Cement admixture and cement composition containing same

Abstract

The cement admixture contains calcium carbonate and calcium oxide in one particle, the mass ratio of the calcium carbonate to the calcium oxide (calcium carbonate / calcium oxide) is 25 / 75-99.5 / 0.5, and the total of the calcium carbonate and the calcium oxide is 80% by mass or more in the cement admixture.

Description

Technical Field

[0001] The present invention relates to a cement admixture and a cement composition containing the same. Background Art

[0002] In recent years, in the civil engineering field, construction field, etc., due to the increase or enlargement of structures using concrete, and the necessity of repairing or strengthening aging structures, an increase in the demand for concrete is expected.

[0003] On the other hand, from an environmental perspective, various studies have been conducted on concrete using cement with low CO2 emissions during manufacturing and cement that effectively utilizes waste.

[0004] For example, Patent Document 1 proposes a fine powder for a concrete composition that can achieve a reduction in the time-dependent change in fluidity and an improvement in material segregation resistance at low cost without significantly modifying the concrete mix or formulation when used as an admixture for concrete.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 4810914 Gazette Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] The fine powder for a concrete composition described in Patent Document 1 contains quicklime fine powder and / or slaked lime fine powder in an amount greater than 0.0% by mass and less than 1.0% by mass in terms of free calcium oxide, and contains 95.0% by mass or more of calcium carbonate fine powder. However, there are no basic evaluations such as setting property, initial strength, and dimensional stability, nor evaluations related to durability such as carbonation resistance, and it can be said that there are doubts about its practicality.

[0010] The present invention has been made to solve the above problems, and an object thereof is to provide a cement admixture having good initial strength presentation and capable of ensuring carbonation resistance.

[0011] Means for Solving the Problems

[0012] The inventors of the present application conducted in-depth research to solve the above problems, and as a result, came up with the following present invention and found that the problems can be solved. That is, the present invention is as follows.

[0013] [1]Cement admixture, which 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 25 / 75 to 99.5 / 0.5, and the total amount of the calcium carbonate and the calcium oxide is 80% by mass or more in the cement admixture.

[0014] [2]The cement admixture as described in [1] above has a mass change rate of 100 to 106% when left standing for 24 hours in an environment of 20°C and 80% RH.

[0015] [3]The cement admixture as described in [1] or [2] above is a carbide of by-product slaked lime.

[0016] [4]The cement admixture as described in any one of [1] to [3] above has a median particle size of 15 to 100 μm.

[0017] [5]Cement composition, which contains cement and the cement admixture as described in any one of [1] to [4] above.

[0018] [6]In the cement composition as described in [5] above, the cement is blast furnace cement.

[0019] Advantages of the Invention

[0020] According to the present invention, a cement admixture with good initial strength presentation and capable of ensuring carbonation resistance can be provided. Description of the Drawings

[0021] Figure 1 is a graph showing the mass change rate of the cement admixture of the present invention when left standing for 24 hours in an environment of 20°C and 80% RH. Detailed Description of the Embodiment

[0022] Hereinafter, an embodiment of the present invention (this embodiment) will be described in detail, but the present invention is not limited to this embodiment. It should be noted that unless otherwise specified, "%" and "parts" in this specification are based on mass.

[0023] [Cement Admixture]

[0024] The cement admixture according to this embodiment is a cement admixture containing calcium carbonate and calcium oxide in one particle, and it is required that the mass ratio of the calcium carbonate to the calcium oxide (calcium carbonate / calcium oxide) is 25 / 75 to 99.5 / 0.5, and the total amount of the calcium carbonate and the calcium oxide is 80% by mass or more in the cement admixture.

[0025] ​The mass ratio of calcium carbonate to calcium oxide (calcium carbonate / calcium oxide) is 25 / 75 to 99.5 / 0.5, preferably 50 / 50 to 97 / 3, and more preferably 70 / 30 to 95 / 5. If the mass ratio is less than 25 / 75 or greater than 99.5 / 0.5, it is difficult to obtain good initial strength presentation and anti-neutralization properties. It should be noted that the mass ratio of calcium carbonate to calcium oxide in the cement admixture can be calculated, for example, from the mass loss part obtained by fluorescence X-ray measurement and thermogravimetry-differential thermal analysis (TG-DTA).

