JP7062668B2 - Cement admixture, cement composition and its manufacturing method - Google Patents

Description

The present invention mainly relates to cement admixtures and cement compositions 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 fields of civil engineering and construction.

One of the deterioration factors of the concrete structure is salt damage in which the reinforcing bar is corroded by the presence of chloride ions, and as a means for suppressing the damage, there is a method of imparting chloride ion permeation resistance to the concrete structure.

A method of reducing the water / cement ratio is known as a method of suppressing chloride ion permeation into a hardened concrete body and imparting chloride ion permeation resistance (see Non-Patent Document 1). However, the method of reducing the water / cement ratio not only impairs workability but also may not be a drastic measure.

In addition, for the purpose of imparting fast strength to cement concrete and preventing corrosion of reinforcing bars, mainly CaO ・ 2Al ₂ O ₃ and sekkou, with a brain specific surface area value of 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 _{2O 3} molar ratio of 0.3 to 0.7 and a brain specific surface area of 2000 to 7000 cm ² / g, excellent chloride ion penetration is used. A method having resistance and suppressing temperature cracking of mass cement has been proposed (see Patent Document 2). Further, a cement admixture containing a calcium ferroaluminate compound having a CaO / Al _{2O 3} molar ratio of 0.15 to 0.7 and a Fe ₂ O ₃ content of 0.5 to 20% by mass has been proposed. (See Patent Document 3).

On the other hand, a method of adding nitrite or the like has also been proposed for the purpose of preventing rust on the reinforcing bar (see Patent Document 4 and Patent Document 5).

Japanese Unexamined Patent Publication No. 47-035020 Japanese Unexamined Patent Publication No. 2005-104828 Japanese Patent No. 5680873 Japanese Unexamined Patent Publication No. 53-003423 Japanese Unexamined Patent Publication No. 01-103970

"Concrete Durability Series, Salt Damage (I)", Gihodo Publishing, Koichi Kishitani, Noriaki Nishizawa et al., Pp. 34-37, May 1986

It imparts an excellent rust preventive effect to the reinforcing bars inside the hardened cement concrete body, has a shielding effect against the penetration of chloride ions from the outside, and further makes the hardened cement concrete body less leached by Ca ions and becomes porous. Provided are a cement admixture, a cement composition, and a method for producing the same, which can suppress the above.

The present invention relates to (1) a cement admixture containing calcium boron aluminate having a CaO / Al _{2O 3} molar ratio of 0.15 to 0.7 and a B ₂ O ₃ content of 0.05 to 10% by mass. (2) The cement admixture of (1), (3) cement, and (1) or (2), in which the degree of powderiness of calcium boron aluminate is 2,000 to 7,000 cm ² / g in terms of brain ratio surface area value. Cement composition containing the cement admixture of (4) CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 and B ₂ O ₃ content of 0.05 to 10% by mass. A calcium boron aluminate obtained by mixing a raw material containing calcia, a raw material containing alumina, and a raw material containing boron, firing at 1400 ° C. or higher, and then pulverizing the mixture so that the brain specific surface area value is 2000 to 7000 cm ² / g. , A method for producing a cement composition, which comprises mixing cement.

By using the cement admixture of the present invention, it has an excellent rust preventive effect and a shielding effect of chloride ions invading from the outside, and further, since there is little leaching of Ca ions from the hardened cement concrete, it is porous. It has the effect of suppressing rusting.

The X-ray diffraction spectrum of the calcium boron aluminum sample and its control is shown.

Hereinafter, the present invention will be described in detail. Unless otherwise specified, parts and% in the present specification are shown on a mass basis. Further, the term "cement concrete" as used herein is a general term for cement paste, cement mortar, and concrete. Further, in the present specification, unless otherwise specified, the numerical range includes the upper limit value and the lower limit value.

Calcium boron aluminate (hereinafter, also abbreviated as CBA) used in the present invention is a mixture of a raw material containing calcia, a raw material containing alumina, a raw material containing boron, etc., and is fired in a kiln or melted in an electric furnace. It is a general term for compounds containing CaO, Al ₂ O ₃ , and B ₂ O ₃ as main components, which are obtained by heat treatment such as, and has a crystal structure in which a boron atom is solidly dissolved in calcium aluminate. ..

