JP4347204B2 - Cement admixture and cement composition - Google Patents

Description

  The present invention relates to a cement admixture and a cement composition.

  Concrete is an excellent material that can be used to build large structures at low cost, but has a problem of cracking due to various factors. The concrete referred to in the present invention includes so-called concrete, cement paste, and mortar. One cause of cracking is cracking due to hydration heat generation. When cement is hydrated, heat of hydration is generated, and when it is placed in large quantities, the heat is accumulated inside the concrete and temperature cracks occur. For this reason, in the placement of mass concrete where the maximum dimension is 80 cm or more and the difference between the concrete and the outside air temperature is assumed to be large, it is necessary to select a method for suppressing the hydration calorific value. The method of using low heat Portland cement with a high content of belite with a low hydration calorific value not only reduces the hydration calorific value at the time of curing, but also facilitates securing fluidity during construction, etc. It has excellent properties. However, cement silos possessed by ready-mix plants are frequently used for ordinary Portland cement, blast furnace cement, and early-strength Portland cement, and it is often difficult to secure silos for low heat Portland cement. For this reason, there is a strong demand for an admixture-type hydration heat suppression material that does not require new capital investment such as the addition of silos, and various materials have been proposed (Non-patent Document 1).

  Organic acids that suppress cement hydration are known as cement hydration heat inhibitors (Patent Documents 1 and 2). When an organic acid is used, the effect of suppressing the heat of hydration can be obtained, but the initial strength development may be reduced, and the setting of the cement may be extremely delayed. In order to solve such problems, an admixture based on organic acids and rapid setting alkali metal inorganic salts such as alkali metal carbonates, silicates, aluminates, and hydroxides has been proposed. (Patent Document 3).

  Dextrin is known as a cement heat hydration inhibitor (Patent Documents 4 and 5). Moreover, as a method for suppressing heat of hydration, a low heat generation low drying shrinkage cement composition obtained by adding amorphous calcium aluminate and gypsum to cement, a special cement with adjusted particle size, and the like have been proposed. (Patent Documents 6 and 7).

  Moreover, an alumina cement composition comprising alumina cement, which is a kind of calcium aluminate, and a setting retarder is known (Patent Documents 8 and 9). This is superior in volume stability compared to conventional alumina cement and is characterized by excellent fluidity, strength development, corrosion resistance, and abrasion resistance, but has not been studied as a cement admixture.

JASS5 Concrete Standard Specification JP 50-80315 A U.S. Pat. No. 3,427,175 Japanese Patent Publication No. 07-12963 Japanese Patent Publication No.57-261 Japanese Patent Laid-Open No. 01-242447 JP-A-57-160947 JP-A 64-9836 JP 2000-16843 A Japanese Patent No. 3278524

  The present invention provides a cement admixture that suppresses hydration heat of cement and suppresses cracking of concrete with little delay in setting.

The present invention relates to a cement admixture containing calcium aluminate and a setting retarder, a cement composition using the same, and a method for producing the same.
Unless otherwise specified, parts and percentages in the present invention are shown on a mass basis.

  By using the cement admixture of the present invention, there is an effect of suppressing the hydration exotherm of cement with little occurrence of setting delay.

Hereinafter, the present invention will be described in detail.
Calcium aluminate is a generic term for compounds mainly composed of CaO and Al ₂ O ₃ , and specific examples thereof include, for example, CaO · 2Al ₂ O ₃ , CaO · Al ₂ O ₃ , 12CaO · 7Al. _{2 O 3, 11CaO · 7Al 2} O 3 · CaF 2, and _{3CaO · 3Al 2 O 3 · CaF} 2 etc. the crystalline calcium aluminate and represented, non mainly containing CaO and _Al 2 _{O 3} component A crystalline compound may be mentioned. In the present invention, it is particularly preferable to use calcium aluminate having a CaO / Al ₂ O ₃ molar ratio of 0.3 to 0.9.

Examples of a method for obtaining calcium aluminate include a method in which a CaO raw material and an Al ₂ O ₃ raw material are heat-treated with a rotary kiln or an electric furnace.
1200-2000 degreeC is preferable and the heat processing temperature at the time of manufacturing a calcium aluminate has the more preferable range of 1400-1600 degreeC. When the heat treatment temperature is low, a predetermined compound may not be obtained, and when the heat treatment temperature is high, it may be uneconomical.

Examples of the CaO raw material for producing calcium aluminate include calcium carbonate such as limestone and shells, calcium hydroxide such as slaked lime, and calcium oxide such as quick lime. Examples of the Al ₂ O ₃ raw material include industrial by-products called bauxite and aluminum residual ash. At this time, in addition to CaO and Al ₂ O ₃ as main components, SiO ₂ , Fe ₂ O ₃ , MgO, TiO ₂ , P ₂ O ₅ , Na ₂ O, K ₂ O, fluorine, chlorine, heavy metals, etc. Although impurities may be included, there is no particular problem as long as the object of the present invention is not substantially impaired.