[0026] The total amount of calcium carbonate and calcium oxide is 80% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more in the cement admixture. If the total amount is less than 80% by mass, it is difficult to obtain good initial strength presentation. It should be noted that the upper limit of the total amount is preferably 95% by mass. It should be noted that the total amount of calcium carbonate and calcium oxide in the cement admixture can be calculated, for example, from the mass loss part obtained by fluorescence X-ray measurement and thermogravimetry-differential thermal analysis (TG-DTA).

[0027] Regarding the cement admixture, in addition to the above-mentioned calcium carbonate and calcium oxide, it preferably contains 4% by mass or less of calcium sulfate, more preferably 2% by mass or less of calcium sulfate, and further preferably 1% by mass of calcium sulfate. If the content of calcium sulfate is within the above range, good initial strength and fluidity can be obtained. In addition, the lower limit is not particularly limited and can be 0% by mass.

[0028] As described above, the cement admixture according to this embodiment contains calcium carbonate and calcium oxide in one particle, and there is no particular limitation on its mixing state. For example, a core-shell structure in which calcium oxide mainly exists in the center and calcium carbonate mainly exists on the outside is preferred. By having a core-shell structure, calcium carbonate that mainly exists on the outside first inhibits the dissolution of excessive calcium, and then calcium oxide that mainly exists near the center reacts with water step by step to dissolve calcium, whereby good initial strength presentation is easily obtained, and good dimensional stability and anti-neutralization properties are more easily ensured.

[0029] Combined with the above core-shell structure, for the cement admixture involved in this embodiment, the mass change rate when standing for 24 hours in an environment of 20°C and 80% RH is preferably 100-106%, more preferably 100-105%, and further preferably 100-104%. For such a state, it can be speculated that the cement admixture forms a core-shell structure. That is, due to the relatively large amount of calcium carbonate on the surface, the penetration of moisture in the atmosphere into the central part is hindered, and the digestion reaction of calcium oxide proceeds slowly. It should be noted that in the present invention, the mass change rate can be calculated as follows: Spread about 10 g of the sample thinly on an aluminum dish with a diameter of about 10 cm, and place it statically in an environmental test chamber of 20°C and 80% RH in such a way that the sample does not splash. Weigh the mass after 24 hours using an electronic balance, and divide the obtained value by the mass before measurement.

[0030] On the other hand, the mass change rate in the case of only calcium carbonate powder is about 100-101%. For the mass change rate of the sample formed by mixing calcium oxide and calcium carbonate in equal amounts respectively, since calcium oxide is exposed to the atmosphere, the digestion reaction based on moisture in the atmosphere proceeds, and the mass change rate becomes 108% or more.

[0031] As described above, in the cement admixture involved in this embodiment, it can be speculated from the mass change rate of about 100-106% that it has a core-shell structure, and it is possible to easily and more efficiently obtain good initial strength presentation, and ensure better dimensional stability and anti-carbonation property.

[0032] From the viewpoint of making the fluidity of the cement composition good, the Blaine specific surface area of the cement admixture involved in this embodiment is preferably 2,500-6,000 cm 2 / g, more preferably 2,700-5,500 cm 2 / g, and further preferably 3,000-4,700 cm 2 / g. It should be noted that the Blaine specific surface area is obtained by measuring based on the specific surface area test described in JIS R 5201:2015 "Physical Test Methods for Cement".

[0033] From the viewpoints of ensuring good fluidity and good initial strength presentation when using the admixture, the median particle size of the cement admixture involved in this embodiment is preferably 15-100 μm, more preferably 25-70 μm. If the median particle size of the cement admixture is within the above range, the admixture particles are uniformly dispersed, and it is easy to obtain good initial strength presentation, and it is easy to ensure good dimensional stability and anti-carbonation property. It should be noted that in the present invention, the median particle size can be obtained by using, for example, a laser diffraction / scattering particle size distribution measuring device manufactured by HORIBA.

