Cement composition

Abstract

To provide a cement composition that allows effective use of mixed cement and calcium aluminate slag for realizing sufficient work life and excellent strength development while reducing energy consumption and CO2 emissions, thereby contributing to reduction of environmental load.SOLUTION: A cement composition comprises a mixed cement and a cement admixture containing the following components (A)-(D) in the specified contents: (A) a calcium aluminate slag powder at least partially subjected to hydration treatment: 20-80 mass%, (B) a gypsum material: 20-80 mass%, (C) an alkali metal sulfate: 1-4 mass%, and (D) an oxycarboxylic acid or a salt thereof: 1-4 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an environmentally friendly cement composition that contributes to reducing carbon dioxide emissions. [Background technology]

[0002] In recent years, the issue of global warming has become a major global issue, and various fields are seeking ways to reduce carbon dioxide emissions. It is known that the cement used in mortar concrete emits a large amount of carbon dioxide during its production. For this reason, one solution being considered is to use blended cement, in which part of the cement is replaced with blast furnace slag powder or fly ash. However, it has been pointed out that mortar concrete using blended cement has problems such as slow strength development and large drying shrinkage. Furthermore, as a measure to improve drying shrinkage and strength development, it is known to use cement admixtures such as expansive additives and rapid hardening admixtures (for example, Patent Documents 1 and 2), but it is also known that carbon dioxide is emitted during the production of calcium-based compounds, which are the main components of these cement admixtures. Therefore, it is desirable to develop products that reduce as much as possible the carbon dioxide emissions generated during the production of these cement admixtures.

[0003] Meanwhile, it is known that calcium aluminate slag is generated as a by-product during metal refining. For example, it is known that calcium aluminate slag is generated when aluminum is used as a deoxidizer in the steel slag produced as a by-product in the stainless steelmaking process. This calcium aluminate slag is widely used in the refining process of steel manufacturers and other companies as a roasting solvent to replace fluorite, or to adjust the composition of refining slag. It has also been proposed to use calcium aluminate slag as a raw material for CaO and Al2O3 in the production of alumina cement (Patent Document 3). Effective utilization of calcium aluminate slag, a by-product, is an important technology currently in demand from the perspectives of energy conservation and carbon dioxide emission reduction.

[0004] The present invention has investigated a new method for utilizing such calcium aluminate slag, and has discovered its effective use in cement compositions using blended cement, which also has the effect of reducing carbon dioxide emissions. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 62-003057 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-210551 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-282486 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a cement composition that contributes to reducing the environmental load by effectively utilizing blended cement and calcium aluminate slag, thereby achieving sufficient pot life and good strength development while saving energy and reducing carbon dioxide emissions. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have found that an environmentally friendly cement composition that can achieve the above-mentioned objectives can be obtained by using blended cement and calcium aluminate slag and further blending certain additives, thereby completing the present invention. That is, the present invention is as described in the following [1] to [3]. [1] A cement composition containing a blended cement and a cement admixture containing the following components (A) to (D) in the following amounts: (A) Calcium aluminate slag powder, at least a portion of which has been hydrated: 20 to 80% by mass (B) Gypsum: 20~80% by mass (C) Alkali metal sulfate: 1 to 4 mass% (D) Oxycarboxylic acid or its salt: 1 to 4% by mass [2] The cement composition according to [1], wherein the proportion of the hydrated calcium aluminate slag powder in the calcium aluminate slag powder is 50 to 100%. [3] The cement composition according to [1] or [2], containing 10 to 30 parts by mass of the cement admixture relative to 100 parts by mass of the total of the mixed cement and the cement admixture. [Effects of the Invention]

[0008] According to the present invention, by using blended cement and calcium aluminate slag, it is possible to obtain a cement composition that is easy to work with and has good strength development, which allows the production of mortar concrete that can significantly reduce the total amount of carbon dioxide emissions, thereby contributing to reducing the environmental load. DETAILED DESCRIPTION OF THE INVENTION

[0009] The cement composition of the present invention contains a blended cement and a cement admixture, and the cement admixture contains 20 to 80 mass% of (A) calcium aluminate slag powder, at least a portion of which has been hydrated, 20 to 80 mass% of (B) gypsum, 1 to 4 mass% of (C) alkali metal sulfate, and 1 to 4 mass% of (D) oxycarboxylic acid or its salt. The details are explained below.

