Powdery cement composition and method for producing same

Abstract

Provided is a powdery cement composition which contains a crushed clinker, gypsum, and limestone fine powder, in which the proportion of an aluminate phase in the crushed clinker is not less than 5 mass%, and which has excellent sulfate resistance even with a large proportion of the limestone fine powder.　A composition according to the present invention comprises a crushed clinker, gypsum, and limestone fine powder, wherein the crushed clinker contains 58-68 mass% of alite, 12-19 mass% of belite, 5-10 mass% of an aluminate phase, and 7-13 mass% of a ferrite phase in terms of calculated values according to the Bogue formula, the proportion of SO3 in the composition is 2.2-3.2 mass%, the proportion of powder having a grain size of not more than 10 μm is not less than 65 mass% in the limestone fine powder, the amount of the limestone fine powder is 5-11 parts by mass relative to the total of 100 parts by mass of the crushed clinker and the gypsum, and the Blaine specific surface area of the composition is 3,700-5,000 cm2 / g.

Description

Powdered cement composition and method for producing the same

[0001] The present invention relates to a powdered cement composition (particularly one containing limestone fine powder) and a method for producing the same.

[0002] Following the adoption of the Paris Agreement in 2015, the Japanese government declared in 2020 that it would aim to achieve carbon neutrality by 2050. In response to this declaration, the construction industry is actively promoting the use of blast furnace cement, fly ash cement, and other cements to reduce clinker consumption and carbon dioxide emissions during concrete production. However, production of ground granulated blast furnace slag and fly ash, which are ingredients in blast furnace cement and fly ash cement, is likely to decrease in the future due to the downsizing of steel mills and coal-fired power plants, which are the sources of production. For this reason, there is a need for technology that can reduce clinker consumption without using ground granulated blast furnace slag or fly ash.

[0003] Meanwhile, various cement compositions containing limestone fine powder are known. For example, Patent Document 1 describes a cement composition containing high-early-strength Portland cement and limestone fine powder, with the limestone fine powder content being 20 to 60 mass %. This cement composition suppresses the generation of heat of hydration over a long period of time, and can prevent cracks caused by the accumulation of heat of hydration.

[0004] Japanese Patent Application Laid-Open No. 2020-93951

[0005] As mentioned above, the generation of heat of hydration can be suppressed by adding limestone fine powder to a cement composition. However, the greater the amount of limestone fine powder added, the worse the sulfate resistance of the hardened product of the cement composition (e.g., concrete). Here, sulfate resistance refers to the ability of concrete to maintain excellent durability without significant expansion over a long period of time when exposed to groundwater or the like containing a high sulfate content.

[0006] On the other hand, sulfate-resistant Portland cement, which has an aluminate phase content adjusted to 4% by mass or less, is known as a cement with excellent sulfate resistance. However, when the aluminate phase content is 4% by mass or less, the cement composition has a problem of poor early strength development. Therefore, in order to ensure excellent early strength development, it is necessary to use a ground clinker having an aluminate phase content of 5% by mass or more. The object of the present invention is to provide a powdered cement composition containing ground clinker, gypsum, and limestone fine powder, in which the aluminate phase content in the ground clinker is 5% by mass or more, and which has excellent sulfate resistance despite the high content of limestone fine powder, and a method for producing the same.

[0007] As a result of extensive research into solving the above problems, the present inventors have found that excellent sulfate resistance can be achieved by using a powdered cement composition that satisfies certain conditions, such as the proportion of powder having a particle size of 10 μm or less in the limestone fine powder being within a specific range, and have completed the present invention.

[0008] The present invention provides the following [1] to [5]: [1] A powdered cement composition containing ground clinker, gypsum, and limestone fine powder, wherein the ground clinker contains, as calculated by the Bogue formula, 58 to 68 mass% of alite, 12 to 19 mass% of belite, 5 to 10 mass% of an aluminate phase, and 7 to 13 mass% of a ferrite phase, and the SO in the powdered cement composition ３ is 2.2 to 3.2% by mass, the proportion of powder having a particle size of 10 μm or less in the limestone fine powder is 65% by mass or more, the amount of the limestone fine powder is 5 to 11 parts by mass per 100 parts by mass of the total amount of the clinker pulverized material and the gypsum, and the Blaine specific surface area of ​​the powdered cement composition is 3,700 to 5,000 cm ２ / g. [2] The powdered cement composition according to [1] above, wherein the proportion of powder having a particle size of more than 20 μm in the limestone fine powder is 18 mass% or less. [3] The powdered cement composition according to [1] or [2] above, wherein the proportion of the total amount of gypsum dihydrate and anhydrous gypsum in the gypsum is 50 mass% or more. [4] The powdered cement composition according to any of [1] to [3] above, wherein the powdered cement composition does not contain fly ash, ground granulated blast furnace slag, or silica fume, or contains one or more selected from fly ash, ground granulated blast furnace slag, and silica fume in a total proportion of 5 mass% or less. [5] A method for producing the powdered cement composition according to any one of [1] to [4] above, wherein raw materials of the powdered cement composition include cement clinker granules, unground gypsum, and limestone granules, and the method comprises a grinding step of simultaneously grinding the cement clinker granules, the unground gypsum, and the limestone granules to obtain the powdered cement composition.

