Mixed cement composition and manufacturing method thereof

Abstract

To provide a mixed cement composition capable of reducing a use amount of cement clinker powder, excellent in strength development properties, while suppressing alkali-aggregate reaction.SOLUTION: A mixed cement composition is a powdery mixed cement composition including: cement clinker powder; plaster; blast furnace slag fine powder; and limestone powder. In a total amount 100 mass% of the cement clinker powder, the blast furnace slag fine powder and the limestone powder, a ratio of the cement clinker powder is 45.0 to 55.0 mass%, a ratio of the blast furnace slag fine powder is 39.8 to 44.7 mass%, and a ratio of the limestone powder is 5.2 to 10.4 mass%. A mass ratio of the blast furnace slag fine powder and the limestone powder (blast furnace slag fine powder / limestone powder) is 4.3 to 7.7.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a blended cement composition and a method for making the same. [Background technology]

[0002] Currently, measures to combat global warming are calling for a significant reduction in carbon dioxide emissions, even in the cement manufacturing industry. Most of the carbon dioxide emissions in the cement manufacturing industry are generated during the production of cement clinker, and in order to reduce carbon dioxide emissions, there is a need to reduce the amount of cement clinker produced. As a cement that can reduce the amount of cement clinker used, blast furnace cement, which is obtained by replacing part of the cement clinker powder with ground granulated blast furnace slag, is known. Patent Document 1 describes a cement composition using ground granulated blast furnace slag, which contains at least the following components (a), (b), and (c) in the following ratios: (a) Cements containing gypsum and ground cement clinker having a hydraulic modulus (HM) of 2.0 to 2.4, a silica modulus (SM) of 1.3 to 3.0, and an iron modulus (IM) of 1.5 to 3.0: 20 to 50% by mass (b) Blaine specific surface area is 5,000 cm 2 / g or more blast furnace slag powder: 30 to 70 mass% (c) Limestone powder: more than 0% by mass to 40% by mass

[0003] On the other hand, in recent years, the production of coal ash, which has been used as a cement clinker raw material, has been declining due to a decline in coal-fired power generation. Therefore, biomass ash has been attracting attention as a cement clinker raw material to replace coal ash. In addition, examples of conventional cement clinker raw materials include construction waste soil, municipal waste incineration ash, and sewage sludge. Biomass ash and the above waste materials contain more alkali than coal ash. Therefore, when the above biomass ash or the like is used as a substitute for coal ash, which is a raw material for cement clinker, the amount of alkali in the produced cement clinker increases. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-254909 Summary of the Invention [Problem to be solved by the invention]

[0005] Although ground granulated blast furnace slag has excellent qualities as a material to be mixed with cement, its production volume is not so large and shortages are expected in the future. Therefore, there is a demand for cement that can reduce the amount of cement clinker powder used by replacing part of the cement clinker powder with a material other than ground granulated blast furnace slag. On the other hand, if the proportion of ground granulated blast furnace slag in the blended cement is small (for example, 40 mass % or less), the alkali-aggregate reaction tends to proceed, resulting in a problem of reduced durability of the hardened body of the blended cement. An object of the present invention is to provide a mixed cement composition that can reduce the amount of cement clinker powder used, has excellent strength development, and suppresses alkali-aggregate reaction. [Means for solving the problem]