[0010] <Mixed cement> The mixed cement used in the cement composition of the present invention is a cement obtained by mixing Portland cement with various admixtures. Portland cement, which emits a large amount of carbon dioxide during production, is partially replaced with various admixtures, thereby reducing carbon dioxide emissions and environmental impact. Examples of the various admixtures include blast furnace slag ground powder, fly ash, and siliceous ground powder. Three types of mixed cements using these materials are specified in the JIS: blast furnace cement, fly ash cement, and silica cement. It is preferable to use these mixed cements. Other admixtures that can be used include limestone ground powder, waste concrete ground powder, and volcanic glass ground powder. From the perspective of reducing environmental impact, it is desirable to use by-products or natural products that emit virtually no or very little carbon dioxide during production.

[0011] As a blended cement, it is particularly preferable to use blast furnace cement. Blast furnace cement is produced by mixing Portland cement with ground granulated blast furnace slag, which is a by-product of the blast furnace (blast furnace) of a steelworks. In particular, the cement specified in JIS A 5211 "Blast Furnace Cement" is preferable. Blast furnace cement is classified into Type A (more than 5% and not more than 30%), Type B (more than 30% and not more than 60%), and Type C (more than 60% and not more than 70%) depending on the amount of blast furnace slag, and any of these can be used. From the perspective of reducing environmental impact, a higher amount of blast furnace slag is better, but Type B is preferable when considering early strength development and marketability.

[0012] <Cement admixture> (A) Calcium aluminate slag The calcium aluminate slag in the present invention is calcium aluminate slag generated as a by-product during metal refining. Specific examples include calcium aluminate slag generated as a by-product during the refining of nickel, molybdenum, vanadium, etc., or alloys with iron such as ferronickel and ferrovanadium. Regarding the chemical components, the molar ratio of CaO to Al2O3 (hereinafter referred to as CaO / Al2O3) is preferably 0.9 to 1.5. If the CaO / Al2O3 ratio is less than 0.9, there is a risk that sufficient initial strength development will not be achieved. On the other hand, if the CaO / Al2O3 ratio exceeds 1.5, there is a risk that it will be difficult to ensure a sufficient usable life. It is more preferable that the CaO / Al2O3 ratio is 0.95 to 1.3.

[0013] The calcium aluminate slag of the present invention may contain, as its mineral phase, krotite (CaO Al2O3), mayenite (12CaO 7Al2O3), gehlenite (2CaO Al2O3 SiO2), calcium aluminoferrite (4CaO Al2O3 Fe2O3), periclase (MgO), akermanite (2CaO MgO 2SiO2), etc. Among these, those containing krotite as the main component (50 mass% or more) are preferred.

[0014] Furthermore, from the viewpoint of early strength development, it is preferable to contain a small amount of mayenite. Mayenite has high initial hydration activity and contributes to early strength development. However, if it is contained in a large amount, it may accelerate the setting of mortar concrete, making it difficult to ensure the usable time. For this reason, the content is preferably 1 to 20 mass%, more preferably 2 to 10 mass%, and even more preferably 3 to 8 mass%. The mayenite content can be measured using an X-ray diffractometer by a calibration curve method, the Rietveld method, or the like.

[0015] In addition, calcium aluminate slag may contain small amounts of metals and metal oxides, such as iron, nickel, molybdenum, vanadium, chromium, and cobalt. The metal and metal oxide content is preferably 5% by mass or less in terms of metal oxide.

