JP2012254896A - Cement admixture, and cement composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cement admixture and a cement composition which impart an excellent antirust effect on an internal reinforcing bar, have an effect of blocking penetration of chloride ions infiltrating from the outside, can suppress porosity formation because of slight eluviation of Ca ions, and further have self-healing ability.SOLUTION: The cement admixture contains a calcium ferroaluminate compound having a CaO/AlOmolar ratio of 0.15-0.7 and an FeOcontent of 0.5-20 mass% and a polysiloxane compound. The calcium ferroaluminate compound preferably has a fineness of 2,000-7,000 cm/g in terms of Blaine specific surface area value. The polysiloxane compound preferably has a 1C-12C hydrophobic alkyl group. The blending ratio between the calcium ferroaluminate compound and the polysiloxane compound is preferably 10/1 to 1/10 in terms of mass ratio. The cement composition contains cement and the cement admixture.

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 required sufficient curing at the beginning in order to inhibit the initial strength development.

  On the other hand, for the purpose of improving the water repellency of the cement composition, it has been conventionally proposed to add a polysiloxane compound (see Patent Document 3). However, these are only intended to improve the water repellency of the cement composition, and are not intended to prevent rusting of the reinforcing bars. Furthermore, when a polysiloxane compound is added to the cement composition, it has a problem of inhibiting hydration and causing a decrease in strength.

  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 used a calcium ferroaluminate compound and a polysiloxane compound having a specific composition to reduce the initial strength as described above, the shielding effect of chloride ions, and the strength of reinforcing bars. The present invention has been completed by solving the problem of corrosion and obtaining the knowledge that a highly durable cement admixture can be obtained.

JP 47-035020 A JP 2005-104828 A JP 55-42272 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, the present invention provides a cement composition that can suppress porosity and further has a self-healing ability to block generated cracks by itself.

The present invention provides (1) a calcium ferroaluminate compound and a polysiloxane 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. Cement admixture to be contained, (2) Cement admixture of (1) having a fineness of calcium ferroaluminate compound of 2,000 to 7,000 cm ² / g in terms of Blaine specific surface area, (3) Polysiloxane compound Is a cement admixture of (1) or (2) having a hydrophobic alkyl group having 1 to 12 carbon atoms, and (4) the mixing ratio of the calcium ferroaluminate compound and the polysiloxane compound is 10 / by mass ratio. A cement admixture according to any one of (1) to (3), which is 1 to 1/10, comprising (5) cement and a cement admixture according to any one of (1) to (4) Composition, (6) cement and, CaO / _Al 2 _{O 3} molar ratio of at Blaine specific surface area value content of 0.5 to 20 mass% of _Fe 2 _{O 3} with 0.15 to 0.7 2,000 A cement composition containing a calcium ferroaluminate compound having a molecular weight of ˜7,000 cm ² / g and a polysiloxane compound.

  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 since there is little leaching of Ca ions from the hardened cement concrete, it can be made porous. It can be suppressed, and has the effect of exhibiting excellent salt blocking properties over 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 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. 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 polysiloxane compound is used in combination with 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%.
The polysiloxane compound of the present invention refers to an organosilicon compound having a siloxane bond in which a polymer is formed by alternately bonding silicon and oxygen. The polysiloxane compound is usually blended into a cement composition for the purpose of water repellency of concrete, but when used in combination with the CFA compound of the present invention, it is preferentially adsorbed to the reinforcing bar and is one of the causes of corrosion of the reinforcing bar. This significantly suppresses the penetration of water. In addition, the polysiloxane compound that could not be adsorbed to the reinforcing bar is adsorbed to the hydrate in the cement and exhibits a water repellent effect. That is, by suppressing the advection of water, it is possible to suppress the penetration of chloride, which is one of the causes of the corrosion of reinforcing bars.
Although it does not specifically limit as a polysiloxane compound of this invention, It has the C1-C12 hydrophobic alkyl, It is characterized by the above-mentioned. Any one having a hydrophobic alkyl group having 1 to 12 carbon atoms may be used, and may be any of linear, branched, and cyclic. Specifically, methyl, ethyl, propyl, butyl, Examples include pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and the like. Of these, hexyl, heptyl, octyl, nonyl, and decyl having 6 to 10 carbon atoms are more preferable. If the carbon number is larger than 12, water repellency may be lowered.
The molecular weight (total number of siloxane units) of the polysiloxane compound of the present invention is preferably 3 to 300, more preferably 3 to 100, and most preferably 3 to 50. When the total number is less than 3, the compound may become unstable, and when it exceeds 300, the increase in viscosity becomes excessive and adversely affects workability.
The polysiloxane compound of the present invention may have a base such as an amino group, an epoxy group, a phenyl group, or an alkoxy group as long as the effects of the present invention are not impaired.
Furthermore, the polysiloxane compound of the present invention uses what is generally called silicone oil having a molecular weight of 2000 or less. Those having a molecular weight of 2000 or more show the properties of rubber and are generally called silicone rubber. Either liquid or powder can be used, but since it can be premixed into cement, an appropriate amount of polyvinyl alcohol (hereinafter referred to as PVA) is mixed as a binder (binding aid) with the polysilane compound, and hot air at 100 ° C to 150 ° C. More preferable are capsules in which PVA obtained by spray drying (spray drying) is used as a protective colloid, and powders mixed with fine powders such as alumina and silica.