The calcium aluminate preferably has a CaO / Al ₂ O ₃ molar ratio of 0.3 to 0.9, more preferably 0.4 to 0.7. When the CaO / Al ₂ O ₃ molar ratio is decreased, a setting delay may be observed, and when the CaO / Al ₂ O ₃ molar ratio is increased, it becomes difficult to ensure the pot life when mixed with cement or hydration. The heat suppression effect may be impaired.

The vitrification rate of calcium aluminate is not particularly limited, and it can be used in the present invention whether crystalline or amorphous. Among these, the CaO / Al ₂ O ₃ molar ratio may be selected from one type in the range of 0.3 to 0.9, two or more types may be selected, or two or more types may be mixed. It is also possible to use one adjusted within a predetermined range.

The fineness of calcium aluminate is preferably 1500 to 8000 cm ² / g, more preferably 3000 to 6000 cm ² / g, in terms of Blaine specific surface area. In the case of coarse grains having a small Blaine specific surface area value, a sufficient effect of suppressing heat of hydration may not be obtained, and a fine powder having a large Blaine specific surface area value may not be able to ensure a sufficient pot life.

  A setting retarder is a general term for ingredients that delay the hydration of Portland cement. Inorganic systems include fluoride, phosphate, borate, sulfate, etc., and organic systems include oxycarboxylates and ketocarboxylates. Organic acids such as saccharides, alcohols and the like are known. In the present invention, it is preferable to use sulfate, organic acid, or saccharide.

  The organic acid is not particularly limited, and examples thereof include carboxylic acid, oxymonocarboxylic acid, oxypolycarboxylic acid, polycarboxylic acid, and salts thereof. Specific examples of carboxylic acids include formic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, heptanoic acid, heptonic acid, gluconic acid, glycolic acid, malic acid, tartaric acid, citric acid Acrylic acid, maleic anhydride and the like. Examples of these salts include alkali metal salts, alkaline earth metal salts, and salts of zinc, copper, aluminum, ammonium, and the like. In the present invention, one or more of these can be used. Although the usage-amount of an organic acid is not specifically limited, Usually, 1-20 parts are preferable in 100 parts of cement admixtures containing a calcium aluminate and an organic acid, and 5-10 parts are more preferable. When the amount of the organic acid used is small, it may be insufficient to ensure the pot life, and when a large amount of the organic acid is blended, there is a possibility that the setting of strength may be impaired due to a delay in setting.

  Dextrin is generally called modified starch and is usually obtained by hydrolyzing starch. Of these, acid roasted dextrin obtained by decomposition by adding an acid is most common. What is obtained by acid soaking, what is obtained by enzymatic digestion of starch, British gum obtained without roasting, or starch added with water, or by adding alkali or concentrated salt solution to alpha It is possible to use one type or two or more types of pregelatinized starch obtained by rapid dehydration and drying of the product as long as the object of the present invention is not impaired. Particularly, the dextrin having a cold water soluble content at 20 ° C. of 5 to 90% is preferable, and 10 to 65% is more preferable. When the cold water soluble content of dextrin at 20 ° C. becomes small, a sufficient hydration heat-inhibiting effect may not be obtained, and when the dextrin cold water soluble content at 20 ° C. becomes large, the setting delay may be caused. Although the usage-amount of dextrin is not specifically limited, Usually, 1-20 parts are preferable in 100 parts of cement admixtures containing calcium aluminate and dextrin, and 5-10 parts are more preferable. If the amount of dextrin used is small, a sufficient hydration heat suppression effect may not be obtained, and if a large amount of dextrin is blended, there is a risk of causing a setting delay.

  Examples of the sulfate include sodium sulfate, potassium sulfate, aluminum sulfate, potassium alum, and calcium sulfate. As calcium sulfate, any of dihydrate gypsum, half-water gypsum, and anhydrous gypsum can be used, but anhydrous gypsum, particularly II type anhydrous gypsum, is more preferable from the viewpoint of securing the pot life and strength development. Although the usage-amount of a sulfate is not specifically limited, Usually, 50 parts or less are preferable in 100 parts of cement admixtures containing a calcium aluminate and a sulfate, and 10-40 parts are more preferable. If the amount of sulfate used is small, it may be insufficient to ensure the pot life, and if a large amount of sulfate is added, it may swell for a long time to cause cracks and reduce strength.

  Cement can be used for ordinary, early strength, ultra-early strength, low heat, moderate heat Portland cement, blast furnace granulated slag, fly ash, various mixed cements mixed with siliceous materials, blast furnace chilled slag, Examples include filler cement mixed with fine limestone powder and Portland cement such as environmentally friendly cement (eco-cement) manufactured from municipal waste incineration ash and sewage sludge incineration ash, one or two of these The above can be used.

  The amount of the cement admixture used in the present invention is not particularly limited, but is usually preferably 1 to 20 parts, more preferably 3 to 10 parts in 100 parts of a cement composition composed of cement and cement admixture. preferable. If the amount of cement admixture used is small, a sufficient hydration heat suppression effect may not be obtained, and if a large amount of cement admixture is used, strength development may be reduced.