[0016] Furthermore, calcium aluminate slag is usually cooled naturally, so the resulting product is crystalline and contains almost no amorphous calcium aluminate. The vitrification rate is not particularly limited, but is preferably less than 15% by mass. The vitrification rate can be measured by the calibration curve method or the Rietveld method using an X-ray diffractometer.

[0017] Calcium aluminate slag, which is usually produced as a by-product during metal refining, is obtained as a lump. Therefore, calcium aluminate slag is pulverized to obtain a powder. The pulverization method is not particularly limited, and for example, it can be roughly crushed using a crusher mill or the like, and then finely pulverized using a ball mill, vibration mill, or the like. The fineness of the slag is 3000 to 8000 cm in terms of Blaine specific surface area. 2 / g. More preferably, it is adjusted to 4000 to 7000 cm 2 / g.

[0018] The calcium aluminate slag powder of the present invention is at least partially hydrated. By hydrating the powder to form a powder with hydrate-coated particle surfaces, the hydration reaction upon contact with water is suppressed, ensuring a sufficient usable life even when used in mortar or concrete. The proportion of hydrated calcium aluminate slag powder in the total calcium aluminate slag powder is preferably at least 50% by mass but not more than 100% by mass. It is more preferably 70% by mass or more, and even more preferably 90% by mass or more. This proportion can be adjusted by mixing hydrated calcium aluminate slag powder and unhydrated calcium aluminate slag powder in a predetermined ratio.

[0019] As a method for hydration, for example, a powder mixer is used, and a predetermined amount of water is sprayed little by little with a sprayer to mix, which is desirable because it can coat the hydrate phase relatively uniformly. Examples of powder mixers that can be used include a Lödige mixer, a Henschel mixer, a Nauta mixer, and a VH powder mixer. The mixing time is adjusted appropriately depending on the amount of mixture and the equipment, but a period of 2 to 30 minutes is preferred. The amount of water sprayed is preferably 0.2 to 3.5 mass% based on the weight of the calcium aluminate slag. Instead of spraying water, other liquids (e.g., aqueous organic solvents, carbonated water) can also be used as long as they react with calcium aluminate to form a hydrate.

[0020] Hydrates formed on the surface of calcium aluminate slag powder particles include, for example, CaO·Al2O3·10H2O, 2CaO·Al2O3·8H2O, 3CaO·Al2O3·6H2O, 3CaO·Al2O3·8H2O, 4CaO·Al2O3·13H2O, 4CaO·Al2O3·19H2O, CaO·H2O, Al2O3·H2O, Al2O3·3H2O, 3CaO·Al2O3·CaSO4·12H2O, 3CaO·Al2O3·3CaSO4·32H2O, 3CaO·Al2O3·CaCO3·12H2O, 3CaO·Al2O3·3CaCO3·30H2O, etc. Other examples include hydrates containing transition metals and other impurity elements contained in calcium aluminate slag.

[0021] From the viewpoint of early strength development, the content of calcium aluminate slag in the cement admixture is 20 to 80 mass %, preferably 30 to 70 mass %, and more preferably 40 to 60 mass %.

[0022] (B) Gypsum Examples of gypsums used in the present invention include anhydrous gypsum, dihydrate gypsum, and hemihydrate gypsum. Among these, anhydrous gypsum is particularly preferred from the viewpoint of strength development. Gypsum includes natural gypsum and chemical gypsum that is artificially produced or by-produced, and any of these can be used. Examples of by-produced gypsum, which is by-produced chemical gypsum, include flue gas desulfurization gypsum, phosphate gypsum, hydrofluoric gypsum, and titanic gypsum. Recycled gypsum derived from waste gypsum board can also be used. From the viewpoint of reducing environmental load, it is preferable to use by-produced gypsum or recycled gypsum. The Blaine specific surface area of ​​the gypsum powder is 3000 to 12000 cm 2 / g is preferred, and 4000 to 10000 cm 2 / g is more preferred.