[0006] As a result of extensive research into solving the above problems, the present inventors have found that the above objects can be achieved by a powdery mixed cement composition comprising cement clinker powder, gypsum, ground granulated blast furnace slag, and limestone powder, wherein, relative to a total amount of 100% by mass of the cement clinker powder, ground granulated blast furnace slag, and limestone powder, the proportion of the cement clinker powder is 42 to 59% by mass, the proportion of the ground granulated blast furnace slag powder is 27 to 55% by mass, and the proportion of the limestone powder is 2 to 26% by mass, and the mass ratio of the ground granulated blast furnace slag powder to the limestone powder is 1.4 to 25.0, and have completed the present invention. That is, the present invention provides the following [1] to [9]. [1] A powdery mixed cement composition comprising cement clinker powder, gypsum, ground granulated blast furnace slag, and limestone powder, characterized in that, in a total amount of 100% by mass of the cement clinker powder, ground granulated blast furnace slag, and limestone powder, the proportion of the cement clinker powder is 42 to 59% by mass, the proportion of the ground granulated blast furnace slag powder is 27 to 55% by mass, and the proportion of the limestone powder is 2 to 26% by mass, and the mass ratio of the ground granulated blast furnace slag powder to the limestone powder (ground granulated blast furnace slag / limestone powder) is 1.4 to 25.0. [2] The mixed cement composition according to [1], wherein the proportion of the aluminate phase in the cement clinker powder is 7 to 17 mass %. [3] The mixed cement composition according to [1] or [2], wherein the amount of the gypsum per 100 parts by mass of the cement clinker powder is 1.5 to 6.0 parts by mass in terms of SO3. [4] The mixed cement composition according to any one of [1] to [3], wherein the proportion of the total alkali content (Na2O + 0.658K2O) in the mixed cement composition (excluding the ground granulated blast furnace slag) is 0.5 to 3.0 mass%. [5] The mixed cement composition according to any one of [1] to [4], wherein the proportion of the total alkali content (Na2O+0.658K2O) in the cement clinker powder is 0.8 to 5.0 mass%.

[0007] [6] A method for producing the mixed cement composition according to any one of [1] to [5] above, comprising a preparation step of mixing cement clinker powder, gypsum, ground granulated blast furnace slag, and limestone powder to prepare the mixed cement composition. [7] The method for producing a mixed cement composition according to [6], wherein an alkali metal-containing substance is mixed in the preparation step. [8] A method for inhibiting alkali-aggregate reaction in a powdery mixed cement containing cement clinker powder, gypsum, and ground granulated blast furnace slag, comprising a limestone powder adding step of mixing the mixed cement with limestone powder to prepare a limestone powder-containing mixed cement such that, relative to a total amount of 100% by mass of the cement clinker powder, the ground granulated blast furnace slag, and the limestone powder, the proportion of the cement clinker powder is 42 to 59% by mass, the proportion of the ground granulated blast furnace slag powder is 27 to 55% by mass, and the proportion of the limestone powder is 2 to 26% by mass, and the mass ratio of the ground granulated blast furnace slag powder to the limestone powder (ground granulated blast furnace slag powder / limestone powder) is 1.4 to 25.0. [9] The method for inhibiting alkali-aggregate reaction in a blended cement according to [8], wherein the blended cement is a blast-furnace cement type B. [Effects of the Invention]

[0008] According to the mixed cement composition of the present invention, by using ground granulated blast furnace slag and limestone powder, the amount of cement clinker powder used can be relatively reduced, and a mixed cement composition can be obtained that has excellent strength development and suppresses alkali-aggregate reaction. DETAILED DESCRIPTION OF THE INVENTION

[0009] The mixed cement composition of the present invention is a powdery mixed cement composition containing cement clinker powder, gypsum, ground granulated blast furnace slag, and limestone powder, wherein, relative to a total amount of 100% by mass of the cement clinker powder, ground granulated blast furnace slag, and limestone powder, the proportion of the cement clinker powder is 42 to 59% by mass, the proportion of the ground granulated blast furnace slag powder is 27 to 55% by mass, and the proportion of the limestone powder is 2 to 26% by mass, and the mass ratio of the ground granulated blast furnace slag to the limestone powder (ground granulated blast furnace slag / limestone powder) is 1.4 to 25.0. In this specification, the term "mixed cement composition" refers to a composition containing cement clinker powder, which is made by mixing a plurality of types of powdery materials.

[0010] The proportion of cement clinker powder in a total of 100% by mass of cement clinker powder, ground granulated blast furnace slag, and limestone powder is 42 to 59% by mass, preferably 43 to 58% by mass, more preferably 44 to 57% by mass, and particularly preferably 44.5 to 56% by mass. If the proportion is less than 42% by mass, strength development decreases. If the proportion exceeds 59% by mass, the effect of inhibiting alkali-aggregate reaction decreases.

[0011] The proportion of the aluminate phase (3CaO·Al2O3) in the cement clinker powder is preferably 7 to 17 mass %. From the viewpoint of improving early strength development, the above proportion is preferably at least 7% by mass, and more preferably at least 8% by mass. Furthermore, from the viewpoint of further improving the fluidity and workability of mortar containing the mixed cement composition, the above ratio is preferably 17% by mass or less, more preferably 15% by mass or less, even more preferably 13% by mass or less, and particularly preferably 12% by mass or less.

