JP5615661B2 - 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.

  With regard to the durability of mortar and concrete, not only engineers in this field but also the general public has come to receive great attention. There are various causes of deterioration of mortar and concrete. One of them, alkali-silica reaction derived from the quality of aggregate, so-called alkali-aggregate reaction, is also called concrete cancer, and no effective suppression method has been found.

  As a method of suppressing the alkali silica reaction, a method of adding an alkali aggregate reaction inhibitor, a method of impregnating concrete, and a method of applying have been proposed (Patent Documents 1 to 5).

  However, conventional alkali-aggregate reaction inhibitors are not practical and are not practical from the viewpoint of economic efficiency because they are mixed with concrete and used in large amounts.

  In addition, as one of the deterioration factors of concrete structures, there is salt damage in which rebar corrosion becomes obvious due to the presence of chloride ions, and as a method to suppress the salt damage, chloride ion penetration resistance is applied to concrete structures. There is a technique to give.

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 6) A method for improving the performance (see Patent Document 7) 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. 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.

  Furthermore, a method of adding nitrite or nitrite-type hydrocalumite has been proposed for the purpose of rust prevention of reinforcing bars (see Patent Documents 8 to 10). 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.

JP-A-62-278151 Japanese Patent Laid-Open No. 10-167781 JP-A-63-274644 JP 2006-62892 A JP 2006-89334 A 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

Koichi Kishitani, Noriaki Nishizawa et al., “Durability series of concrete, salt damage (I)”, Gihodo Publishing, pp. 49-54, May 1986

  The present invention provides a cement admixture and a cement composition that are highly economical because the alkali silica reaction can be effectively suppressed with a small addition rate, and that are also effective in suppressing salt damage.

The present invention provides: (1) the content of lithium is Li ₂ O in terms of 5% or more Na ₂ O and _{K 2} O content of total EDI type less than 0.5%, ABW type or of lithium zeolite is heat treated, Ri in CaO / _Al 2 _{O 3} molar ratio 0.15 to 0.7 Na contain calcium aluminate compounds of the Blaine specific surface area value 2000~7000cm ² / g, calcium aluminate Cement admixture of 10 to 90 parts of calcium aluminate compound and 10 to 90 parts of lithium zeolite in a total of 100 parts of nate compound and lithium zeolite , (2) Lithium type zeolite heats EDI zeolite at 400 ° C amorphous material obtained by treating, CaO / _Al 2 _{O 3} molar ratio of calcium aluminate compounds is 0.5, (1) Cement admixture, and (3) cement and, (1) or and also contains the cement sum material (2), in total 100 parts of the cement and cement admixture, a cement admixture is 1-15 parts A cement composition.

  The cement admixture and the cement composition of the present invention can effectively suppress the alkali-silica reaction with a small addition rate, and thus are economical and effective in suppressing salt damage.

Hereinafter, the present invention will be described in detail.
In the present invention, “parts” and “%” are based on mass unless otherwise specified.

The lithium type zeolite will be described.
Among lithium-type zeolites, lithium-type zeolite having a Si / Al atomic ratio of 1 is preferable because the effect of suppressing the alkali silica reaction is large. As the lithium type zeolite having a Si / Al atomic ratio of 1, there are EDI type, ABW type and LTA type.
Of these, EDI type and ABW type can be synthesized easily by using allophane or kaolinite as a raw material and allowing an aqueous lithium hydroxide solution to act at less than 100 ° C. On the other hand, synthesis of LTA requires hydrothermal treatment under pressure conditions exceeding 100 ° C., and it is difficult to directly synthesize LTA containing lithium. Lithium is supported by an ion exchange reaction after obtaining a type zeolite by hydrothermal synthesis. For this reason, it is difficult to completely replace sodium with lithium, and LTA may not provide a sufficient alkaline silica reaction suppression effect. Therefore, in the present invention, it is preferable to select the EDI type and the ABW type.

  As a method for synthesizing lithium-type zeolite, a method using silica sol and alumina sol as starting materials (T. Matsumoto et al., Journal of the European Ceramic Society, 26, pp. 455-458, 2006) is known. It has been. In addition, a method of reacting lithium hydroxide with allophane as a raw material is also known (Yusuke Okino et al., Abstracts of the 112th Academic Lecture Meeting of the Society of Inorganic Materials, pp. 8-9, 2006).

