JP6719987B2 - Cement admixture, cement composition and hardened cement - Google Patents

Description

The present invention relates to a cement admixture, a cement composition, and a hardened cement product.

In recent years, with increasing interest in a recycling-based society, recycling of steelmaking slag, which has been treated as waste, has been promoted. The steelmaking slag is separated into a metal component, granular slag, and powdery slag by, for example, crushing, beneficiation, and classification treatment as one of the recycling treatment methods. Of these, the metal component can be reused as a steelmaking raw material. Further, although granular slag can be used as a sand material for building materials (for example, Patent Document 1), its use is limited and recycling is not sufficient. The powdery slag contains γ-2CaO·SiO ₂ and can be used as a cement admixture (for example, Patent Documents 2 and 3). However, powdery slag is difficult to collect because it is pulverized during the cooling process of the slag. Moreover, when the powdery slag is collected as a cake-like solid matter by a wet process, the amount of water increases. In order to use such powdery slag as a cement admixture, special drying equipment is required, which is costly and unrealistic.

On the other hand, it is also known to use blast furnace slag fine powder, fly ash, and limestone fine powder as the cement admixture. However, blast furnace slag fine powder has drawbacks such as promoting neutralization and increasing self-shrinkage. Further, the quality of fly ash varies depending on the place of production of coal and the combustion characteristics of the boiler, so that the quality is not stable. Further, limestone fine powder has the drawbacks of high manufacturing cost and insufficient neutralization suppressing effect.

JP, 2014-185050, A JP, 2003-206165, A JP, 2004-51425, A

The present invention has been made in order to solve the above problems, excellent in function as a cement admixture (particularly suppresses neutralization and self-shrinkage and enhances strength), redispersion of granular slag It is an object of the present invention to provide a cement admixture capable of enhancing recycling.
Another object of the present invention is to provide a cement composition and a cement hardened product which can suppress neutralization and self-shrinkage and can enhance strength.

As a result of continuing intensive research to solve the above problems, the present inventors have found that slag fine powder obtained by pulverizing granular slag having a specific composition to have a specific specific surface area is a cement admixture. The inventors have found that they have characteristics suitable for, and completed the present invention.

That is, the present invention is a cement admixture composed of slag fine powder derived from steelmaking slag, wherein F is less than 2.0 mass%, 33 to 53 mass% CaO, 20 to 35 mass% SiO ₂ , and 3 to. It contains 16% by mass of Al ₂ O ₃ and 5 to 10% by mass of MgO, has a basicity (CaO/SiO ₂ ) of 1.0 to 2.1 and a specific surface area of 4800 to 8000 cm ² /g. It is a cement admixture characterized by.

The present invention is also a cement composition containing the cement admixture and cement.
Furthermore, the present invention is a hardened cement product, which is a hardened product of a cement composition.

According to the present invention, there is provided a cement admixture excellent in function as a cement admixture (particularly suppressing neutralization and self-shrinkage and enhancing strength) and capable of enhancing recycling of granular slag. be able to.
Further, according to the present invention, it is possible to provide a cement composition and a cement hardened body which can suppress neutralization and self-shrinkage and can increase strength.

The cement admixture of the present invention is manufactured from steelmaking slag. Specifically, the cement admixture of the present invention includes a step of cooling and solidifying a molten steel-making slag having a predetermined composition, a step of crushing the cooled and solidified steel-making slag, beneficiation and classification, and a step of separating granular components. And a fine powder of slag produced by a method including a step of pulverizing the granular component so that the specific surface area thereof falls within a predetermined range.

As used herein, the term “cement admixture” means an admixture used for a composition containing cement (cement composition) such as cement paste, mortar, and concrete.
Moreover, in this specification, "steel making slag" means the slag which arises in a steel making process. For example, in the steelmaking process of stainless steel, it refers to the slag generated during the melting of stainless steel. In this slag, the molten slag generated in the melting step of melting the raw material in the electric furnace to generate the hot metal of stainless steel, and the desulfurization slag generated in the desulfurization treatment step of removing the sulfur contained from the generated hot metal, The refining slag produced in the refining step of removing carbon contained in the hot metal by a converter and a vacuum degassing apparatus with respect to the hot metal after desulfurization treatment is included. The slag also contains impurities in the raw material, products in the steelmaking process, and ingots of useful metals.

