JP5345821B2 - Cement admixture and cement composition - Google Patents

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.

  One of the causes of deterioration of concrete structures is salt damage in which reinforcing steel corrosion becomes obvious due to the presence of chloride ions. A method to give chloride ion penetration resistance to concrete structures as a method to suppress the salt damage. There is.

  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, the method of reducing the water / cement ratio has a problem that not only the workability is impaired but also a drastic measure is not taken.

Also, for the purpose of imparting early strength to cement concrete and preventing corrosion of reinforcing bars, it contains CaO.2Al ₂ O ₃ and gypsum as the main component and contains fine powder with a Blaine specific surface area value of 8000 cm ² / g. Chloride ion permeation resistance using a cement admixture containing a calcium aluminate having a CaO / Al ₂ O ₃ molar ratio of 0.3 to 0.7 (see Patent Document 1) A method for improving the performance (see Patent Document 2) has been proposed.

  On the other hand, activated silica such as silica fume and fly ash can improve the penetration resistance of chlorine ions without lowering the initial strength with a relatively small addition amount. One of the common reasons for suppressing the penetration of chloride ions in these admixtures is related to the reduction of calcium hydroxide in the hardened cementitious body, and several dozens that are formed when calcium hydroxide is leached into seawater. It is considered that the generation of voids of μm to several hundred μm is suppressed. However, even when activated silica is used, the pozzolanic reaction takes place over a long period of time. Therefore, when immersed in seawater at a young age, there is a problem that the resistance to penetration of chloride ions decreases and the concrete deteriorates. Therefore, in order to improve durability, that is, seawater resistance, it is necessary to suppress the leaching due to the action of seawater by suppressing the generation of calcium hydroxide in the hardened cement body as much as possible from the initial age.

  On the other hand, a method of adding nitrite or nitrite-type hydrocalumite has also been proposed for the purpose of rust prevention of reinforcing bars (see Patent Documents 3 to 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.

Koichi Kishitani, Noriaki Nishizawa et al., “Durability series of concrete, salt damage (I)”, Gihodo Publishing, pp. 49-54, May 1986 JP 47-035020 A JP 2005-104828 A JP-A-53-003423 Japanese Patent Laid-Open No. 01-103970 Japanese Patent Laid-Open No. 04-154648

  Provides excellent rust prevention effect to the reinforcing steel bars inside the hardened cement concrete, has a shielding effect of chloride ion penetration into the cement concrete hardened body entering from the outside, and leaching of Ca ions from the hardened cement concrete Therefore, the present invention provides a cement admixture and a cement composition that can suppress the formation of pores.

The present invention comprises (1) a calcium aluminate compound having a CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 and a Blaine specific surface area value of 3000 to 7000 cm ² / g, fly ash, silica fume and metakaolin. A cement admixture containing one or more pozzolanic substances selected from the group, wherein the blending ratio of the calcium aluminate compound and the pozzolanic substance is 10/1 to 1/10 by mass ratio ( 2) Cement composition comprising 5 to 30 parts of cement composition comprising 100 parts of cement composition comprising cement and cement admixture of (1), and (3) cement And CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 Blaine specific surface area value of 3000 to 7000 cm ² / g calcium aluminate compound And one or more pozzolanic substances selected from the group consisting of fly ash, silica fume and metakaolin, and the mixing ratio of the calcium aluminate compound and the pozzolanic substance is 10/1 to 1 in mass ratio. / 10 cement composition is a.

  By using the cement admixture and the cement composition of the present invention, it gives an excellent rust prevention effect to the reinforcing steel inside the cement concrete hardened body, and shields the chloride ion penetration into the cement concrete hardened body entering from the outside. Furthermore, since there is little leaching of Ca ions from the cement concrete hardened body, there is an effect that porosity can be suppressed.

The present invention will be described in detail below.
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.

  In civil engineering and architectural uses, there are modes of use that are transported from the ready-mix factory to the construction site and placed in large quantities. In such a form of use, the pot life needs to be equal to or greater than that of cement, the pot life needs to be secured for at least 1 hour, and preferably 3 hours or more. Yes.