The material composition of CBA has a CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 and a B ₂ O ₃ content of 0.05 to 10%. The CaO / Al _{2O 3} molar ratio is more preferably 0.4 to 0.6. If the CaO / Al _{2O 3} molar ratio is less than 0.15, the shielding effect of chloride ions may not be sufficient, while if it exceeds 0.7, rapid hardness is exhibited and the pot life is secured. It may not be possible. The content of B ₂ O ₃ in CBA is preferably 0.05 to 10%, more preferably 0.1 to 5%, and most preferably 0.2 to 3%. If the B ₂ O ₃ content is less than 0.05%, a large amount of unreacted aluminum oxide may remain when firing in a kiln, while if it exceeds 10%, the chloride ion permeation resistance deteriorates. There is.

The powderiness of CBA is preferably 2,000 to 7,000 cm ² / g, more preferably 3,000 to 6,000 cm ² / g, and 4,000 to 5 in terms of the specific surface area value of the brain (hereinafter referred to as the brain value). 000 cm ² / g is the most preferable. When the CBA brain value is 2,000 cm ² / g or more, a sufficient chloride ion shielding effect can be obtained, while when it is 7,000 cm ² / g or less, the onset of rapid hardness is suppressed and the pot life is available. Has the effect of being able to be secured.

The raw materials used in the production of CBA are as follows.

The raw material containing calcium is not particularly limited, and examples thereof include the use of quick lime (CaO), slaked lime (Ca (OH) ₂ ), limestone (CaCO ₃ ), etc., which are commercially available as industrial raw materials.

The raw material containing alumina is not particularly limited, and examples thereof include the use of commercially available industrial raw materials such as Al ₂ O ₃ , aluminum hydroxide, and bauxite. In particular, bauxite is preferable because it contains B ₂ O ₃ in addition to Al ₂ O ₃ .

The raw material containing boron is not particularly limited, but _{B 2} O ₃ obtained by crushing _, processing and purifying borate minerals commercially available as industrial raw materials and recovering and purifying from waste hydrochloric acid for cleaning steel materials. Anything can be used.

Further, for example, even if MgO, SiO ₂ , R ₂ O (R is an alkali metal), Fe ₂ O ₃ , TIO ₂ , and Ti ₂ O ₃ are used in combination, they can be used as long as the object of the present invention is not impaired.

CBA is obtained by mixing a raw material containing calcia, a raw material containing alumina, and a raw material containing boron, and if appropriate, other raw materials, and performing heat treatment such as firing in a kiln or melting in an electric furnace. .. The firing temperature is preferably 1200 ° C. or higher, more preferably 1300 ° C. or higher, although it depends on the composition of the raw materials. If the temperature is lower than 1200 ° C., the reaction does not proceed efficiently, and unreacted Al ₂ O ₃ may remain.

Examples of cement that can be used in the embodiment of the present invention include various Portland cements such as ordinary, early-strength, ultra-fast-strength, low-heat, and moderate heat, and various types of Portland cement mixed with blast furnace slag, fly ash, or silica. Examples include mixed cement, filler cement mixed with limestone powder and fine slag powder from blast furnace, and Portland cement such as environment-friendly cement (eco-cement) manufactured from urban waste incineration ash and sewage sludge incineration ash. One or more of these can be used.

In one embodiment of the present invention, the cement and the cement admixture described above can be blended to obtain a cement composition.

The amount of the cement admixture used is not particularly limited, but is usually preferably 1 to 30 parts, more preferably 5 to 15 parts out of 100 parts of the cement composition composed of cement and the cement admixture. If the amount of cement admixture used is less than 1 part, sufficient rust prevention effect, chloride ion shielding effect, and Ca ion leaching suppression effect may not be obtained, while if it exceeds 30 parts, rapid hardness may not be obtained. It may occur and sufficient pot life may not be secured.

