JP2012201522A - Cement admixture and cement composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cement admixture imparting an excellent rust prevention effect to an inside reinforcement, having a blocking effect of infiltration of chloride ion entering from the outside, capable of suppressing porosity increase because of little leaching of Ca ion, and further having self-healing capacity, and to provide a cement composition.SOLUTION: This cement admixture contains a calcium ferroaluminate compound whose CaO/AlOmol ratio is 0.15-0.7 and whose FeOcontent is 0.5-20 mass%, and a deoxidizer. In the cement admixture, the fineness of the calcium ferroaluminate compound is 2,000-7,000 cm2/g in terms of a Blaine specific surface area value, and the deoxidizer is one or two or more of reducing iron powders selected from a group comprising sponge iron powder obtained by reducing and crushing an iron ore, electrolytic iron powder obtained by electrically depositing iron from iron ion solution, spray iron powder obtained by spraying molten ore into water or oil, and crushed iron powder obtained by crushing and grinding an iron lump.

Description

  The present invention mainly relates to a cement admixture and a cement composition used in the civil engineering and construction industries.

  In recent years, there has been an increasing demand for improving the durability of concrete structures in the civil engineering and construction fields.

  As one of the deterioration factors of concrete structures, there is salt damage in which reinforcing steel corrosion becomes obvious due to the presence of chloride ions, and as a method to suppress the salt damage, imparts chloride ion penetration resistance to concrete structures. There is a technique.

  As a method for suppressing chloride ion penetration into the inside of a hardened concrete and imparting chloride ion penetration resistance, a method of reducing the water / cement ratio is known (see Non-Patent Document 1). However, in the method of reducing the water / cement ratio, not only the workability is impaired but also a drastic measure may not be provided.

In addition, for the purpose of imparting early strength to cement concrete and preventing corrosion of reinforcing bars, the main component is CaO.2Al ₂ O ₃ and gypsum, and the Blaine specific surface area value is 8,000 cm ² / g or more. A method of using a cement admixture containing fine powder has been proposed (see Patent Document 1).

Furthermore, using a cement admixture containing calcium aluminate with a CaO / Al ₂ O ₃ molar ratio of 0.3 to 0.7 and a Blaine specific surface area of 2000 to 7000 cm ² / g, excellent chloride ion penetration resistance A method for suppressing temperature cracks in mascons has been proposed (see Patent Document 2). However, these admixtures have a problem of requiring sufficient curing at an early stage in order to inhibit the initial strength development.

  On the other hand, a cement composition in which iron powder or iron ingot is mixed is used as high-strength concrete or heavy concrete (see Patent Document 3). However, these iron powders are merely used as heavy aggregates and have no effect of improving the durability of the cement composition.

  On the other hand, a method of adding nitrite or the like has also been proposed for the purpose of rust prevention of reinforcing bars (see Patent Document 4 and Patent Document 5). However, although nitrite exhibits a rust prevention effect, it does not exert a shielding effect against chloride ions entering from the outside, and nitrite hydrocalumite exhibits a rust prevention effect. However, the hardened cement paste containing the material tends to be porous, but rather has a problem that it easily allows permeation of chloride ions from the outside.

  As a result of various studies, the present inventors have solved the problems of the initial strength reduction, chloride ion shielding effect, and corrosion of reinforcing bars by using a specific composition, and high durability. As a result, the present invention was completed.

JP 47-035020 A JP 2005-104828 A JP 2004-154100 A JP-A-53-003423 Japanese Patent Laid-Open No. 01-103970

Koichi Kishitani, Noriaki Nishizawa et al., “Durability series of concrete, salt damage (I)”, Gihodo Publishing, pp. 34-37, May 1986

  Provides excellent rust prevention effect to the reinforcing steel bars inside the hardened cement concrete, has the effect of shielding chloride ions from entering the hardened cement concrete, and less leaching of Ca ions from the hardened cement concrete Therefore, it is possible to provide a cement composition that can suppress porosity and further has a self-healing effect that blocks generated cracks by itself.

