Bleeding reduction material, cement composition, hydraulic composite, and method for producing bleeding reduction material

Abstract

The present invention relates to a bleeding reduction material that contains at least a carbonate of a cement hydrate, the bleeding reduction material being such that the content ratio of carbon dioxide in the carbonate per ton of cement is 50-350 kg. The present invention also relates to a cement composition that contains at least 2-45 mass% of a bleeding reduction material and 55-98 mass% of cement. The present invention furthermore relates to a method for producing a bleeding reduction material, the method including: a step for kneading cement or a cement hydrate and water so that the water-solids ratio reaches 100-1000% to obtain a cement hydrate slurry; a step for supplying carbon dioxide into the hydrate slurry to obtain a carbonated cement hydrate slurry; and a step for drying the carbonated cement hydrate slurry to obtain a bleeding reduction material.

Description

Bleeding-reducing material, cement composition, hydraulic composite, and method for producing bleeding-reducing material

[0001] The present invention relates to a bleeding-reducing agent capable of reducing bleeding of concrete or mortar (hereinafter referred to as "hydraulic composite"), a cement composition containing the bleeding-reducing agent, a hydraulic composite containing the cement composition, and a method for producing the bleeding-reducing agent.

[0002] (1) Concrete Bleeding: Concrete is primarily composed of water, cement, and aggregate, with the specific gravities of these components varying significantly, approximately 1.0, 3.2, and 2.5, respectively. Therefore, during the period from mixing to hardening, the concrete mix (fresh concrete) experiences material separation, with the cement and aggregate, which have higher specific gravities, settling, while the water, which has a lower specific gravities, rises, resulting in floating water (bleeding). This bleeding accumulates at the interface between the cement paste and aggregate, and between the concrete and reinforcing bars, creating voids and reducing the adhesive strength at these interfaces, leading to reduced concrete strength and settling cracks. Furthermore, even in concretes with the same mix proportions using cements with the same cement mineral composition, fineness, and gypsum content, the amount of floating water (bleeding amount) generated by bleeding varies, and sometimes the amount of bleeding can be excessive.

[0003] Therefore, JASS 5 "Watertight Concrete" has a maximum bleeding amount of 0.3 cm. ３ / cm ２ In particular, in concrete-filled steel pipe structures (CFT structures) where concrete is poured into steel pipes, excessive bleeding can cause defects in the joints and impair the integrity of the structure, so the upper limit for bleeding is even stricter, at 0.1 cm. ３ / cm ２The concrete used in CFT construction is generally high-strength, high-fluidity concrete containing low-heat cement such as moderate-heat Portland cement or low-heat Portland cement, but concrete containing low-heat cement is known to have a particularly high amount of bleeding.

[0004] To address this issue, concrete admixtures and concrete manufacturing methods that mix the above-mentioned concrete components in a specific order have been proposed as a means of reducing bleeding. For example, the invention described in Patent Document 1 (Patent Document 1) describes an admixture for preventing separation of concrete, which is composed of a microbially fermented polysaccharide produced by a bacterial species with the bacterial number Alcaligenes ATTC 31961. However, while this admixture increases the viscosity of concrete to suppress bleeding, it also reduces the fluidity and pumpability of the concrete, leading to poor filling and a decrease in strength and roughness of the concrete surface. This problem is particularly pronounced in high-flow concrete. Furthermore, because this admixture is a natural product produced by a specific bacterial species, there are concerns about quantitative limitations and increased costs in mass production of concrete. Furthermore, the invention described in Patent Document 2 is a method for producing concrete in which mixing water is divided into first mixing water (primary water) and second mixing water (secondary water), the primary water is added to cement and mixed to produce a cement paste, the secondary water is added to the paste and mixed again to produce a second cement paste, and aggregate is then added to the second cement paste and mixed. However, the effect of reducing bleeding with this method is not necessarily sufficient, and productivity can be said to be low because the mixing operation is performed three times.