The amount of water used with respect to the cement composition is preferably a water / cement composition ratio of 0.25 to 0.7, more preferably 0.3 to 0.65. If the amount of water blended is small, the pumping property and workability may be deteriorated, or it may cause shrinkage, etc. On the other hand, if the amount of water blended is excessive, the strength development may be lowered.

In the preparation of the above-mentioned cement admixture and cement composition, each material may be mixed at the time of construction, or a part or all of them may be mixed in advance.

In the cement composition according to the embodiment of the present invention, in addition to cement, cement admixture, fine aggregate such as sand and coarse aggregate such as slag, expansion material, hardened material, water reducing agent, AE water reducing agent. , High-performance water reducing agent, high-performance AE water reducing agent, defoaming agent, thickener, conventional rust preventive, antifreeze, shrinkage reducing agent, coagulation adjuster, clay mineral such as bentonite, anion exchange such as hydrotalcite One or more of the group consisting of admixtures such as body, slag such as blast furnace granulated slag fine powder and blast furnace slow cooling slag fine powder, and limestone fine powder, to the extent that the object of the present invention is not substantially impaired. It can be used together.

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, a Nauta mixer, and the like can be used.

Hereinafter, the contents will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Experimental Example 1)
Reagent 1st grade calcium carbonate and reagent 1st grade aluminum oxide are blended so as to have the molar ratio shown in Table 1 in terms of oxide, and Reagent 1st grade B ₂ O ₃ is shown in Table 1 for the compounding. It was mixed so as to have a content and fired in an electric furnace. A CaO / Al _{2O 3} molar ratio of 0.7 is 1400 ° C, a CaO / Al _{2O 3} molar ratio of 0.6 is 1450 ° C, and a CaO / Al _{2O 3} molar ratio of 0.4 is 1500 ° C. , CaO / Al _{2O 3} molar ratio 0.15 was fired at 1550 ° C. for 3 hours and then slowly cooled to prepare CBA. The brain value was adjusted to 4,000 cm ² / g. For comparison, a sample to which B ₂ O ₃ was not added, a sample to which SiO ₂ was added instead of B ₂ O ₃ , and a sample to which Na ₂ O was added instead of B ₂ O ₃ were also prepared under the same conditions. .. Using X-ray diffraction, the presence or absence of unreacted substances was examined in the prepared sample. The results are shown in Table 1.

(Test method)
X-ray diffraction: When the diffraction peak of the unreacted material (aluminum oxide) was clearly confirmed, it was evaluated as × (poor), when it remained to some extent, it was evaluated as △ (fair), and when it was not confirmed, it was evaluated as ○ (good). ..

From Table 1, it can be seen that by adding an appropriate amount of boron, unreacted aluminum oxide does not remain even at the above firing temperature.

In order to eliminate the diffraction peak of unreacted aluminum oxide in the sample to which boron is not added, the CaO / Al ₂ O ₃ molar ratio of 0.7 is 1500 ° C., and the CaO / Al ₂ O ₃ molar ratio is 0. It is necessary to further bake at 1550 ° C. for No. 6, 1600 ° C. for CaO / Al _{2O 3} molar ratio 0.4, and 1650 ° C. or higher for CaO / Al _{2O 3} molar ratio 0.15. rice field.

FIG. 1 shows an X-ray diffraction spectrum of a sample obtained while changing the blending amount of B ₂ O ₃ with respect to Ca O and Al ₂ O ₃ (denoted as CA ₂ ). The CaO / Al ₂ O ₃ molar ratio in the sample is 0.5, and Al ₂ O ₃ is replaced with Al ₂ O ₃ at a ratio of 0.5, 1.0, and 1.5% by weight in terms of B ₂ O ₃ . Added. The firing conditions were such that the temperature rise rate was 10 ° C./min and the temperature was maintained at 1400 ° C. for 30 minutes. The measurement conditions were Cuα, tube voltage 40 kV, tube current 40 mA, step width 0.02 deg, scanning speed 2.0 deg / min, using a powder X-ray diffractometer (XRD, manufactured by Rigaku, Multiflex type). ..