[0012] The proportion of alite (3CaO SiO2) in the cement clinker powder is preferably 51 to 63 mass%, more preferably 51.5 to 61 mass%, even more preferably 52 to 60 mass%, and particularly preferably 52.5 to 58 mass%. If the proportion is 51 mass% or more, the early strength development is further improved. If the proportion is 63 mass% or less, the fluidity and workability of mortar and the like containing the mixed cement composition are further improved. The proportion of belite (2CaO SiO2) in the cement clinker powder is preferably 10 to 22 mass%, more preferably 12 to 21 mass%, and particularly preferably 14 to 20 mass%, from the viewpoint of strength development, etc. If the proportion is 10 mass% or more, long-term strength development is further improved. The proportion of the ferrite phase (4CaO·Al2O3·Fe2O3) in the cement clinker powder is preferably 7 to 20 mass %, more preferably 8 to 15 mass %, and particularly preferably 9 to 12 mass %, from the viewpoint of strength development and the like.

[0013] In this specification, the proportions of the aluminate phase, alite, belite, and ferrite phase in the cement clinker powder are calculated as proportions in the total amount (100 mass%) of the cement clinker powder based on the chemical components of the cement clinker raw materials and the cement clinker (burned product) using the following Bogue formulas (1) to (4). (1) Alite (mass %) = (4.07 × CaO (mass %)) - (7.60 × SiO2 (mass %)) - (6.72 × Al2O3 (mass %)) - (1.43 × Fe2O3 (mass %)) (2) B-lite (mass%) = (2.87 x SiO2 (mass%)) - (0.754 x C3S (mass%)) (3) Aluminate phase (mass%)=(2.65×Al2O3(mass%))-(1.69×Fe2O3(mass%)) (4) Ferrite phase (mass%) = 3.04 × Fe2O3 (mass%)

[0014] As the raw material for cement clinker, raw materials generally used in the production of cement clinker can be used, such as CaO raw materials such as limestone, quicklime, and slaked lime, silicon-containing raw materials such as silica stone, clay, and volcanic ash, aluminum-containing raw materials such as clay, and iron-containing raw materials such as iron slag and iron cake. In addition to the above raw materials, one or more materials selected from industrial waste, general waste, and construction waste soil can be used as part of the raw materials. These waste materials usually contain substances containing alkali metals such as sodium and potassium. Here, industrial waste refers to waste generated as a result of business activities. Examples of industrial waste include raw concrete sludge, various sludges (e.g., sewage sludge, water purification sludge, steelmaking sludge, etc.), construction waste, concrete waste, various incineration ashes (e.g., coal ash, chicken manure ash, livestock manure ash, biomass ash, sludge incineration ash), foundry sand, rock wool, waste glass, secondary blast furnace ash, various by-products, and unused resources (unused remaining materials, etc.). Municipal waste refers to waste other than industrial waste. Examples of general waste include dried sewage sludge, municipal waste incineration ash, and shells.

[0015] The proportion of the total alkali content (Na2O+0.658K2O) in the cement clinker powder is preferably 0.8 to 5.0 mass %. From the viewpoint of increasing the amount of waste used as a raw material for cement clinker, the above ratio is preferably 0.8% by mass or more, more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, and particularly preferably 2.0% by mass or more. Also, from the viewpoint of further improving the fluidity and workability of mortar or the like containing the mixed cement composition, the above ratio is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.5% by mass or less, and particularly preferably 3.0% by mass or less. Furthermore, if the ratio is within the above range, the alkali-aggregate reaction can be more effectively suppressed.

[0016] A method for producing cement clinker includes mixing the above-mentioned raw materials so that the proportions of the aluminate phase, alite, belite, and ferrite phase in the resulting cement clinker are each desired, and firing the resulting mixture at preferably 1,200 to 1,600°C, more preferably 1,350 to 1,500°C. The lumpy cement clinker obtained by burning is suitably pulverized into powder using a pulverizing means such as a ball mill. In order to adjust the proportion of the total alkali amount (NaO + 0.658KO) in the cement clinker powder and the proportion of the total alkali amount (NaO + 0.658KO) excluding blast furnace slag powder in a mixed cement composition containing the cement clinker powder within a desired numerical range, an alkali metal-containing substance (e.g., a reagent such as NaOH, KOH, NaSO, or KSO) may be added to a lump of cement clinker or powdered cement clinker, and the mixture may be pulverized or mixed to prepare cement clinker powder. Specifically, examples of the method include a method of simultaneously crushing and mixing massive cement clinker obtained by burning with an alkali metal-containing substance, and a method of mixing powdered cement clinker after crushing with an alkali metal-containing substance.