The calcium aluminate compound (hereinafter referred to as CA compound) used in the present invention is a mixture of calcia-containing raw material and alumina-containing raw material, and heat treatment such as firing in a kiln or melting in an electric furnace. resulting Te is intended to generically compounds mainly containing CaO and _Al 2 _{O 3,} present invention has a composition, in CaO / _Al 2 _{O 3} molar ratio in the range of 0.15 to 0.7 It is what. Even if the CA compound contains, for example, SiO ₂ or R ₂ O (R is an alkali metal), it can be used as long as the object of the present invention is not impaired.
The CaO / Al ₂ O ₃ molar ratio of the CA compound is 0.15 to 0.7, preferably 0.4 to 0.6. If it is less than 0.15, the chloride ion shielding effect may not be sufficiently obtained. Conversely, if it exceeds 0.7, rapid hardening may appear, and the pot life may not be secured.
Fineness of CA compound, Blaine specific surface area value (hereinafter, referred to as Blaine value) is preferably 2000~7000cm ² / g, the more preferred ^{3000~6000cm 2 / g, 4000~5000cm 2 /} g being most preferred. If the CA compound is coarse, a sufficient chloride ion shielding effect may not be obtained, and if it is a fine powder exceeding 7000 cm ² / g, rapid hardening will appear and the pot life may not be ensured.

In the present invention, a CA compound having a CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 and a pozzolanic substance are used in combination.
The pozzolanic material of the present invention is not particularly limited, and examples thereof include blast furnace slag, fly ash, silica fume, metakaolin, pulp sludge incineration ash, sewage sludge incineration ash, and waste glass powder. Especially, what consists of 1 type (s) or 2 or more types selected from the group which consists of fly ash, a silica fume, and metakaolin is preferable.

  The compounding ratio of the CA compound of the present invention and the pozzolanic substance is preferably 1/10 to 10/1, more preferably 1/5 to 5/1, in terms of mass ratio. When the pozzolanic substance is more than 1/10, the shielding effect of chloride ions entering from the outside may be insufficient or the rust prevention effect may be insufficient, and conversely, the CA is more effective than 10/1. If the compound is excessive, the Ca leaching effect may be insufficient.

  As the cement, various portland cements such as normal, early strength, super early strength, low heat, and moderate heat, various mixed cements in which blast furnace slag, fly ash, or silica is mixed with these portland cements, limestone powder and blast furnace slow Portland cement such as filler cement mixed with cold slag fine powder, etc., and environmentally friendly cement (eco-cement) manufactured using municipal waste incineration ash and sewage sludge incineration ash as raw materials are listed. Or 2 or more types can be used.

  Although the usage-amount of a cement admixture is not specifically limited, Usually, 1-30 parts are preferable in 100 parts of cement compositions which consist of a cement and a cement admixture, and 5-15 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 CA compound, and a pozzolanic substance are blended to obtain a cement composition.

  The water / binder 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, CA compound, and pozzolanic substance.

  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, rapid hardener, water reducing agent, AE water reducing agent, high performance water reducing agent, high performance AE Water reducing agent, antifoaming agent, thickener, conventional rust preventive, antifreeze, shrinkage reducing agent, polymer emulsion, setting modifier, clay minerals such as bentonite, anion exchanger such as hydrotalcite, blast furnace water granulation One or more of the group consisting of slag such as slag fine powder and blast furnace slow-cooled slag fine powder, limestone fine powder and other admixtures are used in a range that does not substantially impair the object of the present invention. Is possible.

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

  Hereinafter, the contents will be described in more detail, but the present invention is not limited to these.

"Experiment 1"
A cement admixture was prepared by mixing the CA compound shown in Table 1 and the pozzolanic material A at a mass ratio of 1/1. Using the prepared cement admixture, a cement composition is prepared by blending 10 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 this mortar, the rust prevention effect, compressive strength, chloride penetration depth, and Ca ion leaching were examined. The results are also shown in Table 1.

<Materials used>
CA compound A: Reagent primary calcium carbonate and reagent primary aluminum oxide were blended at a predetermined ratio, baked at 1650 ° C. in an electric furnace, and then slowly cooled to synthesize. CaO / Al ₂ O ₃ molar ratio 0.1, Blaine value 4000 cm ² / g
CA compound B: synthesized in the same manner as CA compound A, CaO / Al ₂ O ₃ molar ratio 0.15, Blaine value 4000 cm ² / g
CA compound C: Reagent primary calcium carbonate and reagent primary aluminum oxide were blended in a predetermined ratio, baked at 1550 ° C. in an electric furnace, and then slowly cooled to synthesize. CaO / Al ₂ O ₃ molar ratio 0.4, Blaine value 4000 cm ² / g
CA compound D: synthesized in the same manner as CA compound C, CaO / Al ₂ O ₃ molar ratio 0.5, Blaine value 4000 cm ² / g
CA compound E: synthesized in the same manner as CA compound C, CaO / Al ₂ O ₃ molar ratio 0.6, Blaine value 4000 cm ² / g
CA compound F: Reagent grade 1 calcium carbonate and reagent grade 1 aluminum oxide are blended at a predetermined ratio, baked at 1450 ° C. in an electric furnace, and then slowly cooled to synthesize. CaO / Al ₂ O ₃ molar ratio 0.7, Blaine value 4000 cm ² / g
CA compound G: synthesized in the same manner as CA compound F, CaO / Al ₂ O ₃ molar ratio 0.9, Blaine value 4000 cm ² / g
Pozzolanic material A: Silica fume, commercial product, BET specific surface area 15 m ² / g
Cement: Ordinary Portland cement, commercially available fine aggregate: Standard sand water used in JIS R 5201: Tap water