[0005] (2) Reducing Carbon Dioxide Emissions Currently, measures to reduce greenhouse gases such as carbon dioxide are being sought on a global scale in order to prevent global warming. In particular, reducing carbon dioxide emissions is an urgent issue in the cement manufacturing industry, which accounts for approximately 4% (400 million tons) of the total carbon dioxide emissions of all industries in Japan. Currently, the measures to reduce carbon dioxide emissions in the cement manufacturing industry are primarily reductions in production energy and technologies for separating and capturing carbon dioxide from factory exhaust gases. Furthermore, in recent years, focusing on the fact that cement hydrates in concrete absorb and fix carbon dioxide, there has been active development of technologies for fixing carbon dioxide using concrete containing these hydrates.

[0006] For example, the technology described in Non-Patent Document 1 is a technology in which a molded concrete product is forcibly carbonated in a curing tank to fix a large amount of carbon dioxide in the concrete. Furthermore, the invention described in Patent Document 3 is a method for producing a cement composition, including a step of kneading a portion of cement with water to obtain a cement slurry with a specific water-cement ratio, a step of supplying carbon dioxide into the cement slurry to obtain a carbon dioxide-containing slurry, and a step of kneading the carbon dioxide-containing slurry, the remainder of the cement, and aggregate to obtain a cement composition. This method for producing a cement composition has the advantage of being able to fix more carbon dioxide than a method for producing a cement composition obtained by adding cement all at once.

[0007] Incidentally, in the process of obtaining a carbon dioxide-containing slurry in the invention described in Patent Document 3, a large amount of cement hydrate that has absorbed and fixed carbon dioxide (hereinafter referred to as "carbonated cement hydrate") is produced. However, the effect of the carbonated cement hydrate on the physical properties of concrete is unknown. However, since the carbonated cement hydrate is hydrated and carbonated, it has been commonly believed that the hydrate is merely a powder with reduced hydration activity and can only be used as a filler (extender).

[0008] Japanese Patent Laid-Open No. 5-306153 Japanese Patent Laid-Open No. 2014-61593 Japanese Patent Laid-Open No. 2023-6313

[0009] Torichigaya et al., "CO2 Balance and Quality Evaluation of Carbonated Cured Concrete," Proceedings of the Japan Concrete Institute, 2012, 34(1), pp. 1450-1455

[0010] Therefore, an object of the present invention is to provide a new use of the carbonated cement hydrate other than as a filler.

[0011] The present inventors have investigated the properties of the carbonated cement hydrate in order to develop new uses for the carbonated cement hydrate, and have found that the carbonated cement hydrate has the effect of reducing bleeding in hydraulic composites and increasing the strength of the hydraulic composites, leading to the completion of the present invention. That is, the present invention relates to a bleeding-reducing material having the following composition.

[0012] [1] A bleeding-reducing material containing at least a carbonate of cement hydrate, wherein the content of carbon dioxide in the carbonate per ton of cement is 50 to 350 kg. [2] The bleeding-reducing material has a Blaine specific surface area of ​​5,000 to 15,000 cm. ２ / g. [3] A cement composition comprising at least 2 to 45 mass% of the bleeding-reducing agent according to [1] or [2] above, and 55 to 98 mass% of cement. [4] A hydraulic composite comprising at least the cement composition according to [3] above, aggregate, and water. [5] A unit amount of the cement composition is 1 m of the hydraulic composite. ３ [6] The hydraulic composite according to the above [4], wherein the unit amount of the bleeding-reducing material according to the above [1] or [2] is 200 to 400 kg per 1 m of the hydraulic composite. ３[7] The hydraulic composite according to [4], wherein the carbon dioxide content in the hydraulic composite is 3 kg or more per ton of cement. [8] The hydraulic composite according to [4], wherein the amount of bleeding is reduced and the strength is increased compared to hydraulic composites not containing the bleeding-reducing additive according to [1] or [2]. [9] A method for producing a bleeding-reducing additive, comprising the steps of kneading cement or cement hydrate with water to obtain a cement hydrate slurry having a water-to-solid ratio of 100 to 1000%, supplying carbon dioxide into the hydrate slurry to obtain a carbonated cement hydrate slurry, and drying the carbonated cement hydrate slurry to obtain the bleeding-reducing additive.

