Powder type cement composition

Abstract

To provide a powder type cement composition that contains a limestone fine powder at large content rate, can impart large compressive strength in a case of being used as a material for a concrete or the like and has excellent sulfate resistance.SOLUTION: Provided is a powder type cement composition containing a cement and a limestone fine powder. A mineral composition according to Bogue equation of the powder type cement composition satisfies each of the conditions that an alite content rate is 59-70 mass%, a belite content rate is 7-13 mass%, an aluminate phase content rate is 3-7 mass%, a total content rate of alite and belite is 68-78 mass%, and a mass ratio between alite and belite (alite / belite) is 5-9. A content rate of the limestone fine powder in the powder type cement composition is 5 mass% or over and under 8 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a powdered cement composition. [Background technology]

[0002] In recent years, the cement manufacturing industry has been making various efforts to reduce carbon dioxide emissions with the aim of achieving carbon neutrality. For example, increasing the amount of minor admixtures in Portland cement is being considered. Increasing the amount of minor admixtures will reduce the amount of ground cement clinker, thereby reducing the carbon dioxide generated during the production of cement clinker. Known small-volume admixtures include ground granulated blast furnace slag and fly ash. However, production of ground granulated blast furnace slag and fly ash may decrease in the future due to the downsizing of the steel mills and coal-fired power plants that produce them. For this reason, there is a demand for technology that can reduce the amount of cement clinker used without using ground granulated blast furnace slag or fly ash.

[0003] On the other hand, various cement compositions containing limestone fine powder are known. As one example, Patent Document 1 describes a method for forming a shaped object using a hydraulic composition for additive manufacturing equipment, which method is characterized by including a cement composition preparation step in which cement having a ferrite phase ratio of 4.0 mass% or more as calculated by Borg's formula, inorganic powder (e.g., limestone fine powder) in an amount of 2 to 150 mass parts per 100 mass parts of cement, and water are mixed to obtain a cement composition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-136832 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, various cement compositions containing limestone fine powder are known. When the amount of limestone fine powder is increased, the proportion of cement in the cement composition decreases accordingly, which may result in a decrease in the compressive strength of the hardened product of the cement composition. On the other hand, when a cement composition is used in an environment containing sulfates (for example, in a location where it may come into contact with soil, groundwater, industrial wastewater, etc., which have a high sulfate content), if the cement composition has poor sulfate resistance, a large expansion will occur on the surface of the hardened cement composition (for example, a concrete structure), and as a result, cracks may occur in the concrete structure. An object of the present invention is to provide a powdered cement composition containing a large amount of limestone fine powder, which, when used as a material for concrete or the like, can impart high compressive strength and has excellent sulfate resistance. [Means for solving the problem]

[0006] As a result of extensive research into solving the above problems, the present inventors have found that a powdered cement composition containing cement and limestone fine powder, wherein the cement has a specific mineral composition and the content of the limestone fine powder in the powdered cement composition is within a specific range, can provide high compressive strength (e.g., mortar compressive strength) and also excellent sulfate resistance despite containing a large content of limestone fine powder, and have completed the present invention.

[0007] The present invention provides the following [1] to [8]. [1] A powdered cement composition comprising cement and limestone fine powder, wherein the mineral composition of the powdered cement composition according to the Bogue formula satisfies the following conditions: alite content of 50 to 70 mass%, belite content of 5 to 15 mass%, aluminate phase content of 2 to 10 mass%, a total content of alite and belite of 60 to 80 mass%, and a mass ratio of alite to belite (alite / belite) of 5 to 10; and wherein the content of limestone fine powder in the powdered cement composition is 5 to 15 mass%. [2] The powdered cement composition according to [1] above, wherein the belite satisfies the following conditions: the amount of dissolved sulfur trioxide is 0.3% by mass or more; the amount of dissolved diphosphorus pentoxide is 0.05% by mass or more; and the total amount of dissolved sulfur trioxide and dissolved diphosphorus pentoxide is 0.5 to 4% by mass. [3] The powdered cement composition according to [1] or [2], wherein the aluminate phase satisfies the following conditions: the amount of dissolved sulfur trioxide is 0.03% by mass or more; the amount of dissolved magnesium oxide is 0.8 to 4.0% by mass; and the sum of the amounts of dissolved sulfur trioxide and dissolved magnesium oxide is 1.5 to 5.5% by mass. [4] The powdered cement composition according to any one of [1] to [3] above, wherein the powdered cement composition has a ferrite content of 5 to 12 mass % as a mineral composition according to the Bogue method. [5] The powdery cement composition according to any one of the above [1] to [4], wherein the amount of water-soluble alkali in the powdery cement composition is 0.2 mass % or more. [6] The powdered cement composition according to any one of the above [1] to [5], wherein the content of sulfur trioxide in the powdered cement composition is 2.2 to 4.0 mass %. [7] The Blaine specific surface area of ​​the powdered cement composition is 4,000 to 5,800 cm 2 The powdery cement composition according to any one of the above [1] to [6], wherein the solubility is 0.01% by mass / g. [8] The powdered cement composition according to any one of [1] to [7] above, which does not contain inorganic powders other than ground cement clinker, gypsum, and limestone fine powder, or contains inorganic powders at a content of 5 mass% or less. [Effects of the Invention]