From the top of FIG. 1, it is a spectrum of a sample in which the blending amount of B ₂ O ₃ is 0%, 0.5%, 1.0%, and 5.0%. From the spectrum near 2θ = 30 °, CaAl ₂ O ₄ was generated as a by-product when B ₂ O ₃ was not added, whereas Ca Al ₂ O ₄ was generated when B ₂ O ₃ was added. It can be seen that the peak of origin has disappeared. It can also be seen that the peak near 2θ = 25.5 ° was slightly shifted to the left as the amount of B ₂ O ₃ added increased, and the by-product of Al ₂ O ₃ (corundum) was also suppressed. From the above, it can be understood that the addition of B ₂ O ₃ makes it possible to obtain only a single phase of CA ₂ .

(Experimental Example 2)
Using the CBA shown in Table 2, 7 parts of CBA in 100 parts of the cement composition consisting of cement and CBA were mixed to prepare a cement composition, and a mortar having a water / cement composition ratio of 0.5 was added to JIS R5201: 2015. It was prepared according to the same procedure. Using this mortar, the rust preventive effect, compressive strength, chloride penetration depth, leaching amount of Ca ions, and sulfate resistance were investigated. The results are shown in Table 2.

(Material used)
CBA-A: Calcium carbonate of the first grade of the reagent and aluminum oxide of the first grade of the reagent are mixed in a predetermined ratio, and B ₂ O ₃ of the first grade of the reagent is mixed so that the B ₂ O ₃ content is 0.2%. In the same manner as in Experimental Example 1, the mixture was fired in an electric furnace at 1550 ° C. for 3 hours and then slowly cooled. CaO / Al _{2O 3} molar ratio 0.1, brain value 4,000 cm ² / g.
CBA-B: Experiment No. 1-3, CaO / Al ₂ O ₃ molar ratio 0.15, B ₂ O ₃ : 0.2%, brain value 4,000 cm ² / g.
CBA-C: Experiment No. 1-9, CaO / Al ₂ O ₃ molar ratio 0.4, B ₂ O ₃ : 0.2%, brain value 4,000 cm ² / g.
CBA-D: Experiment No. 1-15, CaO / Al ₂ O ₃ molar ratio 0.6, B ₂ O ₃ : 0.2%, brain value 4,000 cm ² / g.
CBA-E: Experiment No. 1-21, CaO / Al ₂ O ₃ molar ratio 0.7, B ₂ O ₃ : 0.2%, brain value 4,000 cm ² / g.
CBA-F: Calcium carbonate of the first grade of the reagent and aluminum oxide of the first grade of the reagent are mixed in a predetermined ratio, and B ₂ O ₃ of the first grade of the reagent is mixed so that the B ₂ O ₃ content is 0.2%. In the same manner as in Experimental Example 1, the mixture was fired in an electric furnace at 1400 ° C. for 3 hours and then slowly cooled. CaO / Al _{2O 3} molar ratio 0.9, B ₂ O ₃ : 0.2%, brain value 4,000 cm ² / g.
CBA-G: Experiment No. 1-26, CaO / Al ₂ O ₃ molar ratio 0.4, brain value 4,000 cm ² / g. Does not contain boron.
CBA-H: Experiment No. 1-29, CaO / Al ₂ O ₃ molar ratio 0.4, SiO ₂ : 0.5%, brain value 4,000 cm ² / g.
CBA-I: Experiment No. 1-30, CaO / Al ₂ O ₃ molar ratio 0.4, Na ₂ O: 0.5%, brain value 4,000 cm ² / g.
Cement: Ordinary Portland cement, commercially available fine aggregate: Standard sand water used in JIS R5201: 2015: Tap water

