JP2002068800A - Cement admixture and cement composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cement admixture which prevents pop-out phenomenon and shows excellent expansibility and hydration heat inhibition effect, and also to provide a cement composition containing the admixture. SOLUTION: This cement admixture includes an expansion material which includes free lime, calcium ferrite, calcium silicate and gypsum anhydrate and can be obtained by heat treatment of raw materials of CaO, Fe2O3, SiO2 and CaSO4, and dextrin of cold water soluble matter content of 5 to <70%. The dextrin content of the cement admixture is 0.5-15%. The cement composition comprises cement and the cement admixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a cement admixture and a cement composition mainly used in the civil engineering and construction industries.

[0002]

2. Description of the Related Art Cement is an indispensable material for forming civil and architectural structures, and there is no material capable of forming a large structure at a lower cost than cement. However, there is a problem that cracks occur in the cured body using cement. This crack mainly has the following two causes. One is caused by drying shrinkage, and it has been proposed to use a cement admixture that imparts expandability to a concrete structure in order to compensate for the drying shrinkage. Here, the concrete is a general term for cement, mortar and concrete. As a cement admixture that imparts expandability,
A compound containing a CaO-Al ₂ O ₃ -SO ₃ compound as an active ingredient is known (JP-B-42-21840, JP-B-42-19473, JP-B-53-16007, etc.). The second cause of cracking is cracking due to heat of hydration. Cracking due to heat of hydration occurs when the concrete expands unevenly due to the temperature difference between the inside and near the surface of the concrete, and the tensile stress generated near the surface occurs when the tensile strength exceeds the tensile strength of the concrete For,
It is necessary to reduce the heat of hydration.

[0003] In addition, in the raw conplant, the expanding material is put into a bag and mixed with concrete, and in some cases, the expanding material is shipped without being sufficiently kneaded. In such a case, the expansive material is often not uniformly dispersed in the concrete but is agglomerated, and in the hardened concrete, the massive expansive material locally abnormally expands, and the cured body is hardened. A so-called pop-out phenomenon in which the surface bulges, peels, or drops macroscopically may occur. As a method of preventing the pop-out phenomenon, an inactive inorganic powder or the like is mixed in advance with the expanding material, and even if the cement admixture is not sufficiently kneaded, the expanding components do not aggregate and form a lump, A method is conceivable in which a certain degree of dispersion can be expected.However, in this method, by mixing inactive inorganic powder, the expansion component is diluted, and the admixing amount of the cement admixture for imparting the required performance is reduced. The problem that it increases will arise. Recently, the performance required of a cement admixture that imparts expandability has been increasing. In other words, the reality is that the development of a cement admixture capable of imparting excellent expansion performance even at a low admixture rate has been awaited.
Therefore, a method of increasing the amount of cement admixture is not useful because the pop-out phenomenon is prevented. It is necessary to find a method that can prevent the pop-out phenomenon without increasing the amount of the expanding material mixed. In view of such a situation, the present inventors have conducted various studies to solve the above-mentioned problems, and as a result, by blending a specific swelling substance and a dextrin having a cold water-soluble content of less than 5 to 70%, The knowledge that a cement admixture that can solve the problem can be obtained has led to the completion of the present invention.

[0004]

That is, the present invention provides a C
a calcined product obtained by heat-treating aO raw material, Fe ₂ O ₃ raw material, SiO ₂ raw material and CaSO ₄ raw material, and an expanding material containing free lime, calcium ferrite, calcium silicate and anhydrous gypsum; Minutes 5 to 70%
And less than dextrin, wherein the dextrin content in the cement admixture is less than 0.5.
It is a cement admixture characterized by being 15% or less, and is a cement composition containing cement and the cement admixture according to claim 1 or 2.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The expansive substance of the present invention contains free lime, calcium ferrite, calcium silicate and anhydrous gypsum, and its ratio is not particularly limited.
The free lime is preferably 30 to 70 parts, more preferably 40 to 60 parts. Calcium ferrite is 5-22.
5 parts is preferable, and 10 to 15 parts is more preferable. 5 to 22.5 parts of calcium silicate is preferable, and 10 to 1
Five parts are more preferred. Furthermore, anhydrous gypsum is 10-4
0 parts are preferable and 20 to 35 parts are more preferable. If the composition ratio of each compound in the cement admixture is not in the above range, excellent expansion properties may not be obtained. The parts and% used in the present invention represent mass units.