In the above-described stainless steel steelmaking process, as a method for desulfurizing hot metal, by adding a desulfurizing agent while stirring the hot metal with a mechanically driven stirring blade, the sulfur contained in the hot metal is slagged and removed. The KR method can be used. In the KR method, the desulfurization reaction between the hot metal and the desulfurization agent is promoted by stirring, so that a desulfurization agent containing CaO (quick lime, calcium oxide) as a main component can be used. Therefore, it is not necessary to use CaF ₂ (fluorite, calcium fluoride) known to be useful for promoting the desulfurization reaction.

The steelmaking slag contains F, CaO, SiO ₂ , Al ₂ O ₃ and MgO.
The content of F in the steelmaking slag satisfies the standard of the elution amount of F with respect to water specified in the soil environmental standard, and therefore is less than 2.0% by mass, preferably more than 0% by mass and 1.5% by mass or less, Preferably, it should be more than 0 mass% and 0.4 mass% or less. In the present invention, since it is not necessary to use fluorite in the desulfurization treatment, the F content in the steelmaking slag can be reduced. Therefore, the content of F in the slag fine powder produced from the steelmaking slag can be reduced, and the soil environmental standard can be satisfied even in various applications where the concrete admixture made of the slag fine powder is used.

CaO is a main component of the desulfurization agent and an essential component for the desulfurization reaction. Therefore, the content of CaO in the steelmaking slag needs to be 33% by mass or more, preferably 35% by mass or more, and more preferably 40% by mass or more. On the other hand, when the content of CaO in the steelmaking slag is excessive, the basicity (CaO/SiO ₂ ) becomes too high, the fluidity of the slag is lowered, and the desulfurization reaction is not promoted. Therefore, the content of CaO in the steelmaking slag needs to be 53 mass% or less, preferably 50 mass% or less.

SiO ₂ is generated from a raw material of stainless steel or is also generated as a deoxidation reaction product by a reducing agent. The content of SiO _{2 in} the steelmaking slag needs to be 20% by mass to 35% by mass, preferably 25% by mass to 30% by mass, from the viewpoint of efficiently performing the desulfurization treatment of the hot metal of stainless steel. When the content of SiO ₂ is less than 20% by mass, the basicity during desulfurization treatment becomes too high, and the desulfurization reaction cannot be accelerated. On the other hand, when the content of SiO ₂ exceeds 35 mass %, the basicity during desulfurization treatment becomes too low, and a sufficient desulfurization reaction cannot be obtained.

Al ₂ O ₃ is an essential component for ensuring the fluidity of the steelmaking slag. Al ₂ O ₃ is also mixed from the refractory bricks of each pot used for steelmaking and the raw material of stainless steel. The content of Al ₂ O _{3 in} the steelmaking slag needs to be 3% by mass to 16% by mass, preferably 5% by mass to 10% by mass, from the viewpoint of ensuring the fluidity of the steelmaking slag. When the content of Al ₂ O ₃ is less than 3% by mass or more than 16% by mass, the melting point of the steelmaking slag increases and the fluidity of the steelmaking slag decreases.

MgO is one component for ensuring the fluidity of the steelmaking slag. Since MgO is a component in which the refractory used for the inner wall of the melting furnace is worn and melted in the slag, it is not necessary to intentionally add MgO. Usually, if low-cost refractories of general quality are used, the content of MgO in the steelmaking slag will be 5% by mass to 10% by mass, preferably 7% by mass to 9% by mass. If the content of MgO is controlled to be less than 5% by mass, it is necessary to use a refractory material which is less expensive and has high cost, and repair management. On the other hand, when the content of MgO exceeds 10% by mass, the fluidity of the slag is reduced and the refining function is reduced.