[0008] Although the powdered cement composition of the present invention contains a large amount of limestone fine powder, 5 to 15 mass %, when mixed with water, aggregate, etc. to prepare mortar, concrete, etc., it can provide high compressive strength (e.g., mortar compressive strength). Furthermore, when the powdery cement composition of the present invention is mixed with water, aggregate, etc. to prepare mortar, concrete, etc., it can impart excellent sulfate resistance. DETAILED DESCRIPTION OF THE INVENTION

[0009] The powdered cement composition of the present invention (hereinafter sometimes abbreviated as "the composition of the present invention") contains cement and limestone fine powder. The cement comprises ground cement clinker and gypsum. In the present invention, the mineral composition of the powdered cement composition (100% by mass) satisfies the following conditions as calculated by the Bogue formula: alite content of 50 to 70% by mass, belite content of 5 to 15% by mass, aluminate phase content of 2 to 10% by mass, total content of alite and belite of 60 to 80% by mass, and a mass ratio of alite to belite (alite / belite) of 5 to 10.

[0010] The content of alite (chemical formula: 3CaO·SiO2; sometimes abbreviated as C3S) is 50 to 70 mass %, preferably 53 to 68 mass %, more preferably 56 to 66 mass %, and particularly preferably 59 to 64 mass %. If the content is less than 50% by mass, the early strength development (for example, high compressive strength at ages of 7 to 14 days) may decrease.If the content exceeds 70% by mass, the proportion of the aluminate phase decreases, and the early strength development (for example, high compressive strength at ages of 1 to 3 days) may decrease.

[0011] The content of belite (chemical formula: 2CaO·SiO2; sometimes abbreviated as C2S) is 5 to 15 mass%, preferably 6 to 14 mass%, more preferably 6.5 to 13 mass%, and particularly preferably 7 to 12 mass%. If the content is less than 5% by mass, the long-term strength development (for example, high compressive strength after 28 days of age) may decrease. If the content is more than 15% by mass, the proportions of the aluminate phase and alite decrease, and the initial strength development and early strength development may decrease. In the present invention, it is preferable that the belite satisfies the following conditions: the amount of dissolved sulfur trioxide (SO3) is 0.3 mass% or more, the amount of dissolved diphosphorus pentoxide (P2O5) is 0.05 mass% or more, and the total amount of dissolved sulfur trioxide (SO3) and dissolved diphosphorus pentoxide (P2O5) is 0.6 to 4%. By satisfying these conditions, sulfate resistance can be further improved.

[0012] The content of the aluminate phase (chemical formula: 3CaO·Al2O3; sometimes abbreviated as C3A) is 2 to 10 mass%, preferably 2 to 7 mass%, more preferably 3 to 6 mass%, and particularly preferably 4 to 5 mass%. If the content is less than 2 mass%, the early strength development may decrease. If the content exceeds 10 mass%, the sulfate resistance decreases. In the present invention, the aluminate phase preferably satisfies the following conditions: the amount of dissolved sulfur trioxide is 0.03 mass% or more, the amount of dissolved magnesium oxide is 0.8 to 4.0 mass%, and the total amount of dissolved sulfur trioxide and dissolved magnesium oxide is 1.5 to 5.5 mass%. By satisfying these conditions, sulfate resistance can be further improved.

[0013] The total content of alite and belite is 60 to 80 mass %, preferably 63 to 78 mass %, more preferably 66 to 76 mass %, and particularly preferably 68 to 74 mass %. If the content is less than 60% by mass, the long-term strength development may decrease.If the content is more than 80% by mass, the proportion of ground cement clinker in the powdery cement composition of the present invention increases, and the degree of reduction in carbon dioxide emissions during cement production may decrease. The mass ratio of alite to belite (alite / belite) is 5-10, preferably 5.5-9.5, and particularly preferably 6-9. If the mass ratio is less than 5, strength development at an early age will decrease, whereas if the mass ratio exceeds 10, sulfate resistance will decrease and strength development at a long age may decrease.