[10] A method for producing the bleeding-reducing additive according to [9], wherein carbon dioxide is supplied in the step of obtaining the carbonated cement hydrate slurry so that the pH of the carbonated cement hydrate slurry is 5.0 to 11.5.

[11] The method for producing the bleeding-reducing material according to [9] above, wherein in the step of obtaining the carbonated cement hydrate slurry, 80% or more of the carbon dioxide supplied is fixed.

[12] The method for producing the bleeding-reducing material according to [9] above, wherein in the step of obtaining the carbonated cement hydrate slurry, the method for drying the carbonated cement hydrate slurry is one or more selected from the group consisting of natural drying, hot air drying, vacuum drying, cool drying, infrared drying, freeze drying, and contact drying.

[0013] A hydraulic composite using a cement composition containing the bleeding-reducing agent of the present invention has reduced bleeding and improved strength. Furthermore, the method for producing the bleeding-reducing agent of the present invention absorbs and fixes carbon dioxide, thereby contributing to the reduction of carbon dioxide.

[0014] 1 is a schematic diagram of an apparatus for producing carbonated cement slurry.

[0015] As described above, the present invention relates to a bleeding-reducing agent, a cement composition containing the bleeding-reducing agent, a hydraulic composite containing the cement composition, and a method for producing the bleeding-reducing agent. Hereinafter, the present invention will be described in detail, dividing it into the bleeding-reducing agent, the cement composition, the hydraulic composite, and the method for producing the bleeding-reducing agent.

[0016] 1. Bleeding-reducing material The bleeding-reducing material of the present invention contains at least a carbonate of cement hydrate, and the content of carbon dioxide in the carbonate per ton of cement is 50 to 350 kg. If the content is within the above range, the bleeding-reducing effect is high. The content is preferably 100 to 350 kg, more preferably 150 to 350 kg. Furthermore, the Blaine specific surface area of ​​the bleeding-reducing material is preferably 5,000 to 15,000 cm. ２ If the Blaine specific surface area is in the above range, the bleeding reduction effect is high. The Blaine specific surface area is more preferably 6000 to 15000 cm ２ / g, more preferably 7000 to 14000 cm ２ / g.

[0017] The cement is at least one selected from ordinary Portland cement, high-early-strength Portland cement, extra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, blast-furnace cement, and fly ash cement. The cement hydrate is a mixture of cement and water, and examples thereof include cement-containing materials such as ready-mixed concrete sludge, lightweight aerated concrete scraps, and waste concrete.

[0018] 2. Cement Composition The cement composition of the present invention is a composition containing at least 2 to 45% by mass of the bleeding-reducing agent and 55 to 98% by mass of cement. Cement compositions having the bleeding-reducing agent and cement contents within the above ranges exhibit high bleeding reduction effects and strength development. The bleeding-reducing agent and cement contents are preferably 5 to 40% by mass and 60 to 95% by mass, and more preferably 10 to 30% by mass and 70 to 90% by mass, respectively.

[0019] 3. Hydraulic Composite The hydraulic composite of the present invention is concrete or mortar containing at least the above cement composition, aggregate, and water. The unit amount of the above cement composition is preferably 1 m of hydraulic composite. ３ If the unit amount is within this range, the suppression of bleeding, strength development, fluidity, workability, etc. are good. The unit amount is more preferably 200 to 400 kg per 1 m of hydraulic composite material. ３ The unit amount of the bleeding reducing agent in the hydraulic composite is 250 to 400 kg per 1 m of the hydraulic composite, and more preferably 300 to 400 kg per 1 m of the hydraulic composite. ３ If the unit amount is within this range, bleeding suppression, strength development, fluidity, workability, etc. are good.

