Powdery cement composition

Abstract

Provided is a powdery cement composition containing a fine limestone powder in a large proportion, the powdery cement composition, when used as a material for concrete or the like, being capable of giving high compression strength and having excellent sulfate resistance.　The powdery cement composition comprises a cement and a fine limestone powder. The mineralogical composition of the powdery cement composition calculated by the Bogue formula satisfies the conditions of: an alite content of 50-70 mass%; a belite content of 5-15 mass%; an aluminate phase content of 2-10 mass%; a total content of alite and belite of 60-80 mass%; and a mass ratio between alite and belite, alite / belite, of 5-10. The proportion of the fine limestone powder in the powdery cement composition is 5-15 mass%.

Description

Powdered cement composition

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

[0002] In recent years, the cement manufacturing industry has been working on various initiatives to reduce carbon dioxide emissions with the aim of achieving carbon neutrality. For example, increasing the amount of minor admixtures in Portland cement has been considered. Increasing the amount of minor admixtures would reduce the amount of ground cement clinker, thereby reducing the carbon dioxide emitted during cement clinker production. Known minor 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 their sources, steel mills and coal-fired power plants. Therefore, there is a need 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 an additive manufacturing device, the method including a cement composition preparation step of mixing cement having a ferrite phase ratio of 4.0 mass% or more as calculated by Borg's formula, an inorganic powder (e.g., limestone fine powder) in an amount of 2 to 150 mass parts per 100 mass parts of cement, and water to obtain the cement composition.

[0004] JP 2023-136832 A

[0005] As described above, various cement compositions containing limestone fine powder are known. Increasing the amount of limestone fine powder reduces the cement content in the cement composition, potentially reducing the compressive strength of the resulting hardened product. On the other hand, when a cement composition is used in a sulfate-containing environment (e.g., in contact with soil, groundwater, industrial wastewater, or other materials with a high sulfate content), poor sulfate resistance can cause significant expansion at the surface of the hardened product (e.g., a concrete structure), potentially resulting in cracks in the concrete structure. The object of the present invention is to provide a powdered cement composition containing a high content of limestone fine powder, which, when used as a material for concrete or the like, can impart high compressive strength and excellent sulfate resistance.

[0006] As a result of intensive research into solving the above-mentioned 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 according to the Bogue formula of the powdered cement composition satisfies the following conditions: an alite content of 50 to 70 mass%, a belite content of 5 to 15 mass%, an 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 the content of limestone fine powder in the powdered cement composition is 5 to 15 mass%. [2] The powdered cement composition according to [1], wherein the belite satisfies the following conditions: a solid solution amount of sulfur trioxide of 0.3 mass% or more, a solid solution amount of diphosphorus pentoxide of 0.05 mass% or more, and a total solid solution amount of the sulfur trioxide and the diphosphorus pentoxide of 0.5 to 4 mass%. [3] The powdered cement composition according to [1] or [2] above, 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 of [1] to [3] above, wherein the mineral composition of the powdered cement composition according to the Bogue formula is a ferrite content of 5 to 12% by mass. [5] The powdered cement composition according to any of [1] to [4] above, wherein the amount of water-soluble alkali in the powdered cement composition is 0.2% by mass or more. [6] The powdered cement composition according to any of [1] to [5] above, wherein the amount of sulfur trioxide in the powdered cement composition is 2.2 to 4.0% by mass. [7] The powdered cement composition according to any of [1] to [5] above, wherein the Blaine specific surface area is 4,000 to 5,800 cm ２ [8] The powdery cement composition according to any one of the above [1] to [7], which does not contain inorganic powders other than ground cement clinker, gypsum, and limestone fine powder, or which contains inorganic powders at a content of 5 mass% or less, other than ground cement clinker, gypsum, and limestone fine powder.