The present invention provides (1) a calcium ferroaluminate compound having a CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 and an Fe ₂ O ₃ content of 0.5 to 20% by mass and an oxygen scavenger. A cement admixture containing (2) a cement admixture of (1) having a fineness of the calcium ferroaluminate compound of 2,000 to 7,000 cm ² / g in terms of Blaine specific surface area; 3. The cement admixture according to claim 1 or 2, comprising reduced iron powder, (4) the oxygen adsorbent further containing an electrolyte, (3) cement admixture, (5) calcium ferro The cement admixture of any one of (1) to (4), wherein the blending ratio of the aluminate compound and the oxygen scavenger is 10/1 to 1/10 by mass ratio, (6) cement, (1 ) To (5) Cement compositions containing wood, (7) cement and CaO / _Al 2 _{O 3} molar ratio of _Fe 2 content of _{O 3} is Blaine specific surface area value of 0.5 to 20 wt% with 0.15 to 0.7 A cement composition comprising a calcium ferroaluminate compound and an oxygen scavenger, which is 2,000 to 7,000 cm ² / g.

  By using the cement admixture of the present invention, it has an excellent rust prevention effect and a shielding effect of chloride ions entering from the outside, and less leaching of Ca ions from the hardened cement concrete, so that it can be made porous. Further, since it has a self-healing effect of blocking the generated cracks by itself, it exerts an effect of exhibiting excellent salt barrier properties for a long period of time.

Hereinafter, the present invention will be described in detail.
In the present invention, “parts” and “%” are based on mass unless otherwise specified.
The cement concrete referred to in the present invention is a general term for cement paste, cement mortar, and concrete.

The calcium ferroaluminate compound (hereinafter referred to as CFA compound) used in the present invention is a mixture of a raw material containing calcia, a raw material containing alumina, a raw material containing ferrite, etc., and firing in a kiln or melting in an electric furnace. This is a generic term for compounds obtained by heat treatment such as CaO, Al ₂ O ₃ , and Fe ₂ O ₃ as main components.
The composition of the CFA compound is such that the CaO / Al ₂ O ₃ molar ratio is 0.15 to 0.7 and the Fe ₂ O ₃ content is 0.5 to 20%. The CaO / Al ₂ O ₃ molar ratio is more preferably 0.4 to 0.6. If the CaO / Al ₂ O ₃ molar ratio is less than 0.15, the chloride ion shielding effect may not be sufficiently obtained. In some cases, rapid hardening will appear and the pot life cannot be secured.
The content of Fe ₂ O _{3 in} the CFA compound is preferably 0.5 to 20%, more preferably 1 to 10%, and most preferably 3 to 7%. If it is less than 0.5%, a large amount of unreacted aluminum oxide may remain when calcined in the kiln, and even if it exceeds 20%, the effect of allowing the reaction to proceed efficiently becomes a head, and chloride ion penetration resistance. May be worse.

Fineness of CFA compounds, Blaine specific surface area value (hereinafter, referred to as Blaine value) is preferably 2,000~7,000cm ² / g, the more preferably 3,000~6,000cm ² / g, 4,000~ Most preferred is 5,000 cm ² / g. If the CFA compound is coarse, a sufficient chloride ion shielding effect may not be obtained, and if it exceeds 7,000 cm ² / g, rapid hardening will appear and the pot life may not be secured.

In the present invention, a CFA compound having a CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 and an Fe ₂ O ₃ content of 0.5 to 20% and an oxygen scavenger are used in combination.
Although the oxygen scavenger of the present invention is not particularly limited, for example, sponge iron powder obtained by reducing and grinding iron ore, electrolytic iron obtained by electrically depositing iron from an iron ion solution Examples thereof include atomized iron powder obtained by spraying powder, molten ore into water or oil, and crushed iron powder obtained by crushing or grinding an iron lump. In the present invention, these are reduced iron. It is called powder.
In addition, as an oxygen scavenger, organic substances are mainly used, for example, L-ascorbic acid, ersorbic acid and salts thereof, reducing sugars such as glucose, reducing polyphenols such as catechol and pyrogallol, ethylene glycol, glycerin. And the like using polyhydric alcohols such as
The oxygen scavenger absorbs oxygen, which is one of the causes of corrosion of reinforcing bars, and oxidizes it to act as a sacrificial anode material to prevent corrosion of reinforcing bars. Furthermore, volume expansion is achieved by oxidation, and subsequent cementation can be prevented by densifying the cement hardened body.
The oxygen scavenger of the present invention is preferably blended with the reduced iron powder using an electrolyte as an auxiliary agent. The electrolyte is not particularly limited, and examples thereof include metal halides, carbonates, sulfates and hydroxides, and any of them can be used.
Although the compounding quantity of electrolyte is not specifically limited, 0.1-10 parts are preferable with respect to 100 parts of reduced iron powder, and 0.2-4 parts are more preferable. When the electrolytic mass is less than the above range, the oxygen absorption rate is slow, while when it is more than the above range, moisture is absorbed and moisture covers the surface of the iron powder, which may inhibit the reaction with oxygen. is there.
The compounding method of the electrolyte may be simply mechanically mixing the reduced iron powder and the electrolyte, but the method of spraying and drying the aqueous electrolyte solution on the surface of the reduced iron powder, or mixing the reduced iron powder and the aqueous electrolyte solution, It is preferable to adhere this to the iron powder by a method of drying it.