[0020] The fine aggregate may be one or more selected from river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag fine aggregate, lightweight fine aggregate, etc., and the coarse aggregate may be one or more selected from gravel, crushed stone, slag coarse aggregate, lightweight coarse aggregate, etc. In addition to natural aggregate, recycled aggregate may also be used for both the fine aggregate and the coarse aggregate. The unit amount of fine aggregate is preferably 10 ... ３ If the unit amount is within this range, the fluidity and workability are good. The unit amount is more preferably 600 to 900 kg per 1 m of concrete. ３ The unit amount of coarse aggregate is preferably 650 to 850 kg per 1 m of concrete. ３If the unit amount is within this range, the fluidity and workability are good. ３ It weighs 950 to 1050 kg per piece.

[0021] Any water can be used as long as it does not adversely affect the physical properties of the hydraulic composite, such as strength and fluidity, and examples thereof include one or more types selected from tap water, industrial water, supernatant water of ready-mixed concrete, and recovered water. The unit amount of water is preferably 1 / 3 of water per 1 m of concrete. ３ If the unit amount is within this range, the fluidity and workability are good. ３ Each weighs 130 to 180 kg.

[0022] The carbon dioxide content in the hydraulic composite of the present invention is preferably 3 kg or more per ton of cement. A content of 3 kg or more per ton of cement can contribute to a reduction in carbon dioxide. The carbon dioxide content in the hydraulic composite is more preferably 5 to 100 kg, and even more preferably 8 to 80 kg, per ton of cement.

[0023] Furthermore, the hydraulic composite of the present invention is concrete or mortar that has a reduced amount of bleeding and increased strength compared to a hydraulic composite that does not contain a bleeding-reducing agent.

[0024] In addition to the above essential components, the hydraulic composite of the present invention may contain one or more admixtures such as a shrinkage reducing agent, a water reducing agent, and an air-entraining water reducing agent, or an expansive agent, blast furnace slag, fly ash, coal ash, silica fume, silica powder, and limestone powder, depending on the required durability performance such as suppression of cracking, prevention of salt damage, and improvement of freeze-thaw resistance.

[0025] 4. Manufacturing Method of Bleeding-Reducing Material The manufacturing method of the bleeding-reducing material of the present invention includes the steps of kneading cement or cement hydrate with water so that the water-to-solid ratio is 100 to 1000% to obtain a cement hydrate slurry, supplying carbon dioxide into the hydrate slurry to obtain a carbonated cement hydrate slurry, and drying the carbonated cement hydrate slurry to obtain the bleeding-reducing material.

[0026] In the step of obtaining the carbonated cement hydrate slurry, carbon dioxide is supplied so that the pH of the carbonated cement hydrate slurry becomes 5.0 to 11.5. If the pH of the carbonated cement hydrate slurry is within the above range, the content of carbon dioxide in the carbonated cement hydrate slurry becomes 100 to 350 kg of carbon dioxide per ton of cement, and the amount of fixed carbon dioxide increases.

[0027] In the step of obtaining the carbonated cement hydrate slurry, it is preferable to fix 80% or more of the carbon dioxide supplied. If the amount of fixed carbon dioxide is 80% or more, the fixation efficiency of carbon dioxide is high, which can contribute to reducing carbon dioxide.

[0028] In the step of obtaining the bleeding-reducing material, the method for drying the carbonated cement hydrate slurry may be one or more methods selected from natural drying, hot air drying, vacuum drying, cooling drying, infrared drying, freeze drying, and contact drying. According to the drying method, the bleeding-reducing material can be dried without decarbonating the carbon dioxide fixed in the bleeding-reducing material.

[0029] The present invention will be described below with reference to examples, but is not limited to these examples. 1. Materials Used The materials used are shown in Table 1.