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

[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 contains 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: an alite content of 50 to 70% by mass, a belite content of 5 to 15% by mass, an aluminate phase content of 2 to 10% by mass, a 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] Alite (chemical formula: 3CaO.SiO ２ ; C ３ The content of sulphur dioxide (hereinafter abbreviated as S) 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 mass%, the early strength development (for example, high compressive strength at ages of 7 to 14 days) may decrease. If the content exceeds 70 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] Belite (chemical formula: 2CaO.SiO ２ ; C ２The content of sulfur trioxide (SO ) 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 mass%, the long-term strength development (for example, high compressive strength after 28 days of age) may decrease. If the content exceeds 15 mass%, the proportion of aluminate phase and alite decreases, and the early strength development and early stage strength development may decrease. In the present invention, belite is sulfur trioxide (SO ). ３ ) solid solution amount is 0.3 mass % or more, diphosphorus pentoxide (P ２ O ５ ) solid solution amount is 0.05 mass % or more, and sulfur trioxide (SO ３ ) solid solution amount and diphosphorus pentoxide (P ２ O ５ ) is 0.6 to 4%. By satisfying these conditions, sulfate resistance can be further improved.

[0012] Aluminate phase (chemical formula: 3CaO·Al ２ O ３ ; C ３ A) is present in an amount of 2 to 10 mass%, preferably 2 to 7 mass%, more preferably 3 to 6 mass%, and particularly preferably 4 to 5 mass%. If the amount is less than 2 mass%, early strength development may decrease. If the amount is more than 10 mass%, 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% by mass, preferably 63 to 78% by mass, more preferably 66 to 76% by mass, and particularly preferably 68 to 74% by mass. If the content is less than 60% by mass, long-term strength development may be reduced. If the content exceeds 80% by mass, the proportion of ground cement clinker in the powdered cement composition of the present invention increases, and the degree of reduction in carbon dioxide emissions during cement production may be reduced. The mass ratio of alite to belite (alite / belite) is 5 to 10, preferably 5.5 to 9.5, and particularly preferably 6 to 9. If the mass ratio is less than 5, strength development at early ages will be reduced. If the mass ratio exceeds 10, sulfate resistance will be reduced and strength development at long ages may be reduced.

[0014] Ferrite phase (chemical formula: 4CaO·Al ２ O ３ Fe ２ O ３ ; C ４ The content of AF 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 mass% or more, sulfate resistance can be further improved. When the content is 12 mass% or less, the content of other minerals (for example, aluminate phase) can be increased, and early strength development and the like can be further improved.

[0015] The contents of alite (C3S), belite (C2S), aluminate phase (C3A), and ferrite phase (C4AF), which are the mineral compositions of the powdered cement composition of the present invention, are calculated using the following Borg formulas (1) to (4) after correcting by the content of limestone fine powder. (1) C3S (mass%) = (4.07 x CaO (mass%)) - (7.60 x SiO2 (mass%)) - (6.72 x Al2O3 (mass%)) - (1.43 x Fe2O3 (mass%)) - (2.85 x SO ３(mass %)) (However, in formula (1), the value of "CaO (mass %)" does not include free lime.) (2) CS (mass %) = (2.87 × SiO2 (mass %)) - (0.754 × CS (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 may be any common gypsum used as a material for Portland cement (particularly gypsum dihydrate and gypsum hemihydrate which may be generated during the production of cement). The amount of gypsum is determined based on the amount of sulfur trioxide (SO ) in the composition of the present invention from the viewpoint of preventing flash setting due to hydration of the aluminate phase. ３ ) is preferably in an amount such that the content 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, 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 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 limestone fine powder in the composition of the present invention is 5 to 15% by 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. 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, 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 fine limestone 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 blast furnace slag, fly ash, silica fume, etc.

[0020] The amount of water-soluble alkali in the composition of the present invention is preferably 0.2% by mass or more. When the amount is 0.2% by mass or more, the early strength development can be further improved. 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 Analysis of 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 1 / g or less, the fluidity can be further increased.

[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 (particularly, waste materials such as construction waste soil and municipal waste incineration ash are preferably included so that the water-soluble alkali content falls within the above-mentioned preferred range), and then mixing and firing these various raw materials to obtain the above-mentioned clinker mineral composition. The unground gypsum can be one with a particle size common to cement raw materials (in other words, one before grinding with cement clinker). The limestone granules can be, for example, one with a maximum particle size of 5 mm or less and a proportion of powder with a particle size exceeding 20 μm of 95% by mass or more.

[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 performing 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. In this 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.