  The blending ratio of the CFA compound and the oxygen scavenger of the present invention is preferably 10/1 to 1/10, more preferably 1/5 to 5/1, in terms of mass ratio. If the oxygen scavenger exceeds 1/10, the shielding effect of chloride ions entering from the outside may not be sufficient, and conversely, if the CFA compound exceeds 10/1, the rust preventive effect will be insufficient. It may be enough.

  As the cement used in the present invention, various portland cements such as normal, early strength, super early strength, low heat, and moderate heat, various mixed cements obtained by mixing these portland cements with blast furnace slag, fly ash, or silica, Portland cement such as filler cement mixed with limestone powder and blast furnace slow-cooled slag fine powder, as well as environmentally friendly cement (eco-cement) manufactured from municipal waste incineration ash and sewage sludge incineration ash, etc. 1 type or 2 types or more can be used.

  Although the usage-amount of a cement admixture is not specifically limited, Usually, 1-30 parts are preferable in a cement composition which consists of a cement and a cement admixture, and 5-20 parts are more preferable. If the amount of cement admixture is small, sufficient rust prevention effect, chloride ion shielding effect, Ca ion leaching suppression effect may not be obtained, and if used excessively, rapid hardening will appear and sufficient The pot life may not be secured.

  In the present invention, cement and a cement admixture are blended, and cement, a CFA compound, and an oxygen scavenger are blended to obtain a cement composition.

  The water / cement composition ratio of the cement composition of the present invention is preferably 25 to 70%, more preferably 30 to 65%. If the blending amount of water is small, the pumpability and workability may be reduced or shrinkage may be caused. If the blending amount of water is excessive, strength development may be degraded. Here, the binder means the total of cement, CFA compound and oxygen scavenger.

  In the cement admixture and cement composition of the present invention, the respective materials may be mixed at the time of construction, or a part or all of them may be mixed in advance.

  In the present invention, in addition to cement, cement admixture, and fine aggregates such as sand and coarse aggregates such as gravel, expansion material, quick hard material, water reducing agent, AE water reducing agent, high performance water reducing agent, high performance AE Water reducing agent, antifoaming agent, thickening agent, conventional rust inhibitor, antifreeze agent, shrinkage reducing agent, setting modifier, clay minerals such as bentonite, anion exchanger such as hydrotalcite, granulated blast furnace slag fine powder It is possible to use one or two or more of the group consisting of slag such as blast furnace annealed slag fine powder and admixture materials such as limestone fine powder within a range that does not substantially impair the object of the present invention.

  As the mixing device, any existing device can be used, and for example, a tilting mixer, an omni mixer, a Henschel mixer, a V-type mixer, and a Nauta mixer can be used.

  Hereinafter, although an example and a comparative example are given and the contents are explained in detail, the present invention is not limited to these.

"Experiment 1"
CFA compounds and oxygen scavengers shown in Table 1 were mixed at a mass ratio of 2/1 to prepare a cement admixture. Using the prepared cement admixture, a cement composition was prepared by blending 15 parts of cement admixture in 100 parts of cement composition consisting of cement and cement admixture, and adding a mortar with a water / binder ratio of 0.5. It was prepared according to JIS R 5201. Using the cured mortar, the rust prevention effect, compressive strength, chloride penetration depth, Ca ion leaching and self-healing ability were examined. The results are also shown in Table 1.