[0017] The Blaine specific surface area of ​​the cement clinker powder is preferably 2,000 to 6,000 cm 2 / g, more preferably 2,500 to 5,000 cm 2 / g, more preferably 2,800 to 4,000 cm 2 / g, particularly preferably 3,000 to 3,500 cm 2 / g. The above Blaine specific surface area is 2,000 cm 2 / g or more, the strength development is further improved. 2 / g or less, the fluidity and workability of mortar and the like containing the mixed cement composition are further improved.

[0018] The blended cement composition contains gypsum to adjust the setting time and improve workability. The proportion of gypsum in the mixed cement composition is preferably 1.0 to 5.5 mass%, more preferably 1.5 to 5.3 mass%, even more preferably 2.0 to 5.0 mass%, and particularly preferably 2.5 to 4.5 mass%, in terms of SO3, from the viewpoints of strength development and the fluidity and workability of mortar and the like containing the mixed cement composition. Furthermore, the amount of gypsum per 100 parts by mass of cement clinker powder is preferably 1.5 to 6.0 parts by mass, more preferably 2.0 to 5.8 parts by mass, even more preferably 2.5 to 5.5 parts by mass, and particularly preferably 2.8 to 5.0 parts by mass, in terms of SO3, from the viewpoints of strength development and the fluidity and workability of mortar and the like containing the mixed cement composition. Examples of gypsum include natural gypsum dihydrate, flue gas desulfurization gypsum, phosphate gypsum, titanic gypsum, hydrofluoric gypsum, refined gypsum, hemihydrate gypsum, anhydrous gypsum, etc. These may be used alone or in combination of two or more.

[0019] The proportion of ground granulated blast furnace slag in a total of 100% by mass of cement clinker powder, ground granulated blast furnace slag, and limestone powder is 27 to 55% by mass, preferably 27.5 to 54% by mass, more preferably 28 to 53% by mass, even more preferably 29 to 50% by mass, even more preferably 30 to 45% by mass, and particularly preferably 32 to 40% by mass. If the proportion is less than 27% by mass, long-term strength development decreases. If the proportion exceeds 55% by mass, the effect of reducing the amount of ground granulated blast furnace slag used by using another component (limestone powder) instead of ground granulated blast furnace slag is reduced. Normally, when the proportion of ground granulated blast furnace slag in a blended cement is 40% by mass or less, the alkali-aggregate reaction is likely to proceed, and the durability of the hardened blended cement is likely to decrease. However, in the blended cement composition of the present invention, the alkali-aggregate reaction is unlikely to proceed even when the proportion of ground granulated blast furnace slag is 40% by mass or less.

[0020] An example of the ground granulated blast furnace slag is pulverized granulated slag obtained by rapidly cooling with water and crushing molten slag, which is a by-product of producing pig iron in a blast furnace. The basicity of the ground granulated blast furnace slag is preferably 1.7 or more, more preferably 1.75 or more, and particularly preferably 1.8 or more. If the basicity is 1.7 or more, the strength development is further improved. The basicity is calculated using the following formula (5). Basicity = [(CaO + MgO + Al2O3) / SiO2] (5) (The chemical formula in the formula represents the content (%) of the compound represented by the chemical formula in the ground granulated blast furnace slag.)

[0021] The Blaine specific surface area of ​​the ground granulated blast furnace slag is preferably 3,000 to 7,000 cm 2 / g, more preferably 3,500 to 6,000 cm 2 / g, and particularly preferably 4,000 to 5,000 cm 2 / g. The above Blaine specific surface area is 3,000 cm 2 / g or more, the strength development is further improved. 2 / g or less, the fluidity and workability of mortar and the like containing the mixed cement composition are further improved.

