Composite cement composition and method for producing the same

Abstract

To provide a mixed cement composition that can reduce the amount of cement clinker powder to be used, has excellent strength development, and suppresses alkali aggregate reaction.SOLUTION: A powdered mixed cement composition containing cement clinker powder, gypsum, blast furnace slag fine powder, and limestone powder, wherein the proportion of the cement clinker powder is 42-59 mass%, that of the blast furnace slag fine powder is 27-55 mass%, and that of the limestone powder is 2-26 mass%, relative to the total amount of 100 mass% of the cement clinker powder, blast furnace slag fine powder, and limestone powder; and the mass ratio of the blast furnace slag fine powder to the limestone powder (blast furnace slag fine powder / limestone powder) is 1.4 to 25.0.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Currently, due to measures to combat global warming, the cement manufacturing industry is also required to significantly reduce carbon dioxide emissions. A large portion of the carbon dioxide emissions in the cement manufacturing industry is generated during the production of cement clinker, and in order to reduce carbon dioxide emissions, it is required to reduce the production volume of cement clinker. As a cement capable of reducing the amount of cement clinker used, blast furnace cement, which is obtained by substituting a part of the cement clinker powder with fine blast furnace slag powder, is known. As a cement composition using fine blast furnace slag powder, Patent Document 1 describes a cement composition containing at least the components shown in the following (a), (b), and (c) in the following ratios. (a) Cements containing a ground product of cement clinker having a hydraulicity (H.M.) of 2.0 to 2.4, a silicate ratio (S.M.) of 1.3 to 3.0, and an iron ratio (I.M.) of 1.5 to 3.0, and gypsum: 20 to 50% by mass (b) Fine blast furnace slag powder having a Blaine specific surface area of 5,000 cm 2 / g or more: 30 to 70% by mass (c) Limestone powder: more than 0% by mass to 40% by mass

[0003] On the other hand, in recent years, due to the decrease in coal-fired power generation, the production volume of coal ash, which has been used as a cement clinker raw material, has been decreasing. Therefore, biomass ash has attracted attention as a cement clinker raw material to replace coal ash. In addition, as conventionally used cement clinker raw materials, there are wastes such as construction-generated soil, municipal waste incineration ash, and sewage sludge. Since biomass ash and the above-mentioned waste contain more alkalis compared to coal ash, when using the above-mentioned biomass ash, etc. as a substitute for coal ash which is a cement clinker raw material, the amount of alkalis in the produced cement clinker increases.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0006] As a result of intensive studies to solve the above problems, the present inventors have found that a powdery blended cement composition containing cement clinker powder, gypsum, finely ground blast furnace slag, and limestone powder, wherein the proportion of cement clinker powder is 42 to 59% by mass, the proportion of finely ground blast furnace slag is 27 to 55% by mass, and the proportion of limestone powder is 2 to 26% by mass in a total of 100% by mass of the cement clinker powder, finely ground blast furnace slag, and limestone powder, and the mass ratio of finely ground blast furnace slag to limestone powder is 1.4 to 25.0, can achieve the above object, and thus completed the present invention. That is, the present invention provides the following [1] to [9]. [1] A powdery blended cement composition containing cement clinker powder, gypsum, finely ground blast furnace slag, and limestone powder, wherein the proportion of the cement clinker powder is 42 to 59% by mass, the proportion of the finely ground blast furnace slag is 27 to 55% by mass, the proportion of the limestone powder is 2 to 26% by mass, and the mass ratio (finely ground blast furnace slag / limestone powder) of the finely ground blast furnace slag to the limestone powder is 1.4 to 25.0 in a total of 100% by mass of the cement clinker powder, the finely ground blast furnace slag, and the limestone powder. [2] The blended cement composition according to [1], wherein the proportion of the aluminate phase in the cement clinker powder is 7 to 17% by mass. [3] The blended cement composition according to [1] or [2], wherein the amount of the gypsum with respect to 100 parts by mass of the cement clinker powder is 1.5 to 6.0 parts by mass in terms of SO3 conversion value. [4] The blended cement composition according to any one of [1] to [3], wherein the proportion of the total alkali amount (Na2O + 0.658K2O) in the blended cement composition (excluding the finely ground blast furnace slag) is 0.5 to 3.0% by mass. [5] The blended cement composition according to any one of [1] to [4], wherein the proportion of the total alkali amount (Na2O + 0.658K2O) in the cement clinker powder is 0.8 to 5.0% by mass.

