Cement admixture, expansion material, and cement composition

Abstract

Provided is a cement admixture comprising, in each particle thereof, calcium carbonate and calcium oxide, wherein the mass ratio of the calcium carbonate and the calcium oxide (calcium carbonate / calcium oxide) is 5 / 95 to 99.5 / 0.5, and the total amount of the calcium carbonate and the calcium oxide in the cement admixture is not less than 80 mass%.

Description

Cement admixture, expansive material, and cement composition

[0001] The present invention relates to a cement admixture, an expansive material, and a cement composition.

[0002] In recent years, the demand for concrete is expected to increase in the fields of civil engineering and construction due to the increase in the number of structures using concrete and the need to repair or reinforce aging structures. ２ Various types of concrete using cement that produces less waste and cement that makes effective use of waste materials have been investigated.

[0003] For example, Patent Document 1 proposes a fine powder for concrete compositions that, when used as an admixture for concrete, can reduce changes in fluidity over time and improve resistance to material separation at low cost without requiring major revisions to the concrete's blending or mixing.

[0004] Patent No. 4810914

[0005] The fine powder for concrete composition described in Patent Document 1 contains more than 0.0 mass % but less than 1.0 mass % of quicklime fine powder and / or slaked lime fine powder, calculated as free calcium oxide, and 95.0 mass % or more of calcium carbonate fine powder. However, there is no evaluation of basic properties such as setting speed, early strength, and expansion property, or durability such as carbonation resistance, and it can be said that its practicality is questionable.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide a cement admixture that has good expansion properties and early strength development properties and can ensure carbonation resistance.

[0007] As a result of intensive research to solve the above problems, the present inventors have come up with the following invention and found that the above problems can be solved.

[0008] [1] A cement admixture containing calcium carbonate and calcium oxide in each particle, wherein the mass ratio of the calcium carbonate to the calcium oxide (calcium carbonate / calcium oxide) is 5 / 95 to 99.5 / 0.5, and the total amount of the calcium carbonate and the calcium oxide is 80 mass% or more in the cement admixture. [2] The cement admixture according to [1] above, wherein the mass change rate when left to stand for 24 hours in an environment of 20°C and 80% RH is 50% or less compared to the mass change rate of a mixture of calcium carbonate and calcium oxide in the same mass ratio. [3] The cement admixture according to [1] or [2] above, wherein the cement admixture is a carbonate of by-product slaked lime. [4] The cement admixture according to any one of [1] to [3] above, wherein the median diameter is 15 to 100 μm. [5] An expansive agent containing the cement admixture according to any one of [1] to [4] above. [6] A cement composition containing the expansive agent according to [5] above and cement. [7] The cement composition according to [6] above, wherein the cement is blast furnace cement.

[0009] According to the present invention, it is possible to provide a cement admixture that has good expansion properties and early strength development properties and can ensure carbonation resistance.

[0010] Hereinafter, one embodiment of the present invention (the present embodiment) will be described in detail, but the present invention is not limited to this embodiment. In addition, "%" and "parts" in this specification are based on mass unless otherwise specified.

[0011] [Cement admixture] The cement admixture according to this embodiment is a cement admixture containing calcium carbonate and calcium oxide in one particle, and the mass ratio of the calcium carbonate to the calcium oxide (calcium carbonate / calcium oxide) is 5 / 95 to 99.5 / 0.5, and the total amount of the calcium carbonate and the calcium oxide is 80 mass% or more in the cement admixture.

[0012] The mass ratio of calcium carbonate to calcium oxide (calcium carbonate / calcium oxide) is 5 / 95 to 99.5 / 0.5. If the mass ratio is less than 5 / 95 or more than 99.5 / 0.5, good expansion and early strength development may not be achieved, and carbonation resistance may not be ensured. Furthermore, the mass ratio is preferably 10 / 90 to 90 / 10, more preferably 15 / 85 to 70 / 30, and even more preferably 20 / 80 to 50 / 50. Increasing the proportion of calcium carbonate in this mass ratio makes it easier to ensure good early strength development and carbonation resistance, while increasing the proportion of calcium oxide makes it easier to obtain good expansion. The mass ratio of calcium carbonate to calcium oxide in the cement admixture can be calculated, for example, from the mass loss determined by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA).

[0013] The total amount of calcium carbonate and calcium oxide in the cement admixture is 80% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more. If the total amount is less than 80% by mass, it becomes difficult to obtain good early strength development. 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, from the mass loss determined by fluorescent X-ray measurement and differential thermogravimetric analysis (TG-DTA).