Corrosion protection: as mortar endogenous chloride ions, confirm the anticorrosive effect in accelerated test by the 10 kg / m ³ and comprising as the chloride ion addition, it puts reinforcing steel round bars heated curing in 50 ° C. did. 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: Measure compressive strength at age 28 days according to JIS R 5201.
Chloride penetration depth: Evaluate chloride ion penetration resistance. A 10 cmφ × 20 cm cylindrical mortar specimen showing the shielding effect of chloride ions was produced, and the produced mortar specimen was subjected to water curing at 20 ° C. until the age of 28 days, and a salt concentration of 30 ° C. was 3.5. After immersing for 12 weeks in simulated seawater, which is a 10% salt solution, the chloride penetration depth was measured. 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: Determination was made by immersing a 4 × 4 × 16 cm mortar specimen in 10 liters of pure water for 28 days and measuring the concentration of Ca ions dissolved in the liquid phase.

"Experimental example 2"
It carried out similarly to Experimental example 1 except having used together the CA compound D of the fineness shown in Table 2. The results are also shown in Table 2.

"Experiment 3"
The same procedure as in Experimental Example 1 was conducted except that CA compound D was used and a pozzolanic substance shown in Table 3 was used in combination. The results are also shown in Table 3.

<Materials used>
Pozzolanic material B: Commercially available fly ash, brain value 4000 cm ² / g
Pozzolanic material C: Commercially available metakaolin, BET specific surface area 20 m ² / g
Pozzolanic material D: Commercially available pulp sludge incineration ash, brain value 4000 cm ² / g
Pozzolanic material E: Commercial sewage sludge incineration ash, brain value 9000 cm ² / g
To pozzolanic material: commercially available waste glass powder, brain value 4000 cm ² / g
Pozzolanic substance: a mixture of 50 parts of pozzolanic substance and 50 parts of pozzolanic substance, brain value 20000 cm ² / g

"Experimental example 4"
The same procedure as in Experimental Example 1 was conducted except that CA compound D and pozzolanic substance A were used as an admixture with the formulation shown in Table 4.

“Experimental Example 5”
As shown in Table 5, the same procedure as in Experimental Example 1 was performed except that the cement admixture of Experiment No. 1-5 was used and the amount used was changed. 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

  By using the cement admixture and the cement composition of the present invention, it gives an excellent rust prevention effect to the reinforcing steel inside the cement concrete hardened body, and shields the chloride ion penetration into the cement concrete hardened body entering from the outside. In addition, there is little leaching of Ca ions from the hardened cement and concrete, so that the effect of suppressing porosity can be achieved. Suitable for structures, floor slab concrete, etc.

Claims (3)

One selected from the group consisting of a calcium aluminate compound having a CaO / Al ₂ O ₃ molar ratio of 3000 to 7000 cm ² / g with a Blaine specific surface area value of 0.15 to 0.7, fly ash, silica fume and metakaolin. Or the cement admixture which contains 2 or more types of pozzolanic substances, and the mixture ratio of a calcium aluminate compound and a pozzolanic substance is 10/1-1/10 by mass ratio. A cement composition comprising the cement and the cement admixture according to claim 1, wherein the cement admixture is 5 to 30 parts in 100 parts of the cement composition comprising cement and the cement admixture. 1 selected from the group consisting of cement, CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7 with a Blaine specific surface area value of 3000 to 7000 cm ² / g of calcium aluminate compound, fly ash, silica fume and metakaolin A cement composition comprising a seed or two or more kinds of pozzolanic substances, wherein the mixing ratio of the calcium aluminate compound and the pozzolanic substance is 10/1 to 1/10 by mass ratio.