In the present invention, lithium-type zeolite synthesized by any method can be used. The lithium-type zeolite of the present invention includes those obtained by heat-treating lithium-type zeolite.
The heat treatment temperature varies depending on the zeolite. For example, in the case of EDI type, it is preferable that it is 200-700 degreeC. When the lithium-containing EDI-type zeolite is heat-treated at 200 to 700 ° C., it changes into an amorphous substance. That is, the crystal structure of the EDI-type zeolite is maintained up to 200 ° C., and the crystal changes from amorphous to 200 ° C. or more. And although it is in an amorphous state up to 700 ° C., when it exceeds 700 ° C., it crystallizes and changes to eucryptite.
In the case of the ABW type, 300 to 650 ° C. is preferable. When the ABW-type zeolite containing lithium is heat-treated at 300 ° C. to 650 ° C., it changes to an anhydrous ABW-type zeolite. That is, the crystal structure of the ABW type zeolite is maintained up to 300 ° C., and when the temperature exceeds 300 ° C., the crystal structure changes to a completely different crystal structure to become an anhydrous ABW type zeolite. And it is in the state of anhydrous ABW type zeolite up to 650 ° C., but when it exceeds 650 ° C., it changes to γ-eucryptite. And when it heats further, it changes to (beta) -eucryptite at 900-1000 degreeC.
If the heat treatment conditions are not within the above temperature range, there may be a case where a sufficient effect of suppressing expansion due to alkali-silica reaction or a salt damage suppressing effect cannot be obtained.

The heat treatment referred to in the present invention is not particularly limited, but usually means a treatment such as drying or baking. As a specific method, for example, after allophane is reacted in an aqueous lithium hydroxide solution to form a lithium-type zeolite, a predetermined heat treatment may be performed at the stage of the drying operation. After drying under the above conditions, heat treatment may be performed again under predetermined conditions. The time for the heat treatment is not particularly limited, but is preferably about 5 minutes to 24 hours, and more preferably 10 minutes to 12 hours. If the reaction time is less than 5 minutes, the reaction in which the EDI-type zeolite changes to an amorphous substance or the reaction in which the ABW-type zeolite changes to anhydrous ABW may not proceed sufficiently. It may become.
The drying device is not particularly limited, and a drum dryer, a shelf dryer, a cylindrical dryer, a rotary kiln, an electric furnace, or the like can be used.

The lithium content of the lithium-type zeolite of the present invention is not particularly limited, but is usually preferably 5% or more and more preferably 7% or more in terms of Li ₂ O. The maximum amount of lithium that can be supported can be calculated as 13.5% from the theoretical value at which the Si / Al molar ratio is 1. If the lithium content is less than 5%, there may be a case where a sufficient effect of suppressing expansion due to alkali silica reaction cannot be obtained.

The content of sodium or potassium in the lithium zeolite of the present invention is not particularly limited, but usually, the total amount of Na ₂ O and K ₂ O is preferably 0.5% or less, 0.3 % Or less is more preferable. When the total amount of Na ₂ O and K ₂ O exceeds 0.5%, there may be a case where a sufficient effect of suppressing expansion due to the alkali-silica reaction cannot be obtained.

The specific surface area of the lithium-type zeolite of the present invention is not uniquely determined and is not particularly limited, but is usually in the range of ² to 200 m ² / g in terms of BET specific surface area.

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. In general, the compounds mainly composed of CaO and Al ₂ O ₃ are obtained, and the CA compound has a CaO / Al ₂ O ₃ molar ratio of 0.15 to 0.7, and 0.4 to 0. .6 is preferred. If the CaO / Al ₂ O ₃ molar ratio is less than 0.15, the chloride ion shielding effect may not be sufficiently obtained. Time may not be secured. 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.

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.

  The blending ratio of the lithium zeolite and the CA compound in the cement admixture is not particularly limited, but usually 10 to 90 parts of the lithium zeolite is preferable in the total 100 parts of the lithium zeolite and the CA compound. ~ 80 parts are more preferred. The CA compound is preferably 10 to 90 parts, more preferably 20 to 80 parts. If the blending ratio of the lithium-type zeolite and the CA compound is not within the above range, there may be a case where a sufficient alkali silica reaction suppressing effect or salt damage suppressing effect cannot be obtained.

