Hydraulic composition and cement mortar or concrete using the same, concrete for pavement, and manufacturing method thereof

Abstract

To provide a hydraulic composition having good initial strength development and small dry shrinkage even when using a blast furnace cement with large content of a blast furnace slag fine powder, a hydraulic composition that can also be applied to a road concrete for pavement, and a technology for manufacturing concrete that can suppress a used amount of Portland cement and can reduce a discharge amount of carbon dioxide.SOLUTION: In a hydraulic composition containing a cement composition containing Portland cement and a blast furnace slag fine powder and a cement admixture containing calcium aluminate and anhydrous gypsum, a content of the blast furnace slag fine powder is 40-70 mass% in the cement composition, and a content of the cement admixture is 20-40 pts.mass to the sum total 100 pts.mass of the cement composition and the cement admixture.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a hydraulic composition containing Portland cement and finely powdered blast furnace slag.

Background Art

[0002] In recent years, from the viewpoints of effective utilization of by-products and reduction of carbon dioxide emissions, which are the main causative substances of global warming, blended cements such as blast furnace cement and fly ash cement have attracted attention as alternatives to Portland cement. Among these, blast furnace cement is a cement obtained by mixing finely powdered blast furnace slag, which is a by-product of a steelworks, and Portland cement. By mixing the finely powdered blast furnace slag, the amount of Portland cement used can be reduced, and the amount of carbon dioxide emissions can also be reduced. As cement using finely powdered blast furnace slag, it is standardized as blast furnace cement in JIS R 5201. According to this, in type A blast furnace cement, the content of finely powdered blast furnace slag is defined as more than 5% by mass and 30% by mass or less, in type B it is more than 30% by mass and 60% by mass or less, and in type C it is more than 60% by mass and 70% by mass or less. However, in actual distribution and use, type B cement with a finely powdered blast furnace slag content of around 50% by mass accounts for the majority, and types A and C are hardly used.

[0003] In addition, the use of blast furnace cement is limited to large civil engineering structures such as ports and dams, and it is hardly used in the paving field and general construction field. This is because there are problems such as low initial strength development of blast furnace cement, particularly low strength development at low temperatures, and large autogenous shrinkage and drying shrinkage. In particular, in the case of concrete for road paving, it is desired to shorten the period until traffic opening as much as possible. For this purpose, early strength development, specifically, the above early strength development of 24 N / mm 2 is desired.

[0004] As paving concrete, there has been proposed paving concrete obtained by hardening a composition containing cement, pozzolanic fine powder, fine aggregate having a predetermined particle size, water reducing agent, and water (Patent Document 1). However, although the paving concrete is excellent in workability and strength development properties such as flexural strength and compressive strength after 28 days of age, and has a long concrete life, it is inferior in strength development properties at a very early age of about 1 day. Therefore, the problem of shortening the period from the start of paving work to traffic opening remains unsolved. In addition, depending on the curing method, initial cracking may occur, and suppression of initial cracking is also desired. As paving concrete containing blast furnace cement, Patent Document 2 has been proposed. However, the paving concrete contains silica fume as an essential material as pozzolanic fine powder, similar to Patent Document 1. Further, the blast furnace cement used is only Type B blast furnace cement containing 40% of blast furnace slag powder, and no implementation has been carried out for blast furnace cement with a higher content.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention solves the above problems in the blast furnace cement, and provides a hydraulic composition having good initial strength development properties and small dry shrinkage even when using a blast furnace cement having a large content of blast furnace slag fine powder. Further, it provides a hydraulic composition that can also be applied to concrete for road paving. Thus, it provides a concrete manufacturing technology capable of suppressing the amount of Portland cement used and reducing the carbon dioxide emissions.