[0009] The powdered cement composition of the present invention has excellent sulfate resistance despite the high proportion of limestone fine powder. Furthermore, since the powdered cement composition of the present invention contains ground clinker with an aluminate phase content of 5 mass % or more, it has excellent early strength development (e.g., high compressive strength at 1 day old).

[0010] The powdered cement composition of the present invention is a powdered cement composition containing ground clinker, gypsum, and limestone fine powder, wherein (a) the ground clinker contains, as calculated by the Bogue formula, 58 to 68 mass% of alite, 12 to 19 mass% of belite, 5 to 10 mass% of an aluminate phase, and 7 to 13 mass% of a ferrite phase, and (b) the SO in the powdered cement composition. ３(c) the proportion of powder having a particle size of 10 μm or less in the limestone fine powder is 65% by mass or more; (d) the amount of limestone fine powder is 5 to 11 parts by mass per 100 parts by mass of the total amount of the ground clinker and gypsum; (e) the Blaine specific surface area of ​​the powdered cement composition is 3,700 to 5,000 cm ２ / g.

[0011] [Pulverized clinker] The pulverized clinker used in the present invention is obtained by pulverizing cement clinker, which is a main raw material for cement. In the present invention, the mineral composition of the pulverized clinker is calculated by the Bogue formula and is as follows: alite (chemical formula: 3CaO.SiO ２ ; C ３ The proportion of the aluminate phase is 58 to 68 mass%, preferably 58.5 to 67 mass%, and more preferably 59 to 66 mass%. If the proportion is less than 58 mass%, the early strength development (for example, high compressive strength at ages of 7 to 14 days) will decrease. If the proportion exceeds 68 mass%, the proportion of the aluminate phase will decrease, and the early strength development may decrease.

[0012] Belite (chemical formula: 2CaO.SiO ２ ; C ２ The proportion of the aluminate phase (chemical formula: 3CaO.Al) is 12 to 19 mass%, preferably 13 to 18 mass%, and more preferably 14 to 17 mass%. If the proportion is less than 12 mass%, the long-term strength development (for example, high compressive strength after 28 days of age) will decrease. If the proportion exceeds 19 mass%, the proportions of the aluminate phase and alite will decrease, which may decrease the early strength development and early strength development. ２ O ３ ; C ３The proportion of the aluminate phase (chemical formula: 4CaO.Al) is 5 to 10 mass %. From the viewpoint of obtaining excellent early strength development, the proportion of the aluminate phase is preferably 6 mass % or more, more preferably 7 mass % or more, and particularly preferably 8 mass % or more. From the viewpoint of obtaining excellent sulfate resistance, the proportion of the aluminate phase is preferably 9 mass % or less, more preferably 8 mass % or less, and particularly preferably 7 mass % or less. The proportion of the ferrite phase (chemical formula: 4CaO.Al ２ O ３ Fe ２ O ３ ; C ４ The proportion of AF is 7 to 13 mass%, preferably 8 to 12 mass%. If the proportion is less than 7 mass%, chemical resistance decreases. If the proportion exceeds 13 mass%, the proportion of other minerals (for example, aluminate phase) decreases, which may decrease early strength development.

[0013] The proportions of alite (C3S), belite (C2S), aluminate phase (C3A), and ferrite phase (C4AF), which are the mineral composition of the ground clinker, are calculated using the following Bogue formulas (1) to (4). (1) CS (mass%) = (4.07 × CaO (mass%)) - (7.60 × SiO (mass%)) - (6.72 × AlO (mass%)) - (1.43 × FeO (mass%)) (Note that in formula (1), the value of "CaO (mass%)" does not include free lime.) (2) CS (mass%) = (2.87 × SiO (mass%)) - (0.754 × CS (mass%)) (3) CA (mass%) = (2.65 × AlO (mass%)) - (1.69 × FeO (mass%)) (4) CA (mass%) = 3.04 × FeO (mass%)

[0014] [Gypsum] In the present invention, one or more types of gypsum selected from gypsum dihydrate, gypsum anhydride, and gypsum hemihydrate are used. In terms of sulfate resistance and the like, the ratio of the total amount of gypsum dihydrate and gypsum anhydride to the total amount of gypsum (100 mass%) is preferably 50 mass% or more, more preferably 60 mass% or more. The amount of gypsum is determined based on the SO in the powdery cement composition. ３For example, the amount of SO contained in the ground clinker is 2.2 to 3.2 mass%. ３ When the amount of gypsum is set to 1.9% by mass in the powdered cement composition (see Clinker A in Table 1 below), the total amount is 2.6% by mass (see Example 1 in Table 3 below).

