JP2009078939A - Cement admixture and cement composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cement admixture which can effectively suppress the alkali-silica reaction at a low addition rate and is thereby highly economical and which is also effective to suppress the salt damage. <P>SOLUTION: The cement admixture contains a substance obtained by heat-treating a lithium-containing ABW type zeolite at 300-650°C, wherein the content of lithium is ≥5% expressed in terms of Li<SB>2</SB>O and the total content of Na<SB>2</SB>O and K<SB>2</SB>O is ≤0.5%. The cement composition contains cement and the cement admixture. <P>COPYRIGHT: (C)2009,JPO&INPIT

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. Among them, the “alkali silica reaction” derived from the quality of the aggregate, the so-called “alkali aggregate reaction” is also called cancer of concrete, and no effective suppression method has been found at present.

  As a method of suppressing the “alkali silica reaction”, a method of adding an alkali aggregate reaction inhibitor or a method of impregnating or applying concrete is proposed (Patent Documents 1 to 5).

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

  On the other hand, zeolite is an aluminosilicate-based crystalline compound and is a wide variety. There are various industrial utilization methods of zeolite, and utilization methods such as a catalyst, a humidity control material, a molecular sieve, an adsorbent, and an ion exchanger can be mentioned. Applications differ if the composition and crystal structure of the zeolite are different.

  There is an increasing demand for cement admixtures that impart functionality to mortar and concrete, and there is a demand for the development of cement admixtures that exhibit superior effects with smaller addition amounts. The present inventors have found that a substance obtained by heat-treating a lithium-containing ABW zeolite at a specific temperature is extremely useful as a cement admixture. It is not known at all that a material obtained by heat-treating such lithium-containing ABW-type zeolite is used as a cement admixture.

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

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

That is, the present invention includes (1) a cement admixture containing a substance obtained by heat-treating a lithium-containing ABW-type zeolite at 300 to 650 ° C., and (2) a lithium content in terms of Li ₂ O. (1) the cement admixture of 5% or more, (3) the cement admixture of (1) or (2), wherein the total content of Na ₂ O and K ₂ O is 0.5% or less, (4 ) A cement composition containing cement and the cement admixture of any one of (1) to (3).

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

  In the present invention, “parts” and “%” are based on mass unless otherwise specified.

The lithium-containing ABW zeolite of the present invention will be described.
Lithium-containing ABW-type zeolite was named after first reported by Barrer and White (Barrer RM and White ED, J. Chem. Soc., 1951, 1267). That is, it is often written as A (BW) in the meaning of A of zeolite found by Barrer and White. Here, the meaning of A will be supplemented. A is the first letter of the alphabet, meaning “found first” (respect: nomenclature and structure of zeolite, catalyst, Vol. 40, No. 3, pp. 185-190, 1998). Lithium-containing ABW-type zeolite has about 15 to 25% of crystal water. The SiO ₂ content and the Al ₂ O ₃ content are about 30 ± 5%, respectively.

  As a method for synthesizing a lithium-containing ABW-type zeolite, a method in which allophane is used as a raw material and reacting with lithium hydroxide has been known so far (Yusuke Okono et al. pp. 8-9, 2006).

In the present invention, lithium-containing ABW-type zeolite synthesized by any method can be used. The cement admixture of the present invention can be obtained by heat-treating lithium-containing ABW zeolite.
The heat treatment condition needs to be 300 ° C to 650 ° C. If the heat treatment conditions are not within this temperature range, there may be a case where a sufficient expansion suppressing effect due to alkali silica reaction cannot be obtained 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 produce a lithium-containing ABW type lithium zeolite, a heat treatment at 300 to 650 ° C. may be performed at the stage of the drying operation. After drying once under a condition of less than 300 ° C., heat treatment may be performed again under a condition of 300 to 650 ° C. 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 ABW-type zeolite changes to an amorphous substance may not proceed sufficiently, and even if heat treatment is performed for more than 24 hours, energy costs may be wasted.
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.