[0023] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. [Materials] The following cement clinker, unground gypsum, and limestone particles were used as materials. (1) Cement clinker Clinkers 1 to 7 (7 types) that give the mineral compositions shown in Tables 1 to 4 were used as cement clinkers. In Table 1, "C ２ "S" indicates belite. ３ "A" 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, "C ３"S" indicates alite. ２ "S" indicates belite. ３ "A" indicates the aluminate phase. ４ "AF" indicates a ferrite phase. In Tables 3 and 4, "cement composition" indicates a powdered cement composition. (2) Unground gypsum Gypsum dihydrate was used as the unground gypsum. (3) Limestone granules Limestone granules with a maximum particle size of 5 mm or less were used. 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 mineral 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 CaO, SiO2, and SiO3 contents in the powdered cement composition were measured by X-ray fluorescence in accordance with ASTM C114 "Standard Test Methods for Chemical Analysis of Hydraulic Cement." ２ , Al ２ O ３ , Fe ２ O ３ and SO ３ The mineral composition of the base cement was calculated using the Bogue formula in the field of cement chemistry, and then the CaCO3 content was calculated using thermogravimetric analysis as specified in "X2.2.2 Thermogravimetric Analysis (TGA)" of ASTM C114. ３ The amount of limestone was calculated from the weight loss rate caused by decarbonation of the limestone-blended cement, and the mineral composition was corrected according to the following formula (1) to determine the mineral composition of the limestone-blended cement. ｆ =X ｂ ×(100-L) / 100 (1) (wherein, X ｆ is the X in finishing cement ｂis the C of each base cement ３ S.C. ２ S.C. ３ A, C ４ AF content (% by mass), and L is limestone content (% by mass).

[0025] (b) Content of limestone fine powder Calcium carbonate (CaCO ) in limestone fine powder ３ The content of ) was determined by measuring the mass loss in the vicinity of 600°C to 700°C when approximately 30 mg of a 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 Measured by 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. Using a JEOL "FE-SEM JSM-7001F" measuring device, 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 characteristics (a) to (d) below. (a) C ３ S: Polygonal particles, light gray, several tens of μm (b) C ２ S: Elliptical particles, dark gray, several tens of μm (c)C ３ A: Irregular structure observed between silicate phases, dark gray, several μm to several tens of μm (D) C ４ AF: 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, accelerating voltage: 15 kV, probe current: 2.0 to 2.1 × 10 －９ The characteristic X-rays were analyzed using EDS "AZtec Version 3.4" manufactured by Oxford Instruments, and the average value obtained was used as C. ２ S and C ３ The chemical composition (mass%) of A was adopted.

[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 powdered cement composition (composition of the present invention). At this time, the amount of gypsum was adjusted based on the amount of SO in the powdered cement composition. ３ The ratio of SO derived from clinker 1 ３ and 3.8 mass % in total (see "SO 4 " in Example 1 of Table 4). ３ " column). The amount of limestone granules was an amount that resulted in a content of 14.2 mass% in the powdered cement composition (see the "Content of limestone fine powder" column of Example 1 in Table 2). For the obtained powdered cement composition, the water-soluble alkali content, Blaine's 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) were determined. Here, the water-soluble alkali content was determined in accordance with "JCAS-1-04:2004" (Method for analyzing water-soluble components of cement). The Blaine's specific surface area, mortar compressive strength, and expansion rate at 180 days were determined in accordance with "JIS R 5201:2015" (Physical testing methods 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] Experiments were 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. The mineral compositions of clinkers 1 to 7, and the chemical compositions, physical properties, etc. of the cement compositions of Examples 1 to 5 and Comparative Examples 1 and 2 are shown in Tables 1 to 5. In Table 5, "1.4<" indicates that the content exceeded 1.4%.

[0029]

[0030]

[0031]

[0032]

[0033]

[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, wherein the mineral composition of the powdered cement composition according to the Bogue formula satisfies the following conditions: an alite content of 50 to 70 mass%, a belite content of 5 to 15 mass%, an aluminate phase content of 2 to 10 mass%, a total alite and belite content of 60 to 80 mass%, and a mass ratio of alite to belite (alite / belite) of 5 to 10; and wherein the limestone fine powder content in the powdered cement composition is 5 to 15 mass%.

2. The powdered cement composition according to claim 1, 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 claim 1, wherein the aluminate phase 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 sum of the amounts of dissolved sulfur trioxide and dissolved magnesium oxide is 1.5 to 5.5 mass%.

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

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

6. 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. The powdered cement composition according to claim 1, which 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.

Images