[0015] [Limestone Fine Powder] The limestone fine powder used in the present invention has a proportion of powder having a particle size of 10 μm or less of 65% by mass or more (preferably 70% by mass or more). The upper limit of this proportion is not particularly limited, but from the viewpoint of ease of grinding, it is preferably 90% by mass. Of the total amount (100% by mass) of limestone fine powder, the proportion of powder having a particle size of more than 10 μm and less than 20 μm is preferably 30% by mass or less, more preferably 20% by mass or less. Of the total amount (100% by mass) of limestone fine powder, the proportion of powder having a particle size of more than 20 μm is preferably 18% by mass or less, more preferably 15% by mass or less. In the present invention, when the limestone fine powder has the above-mentioned particle size distribution, the sulfate resistance of the powdered cement composition can be improved.

[0016] The amount of limestone fine powder is 5 to 11 parts by mass, preferably 5 to 10 parts by mass, more preferably 5 to 9 parts by mass, even more preferably 6 to 8 parts by mass, and particularly preferably 6 to 7 parts by mass, per 100 parts by mass of the total amount of ground clinker and gypsum. If the amount is 5 parts by mass or more, the amount of ground clinker can be reduced by the amount of increased limestone fine powder, thereby further reducing carbon dioxide emissions during concrete production. If the amount is 11 parts by mass or less, the sulfate resistance of the powdered cement composition can be further improved.

[0017] [Other Materials] The powdered cement composition of the present invention can contain other powdery materials in addition to ground clinker, gypsum, and fine limestone powder. Examples of other powdery materials include fly ash, ground granulated blast furnace slag, and silica fume. The total amount of other powdery materials in the total amount (100% by mass) of the powdered cement composition is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass.

[0018] [Particle size of powdered cement composition] The Blaine specific surface area of ​​the powdered cement composition of the present invention is preferably 3,700 to 5,000 cm ２ / g, more preferably 3,800 to 4,900 cm ２ / g, particularly preferably 3,700 to 4,800 cm ２ / g. The value is 3,700 cm ２ If the value is less than 5,000 cm / g, the sulfate resistance of the powdered cement composition will decrease. ２ If the particle size exceeds 1 / g, the amount of work required for pulverization to obtain a powder having such a particle size becomes excessive.

[0019] [Method for Producing Powdered Cement Composition] The raw materials for the powdered cement composition of the present invention include at least cement clinker granules, unground gypsum, and limestone granules. The cement clinker granules are coarsely crushed cement clinker and can be obtained, for example, by crushing cement clinker to a maximum particle size of 5 mm or less using a crushing means such as a jaw crusher. The cement clinker granules can be, for example, those having a maximum particle size of 5 mm or less and a proportion of particles having a particle size exceeding 20 μm of 95% by mass or more. The cement clinker can be obtained by determining the types and amounts of various raw materials commonly used as cement raw materials, and then mixing and firing these various raw materials so as to obtain the mineral composition of the above-mentioned ground clinker. The unground gypsum can be one with a particle size common to cement raw materials (in other words, before being crushed with cement clinker). As the limestone particles, for example, those having a maximum particle size of 5 mm or less and containing 95 mass % or more of particles having a particle size exceeding 20 μm can be used.

[0020] A preferred example of a method for producing a powdered cement composition includes a grinding step in which cement clinker granules, unground gypsum, and limestone granules are simultaneously ground to obtain a powdered cement composition. By performing such simultaneous grinding, the sulfate resistance of the powdered cement composition can be further improved. In the present invention, the powdered cement composition is usually produced as a premix. In this case, the powdered cement composition is mixed with aggregate, water, and other materials (e.g., admixtures) that are used as needed when preparing concrete or the like.