[0007] [6] A method for manufacturing the blended cement composition according to any one of [1] to [5] above, comprising a preparation step of mixing cement clinker powder, gypsum, blast furnace slag fine powder, and limestone powder to prepare the above blended cement composition. The method for manufacturing a blended cement composition is characterized by this. [7] The method for manufacturing the blended cement composition according to [6] above, wherein an alkali metal-containing substance is mixed in the above preparation step. [8] A method for suppressing alkali-aggregate reaction of a powdery blended cement containing cement clinker powder, gypsum, and blast furnace slag fine powder, comprising mixing the above blended cement and limestone powder, and in a total amount of 100% by mass of the above cement clinker powder, the above blast furnace slag fine powder, and the above limestone powder, the proportion of the above cement clinker powder is 42 to 59% by mass, the proportion of the above blast furnace slag fine powder is 27 to 55% by mass, the proportion of the above limestone powder is 2 to 26% by mass, and the mass ratio of the above blast furnace slag fine powder to the above limestone powder (blast furnace slag fine powder / limestone powder) is 1.4 to 25.0. The method for suppressing alkali-aggregate reaction of a blended cement includes a limestone powder addition step of preparing a limestone powder-containing blended cement. [9] The method for suppressing alkali-aggregate reaction of the blended cement according to [8] above, wherein the above blended cement is blast furnace cement type B.

Advantages of the Invention

[0008] According to the blended cement composition of the present invention, by using blast furnace slag fine powder and limestone powder, the amount of cement clinker powder used can be relatively reduced, a blended cement composition excellent in strength development property and having suppressed alkali-aggregate reaction can be obtained.

Embodiments for Carrying Out the Invention

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

[0010] In 100% by mass of the total amount of the cement clinker powder, the finely ground blast furnace slag, and the limestone powder, the proportion of the cement clinker 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 above proportion is less than 42% by mass, the strength development property will decrease. If the above proportion exceeds 59% by mass, the effect of suppressing the alkali-aggregate reaction will become small.

[0011] The proportion of the aluminate phase (3CaO·Al2O3) in the cement clinker powder is preferably 7 to 17% by mass. From the viewpoint of improving the initial strength development property and the like, the above proportion is preferably 7% by mass or more, and more preferably 8% by mass or more. Also, from the viewpoint of further improving the fluidity and workability of mortar and the like containing the mixed cement composition, the above proportion is preferably 17% by mass or less, more preferably 15% by mass or less, still 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% by mass, more preferably 51.5 to 61% by mass, still more preferably 52 to 60% by mass, and particularly preferably 52.5 to 58% by mass. If the above proportion is 51% by mass or more, the initial strength development property is further improved. If the above proportion is 63% by mass or less, the fluidity and workability of mortar containing the blended cement composition are further improved. The proportion of belite (2CaO·SiO2) in the cement clinker powder is preferably 10 to 22% by mass, more preferably 12 to 21% by mass, and particularly preferably 14 to 20% by mass from the viewpoint of strength development property and the like. If the above proportion is 10% by mass or more, the long-term strength development property is further improved. The proportion of ferrite phase (4CaO·Al2O3·Fe2O3) in the cement clinker powder is preferably 7 to 20% by mass, more preferably 8 to 15% by mass, and particularly preferably 9 to 12% by mass from the viewpoint of strength development property 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 using the following Bogue's calculation formulas (1) to (4) based on the chemical components of the cement clinker raw material and the cement clinker (fired product) as the proportions in the total amount (100% by mass) of the cement clinker powder. (1) Alite (% by mass) = (4.07 × CaO (% by mass)) - (7.60 × SiO2 (% by mass)) - (6.72 × Al2O3 (% by mass)) - (1.43 × Fe2O3 (% by mass)) (2) Belite (% by mass) = (2.87 × SiO2 (% by mass)) - (0.754 × C3S (% by mass)) (3) Aluminate phase (% by mass) = (2.65 × Al2O3 (% by mass)) - (1.69 × Fe2O3 (% by mass)) (4) Ferrite phase (% by mass) = 3.04 × Fe2O3 (% by mass)

