slaked lime added was less than in Comparative Example 3. Specifically, 77.0 (g / L of water) of slaked lime was added in Comparative Example 3, while in Example 2, it was 38.0 (g / L of water).

[0059] In Examples 2 and 3 (and Comparative Example 3), laboratory cement or hydrated lime was added to the mixing water so that the calcium content in the water was 1.0 mol / L. Then, the theoretical amount of CO2 (44 g / L of water) required for complete reaction of 1.0 mol / L of calcium was injected and mixed.

[0060] In Example 1, the research cement was added so that the amount of calcium in the mixing water was 0.5 mol / L, and CO2 was injected at 21.4 (g / L of water).

[0061] In Example 4, the research cement was added so that the amount of calcium in the mixing water was 2.0 mol / L. Then, the theoretical amount of CO2 (88 g / L of water) required for the complete reaction of 2.0 mol / L of calcium was injected.

[0062] In Figure 4 (cement paste mass ratio, etc.), W, P, and C represent water, powder, and cement, respectively. The powder (P) includes solids (such as CaCO3) contained in the mixing water and cement (C).

[0063] Furthermore, each numerical value in the cement paste mass ratio indicates a value (mass) when the cement (C) in the cement paste is set to 100. For example, in the case of Comparative Example 3, P is 104.5 (= 100 + 4.5) and W is 45.5.

[0064] In addition, W / P in Figure 4 is the ratio of water (W) to powder (P). For example, in the case of Comparative Example 3, P is 104.5 and W is 45.5, so W / P is 45.5 / 104.5 x 100 = 43.6 (%). Similar calculations were made for the other test specimens.

[0065] Also, W in Figure 4 mix / C is W mix The ratio of W to cement (C) is mix = Water (W) + solids in the mixing water (CaCO3, etc.). For example, in Comparative Example 3, W mix =45.5+4.5=50. Therefore, W mix / C is 50 / 100×100=50(%). The same calculations were made for other test specimens.

[0066] <Test items> Using each specimen, the fresh properties, compressive strength, and CO2 fixation amount were evaluated as follows. Fresh properties: Measure the zero-stroke flow and mixing temperature when kneaded Compressive strength: Compressive strength tests were conducted after the end of the curing period of 3 days and 7 days. Amount of CO2 fixed: Calculated from the mass loss at 550-800°C by differential thermal analysis

[0067] <Test Results> ·Freshness Fresh properties (flow) are values that indicate the fluidity of the mixture after mixing. If the flow value is low, workability will be poor.

[0068] Figure 5 shows the test results for fresh properties. Figure 6 shows the relationship between W / P and zero-hit flow. The horizontal axis of Figure 6 is W / P, and the vertical axis is zero-hit flow (mm).

[0069] As shown in Figure 6, there was a tendency for the flow to increase as the W / P increased. It was confirmed that even in Example 4, which had the smallest W / P, it was possible to mix it into a cement paste.

[0070] Furthermore, Figure 6 shows that the type of mixing water has little effect on the flow (the results for each test specimen are close to the approximate straight line (dashed line) in the figure).

[0071] ·Compression strength Fig. 7 shows the test results of compressive strength. Fig. 8 shows the compressive strength of each specimen at ages of 3 days and 7 days. The horizontal axis of Fig. 8 is the age (days), and the vertical axis is the compressive strength (N / mm 2 ) and Fig. 9 shows the relationship between W / P and compressive strength (N / mm 2 9 is a graph showing the relationship between W / P and compressive strength (N / mm 2) In FIG. 9, black circles (●) indicate the compressive strength at 3 days old, and black squares (■) indicate the compressive strength at 7 days old.

[0072] Figures 7 to 9 show that the smaller the W / P ratio, the greater the compressive strength. Figure 9 also shows that the type of mixing water has little effect on compressive strength. This confirms that even when using simulated sludge water + CO2 as mixing water, it is possible to obtain compressive strength equivalent to that obtained when using ion-exchanged water.

[0073] About CO2 fixation Figure 10 shows the test results for the amount of CO2 fixed. The amount of CO2 fixed is data measured at a material age of 7 days, and has been corrected for loss on ignition.

[0074] In Examples 1 to 4, simulated sludge water was used as the mixing water and CO2 was further injected, resulting in an increased amount of CO2 fixed compared to Comparative Examples 1, 2, and 4. Furthermore, even when simulated sludge water was used, the same amount of CO2 was fixed as in Comparative Example 3 (the aforementioned Reference Example).

[0075] From the above results, it was confirmed that even when sludge water is used as mixing water, a cement composition (e.g., concrete) with performance equivalent to that of a normal cement composition can be produced, and that CO2 can be fixed to the same extent as in the reference example.

[0076] The above-described embodiments are provided to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and the present invention includes equivalents thereof.

Claims

1. a washing water obtaining step of obtaining washing water for washing the residual cement composition left in the cement composition supply equipment; a recovered water obtaining step of obtaining recovered water by removing aggregates having a particle size of 75 μm or more from the washing water; The recovered water is ２ The mixed solution was used as mixing water, and CO ２ CO for producing a blended cement composition ２ A mixed cement composition manufacturing process; CO ２ A method for producing a blended cement composition.

2. The CO according to claim 1 ２ 1. A method for producing a mixed cement composition, comprising: The CO mixed with the recovered water ２ is 88.0 g / L water or less, CO characterized by ２ A method for producing a blended cement composition.

3. The CO according to claim 1 ２ 1. A method for producing a mixed cement composition, comprising: A slaked lime mixing step of mixing slaked lime with the recovered water is included. CO characterized by ２ A method for producing a blended cement composition.

4. The CO according to claim 3 ２ 1. A method for producing a mixed cement composition, comprising: The amount of slaked lime mixed with the recovered water is 38.0 g / L of water or less. CO characterized by ２ A method for producing a blended cement composition.

5. The CO according to claim 1 or claim 3 ２ 1. A method for producing a mixed cement composition, comprising: The calcium concentration contained in the recovered water is 2.0 mol / L or less. CO characterized by ２ A method for producing a blended cement composition.

6. The CO according to claim 1 ２ 1. A method for producing a mixed cement composition, comprising: The CO ２ is mixed in a stoichiometric amount such that the calcium source contained in the recovered water is completely reacted. CO characterized by ２ A method for producing a blended cement composition.

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