[0022] The proportion of limestone powder in a total of 100% by mass of cement clinker powder, ground granulated blast furnace slag, and limestone powder is 2 to 26% by mass, preferably 4 to 24% by mass, more preferably 6 to 20% by mass, even more preferably 7 to 18% by mass, and particularly preferably 8 to 16% by mass. If the proportion is less than 2% by mass, the effect of inhibiting alkali-aggregate reaction is reduced. Furthermore, the effect of reducing the amount of ground granulated blast furnace slag used by using another component (limestone powder) instead of ground granulated blast furnace slag is reduced. If the proportion exceeds 26% by mass, strength development is reduced.

[0023] The mass ratio of ground granulated blast furnace slag to powdered limestone (ground granulated blast furnace slag / powdered limestone) is 1.4 to 25.0, preferably 1.5 to 22.0, more preferably 2.0 to 20.0, and particularly preferably 2.8 to 18.0. If the ratio is less than 1.4, the effect of inhibiting alkali-aggregate reaction decreases. If the ratio exceeds 25.0, the initial strength development decreases. Furthermore, the effect of reducing the amount of ground granulated blast furnace slag used by using another component (powdered limestone) instead of ground granulated blast furnace slag is reduced.

[0024] The content of calcium carbonate in the limestone powder is preferably 90% by mass or more, more preferably 95% by mass or more. If the content is 90% by mass or more, strength development is further improved. The limestone powder can be crushed limestone, or carbonated powder of raw concrete sludge or concrete. These powders can fix carbon dioxide gas that would otherwise be released into the atmosphere.

[0025] The Blaine specific surface area of ​​the limestone powder is preferably 3,000 to 20,000 cm 2 / g, more preferably 3,500 to 18,000 cm 2 / g, more preferably 4,000 to 15,000 cm 2 / g, more preferably 4,200 to 10,000 cm 2 / g, particularly preferably 4,500 to 9,500 cm 2 / g. The above Blaine specific surface area is 3,000 cm 2 / g or more, the strength development is further improved. 2 / g or less, the fluidity and workability of mortar and the like containing the mixed cement composition are further improved.

[0026] The proportion of the total amount of cement clinker powder, ground granulated blast furnace slag, and limestone powder in the total amount (100% by mass) of the powdery mixed cement composition of the present invention is not particularly limited, but is preferably 80% by mass or more, more preferably 85% by mass or more, and particularly preferably 90% by mass or more. Examples of materials (other materials) other than cement clinker powder, ground granulated blast furnace slag, and limestone powder include silica fume.

[0027] The proportion of the total alkali content (Na2O + 0.658K2O) in the mixed cement composition of the present invention (excluding the above ground granulated blast furnace slag) is preferably 0.5 to 3.0 mass%, more preferably 0.6 to 2.5 mass%, even more preferably 0.8 to 2.0 mass%, and particularly preferably 1.0 to 1.8 mass%. If the proportion is 0.5 mass% or more, the amount of waste material used as a raw material for cement clinker can be increased. If the proportion is 3.0 mass% or less, the fluidity and workability of mortar containing the mixed cement composition can be further improved. In addition, the alkali-aggregate reaction can be further suppressed. The reason why the proportion of the total alkali content is the proportion in the cement composition excluding the ground granulated blast furnace slag is that the alkali components in the ground granulated blast furnace slag have a slower elution rate than the alkali components in the cement clinker powder, and therefore their influence on the alkali-aggregate reactivity, fluidity, workability, etc. is negligibly small.

[0028] The mixed cement composition of the present invention is one in which the alkali-aggregate reaction is suppressed. Therefore, the mixed cement composition of the present invention is suitable for cases where the alkali-aggregate reaction is expected to proceed easily, such as when using aggregate that is likely to cause the alkali-aggregate reaction, or when an alkali accelerator is added to accelerate hardening in cold regions.

[0029] The method for producing the mixed cement composition of the present invention may include a method including a preparation step of mixing cement clinker powder, gypsum, ground granulated blast furnace slag, and limestone powder to prepare the above-mentioned mixed cement composition. The method for mixing the materials is not particularly limited, and examples include (i) a method of mixing a composition containing cement clinker powder, gypsum, and ground granulated blast furnace slag (e.g., blast furnace cement types A to C) with limestone powder, (ii) a method of mixing cement clinker, blast furnace slag, limestone, and gypsum while simultaneously grinding them, and (iii) a method of mixing pre-ground cement (a mixture of clinker powder and gypsum), pre-ground ground granulated blast furnace slag, and pre-ground limestone powder. In the above method (iii), blast furnace slag and gypsum may be mixed in advance while being simultaneously pulverized.