(Evaluation methods)
Anti-corrosion effect: Chloride ions were added to the mortar so as to be 10 kg / m ³ , and a rust-preventive effect was confirmed in an accelerated test in which a reinforcing bar of round steel was added and heated to 50 ° C. Good if no rust occurs on the reinforcing bar at the age of 1 year, acceptable if rust occurs within 1/10 of the area, and not possible if rust occurs over 1/10 of the area. ..
Compressive strength: The compressive strength was measured at 1 day and 28 days of age according to JIS R5201: 2015.
Chloride penetration depth: Evaluate chloride ion penetration resistance. After demolding, a 10 cm φ × 20 cm columnar mortar specimen that had been cured in water at 20 ° C until the age of 28 days was immersed in simulated seawater (salt concentration 3.5%) at 30 ° C for 12 weeks, and then fluoroscein-silver nitrate. The chloride penetration depth was measured by the method. The chloride penetration depth was determined as the portion of the cross section of the mortar specimen that did not change brown, and the average value was calculated by measuring 8 points with a caliper.
Leakage of Ca ions: A mortar specimen (4 x 4 x 16 cm) cured in an environment of 20 ° C. and 60% humidity up to 28 days of age was immersed in 10 liters of pure water for 28 days and dissolved in the liquid phase. The Ca ion concentration was measured.
Sulfate resistance: A mortar specimen (4 x 4 x 16 cm) cured in an environment of 20 ° C. and 60% humidity up to 28 days of age was immersed in a 10% Na ₂ SO ₄ solution for 25 weeks to increase the expansion rate. It was measured.

From Table 2, by containing boron, it is possible to maintain the rust preventive effect and the chloride ion permeation inhibitory effect, suppress the decrease in the initial strength, and further improve the leaching resistance and sulfate resistance of Ca ions. It is understood that it can be improved.

(Experimental Example 3)
Reagent 1st grade calcium carbonate and reagent 1st grade aluminum oxide are mixed so as to have a CaO / Al _{2O 3} molar ratio of 0.4, and reagent 1st grade B ₂ O ₃ is contained so as to have the content shown in Table 3. The same procedure as in Experimental Example 2 was carried out except that CBA prepared by blending and firing in an electric furnace in the same manner as in Experimental Example 1 and then slowly cooling was used. The results are shown in Table 3.

From Table 3, by appropriately containing boron, it is possible to maintain the rust preventive effect and the chloride ion permeation inhibitory effect, suppress the decrease in the initial strength, and further, the leaching resistance of Ca ions and the sulfate resistance. The sex can be improved.

(Experimental Example 4)
The procedure was the same as in Experimental Example 2 except that CBA-D having a powderiness shown in Table 4 was used. The results are shown in Table 4.

(Experimental Example 5)
The same procedure as in Experimental Example 2 was carried out except that CBA-D was used and the amount of CBA used in 100 parts of the cement composition composed of cement and CBA was set to the amount shown in Table 5. For comparison, a test using a conventional rust preventive material was also performed. 10 parts of the rust preventive material was used for every 100 parts of cement. The results are shown in Table 5.

(Material used)
Conventional rust preventive material a: Lithium nitrite, commercial product Conventional rust preventive material b: Nitrite type hydrocarbimite, commercial product

By using the cement admixture of the present invention, excellent rust prevention effect, chloride ion shielding effect, Ca ion leaching suppression effect and sulfate resistance are exhibited, so that it is mainly used in the civil engineering and construction industries. Suitable for a wide range of applications such as marine and river irrigation structures, water tanks, and slab concrete.

Claims (4)

A cement admixture containing calcium boron aluminate having a CaO / Al _{2O 3} molar ratio of 0.15 to 0.7 and a B ₂ O ₃ content of 0.05 to 10% by mass. The cement admixture according to claim 1, wherein the degree of powderiness of calcium boron aluminate is 2,000 to 7,000 cm ² / g in terms of the specific surface area value of the brain. A cement composition containing cement and the cement admixture according to claim 1 or 2. A raw material containing calcia, a raw material containing alumina, and a raw material containing boron so that the CaO / Al _{2O 3} molar ratio is 0.15 to 0.7 and the B ₂ O ₃ content is 0.05 to 10% by mass. And the process of mixing
A step of calcining the mixed raw materials at 1400 ° C. or higher and then pulverizing the mixture so that the specific surface area value of the brain is 2000 to 7000 cm ² / g to obtain calcium boron aluminate.
A method for producing a cement composition, which comprises a step of mixing the obtained calcium boron aluminate with cement.

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