[0030]

[0031] 2. Production of Bleeding-Reducing Material (1) Production Example Using Ordinary Portland Cement as Raw Material 10 kg of ordinary Portland cement and 30 kg of tap water were mixed for 120 seconds using a hand mixer to prepare 10 batches of cement slurry. The temperature of the slurry was 23°C. Next, as shown in Figure 1, the cement slurry was circulated by a pump between a carbon dioxide reaction tank filled with carbon dioxide gas and a slurry tank for 8 hours to carbonate the cement hydrate in the slurry. The pH of the carbonated cement hydrate slurry thus obtained was 8.0. The ratio of carbon dioxide fixed by the cement hydrate slurry to the amount of carbon dioxide supplied was 95%. Next, the supernatant water of the carbonated cement hydrate slurry was decanted off, and the residue was air-dried at 30°C for 3 days and pulverized to obtain a mixture having a Blaine specific surface area of ​​13,550 cm. ２ / g of Bleeding Reducer (N) (abbreviated as BR(N)) was produced.

[0032] (2) Production Example Using Fresh Concrete Sludge as Raw Material The fresh concrete sludge (A) and (B) were prepared by separating and removing aggregate from fresh concrete sludge (A) and (B) collected from a ready-mixed concrete plant (A) and a ready-mixed concrete plant (B), respectively, that did not use limestone aggregate. The coarse aggregate content in the fresh concrete sludge was 0% by mass. Specifically, the cement hydrate slurry was prepared by mixing 10 batches of cement hydrate slurry prepared by mixing 30 kg of fresh concrete sludge (solid content: 10 kg) and the water in the fresh concrete sludge and tap water for 120 seconds using a hand mixer. The temperature of the slurry was 23°C. The amount of water relative to the solid content in the fresh concrete sludge (hereinafter referred to as the "water-solid ratio") was calculated by drying the fresh concrete sludge at 105°C for one day, determining the mass of the solid content and water, and then using the following formula (1): Water-solid ratio = mass of water / weight of solid content × 100 (%) (1)

[0033] Next, in the same manner as in the above production example using ordinary Portland cement as a raw material, the cement hydrate slurry was circulated by a pump between a carbon dioxide reaction tank filled with carbon dioxide gas and a slurry tank for 8 hours as shown in Figure 1, to carbonate the cement hydrate in the slurry. The pH of the carbonated cement hydrate slurries (A) and (B) thus obtained, derived from fresh concrete sludge (A) and (B), respectively, was both 8.0. The ratios of carbon dioxide fixed by the carbonated cement hydrates (A) and (B) to the amount of carbon dioxide supplied were 93% and 94%, respectively.

[0034] Next, the supernatant water of the carbonated cement hydrate slurries (A) and (B) was removed by decantation, and the residue was naturally dried at 30°C for 3 days and pulverized to obtain a slurried product having a Blaine specific surface area of ​​14,200 cm ２ / g of Bleeding Reducer (A) (abbreviated as BR(A)) and a Blaine specific surface area of ​​14600 cm ２ / g of Bleeding Reducer (B) (abbreviated as BR(B)) was produced.

[0035] (3) Measurement of the amount of carbon dioxide fixed by the bleeding-reducing additive The loss at 550 to 850 ° C (amount of calcium carbonate decarbonation) and the loss on ignition up to 950 ° C were measured by thermogravimetry-differential thermal analysis (TG-DTA), and the amount of carbon dioxide fixed by the bleeding-reducing additives (N), (A), and (B) was calculated using the following formula (2). As a result, as shown in Table 1, the amounts of carbon dioxide fixed by the bleeding-reducing additives (N), (A), and (B) were 214 kg per ton of cement used as the raw material, 146 kg per ton of solids of the ready-mixed concrete sludge (A) used as the raw material, and 208 kg per ton of solids of the ready-mixed concrete sludge (B) used as the raw material, respectively. 1000 × [Ta - {Tb × (100 - La) / (100 - Lb)}] / {100 × (100 - La) / (100 - Lb)} (2) In the above formula (2), Ta is the decarbonation amount (mass%) of calcium carbonate of the bleeding-reducing additive, Tb is the decarbonation amount (mass%) of calcium carbonate of the raw material solid content (ordinary Portland cement or solid content of ready-mixed concrete sludge), La is the ignition loss (mass%) of the bleeding-reducing additive, and Lb is the ignition loss (mass%) of the raw material solid content.

