Cement admixture and cement composition

Abstract

This cement admixture contains calcium carbonate and calcium hydroxide in each particle thereof. The mass ratio (calcium carbonate / calcium hydroxide) of the calcium carbonate to the calcium hydroxide is 30 / 70 to 97 / 3. The total amount of the calcium carbonate and the calcium hydroxide in the cement admixture is 50 mass% or more.

Description

[Technical Field]

[0001] The present invention relates to a cement admixture and a cement composition used in the fields of civil engineering, construction, etc. [Background technology]

[0002] BACKGROUND ART In recent years, in the fields of civil engineering, construction, etc., demand for concrete is expected to increase due to an increase in the number and size of structures using concrete, and the need to repair or reinforce aging structures. On the other hand, from an environmental perspective, various types of concrete using cement that emits less CO2 during production and cement that makes effective use of waste materials have been studied.

[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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4810914 Summary of the Invention [Problem to be solved by the invention]

[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 basic evaluation of the setting property, early strength, drying shrinkage property, etc., 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 early strength development and can ensure good setting properties and drying shrinkage properties. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by a cement admixture containing calcium carbonate and calcium hydroxide in each particle, with the mass ratio between these in a predetermined range and with a high total content of calcium carbonate and calcium hydroxide, thereby completing the present invention. That is, the present invention is as follows.

[0008] [1] A cement admixture containing calcium carbonate and calcium hydroxide in one particle, wherein the mass ratio of the calcium carbonate to the calcium hydroxide (calcium carbonate / calcium hydroxide) is 30 / 70 to 97 / 3, and the total amount of the calcium carbonate and the calcium hydroxide is 50 mass% or more in the cement admixture. [2] The cement admixture according to [1], wherein the time required for a mixed solution obtained by mixing the cement admixture and water in a mass ratio of 1:300 to change from pH 8 to pH 11 is 10 to 30 seconds. [3] The cement admixture according to [1] or [2], which is a carbonate of by-product slaked lime. [4] The cement admixture according to any one of [1] to [3], wherein the median diameter is 20 to 60 μm. [5] A cement composition comprising the cement admixture according to any one of [1] to [4] and cement. [6] The cement composition according to [5], wherein the cement is blast furnace cement. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a cement admixture that exhibits good early strength development and can ensure good setting properties and drying shrinkage properties. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the results of pH measurement of cement admixture A and cement admixture B. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, one embodiment of the present invention (the present embodiment) will be described in detail. Note that parts and % used in this specification are based on mass unless otherwise specified.

[0012] [Cement admixture] The cement admixture according to this embodiment contains calcium carbonate and calcium hydroxide in one particle. The coexistence of calcium carbonate and calcium hydroxide in one particle allows for better early strength development than when they are present separately. On the other hand, when calcium carbonate and calcium hydroxide are mixed in powder form, the elution of alkali is uneven, making it difficult to achieve good early strength development.

[0013] The mass ratio of calcium carbonate to calcium hydroxide (calcium carbonate / calcium hydroxide) is 30 / 70 to 97 / 3, preferably 50 / 50 to 90 / 10, and more preferably 70 / 30 to 85 / 15. If the mass ratio is less than 30 / 70 or more than 97 / 3, it becomes difficult to obtain good early strength development and setting properties.

[0014] The total content of calcium carbonate and calcium hydroxide in the cement admixture is 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more. If the total content is less than 50% by mass, it becomes difficult to achieve good early strength development. The upper limit of the total content is 95% by mass.

[0015] As described above, the cement admixture according to this embodiment contains calcium carbonate and calcium hydroxide 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 hydroxide 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 hydroxide present in large amounts near the center to gradually elute calcium, making it easier to achieve good early strength development and also easier to ensure good setting properties and drying shrinkage properties.

[0016] In relation to the core-shell structure, in the cement admixture according to this embodiment, the time required for a mixed solution obtained by mixing the cement admixture and water at a mass ratio of 1:300 to change from pH 8 to pH 11 is preferably 10 to 30 seconds, more preferably 13 to 25 seconds. This aspect suggests that the cement admixture has a core-shell structure. That is, in the mixed solution, calcium carbonate, which is present in large amounts on the surface, dissolves first. Because calcium carbonate has a lower pH than calcium hydroxide, the pH remains near 8 to 9 for a while (for example, 5 to 10 seconds) immediately after the mixed solution is prepared. Thereafter, as calcium hydroxide near the center dissolves, the pH begins to increase and eventually reaches near 11.

[0017] On the other hand, the pH of the mixture containing only calcium carbonate powder remains around 8 even after 30 seconds. In the mixture containing equal amounts of calcium hydroxide and calcium carbonate, the strong basicity of calcium hydroxide dominates, so the pH rises immediately after preparation of the mixture, reaching around pH 11 within about 10 seconds. As described above, in the cement admixture according to this embodiment, the time required for the pH to change from 8 to 11 is about 10 to 30 seconds, which is presumed to be due to the presence of a core-shell structure, which makes it easier to obtain good early strength development more efficiently and also makes it possible to ensure good setting properties and drying shrinkage properties.