[0014] In addition to the calcium carbonate and calcium oxide, the cement admixture preferably contains 4% by mass or less of calcium sulfate, 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, good early strength and fluidity are obtained. The lower limit is not particularly limited, but may be 0% by mass.

[0015] As described above, the cement admixture according to this embodiment contains calcium carbonate and calcium oxide in each particle, and although the state of their mixture is not particularly limited, it is preferable that the admixture has a core-shell structure in which calcium oxide is mainly present in the center and calcium carbonate is mainly present on the outside. The core-shell structure allows the calcium carbonate present in large amounts on the outside to first suppress excessive calcium elution, and then the calcium oxide present in large amounts near the center reacts with water in stages to elute calcium, making it easier to obtain good expansion properties and early strength development, and also making it easier to ensure carbonation resistance.

[0016] In relation to the core-shell structure, the cement admixture of this embodiment exhibits a mass change rate of preferably 50% or less, more preferably 40% or less, and even more preferably 35% or less, when left standing for 24 hours in an environment at 20°C and 80% RH, compared to the mass change rate of a mixture of calcium carbonate and calcium oxide in the same mass ratio as the cement admixture of the present invention. This suggests that the cement admixture has a core-shell structure. That is, the calcium carbonate present in large amounts on the surface inhibits the penetration of atmospheric moisture into the center, slowing the slaking reaction of calcium oxide. On the other hand, a mixture of calcium oxide and calcium carbonate has calcium oxide exposed to the atmosphere, which facilitates the slaking reaction due to atmospheric moisture. In this invention, the mass change rate can be calculated by spreading approximately 10 g of a sample thinly on an aluminum dish with a diameter of approximately 10 cm, placing the sample in an environmental test chamber at 20°C and 80% RH without allowing the sample to move about, weighing the mass change after 24 hours on an electronic balance, and dividing the result by the mass before measurement.

[0017] In this way, the mass change rate of the cement admixture according to this embodiment is 50% or less of the mass change rate of a mixture in which calcium carbonate and calcium oxide are mixed in the same mass ratio as the cement admixture, which is presumed to have a core-shell structure, making it easier to obtain good expansion properties and early strength development more efficiently and also making it possible to ensure better carbonation resistance.

[0018] The Blaine specific surface area of ​​the cement admixture according to this embodiment is 2,500 to 6,000 cm from the viewpoint of improving the fluidity of the cement composition. ２ / g, and 2,700 to 5,500 cm ２ / g, and more preferably 3,000 to 4,700 cm ２ / g. The Blaine specific surface area is measured based on the specific surface area test described in JIS R 5201:2015 "Physical testing methods for cement."

[0019] From the viewpoint of ensuring good fluidity and good early strength development when the admixture is used, the median diameter of the cement admixture according to this embodiment is preferably 15 to 100 μm, more preferably 25 to 70 μm. When the median diameter of the cement admixture is within the above range, the admixture particles are uniformly dispersed, making it easier to obtain good expansion properties and early strength development, and also easier to ensure carbonation resistance. In the present invention, the median diameter can be determined, for example, using a laser diffraction / scattering particle size distribution analyzer manufactured by HORIBA.

[0020] The cement admixture described above can be produced by carbonating commercially available slaked lime that has been particle-sized, but in this embodiment, it is preferable to use by-product slaked lime from the viewpoints of effective utilization of waste materials and ease of adjusting the mass ratio of calcium carbonate to calcium oxide. In other words, the cement admixture according to this embodiment is preferably a carbonate of by-product slaked lime.

[0021] Examples of by-product slaked lime include acetylene by-product slaked lime such as by-product slaked lime produced in the acetylene gas production process by the calcium carbide method (there are wet and dry products depending on the acetylene gas production method), and by-product slaked lime contained in dust captured in the wet dust collection process of a calcium carbide electric furnace. By-product slaked lime contains, for example, 65 to 95% (preferably 70 to 90%) calcium hydroxide, 0.1 to 10% calcium carbonate, 0.1 to 6.0% (preferably 0.1 to 3.0%) iron oxide, etc. These proportions are determined by the mass loss (Ca(OH) ２ : Around 405 ° C to 515 ° C, CaCO ３ The volume average particle size measured by the laser diffraction / scattering method is about 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 in chemical products" is preferably 10% or less. In addition, CaS, Al ２ S ３ , and CaC ２ Sulfur compounds such as CaS may be included, but it is preferable that the content is 2% or less.

