JPH0881252A - Production of highly durable concrete structural material - Google Patents

Abstract

PURPOSE: To obtain a concrete structural material, excellent in weather resistance and having high durability by kneading a cement with an admixture and kneading water comprising an alkaline aqueous solution, forming the kneaded material and then curing the formed material. CONSTITUTION: This method for producing a highly durable structural material is to mix (A) a cement (e.g. ordinary Portland cement) with (B) an admixture and (C) a kneading water comprising an alkaline aqueous solution (e.g. a saturated aqueous solution of calcium hydroxide), then knead and form the resultant mixture and subsequently cure the formed mixture according to a prescribed curing method. An admixture comprising fibers (e.g. hemp pulp), silica, clay, sand and a plasticizer is preferred as the component (B). The amount of the blended kneading water is preferably 20-23wt.% based on the total weight of the components (A) and (B). Thereby, a sufficient amount of the alkali can be supplied into micropores in a hardened cement and rusting of reinforcing bars in the structural material can be delayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a highly durable structural material, and more particularly to a method for producing a highly durable concrete structural material in which the time when rust occurs in the reinforcing bars in concrete is delayed. .

[0002]

2. Description of the Related Art Conventionally, a reinforcing material is often inserted in a concrete structural material in order to reinforce its strength. In such a case, the reinforcing bar rusts and expands, and the expansion pressure causes cracks in the concrete. Or destroyed. Various measures have been taken to prevent such a phenomenon, one of which is a method of applying anticorrosion treatment to the reinforcing bar. For example, coating with anticorrosion liquid such as oil or cement paste, epoxy resin or vinyl resin. The second method is to increase the cover thickness of the hardened cement body to cover the reinforcing bar thickly and keep it away from the exposed surface, and the third method is the inside of the hardened cement body. The method is to block the corrosive substances such as carbon dioxide gas, chlorine ion, sulfur trioxide, water, etc.

[0003]

However, in the first method as described above, the surface coating is not uniformly performed, and there is a great risk of having pinholes, etc. Therefore, if there is a pinhole etc., corrosion is rather accelerated. There is a problem that such a surface coating is not only expensive, but also loses its adhesiveness with the cement hardened body over time and becomes structurally weak. In the second method, the size of the hardened cement is thick and large, so
If it is a wall material, its own weight will increase and it will be uneconomical for the whole building, and if cracks occur in the hardened cement body, the corrosion of the reinforcing bars will start from there and the effect as thickness will be lost. . Furthermore, in the third method, even if the inside of the hardened cement is made dense, if the hardened cement is used, the hydrate is porous, so that it is not so promising.

The inventors of the present invention have made various studies on such problems, and as a result, pay attention to the fact that the reinforcing bar is chemically stable in a certain alkaline region, and the cement hardened concrete is also resistant to alkali. Therefore, it was found that the corrosion of the reinforcing bar can be delayed by coexisting the hardened cement product and the alkaline component, and the present invention has been completed here. Therefore, an object of the present invention is to retain a sufficient amount of an alkaline component in the micropores of a hardened cement product, delay the generation of rust in the reinforcing bar in the structural material, and maintain high durability for a long time. It is to provide a method for manufacturing a concrete structural material.

[0005] Further, the applicant is the Japanese Patent Application No. 6-109175,
Japanese Patent Application No. Hei 6-109176 and "Application of High Durability Concrete Structure Material" filed on the same day as the present application disclose a method for improving durability by using an alkaline aqueous solution, and these methods improve durability. It is a very effective means for improving the quality, but during the manufacturing process, Japanese Patent Application No. 6-109176.
In the No. issue, the step of infiltrating an alkaline aqueous solution into the fine pores of the hardened body, and in the “method for producing a highly durable concrete structural material” filed on the same day as the present application, the step of spraying the alkaline aqueous solution on the uncured molded body There has been a demand for simplification of the process without adding to the process and increasing the number of manufacturing processes.