[0034] The above cement admixture can be produced by carbonating commercially available slaked lime whose particle size has been adjusted. In the present embodiment, from the viewpoints of effective utilization of waste and easy adjustment of the mass ratio of calcium carbonate to calcium oxide, by-product slaked lime is preferably used. That is, the cement admixture according to the present embodiment is preferably a carbonated product of by-product slaked lime.

[0035] Examples of the by-product slaked lime include by-product slaked lime by-produced in the manufacturing process of acetylene gas using the calcium carbide method (depending on the acetylene gas manufacturing method, there are wet products and dry products), and by-product slaked lime contained in the dust captured in the wet dust collection process of a calcium carbide electric furnace. The by-product slaked lime contains, for example, 65 to 95% (preferably 70 to 90%) of calcium hydroxide, 0.1 to 10% of calcium carbonate, 0.1 to 6.0% (preferably 0.1 to 3.0%) of iron oxide, etc. Their proportions can be confirmed by the mass loss part obtained by fluorescence X-ray measurement and thermogravimetry-differential thermal analysis (TG-DTA) (Ca(OH)2: around 405°C to 515°C, CaCO3: around 650°C to 765°C). The volume average particle size measured by the laser diffraction / scattering method is about 50 to 100 μm. In addition, the moisture content measured by the drying loss method specified in JIS K0068:2001 "Method for Determination of Moisture in Chemical Products" is preferably 10% or less. Additionally, it may contain sulfur compounds such as CaS, A12S3, and CaC2·CaS, but is preferably 2% or less.

[0036] In addition, the Blaine specific surface area of the by-product slaked lime is preferably 2,500 to 6,000 cm 2 / g, more preferably 3,000 to 5,500 cm 2 / g. By making the Blaine specific surface area of the by-product slaked lime 2,500 to 6,000 cm 2 / g, the desired carbonation treatment can be easily performed.

[0037] From the viewpoint of operability, the median particle size of the by-product slaked lime is preferably 1 to 300 μm, more preferably 10 to 100 μm.

[0038] The cement admixture according to the present embodiment can be produced, for example, using carbon dioxide gas at a temperature of 100°C or higher and a CO2 concentration of 5% by volume or higher. As the 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 carbon dioxide gas, the surface of the main component calcium hydroxide is carbonated to become calcium carbonate, and a cement admixture mainly containing calcium oxide in the center can be produced.

[0039] The temperature of the carbon dioxide gas is above 100°C, preferably above 450°C, more preferably above 480°C. There is no particular limitation on the upper limit, but from the perspective of manufacturing cost, it is preferably below 1000°C, more preferably below 800°C, and further preferably below 700°C.

[0040] The CO2 concentration in the carbon dioxide gas is 5 vol% or more, preferably 10 - 100 vol%, more preferably 20 - 100 vol%.

[0041] As the carbon dioxide gas, the waste gas generated by cement factories and coal-fired thermal power plants, the waste gas generated in the waste gas treatment of painting factories, etc. can be used, and can be appropriately adjusted to achieve the above temperature and CO2 concentration.

[0042] The cement admixture according to this embodiment is preferably manufactured by heat-treating the raw materials before the carbonation treatment of the above carbon dioxide gas. Thereby, the mass ratio of calcium carbonate to calcium oxide in the cement admixture can be easily adjusted, and the above core-shell structure can be efficiently formed.

[0043] As the atmosphere temperature of the heat treatment, it is preferably 400°C or more, more preferably 420°C or more, and further preferably 450°C or more. There is no particular limitation on the upper limit, but from the perspective of manufacturing cost, it is preferably below 600°C.

[0044] In addition to the temperature of the above carbon dioxide gas, CO2 concentration and heat treatment, by adjusting the carbonation time, etc., the mass ratio of calcium carbonate to calcium oxide can be easily adjusted, and the above core-shell structure can be efficiently formed. For example, by raising the atmosphere temperature of the heat treatment, the proportion of calcium oxide can be increased, and by raising the temperature and CO2 concentration of the carbon dioxide gas, the proportion of calcium carbonate can be increased.