[0018] The pH can be measured by adding 1 g of sample to 300 ml (300 g) of pure water at once while stirring with a stirrer, without generating dust, and then measuring the pH change every second with a pH meter. The stirring speed is 600 rpm, and the water temperature during measurement is 20°C. The sample has a Blaine specific surface area of ​​4500 to 4700 cm. 2 It is preferable to use one having a Blaine specific surface area of ​​1 / g. The Blaine specific surface area is measured based on the specific surface area test described in JIS R 5201 "Physical Testing Methods for Cement."

[0019] From the viewpoint of ensuring good fluidity during use of the admixture and good early strength development due to uniform dispersion of the admixture particles, the median diameter of the cement admixture according to this embodiment is preferably 20 to 60 μm, more preferably 25 to 50 μm. The median diameter can be determined, for example, using a laser diffraction / scattering particle size distribution analyzer manufactured by HORIBA Corporation.

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

[0021] Examples of by-product slaked lime, which is the raw material for carbonated by-product slaked lime, include by-product slaked lime produced during the acetylene gas production process using the calcium carbide method (there are wet and dry products depending on the acetylene gas production method), and by-product slaked lime contained in the dust captured during 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, and 0.1 to 6.0% (preferably 0.1 to 3.0%) iron oxide. These proportions can be confirmed by X-ray fluorescence measurement and mass loss determined by differential thermogravimetric analysis (TG-DTA) (Ca(OH)2: approximately 405°C to 515°C, CaCO3: approximately 650°C to 765°C). The volume average particle size measured by laser diffraction / scattering is approximately 50 to 100 μm. Furthermore, the moisture content measured by the loss on drying method in JIS K0068 "Method for measuring moisture content in chemical products" is preferably 10% or less. Furthermore, sulfur compounds such as CaS, A12S3, and CaC2·CaS may be contained, but the content is preferably 2% or less.

[0022] The Blaine specific surface area of ​​this by-product slaked lime is 2500 to 6000 cm 2 / g, and 3000 to 5500 cm 2 / g. 2 / g, the desired carbonation treatment becomes easier.

[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 by-product slaked lime can be carbonated, for example, by placing the by-product slaked lime in a carbon dioxide-containing gas atmosphere at a temperature in the range of 0 to 75° C., and heating and / or humidifying as necessary.

[0025] The carbon dioxide-containing gas may be exhaust gas generated from a cement factory or a coal-fired power plant, exhaust gas generated during exhaust treatment in a paint factory, etc. In such cases, there is no need for heating or humidification, etc. The proportion of carbon dioxide in the carbon dioxide-containing gas is preferably 5% by volume or more, preferably 10 to 100% by volume, and more preferably 15 to 100% by volume.

[0026] The carbon dioxide-containing gas may contain moisture (water vapor). For example, the relative humidity at 20° C. is preferably 80% RH or higher, and more preferably 90% RH or higher.

[0027] The carbonation rate of the by-product slaked lime can be adjusted by adjusting the carbon dioxide concentration, temperature, humidity, carbonation time, etc. Therefore, the surface of the main component, calcium hydroxide, is carbonated to form calcium carbonate, and the core-shell structure described above can be efficiently formed. In addition, the mass ratio of calcium carbonate to calcium hydroxide can be easily adjusted.

[0028] The Blaine specific surface area of ​​the carbonated by-product slaked lime produced in this way is 2500 to 6000 cm 2 / g, and 3000 to 5500 cm 2 / g, and more preferably 4000 to 5000 cm 2 / g. 2 / g, good early strength development is more easily obtained, and good setting properties and drying shrinkage properties are more easily ensured.

[0029] [Cement composition] The cement composition according to this embodiment contains the cement admixture according to this embodiment and cement.

[0030] The cement according to the present embodiment is not particularly limited, but examples thereof include various types of Portland cement 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 blended cement 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, with blast furnace cement being more preferred.

[0031] The cement composition may contain known additives that can be commonly blended, provided that they do not impair the effects of the present invention. 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.

[0032] The cement composition preferably contains the cement admixture according to this embodiment in an amount of 1 to 30 mass %, more preferably 2 to 20 mass %, and even more preferably 3 to 10 mass %, from the viewpoint of effectively exhibiting the functions of the cement admixture.

[0033] 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.

[0034] 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. [Example]

[0035] The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these examples as long as it does not deviate from the gist of the invention.

[0036] [Experimental Example 1] (Preparation of cement admixture) Cement admixture A As a by-product slaked lime, by-product slaked lime (density: 2.21 g / cm) produced in the acetylene gas manufacturing process using the calcium carbide method was used. 3 , Blaine specific surface area: 4680 cm 2 This was carbonated under the following conditions, and then crushed and sieved to obtain cement admixture A (calcium carbonate / calcium hydroxide = 75 / 25 (mass ratio), total amount of calcium carbonate and calcium hydroxide in cement admixture A: 94 mass%, density: 2.53 g / cm 3 , Blaine specific surface area 4520cm 2 / g, median diameter 32 μm) was prepared.