[0006]

The problems to be solved by the present invention are achieved by the following inventions. (1) In a method for producing a concrete structural material obtained by mixing a predetermined amount of cement, a kneading material, and kneading water, kneading and molding, then using an alkaline aqueous solution for the kneading water. A method for producing a high-durability concrete structural material. (2) In the method for producing a highly durable concrete structural material according to claim 1, the admixture comprises fibers, silica, clay, sand and a plasticizer, and the admixture of the admixture and cement is cement 25 to 25. 60% by weight, fibers 1-10% by weight,
A method for producing a highly durable concrete structural material, which comprises 10 to 50% by weight of silica and 0.1 to 3% by weight of a plasticizer. (3) The method for producing a highly durable concrete structural material according to claim 1 or 2, wherein the component of the alkaline aqueous solution is calcium hydroxide. (4) The compounding amount of the kneading water is 20% by weight to 23% by weight with respect to the weight of the binder in which the cement and the admixture are compounded. For manufacturing a highly durable concrete structural material. (5) The method for producing a highly durable concrete structure material according to any one of claims 1 to 4, wherein the kneading water has a PH of 9 or more. (6) The method for producing a highly durable concrete structural material according to any one of claims 1 to 5, wherein the curing is performed in the air, steam, or autoclave.

The present invention will be described in more detail below. In the method for producing a highly durable concrete structural material of the present invention, a mixture of cement, an admixture and kneading water is kneaded,
This is characterized in that an alkaline aqueous solution is used as kneading water when molding with a molding machine or the like, and since the molded body itself becomes strongly alkaline by this, an alkaline component is retained in the fine pores formed after curing. Because you can
This has an excellent effect of delaying the generation of rust on the reinforcing bars in the structural material and maintaining durability for a long period of time. Further, since an alkaline aqueous solution is used for the kneading water, the alkaline component is excessively deposited because the water content of the alkaline aqueous solution is consumed in the process of hardening the cement of the molded product, and the alkaline component is present in the pores formed when the cement is hardened. Are filled and fixed to densify the hardened body, and the reinforcing bar is chemically stable in the passivation region, so that rust does not occur.

The cement molded product used in the present invention is molded with a low water cement ratio, and the ratio of the binder and water containing the cement and the admixture is 23% or less. The ratio with water is 20% to 23%, preferably 21% to 22%.

The reinforcing bar used in the present invention is used as a reinforcing material, and therefore an inexpensive iron wire is preferable, and the diameter of this iron wire is preferably 0.8 mm to 13 mm.

The alkaline agent used in the present invention includes:
Examples include caustic soda, caustic potash, lime (quick lime or slaked lime), sodium carbonate, sodium bicarbonate, magnesium hydroxide, aluminum hydroxide and the like. Particularly preferable among these is lime, that is, a saturated aqueous solution of calcium hydroxide. The alkaline agent used in the present invention is preferably used in an aqueous solution, but a water-soluble organic solvent such as alcohol, a surfactant or the like may be added to the aqueous solution.

The concentration of the alkaline agent in the kneading water for kneading the binder is 9 or more in PH, preferably 10 or more in PH. Converted to calcium hydroxide concentration, 1.2
It is at least mg / l, preferably at least 5 mg / l. When this concentration is less than 1.2 mg / l, sufficient rust cannot be prevented from being generated, and when it exceeds 16 mg / l, the effect is not changed and it is not economically disadvantageous.
On the contrary, it may cause corrosion, which is not preferable.

The material for forming the hardened cement material or concrete structure used in the present invention is cement,
Materials known in the technical field used for forming mortar or concrete such as aggregates and admixtures are used. As this cement, any one of ordinary Portland cement, Portland cement such as early strength Portland cement and super early strength Portland cement, mixed cement such as blast furnace cement, silica cement, fly ash cement, and alumina cement can be used. . As an admixture, it improves the workability of concrete, facilitates molding, and promotes the development of initial strength. AE agents, high-performance water reducing agents, hardening accelerators, fine powder particles, fibers, silica, sand, At least one or more of clay and plasticizer can be added. The concrete structural material used in the present invention is particularly preferably composed of cement, fibers, silica, and a plasticizer, and clay and sand can be further mixed therein, and the porosity of 10% to 25% and 8M.
It is a concrete structural material having a bending strength of Pa or more.

The fibers used in the present invention include inorganic fibers such as wollastonite and asbestos, natural organic fibers such as pulp and synthetic fibers, and more specifically, the natural organic fibers include NBK pulp and LBK. Pulp, cotton pulp,
Examples include pulp such as hemp pulp, wood flour, sawdust, cork flour, various fibers, and the like, and synthetic fibers include vinyl chloride, nylon, polyamide, polyester, polyurethane, vinylon, polyethylene, aramid fiber, carbon fiber, and the like. . These fibers may be used in any length,
The length is preferably 1 mm to 20 mm, more preferably 2 mm to 10 mm. The fiber diameter is preferably 0.001 mm to 2 mm.