The steelmaking slag may further contain components such as Fe ₂ O ₃ , MnO, and Cr ₂ O ₃ in addition to the above components. The contents of these components in the steelmaking slag are not particularly limited.
The basicity (CaO/SiO ₂ ) of the steelmaking slag has a great influence on the desulfurization reaction of hot metal. In particular, if the desulfurization treatment method is the mechanical stirring KR method and fluorite that has been used to improve the fluidity of slag is not used, the basicity of the steelmaking slag is adjusted to improve the fluidity of the steelmaking slag. Must be secured. Therefore, the basicity of the steelmaking slag needs to be 1.0 to 2.1, preferably 1.3 to 1.6. When the basicity of the steelmaking slag is less than 1.0, a sufficient desulfurization reaction does not occur between CaO contained in the steelmaking slag and S contained in the hot metal during the desulfurization treatment. On the other hand, if the basicity of the steelmaking slag exceeds 2.1, the fluidity of the steelmaking slag becomes low during the desulfurization treatment, and the contact interface between the hot metal and the steelmaking slag decreases, and the desulfurization reaction cannot be accelerated.

The composition of steelmaking slag should be adjusted according to the mixing ratio of the raw materials and the empirical rule about the element distribution ratio between the slag and the stainless steel, and the type and mixing ratio of the raw materials of the slag generation source should be adjusted for each steel type to be melted. The composition and basicity can be controlled by.

The method for cooling and solidifying the molten steel-making slag is not particularly limited, and a method known in the art can be used. For example, molten steelmaking slag is put in a slag pan and cooled over 24 hours by a cooling method that combines air cooling by natural cooling in the atmosphere and water spray cooling in which water is cooled in a slag pan. It In the cooling process of the steelmaking slag, the steelmaking slag is put into a slag pan and solidification starts from about 1100°C to about 700°C at which the change in the crystal structure of γ-2CaO·SiO (ie, phase transformation) is almost completed. It is preferable to perform gradual cooling so that the temperature decreases at a rate of 1.0° C./min or less until the temperature decreases (that is, between about 1100° C. and about 700° C.). When the temperature of the steelmaking slag is about 700° C. or higher, when the temperature of the steelmaking slag is lowered at a rate of more than 1.0° C./minute, for example, by increasing the amount of water sprayed or by directly spraying water on the steelmaking slag, cooling and solidification occurs. A brittle slag with a low internal density may be obtained later. In order to sufficiently cool and solidify the steelmaking slag so that it can be sufficiently crushed in the next crushing treatment, the steelmaking slag is cooled for 28 to 30 hours or longer depending on the outside air temperature. Preferably.

When the steel-making slag is cooled and solidified at the cooling rate as described above, free lime (f-CaO), free magnesia (f-MgO), γ-2CaO. contained in the steel-making slag and capable of causing a hydration reaction. A soft portion containing SiO and the like and a dense and hard mineral phase (formed of SiO ₂ , Al ₂ O _3, etc.) form different phases separated from each other. Then, in the cooling process, the soft portion containing γ-2CaO·SiO and the like is pulverized by volume expansion due to the change in the crystal structure of γ-2CaO·SiO and the like. Further, when the cooled and solidified steelmaking slag undergoes a wet crushing treatment described below, the soft portion between the hard mineral phases is finely crushed, so that many of the hard mineral phases are separated from each other and become lumpy, Further, when the massive mineral phase is crushed, it becomes granular. Therefore, in the pulverizing process, the soft part is mainly powdered, and the hard mineral phase is hard to be powdered. Therefore, the soft part is hardened by the classification process described later from the soft part to the hard mineral phase (granular Min) can be separated and collected.

The method for pulverizing the cooled and solidified steelmaking slag is not particularly limited, and a method known in the art can be used. For example, the steel slag cooled and solidified may be crushed by the jaw crusher and then crushed by the rod mill.
In the jaw crusher crushing process, the steelmaking slag is sandwiched and pressed between the fixed teeth of the jaw crusher and the movable teeth that move toward and away from the fixed teeth in the air. Compressed and crushed. The steelmaking slag is roughly dry-crushed by this treatment. At this time, in the steelmaking slag, the hard mineral phase is separated into a large number of lumps due to the collapse of the soft portion between the hard mineral phases.

In the rod mill crushing process, the steelmaking slag is put into a rod mill containing water and is immersed in water, and is further finely wet crushed by rotating the rod mill. In the process of this wet crushing, the soft part contained in the steelmaking slag becomes more brittle by the hydration reaction, and is crushed into fine powder and suspended in water. The soft portion thus crushed into fine powder is called "fine powder" below. On the other hand, the massive hard mineral phase is crushed into particles in the rod mill. The hard mineral phase thus crushed into particles is referred to as "granular content" below.