(Materials used)
CFA Compound A: Reagent primary calcium carbonate and reagent primary aluminum oxide are blended at a predetermined ratio, and reagent primary iron oxide is blended so that the Fe ₂ O ₃ content is 3%, at 1550 ° C. After firing in an electric furnace, it is synthesized by slow cooling. CaO / Al ₂ O ₃ molar ratio 0.1, Blaine value 4,000 cm ² / g
CFA Compound B: Reagent primary calcium carbonate and reagent primary aluminum oxide are blended at a predetermined ratio, and reagent primary iron oxide is blended so that the Fe ₂ O ₃ content is 3%, at 1550 ° C. After firing in an electric furnace, it is synthesized by slow cooling. CaO / Al ₂ O ₃ molar ratio 0.15, Blaine value 4,000 cm ² / g
CFA compound C: Reagent primary calcium carbonate and reagent primary aluminum oxide are blended at a predetermined ratio, and reagent primary iron oxide is blended so that the Fe ₂ O ₃ content is 3%. At 1500 ° C. After firing in an electric furnace, it is synthesized by slow cooling. CaO / Al ₂ O ₃ molar ratio 0.15, Blaine value 4,000 cm ² / g
CFA compound D: Reagent primary calcium carbonate and reagent primary aluminum oxide are blended at a predetermined ratio, and reagent primary iron oxide is blended so that the Fe ₂ O ₃ content is 3%, at 1450 ° C. After firing in an electric furnace, it is synthesized by slow cooling. CaO / Al ₂ O ₃ molar ratio 0.6, Blaine value 4,000 cm ² / g
CFA compound E: Reagent primary calcium carbonate and reagent primary aluminum oxide are mixed at a predetermined ratio, and reagent primary iron oxide is mixed so that the Fe ₂ O ₃ content is 3%. After firing in an electric furnace, it is synthesized by slow cooling. CaO / Al ₂ O ₃ molar ratio 0.7, Blaine value 4,000 cm ² / g
CFA compound F: Reagent primary calcium carbonate and reagent primary aluminum oxide are mixed at a predetermined ratio, and reagent primary iron oxide is mixed so that the Fe ₂ O ₃ content is 3%. After firing in an electric furnace, it is synthesized by slow cooling. CaO / Al ₂ O ₃ molar ratio 0.9, Blaine value 4,000 cm ² / g
CFA compound G: Reagent primary calcium carbonate and reagent primary aluminum oxide are blended at a predetermined ratio, and Fe ₂ O ₃ component is not blended, and calcined in an electric furnace at 1550 ° C., and then slowly cooled to synthesize . CaO / Al ₂ O ₃ molar ratio 0.6, Blaine value 4,000 cm ² / g
Deoxidizer A: Coated reduced iron powder cement obtained by mixing an aqueous solution containing 100 parts of sponge iron powder and 1.0 part of sodium bromide using an industrial mixer, drying by self-heating of the mixture, and cooling: Normal Portland cement, commercially available fine aggregate: Standard sand water used in JIS R 5201: Tap water

(Evaluation method)
Rust prevention effect: A mortar specimen containing round steel bars with chloride ions added to the internal chloride ion to 10 kg / m ³ was prepared, and it was removed from the mold one day later. After carrying out sealing curing at 20 ° C until 50 ° C, the rust prevention effect was confirmed by an accelerated test by heating to 50 ° C. The case where rust did not occur in the reinforcing bars was good, the case where rust occurred within an area of 1/10 was acceptable, and the case where rust occurred beyond an area of 1/10 was deemed impossible.
Compressive strength: Measures compressive strength at 1 day and 28 days of age according to JIS R 5201.
Chloride penetration depth: Evaluate chloride ion penetration resistance. A 10 cmφ × 20 cm columnar mortar specimen showing the shielding effect of chloride ions was prepared, demolded one day later, and immediately put into simulated seawater, which is a salt solution with a salt concentration of 3.5% at 30 ° C. for 12 weeks. After immersion, measure chloride penetration depth. The chloride penetration depth was determined by the fluorescein-silver nitrate method, the portion of the cross section of the mortar specimen where the tea did not change was regarded as the chloride penetration depth, and the average value was obtained by measuring 8 points with calipers.
Ca ion leaching: A 4 × 4 × 16 cm mortar specimen is prepared, demolded one day later, and immediately immersed in 10 liters of pure water for 28 days, and the concentration of dissolved Ca ions in the liquid phase is measured. It was judged by.
Self-healing ability: After producing a 10 × 10 × 40 cm mortar specimen mixed with 0.15% by mass of 6 mm nylon fiber, demolding after one day, and performing sealing at 20 ° C. until the age of 7 days, Cracks with a width of 0.3 mm were introduced by bending stress. After immersing in simulated seawater for 180 days, the crack width was measured. ◎ indicates that the crack is completely closed, ○ indicates that the crack width has been reduced to 0.1 mm or less, and △ indicates that the crack width has been reduced to approximately 0.2 mm. X indicates that the crack width has not been reduced or has expanded.