[0045] [Cement composition]

[0046] The cement composition according to this embodiment contains cement and the cement admixture of this embodiment.

[0047] The cement according to this embodiment is not particularly limited, and examples include various Portland cements such as ordinary, early strength, medium heat, low heat, and white; environmental protection cements manufactured from municipal solid waste incineration ash and sewage sludge incineration ash; and blended cements containing blast furnace slag, silica fume, limestone, fly ash, gypsum, etc. Among them, as the cement that can obtain good initial strength presentation, Portland cement and blast furnace cement are preferred, and blast furnace cement is more preferred.

[0048] Within the scope that does not hinder the effects of the present invention, the cement composition may contain known additives that can be commonly compounded. As the additives, there is no particular limitation, and examples include rust inhibitors, colorants, polymers, fibers, fluidizers, neutralization inhibitors, waterproof agents, thickeners, waterproof agents, retarders, early strength agents, accelerators, water reducers, high-performance (AE) water reducers, foaming agents, foaming agents, AE agents, drying shrinkage reducing agents, quick-setting agents, expansion agents, cold resistance accelerators, efflorescence prevention agents, alkaline aggregate reaction inhibitors, black spot reducing agents, environmental purification admixtures, etc. These additives can be used alone or in combination of two or more kinds.

[0049] From the viewpoint of effectively exerting the function of this cement admixture, the cement admixture according to this embodiment in the cement composition is preferably 1 to 30% by mass, more preferably 2 to 25% by mass, and still more preferably 3 to 20% by mass.

[0050] The cement composition preferably contains aggregates. As the aggregates used, the same fine aggregates and coarse aggregates as those used in ordinary cement mortar and concrete can be used. That is, river sand, river pebbles, mountain sand, mountain pebbles, crushed stone, crushed sand, limestone aggregate, lime sand, silica sand, colored sand, artificial aggregate, blast furnace slag aggregate, sea sand, sea pebbles, artificial lightweight aggregate, and heavy aggregate, etc. can be used, or they can be combined.

[0051] Relative to 100 parts by mass of cement in the cement composition, the content ratio of the aggregate is preferably 40 parts by mass or more and 500 parts by mass or less, more preferably 50 parts by mass or more and 400 parts by mass or less, and still more preferably 60 parts by mass or more and 350 parts by mass or less.

[0052] The cement composition of this embodiment can be prepared by mixing each material during construction, or a part or all of them can be mixed in advance. In addition, the mixing method of each material and water is not particularly limited, and each material can be mixed during construction, or a part or all of them can be mixed in advance. In addition, it is also possible to mix the remaining materials after mixing a part of the materials with water.

[0053] As the mixing device, any existing device can be used. For example, a tilting mixer, an OMNI mixer, a Henschel mixer, a V-type mixer, and a Nauta mixer, etc. can be used.

[0054] Examples

[0055] Hereinafter, the present invention will be further described based on experimental examples, but the present invention is not limited thereto.

[0056] <Experimental Example 1>

[0057] (Manufacture of Cement Admixture)

[0058] · Cement Admixture A

[0059] As a raw material, by - product slaked lime (density: 2.21 g / cm 3 , Blaine specific surface area: 4,680 cm 2 / g, Ca(OH)2 content rate: 84 mass%) produced as a by - product in the manufacturing process of acetylene gas by the calcium carbide method was heat - treated in an atmosphere at a temperature of 450°C, and then carbonated with carbon dioxide gas at a temperature of 450°C and a CO2 concentration of 50 vol%, followed by pulverization and screening, thereby manufacturing cement admixture A (calcium carbonate / calcium oxide = 80 / 20 (mass ratio), total amount of calcium carbonate and calcium oxide in cement admixture A is 94 mass%, calcium sulfate content is 2.0 mass%, density 2.95 g / cm 3 , Blaine specific surface area 4,520 cm 2 / g, median particle size 60 μm). It should be noted that the calcium sulfate content, the mass ratio of calcium carbonate to calcium oxide, and the total amount are calculated from the mass loss part obtained by using fluorescence X - ray measurement and thermogravimetry - differential thermal analysis (TG - DTA).