[0014] The content of the ferrite phase (chemical formula: 4CaO·Al2O3·Fe2O3; sometimes abbreviated as C4AF) is not particularly limited, but is preferably 5 to 12 mass %, more preferably 6 to 11 mass %, and particularly preferably 7 to 10 mass %. When the content is 5% by mass or more, sulfate resistance can be further improved, and when the content is 12% by mass or less, the content of other minerals (for example, aluminate phase) can be increased, thereby further improving early strength development and the like.

[0015] The mineral contents of the powdered cement composition of the present invention, that is, alite (C3S), belite (C2S), aluminate phase (C3A), and ferrite phase (C4AF), are calculated using the following Borg formulas (1) to (4) after correcting for the content of limestone fine powder. (1) C3S(mass%)=(4.07×CaO(mass%))-(7.60×SiO2(mass%))-(6.72×Al2O3(mass%))-(1.43×Fe2O3(mass%))-(2.85×SO3(mass%)) (However, in formula (1), the value of "CaO (mass%)" does not include free lime.) (2) C2S(mass%)=(2.87×SiO2(mass%))-(0.754×C3S(mass%)) (3) C3A(mass%)=(2.65×Al2O3(mass%))-(1.69×Fe2O3(mass%)) (4) C4AF(mass%)=3.04×Fe2O3(mass%)

[0016] In the present invention, the gypsum contained in the cement can be general gypsum used as a material for Portland cement (particularly gypsum dihydrate and gypsum hemihydrate which may be produced during the production of cement). From the viewpoint of preventing flash setting due to hydration of the aluminate phase, the amount of gypsum is preferably an amount such that the content of sulfur trioxide (SO3) in the composition of the present invention is 2.2 to 4.0 mass% (preferably 2.4 to 3.5 mass%, more preferably 2.5 to 3.0 mass%).

[0017] The Blaine specific surface area of ​​the limestone fine powder, which is one of the materials of the composition of the present invention, is preferably 3,000 to 8,000 cm 2 / g, more preferably 4,000 to 7,000 cm 2 / g, and particularly preferably 4,500 to 6,000 cm 2 / g. The value is 3,000 cm 2 / g or more, the strength development can be further improved. 2 When the viscosity is 1000 ppm or less, the fluidity can be further improved. In the present invention, the content of calcium carbonate in the limestone fine powder is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

[0018] The content of the limestone fine powder in the composition of the present invention is 5 to 15 mass %. If the content is less than 5% by mass, the object of the present invention of reducing carbon dioxide emissions during cement production by increasing the amount of limestone fine powder used cannot be fully achieved, and if the content exceeds 15% by mass, the compressive strength of the composition of the present invention decreases. From the viewpoint of reducing carbon dioxide emissions during cement production by increasing the amount of limestone fine powder used, the content of limestone fine powder in the composition of the present invention is preferably 6% by mass or more, more preferably 7% by mass or more, even more preferably 8% by mass or more, even more preferably 9% by mass or more, even more preferably 10% by mass or more, and particularly preferably 11% by mass or more. From the viewpoint of increasing the compressive strength of the composition of the present invention, the content is preferably 14% by mass or less, and more preferably 13% by mass or less.

[0019] The cement composition of the present invention preferably does not contain inorganic powders other than ground cement clinker, gypsum, and limestone fine powder (hereinafter also referred to as "other inorganic powders"), or contains them in an amount of 5% by mass or less (preferably 3% by mass or less, more preferably 1% by mass or less). Examples of other inorganic powders include ground granulated blast furnace slag, fly ash, and silica fume.

[0020] The amount of water-soluble alkali in the composition of the present invention is preferably 0.2% by mass or more, which can further improve the early strength development. In the present invention, the "amount of water-soluble alkali" refers to a value calculated in accordance with the method of "JCAS-1-04:2004" (method for analyzing water-soluble components in cement). The Blaine specific surface area of ​​the composition of the present invention is preferably 4,000 to 5,800 cm 2 / g, more preferably 4,200 to 5,600 cm 2 / g. The value is 4,000 cm 2 / g or more, the strength development can be further improved. 2 When the viscosity is 1000 ppm or less, the fluidity can be further improved.

[0021] An example of the raw materials (before grinding) for the composition (after grinding) of the present invention is a combination of cement clinker, unground gypsum, and limestone granules. Cement clinker can be obtained by determining the types and amounts of various raw materials used as cement raw materials so as to obtain the above-mentioned clinker mineral composition (in particular, it is preferable that waste materials such as construction soil and municipal waste incineration ash are included so that the amount of water-soluble alkali falls within the above-mentioned preferred range), and then mixing and firing these various raw materials. As the unpulverized gypsum, one having a particle size that is common as a raw material for cement (in other words, one before being pulverized together with cement clinker) can be used. As the limestone particles, for example, those having a maximum particle size of 5 mm or less and containing 95 mass % or more of powder having a particle size exceeding 20 μm can be used.