[0022] The Blaine specific surface area of ​​this by-product slaked lime is 2,500 to 6,000 cm ２ / g, and 3,000 to 5,500 cm ２ / g. It is more preferable that the Blaine specific surface area of ​​the by-product slaked lime is 2,500 to 6,000 cm ２ / g, the desired carbonation treatment can be easily carried out.

[0023] From the viewpoint of ease of handling, the median diameter of the by-product slaked lime is preferably 1 to 300 μm, and more preferably 10 to 100 μm.

[0024] The cement admixture according to this embodiment can be used in a range of temperatures, for example, 100°C or higher, CO ２It can be produced using carbon dioxide gas with a concentration of 5% by volume or more. The raw material can be the by-product slaked lime, etc., which contains calcium hydroxide as a main component. By carbonating the raw material in carbon dioxide gas, the surface of the main component calcium hydroxide is carbonated to form calcium carbonate, and a cement admixture can be produced in which calcium oxide is mainly present in the center.

[0025] The temperature of the carbon dioxide gas is 100° C. or higher, preferably 450° C. or higher, and more preferably 480° C. or higher. There is no particular upper limit, but from the viewpoint of production costs, it is preferably 1000° C. or lower, more preferably 800° C. or lower, and even more preferably 700° C. or lower.

[0026] CO in carbon dioxide ２ The concentration is 5% by volume or more, preferably 10 to 100% by volume, and more preferably 20 to 100% by volume.

[0027] As the carbon dioxide gas, exhaust gases generated from cement factories and coal-fired power plants, exhaust gases generated during exhaust treatment in paint factories, etc. can be used. ２ The concentration can be adjusted appropriately.

[0028] The cement admixture according to this embodiment is preferably produced by heat treating the raw materials before the carbonation treatment with carbon dioxide, which makes it possible to easily adjust the mass ratio of calcium carbonate to calcium oxide in the cement admixture and efficiently form the core-shell structure described above.

[0029] The atmospheric temperature for the 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 particular upper limit, but from the viewpoint of production costs, it is preferably 1300° C. or lower.

[0030] The temperature of the carbon dioxide gas and CO ２By adjusting the concentration, heat treatment, and carbonation time, the mass ratio of calcium carbonate to calcium oxide can be easily adjusted, and the core-shell structure described above can be efficiently formed. For example, by increasing the atmospheric temperature of the heat treatment, the proportion of calcium oxide can be increased, and by adjusting the temperature of the carbon dioxide gas and the CO ２ By increasing the concentration, the proportion of calcium carbonate can be increased.

[0031] [Expansive Material] The expansive material according to this embodiment includes the cement admixture of the present invention.

[0032] The content of the cement admixture in the expansive material is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. It may also be 100% by mass.

[0033] The cement admixture in the expansive agent preferably has a mass ratio of calcium carbonate to calcium oxide (calcium carbonate / calcium oxide) of 5 / 95 to 25 / 75, more preferably 10 / 90 to 23 / 77, and even more preferably 15 / 85 to 20 / 80. When the mass ratio of calcium carbonate to calcium oxide is within the above range, good expansion properties are easily obtained.

[0034] [Cement Composition] The cement composition according to this embodiment contains the expansive material of the present invention and cement.

[0035] The cement according to this embodiment is not particularly limited, but examples thereof include various Portland cements such as ordinary, early strength, medium heat, low heat, and white; ecocement produced using municipal waste incineration ash and sewage sludge incineration ash as raw materials; and mixed cements containing blast furnace slag, silica fume, limestone, fly ash, gypsum, etc. Among these, Portland cement and blast furnace cement are preferred as cements that can provide good early strength development, and blast furnace cement is more preferred.

[0036] The cement composition may contain known additives that can be generally blended, provided that the effects of the present invention are not impaired. Examples of additives include, but are not limited to, rust inhibitors, colorants, polymers, fibers, fluidizing agents, carbonation inhibitors, waterproofing agents, thickeners, waterproofing agents, retarders, early-strengthening agents, accelerators, water-reducing agents, high-performance (AE) water-reducing agents, foaming agents, air-entraining agents, drying shrinkage-reducing agents, quick-setting agents, expansion agents, cold-resistance accelerators, efflorescence inhibitors, alkali-aggregate reaction inhibitors, black spot-reducing agents, and environmental cleanup admixtures. These additives may be used alone or in combination of two or more.