[0007] The calcium ferrite of the present invention is Ca
O—Fe ₂ O ₃ is a general term for compounds and is not particularly limited, but generally, CaO is C, Fe ₂
Assuming that O ₃ is F, compounds such as C ₂ F and CF are well known. In the present invention, since the expansion performance becomes good,
Preferably, C ₂ F is used. The calcium silicate of the present invention is a general term for CaO—SiO ₂ compounds, and is not particularly limited. Generally, when CaO is C and SiO ₂ is S, C ₃ S And C
Compounds such as ₂ S are known.

When producing the cement admixture of the present invention, C
The aO raw material, the Fe ₂ O ₃ raw material, the SiO ₂ raw material, and the CaSO ₄ raw material are heat-treated to synthesize a calcined product composed of free lime, calcium ferrite, calcium silicate and anhydrous gypsum, which is then pulverized to produce. Free lime, calcium ferrite, calcium silicate, and anhydrous gypsum are separately synthesized, and in a mixture of these, storage performance is greatly reduced by storage. Heat-treated CaO raw material, Fe ₂ O ₃ raw material, SiO ₂ raw material and CaSO ₄ raw material to synthesize a calcined product composed of free lime, calcium ferrite, calcium silicate and anhydrous gypsum, and pulverized this to produce As a method of confirming whether or not the particles are present, for example, coarse particles of cement admixture, specifically, particles larger than 100 μm are examined with a microscope (SEM-ED
The composition can be easily discriminated by observing by S) or the like and analyzing the composition to confirm that free lime, calcium ferrite, calcium silicate and anhydrous gypsum are mixed in the particles.

The heat treatment temperature for producing the cement admixture of the present invention is preferably in the range of 1100 to 1600 ° C, more preferably in the range of 1200 to 1500 ° C. 1
If the temperature is lower than 100 ° C., the obtained cement admixture has insufficient expansion performance. If the temperature exceeds 1600 ° C., anhydrous gypsum may be decomposed.

Examples of the CaO raw material include limestone and slaked lime. Examples of the Fe ₂ O ₃ raw material include copper karami and iron powder and commercially available iron oxide. Examples of the SiO ₂ raw material include silica stone and clay. As raw materials for CaSO ₄ , gypsum dihydrate, gypsum hemihydrate, gypsum anhydrous and the like can be mentioned.

Further, impurities are present in the expanding material of the present invention. Specific examples include MgO, TiO ₂ , P
Examples thereof include ₂ O ₅ , Na ₂ O, and K ₂ O, which are not particularly problematic as long as the object of the present invention is not substantially impaired. Among them, SiO ₂ has a silicic acid content of 1%. It is preferably in the range of less than 0. When the silicate ratio is 1.0 or more, excellent expansion performance may not be obtained. The silicic acid ratio referred to in the present invention means the amount of SiO _{2, the} amount of Al ₂ O _{3 and the} amount of F
It is calculated from the following equation from the amount of e ₂ O ₃ . Silicic acid ratio = SiO ₂ / (Al ₂ O ₃ + Fe ₂ O ₃ ) The amount of SiO ₂ in the expanding material is preferably 5.0% or less, more preferably 3.0% or less. If it exceeds 5.0%, excellent expansion performance may not be obtained.

Although the particle size of the expanding material of the present invention is not particularly limited, it is usually 1500 in terms of Blaine specific surface area.
6000 cm ² / g is preferable, and 2500 to 4000
cm ² / g is more preferred. 1500cm is less than ² / g, may strength development is deteriorated, 6000 cm ²
/ G, excellent expansion performance may not be obtained.

The dextrin used in the present invention is generally called modified starch, and is usually obtained by hydrolyzing starch. Above all, acid-roasted dextrin obtained by adding a dilute acid and decomposing is most common, and is obtained by an acid dipping method, maltodextrin obtained by enzymatic decomposition of starch, and British gum obtained by non-roasting Or one or more kinds of pregelatinized starch obtained by heating starch obtained by adding water to a starch, or adding a solution of an alkali or a concentrated salt to rapidly pregelatinize and then dehydrating and drying the pregelatinized starch. Can be used as long as the object of the present invention is not hindered.

In particular, the content of cold water soluble matter at 20 ° C. is 5-7.
It is preferably in the range of less than 0%, and more preferably in the range of 10 to 50% in cold water soluble matter. If the amount of the soluble component in cold water is less than 5% or 70% or more, sufficient effects of suppressing heat of hydration and preventing pop-out may not be obtained. Here, the cold water soluble content of dextrin is
This means the amount of dextrin dissolved in distilled water at a temperature of 21 ° C. Specifically, 10 g of dextrin is placed in a 200 ml flask, and 15 g of distilled water at a temperature of 21 ° C.
After adding 0 ml and keeping the temperature at 21 ± 1 ° C. for 1 hour, the mixture is filtered off, and the filtrate is evaporated to dryness. The dextrin obtained is expressed in terms of the ratio to the test dextrin as the soluble component in cold water. .