[0023] The content of gypsum in the cement admixture is 20 to 80 mass %, preferably 30 to 70 mass %, and more preferably 40 to 60 mass %, from the viewpoint of the fluidity and strength development of the cement composition.

[0024] (C) Alkali metal sulfate Examples of alkali metal sulfates used in the present invention include sodium sulfate, potassium sulfate, and lithium sulfate. Sodium sulfate is particularly preferred. The content of the alkali metal sulfate in the cement admixture is 1 to 4 mass%. If it is less than 1 mass%, sufficient early strength development may not be achieved, and if it exceeds 4 mass%, it may not be possible to achieve a sufficient usable life. 1.5 to 3 mass% is preferred.

[0025] (D) Hydroxycarboxylic acid or its salt Examples of hydroxycarboxylic acids used in the present invention include citric acid, gluconic acid, malic acid, and tartaric acid, and examples of their salts include sodium citrate, potassium citrate, and sodium gluconate. One or more of these can be used. Among these, citric acid and / or tartaric acid are preferred in terms of compatibility with calcium aluminate slag. The content of the hydroxycarboxylic acid or its salt in the cement admixture is 1 to 4% by mass. If it is less than 1% by mass, sufficient pot life cannot be obtained, and if it exceeds 4% by mass, early strength development decreases. Furthermore, it is preferably 1.5 to 3% by mass.

[0026] In addition, carbonates, nitrates, nitrites and hydroxides of alkali metals or alkaline earth metals, aluminum sulfate, etc. may be added to the cement admixture within the range that does not impair the features of the present invention.

[0027] <Cement composition> The cement composition of the present invention contains a mixed cement and the above-mentioned cement admixture. The amount of the cement admixture is preferably 10 to 30 parts by mass, more preferably 15 to 25 parts by mass, per 100 parts by mass of the total of the mixed cement and the cement admixture, from the viewpoints of strength development, durability, and fluidity of the kneaded product.

[0028] By adding aggregate and water to the cement composition of the present invention, environmentally friendly mortar or concrete can be produced. The production method of mortar or concrete is not particularly limited. For example, the materials constituting the cement composition can be charged all at once into a mortar mixer or concrete mixer and mixed, and then aggregate and water can be added sequentially and kneaded to produce mortar or concrete. Alternatively, a premix of powder materials other than the mixed cement can be prepared and then charged into the mixer together with the mixed cement to produce mortar or concrete. Alternatively, the premix of powder materials other than the mixed cement can be mixed, and then the premix of powder materials other than the mixed cement can be charged into a mixer or agitating mixer truck and kneaded to produce mortar or concrete.

[0029] The aggregate used in producing mortar or concrete is not particularly limited, and aggregates commonly used in mortar or concrete can be used. Specific examples include fine aggregates such as river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, and mixtures thereof, and coarse aggregates such as river gravel, mountain gravel, land gravel, crushed stone, and mixtures thereof. The amount of aggregate (the total amount when fine and coarse aggregates are used in combination) is preferably 200 to 700 parts by mass, more preferably 200 to 600 parts by mass, per 100 parts by mass of the cement composition, from the viewpoints of fluidity, crack prevention, and material separation prevention. Furthermore, when fine and coarse aggregates are used in combination, the fine aggregate ratio is preferably 5 to 60%.

[0030] The water used in producing mortar or concrete is not particularly limited, and tap water, etc. can be used. The blending ratio of water to 100 parts by mass of the cement composition is preferably 30 to 100 parts by mass, more preferably 40 to 70 parts by mass.

[0031] Furthermore, various admixtures (materials) used in general mortar and concrete can be added to the mortar or concrete within the scope of the present invention, such as cement dispersants such as water reducing agents, air-entraining water reducing agents, high-performance water reducing agents, superplasticizers, strength promoters, set adjusters, polymers for cement admixture, foaming agents, foaming agents, waterproofing agents, rust inhibitors, shrinkage reducing agents, expanding agents, thickeners, water retention agents, pigments, water repellents, anti-efflorescence agents, defoamers, and fibers. [Example]

[0032] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.