In the present invention, in addition to cement admixtures, aggregates such as sand and gravel, water reducing agents, thickeners, reinforcing fibers, expansion materials, rust inhibitors, antifreeze agents, clay minerals, zeolites, hydrotalcite, hydrokarma It is possible to use one or two or more of ion exchangers such as yttrium, polymer emulsion, powder polymer and the like within a range not impairing the object of the present invention.
Hereinafter, the present invention will be described in more detail based on examples.

A calcined raw material and an alumina raw material were mixed, and a melt melted at 1600 ° C. using an electric furnace was blown off with compressed air and cooled to synthesize a clinker having a CaO / Al ₂ O ₃ molar ratio shown in Table 1. These clinker were pulverized and adjusted to a brain specific surface area value of 4000 ± 200 cm ² / g to obtain a sample (hereinafter abbreviated as CA). A cement admixture was prepared by blending 10 parts of dextrin as a setting retarder with 100 parts of these CAs. Unit cement content 315 kg / ^{m 3,} unit water ^{170kg / m 3, s / a} = 48% and the concrete (fine aggregate ratio in the aggregate) as a basic formulation, in total 100 parts of the cement and cement admixture, 5 parts of cement admixture was mixed and the concrete was kneaded, and the curing time, compressive strength, and simple heat insulation temperature rise were measured. The results are shown in Table 1.

<Materials used>
Calcia Source: Quicklime, Commercial Alumina Source: Bauxite, Commercial Cement: Blast Furnace Cement Class B, Commercial Fine Aggregate: Himekawa Natural Sand Rough Aggregate: Himekawa Crushed Water: Tap Water Condensation Retardant: Oji Cornstarch Dextrin

<Measurement method>
Curing time: The time when the concrete temperature kneaded and rose 5 ° C from the temperature.
Compressive strength: Conforms to JIS R 5201.
Temperature rise: Concrete was packed in a cylindrical foamed polystyrene container having a diameter of 15 cm, a height of 30 cm, and a thickness of 5 cm and sealed, and then the temperature at the center of the concrete was measured. The difference between the maximum temperature and the kneading temperature was defined as the temperature rise.

As shown in Table 1, the combined use of calcium aluminate and dextrin having a CaO / Al ₂ O ₃ molar ratio of 0.5 to 0.7 suppresses the temperature rise of concrete as compared to the case where no admixture is added. Can do. In addition, when only dextrin is used, the setting of the concrete is significantly delayed, whereas the setting time can be controlled by the CaO / Al ₂ O ₃ molar ratio of calcium aluminate. In addition, when the CaO / Al ₂ O ₃ molar ratio is close to 1, such as alumina cement, a phenomenon in which the setting time is shortened is recognized.

The CaO / Al ₂ O ₃ molar ratio of CA used is fixed to 0.5 and the Blaine specific surface area value is 4000 ± 200 cm ² / g, and the type and amount of setting retarder used are changed as shown in Table 2. Except that, the same procedure as in Example 1 was performed. The results are shown in Table 2.

When changing the type of setting retarder, it is necessary to adjust the addition rate according to the type, but the temperature rise of the concrete is suppressed by combining with calcium aluminate with the optimal CaO / Al ₂ O ₃ molar ratio. In addition, it is possible to ensure an appropriate setting time.

Prepare a cement admixture in which CaO / Al ₂ O ₃ molar ratio of CA used is 0.5, Blaine specific surface area value is 4000 ± 200 cm ² / g, and 10 parts of dextrin is blended as a setting retarder for these 100 parts. did. The same procedure as in Example 1 was performed except that the blending amount of the cement admixture in 100 parts of the cement and the cement admixture was changed as shown in Table 3. The results are shown in Table 3.

  Increasing the substitution rate of the admixture tends to decrease the compressive strength of the concrete, but the effect of suppressing the temperature rise becomes more remarkable.

The same procedure as in Example 3 was performed except that the Blaine specific surface area value of CA used was changed as shown in Table 4. The results are shown in Table 4.

  It can be seen that by increasing the fineness of calcium aluminate, the setting time tends to be shortened, but the effect of suppressing the temperature rise of concrete can be obtained.

By using the cement admixture of the present invention, it is possible to efficiently suppress the hydration heat of the cement without causing a delay in setting of the concrete and to suppress cracking of the concrete. This technique is effective mainly when building large concrete structures.

Claims (3)

Calcium aluminate having a CaO / Al ₂ O ₃ molar ratio of 0.5 to 0.7 and a Blaine specific surface area of 3000 to 6000 cm ² / g, and any one of an organic acid or a dextrin as a setting retarder, or A cement admixture comprising two kinds , wherein the setting retarder is 5 to 10 parts in 100 parts of the cement admixture. A cement composition comprising the cement and the cement admixture according to claim 1. The cement composition according to claim 2, wherein the cement admixture is 3 to 5 parts in 100 parts of the cement composition.