JP2000327382A - Admixture for cement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an admixture that can maintain the fluidity for a long time, reduces the transportation trouble with reduced slump loss in the pumping and facilitates the cement casting into the framework by pulverizing an organic compound that is insoluble or slightly soluble in water in a specific temperature range and melts at a specific temperature in a specific average particle size and admixing a retardant to the powder. SOLUTION: The organic compound to be employed is insoluble or slightly soluble in water at 4-20 deg.C, melts at 30-100 deg.C and the average particle size is adjusted to 10-500 microns. In an embodiment, this organic compound is selected from the group consisting of wax, fat and oil, fatty acid, fatty acid ester, metallic soap, higher alcohol and thermoplastic resin. In a preferred embodiment, the retardant is selected from fluoride, phosphate, borate, hydroxycarboxylic acid (or its salt), ketocarboxylic acid (or its salt), saccharide or sugar alcohol. According to the slump flow test (JIS A 1101), the value is 18.0 cm, in the case of no addition of the retardant, while 13.0-14.0 cm in the case of 0.5 wt.% based on the cement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an additive for cement capable of imparting high fluidity to concrete and suppressing the occurrence of cracks in concrete due to a rise or fall in temperature due to heat of hydration of cement.

[0002]

2. Description of the Related Art In recent years, the use of concrete classified as mass concrete has increased for large structures such as high-rise buildings and nuclear power plants. In this mass concrete, internal and external restraint stresses act as the temperature rises and falls due to the heat of hydration of the cement, and cracks are likely to occur. Also, the use of concrete classified as high-strength concrete is increasing. In this high-strength concrete, since the water-cement ratio is kept low, the temperature inside the concrete rises and cracks in the concrete are likely to occur due to temperature stress, and the concrete strength expected over a long period of time over time Growth is lost.
Furthermore, it is easy to give a residual strain to a reinforcing bar.

[0003] In order to prevent damage such as cracks due to such causes, a method of suppressing a rise in the temperature of concrete has been adopted. For example, in mass concrete, liquid nitrogen gas or ice chips are mixed to cool the concrete, a retarder such as fluoride or carboxylic acid is added, or hydration reaction is performed by passing cooling water through a pipe embedded in the concrete. Suppression is being done.

Further, in order to facilitate the concrete placing operation, it is common practice to add a chemical substance which imparts fluidity. Examples of such additives include copolymers of polyethylene glycol and maleic anhydride in JP-A-63-285140 and JP-A-2-163108, imidized acrylic polymers in JP-A-9-508612, and No. 6,293,543 discloses that acrylamidoalkylsulfonic acid can be added.

[0005]

In the above-described method of cooling concrete to prevent cracking, it is necessary to install a large-scale device near the site, and it is difficult to cool the poured concrete uniformly. In many cases. For this reason, it has not necessarily reached an effective crack prevention technology.

[0006] In another method of adding a retarder, the hydration reaction of cement is delayed to suppress rapid generation of heat of hydration and prevent a temperature rise. However, since the reaction rate of the hydration reaction is slow, there has been a disadvantage that it takes time for the entire cast concrete to solidify. Therefore, if the amount of the retarder added is reduced to adjust the solidification time, the heat of hydration of the poured concrete will stay in the center of the concrete due to the heat insulation effect of the concrete itself, and the temperature of the concrete will be reduced substantially. In many cases, the rise could not be suppressed.

To remedy the disadvantages of such retarders,
As a method of preventing only the hydration reaction that causes a rapid rise in temperature that causes cracks without significantly suppressing the hydration reaction required for the normal strength development of concrete, a microcapsule contains a retarder The applicants of the present invention have proposed this in Japanese Patent Application Laid-Open No. Hei 10-81552.

[0008]

The cement admixture of the present invention is insoluble or hardly soluble in water at a temperature in the range of 4 to 20 ° C, and has a melting temperature in the range of 30 to 100 ° C.
And a compound in which a retarder is mixed in a powder having an average particle size of 10 to 500 microns. The retarder is selected from at least one of fluoride, phosphate, borate, oxycarboxylic acid or its salt, ketocarboxylic acid or its salt, and sugar or sugar alcohol. The organic compound is selected from at least one of waxes, oils, fatty acids, fatty acid esters, metal soaps, higher alcohols, and thermoplastic resins. More preferably, the organic compound is spherical fine particles having an average particle size of 50 to 300 microns.