[0014] As raw materials for cement clinker, common raw materials used in the production of cement clinker can be used. Specifically, CaO raw materials such as limestone, quicklime, and slaked lime, silicon-containing raw materials such as silica, clay, and volcanic ash, aluminum-containing raw materials such as clay, and iron-containing raw materials such as iron slag and iron cake can be used. Furthermore, in addition to the above raw materials, one or more selected from industrial waste, general waste, and construction-generated soil can be used as part of the raw materials. Usually, these wastes contain substances containing alkali metals such as sodium and potassium. Here, industrial waste refers to waste generated along with business activities. Examples of industrial waste include raw concrete sludge, various sludges (e.g., sewage sludge, water purification sludge, iron-making sludge, etc.), construction waste materials, concrete waste materials, various incineration ashes (e.g., coal ash, chicken manure ash, livestock manure ash, biomass ash, sludge incineration ash), foundry sand, rock wool, waste glass, blast furnace secondary ash, various by-products, unused resources (materials remaining without being used, etc.). General waste refers to waste other than industrial waste. Examples of general waste include dried sewage sludge powder, municipal waste incineration ash, shells, etc.

[0015] The proportion of the total alkali content (Na2O + 0.658K2O) in the cement clinker powder is preferably 0.8 to 5.0% by mass. From the perspective of being able to use a larger amount of waste as a raw material for cement clinker, the above proportion is preferably 0.8% by mass or more, more preferably 1.0% by mass or more, still more preferably 1.5% by mass or more, and particularly preferably 2.0% by mass or more. Also, from the perspective of further improving the fluidity and workability of mortar containing a blended cement composition, etc., the above proportion is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, still more preferably 3.5% by mass or less, and particularly preferably 3.0% by mass or less. Moreover, if the above proportion is within the above numerical range, the effect of further suppressing the alkali-aggregate reaction can be obtained.

[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 blended cement composition is preferably 1.0 to 5.5% by mass, more preferably 1.5 to 5.3% by mass, still more preferably 2.0 to 5.0% by mass, and particularly preferably 2.5 to 4.5% by mass in terms of SO3 conversion value from the viewpoints of strength development, fluidity and workability of mortar containing the blended cement composition, etc. Also, the amount of gypsum relative to 100 parts by mass of the cement clinker powder is preferably 1.5 to 6.0 parts by mass, more preferably 2.0 to 5.8 parts by mass, still 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 conversion value from the viewpoints of strength development, fluidity and workability of mortar containing the blended cement composition, etc. Examples of gypsum include natural dihydrate gypsum, flue gas desulfurization gypsum, phosphogypsum, titanium gypsum, fluorogypsum, refined gypsum, hemihydrate gypsum, and anhydrite gypsum, etc. These may be used alone or in combination of two or more.

[0019] In 100% by mass of the total amount of the cement clinker powder, blast furnace slag fine powder, and limestone powder, the proportion of the blast furnace slag fine powder is 27 to 55% by mass, preferably 27.5 to 54% by mass, more preferably 28 to 53% by mass, still more preferably 29 to 50% by mass, still more preferably 30 to 45% by mass, and particularly preferably 32 to 40% by mass. If the above proportion is less than 27% by mass, the long-term strength development will decrease. If the above proportion exceeds 55% by mass, the effect of reducing the usage amount of blast furnace slag fine powder by using other components (limestone powder) instead of blast furnace slag fine powder will become small. Generally, when the proportion of blast furnace slag fine powder in the blended cement is 40% by mass or less, the alkali-aggregate reaction tends to proceed and the durability of the hardened body of the blended cement tends to decrease. However, in the blended cement composition of the present invention, even when the proportion of blast furnace slag fine powder is 40% by mass or less, the alkali-aggregate reaction hardly proceeds.