Means for Solving the Problems

[0007] As a result of intensive studies on hydraulic compositions using cement compositions containing fine blast furnace slag powder, the inventors have found that the above problems can be solved by blending a predetermined cement admixture, and completed the invention. That is, the present invention provides the following [1] to [4]. [1] A hydraulic composition comprising a cement composition containing Portland cement and fine blast furnace slag powder, and a cement admixture containing calcium aluminate and anhydrous gypsum, wherein the content ratio of the fine blast furnace slag powder is 40 to 70% by mass in the cement composition, and the cement admixture is 20 to 40 parts by mass with respect to 100 parts by mass in total of the cement composition and the cement admixture. [2] The hydraulic composition according to [1], wherein the molar ratio of CaO to Al2O3 of the calcium aluminate is 0.9 to 1.5 and the vitrification rate is less than 50%. [3] Mortar or concrete containing the hydraulic composition according to [1] or [2]. [4] Paving concrete containing the hydraulic composition according to [1] or [2]. [5] A method for producing the mortar or concrete according to [3], characterized in that after producing a kneaded product containing the cement composition, aggregate and water, the cement admixture is kneaded. [6] A method for producing the paving concrete according to [4], characterized in that after producing a base concrete containing the cement composition, fine aggregate, coarse aggregate and water, the cement admixture is kneaded. [Effects of the Invention]

[0008] Even when using blast furnace cement with a high content of fine blast furnace slag powder, a hydraulic composition excellent in initial strength development and drying shrinkage reduction effect can be obtained. In particular, type C blast furnace cement with a high content of fine blast furnace slag powder can be effectively utilized. Thus, it is possible to manufacture concrete that can suppress the amount of Portland cement used and reduce the carbon dioxide emissions. Further, the hydraulic composition of the present invention can be applied to concrete for road paving.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described. The hydraulic composition of the present invention is a hydraulic composition comprising a cement composition containing Portland cement and fine blast furnace slag powder, and a cement admixture containing calcium aluminate and anhydrous gypsum, wherein the content of fine blast furnace slag powder in the cement composition is 40 to 70% by mass, and the amount of the cement admixture admixed is 30 to 60% by mass with respect to 100 parts by mass of the cement composition.

[0010] The Portland cement used in the present invention includes various Portland cements such as ordinary, early strength, and moderate heat Portland cements. Any one type of Portland cement can be used, or two or more types of cements may be used in combination. Ordinary Portland cement is preferred in terms of versatility.

[0011] The fine blast furnace slag powder used in the present invention is fine powder obtained by pulverizing granulated blast furnace slag generated in the pig iron manufacturing process, and it is preferable to use fine blast furnace slag powder for concrete defined in Japanese Industrial Standards. As the fineness, the Blaine specific surface area is preferably 3000 to 8000 cm 2 / g, and more preferably 3500 to 6000 cm 2 / g.

[0012] The content rate of the fine powder of blast furnace slag in the cement composition of the present invention is 40 to 70% by mass. From the viewpoint of reducing the carbon dioxide emission amount, it is preferable that the content rate of the fine powder of blast furnace slag is larger. When it is less than 40% by mass, it is difficult to say that a sufficient reduction effect can be obtained. In addition, the effect of reducing drying shrinkage by adding a cement admixture in the present invention is remarkable at 40% by mass or more, and it is difficult to say that it is necessarily sufficient when it is less than 40% by mass. On the other hand, when the content rate of the fine powder of blast furnace slag exceeds 70% by mass, it becomes difficult to obtain sufficient initial strength developability even when adding the cement admixture of the present invention. In particular, it becomes difficult to obtain initial strength developability under a low temperature environment. The lower limit value of the content rate of the fine powder of blast furnace slag is preferably 50% by mass or more, and more preferably 55% by mass or more. Further, more than 60 parts by mass and 70 parts by mass or less corresponding to blast furnace cement type C are particularly preferable.

[0013] The cement admixture in the present invention contains calcium aluminate and anhydrous gypsum. From the viewpoint of initial strength developability, the content of calcium aluminate is preferably 40 to 70% by mass in the cement admixture. Also, from the viewpoint of initial strength developability, the content of anhydrous gypsum is preferably 50 to 200 parts by mass, and more preferably 70 to 150 parts by mass with respect to 100 parts by mass of calcium aluminate.