[0030] In addition, in the method for producing a mixed cement composition, in order to adjust the proportion of the total alkali content (Na2O + 0.658K2O) in the mixed cement composition (excluding the above ground granulated blast furnace slag) within a desired numerical range, an alkali metal-containing substance (e.g., a reagent such as NaOH, KOH, Na2SO4, or K2SO4) may be added and mixed when mixing the materials of the mixed cement composition in the preparation step or after mixing the materials. In the preparation step, the blending amounts of the respective materials may be appropriately adjusted so that the blending ratio of the respective materials in the resulting mixed cement composition is as desired. In the above method (i), a component measuring step may be carried out before the preparation step to measure the proportions of the cement clinker powder and the ground granulated blast furnace slag in the composition containing the cement clinker powder, gypsum, and ground granulated blast furnace slag.The amount of limestone powder to be mixed in the preparation step can be determined based on the measured proportions of the cement clinker powder and the ground granulated blast furnace slag.

[0031] In addition, in the method for producing a mixed cement composition, at least some of the materials constituting the mixed cement composition may be prepared separately without being mixed in advance, and when the hydraulic composition is prepared by mixing each material with water, all of the materials constituting the mixed cement composition may be mixed with water. Specifically, there is a method in which limestone powder prepared separately from the blast furnace cement is mixed when mixing the blast furnace cement with water.

[0032] A hydraulic composition can be prepared by mixing the mixed cement composition of the present invention with water. The hydraulic composition may contain aggregate (fine aggregate, coarse aggregate) and other materials that are blended as needed. Examples of other materials that are blended as needed include various additives such as water-reducing agents, antifoaming agents, and shrinkage-reducing agents. In this specification, the hydraulic composition refers to a hardenable composition containing a cement composition and water, and includes the hydraulic composition in its pre-hardened form and its hardened form. Examples of the hydraulic composition include paste, mortar, and concrete. The compressive strength of the mixed cement composition of the present invention at 7 days, measured by the method described in "JIS R 5201:2015 Physical testing methods for cement," is preferably 26 MPa or more, more preferably 27 MPa or more, and particularly preferably 28 MPa or more.

[0033] Furthermore, by mixing limestone powder with a powdery mixed cement containing cement clinker powder, gypsum, and ground granulated blast furnace slag, and preparing the resulting mixed cement so that it satisfies the requirements for the mixed cement composition of the present invention, it is possible to suppress the alkali-aggregate reaction of the mixed cement. Specifically, the present invention includes a method for inhibiting alkali-aggregate reaction in a mixed cement, which includes a limestone powder addition step of mixing a powdered mixed cement containing cement clinker powder, gypsum, and ground granulated blast furnace slag with limestone powder to prepare a limestone powder-containing mixed cement so that, relative to a total amount of 100% by mass of the cement clinker powder, ground granulated blast furnace slag, and limestone powder, the proportion of cement clinker powder is 42 to 59% by mass, the proportion of ground granulated blast furnace slag powder is 27 to 55% by mass, and the proportion of limestone powder is 2 to 26% by mass, and the mass ratio of the ground granulated blast furnace slag powder to the limestone powder (ground granulated blast furnace slag / limestone powder) is 1.4 to 25.0.

[0034] Before the limestone powder adding step, a mixed cement component measuring step may be carried out in which the proportions of cement clinker powder, ground granulated blast furnace slag, etc. in a composition containing cement clinker powder, gypsum, and ground granulated blast furnace slag are measured. The amount of limestone powder to be mixed in the mixed cement preparation step can be determined based on the measured proportions of cement clinker powder, ground granulated blast furnace slag, etc. In addition, in the mixed cement preparation step, in addition to the limestone powder, ground granulated blast furnace slag, gypsum, and alkali metal-containing substances (e.g., reagents such as NaOH, KOH, Na2SO4, and K2SO4) may be appropriately mixed so that the resulting mixed cement satisfies the above-mentioned mixed cement composition of the present invention.