[0060] · Cement admixture B

[0061] As a raw material, limestone fine powder (manufactured by Joetsu Mining, 100 mesh, density: 2.74 g / cm 3 , Blaine specific surface area: 4,550 cm 2 / g) and calcium oxide (obtained by firing by - product slaked lime produced in the manufacturing process of acetylene gas by the calcium carbide method at 1,000°C for 3 hours, density: 3.21 g / cm 3 , Blaine specific surface area: 4,490 cm 2 / g) were mixed in such a way that the calcium carbonate / calcium oxide in cement admixture B became 80 / 20 (mass ratio), and then screened to produce cement admixture B (calcium carbonate / calcium oxide = 80 / 20 (mass ratio), total amount of calcium carbonate and calcium oxide in cement admixture B is 99 mass%, calcium sulfate content is 0.9 mass%, density 2.98 g / cm 3 , Blaine specific surface area 4,520 cm 2 / g, median particle size 50 μm). It should be noted that the calcium sulfate content, the mass ratio of calcium carbonate to calcium oxide, and the total amount are calculated from the mass loss part obtained by using fluorescence X - ray measurement and thermogravimetry - differential thermal analysis (TG - DTA).

[0062] · Cement admixture C

[0063] Use calcium oxide used in cement admixture B as cement admixture C (calcium carbonate / calcium oxide = 0 / 100 (mass ratio), total amount of calcium oxide in cement admixture C is 91% by mass, content of calcium sulfate is 2.4% by mass, density is 3.21 g / cm 3 、Blaine specific surface area is 4,490 cm 2 / g, median particle size is 57 μm). It should be noted that the content of calcium sulfate, the mass ratio of calcium carbonate to calcium oxide and the total amount are calculated from the mass loss part obtained by using fluorescence X-ray determination and thermogravimetric-differential thermal analysis (TG-DTA).

[0064] · Cement admixture D

[0065] As raw materials, commercially available slaked lime (manufactured by Ueda Lime Manufacturing, density: 2.27 g / cm 3 、Blaine specific surface area: 12,670 cm 2 / g, Ca(OH)2 content rate: 99% by mass) is used. After heat treatment in an atmosphere at a temperature of 450 °C, carbonation treatment is carried out using carbon dioxide gas at a temperature of 450 °C and a CO2 concentration of 50% by volume, followed by pulverization and screening, thereby manufacturing cement admixture D (calcium carbonate / calcium oxide = 80 / 20 (mass ratio), total amount of calcium carbonate and calcium oxide in cement admixture D is 99% by mass, content of calcium sulfate is 0.1% by mass, density is 2.81 g / cm 3 、Blaine specific surface area is 10,740 cm 2 / g, median particle size is 11.7 μm). It should be noted that the content of calcium sulfate, the mass ratio of calcium carbonate to calcium oxide and the total amount are calculated from the mass loss part obtained by using fluorescence X-ray determination and thermogravimetric-differential thermal analysis (TG-DTA).

[0066] (Measurement of mass change rate of each admixture)

[0067] Measure the mass change rates of cement admixtures A to D respectively. Specifically, spread about 10 g of the sample thinly on an aluminum dish with a diameter of about 10 cm, place it statically in an environmental test chamber at 20 °C and 80% RH in such a way that the sample does not splash, weigh the mass after 24 hours and 48 hours using an electronic balance, and divide the obtained values by the mass before measurement to calculate the mass change rate. The results are shown in Figure 1 .

[0068] According to Figure 1The mass change rate of cement admixtures A and D after 24 hours is in the range of 100-106%. On the other hand, the mass change rate of cement admixture B after 24 hours is about 109%, and the mass change rate increases compared with cement admixtures A and D. For cement admixtures A and D, although the mass ratio of calcium carbonate to calcium oxide is the same and the total amount of calcium carbonate and calcium oxide is at the same level compared with cement admixture B, the mass change rate after 24 hours is low. Therefore, it is speculated that they have a core-shell structure.

