JPH0611674B2 - How to prevent deterioration of hardened concrete - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of preventing deterioration of hardened concrete due to an aggregate that causes a salt content and / or an alkaline aggregate reaction to be contained. More specifically, deterioration of hardened concrete is prevented by preventing corrosion of steel in concrete containing salt and by suppressing the same reaction in concrete containing aggregate that causes alkaline aggregate reaction. Regarding how to prevent.

[Conventional technology]

It is well known that hardened materials such as cement, mortar and concrete gradually deteriorate from the surface in a natural environment. In particular, in the case of a cement-based material such as reinforced concrete in which a corrosive metal material is embedded, if the above-mentioned deterioration progresses, rust occurs in the metal material inside and cracks occur in the concrete. In addition, in the concrete in which the aggregate that causes the alkali-aggregate reaction is mixed, as the alkali-aggregate reaction proceeds, the aggregate that is the composition of the concrete expands, and the concrete also cracks.

As a method for preventing the deterioration of the cement-based material as described above and repairing the deteriorated cement-based material, JP-A-1-10
Japanese Patent No. 3970 describes a method of coating a surface of a hardened concrete with a cement composition containing 0.1 to 25% of lithium nitrite with respect to the weight of the cement. According to this method, from the composition coated on the surface layer of hardened concrete, lithium nitrite gradually penetrates deeply into the interior of the hardened concrete for a long time to prevent corrosion of the steel material embedded in the concrete. At the same time, the alkaline aggregate reaction is suppressed. At the same time, the cement space or the mortar suppresses backfilling of the defective portion and deterioration from the surface.

[Problems to be Solved by the Invention]

The method of coating the surface of the hardened concrete with a cement composition containing the above lithium nitrite shows an excellent deterioration preventing function as described above, but when the coating layer absorbs water from the outside and water enters the inside, the steel material Since it has the effect of promoting the corrosion and the reaction of alkali-aggregate, there is a problem that the above-mentioned deterioration prevention property is not fully utilized. Further, since some lithium nitrite is dissolved in rainwater and flows out, it is difficult to say that the deterioration preventing effect lasts for a long time.

The object of the present invention is to prevent the water absorption of hardened concrete, enhance the effect of preventing deterioration of hardened concrete due to corrosion of steel and alkali-aggregate reaction, and keep the effect for a long time, and a cement-based coating with high strength. It is to provide a method for preventing deterioration of hardened concrete capable of forming a layer.

[Means for Solving the Problems] The above-mentioned object is to make the surface of hardened concrete containing an aggregate causing a salt content and / or an alkali aggregate reaction into a cement (based on a dry weight) 1% of lithium nitrite.
~ 25% by weight, 0.1-15% by weight polypropylene blended cement paste, mortar or concrete,
Or 1 to 25% by weight of lithium nitrite, 0.1 to 5% by weight of polypropylene, and 0.5 to 10% by weight of asphalt.
It is achieved by coating with a cement paste, mortar or concrete formulated.

Alternatively, a composition containing lithium nitrite, polypropylene and optionally asphalt in the above proportions is blended into an uncured concrete composition in an amount of 0.05-8 wt% based on the weight of cement in the concrete, This is accomplished by hardening the concrete.

Furthermore, as another alternative, the surface of the hardened concrete is
A coating consisting of an aqueous dispersion containing 1 to 25% by weight lithium nitrite, 0.1 to 12% by weight polypropylene, 1 to 25% by weight asphalt and 1 to 25% by weight acrylic resin, based on the weight of the coating composition. It is achieved by coating with a composition for use.

In the present invention, the hardened concrete to which the coating composition is applied may be either before the deterioration has progressed or already deteriorated. In particular, concrete such as reinforced concrete and steel frame concrete in which a steel material or other corrosive metal material is embedded, or concrete in which an aggregate that causes an alkaline aggregate reaction is mixed is a preferable example.

The coating composition such as cement paste, mortar and concrete used in the present invention is a mixture of cement, fine aggregate and coarse aggregate in an aqueous solution of lithium nitrite, an aqueous dispersion of polypropylene, and further asphalt if desired. Then, it can be easily prepared by adding a necessary amount of water.

The compounding amount of lithium nitrite is 1 to 25% by weight based on the dry weight of cement in the coating composition comprising cement paste, mortar or concrete. If the amount of lithium nitrite added exceeds 25% by weight with respect to the cement, problems in construction work such as prolongation of setting time will occur, and if it is less than 1% by weight, the effect will be poor and the object will not be achieved.