Further, the crushing treatment separates the metal contained in the steelmaking slag from the granular portion together with the soft portion. At this time, if the steel-making slag is sufficiently solidified by cooling, the metal can be easily separated during the crushing process.

The method for beneficiating the crushed steelmaking slag is not particularly limited, and a method known in the art can be used. For example, the steelmaking slag that has been subjected to the pulverization treatment may be subjected to a specific gravity separation treatment and a magnetic separation treatment. In the gravity separation treatment, steelmaking slag can be put into treated water and a specific gravity sorter can be used to sort using the difference in specific gravity of minerals. The steelmaking slag that has been selected as having high specific gravity by the specific gravity separation treatment is subsequently subjected to magnetic separation processing. On the other hand, the steelmaking slag selected as having low specific gravity is subsequently subjected to classification treatment. The classification treatment is not particularly limited, but a sieve classification treatment can be used.

In the magnetic separation process, the ingot can be separated and recovered by the magnetic separator with respect to the steelmaking slag having a high specific gravity including the ingot.
In the sieving and classifying process, the steelmaking slag with a low specific gravity taken out from the specific gravity sorter and contained in the treated water is supplied onto the vibrating screen (sieve) of the vibrating sieving machine, and the size of the screen opening is increased. Those (for example, 5 mm) or less are selected. The steelmaking slag that has not passed through the screen and has a particle size of more than 5 mm is returned to the rod mill crushing process 32 together with the treated water, and the wet crushing process is performed.

The steelmaking slag having a particle diameter of 5 mm or less that has passed through the screen is in a sand slime state in which the granular content, the fine powdery content and the treated water are mixed, and the granular content can be separated by performing the Akins classification treatment. In other words, the steelmaking slag contained in the treated water is sent together with the treated water to the Akins classifier, which is a spiral type classifier, to be classified, whereby granular particles with a specific particle size (about 0.15 mm) or more are obtained. Are separated from the finely divided particles suspended in water. As a result, granular particles having a particle size of 0.15 mm or more and 5 mm or less are selected.

In addition, the steelmaking slag after the removal of particulates is in a slime state in which fine powder and treated water are mixed, and it is possible to separate the fine powder from treated water by performing a thickener/dewatering treatment. it can. In this treatment, the steelmaking slag contained in the treated water is sent to a thickener together with the treated water for classification, and fine powder components are separated from the slime. Further, the fine powdery matter separated in the state of containing water is subjected to dehydration treatment and can be recovered in the form of dehydrated cake.

The method for pulverizing the granular material is not particularly limited, and a method known in the art can be used. For example, it may be pulverized using a vertical roller mill capable of fine pulverization. Further, it is preferable that the pulverization of the granules is performed by blowing hot air into the vertical roller mill while drying the granules. By pulverizing in this way, the amount of water in the obtained slag fine powder is reduced, and when used as a raw material for various purposes, the granulating property can be dramatically improved.
Milling of the particulate matter is taken into consideration for use as a cement admixture, a specific surface area of 4800cm ² / g~8000cm ² / g, carried out preferably to a 4800cm ² / g~5800cm ² / g. If the specific surface area is less than 4800 cm ² /g, the densification of the hardened cement will be insufficient and the effect of suppressing neutralization will not be sufficiently obtained. On the other hand, if the specific surface area exceeds 8000 cm ² /g, the crushing cost will increase significantly.

The slag fine powder produced as described above has substantially the same composition and basicity as the steelmaking slag used as the raw material. That is, the slag fine powder contains less than 2.0 mass% F, 33 to 53 mass% CaO, 20 to 35 mass% SiO ₂ , 3 to 16 mass% Al ₂ O ₃ and 5 to 10 mass%. It contains MgO and has a basicity (CaO/SiO ₂ ) of 1.0 to 2.1.
Further, since the slag fine powder is formed of the granular component separated from the fine powdery component, it does not contain γ-2CaO·SiO ₂ . Here, in the present specification, “does not include γ-2CaO·SiO ₂ ”does not mean that γ-2CaO·SiO ₂ is not contained at all, and γ-2CaO· that is mixed as an impurity. It means that SiO ₂ may be contained.
Since the cement admixture of the present invention is made of slag fine powder, it can enhance the recycling of granular slag and has an excellent neutralization suppressing effect.