[0037] The content of the expansive agent according to the present embodiment in the cement composition is preferably 1 to 30 mass %, more preferably 2 to 25 mass %, and even more preferably 3 to 20 mass %, from the viewpoint of effectively exhibiting the function of the expansive agent.

[0038] The cement composition preferably contains aggregate. The aggregate used may be the same fine aggregate or coarse aggregate as that used in ordinary cement mortar or concrete. 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, heavy aggregate, etc., or a combination of these may be used.

[0039] The content 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, per 100 parts by mass of cement in the cement composition.

[0040] The cement composition of this embodiment may be prepared by mixing the respective materials at the time of application, or may be prepared by mixing some or all of them in advance. The method of mixing the respective materials and water is not particularly limited, and the respective materials may be mixed at the time of application, or may be mixed some or all of them in advance. Alternatively, some of the materials may be mixed with water, and then the remaining materials may be mixed.

[0041] Any existing mixer can be used as the mixer, and examples of such mixers include a tilting mixer, an omni mixer, a Henschel mixer, a V-type mixer, and a Nauta mixer.

[0042] The present invention will be further explained below based on experimental examples, but the present invention is not limited to these.

[0043] <Experimental Example 1> (Production of cement admixture) Cement admixture A: As a raw material, by-product slaked lime (density: 2.21 g / cm 3 ) produced in the acetylene gas production process by the calcium carbide method was used. ３ , Blaine specific surface area: 4,680 cm ２ / g, Ca(OH) ２ This was heat-treated in an atmosphere at a temperature of 1000°C, and then heated at a temperature of 450°C and CO ２ The mixture was carbonated with carbon dioxide gas having a concentration of 50% by volume, and then crushed and sieved to obtain cement admixture A (calcium carbonate / calcium oxide = 15 / 85 (mass ratio), total amount of calcium carbonate and calcium oxide in cement admixture A: 94 mass%, density: 2.95 g / cm ３ , Blaine specific surface area: 4,520 cm ２ The mass ratio and total amount of calcium carbonate and calcium oxide were calculated from the mass loss determined by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA).

[0044] Cement admixture B: As a raw material, limestone fine powder (manufactured by Joetsu Mining Co., Ltd., 100 mesh, density: 2.74 g / cm ３ , Blaine specific surface area: 4,550 cm ２ / g) and calcium oxide (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 / cm ３ , Blaine specific surface area: 4,490 cm ２ / g) was mixed with the calcium carbonate / calcium oxide in cement admixture B so that the calcium carbonate / calcium oxide ratio in cement admixture B was 15 / 85 (mass ratio), and sieved to obtain cement admixture B (calcium carbonate / calcium oxide = 15 / 85 (mass ratio), total amount of calcium carbonate and calcium oxide in cement admixture B: 99 mass%, density: 2.98 g / cm ３ , Blaine specific surface area: 4,520 cm ２ The mass ratio and total amount of calcium carbonate and calcium oxide were calculated from the mass loss determined by fluorescent X-ray measurement and differential thermogravimetric analysis (TG-DTA).

[0045] Cement admixture C The calcium oxide used in cement admixture B was replaced with cement admixture C (calcium carbonate / calcium oxide = 0 / 100 (mass ratio), total amount of calcium oxide in cement admixture C: 91 mass%, density: 3.21 g / cm ３ , Blaine specific surface area: 4,490 cm ２ / g, median diameter: 57 μm). The mass ratio and total amount of calcium carbonate and calcium oxide were calculated from the mass loss determined by fluorescent X-ray measurement and differential thermogravimetric analysis (TG-DTA).

[0046] Cement admixture D: As a raw material, commercially available slaked lime (Ueda Lime Manufacturing, density: 2.27 g / cm ３ , Blaine specific surface area: 12,670 cm ２ / g, Ca(OH) ２ This was heat-treated in an atmosphere at a temperature of 600°C, and then heated in a CO atmosphere at a temperature of 450°C. ２ The mixture was carbonated with carbon dioxide gas having a concentration of 50% by volume, and then crushed and sieved to obtain cement admixture D (calcium carbonate / calcium oxide = 15 / 85 (mass ratio), total amount of calcium carbonate and calcium oxide in cement admixture D: 99 mass%, density: 2.97 g / cm ３ , Blaine specific surface area: 10,740 cm ２ The mass ratio and total amount of calcium carbonate and calcium oxide were calculated from the mass loss determined by X-ray fluorescence measurement and differential thermogravimetric analysis (TG-DTA).