[0020] Examples of the blast furnace slag fine powder include pulverized products of granulated slag obtained by rapidly cooling and crushing molten slag by-produced during the production of pig iron in a blast furnace with water, etc. Further, the basicity of the fine blast furnace slag powder is preferably 1.7 or more, more preferably 1.75 or more, and particularly preferably 1.8 or more. When the basicity is 1.7 or more, the strength development property is further improved. Note that the basicity is calculated using the following formula (5). Basicity = [(CaO + MgO + Al2O3) / SiO2] ···(5) (The chemical formulas in the formula represent the content (%) of the compound represented by the chemical formula in the fine blast furnace slag powder.)

[0021] The Blaine specific surface area of the fine blast furnace slag powder 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. When the Blaine specific surface area is 3,000 cm 2 / g or more, the strength development property is further improved. When the Blaine specific surface area is 7,000 cm 2 / g or less, the fluidity and workability of mortar containing the blended cement composition are further improved.

[0022] In 100% by mass of the total amount of cement clinker powder, fine blast furnace slag powder, and limestone powder, the proportion of limestone powder is 2 to 26% by mass, preferably 4 to 24% by mass, more preferably 6 to 20% by mass, still more preferably 7 to 18% by mass, and particularly preferably 8 to 16% by mass. When the proportion is less than 2% by mass, the effect of suppressing the alkali-aggregate reaction becomes small. Also, when reducing the amount of fine blast furnace slag powder by using other components (limestone powder) instead of the fine blast furnace slag powder, the effect becomes small. When the proportion exceeds 26% by mass, the strength development property decreases.

[0023] The mass ratio of the fine blast furnace slag powder to the limestone powder (fine blast furnace slag powder / limestone powder) 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. When the above ratio is less than 1.4, the effect of suppressing the alkali-aggregate reaction decreases. When the above ratio exceeds 25.0, the initial strength development property decreases. Also, by using other components (limestone powder) instead of the fine blast furnace slag powder, the effect of reducing the usage amount of the fine blast furnace slag powder becomes small.

[0024] The calcium carbonate content 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, the strength development property is further improved. The limestone powder may be pulverized limestone, or may be carbonated raw sludge or concrete powder. According to these powders, carbon dioxide gas that would originally be discharged into the atmosphere can be fixed in the above powders.

[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, still more preferably 4,000 to 15,000 cm 2 / g, still more preferably 4,200 to 10,000 cm 2 / g, and particularly preferably 4,500 to 9,500 cm 2 / g. If the above Blaine specific surface area is 3,000 cm 2 / g or more, the strength development property is further improved. If the above Blaine specific surface area is 20,000 cm 2 / g or less, the fluidity and workability of mortar etc. containing the blended cement composition are further improved.

[0026] The proportion of the total amount of the cement clinker powder, the fine blast furnace slag powder, and the limestone powder in the total amount (100% by mass) of the powdery blended 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 than cement clinker powder, blast furnace slag fine powder, and limestone powder (other materials) include silica fume and the like.

[0027] The proportion of the total alkali content (Na2O + 0.658K2O) in the mixed cement composition of the present invention (excluding the above-mentioned blast furnace slag fine powder) is preferably 0.5 to 3.0% by mass, more preferably 0.6 to 2.5% by mass, still more preferably 0.8 to 2.0% by mass, and particularly preferably 1.0 to 1.8% by mass. If the above proportion is 0.5% by mass or more, the amount of waste used as a raw material for cement clinker can be increased. If the above proportion is 3.0% by mass or less, the fluidity and workability of mortar and the like containing the mixed cement composition can be further improved. Further, the alkali-aggregate reaction can be more suppressed. Note that the proportion of the total alkali content is defined as the proportion in the cement composition excluding the blast furnace slag fine powder because the elution rate of the alkali component in the blast furnace slag fine powder is smaller than that of the alkali component in the cement clinker powder, and the influence on the alkali-aggregate reactivity, fluidity, workability, etc. is negligibly small.