[0022] A preferred example of a method for producing the composition of the present invention includes a grinding step in which cement clinker, unground gypsum, and limestone granules are simultaneously ground to obtain the composition of the present invention (in powder form). By carrying out such simultaneous grinding, the sulfate resistance of the composition of the present invention can be further improved. The composition of the present invention is usually produced as a premix product, in which case the composition of the present invention is mixed with aggregate, water, and other materials (e.g., admixtures) that are used as needed when preparing concrete or the like. [Example]

[0023] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. [material] The following materials were used: cement clinker, unground gypsum, and limestone granules. (1) Cement clinker As cement clinkers, clinkers 1 to 7 (7 types) giving the mineral compositions shown in Tables 1 to 4 were used. In Table 1, "C2S" indicates belite, and "C3A" indicates an aluminate phase. In Table 2, "content of limestone fine powder" and "amount of water-soluble alkali" both indicate values ​​(%) based on mass relative to the total amount (100 mass%) of the powdered cement composition. "Blaine specific surface area" indicates the value of the powdered cement composition. In Table 3, "C3S" indicates alite, "C2S" indicates belite, "C3A" indicates an aluminate phase, and "C4AF" indicates a ferrite phase. In Tables 3 and 4, "cement composition" refers to a powdered cement composition. (2) Unground gypsum Gypsum dihydrate was used as the unground gypsum. (3) Limestone grains The limestone granules used had a maximum particle size of 5 mm or less, and the calcium carbonate content in the limestone granules was 70 mass % or more.

[0024] The methods for measuring the values ​​in Tables 1 to 4 are as follows. (a) Chemical composition of powdered cement composition and mineralogical composition of cement clinker The mineral composition of cement clinker was determined in accordance with "ANNEXES A1. CALCULATION OF POTENTIAL CEMENT PHASE COMPOSITION" in ASTM C150-22 "Standard Specification for Portland Cement." Specifically, the mineral composition of the base cement was calculated using a formula known in the cement chemistry field as the Bogue formula, using the CaO, SiO2, Al2O3, Fe2O3, and SO3 contents of the powdered cement composition measured by X-ray fluorescence in accordance with ASTM C114 "Standard Test Methods for Chemical Analysis of Hydraulic Cement." The mineral composition of the limestone-blended cement was then calculated using the amount of limestone calculated from the weight loss rate caused by the decarbonation of CaCO3 by thermogravimetric analysis as specified in "X2.2.2 Thermogravimetric Analysis (TGA)" of ASTM C114, correcting the mineral composition according to the following formula (1). X f =X b ×(100-L) / 100 (1) (In the formula, X f is the finishing cement, X b are the contents (mass%) of C3S, C2S, C3A, and C4AF in the base cement, and L is the limestone content (mass%).

[0025] (b) Limestone fine powder content The calcium carbonate (CaCO3) content in the limestone fine powder was determined by measuring the mass loss around 600-700°C when approximately 30 mg of the sample was heated to 1,000°C at a heating rate of 20°C / min in a nitrogen atmosphere using a high-temperature differential scanning calorimeter (TG-DTA2000SR manufactured by NETZSCH), and then calculating the ratio of this mass loss to the mass loss of the standard reagent.

[0026] (c) Chemical composition of cement clinker minerals Measurement was performed using energy dispersive X-ray spectroscopy in a scanning electron microscope (hereinafter referred to as "SEM-EDS"). The powdered cement composition was embedded in epoxy resin, and then the resin surface was mirror-polished. After mirror-polishing, carbon was vapor-deposited on the resin surface to prepare a sample for SEM measurement. The measurement device used was a JEOL "FE-SEM JSM-7001F," and the structural image of the cement particles on the mirror surface of the sample was observed under the following conditions. In the structural image, each mineral was identified based on the following characteristics (a) to (d). (a) C3S: polygonal particles, light gray, several tens of μm (b)C2S: elliptical particles, dark gray, several tens of μm (c) C3A: Irregular structure observed between silicate phases, dark gray, several μm to several tens of μm (d) C4AF: Irregular structure observed between silicate phases, white, several μm to several tens of μm For the above four minerals, 15 or more points for each mineral in five or more different cement clinker grains were measured. Acceleration voltage: 15 kV, probe current: 2.0-2.1 × 10 -9Characteristic X-rays were analyzed at C2S and C3A. EDS was performed using Oxford Instruments' AZtec Version 3.4, and the average values ​​obtained were used as the chemical compositions (mass%) of C2S and C3A.

