Cement admixtures, cement compositions

Abstract

To provide a cement admixture that has good storage stability and can ensure early strength development and crack resistance. [Solution] A cement admixture in which the hydration reaction rate after 30 minutes of mixing with a water ratio of 2:1 is 30-90%, and the maximum particle size is 300 μm or less.

Description

[Technical Field]

[0001] This invention relates to cement admixtures and cement compositions. [Background technology]

[0002] In recent years, the demand for concrete is expected to increase in the civil engineering and construction sectors due to the increasing number and size of concrete structures, as well as the need to repair or reinforce aging structures.

[0003] For example, Patent Document 1 proposes a fine powder for concrete compositions that, when used as an admixture in concrete, can reduce changes in fluidity over time and improve resistance to material segregation at low cost without requiring a major revision of the concrete's mix or composition. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 4810914 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The fine powder for concrete compositions described in Patent Document 1 contains more than 0.0% by mass and / or less than 1.0% by mass of quicklime fine powder and / or slaked lime fine powder in terms of free calcium oxide, and contains 95.0% by mass or more of calcium carbonate fine powder. However, there is no basic evaluation of properties such as early strength development and crack resistance, so its practicality remains questionable.

[0006] Furthermore, cement admixtures used in combination with cement are preferably made with small particle sizes to ensure good mixability, but on the other hand, they are susceptible to deterioration during storage due to hydration reactions, oxidation reactions, etc.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a cement admixture that has good storage stability and can ensure early strength development and crack resistance. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the inventors have come up with the following invention and found that it can solve the problems. That is, the present invention is as follows.

[0009] [1] A cement admixture in which the hydration reaction rate after 30 minutes when mixed with water at a ratio of 2:1 is 30-90%, and the maximum particle size is 300 μm or less. [2] Braine value is 3,000-10,000 cm 2 The cement admixture described in [1] above, which is / g. [3] The cement admixture according to [1] or [2] above, comprising composite particles containing calcium carbonate and calcium oxide, wherein the mass ratio of calcium carbonate to calcium oxide (calcium carbonate / calcium oxide) is 5 / 95 to 99.5 / 0.5, and the total amount of calcium carbonate and calcium oxide is 80% by mass or more. [4] A cement admixture according to any one of the above [1] to [3], further comprising an alkali metal sulfate. [5] A cement composition comprising a cement admixture described in any one of [1] to [4] above and cement. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a cement admixture that has good storage stability and can ensure early strength development and crack resistance. [Modes for carrying out the invention]

[0011] Hereinafter, an embodiment of the present invention (this embodiment) will be described in detail, but the present invention is not limited to the embodiment. In the present specification, “%” and “parts” are based on mass unless otherwise specified.

[0012] [Cement admixture] The cement admixture according to this embodiment is required to have a hydration reaction rate of 30 to 90% after kneading at a mixing material water ratio of 2 / 1 for 30 minutes and a maximum particle size of 300 μm or less.

[0013] The cement admixture of the present invention has a hydration reaction rate of 30 to 90% after kneading at a mixing material water ratio of 2 / 1 for 30 minutes. The mixing material water ratio represents the mass ratio of the cement admixture of the present invention to the kneading water. There is no particular restriction on the kneading method of the cement admixture and water, but it is desirable to ensure uniform mixing. During kneading, samples are appropriately taken to confirm uniformity and ensure homogeneity. As the device used for kneading, any existing mixing device can be used, for example, a tilting barrel mixer, an omnimixer, a Henschel mixer, a V-type mixer, and a Nauta mixer can be used.

[0014] In the present invention, the hydration reaction rate (α) can be obtained by the following formula. α (%) = (W1 - W2) / W1 × 100 W1: Content rate (mass %) of free lime (f-CaO) before hydration reaction W2: Content rate (mass %) of free lime (f-CaO) after hydration reaction

[0015] The content rate (W) of free lime (f-CaO) before and after the hydration reaction in the above formula can be determined by using differential thermal gravimetric analysis (TG-DTA) to quantify the content rate of Ca(OH)2 from the mass reduction amount at 250 to 500 °C and the content rate of CaCO3 from the mass reduction amount at 500 to 850 °C, respectively, and can be obtained by the following formula.