[0014] The calcium aluminate used in the present invention is a compound composed of CaO and Al2O3, and the molar ratio of the contents of CaO and Al2O3 (CaO / Al2O3 molar ratio) is preferably 0.9 to 1.5. When the CaO / Al2O3 molar ratio is less than 0.9, the developability of the initial strength may decrease. Also, when the CaO / Al2O3 molar ratio exceeds 1.5, it may become difficult to ensure workability when made into mortar or concrete. The CaO / Al2O3 molar ratio is more preferably 0.95 to 1.45, and even more preferably 1.0 to 1.4.

[0015] In addition, the calcium aluminate in the present invention mainly consists of crystalline calcium aluminate. Specifically, the vitrification rate of calcium aluminate is preferably less than 50%. If it exceeds 50%, it may be difficult to ensure workability when made into mortar or concrete. The vitrification rate is more preferably 5 to 45%, and even more preferably 10 to 40%. The vitrification rate can be measured by the calibration curve method or the Rietveld method using an X-ray diffractometer.

[0016] Calcium aluminate can be produced using CaO raw materials such as limestone (calcium carbonate), quicklime, and slaked lime, and Al2O3 raw materials such as aluminum oxide, aluminum hydroxide, bauxite, and shale. Also, by-product calcium aluminate slag can be used as a raw material. A mixture of these raw materials with a predetermined CaO / Al2O3 molar ratio is melted and fired at 1400 °C or higher using a melting furnace, industrial kiln, etc., to obtain calcium aluminate. Note that within a range that does not affect the performance expression of the present invention, a small amount of impurities derived from natural raw materials, etc., may be included. Such impurities include SiO2, Al2O3, Fe2O3, MgO, MnO, TiO2, SO3, P2O5, etc. The melt-fired product is prepared into powder by pulverization. As the powder fineness, the Blaine specific surface area is preferably 2000 - 7000 cm 2 / g, and more preferably 3000 - 6000 cm 2 / g.

[0017] The anhydrous gypsum used in the present invention can be natural anhydrous gypsum or various anhydrous gypsums produced industrially or as by-products. Examples of industrially produced anhydrous gypsum include fluoro-gypsum and phosphogypsum. As the powder fineness of anhydrous gypsum, the Blaine specific surface area is preferably 5000 - 9000 cm 2 / g, and more preferably 6000 - 8000 cm 2 / g.

[0018] The cement admixture can further contain metal salts such as aluminum sulfate, alkali metal sulfates, and alkali metal carbonates. As the aluminum sulfate, aluminum sulfate and its hydrates can be used. Examples of the alkali metal sulfates include lithium sulfate, potassium sulfate, and sodium sulfate. Examples of the alkali metal carbonates include lithium carbonate, potassium carbonate, and sodium carbonate. One or more of these can be used. In particular, from the viewpoint of early strength development under low-temperature environments, it is preferable to use an alkali metal sulfate and an alkali metal carbonate in combination. As for the content of each metal salt, based on 100 parts by mass of calcium aluminate, the aluminum sulfate is preferably 1 to 15 parts by mass, more preferably 2 to 10 parts by mass. Also, the alkali metal sulfate is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass. Further, the alkali metal carbonate is preferably 1 to 15 parts by mass, more preferably 2 to 10 parts by mass.

[0019] The hydraulic composition of the present invention contains 20 to 40 parts by mass of the cement admixture with respect to a total of 100 parts by mass of the above cement composition and the above cement admixture. If it is less than 20 parts by mass, sufficient early strength development and drying shrinkage reduction effects cannot be obtained. If it exceeds 40 parts by mass, workability as concrete cannot be sufficiently obtained, and there is a risk of deterioration in workability. 23 to 38 parts by mass is preferable, and 25 to 35 parts by mass is more preferable. Hereinafter, the cement composition and the cement admixture may be collectively referred to as a binder in some cases. A binder is a term generally used in concrete and specifically means a general term for substances that react with water to generate substances that contribute to the development of concrete strength.