[0027] [Example 1] Clinker 1 shown in Tables 1 and 2, gypsum, and limestone particles were charged into a ball mill and pulverized simultaneously to obtain a powdery cement composition (the composition of the present invention). In this case, the amount of gypsum was determined so that the proportion of SO3 in the powdered cement composition would be 3.8 mass% in total together with the SO3 derived from clinker 1 (see the "SO3" column of Example 1 in Table 4). The amount of limestone particles was such that the content in the powdery cement composition was 14.2 mass % (see the column "Content of limestone fine powder" in Example 1 of Table 2). The obtained powdered cement compositions were measured for the water-soluble alkali content, Blaine specific surface area (see Table 2), mineral composition (see Table 3), chemical composition (see Table 4), mortar compressive strength (3 days, 7 days, 28 days), and expansion rate at 180 days (see Table 5). The amount of water-soluble alkali was determined in accordance with "JCAS-1-04:2004" (Method for analyzing water-soluble components in cement). The Blaine specific surface area, mortar compressive strength, and expansion rate at 180 days were determined in accordance with "JIS R 5201:2015" (Physical testing method for cement). Furthermore, if the expansion rate at 180 days is "0.05% or less," the "sulfate resistance" is considered to be "high" (very good), and if it is "more than 0.05% and less than 0.10%, the "sulfate resistance" is considered to be "moderate" (good).

[0028] [Examples 2 to 5, Comparative Examples 1 and 2] The experiment was carried out in the same manner as in Example 1, except that the type of clinker and the amount of limestone fine powder were changed as shown in Table 3. Tables 1 to 5 show the mineral compositions of clinkers 1 to 7, and the chemical compositions and physical properties of the cement compositions of Examples 1 to 5 and Comparative Examples 1 and 2. In Table 5, "1.4<" indicates that the content exceeded 1.4%.

[0029] [Table 1]

[0030] [Table 2]

[0031] [Table 3]

[0032] [Table 4]

[0033] [Table 5]

[0034] From Table 5, it can be seen that Examples 1 to 5 have high compressive strength and low expansion coefficients (excellent sulfate resistance), while Comparative Examples 1 and 2 have high expansion coefficients and poor sulfate resistance.

Claims

1. A powdered cement composition comprising cement and limestone fine powder, The mineral composition of the powdered cement composition according to the Bogue formula satisfies the following conditions: an alite content of 59 to 70 mass%, a belite content of 7 to 13 mass%, an aluminate phase content of 3 to 7 mass%, a total content of alite and belite of 68 to 78 mass%, and a mass ratio of alite to belite (alite / belite) of 5 to 9; A powdered cement composition characterized in that the content of limestone fine powder in the powdered cement composition is 5% by mass or more and less than 8% by mass.

2. 2. The powdered cement composition according to claim 1, wherein the belite satisfies the following conditions: a solid solution amount of sulfur trioxide is 0.3% by mass or more, a solid solution amount of diphosphorus pentoxide is 0.05% by mass or more, and the total of the solid solution amounts of sulfur trioxide and diphosphorus pentoxide is 0.5 to 4% by mass.

3. 2. The powdered cement composition according to claim 1, wherein the aluminate phase satisfies the following conditions: a solid solution amount of sulfur trioxide is 0.03 mass% or more, a solid solution amount of magnesium oxide is 0.8 to 4.0 mass%, and the sum of the solid solution amounts of sulfur trioxide and magnesium oxide is 1.5 to 5.5 mass%.

4. 2. The powdered cement composition according to claim 1, wherein the ferrite content of the powdered cement composition is 5 to 12 mass % as determined by the Bogue mineral composition formula.

5. 2. The powdered cement composition according to claim 1, wherein the amount of water-soluble alkali in the powdered cement composition is 0.2% by mass or more.

6. 2. The powdered cement composition according to claim 1, wherein the content of sulfur trioxide in the powdered cement composition is 2.2 to 4.0 mass%.

7. The Blaine specific surface area of ​​the powdered cement composition is 4,000 to 5,800 cm ２ 2. The powdered cement composition according to claim 1, wherein the hydroxyl group is 0.15 or 0.

15.

8. 2. The powdered cement composition according to claim 1, wherein the powdered cement composition does not contain inorganic powders other than ground cement clinker, gypsum, and limestone fine powder, or contains inorganic powders in an amount of 5 mass% or less.

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