[0016] W (mass %) = 100 - Ca(OH)2 - CaCO3 Ca(OH)2: Ca(OH)2 content (mass %) CaCO3: CaCO3 content (by mass)

[0017] If the hydration reaction rate exceeds 90%, the storage stability of the cement admixture may be poor. On the other hand, if the hydration reaction rate falls below 30%, the early strength development and crack resistance may be poor. From the viewpoint of improving fluidity and carbonation resistance, the hydration reaction rate is preferably 45-88%, and more preferably 60-85%. This hydration reaction rate can be adjusted to a desirable range by adjusting the particle size distribution of the cement admixture through crushing, sieving, etc.

[0018] The cement admixture of the present invention has a maximum particle diameter of 300 μm or less. Furthermore, from the viewpoint of improving strength development, it is preferable that it be 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. There is no particular lower limit, but it is preferable that it be 50 μm or more. In the present invention, the maximum particle diameter of the cement admixture can be measured, for example, by a laser diffraction / scattering particle size distribution analyzer manufactured by HORIBA Corporation.

[0019] The Blaine value (Blaine specific surface area) of the cement admixture according to this embodiment is 3,000 to 10,000 cm² from the viewpoint of improving fluidity. 2 It is preferable that the amount is / g, and the range is 4,000 to 8,000 cm³. 2 It is more preferable that the amount is / g, and the amount is 5,000 to 7,000 cm 2 It is even more preferable that the value be / g. The Blaine value can be measured based on the specific surface area test described in JIS R 5201:2015 "Physical Testing Methods for Cement".

[0020] The median diameter of the cement admixture of the present invention, based on volume, is preferably 15 to 200 μm, and more preferably 50 to 150 μm, from the viewpoint of improving fluidity and early strength development. When the median diameter of the cement admixture is within the above range, the admixture particles are easily dispersed uniformly. In this invention, the median diameter can be determined, for example, by using a laser diffraction / scattering particle size distribution analyzer manufactured by HORIBA Corporation.

[0021] The average particle size of the cement admixture of the present invention, based on volume, is preferably 15 to 200 μm, and more preferably 50 to 150 μm, from the viewpoint of improving fluidity and early strength development. When the median diameter of the cement admixture is within the above range, the admixture particles are easily dispersed uniformly. In this invention, the median diameter can be determined, for example, by using a laser diffraction / scattering particle size distribution analyzer manufactured by HORIBA Corporation.

[0022] The ratio of the average particle diameter to the median diameter by volume in the cement admixture of the present invention is preferably 1.0 to 1.5, and more preferably 1.1 to 1.4. By having the ratio of the average particle diameter to the median diameter by volume in the cement admixture within the above range, a uniform particle size distribution can be achieved, improving early strength development, crack resistance, fluidity, and carbonation resistance.

[0023] The cement admixture according to this embodiment contains calcium carbonate and calcium oxide, and preferably contains composite particles with a mass ratio of calcium carbonate to calcium oxide (calcium carbonate / calcium oxide) of 5 / 95 to 99.5 / 0.5, more preferably 10 / 90 to 90 / 10, even more preferably 15 / 85 to 70 / 30, and still more preferably 20 / 80 to 50 / 50. In this mass ratio, increasing the proportion of calcium carbonate tends to improve early strength development and carbonation resistance, while increasing the proportion of calcium oxide tends to improve crack resistance. The mass ratio of calcium carbonate to calcium oxide in the cement admixture can be calculated, for example, by the mass loss obtained by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA).

[0024] The cement admixture according to this embodiment preferably contains composite particles in which the total amount of calcium carbonate and calcium oxide is 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. When the total amount is within the above range, early strength development tends to improve. Furthermore, the upper limit of the total amount is preferably 95% by mass. The total amount of calcium carbonate and calcium oxide in the cement admixture can be calculated, for example, by the mass loss obtained by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA).