When the lithium-containing ABW-type zeolite is heat-treated at 300 to 650 ° C., it changes to 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 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.
The cement admixture of the present invention is an anhydrous ABW zeolite obtained by heat-treating a lithium-containing ABW zeolite at 300 to 650 ° C.

The lithium content of the cement admixture 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. From the theoretical Si / Al molar ratio (= 1) of the zeolite, the lithium content is the maximum amount (13.5%) that can be supported in an amount corresponding to this charge balance. 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 cement admixture 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.

Since the specific surface area of the cement admixture of the present invention depends on the specific surface area of the lithium-containing ABW zeolite before heat treatment, it is not uniquely determined and is not particularly limited. The specific surface area is in the range of 1 to 50 m ² / g.

  Although the usage-amount of the cement admixture of this invention is not specifically limited, Usually, 3-20 parts are preferable in a cement composition which consists of cement and a cement admixture, and 5-15 parts are more preferable. . If the amount is less than 3 parts, the effects of the present invention, that is, the effect of suppressing expansion due to the alkali silica reaction and the effect of suppressing salt damage may not be sufficiently obtained. In addition, strength development may be reduced.

  Cement includes various Portland cements 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 aggregates such as sand, coarse aggregates such as gravel, expanded materials and quick hard materials, water reducing agents, AE water reducing agents, high performance water reducing agents, high performance AE water reducing agents, antifoaming agents, thickening agents , Antirust agent, antifreeze agent, shrinkage reducing agent, polymer emulsion, setting agent, various additives such as clay minerals such as bentonite and anion exchanger such as hydrotalcite, granulated blast furnace slag fine powder and blast furnace slow cooling It is possible to use one or more of the group consisting of slag fine powder, limestone fine powder, admixture materials such as fly ash and silica fume, etc. in a range that does not substantially impair the object of the present invention. .

"Example 1"
The lithium-containing ABW-type zeolite was heat-treated at the temperature shown in Table 1 for 3 hours to obtain a cement admixture. 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.
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.
Commercially available alkaline silica reaction inhibitor (1): Ca-type zeolite Commercially available alkaline silica reaction inhibitor (2): Lithium nitrite aqueous solution (concentration 30%)
Water: tap 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 determined not to be harmless.
Chemical composition: Measured according to JIS R 5201.
Seawater resistance: A mortar specimen for measuring compressive strength was subjected to water curing at 20 ° C. until the age of 28 days, and then the specimen was immersed in simulated seawater for 4 weeks. Seawater resistance was evaluated by measuring the penetration depth of chloride ions. The penetration depth of chloride ions was confirmed by the fluorescein-silver nitrate method.

<Synthesis of lithium-containing ABW-type zeolite>
EDI type zeolite containing lithium 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 was 2.0, the SiO ₂ / Al ₂ O ₃ molar ratio was 1.73, the reaction temperature was 90 ° C., the reaction time was 48 hours, and stirring was performed. The reaction was carried out. 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 diffraction (XRD), it was an ABW type zeolite. Further, the lithium content was 9% Li ₂ O conversion.

<Materials used>
Allophane: those purified elutriation those Tochigi Prefecture, commercially available, SiO ₂ content of 33.6%, _Al 2 _{O 3} content of 33.1%, _Fe 2 _{O 3} content of 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 product, reagent grade 1 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 determined 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. It can also be seen that the penetration of chloride ions is effectively suppressed.

"Example 2"
Example 1 except that a material obtained by heat-treating lithium-containing ABW zeolite at 400 ° C. was used as the cement admixture, and the amount of the cement admixture used in 100 parts of the cement composition was changed as shown in Table 2. As well as. 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. It can also be seen that the penetration of chloride ions is effectively suppressed. And the effect becomes more remarkable when there is much usage-amount of a cement admixture.

  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 (4)

A cement admixture containing a substance obtained by heat-treating lithium-containing ABW-type zeolite at 300 to 650 ° C. The content of lithium, cement admixture according to claim 1 is 5% or more by Li 2 _O conversion. The cement admixture according to claim 1 or 2, wherein the total content of Na ₂ O and K ₂ O is 0.5% or less. The cement composition containing a cement and the cement admixture of any one of Claims 1-3.