[0036] 3. Production of Concrete Containing Bleeding-Reducing Admixture Concrete containing the bleeding-reducing admixture was produced according to the formulation shown in Table 2 and in accordance with JIS A 1138 "Laboratory concrete production method."

[0037] 4. Calculation of the amount of carbon dioxide fixed in concrete, and measurement of the amount of bleeding and compressive strength of concrete (i) Calculation of the amount of carbon dioxide fixed in concrete The amount of carbon dioxide fixed in concrete was calculated from the amount of bleeding-reducing material mixed into the concrete and the amount of carbon dioxide fixed contained in it. The results are shown in Table 2.

[0038] (ii) Measurement of Bleeding Amount and Compressive Strength of Concrete The bleeding amount of the concrete was measured in accordance with JIS A 1123 "Test Method for Bleeding of Concrete." The compressive strength of the concrete was measured in accordance with JIS A 1108 "Test Method for Compressive Strength of Concrete" using concrete specimens that had been cured underwater for 28 days. The results are shown in Table 2.

[0039]

[0040] As shown in Table 2, compared to Comparative Examples 1 to 4, Examples 1 to 7 of the present invention all have a smaller amount of bleeding and / or a higher compressive strength.

Claims

1. A bleeding reducing material which contains at least a carbonate of cement hydrate, and in which the carbonate has a carbon dioxide content of 50 to 350 kg per ton of cement.

2. The Blaine specific surface area of ​​the above bleeding reduction material is 5000 to 15000 cm ２ The bleeding reducing material according to claim 1, wherein the bleeding reducing material has a viscosity of 1000:1 or more.

3. A cement composition comprising at least 2 to 45 mass% of the bleeding reducing material according to claim 1 or 2, and 55 to 98 mass% of cement.

4. A hydraulic composite comprising at least the cement composition according to claim 3, aggregate, and water.

5. The unit amount of the above cement composition is 1 m of hydraulic composite. ３ The hydraulic composite according to claim 4, wherein the weight is 200 to 400 kg per unit area.

6. The unit amount of the bleeding reducing material according to claim 1 or 2 is 1 m of hydraulic composite. ３ The hydraulic composite according to claim 4, wherein the weight is 4 to 180 kg per unit area.

7. The hydraulic composite according to claim 4, wherein the content of carbon dioxide in the hydraulic composite is 3 kg or more per ton of cement.

8. The hydraulic composite according to claim 4, which has a reduced amount of bleeding and increased strength compared to a hydraulic composite not containing the bleeding reducing material according to claim 1 or 2.

9. [9] A method for producing a bleeding-reducing material, comprising the steps of: kneading cement or cement hydrate with water so that the water-solid ratio is 100 to 1000% to obtain a cement hydrate slurry; supplying carbon dioxide into the hydrate slurry to obtain a carbonated cement hydrate slurry; and drying the carbonated cement hydrate slurry to obtain the bleeding-reducing material.

10. The method for producing a bleeding reducing material according to claim 9, wherein in the step of obtaining the carbonated cement hydrate slurry, carbon dioxide is supplied so that the pH of the carbonated cement hydrate slurry becomes 5.0 to 11.

5.

11. The method for producing a bleeding reducing material according to claim 9, wherein in the step of obtaining the carbonated cement hydrate slurry, 80% or more of the carbon dioxide supplied is fixed.

12. A method for producing a bleeding reducing material as described in claim 9, wherein in the step of obtaining the bleeding reducing material, the method for drying the carbonated cement hydrate slurry is one or more selected from natural drying, hot air drying, vacuum drying, cooling drying, infrared drying, freeze drying, and contact drying.

Images