The retarder used in the present invention may be any of the various acids or sugars described above, and is not limited to a specific substance. A particularly preferred retarder is an oxycarboxylic acid having a hydroxy group and a carboxylic acid group in the molecule. Specifically, gluconic acid, glucoheptonic acid, arabonic acid,
Compound names such as malic acid and citric acid are disclosed in JP-A-61-40.
854, JP-A-6-263502, JP-A-10-5
No. 3444 and the like. The carboxylic acid groups of these substances form a complex with calcium ions of the cement involved in the hydration reaction, thereby exhibiting a retarding effect.

According to the present invention, the retarder is mixed with a powder of an organic compound having a melting temperature range of 30 ° C. to 100 ° C. The reason why the melting temperature of the organic compound must be 30 ° C. or higher is that when the action of suppressing the hydration reaction by the retarder is not necessary, for example, a large amount of heat is radiated from near the surface of the poured concrete and is caused by heat of hydration If no rapid temperature rise occurs, the organic compound does not melt and is insoluble or hardly soluble in water, so that the retarder is not released to concrete while being fixed. As a result, the concrete solidifies by the usual hydration reaction without being affected by the retarder. Conversely, when the melting temperature is 30 ° C. or lower, the retarder is easily released, and the solidification of the concrete tends to be slow. On the other hand, when the melting temperature is 100 ° C. or higher, even if the temperature of the concrete rises to the boiling point of water due to the hydration reaction, the organic compound does not melt and the retarder remains immobilized, and the effect of suppressing the temperature rise does not work, resulting in a high temperature. This is because water evaporates rapidly from the waste concrete and a normal hydration reaction cannot be expected.

The melting temperature of the present invention includes not only the "melting point" indicating the melting temperature of a crystalline substance but also a substance having no definite melting point, such as a mixture or a thermoplastic resin, which softens from a solid state. It also includes the temperature at which liquefaction occurs.

In the present invention, as a method of mixing a retarder in the powder of an organic compound, the method described in the above-mentioned JP-A-10-815 is used.
The method is not limited to capsule methods such as the interfacial polymerization method, the In-Situ method, the insolubilization reaction method, the coacervation method, the in-liquid drying method, the spray drying method, and the fluidized bed method described in No. 52.
For example, after mixing a retarder with the liquefied organic compound, the organic compound may be cooled and solidified, and then the solidified product may be pulverized to be prepared. Alternatively, a porous solid organic compound may be impregnated with a retarder and then pulverized, or may be prepared by directly impregnating a porous organic compound powder with a retarder. Further, a case where the retarder is adsorbed and fixed on the surface of the powder of the organic compound may be used. In the admixture for cement of the present invention, not only the case where the retarder is present in the organic compound powder but also the case where the retarder is exposed on the surface of the powder may be used.

In other words, "mixing a retarder with the powder of the organic compound" means that the retarder before being added to the cement composition is fixed by the organic compound and the organic compound and the retarder are integrated. State. Then, the powder of the organic compound is melted by the heat of hydration of the cement and changes to a liquid state, and the integrated retarder is released into the cement composition, thereby delaying the hydration reaction. Suppress rapid temperature rise.

Further, the admixture for cement of the present invention has an action of imparting fluidity to the cement composition.
This fluidity is exhibited by either a chemical action due to a functional group of an organic compound which is a component of the admixture for cement, or a physical action based on physical properties of the organic compound. For example, in the chemical action, the functional group of the organic compound is chemically bonded or chemisorbed to the particle surface of the aggregate, which is a cement composition, and the surface activity thereof lowers the viscosity of concrete or reduces the surface tension of water. Or lower it. The physical action includes a case where spherical fine particles of the organic compound act as a solid lubricant between particles such as aggregates and cement to make particles such as aggregates slippery.