[0033] The materials used in the examples are listed below. (A) Calcium aluminate slag (symbol: CAS) Calcium aluminate slag generated during metal refining was used as slag produced after refining ferrovanadium. This calcium aluminate slag contained 0.66 mass% vanadium in oxide equivalent. The CaO / Al2O3 molar ratio was 1.1. The mineral composition included 80 mass% krotite, 5 mass% mayenite, 10 mass% gehlenite, and 2 mass% periclase. The vitrification rate was 2%. The mineral content and vitrification rate were calculated by the Rietveld method using an X-ray diffractometer. This calcium aluminate slag was coarsely crushed and then pulverized in a ball mill to obtain a slag with a Blaine specific surface area of ​​5020 cm2. 2 / g of powder. 50 kg of this calcium aluminate slag powder was placed in a Lödige mixer, and 250 g of water was added by spraying with a sprayer while the mixer was rotating. After mixing for 10 minutes, a hydrated calcium aluminate slag powder was obtained. (B) Gypsum Type II anhydrous gypsum (by-product gypsum), Blaine specific surface area: 7000 cm 2 / g (C) Alkali metal sulfate Sodium sulfate, reagent grade 1 (D) Hydroxycarboxylic acid or its salt (1) Citric acid, reagent grade 1 (2) Tartaric acid, reagent grade 1

[0034] <Preparation of cement admixture> A cement admixture was prepared by mixing hydrated calcium aluminate slag powder, unhydrated calcium aluminate slag powder, anhydrous gypsum, sodium sulfate, citric acid, and tartaric acid in a predetermined ratio. The composition of the prepared cement admixture is shown in Table 1.

[0035] [Table 1]

[0036] <Preparation of mortar specimen> Each cement admixture was mixed with blast furnace cement (Type B, manufactured by Taiheiyo Cement Corporation, symbol: BB) or fly ash cement (normal Portland cement (manufactured by Taiheiyo Cement Corporation) mixed with fly ash (manufactured by Chugoku Electric Power Co., JIS Type II product) at a replacement rate of 15%, symbol: FB) in the proportions shown in Table 2. The cement compositions were mixed with fine aggregate (JIS standard sand) and water (tap water), and then kneaded to prepare mortar. The mortar was formulated with 450 g of cement composition, 1350 g of fine aggregate, and 225 g of water. The mixture was kneaded for 3 minutes using a mortar mixer. This mortar was placed in a formwork to prepare specimens for evaluation tests. The test method for the evaluation tests is described below.

[0037] (Test Method) (1) Pot life The temperature at the center of a φ5 x 10 cm test piece was measured, and the usable time was determined as the time from the completion of mixing until the temperature rose by 1°C. (2) Compression strength test The compressive strength of each material age was tested in accordance with the Soil Science Society standard JSCE-G541 "Test method for compressive strength of filling mortar." The curing temperature was kept at 20°C until just before the test.

[0038] (Test results) The test results are shown in Table 2. The cement composition of the present invention can be set to have a pot life of 30 minutes or more, and exhibited good early strength development in 24 hours. It also exhibited good compressive strength at 14 days of age.

[0039] [Table 2]

Claims

1. A cement composition containing a mixed cement and a cement admixture containing the following components (A) to (D) in the following amounts: (A) Calcium aluminate slag powder, at least a portion of which has been hydrated: 20 to 80% by mass (B) Gypsum: 20 to 80% by mass (C) Alkali metal sulfate: 1 to 4 mass% (D) Oxycarboxylic acid or its salt: 1 to 4 mass%

2. 2. The cement composition according to claim 1, wherein the proportion of the hydrated calcium aluminate slag powder in the calcium aluminate slag powder is 50 to 100%.

3. The cement composition according to claim 1 or 2, wherein the cement admixture is contained in an amount of 10 to 30 parts by mass relative to a total of 100 parts by mass of the mixed cement and the cement admixture.

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