[0047] (Measurement of Mass Change Rate of Each Admixture) The mass change rate of each cement admixture A to D was measured. Specifically, about 10 g of sample was thinly spread on an aluminum dish with a diameter of about 10 cm, and the sample was left to stand in an environmental test chamber at 20°C and 80% RH without floating around. The mass after 24 hours was measured using an electronic balance, and the value was divided by the mass before measurement to calculate the mass change rate. The results are shown in Table 1.

[0048]

[0049] From Table 1, it can be seen that the mass change rates after 24 hours for cement admixtures A and D were within a range of 50% or less compared to admixture B. Compared to cement admixture B, cement admixtures A and D have the same mass ratio of calcium carbonate to calcium oxide and similar total amounts of calcium carbonate and calcium oxide, but have a lower mass change rate after 24 hours, which suggests that they have a core-shell structure.

[0050] (Preparation and evaluation of cement compositions) Sand was mixed with the cement composition consisting of the cement admixture and cement of each example, and water (tap water and sewerage water) was added so that the water / cement ratio was 0.5 (mass ratio), and the following evaluations were carried out. The results are shown in Table 2. The cement admixture was mixed into the cement composition so that it accounted for 10% of the cement admixture, and 300 parts by mass of sand was mixed with 100 parts by mass of cement. The materials used were as follows: Cement: Ordinary Portland cement (research cement, density 3.16 g / cm ３ , Blaine specific surface area 3,260 cm ２ / g) to ground granulated blast furnace slag (commercially available, density 3.91 g / cm ３ , Blaine specific surface area 4,190 cm ２ / g) was substituted by 42%. Sand: fine aggregate (manufactured by the Cement Association, standard sand for JIS strength tests). Water: tap water.

[0051] Compressive strength: The strength was measured at ages of 3 days, 7 days, and 28 days according to the method specified in JIS R 5201:2015 "Physical testing methods for cement." After demolding, the samples were cured in water.

[0052] Expansion The length change rate of mortar containing expansive additive type 30 was measured on the 7th day of age in accordance with the method specified in Appendix A of JIS A 6202:2017 "Expansive additives for concrete" "Test method for expansion of expansive additive mortar."

[0053] Carbonation resistance Test specimens were made of mortar, and 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," except that the test specimen dimensions were 40 mm x 40 mm x 160 mm.

[0054] Fluidity The flow value of the mortar was measured in accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement."

[0055]

[0056] When cement admixtures A and D, which contain calcium carbonate and calcium oxide in a specified ratio per particle, were used, the cement composition had good expansion properties, carbonation resistance, and fluidity, and showed better early strength development than other admixtures.

[0057] <Experimental Example 2> Measurement of the mass change rate of the cement admixture and preparation and evaluation of a cement composition were carried out in the same manner as in Experimental Example 1, except that the carbonation conditions in the preparation of cement admixture A were changed to prepare a cement admixture with the calcium carbonate / calcium oxide mass ratio shown in Table 3. The results are shown in Table 3.

[0058]

[0059] <Experimental Example 3> Cement compositions were prepared and evaluated in the same manner as in Experimental Example 1, except that in the preparation of cement admixture A, a cement admixture having a median diameter shown in Table 4 was prepared by pulverization and sieving. The results are shown in Table 4.

[0060]

[0061] From the above results, it was confirmed that the cement admixture of the present invention contains calcium carbonate and calcium oxide in each particle, 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 in the cement admixture is 80 mass% or more, so that the cement admixture has good expansion properties and early strength development, and can also ensure carbonation resistance.

[0062] The present invention can be suitably used as a cement admixture, particularly in the fields of civil engineering and construction.

Claims

1. A cement admixture containing calcium carbonate and calcium oxide in one particle, wherein the mass ratio of the calcium carbonate to the calcium oxide (calcium carbonate / calcium oxide) is 5 / 95 to 99.5 / 0.5, and the total amount of the calcium carbonate and the calcium oxide in the cement admixture is 80 mass% or more.

2. The cement admixture according to claim 1, wherein the mass change rate when left to stand for 24 hours in an environment of 20°C and 80% RH is 50% or less compared to the mass change rate of a mixture of calcium carbonate and calcium oxide in the same mass ratio.

3. The cement admixture according to claim 1 or 2, which is a carbonate of by-product slaked lime.

4. The cement admixture according to claim 1 or 2, having a median diameter of 15 to 100 μm.

5. An expansive material comprising the cement admixture according to claim 1 or 2.

6. A cement composition comprising the expansive material according to claim 5 and cement.

7. The cement composition of claim 6, wherein the cement is a blast furnace cement.

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