The silica used in the present invention may be of any type or obtained by any manufacturing method, and examples thereof include amorphous silica, silica fume, amorphous silica (amorphous silica) and fly ash. The average particle size of these silicas is 0.1 μm to 10 μm.
It is 0 μm. In the present invention, bending strength can be improved by adding these silicas to the cement component. Further, when sand, clay, etc. are added to the formulation of the cement structure of the present invention, there is an effect of improving the strength and improving the formability during extrusion forming, and improving the surface finish of the product after curing. Examples of such clays include shale clay, kibushi clay, frog eye clay, kaolin and the like, and further examples of sand include river sand, sea sand, sand stone and the like.

The molded product used in the present invention is put in an autoclave chamber and cured at high temperature and high pressure. This high-temperature / high-pressure curing is carried out at a temperature of 150 ° C. to 200 ° C. and a curing time of 2 hours to 10 hours by sending the molded body to the autoclave chamber. At this time, the temperature rising rate is 50 ° C./h to 80 ° C./h
Therefore, the maximum temperature of 170 ° C to 190 ° C is preferable. This regimen can also be repeated as needed. Further, the molded body may be cured in air, and the curing in air is left for 1 to 7 days. Further, the molded body used in the present invention is placed in a curing chamber and steam-cured before being demolded. In this steam curing, high temperature steam is sent to the curing chamber under the atmospheric pressure at a temperature of 40
C. to 85.degree. C., and curing time is 2 hours to 36 hours.
At this time, the rate of temperature rise is 12 ° C / h to 33 ° C / h, and the maximum temperature is preferably 60 ° C to 75 ° C. Further, the pre-positioning time before steam curing is preferably 1 to 12 hours. Further, this curing can be carried out by combining the above-mentioned curing methods as needed. Of these cures, high temperature and high pressure cures are preferred.

[0016]

In the production method of the present invention, an alkaline aqueous solution in which calcium hydroxide is dissolved to adjust the pH to 9 or more is used as the kneading water, and by using this alkaline aqueous solution as the kneading water, the cement and the admixture are mixed with each other. The kneaded material of the binder itself is made alkaline, and when this kneaded material is molded and the cement in the molded body reacts with the water in the alkaline aqueous solution when hydrated (reacts), it is generated by hydration of the cement. In the fine pores formed between the minerals, calcium hydroxide generated when the cement is hydrated, and calcium hydroxide, which is the alkaline component in the alkaline aqueous solution, is filled and densified. Calcium oxide has a pH of about 12.5 and creates an atmosphere that does not rust iron.

[0017]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Example 1 Cement 50% by weight, silica powder (average particle size 10 μm)
30% by weight, fly ash 11.5% by weight, pulp 7
In a binder composed of 1% by weight and 1.5% by weight of methylcellulose, 16 mg of calcium hydroxide was dissolved in 1 liter of water to prepare a kneading water having a pH of 12.5, and the water content ratio of the kneading water and the binder was 21% by weight. After blending so as to obtain a uniform kneaded product. Then, this kneaded product was made to have a diameter of 10
600m width by extrusion with mm rebar
m, a thickness of 25 mm, and a length of 3,000 mm were produced. This cement compact was carried into an autoclave chamber, and the temperature was 179 ° C. (10 kgf / cm ² ), and the curing time was 5
Autoclaved in time.

As a comparative test, a conventional manufacturing method, in which a water content ratio of 21% by weight with respect to the above-mentioned compound was kneaded, molded and then autoclaved under the same conditions as above.

Table 1 shows the results of a bending strength test conducted under the following conditions by manufacturing a test piece of 15 × 70 × 200 mm for strength test during the production of the cement compact.