  From Table 1, by using a CFA compound and an oxygen scavenger in combination, it is possible to maintain the rust prevention effect and chloride ion permeation suppression effect, increase the initial strength, and further, Ca ion leaching resistance and self-healing ability. Can be improved.

"Experimental example 2"
The same procedure as in Experimental Example 1 was conducted except that the CFA compound D having a fineness shown in Table 2 and the oxygen scavenger A were used in combination. The results are also shown in Table 2.

  From Table 2, by adjusting the fineness of the CFA compound, it is possible to maintain the rust prevention effect and the chloride ion permeation suppression effect, to suppress the strength reduction, and further, Ca ion leaching resistance, self-healing ability Can be improved.

"Experiment 3"
The same procedure as in Experimental Example 1 was conducted except that CFA compound D was used and the oxygen scavenger shown in Table 3 was used in combination. The results are also shown in Table 3.

<Materials used>
Deoxidizer A: Coated reduced iron powder oxygen absorber obtained by mixing an aqueous solution containing 100 parts of sponge iron powder and 1.0 part of sodium carbonate using an industrial mixer, drying by self-heating of the mixture, and cooling. C: Coated reduced iron powder oxygen scavenger obtained by mixing an aqueous solution containing 100 parts of sponge iron powder and 1.0 part of sodium sulfate using an industrial mixer, drying by self-heating of the mixture, and cooling. Coated reduced iron powder oxygen scavenger obtained by mixing an aqueous solution containing 100 parts of iron powder and 1.0 part of calcium hydroxide using an industrial mixer, drying the mixture by self-heating, and cooling it: electrolytic iron powder An aqueous solution containing 100 parts of sodium bromide and 1.0 part of sodium bromide was mixed using an industrial mixer, dried by self-heating of the mixture, and cooled to obtain a coated reduced iron powder oxygen scavenger: 100 parts of electrolytic iron powder And water solution containing 1.0 part of sodium carbonate Is mixed with an industrial mixer, dried by self-heating of the mixture, and cooled to obtain a coated reduced iron powder oxygen scavenger: an aqueous solution containing 100 parts of electrolytic iron powder and 1.0 part of sodium sulfate. Mixing with a mixer, drying by self-heating of the mixture, and cooling to obtain a coated reduced iron powder oxygen scavenger: An aqueous mixer containing 100 parts of electrolytic iron powder and 1.0 part of calcium hydroxide was added to an industrial mixer. Using an industrial mixer, an aqueous solution containing 100 parts of atomized iron powder and 1.0 part of sodium bromide was obtained by mixing and drying by self-heating of the mixture and cooling. An aqueous solution containing 100 parts of coated reduced iron powder oxygen scavenger co: atomized iron powder and 1.0 part of sodium carbonate obtained by mixing, drying by self-heating of the mixture and cooling was mixed using an industrial mixer, Self-heating of the mixture Coated reduced iron powder oxygen scavenger obtained by further drying and cooling: An aqueous solution containing 100 parts of atomized iron powder and 1.0 part of sodium sulfate was mixed using an industrial mixer and dried by self-heating of the mixture. Coated reduced iron powder oxygen scavenger obtained by cooling: An aqueous solution containing 100 parts of atomized iron powder and 1.0 part of calcium hydroxide was mixed using an industrial mixer, dried by self-heating of the mixture, and cooled. Coated reduced iron powder oxygen scavenger obtained by mixing an aqueous solution containing 100 parts of crushed iron powder and 1.0 part of sodium bromide using an industrial mixer, dried by self-heating of the mixture, and cooled. Obtained coated reduced iron powder oxygen scavenger: A coating obtained by mixing an aqueous solution containing 100 parts of crushed iron powder and 1.0 part of sodium carbonate using an industrial mixer, drying by self-heating of the mixture, and cooling. Reduced iron powder oxygen scavenger Coated reduced iron powder oxygen scavenger obtained by mixing an aqueous solution containing 100 parts of crushed iron powder and 1.0 part of sodium sulfate using an industrial mixer, drying by self-heating of the mixture, and cooling: crushed iron powder An aqueous solution containing 100 parts of calcium hydroxide and 1.0 part of calcium hydroxide was mixed using an industrial mixer, dried by self-heating of the mixture, and cooled to obtain a coated reduced iron powder oxygen scavenger: 100 parts of sponge iron powder Deoxygenating agent: 100 parts of electrolytic iron powder Deoxidizing agent Te: 100 parts of atomized iron powder Deoxygenating agent: 100 parts of crushed iron powder Deoxygenating agent Na: 100 parts of sponge iron powder and 0.1 part of sodium bromide An aqueous solution containing 100 parts of sponge iron powder and 0.2 part of sodium bromide was obtained by mixing the aqueous solution with an industrial mixer, drying by self-heating of the mixture, and cooling. Mix using an industrial mixer and mix Coated reduced iron powder oxygen scavenger obtained by drying and cooling by self-heating: Mixing an aqueous solution containing 100 parts of sponge iron powder and 4 parts of sodium bromide using an industrial mixer, and drying by self-heating of the mixture Coated reduced iron powder oxygen scavenger obtained by cooling: An aqueous solution containing 100 parts of sponge iron powder and 10 parts of sodium bromide is mixed using an industrial mixer, dried by self-heating of the mixture, and cooled. Coated reduced iron powder