[0025] The cement admixture of the present invention preferably contains 50% by mass or more of the above-mentioned composite particles, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0026] When the cement admixture of the present invention contains composite particles comprising calcium carbonate and calcium oxide, the arrangement of these particles is not particularly limited, but it is preferable, for example, to have a core-shell structure in which calcium oxide is mainly present in the center and calcium carbonate is mainly present on the outside. With a core-shell structure, the calcium carbonate, which is abundant on the outside, first suppresses the elution of excess calcium, and then the calcium oxide, which is abundant near the center, reacts with water in stages, eluting calcium. Due to these reaction characteristics, it is possible to maintain the stability of the entire cement composition, and improvements in crack resistance, early strength development, and carbonation resistance can be expected. Furthermore, optimizing the ratio and distribution of calcium carbonate and calcium oxide in the manufacturing process of the composite particles is important for ensuring homogeneity and consistency of performance.

[0027] In relation to the core-shell structure described above, the composite particles preferably have a mass change rate of 70% or more, more preferably 80% or more, and even more preferably 90% or more when left standing for 24 hours in a 40°C 90%RH environment. This embodiment suggests that the cement admixture has a core-shell structure. That is, the calcium carbonate abundant on the surface inhibits the penetration of moisture from the atmosphere into the center, and the digestion reaction of calcium oxide proceeds slowly. On the other hand, a mixture of calcium oxide and calcium carbonate is in a form where the calcium oxide is exposed to the atmosphere, so the digestion reaction by moisture from the atmosphere proceeds easily. In this invention, the mass change rate can be calculated by spreading about 10 g of the sample thinly on an aluminum dish about 10 cm in diameter, leaving it standing in a 40°C 90%RH environmental test chamber so that the sample does not agitate, weighing the mass change after 24 hours using an electronic balance, and dividing the value by the mass before measurement.

[0028] Thus, the fact that the mass change rate of the above composite particles is 50% or less compared to the mass change rate of a mixture of calcium carbonate and calcium oxide in the same ratio suggests that it has a core-shell structure, making it easier to obtain good crack resistance and early strength development more efficiently, and also enabling better resistance to carbonation.

[0029] The particles described above can be produced by carbonating commercially available slaked lime that has undergone particle size adjustment. However, in this embodiment, it is preferable to use by-product slaked lime from the viewpoint of effective utilization of waste and ease of adjusting the mass ratio of calcium carbonate to calcium oxide. In other words, the composite particles are preferably the carbon oxide of by-product slaked lime.

[0030] By-product slaked lime includes acetylene by-product slaked lime produced in the acetylene gas production process using the calcium carbide method (there are wet and dry types depending on the acetylene gas production method), and by-product slaked lime contained in the dust captured in the wet dust collection process of a calcium carbide electric furnace. By-product slaked lime, for example, contains 65-95% (preferably 70-90%) calcium hydroxide, and the rest contains 0.1-10% calcium carbonate and 0.1-6.0% (preferably 0.1-3.0%) iron oxide. These proportions can be confirmed by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA) to determine the mass loss (Ca(OH)2: around 405°C-515°C, CaCO3: around 650°C-765°C). The volume-average particle size measured by laser diffraction and scattering is approximately 50 to 100 μm. Furthermore, the moisture content measured by the loss on drying method specified in JIS K 0068:2001 "Method for Measuring Moisture Content of Chemical Products" is preferably 10% or less. In addition, sulfur compounds such as CaS, A12S3, and CaC2·CaS may be included, but it is preferable that the amount be 2% or less.

[0031] Furthermore, the Blaine value of this by-product slaked lime is 2,500 to 6,000 cm³. 2 It is preferable that the amount is / g, and the range is 3,000 to 5,500 cm³. 2It is more preferable that the blain value of the by-product slaked lime is 2,500 to 6,000 cm³. 2 Being / g makes it easier to perform the desired carbonation treatment.