Test conditions Loading method: Central line bisectoral loading Span 150 mm Loading speed 0.5 mm / min From the cement molded product, as a test sample for exposure test, 4
Cut out 0 × 40 × 160 mm, leave it for a predetermined period outdoors, and split the above-mentioned specimen after the period ends, and
% Phenolphthalein was sprayed, and the degree of discoloration was measured with a caliper. Next, as a salt impregnation test, a salt solution having a salt concentration of 3% by weight was produced, the specimen was immersed, and the specimen was cleaved after a predetermined period of time, and a 0.1% fluorescein sodium aqueous solution and a fracture surface were prepared. A 0.1N silver nitrate solution was sprayed, and the degree of discoloration was measured with a caliper. The above test results are as shown in Table 1.

[0021]

[Table 1] As is clear from Table 1, the concrete structural material obtained by using the saturated aqueous solution of calcium hydroxide of the present invention as the kneading water is compared with the concrete structure material obtained by the method not using the conventional saturated aqueous solution of calcium hydroxide. It can be seen that the strength is not inferior, and the excellent effect of preventing neutralization and chlorine permeability is exhibited. Therefore, it has excellent weather resistance and high durability. Example 2 The cement compact obtained in Example 1 was allowed to stand for 7 days instead of being autoclaved and left to cure in air, and then the same test as in Example 1 was carried out. The results obtained are shown in Table 2.

[0022]

[Table 2] As is clear from Table 2, the concrete structural material obtained by using the saturated aqueous solution of calcium hydroxide of the present invention as the kneading water is compared with that obtained by the conventional method not using the saturated aqueous solution of calcium hydroxide. It can be seen that the strength is not inferior to the strength, and the excellent effect of preventing neutralization and chlorine permeability is exhibited. Therefore, it has excellent weather resistance and high durability. Example 3 The cement compact obtained in Example 1 was carried into a steam curing chamber instead of being autoclaved, and the temperature rising rate was 15 ° C.
/ H to 20 ° C / h, high-temperature steam was sent to the curing chamber, and steam curing was performed under atmospheric pressure at a curing temperature of 60 ° C and a curing time of 4 hours. The same test as in Example 1 was performed, and the obtained results are shown in Table 3.

[0023]

[Table 3] As is clear from Table 3, the concrete structural material obtained by using the saturated aqueous solution of calcium hydroxide of the present invention as the kneading water is compared with that obtained by the conventional method not using the saturated aqueous solution of calcium hydroxide. It can be seen that the strength is not inferior to the strength, and the excellent effect of preventing neutralization and chlorine permeability is exhibited. Therefore, it has excellent weather resistance and high durability.

[0024]

According to the method for producing a concrete structural material of the present invention, by using an alkaline aqueous solution as the kneading water for the binder composed of the cement and the admixture, the molded body itself is made strongly alkaline and the cement is hydrated. In the pores formed at this time, alkali can be deposited and filled in the fine pores. As a result, invasion of carbon dioxide gas, sulfurous acid gas, and the like can be prevented, and therefore, the progress of neutralization can be prevented. It also has excellent salt damage resistance by blocking chlorine ions. Therefore, the concrete structural material obtained by the production method of the present invention has excellent weather resistance and high durability.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hito Yoshimi 1-297 Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Materials Co., Ltd. Cement Research Institute

Claims (6)

[Claims] 1. A method for producing a concrete structural material obtained by mixing a predetermined amount of cement, an admixture, and kneading water, kneading and molding, and then using a predetermined curing method to use an alkaline aqueous solution as the kneading water. A method for producing a highly durable concrete structural material characterized by the above. 2. The method for producing a highly durable concrete structural material according to claim 1, wherein the admixture material is fiber, silica,
It consists of clay, sand and a plasticizer, and the compounding amount of the admixture and cement is 25 to 60% by weight of cement and 1 to 10 of fibers.
Wt%, silica 10-50 wt%, and plasticizer 0.1-
3% by weight of the method for producing a highly durable concrete structural material. 3. The method for producing a highly durable concrete structural material according to claim 1, wherein a component of the alkaline aqueous solution is calcium hydroxide. 4. The compounding amount of the kneading water is 20% by weight to 23% by weight based on the weight of the binder in which the cement and the admixture are mixed, and the blending amount is 20% by weight to 23% by weight. The method for producing a highly durable concrete structural material according to. 5. The method for producing a highly durable concrete structural material according to claim 1, wherein the kneading water has a PH of 9 or more. 6. The method for producing a highly durable concrete structural material according to claim 1, wherein the curing is performed in air, steam, or autoclave. .