[0020] The hydraulic composition of the present invention is used as mortar or concrete by adding aggregates and water. As the aggregates, fine aggregates and coarse aggregates used in the production of ordinary mortar and concrete can be used. Examples of such fine aggregates and coarse aggregates include river sand, sea sand, mountain sand, crushed sand, artificial fine aggregates, slag fine aggregates, recycled fine aggregates, silica sand, river gravel, land gravel, crushed stone, artificial coarse aggregates, slag coarse aggregates, recycled coarse aggregates, etc. The blending amount of the aggregates is preferably 200 to 700 parts by mass, more preferably 200 to 600 parts by mass, based on 100 parts by mass of the binder. Also, when using fine aggregates and coarse aggregates in combination, the fine aggregate ratio is preferably 10 to 60%. As the unit amount of the aggregates in the concrete, either the fine aggregate or the coarse aggregate is preferably 500 to 1400 kg / m 3 is preferred, and more preferably 600 to 1000 kg / m 3 is preferred.

[0021] The water used for mortar or concrete is not particularly limited, and tap water or the like can be used. The blending amount of water is preferably 25 to 50 parts by mass, more preferably 30 to 40 parts by mass, based on 100 parts by mass of the binder, from the viewpoints of early strength development and workability. As the unit water amount in the concrete, 100 to 300 kg / m 3 is preferred, and 120 to 200 kg / m 3 is more preferred.

[0022] The mortar or concrete of the present invention preferably further contains a retarder. By adding a predetermined amount of the retarder, the construction time (workable time) of the mortar or concrete can be ensured. Examples of the retarder include organic acids such as citric acid, gluconic acid, malic acid, tartaric acid or their salts, borates such as boric acid and sodium borate, phosphates, saccharides, etc. The addition amount of the retarder is appropriately adjusted within the range of 0.1 to 5.0 parts by mass based on 100 parts by mass of the binder.

[0023] In the mortar or concrete using the hydraulic composition of the present invention, in addition to the above components, various admixtures (materials) may be further added as necessary, as long as the characteristics of the present invention are not impaired. For example, water reducing agents, high performance water reducing agents, air entraining agents, air entraining water reducing agents, high performance air entraining water reducing agents, thickening agents, expansive materials, shrinkage reducing agents, cement polymers, waterproofing materials, rust preventives, antifreezing agents, water retaining agents, pigments, efflorescence preventives, foaming agents, defoaming agents, water repellents, fibers and the like can be mentioned.

[0024] Despite containing a large amount of fine blast furnace slag powder, the hydraulic composition according to the present invention can produce mortar or concrete with good initial strength development and small drying shrinkage. Specifically, when evaluated as concrete, the compressive strength at 1 day of age is 24 N / mm 2 or more, and the drying shrinkage (length change rate) at 91 days of the drying period after 7 days of curing is 0 to -350×10 -6 , more preferably 0 to -300×10 -6 and small concrete can be obtained. Regarding the compressive strength at 1 day of age, even in a low temperature environment (for example, 5°C), concrete with a compressive strength of 24 N / mm 2 or more can be obtained. The concrete of the present invention having such characteristics can be suitably used particularly as concrete for road paving.

[0025] (Method for producing mortar or concrete) The method for producing mortar or concrete of the present invention is not particularly limited, but after producing a kneaded material containing the cement composition, aggregate and water, it is preferable to mix the cement admixture into this kneaded material. The cement admixture is mixed in an amount of 20 to 40 parts by mass with respect to 100 parts by mass of the total (binder) of the above cement composition and the above cement admixture. When mixing the cement admixture, it is preferable to add a retarder together. The addition amount of the retarder is appropriately adjusted in the range of 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the binder so that the workable time becomes 30 minutes or more. The retarder is preferably added as an aqueous solution previously dissolved in water.