[0032] From the viewpoint of ease of handling, the median diameter of the by-product slaked lime by volume is preferably 1 to 300 μm, and more preferably 10 to 100 μm.

[0033] The above-mentioned composite particles can be produced, for example, using carbon dioxide at a temperature of 100°C or higher and a CO2 concentration of 5% by volume or higher. As a raw material, the above-mentioned by-product slaked lime, mainly composed of calcium hydroxide, can be used. By carbonating the raw material in the above-mentioned carbon dioxide, the surface of the main component, calcium hydroxide, is carbonated to form calcium carbonate, and a cement admixture in which calcium oxide mainly exists at the center can be produced.

[0034] The temperature of the carbon dioxide is 100°C or higher, preferably 450°C or higher, and more preferably 480°C or higher. There is no upper limit, but from the viewpoint of manufacturing costs, it is preferably 1000°C or lower, more preferably 800°C or lower, and even more preferably 700°C or lower.

[0035] The CO2 concentration in the carbon dioxide gas is 5% by volume or more, preferably 10 to 100% by volume, and more preferably 20 to 100% by volume.

[0036] As carbon dioxide, exhaust gas generated from cement plants and coal-fired power plants, exhaust gas generated from exhaust treatment at paint factories, etc., can be used and can be appropriately adjusted to achieve the above temperature and CO2 concentration.

[0037] The above-mentioned composite particles are preferably manufactured by heat-treating the raw materials before the carbonation treatment with carbon dioxide. This makes it easy to adjust the mass ratio of calcium carbonate to calcium oxide in each particle, and allows for the efficient formation of the core-shell structure described above.

[0038] The ambient temperature for heat treatment is preferably 600°C or higher, more preferably 750°C or higher, and even more preferably 900°C or higher. There is no specific upper limit, but from the viewpoint of manufacturing costs, it is preferable to keep it below 1300°C.

[0039] In addition to adjusting the temperature and CO2 concentration of the carbon dioxide gas and the heat treatment, as well as the carbonation time, the mass ratio of calcium carbonate to calcium oxide can be easily adjusted, and the aforementioned core-shell structure can be efficiently formed. For example, the proportion of calcium oxide can be increased by raising the ambient temperature during heat treatment, and the proportion of calcium carbonate can be increased by raising the temperature and CO2 concentration of the carbon dioxide gas.

[0040] The cement admixture preferably contains 4% by mass or less of calcium sulfate in addition to the calcium carbonate and calcium oxide mentioned above, more preferably 2% by mass or less, and even more preferably 1% by mass or less. When the calcium sulfate content is within the above range, early strength and fluidity tend to improve. The lower limit is not particularly limited, but it may be 0% by mass.

[0041] The cement admixture according to this embodiment preferably further contains an alkali metal sulfate from the viewpoint of fluidity and early strength development. The alkali metal preferably contains at least one of lithium, sodium, and potassium, with sodium being more preferred.

[0042] The alkali metal sulfate content in the cement admixture is preferably 10 to 40% by mass, and more preferably 20 to 30% by mass. When the alkali metal sulfate content is within the above range, early strength development and fluidity can be improved.

[0043] [Cement composition] The cement composition according to this embodiment comprises the cement admixture of the present invention and cement.

[0044] Examples of cements according to this embodiment include various types of Portland cement such as ordinary, rapid-hardening, moderate-heat, low-heat, and white; eco-cement produced from municipal solid waste incineration ash and sewage sludge incineration ash; and mixed cements containing blast furnace slag, silica fume, limestone, fly ash, gypsum, etc. Among these, ordinary Portland cement or blast furnace cement is preferred as a cement that can obtain good initial strength development, and blast furnace cement is more preferred. The blast furnace cement may be blast furnace cement as specified in JIS R 5211:2009 "Blast Furnacement", or blast furnace cement obtained by mixing blast furnace slag with ordinary Portland cement, etc., and containing blast furnace slag in a content greater than or equal to that specified in the above JIS.