[0028] The mixed cement composition of the present invention has suppressed alkali-aggregate reaction. Therefore, the mixed cement composition of the present invention is suitable when using aggregates that are feared to be prone to alkali-aggregate reaction, or when adding an alkali accelerator for accelerating hardening in cold regions or the like, where alkali-aggregate reaction is expected to proceed easily.

[0029] Examples of the method for producing the mixed cement composition of the present invention include a method including a preparation step of mixing cement clinker powder, gypsum, blast furnace slag fine powder, and limestone powder to prepare the above-mentioned mixed cement composition. The mixing method of each material is not particularly limited, and examples include: (i) a method of mixing a composition containing cement clinker powder, gypsum, and finely ground blast furnace slag (e.g., blast furnace cements A to C) with limestone powder; (ii) a method of mixing while simultaneously grinding cement clinker, blast furnace slag, limestone, and gypsum; (iii) a method of mixing cement (a mixture of clinker powder and gypsum) ground in advance, finely ground blast furnace slag powder ground in advance, and limestone powder ground in advance, etc. In the method (iii) above, a mixture obtained by simultaneously grinding and mixing blast furnace slag and gypsum in advance may be used.

[0030] In addition, in the method for producing a blended cement composition, for the purpose of making the proportion of the total alkali content (Na2O + 0.658K2O) in the blended cement composition (excluding the above-mentioned finely ground blast furnace slag) within a desired numerical range, in the above preparation step, when mixing each material of the blended cement composition, or after mixing each material, an alkali metal-containing substance (e.g., reagents such as NaOH, KOH, Na2SO4, K2SO4) may be added and mixed. In the preparation step, the blending amount of each material may be appropriately adjusted so that the blending ratio of each material in the resulting blended cement composition is as desired. In the method (i) above, before the preparation step, a component measurement step may be performed to measure the proportion of each of the cement clinker powder and the finely ground blast furnace slag in the composition containing the cement clinker powder, gypsum, and finely ground blast furnace slag. Based on the measured proportions of the cement clinker powder and the finely ground blast furnace slag, the blending amount of the limestone powder to be mixed in the preparation step can be determined.

[0031] In addition, in the method for producing a blended cement composition, at least a part of each material constituting the blended cement composition may be separately prepared without pre-mixing, and when mixing each material and water to prepare a hydraulic composition, all the materials and water constituting the blended cement composition may be mixed. Specifically, when mixing blast furnace cement and water, a method of mixing limestone powder prepared separately from the blast furnace cement may be mentioned.

[0032] The hydraulic composition can be prepared by mixing the blended cement composition of the present invention with water. The hydraulic composition may contain aggregates (fine aggregates, coarse aggregates) and other materials blended as required. Examples of other materials blended as required include various additives such as water reducing agents, defoaming agents, and shrinkage reducing agents. In this specification, a hydraulic composition is a curable composition containing a cement composition and water, and includes the form before hardening and the form after hardening of the hydraulic composition. Examples of the hydraulic composition include paste, mortar, and concrete. The compressive strength at 7 days of age measured by the method described in "JIS R 5201:2015 Methods of physical tests for cement" of the blended cement composition of the present invention is preferably 26 MPa or more, more preferably 27 MPa or more, and particularly preferably 28 MPa or more.