[0021] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. [Materials for Powdered Cement Composition] The following cement clinker granules, unground gypsum, and limestone granules were used as materials. (1) Cement Clinker Granules Clinkers A to C (three types) having the chemical and mineral compositions shown in Tables 1 and 2 were used as cement clinkers. Clinkers A to C (all with a maximum particle size of approximately 5 cm) were each crushed using a jaw crusher (product name: BB300; manufacturer: Retsch) to obtain clinker granules A to C. Clinker granules A to C all had a maximum particle size of 1.2 mm or less and contained 95% or more by mass of granules with a particle size exceeding 20 μm. Clinker granules A, B, and C correspond to clinkers A, B, and C, respectively.

[0022] (2) Unpulverized gypsum As unpulverized gypsum, (i) gypsum containing 100% by mass of gypsum dihydrate, (ii) gypsum containing 100% by mass of anhydrous gypsum, (iii) gypsum containing a mixture of 66% by mass of gypsum dihydrate and 34% by mass of gypsum hemihydrate, and (iv) gypsum containing a mixture of 71% by mass of gypsum dihydrate and 29% by mass of gypsum hemihydrate. Four types were used. Note that the unpulverized gypsum (i) to (iv) were all obtained by crushing gypsum having a maximum particle size of about 10 cm using a jaw crusher (product name: BB300; manufacturer: Retsch). The unpulverized gypsum (i) to (iv) all had a maximum particle size of 1.2 mm or less, and the proportion of particles having a particle size exceeding 20 μm was 95% by mass or more.

[0023] (3) Limestone Granules: The limestone granules used had a maximum particle size of 1.2 mm or less and contained 99% or more by mass of particles with a particle size exceeding 20 μm. The calcium carbonate content of the limestone granules was 95% or more by mass. (4) Limestone Fine Powder A (Material Used in Comparative Examples 1 and 2): Limestone fine powder was used in which the proportion of powder with a particle size exceeding 20 μm was approximately 35 to 40% by mass (see "Particle Size Distribution (%) of Limestone Fine Powder" for Comparative Examples 1 and 2 in Table 3). Note that the particle size distribution (%) of the limestone fine powder in Table 3 differs slightly between Comparative Example 1 and Comparative Example 2 due to measurement error. (5) Limestone fine powder B (material used in Comparative Example 3) A limestone fine powder was used in which the proportion of powder having a particle size exceeding 20 μm was approximately 20 to 25 mass % (see “Particle size distribution (%) of limestone fine powder” in Comparative Example 3 in Table 3).

[0024] [Example 1] Clinker granules A obtained by roughly crushing clinker A shown in Tables 1 and 2, uncrushed gypsum (gypsum dihydrate: 100% by mass), and limestone granules were charged into a ball mill and crushed simultaneously (also referred to as "simultaneous crushing" in this specification) to obtain a powdered cement composition. In this case, the amount of limestone granules was set to 6 parts by mass relative to a total of 100 parts by mass of clinker granules A and uncrushed gypsum. The amount of uncrushed gypsum was set to 6 parts by mass relative to the total of 100 parts by mass of SO in the powdered cement composition. ３ The ratio of SO derived from clinker A ３ The amount of limestone fine powder was set to be 2.6% by mass in total. The obtained powdery cement composition was measured for (i) particle size distribution of the limestone fine powder, (ii) Blaine specific surface area of ​​the powdery cement composition, and (iii) expansion coefficient at 180 days when a hardened body of the powdery cement composition was immersed in a sodium sulfate solution by the following methods.

[0025] The particle size distribution of the limestone fine powder was obtained by sieving the powdered cement composition using sieves with opening sizes of 10 μm and 20 μm and a vacuum suction type sieving machine (product name: Air Jet Sieve e200LS; manufacturer: Hosokawa Micron Corporation), and then determining the amount of limestone component for each of the three resulting powders using TG-DTA. The amount of limestone component was calculated using the following formula (1): Amount of limestone component (mass%) = Q × 100 / 44 (1) (In formula (1), Q is the amount of weight loss (decarbonation amount) (mass%) at 650 to 800°C.) The TG-DTA equipment and measurement conditions were as follows: (i) Product name of thermogravimetric analyzer: "Thermo plus EV02 TG8121" (manufactured by Rigaku Corporation) (ii) Measurement conditions: Amount of sample: 20 mg; Heating rate: 10°C / min; Nitrogen gas flow atmosphere: 300 mL / min

[0026] The Blaine specific surface area of ​​the powdered cement composition was measured in accordance with the method described in "JIS R 5201:2015" (Physical Testing Methods for Cement). The expansion coefficient of the hardened product of the powdered cement composition was measured in accordance with the method described in "ASTM C 1012." The smaller the expansion coefficient, the better the sulfate resistance. The results are shown in Table 3. In Table 3, "Particle size distribution (%) of limestone fine powder" is based on mass and refers to the "proportion of powder having a particle size of 10 μm or less" ("up to 10 μm" in Table 3), the "proportion of powder having a particle size of more than 10 μm and not more than 20 μm" ("10-20 μm" in Table 3), and the "proportion of powder having a particle size of more than 20 μm" ("20 μm or more" in Table 3). "Blaine specific surface area (cm ２ / g) represents the Blaine specific surface area of ​​the powdered cement composition. ３ "Proportion (%)" indicates the proportion (mass %) of sulfur trioxide contained in the powdered cement composition. "Expansion rate (%) at 180 days" indicates the expansion rate according to the method described in the above-mentioned "ASTM C 1012."