[0035] The mixed cement containing cement clinker powder, gypsum, and ground granulated blast furnace slag that is the target of the method for inhibiting alkali-aggregate reaction in mixed cement is not particularly limited, but an example thereof is blast furnace cement type B. Type B blast furnace cement has a proportion of blast furnace slag powder exceeding 30% by mass but not exceeding 60% by mass, and is prone to alkali-aggregate reaction. However, by mixing limestone powder into Type B blast furnace cement, the alkali-aggregate reaction of Type B blast furnace cement can be suppressed. [Example]

[0036] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Ground blast furnace slag; Blaine specific surface area: 4,230 cm 2 / g, density: 2.92g / cm 3 , basicity: 1.80, corresponds to 4000 ground granulated blast furnace slag as specified in "JIS A 6206:2013 (ground granulated blast furnace slag for concrete)" (2) Limestone powder; Blaine specific surface area: 9,040 cm 2 / g, calcium carbonate content: 95% by mass or more, density: 2.72 g / cm 3 , Total alkali content in limestone powder: 0 mass% [Production of blast furnace slag mixture] The above ground blast furnace slag and gypsum (flue gas desulfurization gypsum) were mixed to produce a blast furnace slag mixture (a mixture of ground blast furnace slag and gypsum) with a gypsum content of 2.0 mass% (SO3 equivalent). [Manufacturing of Cement A to B] Using the reagents as raw materials, cement clinker was burned in a test kiln to prepare cement clinker having the mineral composition shown in Table 1. The obtained cement clinker, gypsum dihydrate (flue gas desulfurization gypsum), and gypsum hemihydrate were pulverized and mixed using a mill to obtain cements A to B containing cement clinker powder and gypsum. The amount of gypsum was determined so that the ratio of gypsum in the cement would be the value shown in Table 1.

[0037] [Table 1]

[0038] [Examples 1 to 17, Comparative Examples 1 to 6] The types of cement shown in Table 2 (a mixture of cement clinker powder and gypsum), a blast furnace slag mixture (a mixture of ground blast furnace slag and gypsum), and limestone powder were mixed in the amounts shown in Table 2 to obtain mixed cement compositions. The proportions of cement clinker powder and the like in 100 mass% of the total amount of cement clinker powder (shown as "clinker" in Table 2), ground granulated blast furnace slag (shown as "blast furnace slag" in Table 2), and limestone powder (shown as "limestone" in Table 2) contained in the mixed cement composition, and the amount of gypsum (SO3 equivalent value) per 100 parts by mass of cement clinker powder are as shown in Table 2.

[0039] The compressive strength of the mixed cement composition was measured at ages of 3 days, 7 days, and 28 days in accordance with the method described in "JIS R 5201:2015 Physical testing methods for cement." In addition, alkali-aggregate reactivity tests were conducted on the mixed cement compositions, and the expansion coefficients of the hardened bodies of the mixed cement compositions were measured after 2, 4, 8, and 13 weeks. These tests were conducted in accordance with JIS A 1146:2017, "Test Method for Alkali-Silica Reactivity of Aggregates (Mortar Bar Method)," and the same aggregate was used. A smaller expansion coefficient indicates greater suppression of alkali-aggregate reaction and superior durability. For each mixed cement composition, the total alkali content (excluding the ground granulated blast furnace slag) was approximately 0.2 to 0.3% by mass. However, when preparing the mortar in the above tests, an aqueous NaOH solution (reagent) was added to adjust the total alkali content (excluding the ground granulated blast furnace slag) to the values ​​shown in Table 3. The results are shown in Table 3.

[0040] [Table 2]

[0041] [Table 3]

[0042] From Table 2, it can be seen that the compressive strengths of Examples 1 to 4 at 28 days (56.2 to 58.7 MPa) are greater than the compressive strengths of Comparative Example 1 (cement clinker powder: 55.2 mass%, ground granulated blast furnace slag: 44.8 mass%, limestone powder: 0 mass%) and Comparative Example 2 (cement clinker powder: 54.7 mass%, ground granulated blast furnace slag: 24.7 mass%, limestone powder: 20.6 mass%) at 28 days (51.3 to 53.3 MPa). Furthermore, the expansion rates of Examples 1 to 4 at 13 weeks of age (0.30 to 0.32%) were smaller than those of Comparative Examples 1 and 2 at 13 weeks of age (0.33 to 0.37%), indicating that alkali-aggregate reaction was suppressed.