In the present invention, the average particle size of the organic compound powder is preferably from 10 to 500 microns. Above 500 microns it is much larger than normal cement particles,
As a result, the concrete strength is reduced. On the other hand, when the thickness is less than 10 microns, the action of the organic compound to fix the retarder in the concrete is weak, and the retarder is easily released into the cement composition without using heat of hydration. A particularly preferred average particle size is 50 to
300 microns. The average particle size in this range is most likely to exert the physical effect of increasing the fluidity of the above-mentioned concrete, and the powder is easily dispersed uniformly in the cement composition, thereby exhibiting a wide range of effects of suppressing the hydration reaction. Because you can.

The organic compound is insoluble or hardly soluble in water in the temperature range of 4 to 20 ° C. and has a melting temperature of 3
It must have physical properties between 0 ° C and 100 ° C.
In the present invention, any organic compound having the above-mentioned physical properties may be used, and the present invention is not limited to a specific compound. Known compounds having such physical properties include waxes, fats and oils, fatty acids, fatty acid esters, metal soaps, higher alcohols, and thermoplastic resins. The wax refers to an ester compound of a fatty acid and a monohydric or dihydric higher alcohol, and the fat / oil refers to an ester compound of a fatty acid and glycerin. In addition, fatty acids refer to carboxylic acids obtained by hydrolysis from fats and oils, fatty acid esters refer to ester compounds of fatty acids and lower alcohols, and metal soaps refer to heavy metal salts of the fatty acids.
The thermoplastic resin generally refers to a linear polymer. The above definitions of these compounds are merely general categories and do not specify the organic compounds of the present invention.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A method for producing an admixture for cement according to the present invention will be described.

Example 1 Water-insoluble synthetic polymer wax having a melting temperature of 40 ° C. to 45 ° C. and a temperature range of 4 ° C. to 20 ° C. (trade name: CX-ST200, manufactured by Nippon Shokubai Co., Ltd.)
Was heated to 70 ° C. and melted, and an oxycarboxylate retarder (trade name: PARIC T, manufactured by Fujisawa Pharmaceutical Co., Ltd.) was mixed therewith in a weight ratio of wax: retarder = 6: 4. To prepare a mixed solution. This mixed solution is sprayed and dried by a spray drier (manufactured by Ohara Kakoki Co., Ltd.) to obtain spherical particles (average particle size of about 250
A cement admixture was prepared in which microparticles of retarders were scattered at about 40% by weight.

Example 2 Water-insoluble carnauba wax having a melting temperature of 72 ° C. to 86 ° C. and a temperature range of 4 ° C. to 20 ° C. was heated to 95 ° C. and melted. (Trade name; PARIC T, manufactured by Fujisawa Pharmaceutical Co., Ltd.) at a weight ratio of carnauba wax: delaying agent = 5: 5 to prepare a mixed solution. After cooling the mixed solution to a solid state, the solid matter was further pulverized with a ball mill to obtain irregular shaped particles of carnauba wax (average particle size of about 3).
(00 micron) of about 50% by weight of fine particles of a retarder was prepared.

EXAMPLE 3 2-Methyloctadecanoic acid, which has a melting point of 55.degree. C. and a temperature in the range of 4.degree.
The mixture is heated to 0 ° C. and melted, and sodium gluconate as a retarder is mixed in a weight ratio of 2-methyloctadecanoic acid: Na gluconate = 4: 6 to prepare a mixed solution. This mixed solution was sprayed and dried with a spray drier (manufactured by Ohara Kakoki Co., Ltd.) to obtain 2-
A cement admixture of the present invention was prepared in which the above-mentioned sodium gluconate fine particles were scattered at about 60% by weight in methyl octadecanoic acid particles (average particle size: about 50 microns).