[0026] (Method for manufacturing paving concrete) In the method for manufacturing paving concrete of the present invention, after manufacturing base concrete containing the cement composition, fine aggregate, coarse aggregate and water, it is preferable to mix the cement admixture into this base concrete. Specifically, after manufacturing base concrete in a raw concrete improvement or concrete plant, it is transported to the construction site by a concrete mixer truck, and the cement admixture is added at the construction site. A water reducing agent and an AE agent are appropriately added to the base concrete and adjusted to a predetermined slump and air content. The cement admixture is mixed in an amount of 20 to 40 parts by mass with respect to 100 parts by mass in total (binder) of the above cement composition and the above cement admixture. When mixing the cement admixture, it is preferable to add a retarder together. The addition amount of the retarder is appropriately adjusted in the range of 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the binder according to the construction time at the site. The retarder is preferably added as an aqueous solution previously dissolved in water. The amount of water added together with the retarder is included in the concrete mix of the paving concrete. For this reason, the unit water amount in the base concrete is adjusted in consideration of the amount of water added together with the retarder. The amount of water (water-binder ratio) with respect to 100 parts by mass of the binder is preferably 25 to 50 parts by mass. Particularly when constructing in a low-temperature environment, in order to obtain sufficient initial strength development property, 25 to 40 parts by mass is preferable.

Examples

[0027] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

[0028] 〔Example 1〕 (1) Preparation of calcium aluminate The raw materials used were limestone (CaO content: 56% by mass, Al2O3, MgO, and SiO2 contents all less than 0.5% by mass) and bauxite shale (Al2O3 content: 87% by mass, Fe2O3 content: 1% by mass, SiO2 content: 5% by mass, CaO and MgO contents all less than 0.5% by mass), which were formulated so that the CaO / Al2O3 molar ratio was 1.3. The formulated mixture was fired in an electric furnace at 1500 °C for 3 hours. After firing, it was taken out of the furnace and immediately immersed in water, recovered from the water after about 5 minutes, and dried in a dryer at 200 °C to obtain the calcium aluminate of the present invention. This calcium aluminate was pulverized with a mill to obtain a powder with a Blaine specific surface area of 4000 cm 2 / g. As a result of analyzing the prepared calcium aluminate with an X-ray diffractometer, it was found that the main component was CaO·Al2O3 and the vitrification rate was 15%.

[0029] (2) Preparation of cement admixture Anhydrous gypsum and various inorganic salts were added to the above calcium aluminate and mixed for 10 minutes to prepare a cement admixture (symbol: Ad). Anhydrous gypsum (commercial product; Blaine specific surface area 7100 cm 2 / g) was used in the experiment with 100 parts by mass for every 100 parts by mass of calcium aluminate, 6 parts by mass of sodium sulfate (commercial reagent), and 6 parts by mass of lithium carbonate (commercial reagent).

[0030] (3) Preparation of concrete The materials used are shown in Table 1. The cement compositions were assumed to be Types A, B, and C of blast furnace cement, and the content of fine blast furnace slag powder was 25, 50, and 65% by mass. Table 1 shows the concrete mix when the binder was 100 parts by mass. The water content was set to 35 parts by mass per 100 parts by mass of the binder, and 0.50 - 0.55% by mass of an admixture was added to the cement composition. Materials used excluding cement admixtures and retarders were charged into a concrete mixer in predetermined amounts and kneaded for 2 minutes to prepare base concrete. At the level of mixing the cement admixtures, into this base concrete, the cement admixtures and water in which the retarder was dissolved were added and kneaded for an additional 1 minute. The amount of the cement admixtures mixed was 30 parts by mass with respect to 100 parts by mass of the binder. As the retarder, 0.6 part by mass of the retarder was added with respect to 100 parts by mass of the binder so that the available working time would be 30 minutes or more. The prepared concrete was filled into a predetermined formwork, cured for a predetermined period, demolded, and then an evaluation test was carried out.