[0033] Further, by mixing limestone powder with a powdery blended cement containing cement clinker powder, gypsum, and blast furnace slag fine powder so that the resulting blended cement satisfies the above-described blended cement composition of the present invention, the alkali-aggregate reaction of the above blended cement can be suppressed. Specifically, a limestone powder addition step for preparing a limestone powder-containing blended cement is included, in which a powdery blended cement containing cement clinker powder, gypsum, and blast furnace slag fine powder is mixed with limestone powder so that in a total amount of 100% by mass of the cement clinker powder, blast furnace slag fine powder, and limestone powder, the proportion of the cement clinker powder is 42 to 59% by mass, the proportion of the blast furnace slag fine powder is 27 to 55% by mass, the proportion of the limestone powder is 2 to 26% by mass, and the mass ratio of the blast furnace slag fine powder to the limestone powder (blast furnace slag fine powder / limestone powder) is 1.4 to 25.0. Examples include a method for suppressing the alkali-aggregate reaction of the blended cement.

[0034] Before the above limestone powder addition step, a mixed cement component measurement step of measuring the proportion of each of the cement clinker powder and the fine blast furnace slag powder in the composition containing the cement clinker powder, gypsum, and the fine blast furnace slag powder may be performed. Based on the measured proportion of each of the cement clinker powder and the fine blast furnace slag powder, etc., the blending amount of the limestone powder to be mixed in the mixed cement preparation step can be determined. In addition, in the mixed cement preparation step, in addition to the limestone powder, fine blast furnace slag powder, gypsum, and alkali metal-containing substances (for example, reagents such as NaOH, KOH, Na2SO4, K2SO4, etc.) may be appropriately mixed so that the obtained mixed cement satisfies the above-described mixed cement composition of the present invention.

[0035] The mixed cement containing the cement clinker powder, gypsum, and the fine blast furnace slag powder, which is the object of the method for suppressing the alkali-aggregate reaction of the mixed cement, is not particularly limited, and examples thereof include blast furnace cement type B. Blast furnace cement type B has a proportion of fine blast furnace slag powder exceeding 30% by mass and not exceeding 60% by mass, and is prone to the progress of the alkali-aggregate reaction. However, by mixing limestone powder with blast furnace cement type B, the alkali-aggregate reaction of blast furnace cement type B can be suppressed.

Examples

[0036] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. [Materials Used] (1) Fine blast furnace slag powder; Blaine specific surface area: 4,230 cm 2 / g, density: 2.92 g / cm 3 , basicity: 1.80, corresponding to fine blast furnace slag powder 4000 specified in "JIS A 6206:2013 (Fine Blast Furnace Slag Powder 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 amount in limestone powder: 0% by mass [Production of Blast Furnace Slag Mixture] The above-mentioned fine blast furnace slag powder and dihydrate gypsum (flue gas desulfurization gypsum) were mixed to produce a blast furnace slag mixture (a mixture of fine blast furnace slag powder and gypsum) with a gypsum content of 2.0% by mass (in terms of SO3). [Production of Cements A - B] Using reagents as raw materials and a test kiln, cement clinker was fired to prepare a cement clinker having the mineral composition shown in Table 1. The obtained cement clinker, dihydrate gypsum (flue gas desulfurization gypsum), and hemihydrate gypsum were ground and mixed using a mill to obtain cements A - B containing cement clinker powder and gypsum. The amount of gypsum was determined so that the proportion of gypsum in the cement would be the value shown in Table 1.

[0037]

Table 1

[0038] [Examples 1 - 17, Comparative Examples 1 - 6] Cements of the types shown in Table 2 (mixtures of cement clinker powder and gypsum), blast furnace slag mixtures (mixtures of fine blast furnace slag powder and gypsum), and limestone powder were mixed in the amounts shown in Table 2 to obtain a mixed cement composition. Note that, in the mixed cement composition, the proportion of cement clinker powder, etc. in the total amount of 100% by mass of cement clinker powder (indicated as "clinker" in Table 2), fine blast furnace slag powder (indicated as "blast furnace slag" in Table 2), and limestone powder (indicated as "limestone" in Table 2), and the amount of gypsum (SO3 conversion value) per 100 parts by mass of cement clinker powder are as shown in Table 2.