The cement admixtures of Examples 1, 2, and 3 were evaluated in the following concrete. Cement; Portland cement Coarse aggregate; Mixing two types of crushed stones with different coarse particle ratio Fine aggregate; Sand, fine aggregate ratio 48.2% Water reducing agent; (trade name) Palic K (Fujisawa Pharmaceutical Co., Ltd.);
0.25% by weight (based on cement) Air content; 4.0% water cement ratio; 50% slump; 18.0 cm, measured according to JIS A 1101

Cement, water and a water reducing agent were first kneaded for 3 minutes using a forced kneading mixer at the above mixing ratio, and then the aggregate and the admixture for cement of the example were added and kneaded for 3 minutes. The retarder component is 0.5% by weight based on the cement.
The cement admixtures of the examples were added to concrete in appropriate amounts. The kneaded concrete was subjected to a slump flow test (JIS A 1101), and was poured into a mold having a height of 50 cm, a width of 33 cm, and a thickness of 15 cm, and the change over time in the temperature at the center of the mold was measured. . The mold was covered with a heat insulating material so as not to be affected by the ambient temperature. Further, in order to compare the performance of the admixture for cement, a comparative test was conducted by adding a retarder (trade name) PALICK T to the above-mentioned concrete in a commercially available state without being mixed in an organic compound. .

Table 1 shows the evaluation results.

[0024]

[Table 1]

It can be seen that the admixture for cement of the present invention has a low slump flow of 13.0 to 14.0 cm and imparts fluidity to concrete. In addition, the maximum temperature due to the hydration reaction is about 1 compared to concrete without a retarder.
It can be seen that the temperature is lowered by about 5 ° C., and a rapid temperature rise is suppressed, and the temperature changes slowly. That is, the admixture for cement of the present invention can start the hydration reaction from the early stage of kneading similarly to concrete without a retarder without exhibiting a retarding effect before the temperature rise due to heat of hydration, When the temperature starts to rise and the concrete temperature rises, it suppresses the hydration reaction and acts to slowly raise and lower the temperature.

[0026]

When the admixture for cement according to the present invention is mixed, the concrete is given fluidity and the fluidity is maintained for a long time, so that slump loss in pumping is reduced and transport trouble is reduced. In addition, the work of casting into the formwork can be facilitated.

Further, when the temperature of the concrete rises due to the hydration reaction after casting, the admixture for cement of the present invention changes to a liquid state and releases the retarder into the concrete. Suppress the reaction to prevent rapid temperature rise. Conversely, the temperature rise is unlikely to occur near the surface of the poured concrete due to the heat radiation effect, so the admixture for cement does not dissolve in water and does not melt. The hydration reaction is maintained. As a result, the temperature distribution of the entire cast concrete becomes uniform, and the internal restraint stress resulting from the temperature difference is reduced to prevent cracks.

In addition, as a result of suppressing the temperature rise such that the temperature reaches the temperature required for the normal hydration reaction, the external expansion stress is reduced by suppressing the thermal expansion and rapid temperature drop of the whole concrete, and Prevent cracking.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 24/24 C04B 24/24 Z // C04B 103: 20 (72) Inventor Kazushi Aoki Hama, Hachioji-shi, Tokyo Town 1456, Inc. Three Bond Co., Ltd. (72) Inventor Naohiro Nishiyama 2570-4 Nishimatsu Construction Co., Ltd. (72) Inventor Hirozo Mitsuhashi 3-11-21 Teraoka, Izumi-ku, Sendai, Miyagi F-term (reference) 4G012 MB08 MB42 MC01 MC11 MC12

Claims (4)

[Claims] An insoluble or poorly soluble water in a temperature range of 4 to 20 ° C and a melting temperature range of 30 ° C to
An organic compound having an average particle size of 10 ° C.
An admixture for cement, wherein a retarder is mixed in a powder of up to 500 microns. 2. The method according to claim 1, wherein the retarder is selected from at least one of fluoride, phosphate, borate, oxycarboxylic acid or its salt, ketocarboxylic acid or its salt, and sugar or sugar alcohol. The admixture for cement according to claim 1, characterized in that: 3. The organic compound according to claim 1, wherein the organic compound is a wax, a fat, a fatty acid, a fatty acid ester, a metal soap, a higher alcohol,
The admixture for cement according to claim 1, wherein the admixture is selected from at least one of thermoplastic resins. 4. The admixture for cement according to claim 3, wherein the powder of the organic compound is spherical fine particles having an average particle diameter of 50 to 300 microns.