An expanding substance in the cement admixture of the present invention;
The blending ratio of dextrin is not particularly limited, but usually, in 100 parts of the cement admixture, the expansive substance is 85%.
It is preferably from 9 to 99.5 parts, more preferably from 90 to 97 parts. If the amount of the expanding substance is less than 85 parts, sufficient expansion performance may not be obtained, and if it exceeds 99.5 parts, a sufficient effect of suppressing the pop-out phenomenon or an effect of suppressing the heat of hydration may not be obtained. is there. Dextrin is preferably 0.5 to 15 parts, more preferably 3 to 10 parts. If the amount is less than 0.5 part, a sufficient effect of preventing pop-out and the effect of suppressing the heat of hydration may not be obtained, and if it exceeds 15 parts, poor curing may occur.

Although the particle size of the cement admixture of the present invention is not particularly limited, it is generally 2% in terms of Blaine specific surface area.
500-6000 cm ² / g is preferable, and 3000-5
000 cm ² / g is more preferred. Is less than 2500 cm ² / g, there is a case where the effect of suppressing sufficient pop-out can not be obtained in some cases expanded performance and excellent more than 6000 cm ² / g is not obtained.

Although the amount of the cement admixture of the present invention is not particularly limited, it is usually 3 to 3 parts per 100 parts of the cement composition comprising the cement and the cement admixture.
12 parts is preferable, and 5 to 9 parts is more preferable. If the amount is less than 3 parts, the effect of the present invention may not be sufficiently obtained.
If it is used beyond the part, the strength expression may be deteriorated.

The cement composition of the present invention refers to JIS R 5210
Various Portland cements specified in JIS R 5211,
JIS R 5212, or various mixed cement specified in JIS R 5213, blast furnace cement produced with an admixture ratio of more than specified in JIS, fly ash cement and silica cement, filler cement mixed with limestone powder, In addition, one or more of alumina cement and the like are used in combination with the cement admixture of the present invention.

In the present invention, in addition to aggregates such as sand and gravel, a water reducing agent, AE
Water reducer, high performance water reducer, high performance AE water reducer, defoamer, thickener, rust preventive, antifreeze, shrinkage reducer, polymer emulsion, setting regulator, cement quick hardener, bentonite, zeolite, etc. One or more of the above-mentioned clay minerals and ion exchangers such as hydrotalcite can be used in a range that does not substantially impair the object of the present invention.

In the present invention, the method of mixing the respective materials is not particularly limited, and the respective materials may be mixed at the time of construction, or some or all may be mixed in advance. . As the mixing device, any existing device can be used. For example, a tilting mixer, an omni mixer, a Henschel mixer, a V-type mixer, a Nauta mixer and the like can be used.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below.

Example 1 CaO raw material, Fe ₂ O ₃ raw material, SiO ₂ raw material and CaSO ₄
The raw materials were blended, mixed and pulverized, and then heat-treated at 1350 ° C. for 2 hours to produce an expanded material having a ratio of each compound in 100 parts of the expanded material as shown in Table 1, and a Blaine specific surface area of 35
Milled to 00 ± 200 cm ² / g. These expanding substances 9
5 parts and 5 parts of dextrin are mixed to form a cement admixture, and 7 parts of the cement admixture is used for 100 parts of the cement composition composed of cement and the cement admixture.
/ Cement composition ratio = 50%, cement composition / sand ratio =
One-third of the mortar was prepared, and the length change rate was measured, and a pop-out test was performed. Table 2 shows the results. As a comparative example, a similar experiment was performed on an expanded material obtained by mixing two types of commercially available expanding materials and those obtained by separately synthesizing free lime, calcium ferrite, calcium silicate, and anhydrous gypsum. In addition, the expanding substance was measured by a powder X-ray diffraction method (X
RD), and confirmed that free lime, C ₂ F, C ₃ S and anhydrous gypsum were the main constituent compounds. The chemical composition was determined by chemical analysis, and the compound composition was calculated by calculation from the result of chemical analysis.