[0043] It can be seen that the compressive strengths of Examples 5 to 8 at 28 days (54.0 to 56.6 MPa) are greater than the compressive strengths of Comparative Example 3 (cement clinker powder: 45.2 mass%, ground granulated blast furnace slag: 54.8 mass%, limestone powder: 0 mass%) and Comparative Example 4 (cement clinker powder: 44.7 mass%, ground granulated blast furnace slag: 29.6 mass%, limestone powder: 25.8 mass%) at 28 days (46.6 to 50.3 MPa). Furthermore, it can be seen that the expansion rate (0.19%) of Comparative Example 4 (mass ratio of ground blast furnace slag to limestone powder: 1.1) at 13 weeks of age is smaller than the expansion rates (0.11 to 0.15%) of Examples 5 to 8 at 13 weeks of age. The expansion rate of Comparative Example 3 at 13 weeks (0.11%) is the same as that of Example 5 at 13 weeks (0.11%). This is thought to be because Comparative Example 3 does not use limestone powder and contains a large proportion of ground granulated blast furnace slag. It can be seen that the expansion rates of Examples 12 to 14 at an age of 13 weeks (0.10 to 0.22%) are smaller than the expansion rate of Comparative Example 5 at an age of 13 weeks (0.32%). It can be seen that the compressive strengths of Examples 15 to 17 at an age of 28 days (54.3 to 57.8 MPa) are greater than the compressive strength of Comparative Example 6 at an age of 28 days (51.3 MPa).

Claims

1. A powdery mixed cement composition comprising cement clinker powder, gypsum, ground granulated blast furnace slag, and limestone powder, the proportion of the cement clinker powder is 45.0 to 55.0 mass%, the proportion of the ground granulated blast furnace slag is 39.8 to 44.7 mass%, and the proportion of the limestone powder is 5.2 to 10.4 mass%, based on a total amount of 100 mass% of the cement clinker powder, the ground granulated blast furnace slag, and the limestone powder; A powdery mixed cement composition characterized in that the mass ratio of the ground granulated blast furnace slag to the ground limestone (ground granulated blast furnace slag / ground limestone) is 4.3 to 7.

7.

2. 2. The mixed cement composition according to claim 1, wherein the proportion of the aluminate phase in the cement clinker powder is 7 to 17 mass%.

3. The amount of the gypsum relative to 100 parts by mass of the cement clinker powder is SO ３ The mixed cement composition according to claim 1 or 2, wherein the converted value is 1.5 to 6.0 parts by mass.

4. The total alkali content (Na) in the mixed cement composition (excluding the ground granulated blast furnace slag) ２ O+0.658K ２ The mixed cement composition according to any one of claims 1 to 3, wherein the proportion of 0) is 0.5 to 3.0 mass%.

5. The total alkali content (Na ２ O+0.658K ２ The mixed cement composition according to any one of claims 1 to 4, wherein the proportion of 0) is 0.8 to 5.0 mass%.

6. A method for producing the mixed cement composition according to any one of claims 1 to 5, A method for producing a mixed cement composition, comprising a preparation step of mixing cement clinker powder, gypsum, ground granulated blast furnace slag, and limestone powder to prepare the mixed cement composition.

7. The method for producing a mixed cement composition according to claim 6, wherein an alkali metal-containing substance is mixed in the preparation step.

8. A method for inhibiting alkali-aggregate reaction in a powdery mixed cement containing cement clinker powder, gypsum, and ground granulated blast furnace slag, comprising: and a limestone powder adding step of mixing the mixed cement with limestone powder to prepare a limestone powder-containing mixed cement such that, relative to a total amount of 100% by mass of the cement clinker powder, the ground granulated blast furnace slag, and the limestone powder, the proportion of the cement clinker powder is 45.0 to 55.0% by mass, the proportion of the ground granulated blast furnace slag powder is 39.8 to 44.7% by mass, and the proportion of the limestone powder is 5.2 to 10.4% by mass, and the mass ratio of the ground granulated blast furnace slag powder to the limestone powder (ground granulated blast furnace slag powder / limestone powder) is 4.3 to 7.

7. Method for inhibiting alkali-aggregate reaction in blended cement.

9. 9. The method for inhibiting alkali-aggregate reaction in a blended cement according to claim 8, wherein the blended cement is a blast-furnace cement type B.

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