[0027] [Example 2] An experiment was carried out in the same manner as in Example 1, except that the type of unground gypsum was changed to anhydrous gypsum. [Example 3] The type of clinker was changed to clinker B, and the type of unground gypsum was changed to a mixture of gypsum dihydrate and gypsum hemihydrate (gypsum dihydrate: 66 mass%), and the amount of unground gypsum was changed to sulfur trioxide (SO ３ An experiment was conducted in the same manner as in Example 1, except that the ratio of gypsum to clinker was set to 2.8% by mass. [Comparative Example 1] An experiment was conducted in the same manner as in Example 1, except that instead of the simultaneous grinding method, a method was used in which clinker and unground gypsum were ground together to obtain cement, and then this cement was mixed with limestone fine powder A to obtain a powdered cement composition (also referred to as "separate grinding" in this specification). [Comparative Example 2] An experiment was conducted in the same manner as in Example 2, except that a separate grinding method was used instead of the simultaneous grinding method. [Comparative Example 3] An experiment was conducted in the same manner as in Example 3, except that a separate grinding method was used instead of the simultaneous grinding method. [Reference Example 1] An experiment was conducted in the same manner as in Example 1, except that the type of clinker was changed to clinker C and the type of unground gypsum was changed to a mixture of gypsum dihydrate and gypsum hemihydrate (gypsum dihydrate: 71% by mass). The results are shown in Table 3.

[0028]

[0029]

[0030]

[0031] From Table 3, in Examples 1 to 3, although clinker pulverized material having an aluminate phase ratio of 5% by mass or more (see clinkers A to B in Table 2) was used, a simultaneous grinding method was used when preparing the powdered cement composition, and as a result, the proportion of powder having a particle size of 10 μm or less as the particle size distribution of the limestone fine powder was larger than when the separation and grinding method was used. Therefore, compared to Comparative Examples 1 to 3 (experimental examples using the separation and grinding method), the expansion rate at 180 days was very small and the sulfate resistance was excellent. Furthermore, when comparing Example 3 with Reference Example 1, although Example 3 used clinker pulverized material having an aluminate phase ratio of 9.0% by mass (see clinker B in Table 2), it can be seen that excellent sulfate resistance (both expansion rates are within the range of 0.05 to 0.06%) was obtained, which is comparable to Reference Example 1, which used clinker pulverized material having an aluminate phase ratio of 4.4% by mass (see clinker C in Table 2).

Claims

1. A powdered cement composition comprising ground clinker, gypsum, and limestone fine powder, wherein the ground clinker contains, as calculated by the Bogue formula, 58 to 68 mass% alite, 12 to 19 mass% belite, 5 to 10 mass% aluminate phase, and 7 to 13 mass% ferrite phase, and the SO in the powdered cement composition. ３ is 2.2 to 3.2 mass%, the proportion of powder having a particle size of 10 μm or less in the limestone fine powder is 65 mass% or more, the amount of the limestone fine powder is 5 to 11 mass parts per 100 mass parts of the total amount of the ground clinker and the gypsum, and the Blaine specific surface area of ​​the powdered cement composition is 3,700 to 5,000 cm ２ / g.

2. A powdered cement composition according to claim 1, wherein the proportion of powder having a particle size exceeding 20 μm in the fine limestone powder is 18% by mass or less.

3. A powdered cement composition according to claim 1, wherein the total amount of gypsum dihydrate and anhydrous gypsum in the gypsum is 50% by mass or more.

4. The powdered cement composition according to claim 1, which does not contain fly ash, ground granulated blast furnace slag, or silica fume, or which contains one or more selected from fly ash, ground granulated blast furnace slag, and silica fume in a total amount of 5 mass% or less.

5. A method for producing the powdered cement composition according to any one of claims 1 to 4, wherein the raw materials for the powdered cement composition include cement clinker granules, unground gypsum, and limestone granules, and the method comprises a grinding step of simultaneously grinding the cement clinker granules, the unground gypsum, and the limestone granules to obtain the powdered cement composition.

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