<Materials Used> Cement: Commercial ordinary Portland cement Dextrin: Commercial product, cold water soluble 30% Water: Tap water Sand: ISO679 compliant, standard sand CaO raw material: Reagent 1st grade calcium carbonate Fe ₂ O ₃ raw material: Reagent Primary ferric oxide SiO ₂ raw material: Reagent primary silicon dioxide CaSO ₄ raw material: Reagent primary anhydrous gypsum Free lime: CaO raw material synthesized by firing at 1350 ° C. for 3 hours. C ₂ F: synthesized by mixing 2 mol of CaO raw material and 1 mol of Fe ₂ O ₃ raw material and firing at 1350 ° C. for 3 hours. C ₃ S: 3 mol of CaO raw material and 1 mol of SiO ₂ raw material are mixed and fired at 1600 ° C. for 3 hours to synthesize. Anhydrite: calcined CaSO ₄ raw material at 1350 ° C. for 3 hours for synthesis. Intumescent material a: Commercially available calcium sulfoaluminate-based intumescent material Intumescent material b: Commercially available lime-based intumescent material

<Measurement method> Chemical analysis: Measured according to JIS R 5202. Compound composition: First, the free lime content was measured according to JIS R 5202, and the other compounds were determined by calculation. That is, the amount of C ₂ F is calculated from the amount of Fe ₂ O ₃ ,
The amount of C ₃ S was calculated from the amount of iO ₂ , and then the amount of anhydrous gypsum was calculated from the amount of SO ₃ . Length change rate: Measured according to JIS A 6202. Pop-out test: A mortar was prepared in advance using a material other than the cement admixture, the mortar was put into a tilting mixer, and the cement admixture was added later while agitating the mixer at a speed of 12 revolutions / minute. After a minute, it was discharged and poured into a mold having a length of 50 cm, a width of 30 cm and a height of 6 cm, and a pop-out phenomenon was observed. Temperature of the central part of the mortar: The maximum temperature of the central part of the mortar when the mortar is placed in a styrene foam cylindrical container having a depth of 30 cm, an inner diameter of 13 cm and a thickness of 10 cm and cured in a constant temperature room at 20 ° C. Was measured automatically.

[0025]

[Table 1]

[0026]

[Table 2]

From Tables 1 and 2, it can be seen that the mortar using the cement admixture of the present invention, as compared with the comparative example, exhibited a pop-out phenomenon, and also exhibited excellent expansion performance and an effect of suppressing heat of hydration. I understand.

Example 2 The same procedure as in Example 1 was carried out except that the expanding substance D used in Example 1 was used, and the type and amount of dextrin were changed as shown in Table 3 to obtain a cement admixture. . A similar experiment was performed on a commercially available expandable material that did not contain dextrin. The results are also shown in Table 3.

<Materials used> Dextrin: Commercial product, soluble in cold water 3% Dextrin: Commercial product, soluble in cold water 4% Dextrin: Commercial product, soluble in cold water 5% Dextrin: Commercial product, soluble in cold water 10 % Dextrin: Commercial product, cold water soluble content 30% Dextrin: Commercial product, cold water soluble content 50% Dextrin: Commercial product, cold water soluble content 69% Dextrin: Commercial product, cold water soluble content 70%

[0030]

[Table 3]

From Table 3, it can be seen that the cold water soluble content of the present invention is 5 to 70%.
It can be seen that the mortar using the cement admixture to which less than the dextrin was added exhibited a pop-out phenomenon, and exhibited excellent expansion performance and an effect of suppressing heat of hydration, as compared with the comparative example.

Example 3 The cement admixture consisting of 95 parts of the intumescent substance D and 5 parts of dextrin used in Example 2 was used, and the amount of the cement admixture with respect to 100 parts of the cement composition was changed as shown in Table 4. Except for this, the procedure was the same as in Example 2. The results are also shown in Table 4.

[0033]

[Table 4]

From Table 4, it can be seen that the mortar containing the cement admixture of the present invention prevents the pop-out phenomenon as the amount of the mortar increases, and also has excellent expansion performance and hydration as the amount of the mortar increases. It turns out that it shows the heat suppression effect.

[0035]

By using the cement admixture of the present invention, it is possible to prevent the pop-out phenomenon of concrete, and to show an excellent expansion performance and an effect of suppressing heat of hydration.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Ohashi 2209 Aomi, Aomi-cho, Nishikubiki-gun, Niigata Inside the Aomi Plant of Denki Kagaku Kogyo Co., Ltd. 4G012 MA01 MB12 PB03 PB04 PB11 PB39

Claims (3)

[Claims] 1. A calcined material obtained by heat-treating a CaO raw material, a Fe ₂ O ₃ raw material, a SiO ₂ raw material and a CaSO ₄ raw material, and an expanded material containing free lime, calcium ferrite, calcium silicate and anhydrous gypsum. And a dextrin having a cold water soluble content of 5 to less than 70%. 2. The cement admixture according to claim 1, wherein the dextrin content in the cement admixture is 0.5 to 15%. 3. A cement composition comprising a cement and the cement admixture according to claim 1 or 2.