[0039] For the mixed cement composition, in accordance with the method described in "JIS R 5201:2015 Methods of Physical Tests for Cement", the compressive strengths at 3 days, 7 days, and 28 days of age were measured. In addition, an alkali-aggregate reactivity test was conducted on the blended cement composition, and the expansion rates of the hardened bodies of the blended cement composition were measured at 2 weeks, 4 weeks, 8 weeks, and 13 weeks after curing. The above test was carried out in accordance with "JIS A 1146:2017 Test Method for Alkali-Silica Reactivity of Aggregates (Mortar Bar Method)", and the same aggregates were used. The smaller the numerical value of the above expansion rate, the more the alkali-aggregate reaction is suppressed, indicating excellent durability. In each blended cement composition, the proportion of the total alkali amount in the blended cement composition (excluding the above-mentioned blast furnace slag fine powder) was about 0.2 to 0.3% by mass. However, when preparing the mortar in the above test, an aqueous solution of NaOH (reagent) was mixed so that the proportion of the total alkali amount in the blended cement composition (excluding the above-mentioned blast furnace slag fine powder) became 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 at 28 days of age (56.2 to 58.7 MPa) of Examples 1 to 4 are greater than the compressive strengths at 28 days of age (51.3 to 53.3 MPa) of Comparative Example 1 (cement clinker powder: 55.2% by mass, blast furnace slag fine powder: 44.8% by mass, limestone powder: 0% by mass) and Comparative Example 2 (cement clinker powder: 54.7% by mass, blast furnace slag fine powder: 24.7% by mass, limestone powder: 20.6% by mass). In addition, the expansion rates at 13 weeks of age (0.30 to 0.32%) of Examples 1 to 4 are smaller than the expansion rates at 13 weeks of age (0.33 to 0.37%) of Comparative Examples 1 to 2, indicating that the alkali-aggregate reaction is suppressed.

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

Claims

1. A powdered mixed cement composition comprising cement clinker powder, gypsum, finely ground blast furnace slag, and limestone powder, wherein, in 100% by mass of the total amount of the cement clinker powder, the finely ground blast furnace slag, and the limestone powder, the proportion of the cement clinker powder is 42 to 59% by mass, the proportion of the finely ground blast furnace slag is 27 to 40% by mass, and the proportion of the limestone powder is 8 to 26% by mass, and the mass ratio of the finely ground blast furnace slag to the limestone powder (finely ground blast furnace slag / limestone powder) is 1.4 to 3.8, characterized in that it is a powdered mixed cement composition.

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% by mass.

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

4. The proportion of the total alkali content (Na ２ 2O + 0.658K ２ 2O) in the above-mentioned blended cement composition (excluding the above-mentioned fine powder of blast furnace slag) is 0.5 to 3.0% by mass. The blended cement composition according to any one of claims 1 to 3.

5. The proportion of the total alkali content (Na ２ 2O + 0.658K ２ 2O) in the above cement clinker powder is 0.8 to 5.0% by mass, and the blended cement composition according to any one of claims 1 to 4.

6. A method for producing the mixed cement composition according to any one of claims 1 to 5, characterized by including a preparation step of mixing cement clinker powder, gypsum, finely ground 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 suppressing alkali-aggregate reaction of a powdered mixed cement containing cement clinker powder, gypsum, and finely ground blast furnace slag, including a limestone powder addition step of mixing the mixed cement with limestone powder to prepare a limestone powder-containing mixed cement such that, in 100% by mass of the total amount of the cement clinker powder, the finely ground blast furnace slag, and the limestone powder, the proportion of the cement clinker powder is 42 to 59% by mass, the proportion of the finely ground blast furnace slag is 27 to 40% by mass, the proportion of the limestone powder is 8 to 26% by mass, and the mass ratio of the finely ground blast furnace slag to the limestone powder (finely ground blast furnace slag / limestone powder) is 1.4 to 3.8, which is a method for suppressing alkali-aggregate reaction of a mixed cement.

9. The method for suppressing alkali-aggregate reaction of a mixed cement according to claim 8, wherein the mixed cement is blast furnace cement type B.

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