[0045] The cement composition may contain known additives that are commonly used, as long as they do not impair the effects of the present invention. Examples of additives, though not particularly limited, include rust inhibitors, colorants, polymers, fibers, fluidizers, carbonation inhibitors, waterproofing agents, thickeners, waterproofing agents, retarders, rapid strengthening agents, accelerators, water-reducing agents, high-performance (AE) water-reducing agents, foaming agents, foaming agents, AE agents, drying shrinkage reducers, rapid setting agents, swelling agents, cold-hardening accelerators, efflorescence inhibitors, alkali-aggregate reaction inhibitors, blackening unevenness reducers, and environmental remediation admixtures. These additives can be used individually or in combination of two or more.

[0046] From the viewpoint of effectively exhibiting the function of the admixture, the amount of cement admixture in the cement composition is preferably 1 to 30% by mass, more preferably 2 to 25% by mass, and even more preferably 3 to 20% by mass.

[0047] The cement composition may contain aggregates, and fine and coarse aggregates similar to those used in ordinary cement mortar and concrete can be used. Specifically, river sand, river gravel, mountain sand, mountain gravel, crushed stone, crushed sand, limestone aggregate, lime sand, silica sand, colored sand, artificial aggregate, blast furnace slag aggregate, sea sand, sea gravel, artificial lightweight aggregate, and heavy aggregate can be used, and these can also be combined.

[0048] The content ratio of the aggregate is preferably 40 to 500 parts by mass, more preferably 50 to 400 parts by mass, and even more preferably 60 to 350 parts by mass with respect to 100 parts by mass of the cement in the cement composition.

[0049] The cement compositions of the present embodiment may be prepared by mixing each material during construction, or a part or all of them may be mixed in advance. Also, the mixing method of each material and water is not particularly limited, and each material may be mixed during construction, or a part or all of them may be mixed in advance. Further, after mixing a part of the materials with water, the remaining materials may be mixed.

[0050] As the mixing device, any existing device can be used. For example, a tilting drum mixer, an omnimixer, a Henschel mixer, a V-type mixer, a Nauta mixer, etc. can be used.

Examples

[0051] Hereinafter, the present invention will be further described based on experimental examples, but the present invention is not limited thereto.

[0052] <Experimental Example 1> (Manufacture and evaluation of cement admixture) · Cement admixture A As raw materials, massive limestone (density: 2.69 to 2.71 g / cm 3 , size width: 35 to 85 mm, calcium carbonate content (in terms of CaO): 55.8% by mass) was used, heated in an atmosphere at a temperature of 1,000 °C for 1 hour, the material with a size of 3 mm or less was selected from the fired product and pulverized, and further carbonated with carbon dioxide gas at a temperature of 60 °C and a CO2 concentration of 25% by volume to obtain cement admixture A (calcium carbonate / calcium oxide = 40 / 60 (mass ratio), the total amount of calcium carbonate and calcium oxide in cement admixture A is 94% by mass, density 2.95 g / cm 3A cement admixture A was prepared. The prepared cement admixture A was further crushed and sieved to obtain the Blaine value, median diameter, and average particle size listed in Table 1 below, and each was evaluated. The mass ratio and total amount of calcium carbonate to calcium oxide were calculated from the mass loss obtained by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA).

[0053] Cement admixture B The raw material is fine limestone powder (manufactured by Joetsu Mining Co., Ltd., 100 mesh, density: 2.74 g / cm³). 3 Brain specific surface area: 4,550 cm² 2 ( / g) and calcium oxide (by-product slaked lime, a by-product of the acetylene gas production process using the calcium carbide method, calcined at 1,000°C for 3 hours; density: 3.21 g / cm³) 3 Brain specific surface area 4,490 cm² 2 Mix the calcium carbonate and calcium oxide in cement admixture B so that the calcium carbonate / calcium oxide ratio is 15 / 85 (mass ratio), resulting in cement admixture B (calcium carbonate / calcium oxide = 15 / 85 (mass ratio), total amount of calcium carbonate and calcium oxide in cement admixture B is 99% by mass, density 2.98 g / cm³). 3 A cement admixture B was prepared. The prepared cement admixture B was further crushed and sieved to obtain the Blaine value, median diameter, and average particle size listed in Table 1 below, and each was evaluated. The mass ratio and total amount of calcium carbonate to calcium oxide were calculated from the mass loss obtained by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA).