By coating cement paste, mortar, and concrete containing lithium nitrite on the surface of hardened concrete, lithium nitrite gradually migrates from the surface coating layer into the base concrete over a long period of time, and lithium nitrite An impregnation layer is formed. Most conventional surface treatment agents for concrete have been applied by spraying, roller brushing, etc. However, since the treatment liquid is only given temporarily, it is impossible to impregnate the hardened concrete with a sufficient amount. There is also a method in which a treatment liquid is impregnated into a sheet or the like and applied to the concrete surface, but it must be removed in a short time and long-term impregnation cannot be expected. As described in JP-A-1-103970, when cement paste, mortar, or concrete itself which is a base conditioning material contains lithium nitrite which is a treatment liquid, it cures lithium nitrite for a relatively long time. However, some lithium nitrite dissolves in rainwater and flows out, so a sufficient sustaining effect is not achieved.

According to the present invention, when the base conditioning material mixed with polypropylene together with lithium nitrite is used, the elution of lithium nitrite is prevented and the lithium nitrite permeates into the concrete for a long period of time. Nitrite ions impregnated in concrete act to prevent corrosion of steel in concrete, and lithium prevents alkali-aggregate reaction.

The polypropylene compounded with the lithium nitrite may be either crystalline polypropylene or atactic polypropylene. From the viewpoint of adhesive strength, mechanical strength and water resistance of the coating layer formed from the coating composition, polypropylene having a weight average molecular weight of about 3000 or more is preferable.

The blending amount of polypropylene is 0.1 to 15% by weight based on the dry weight of cement in the coating composition made of cement paste, mortar or concrete. When asphalt is blended in the coating composition, the blending amount of polypropylene is 0.1 to 5% by weight. If the content of polypropylene is less than 0.1% by weight, a sufficient waterproof effect cannot be obtained, and if it is too large, the mechanical strength of the coating layer decreases.
The preferred blending amount of polypropylene is 5 to 10% by weight, and when asphalt is used in combination, it is 1 to 3% by weight.

The asphalt may be either natural or petroleum algalt, generally those that melt at about 60 ° C to about 160 ° C are used. The asphalt content is 0.5 to 10 based on the dry weight of cement in the coating composition consisting of cement paste, mortar or concrete.
% By weight. Too much asphalt impairs the stability of the aqueous dispersion containing polypropylene and lithium nitrite and reduces the adhesion of the coating formed from the coating composition.

Cement paste used in the present invention, a coating composition based on mortar or concrete is a mixture of cement, fine aggregate, coarse aggregate lithium nitrite, polypropylene, if necessary asphalt, and water. It can be easily prepared by blending. As a preferable preparation method, polypropylene is kneaded with a small amount of water while applying a shearing force, and necessary hot-melt asphalt and water are added thereto. Lithium nitrite may be added as an aqueous solution. In order to coat the surface of the hardened concrete, the usual methods such as ironing, spraying, and placing with a mold applied are adopted.

Various additives can be added to the coating composition as long as the object of the invention is not impaired. Examples of the additives include polyvinyl alcohol that enhances the dispersibility of polypropylene; additives that improve workability such as water-reducing agents and sizing agents; and nitrite for promoting curing and imparting nitrite ions to higher concentrations. Examples include calcium nitrate.

As the coating composition applied to the surface of the hardened concrete, based on the total weight of the coating, 1 to 25% by weight of lithium nitrite, 0.5 to 10% by weight of asphalt, and polypropylene.
It is also possible to use a coating consisting of an aqueous dispersion containing 0.1 to 5% by weight and an acrylic resin of 1 to 25% by weight.

Examples of the acrylic resin include a polymer of a lower alkyl ester of methacrylic acid having a lower alkyl group and a lower alkyl ester of acrylic acid and a copolymer containing them as a main component, and specific examples thereof include polymethyl methacrylate, Polyethyl acrylate, copolymer of methyl methacrylate and ethyl acrylate, copolymer of methyl methacrylate and butyl acrylate, copolymer of methyl methacrylate and butyl methacrylate, butyl acrylate and styrene And a copolymer of butyl acrylate and ethylene. The amount of the acrylic resin compounded is 1 to 25% by weight (based on the total weight of the coating) in view of the strength and water resistance of the coating film.

The coating material containing the acrylic resin can be prepared by kneading polypropylene and the acrylic resin under shearing force, mixing a small amount of water, and further adding asphalt and water which are heated and melted. Lithium nitrite may be added as an aqueous solution.