  The blending ratio of the CFA compound and the polysiloxane compound 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 polysiloxane compound is more than 1/10, the shielding effect of chloride ions entering from the outside may not be sufficient. Conversely, if the CFA compound is more than 10/1, the rust-preventing effect is obtained. It may be insufficient.

  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 a polysiloxane compound 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, the strength development may be degraded. Here, the binder means the total of cement, CFA compound and polysiloxane compound.

  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 fine aggregates such as cement, cement admixtures, and coarse aggregates such as sand and gravel, etc., expansive materials, rapid hardening materials, water reducing agents, AE water reducing agents, high performance water reducing agents, high performance AEs. 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 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 polysiloxane compounds 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 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, 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 0.2, 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 0.4, 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
Polysiloxane compound A: A polysiloxane compound having a total of 20 siloxanes having a linear hexyl group encapsulated with PVA.
Cement: Ordinary Portland cement, commercially available fine aggregate: Standard sand water used in JIS R 5201: Tap water

(Evaluation method)
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: 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: 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.
Self-healing ability: A 10 × 10 × 40 cm mortar specimen in which 0.15% by mass of 6 mm nylon fiber was mixed was prepared, and a crack having a width of 0.3 mm was 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 is reduced to 0.1 mm or less, and △ indicates that the crack width is reduced to about 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 a polysiloxane compound in combination, it is possible to maintain the rust prevention effect and the chloride ion permeation suppression effect, increase the initial strength, and further, Ca ion leaching resistance, self-healing It turns out that 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 polysiloxane compound 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 It can be seen that can be improved.

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

<Materials used>
Polysiloxane compound A: Polysiloxane compound with a total of 5 siloxanes having linear hexyl groups encapsulated with PVA Polysiloxane compound C: Polysiloxane compound with a total of 30 siloxanes having linear hexyl groups encapsulated with PVA Polysiloxane compound d: Polysiloxane compound with 100 total siloxanes having linear hexyl groups encapsulated with PVA Polysiloxane compound E: Polysiloxane compound with 300 total siloxanes having linear hexyl groups with PVA Encapsulated polysiloxane compound F: Polysiloxane compound with a total of 20 siloxanes having linear methyl groups encapsulated with PVA Polysiloxane compound K: Total number of siloxanes with a linear decyl group Polysiloxane compound encapsulated with PVA polysiloxane compound C: Polysiloxane compound with a total of 20 siloxanes having linear dodecyl groups Polysiloxane compound co: Polysiloxane compound with a total of 20 siloxanes having cyclic hexyl groups Polysiloxane compound encapsulated with PVA Polysiloxane compound S: Polysiloxane compound with a total of 20 siloxanes having branched hexyl groups (iso-hexyl groups) encapsulated with PVA Polysiloxane compound S: Linear hexyl Polysiloxane compounds having 20 siloxane groups having amino groups and amino groups encapsulated by PVA Polysiloxane compounds: Polysiloxane compounds having 20 siloxane groups having linear hexyl groups and alkoxy groups Polysiloxane compound shall encapsulated by VA cell: liquid polysiloxane compound of siloxane total 20 having a linear hexyl

  From Table 3, by preparing the total number of polysiloxanes and the molecular weight of the hydrophobic alkyl group, it is possible to maintain the rust prevention effect and the chloride ion permeation suppression effect, and to suppress the decrease in strength. It can be seen that resistance and self-healing ability can be improved.

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

  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. You can see that

“Experimental Example 5”
The experiment was performed in the same manner as in Experimental Example 1 except that an admixture prepared by mixing CFA compound A and polysiloxane compound 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, It turns out that 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 (6)

A cement admixture containing a calcium ferroaluminate compound and a polysiloxane 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. 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 polysiloxane compound has a hydrophobic alkyl group having 1 to 12 carbon atoms. The cement admixture according to any one of claims 1 to 3, wherein a blending ratio of the calcium ferroaluminate compound and the polysiloxane compound is 10/1 to 1/10 by mass ratio. The cement composition containing a cement and the cement admixture of any one of Claims 1-4. 2,000 to 7,000 cm ² / cm in terms of the specific surface area of cement and a 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 A cement composition comprising a calcium ferroaluminate compound which is g and a polysiloxane compound.