[0054] Cement admixture C The calcium oxide used in cement admixture B is used in cement admixture C (calcium carbonate / calcium oxide = 0 / 100 (mass ratio), total amount of calcium oxide in cement admixture C is 91% by mass, density 3.21 g / cm³). 3 The material was then ground and sieved to achieve the Blaine value, median diameter, and average particle size listed in Table 1 below, and each evaluation was performed. The mass ratio and total amount of calcium carbonate to calcium oxide were calculated from the mass loss obtained by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA).

[0055] Cement admixture D The raw material used is commercially available slaked lime (manufactured by Ueda Lime Co., Ltd., density: 2.27 g / cm³). 3 Brain specific surface area: 12,670 cm² 2 Using a mixture of 1 / g and 99% by mass of Ca(OH)2, the mixture was heat-treated in an atmosphere at 600°C, followed by carbonation treatment with carbon dioxide at 450°C and a CO2 concentration of 50% by volume. The result was a cement admixture D (calcium carbonate / calcium oxide = 15 / 85 (mass ratio), total amount of calcium carbonate and calcium oxide in cement admixture D 99% by mass, density 2.97 g / cm³). 3 A cement admixture D was prepared. The prepared cement admixture D was further crushed and sieved to obtain the Blaine value, median diameter, and average particle size listed in Table 1 below, and each was evaluated. The mass ratio and total amount of calcium carbonate to calcium oxide were calculated from the mass loss obtained by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA).

[0056] • Hydration rate Each prepared cement admixture was mixed with water using a mixer at an admixture-to-water ratio of 1 / 2 for 5 minutes, and then allowed to stand for 30 minutes. Differential thermogravimetric analysis (TG-DTA) was used to measure the CaCO3 and Ca(OH)2 content of the cement admixtures before and after mixing, and the hydration reaction rate was calculated from the f-CaO content before and after the hydration reaction. The results are shown in Table 1.

[0057] • Mass change rate Approximately 10g of each cement admixture immediately after manufacturing was spread thinly on an aluminum dish about 10cm in diameter. The dish was then placed in an environmental test chamber at 40°C and 90% RH humidity to prevent the sample from being stirred up. The change in mass after 24 hours was weighed using an electronic balance and the result was calculated by dividing the measured mass by the mass before measurement.

[0058] Each cement admixture was sealed in a plastic bag immediately after preparation and stored for one month under conditions of 40°C and 90% humidity. The free lime (f-CaO) content in the carbonated quicklime before and after storage was measured using differential thermogravimetric analysis (TG-DTA). Admixtures with a free lime content of less than ±10% compared to before storage were evaluated as "acceptable (○)," and those with a free lime content exceeding ±20% were evaluated as "unacceptable (×)."

[0059] [Table 1]

[0060] (Preparation and evaluation of cement compositions) The cement admixture and cement (ordinary Portland cement, density 3.16 g / cm³) in each example. 3 , Brain specific surface area 3,260 cm² 2 A cement composition was prepared by mixing ( / g) with fine aggregate (JIS standard sand for strength testing, manufactured by the Cement Association). Water (tap water) was further mixed into the prepared cement composition so that the water / cement ratio was 0.5 (mass ratio) to make mortar, and the following evaluation was performed. The results are shown in Table 2 below. A reference example was used in which fine aggregate was mixed at a ratio of 300 parts by mass to 100 parts by mass of cement, and each example and comparative example was obtained by replacing 3% by mass of the cement in the reference example with a cement admixture.