[0031]

Table 1

[0032]

Table 2

[0033] (4) Evaluation Test 1) Compressive Strength The compressive strength was measured in accordance with JIS A 1108 "Test Method for Compressive Strength of Concrete". After filling the concrete into a formwork of φ10×20 cm, it was cured in air, demolded after 24 hours, and the compressive strength at an age of 1 day was measured. After demolding, it was cured in water, and the compressive strengths at ages of 7, 28, and 91 days were measured. 2) Dry Shrinkage The test was carried out in accordance with JIS A 1129-2 "Method for Measuring Length Change of Mortar and Concrete - Part 2: Contact Gauge Method". After filling the concrete into a formwork of 10×10×40 cm, it was demolded in 24 hours, cured in water until the age of 7 days, then the base length was measured, and it was left standing at 20°C and 60% RH, and the length changes at drying periods of 7, 28, and 91 days were measured.

[0034] (5) Test Results The test results are shown in Table 3. It can be seen that the concrete added with the cement admixture in the present invention has a small drying shrinkage. For Level No. 1-6 with a slag content of 65%, the length change rate at 91 days of the drying period was -229×10 -6 and showed a particularly small value. Furthermore, when comparing the difference in the length change rate (drying shrinkage reduction amount) between the concrete added with the cement admixture and the non-added one, the higher the content of fine powder of blast furnace slag, the greater the drying shrinkage reduction amount when the cement admixture is added. It was found that the effect of the present invention is particularly significant at Level No. 1-6 equivalent to Type C blast furnace cement with a blast furnace slag replacement rate of 65%.

[0035] [Table 3]

[0036] [Example 2] Tests were carried out using a cement composition with a slag content of 65% by mass, while varying the mixing amount of the cement admixture. The concrete mixes for each level are shown in Table 4. Also, the test results are shown in Table 5. It was confirmed that when the mixing amount of the cement admixture is 23 to 38 parts by mass with respect to 100 parts by mass of the binder, good initial strength development and sufficient drying shrinkage reduction effect can be obtained.

[0037] [Table 4]

[0038] [Table 5]

[0039] [Example 3] Tests were conducted on the strength development at low temperature environment (5°C). The production and curing of the concrete were carried out at 5°C, and the test was carried out in the same manner as in Example 1 except that a retarder was added at 0.15% by mass based on the binder. The test results are shown in Table 6. The concrete (level No. 3-6) containing 65% by mass of blast furnace slag fine powder in the present invention has a strength development property of 24 N / mm 2 or more at the age of 1 day even in a low-temperature environment.

[0040]

Table 6

[0041] 〔Example 4〕 Using a cement composition with a slag content of 65% by mass, a test was conducted in a low-temperature environment (5°C) by varying the mixing amount of the cement admixture. The test was carried out with the same concrete mix as in Example 2 except that 0.15 parts by mass of a retarder was added per 100 parts by mass of the binder. The test results are shown in Table 7. When the mixing amount of the cement admixture is 23 to 38 parts by mass, it was confirmed that good initial strength development property of 24 N / mm 2 or more can be obtained at the age of 1 day even in a low-temperature environment.

[0042]

Table 7

Claims

1. A hydraulic composition comprising a cement composition containing Portland cement and finely powdered blast furnace slag, and a cement admixture containing calcium aluminate and anhydrous gypsum, wherein the content of the finely powdered blast furnace slag is 40 to 70% by mass in the cement composition, and the cement admixture is 20 to 40 parts by mass with respect to a total of 100 parts by mass of the cement composition and the cement admixture.

2. The molar ratio of CaO to Al in the calcium aluminate ２ O ３ is 0.9 to 1.5, and the vitrification rate is less than 50%. The hydraulic composition according to claim 1.

3. Mortar or concrete containing the hydraulic composition according to Claim 1 or 2.

4. Paving concrete containing the hydraulic composition according to Claim 1 or 2.

5. A method for producing mortar or concrete according to Claim 3, characterized in that after producing a kneaded material containing the cement composition, aggregate and water, the cement admixture is kneaded.

6. A method for producing paving concrete according to Claim 4, characterized in that after producing base concrete containing the cement composition, fine aggregate, coarse aggregate and water, the cement admixture is kneaded.

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