  From Table 3, even if any oxygen scavenger is used, the rust prevention effect and the chloride ion permeation suppression effect can be maintained, the strength reduction can be suppressed, and the Ca ion leaching resistance and self-healing ability can be maintained. Can be improved.

"Experimental example 4"
The same procedure as in Experimental Example 1 was carried out except that the mixture shown in Table 4 was used as an admixture using CFA compound D and oxygen scavenger a.

  From Table 4, the admixture of the present invention maintains the rust prevention effect and the chloride ion permeation suppression effect, can suppress the strength reduction, and further improve the leaching resistance and self-healing ability of Ca ions. Can do.

“Experimental Example 5”
The experiment was conducted in the same manner as in Experimental Example 1 except that an admixture prepared by mixing CFA compound A and oxygen scavenger A at a mass ratio of 2/1 was used to obtain the usage amount shown in Table 5. For comparison, a conventional rust preventive material was used in the same manner. The results are also shown in Table 5.

(Materials used)
Conventional rust-proofing material A: Lithium nitrite, commercial product Conventional rust-proofing material B: Nitrite-type hydrocalumite, commercial product

  From Table 5, by adjusting the use amount of the admixture of the present invention, it is possible to maintain a rust prevention effect and a chloride ion permeation suppression effect, and to suppress a decrease in strength, and further, leaching resistance of Ca ions, Self-healing ability can be improved.

  By using the cement admixture of the present invention, it has excellent rust prevention effect, chloride ion shielding effect, Ca ion leaching suppression effect and self-healing ability. Suitable for a wide range of applications such as water irrigation structures, river tanks, and floor slab concrete.

Claims (7)

A cement admixture containing a calcium ferroaluminate compound having a CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 and an Fe ₂ O ₃ content of 0.5 to 20% by mass and an oxygen scavenger. The cement admixture according to claim 1, wherein the calcium ferroaluminate compound has a fineness of 2,000 to 7,000 cm ² / g in terms of Blaine specific surface area. The cement admixture according to claim 1 or 2, wherein the oxygen scavenger contains reduced iron powder. The cement admixture according to claim 3, wherein the oxygen scavenger further contains an electrolyte. The cement admixture according to any one of claims 1 to 4, wherein a blending ratio of the calcium ferroaluminate compound and the oxygen scavenger is 10/1 to 1/10 by mass ratio. The cement composition containing a cement and the cement admixture of any one of Claims 1-5. Cement and CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 and Fe ₂ O ₃ content of 0.5 to 20% by mass Blaine specific surface area value of 2,000 to 7,000 cm ² / g A cement composition comprising a calcium ferroaluminate compound and an oxygen scavenger.