The cement admixture of the present invention is used by adding it to cement. That is, the cement admixture of the present invention can be used in a cement composition.
The cement composition generally comprises a cement admixture, cement and water.
The cement is not particularly limited, and cement known in the art can be used. As examples of cement, various types of portland cement such as normal, early strength, ultra-early strength, low heat, and moderate heat, mixed cement, ecocement and the like can be used.

The ratio of the cement admixture to the cement admixture and the total amount of cement is not particularly limited, but is generally 5% by mass to 55% by mass, preferably 25% by mass to 40% by mass.
The ratio of cement to the total amount of cement admixture and cement is not particularly limited, but is generally 45% by mass to 95% by mass, preferably 60% by mass to 75% by mass.
When the proportion of the cement admixture is less than 5% by mass and the proportion of the cement is more than 95% by mass, the amount of the cement admixture is too small, and the effect of the cement admixture may not be sufficiently obtained. On the other hand, if the proportion of the cement admixture exceeds 55% by mass and the proportion of cement is less than 45% by mass, the strength of the hardened cement product obtained from the cement composition may not be sufficiently ensured.

The ratio of water to the total amount of cement admixture and cement may be appropriately set according to the type of cement composition and is not particularly limited. For example, the proportion of water is generally 25% to 65% by weight. In particular, from the viewpoint of obtaining a cement composition that gives a hardened cement product having excellent durability, the proportion of water relative to the total amount of cement admixture and cement is preferably 25% by mass to 55% by mass. When the proportion of this water is less than 25% by mass, the heat of hydration becomes high, the drying shrinkage strain becomes large, and the economical efficiency is likely to decrease. On the other hand, if the proportion of this water exceeds 65% by mass, the amount of bleeding increases and the effect of the concrete admixture may not be sufficiently obtained.

From the viewpoint of improving the strength, the cement composition may further include at least one kind of fine aggregate and coarse aggregate. The fine aggregate and the coarse aggregate are not particularly limited, and those known in the art can be used. Examples of fine aggregates include natural fine aggregates such as river sand, mountain sand, sea sand, and natural lightweight fine aggregates (for example, perlite and leech stone), crushed sand, artificial lightweight fine aggregates, blast furnace slag fine aggregates, and the like. Artificial fine aggregate, lightweight by-product fine aggregate, and the like. Examples of the coarse aggregate include crushed stone, river gravel, natural lightweight coarse aggregate (for example, pearlite and leeved stone), by-product lightweight coarse aggregate, artificial lightweight coarse aggregate, recycled aggregate, and the like. These can be used alone or in combination of two or more.

The blending amount of fine aggregate in the cement composition is not particularly limited, but is preferably 100 parts by mass to 500 parts by mass with respect to 100 parts by mass of cement.
If the amount of the fine aggregate is less than 100 parts by mass, the effect of adding the fine aggregate may not be sufficiently obtained. In addition, the heat of hydration becomes high, the drying shrinkage strain becomes large, and the economical efficiency may decrease. On the other hand, when the amount of the fine aggregate added exceeds 500 parts by mass, the strength of the hardened cement product obtained from the cement composition may decrease.
The blending amount of the coarse aggregate in the cement composition is not particularly limited, and may be appropriately set according to the amount of the fine aggregate used.

Further, coarse slag derived from steelmaking slag may be used as at least a part of the fine aggregate. In particular, by using the granular slag (granular content) obtained during the production of the cement admixture (fine slag powder) of the present invention as at least a part of the fine aggregate, the coarse grain slag obtained from the steelmaking slag It becomes possible to further enhance recycling. Also, this coarse-grained slag has the same composition and basicity as the cement admixture (that is, less than 2.0 wt% F, 33-53 wt% CaO, 20-35 wt% SiO ₂ , 3-). Since it contains 16% by mass of Al ₂ O ₃ and 5 to 10% by mass of MgO and has a basicity (CaO/SiO ₂ ) of 1.0 to 2.1), it has good compatibility with a cement admixture. ..