[0037] <Carbonation treatment> Carbonation was carried out in a temperature and humidity controlled room at 20°C, 60% RH, and a carbon dioxide concentration of 5% by volume.

[0038] Cement admixture B Limestone powder (manufactured by Joetsu Mining Co., Ltd., 100 mesh, density: 2.74 g / cm 3 , specific surface area: 4550cm 2 / g) and the by-product slaked lime described above were mixed so that the calcium carbonate / calcium hydroxide ratio in cement admixture B was 75 / 25 (mass ratio), and the mixture was sieved to obtain cement admixture B (calcium carbonate / calcium hydroxide = 75 / 25 (mass ratio), the total amount of calcium carbonate and calcium hydroxide in cement admixture B was 99 mass%, and the density was 2.61 g / cm3 , Blaine specific surface area 4520cm 2 / g, median diameter 21 μm) was prepared.

[0039] Cement admixture C The above-mentioned by-product slaked lime was used as cement admixture C (calcium carbonate / calcium hydroxide = 0 / 100 (mass ratio), the total amount of calcium carbonate and calcium hydroxide in cement admixture C was 91 mass%, and the density was 2.21 g / cm 3 , Blaine specific surface area 4680cm 2 / g, median diameter 47 μm).

[0040] (pH measurement of each admixture) Cement admixtures A and B were each measured using a pH meter (D-53S) manufactured by HORIBA. Specifically, while stirring 300 ml (300 g) of pure water with a stirrer, 1 g of sample was added all at once, to the extent that dust would not be generated, and the pH change every second after the addition was measured with the pH meter. The stirring speed was 600 rpm, and the water temperature during measurement was 20°C. The results are shown in Figure 1.

[0041] As can be seen from Figure 1, the time required for cement admixture A to change from pH 8 to pH 11 was 15 seconds, which was within the range of 10 to 30 seconds. On the other hand, the time required for cement admixture B to change from pH 8 to pH 11 was 7 seconds, which was a faster increase in pH than cement admixture A.

[0042] (Preparation and evaluation of cement compositions) Sand was mixed into a cement composition consisting of each example's cement admixture and cement, and water (tap water) was added so that the mass ratio of water to cement was 0.5, and the following evaluations were carried out. The results are shown in Table 1. The cement admixture was mixed into the cement composition so that it accounted for 5% of the cement admixture, and 300 parts of sand were mixed with 100 parts of cement. The materials used were as follows: Cement: B-type blast furnace cement (commercial product, density 3.05 g / cm 3 , Blaine specific surface area 3700cm 2 / g, slag replacement rate: 42.8%) Sand: Fine aggregate (manufactured by the Cement Association, JIS strength test standard sand) ·water:

[0043] Compression strength The strength was measured at ages of 3, 7 and 28 days in accordance with JIS R 5201 "Physical Testing Methods for Cement." After demolding, the concrete was cured underwater.

[0044] ·Condensation The time taken for the setting to begin and end was measured in accordance with JIS R 5201 "Physical Testing Methods for Cement."

[0045] Drying shrinkage The length change rate on the 28th day of age was measured in accordance with Appendix A of JIS A 1129 "Method for measuring length change in mortar and concrete," which is a test method for free shrinkage strain due to drying of mortar and concrete.

[0046] [Table 1]

[0047] Cement admixture A, which contains calcium carbonate and calcium hydroxide in a specified ratio per particle, has good setting properties and drying shrinkage characteristics, while also showing better initial strength development at 3 days of age than other admixtures.

[0048] [Experimental Example 2] In the preparation of cement admixture A, the carbonation conditions were changed to prepare cement admixtures with calcium carbonate / calcium hydroxide mass ratios shown in Table 2, and cement compositions were prepared and evaluated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0049] [Table 2]

[0050] [Experimental Example 3] In preparing cement admixture A, a cement admixture having a median diameter shown in Table 2 was prepared by pulverization and sieving, and a cement composition was prepared and evaluated in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0051] [Table 3] [Industrial Applicability]

[0052] 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 hydroxide in one particle, a mass ratio of the calcium carbonate to the calcium hydroxide (calcium carbonate / calcium hydroxide) of 30 / 70 to 97 / 3; The total amount of the calcium carbonate and the calcium hydroxide in the cement admixture is 50% by mass or more, The cement admixture is such that the time required for a mixed solution obtained by mixing the cement admixture with water at a mass ratio of 1:300 to change from pH 8 to pH 11 is 10 to 30 seconds.

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

3. The cement admixture according to claim 1 or 2, wherein the median diameter is 20 to 60 μm.

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

5. 5. The cement composition of claim 4, wherein the cement is a blast furnace cement.

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