  Although the usage-amount of the cement admixture of this invention is not specifically limited, Usually, 1-15 parts are preferable in 100 parts of cement compositions which consist of a cement and a cement admixture, and 3-10 parts are more preferable. . If it is less than 1 part, the effect of the present invention, that is, the effect of suppressing expansion due to the alkali silica reaction or the effect of suppressing salt damage may not be sufficiently obtained, and if it exceeds 15 parts, further enhancement of the effect cannot be expected. In addition, strength development may be reduced.

  Cement includes various types of Portland cement such as normal, early strength, ultra-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 cooling. Portland cement such as filler cement mixed with slag fine powder, etc., and environmentally friendly cement (eco-cement) manufactured using municipal waste incineration ash and sewage sludge incineration ash as raw materials. Two or more types can be used.

  The cement admixture and cement composition of the present invention may be mixed at the time of construction, or may be partially or wholly mixed in advance.

  In the present invention, fine aggregate such as sand, coarse aggregate such as gravel, rapid hardwood, water reducing agent, AE water reducing agent, high performance water reducing agent, high performance AE water reducing agent, antifoaming agent, thickener, rust prevention Additives, anti-freezing agents, shrinkage reducing agents, polymer emulsions, setting modifiers, various additives such as bentonite and other clay minerals and anion exchangers such as hydrotalcite, ground granulated blast furnace slag and ground granulated blast furnace slag It is possible to use together 1 type, or 2 or more types of the group which consists of admixture materials, such as limestone fine powder, fly ash, and silica fume, in the range which does not inhibit the objective of this invention substantially.

"Experiment 1"
Cement admixtures were prepared by blending 50 parts of various lithium zeolites shown in Table 1 and 50 parts of various CA compounds. A cement composition was prepared by blending 7 parts of cement admixture in a total of 100 parts of cement and cement admixture. Further, 225 parts of sand and 50 parts of water were blended to prepare a mortar. Using this mortar, an alkali silica reactivity test was carried out. Moreover, the penetration depth of chloride ions when immersed in simulated seawater and the measurement of bending strength were also performed. Further, as a comparative example, a test was also conducted when the same amount of a commercially available alkali silica reaction inhibitor was used. The results are shown in Table 1.

<Materials used>
Cement: Commercially available ordinary Portland cement sand: Measured according to sanucite pyroxene andesite, JIS A 1145 (chemical method). It is determined that the amount of dissolved silica is 750 mmol / l and the decrease in alkali concentration is 200 mmol / l, which is not harmless.
Lithium type zeolite A: EDI type zeolite containing lithium (Li-EDI), Li ₂ O content 7.1%, BET specific surface area 50 m ² / g.
Lithium type zeolite B: ABW type zeolite containing lithium (Li-ABW), Li ₂ O content 9.0%, BET specific surface area 40 m ² / g.
Lithium-type zeolite C: amorphous material obtained by heat-treating lithium-containing EDI-type zeolite (Li-EDI) at 400 ° C., Li ₂ O content 9.0%, BET specific surface area 30 m ² / g .
Lithium type zeolite D: anhydrous Li-ABW obtained by heat-treating lithium-containing ABW type zeolite (Li-ABW) at 400 ° C., Li ₂ O content 10.8%, BET specific surface area 20 m ² / g.
Commercially available alkaline silica reaction inhibitor (1): Ca-type zeolite Commercially available alkaline silica reaction inhibitor (2): Lithium nitrite aqueous solution (concentration 30%)

CA Compound A: Reagent grade 1 calcium carbonate and reagent grade 1 aluminum oxide are 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, brane value 4000 cm ² / g
CA compound C: Reagent grade 1 calcium carbonate and reagent grade 1 aluminum oxide are blended at 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: 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: synthesized in the same manner as CA compound F, CaO / Al ₂ O ₃ molar ratio 0.9, Blaine value 4000 cm ² / g
Expandable material: expanded material, free lime - calcium silicate (3CaO · SiO ₂₎ - Calcium aluminosilicate ferrite _{(4CaO · Al 2 O 3 ·} Fe 2 O 3) - Calcium aluminate _{(3CaO · Al 2 O 3)} - anhydrous gypsum-based , Free lime content 55%, Calcium silicate content 25%, Calcium aluminoferrite content 5%, Calcium aluminate content 5%, Anhydrous gypsum content 10%, Blaine value 3000 cm ² / g, Commercial water: Water water

<Measurement method>
Alkali-silica reactivity test (mortar bar method): Measured according to JIS A 1146. Those showing an expansion of 0.100% or more are judged not harmless.
Chemical composition: Measured according to JIS R 5201.
Chloride ion penetration depth: After performing water curing at 20 ° C. until the age of 28 days, the specimen was immersed in simulated seawater for 4 weeks, and the chloride ion penetration depth was examined. The penetration depth of chloride ions was confirmed by the silver nitrate-fluorescein method.
Bending strength: measured according to JIS R 5201.