[0061] • Crack resistance Mortar was filled into a formwork (40mm x 40mm x 160mm) and cured in an atmosphere of 20°C and 60% RH. After 7 days, the formwork was removed, and the surface condition of the resulting hardened body was checked. Those without cracks were marked with "○", and those with cracks were marked with "×".

[0062] ·Liquidity The flow value of the mortar was measured in accordance with the method specified in JIS R 5201:2015 "Physical Testing Methods for Cement". The flow value is preferably 185-200 mm, more preferably 190-200 mm, and even more preferably 195-200 mm.

[0063] • Compression strength The compressive strength of mortar was measured at 1, 7, and 28 days of age, in accordance with the method specified in JIS R 5201:2015 "Physical Testing Methods for Cement". After demolding, curing was performed underwater. The compressive strength at 1 day of age was 10-20 N / mm². 2 Preferably, this would be 15-20 N / mm 2 It is more preferable that the compressive strength at 7 days of age is 50-65 N / mm². 2 Preferably, this would be 60-65 N / mm 2 This is more preferable. The compressive strength at 28 days of age is 60-70 N / mm². 2 Preferably, this would be 65-70 N / mm 2 It would be more preferable if this were the case.

[0064] ·Neutralization resistance Except for preparing the specimens from mortar and setting the specimen dimensions to 40mm x 40mm x 160mm, the carbonation depth after 28 days of accelerated carbonation was measured in accordance with the method specified in JIS A 1153:2012 "Test Method for Accelerated Carbonation of Concrete". The carbonation depth after 28 days of accelerated carbonation is preferably 1.0 to 2.0 mm, and more preferably 1.0 to 1.5 mm.

[0065] [Table 2]

[0066] <Experimental Example 2> As cement, we used ordinary Portland cement and blast furnace slag fine powder (density approximately 2.9-3.1 g / cm³) as used in Experimental Example 1. 3 A blast furnace cement was prepared by mixing (particle size range 5-50 μm) in the proportions shown in Table 3 below, and the cement composition was prepared and evaluated in the same manner as in Experimental Example 1, except that the prepared blast furnace cement was used as the cement. The results are shown in Table 3 below.

[0067] [Table 3]

[0068] <Experimental Example 3> Cement admixture 1-1' was prepared by mixing cement admixture 1-1 used in Experimental Example 1 with sodium sulfate (99% purity, particle size range 0.1-0.5 mm) in a 3:1 ratio. The cement composition was prepared and evaluated in the same manner as in Experimental Example 2, except that cement admixture 1-1' was used. The hydration reaction rate of cement admixture 1-1' was 85%, and the maximum particle size was 100 μm. For comparative examples, cement admixture 1-1' was not used, and the cement was replaced with sodium sulfate so that the sodium sulfate content was the same as that of the comparative example with the same cement composition. The evaluation was performed in the same manner as in the example, except that the prepared cement admixture 1-1' was not used, and the cement was replaced with sodium sulfate so that the sodium sulfate content was the same. The results are shown in Table 4 below.

[0069] [Table 4] [Industrial applicability]

[0070] The present invention can be suitably used as a cement admixture, particularly in the fields of civil engineering and construction.

Claims

1. The hydration reaction rate after 30 minutes of mixing with an admixture at a water-to-admixture ratio of 2:1 is 30-90%. A cement admixture with a maximum particle size of 300 μm or less.

2. Brain value is 3,000 to 10,000 cm ２ The cement admixture according to claim 1, wherein the amount is / g.

3. A cement admixture according to claim 1 or 2, comprising composite particles containing calcium carbonate and calcium oxide, wherein the mass ratio of calcium carbonate to calcium oxide (calcium carbonate / calcium oxide) is 5 / 95 to 99.5 / 0.5, and the total amount of calcium carbonate and calcium oxide is 80% by mass or more.

4. The cement admixture according to claim 1 or 2, further comprising an alkali metal sulfate.

5. A cement composition comprising the cement admixture according to claim 1 or 2 and cement.

Images