[0069] (Manufacture and Evaluation of Cement Composition)

[0070] Sand was mixed into the cement composition containing cement and each example of the cement admixture, and mixed with water (tap water) so that the water / cement ratio was 0.5 (mass ratio), and the following evaluation was carried out. The results are shown in Table 1. It should be noted that the cement admixture was mixed so as to be 10% in the cement composition, and 300 parts by mass of sand was mixed with respect to 100 parts by mass of cement. In addition, the materials used are as follows.

[0071] · Cement: Ordinary Portland cement (cement for research, density 3.16 g / cm 3 , Blaine specific surface area 3,260 cm 2 / g) in which 42% of blast furnace slag fine powder (commercial product, density 3.91 g / cm 3 , Blaine specific surface area 4,190 cm 2 / g) was replaced.

[0072] · Sand: Fine aggregate (manufactured by the Cement Association, standard sand for JIS strength test).

[0073] · Water: Tap water.

[0074] · Compressive strength

[0075] According to the method specified in JIS R 5201:2015 "Physical Testing Methods for Cement", the strength at the ages of 3 days, 7 days, and 28 days was measured. It should be noted that water curing was carried out after demolding.

[0076] · Dimensional stability

[0077] According to the method specified in Appendix A "Test Method for Free Shrinkage Strain Caused by Drying of Mortar and Concrete" of JIS A 1129:2010 "Test Method for Measuring the Length Change of Mortar and Concrete", the length change rate at the age of 28 days was measured.

[0078] · Resistance to carbonation

[0079] Specimens were made of mortar, with the specimen size being 40 mm × 40 mm × 160 mm. Other than that, in accordance with the method specified in JIS A1153:2012 "Test Method for Accelerated Carbonation of Concrete", the carbonation depth after 28 days of accelerated carbonation was measured.

[0080] · Fluidity

[0081] In accordance with the method specified in JIS R 5201:2015 "Physical Test Methods for Cement", the flow value of the mortar was measured.

[0082] [Table 1]

[0083] Table 1

[0084]

[0085] When using cement admixtures A and D that contain calcium carbonate and calcium oxide in a specified ratio in one particle, the dimensional stability, carbonation resistance, and fluidity of the cement composition are good, and the initial strength at 3 days of age shows good performance compared to other admixtures.

[0086] <Experimental Example 2>

[0087] In the production of cement admixture A, the carbonation conditions were changed to produce cement admixtures with the calcium carbonate / calcium oxide mass ratios shown in Table 2. Other than that, the same operations as in Experimental Example 1 were carried out to measure the mass change rate of the cement admixture and to produce and evaluate the cement composition. The results are shown in Table 2.

[0088] [Table 2]

[0089] Table 2

[0090]

[0091] <Experimental Example 3>

[0092] In the production of cement admixture A, the cement admixture with the median particle size shown in Table 3 was produced by crushing and screening. Other than that, the same operations as in Experimental Example 1 were carried out to produce and evaluate the cement composition. The results are shown in Table 3.

[0093] [Table 3]

[0094] Table 3

[0095]

[0096] Based on the above results, it is confirmed that the cement admixture of the present invention contains calcium carbonate and calcium oxide in one particle, the mass ratio of calcium carbonate to calcium oxide (calcium carbonate / calcium oxide) is 25 / 75 to 99.5 / 0.5, and the total of calcium carbonate and calcium oxide is 80% by mass or more in the cement admixture, so that the initial strength shows good performance and the carbonation resistance can be ensured.

[0097] Industrial applicability

[0098] The present invention can be particularly suitably used as a cement admixture used in the fields of civil engineering and construction.

Claims

1. A cement admixture which contains 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 25 / 75 to 99.5 / 0.5, and the total amount of the calcium carbonate and the calcium oxide is 80% by mass or more in the cement admixture.

2. The cement admixture according to claim 1, wherein the mass change rate after standing for 24 hours in an environment of 20 °C and 80% RH is 100 to 106%.

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

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

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

6. The cement composition according to claim 5, wherein, The cement is blast furnace cement.

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