<Synthesis of lithium-type zeolite>
Lithium-type zeolite was synthesized by reacting allophane and lithium hydroxide as raw materials in water. At this time, the Li ₂ O / Al ₂ O ₃ molar ratio is 2.0, the SiO ₂ / Al ₂ O ₃ molar ratio is 1.73, the reaction temperature is 60 or 90 ° C., the reaction time is 24 hours, The reaction was carried out with stirring. The obtained composite was separated into solid and liquid, washed with warm water at 60 ° C., and dried at 70 ° C. Allophane was used in an amount of 10 kg, and lithium hydroxide was dissolved in water. The lithium hydroxide solution was 100 kg. As a result of identifying the synthesized product by powder X-ray diffractometry (XRD), it was an EDI type zeolite when the reaction temperature was 60 ° C. When the reaction temperature was 90 ° C., it was ABW type zeolite.

<Materials used>
Allophane: water-purified product from Tochigi Prefecture, commercial product, SiO ₂ content 33.6%, Al ₂ O ₃ content 33.1%, Fe ₂ O ₃ content 2.3%, CaO content Amount 0.4%, MgO content 0.1%, Na ₂ O content 0.03%, K ₂ O content 0.02%, ignition loss 30.1%
Lithium hydroxide: Commercial water: Tap water

  From Table 1, the expansion rate of the mortar blended with the cement admixture of the present invention is 0.100% or less, all judged to be harmless, and the expansion of the mortar of the comparative example not blended with the cement admixture of the present invention. The rate exceeds 0.100% and is determined not to be harmless. Moreover, it turns out that the mortar which mix | blended the cement admixture of this invention has a small chloride ion penetration depth and high bending strength.

"Experimental example 2"
The same procedure as in Experimental Example 1 was conducted except that lithium type zeolite C and CA compound D were used and the mixing ratio of lithium type zeolite C and CA compound in the cement admixture was changed as shown in Table 2. The results are also shown in Table 2.

  From Table 2, when the cement admixture of this invention is used, the expansion | swelling by alkali silica reaction is suppressed effectively. Moreover, it turns out that the penetration | invasion of a chloride ion is also suppressed effectively.

"Experiment 3"
A cement admixture comprising 50 parts of lithium-type zeolite C and 50 parts of a CA compound was used as the cement admixture, and the amount of cement admixture used in 100 parts of the cement composition was changed as shown in Table 3. The same operation as in Example 1 was performed. The results are also shown in Table 3.

  From Table 3, when the cement admixture of this invention is used, the expansion | swelling by alkali silica reaction is suppressed effectively. Moreover, it turns out that the penetration | invasion of a chloride ion is also suppressed effectively. The effect becomes more remarkable when the amount of cement admixture used is large.

  Since the cement admixture of the present invention can effectively suppress the alkali silica reaction with a small addition rate, it is rich in economic efficiency. Furthermore, it is also effective in suppressing salt damage. Therefore, it can be widely used in the civil engineering and construction fields.

Claims (3)

An EDI type, an ABW type, or a lithium type zeolite that is a heat-treated product thereof, having a lithium content of 5% or more in terms of Li ₂ O and a total content of Na ₂ O and K ₂ O of less than 0.5% ; , CaO / _Al 2 _{O 3} molar ratio 0.15 to 0.7 Ri Na contain calcium aluminate compounds of the Blaine specific surface area value 2000~7000cm ² / g, the sum of calcium aluminate compounds and the lithium-type zeolite 100 Cement admixture which is 10 to 90 parts of calcium aluminate compound and 10 to 90 parts of lithium type zeolite . Lithium-type zeolite is an amorphous substance obtained by heat-treating EDI-type zeolite at 400 ° C., CaO / Al of calcium aluminate compound ₂ O ₃ The cement admixture according to claim 1, wherein the molar ratio is 0.5. A cement composition comprising the cement and the cement admixture according to claim 1 , wherein the cement admixture is 1 to 15 parts in a total of 100 parts of the cement and the cement admixture .