The amount of the coarse-grained slag in the cement composition is not particularly limited, but is preferably 30 parts by mass to 80 parts by mass, more preferably 30 parts by mass to 60 parts by mass with respect to 100 parts by mass of the total amount of the cement admixture and the cement. It is a department. If the amount of the coarse-grained slag is less than 30 parts by mass, the unit water amount may increase or the bleeding amount may increase. On the other hand, if the amount of the coarse slag compounded exceeds 80 parts by mass, the effect of the cement admixture may be reduced.

The cement composition may further contain known additives in addition to the components described above, as long as the effects of the present invention are not impaired. Examples of known additives include coarse aggregate, water reducing agent, defoaming agent, thickening agent, rust preventive, low shrinking agent, expanding agent, dispersant and the like. Further, when the cement composition is used in a place where there is a risk of freezing, a commercially available AE agent may be blended with the cement composition to adjust the amount of air.

The cement composition can be produced according to a method known in the art. Specifically, a cement admixture may be added to cement, and water and fine aggregate may be added and mixed. The mixing method is not particularly limited, and mixing may be performed using a mixing device known in the art.

The cement composition becomes a hardened cement product by being hardened by a method known in the art. Since this cement hardened product is formed from a cement composition using a cement admixture that gives an excellent neutralization suppressing effect, it has an excellent neutralization suppressing effect. As a result, cracking and peeling of the hardened cement body due to corrosion of the reinforcing bar can be reduced, so that the covering thickness of the hardened cement body on the reinforcing bar can be reduced.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
(Example 1: Cement admixture)
In the steelmaking process of stainless steel, the hot metal was desulfurized by the KR method using a desulfurizing agent containing CaO as a main component. The molten steelmaking slag generated in this steelmaking process was collected in a slag pan. The steelmaking slag in the molten state comprises 1.1% by mass of F, 38.7% by mass of CaO, 25.8% by mass of SiO ₂ , 8.7% by mass of Al ₂ O ₃ and 9.4% by mass. MgO, 3.4 wt% of _Fe 2 _O 3, 2.3 wt% of MnO, wherein the _Cr 2 _{O 3} 3.3 wt%, basicity (CaO / SiO ₂₎ was 1.5. Next, the molten steelmaking slag placed in the slag pan is cooled at about 1100° C. to about 700° C. by a cooling method that combines air cooling by natural cooling in the atmosphere and sprinkling cooling for spraying and cooling the slag pan. The temperature was cooled at a rate of 0.8° C./minute or less during 7.8 hours.

Next, the cooled and solidified steelmaking slag was crushed by a jaw crusher and then crushed by a rod mill. Next, after subjecting the steelmaking slag that has been subjected to crushing treatment to specific gravity separation treatment, for the steelmaking slag that has been selected as having high specific gravity, magnetic separation is performed to separate and recover the metal, and it is also assumed that the specific gravity is low. The selected steelmaking slag was subjected to sieving and classification treatment using a screen having a mesh size of 5 mm. Next, the steelmaking slag having a particle diameter of 5 mm or less that passed through the screen was subjected to Akins classification treatment to select a granular component having a particle diameter of 0.15 mm or more and 5 mm or less. The steel-making slag from which the particulate matter had been removed was subjected to a thickener/dewatering treatment to recover fine powdery matter in the form of a dehydrated cake. Next, the selected granules (coarse-grained slag) were pulverized by using a vertical roller mill until the specific surface area became 4950 cm ² /g to obtain a cement admixture A made of fine slag powder. Moreover, the selected admixture was pulverized by using a vertical roller mill until the specific surface area became 5010 cm ² /g to obtain a cement admixture B composed of fine slag powder.

(Example 2: Cement composition)
Sample No. 1 was prepared by adding the cement admixture A or B obtained in Example 1 to ordinary Portland cement, and adding water, coarse aggregate and fine aggregate to the mixture and mixing. Cement compositions 1 and 2 were prepared. Crushed stone was used as the coarse aggregate, and crushed sand was used as the fine aggregate. In addition, the sample No. In the cement composition of No. 2, a part of the crushed sand was replaced with the granular component (coarse-grained slag) obtained during the production of the cement admixture of Example 1. The compounding amount and ratio of each component and the water cement ratio are shown in Table 1.

(Comparative Example 1)
Fine limestone powder (specific surface area 4850 cm ² /g) was added to ordinary Portland cement, and water, coarse aggregate and fine aggregate were added to and mixed with each other to obtain Sample No. A cement composition No. 3 was prepared. Crushed stone was used as the coarse aggregate, and crushed sand was used as the fine aggregate. The compounding amount and ratio of each component and the water cement ratio are shown in Table 1.

(Comparative example 2)
Sample No. 1 was prepared by adding water, coarse aggregate and fine aggregate to ordinary Portland cement and mixing them. A cement composition of No. 4 was prepared. Crushed stone was used as the coarse aggregate, and crushed sand was used as the fine aggregate. The compounding amount and ratio of each component and the water cement ratio are shown in Table 1.

The accelerated neutralization test, the 28-day compressive strength test, and the drying shrinkage strain of the cement composition obtained above were evaluated.
An accelerated neutralization test was conducted. The test method was performed according to JIS A1153. Specifically, for each cement composition, three 10 cm×10 cm×40 cm prismatic specimens were prepared, demolded at a material age of 1 day, and then cured in water until a material age of 28 days (4 weeks), After standing still in a constant temperature and high humidity room at room temperature of 20° C. and humidity of 60% for 56 days (8 weeks), accelerated neutralization was performed using an accelerated neutralization tester. The temperature inside the tester was 20° C.±2 degrees, the humidity was 60° C.±5%, and the carbon dioxide concentration was 5±0.2%. On the day of measuring the neutralization depth, cut the specimen, apply the phenolphthalein solution to the cross section, and then use the distance from the end surface of the cross section to the part colored red purple as the neutralization depth. It was measured. The measurement days were 1 week, 4 weeks, 8 weeks, 13 weeks, and 26 weeks after the test specimen was left standing in the accelerated neutralization tester. The neutralization depth of 1.0 mm or less was accepted.

The compressive strength test of 28 days old was measured according to JIS A1108. Specifically, each cement composition was aged in water for 28 days to prepare a test specimen, and the compressive strength was measured by a compressive strength measuring device. A compressive strength of 40 N/mm ² or more was passed.
The dry shrinkage strain was measured according to JIS A1129. A drying shrinkage strain of 800×10 ⁻⁶ or less was regarded as acceptable.
Table 2 shows the evaluation results. In Table 2, the results of the accelerated neutralization test, the compressive strength test of 28-day-old material, and the drying shrinkage strain that passed all are ◯, the accelerated neutralization test, the compressive strength of 28-day-old material. Also shown is a comprehensive evaluation, in which the test and the result of any one of the dry shrinkage strains were unacceptable as x.

As shown in Table 2, sample No. Cement compositions 1 and 2 (Examples) were sample No. Compared with the cement compositions of 3 and 4 (comparative example), the effect of suppressing neutralization was excellent, the 28-day compressive strength was high, and the dry shrinkage strain was also small.

As can be seen from the above results, according to the present invention, it is possible to enhance the function as a cement admixture, in particular, suppress neutralization and self-shrinkage and increase the strength), and enhance the recycling of granular slag. Cement admixture can be provided. Further, according to the present invention, it is possible to provide a cement composition and a cement hardened body which can suppress neutralization and self-shrinkage and can increase strength.

Claims (7)

A cement admixture consisting of slag fine powder derived from steelmaking slag,
F less than 2.0 wt%, 33-50 wt% of CaO,. 20 to 30 mass% of _SiO 2, comprising 3 to 16 wt% of _Al 2 _{O 3} and 5-10 wt% of MgO, basicity ( CaO / SiO ₂₎ is 1.0-2.1, cement admixture having a specific surface area, characterized in that a 4800~8000cm ² / g. The cement admixture according to claim 1, wherein the cement admixture does not contain γ-2CaO·SiO ₂ . A cement composition comprising the cement admixture according to claim 1 or 2 and cement. 4. The cement according to claim 3, wherein the ratio of the cement admixture is 5 to 55 mass% and the ratio of the cement is 45 to 95 mass% with respect to the total amount of the cement admixture and the cement. Composition. The cement composition according to claim 3 or 4, wherein the cement admixture contains water in a proportion of 25 to 65 mass% with respect to the total amount of the cement. The cement composition according to any one of claims 3 to 5, further containing at least one kind of fine aggregate and coarse aggregate. A hardened cement product, which is a hardened product of the cement composition according to any one of claims 3 to 6.