Further, lithium nitrite, polypropylene and, if necessary, further asphalt are (1-25) / (1-15) / (0.5-1) into the uncured concrete composition.
0 to 8% by weight of the composition for preventing deterioration, which is included in a weight ratio of
It is also possible to mix (the ratio of the solid content of the composition for preventing deterioration based on the weight of cement in the concrete) and then cure the concrete according to a conventional method. In order to obtain sufficient water resistance, water permeation prevention and strength imparting, it is preferable to prepare an aqueous dispersion containing these compounding ingredients and then mix it into the uncured concrete composition.

〔Example〕

Example 1 and Comparative Example 1 100 parts by weight of Portland cement No. 5 silica sand 100 〃 lithium nitrite 10 〃 polypropylene 10 〃 A water / cement weight ratio of 0.65 was prepared as a mortar. This mortar (area of postcard size) ×
A rectangular parallelepiped sample obtained by placing it in a mold (thickness 3 cm) and curing it in a room at 20 ° C. for 14 days was measured for water absorption and water permeability according to JIS A1404.

Further, the above mortar was coated on the surface of the hardened concrete, and the adhesion strength of the mortar layer to the hardened concrete was measured as follows.

In other words, the hardened concrete was applied to a thickness of about 15 mm, and after hardening, a steel block having an area of 4 cm × 4 cm was adhered to the surface thereof with an epoxy resin adhesive. Then, a block sample consisting of a steel block / mortar layer / hardened concrete having a size whose cross section corresponds to the steel block area (4 cm × 4 cm) was cut out. Using the Kenken tensile tester, pull the block sample in the direction perpendicular to the adhesive interface,
The strength at break of the adhesive interface between the mortar layer and the steel block was measured.

For comparison, in the above-mentioned mortar composition, polypropylene in which styrene-butadiene-rubber (SBR) was replaced by an equal amount (as solid content) was used, and water absorption rate, water permeability and adhesion strength were measured in the same manner as above. The measurement was performed.

Table 1 shows the results of measuring the water absorption rate, the water permeability and the adhesion strength of the three samples.

Example 2 and Comparative Example 2 About 320 parts by weight of Portland cement Sand 950 〃 Gravel 1050 〃 Lithium nitrite 6 〃 Asphalt 6 〃 Polypropylene 1 〃 Water 190 〃 Standard curing in water at 20 ° C for 28 days The adhesive strength, water absorption and water permeability were measured in the same manner as in Example 1.

For comparison, the composition of 6 parts by weight of asphalt and 1 part of polypropylene in the above composition was not used, and 6 parts by weight (solid content) of styrene-butadiene-rubber (SBR) was used instead of them. Then, the test was conducted. The results are shown in Table 2.

Example 3 Lithium nitrite 100 parts by weight Asphalt 100〃 Polypropylene 10〃 Polymethylmethacrylate 100〃 Crylate resin An aqueous dispersion having the above composition and a solid content of 65% was prepared as follows.

Knead polypropylene at 90 ℃ with a small amount of polyvinyl alcohol and water for 20 minutes at 90 ℃, then at 50 ℃
In, a large amount of water was added, and then asphalt at about 150 ° C. was gradually added to obtain a polypropylene / asphalt aqueous dispersion (solid content concentration 70%). On the other hand, polymethylmethacrylate resin was kneaded with a small amount of polyvinyl alcohol and water at 105 ° C for 20 minutes using a kneader, and water was added to the mixture to prepare an aqueous dispersion of acrylic resin
65%). Next, the polypropylene / asphalt aqueous dispersion and the acrylic resin aqueous dispersion were combined, and an aqueous lithium nitrite solution was added thereto.

1000 g / m ^{2 of the} obtained aqueous dispersion (wet base)
Was applied on a concrete board to form a waterproof film. According to the method of JIS A1404, the water absorption rate and the water permeability of the waterproof membrane were 0% and 0%, respectively.

〔The invention's effect〕

According to the method of the present invention, a coating layer of cement, mortar or concrete containing lithium nitrite and polypropylene is formed on the surface of the hardened concrete, and the coating layer has a waterproof property and shows high adhesion strength to the hardened concrete. Therefore, lithium nitrite is prevented from flowing out by rainwater and the like, and water is prevented from entering the hardened concrete. Alternatively, according to another method of the present invention, both lithium nitrite and polypropylene are directly mixed into uncured concrete, and the same action as described above is exhibited.

As a result, salt damage, deterioration due to alkali-aggregate reaction, or it is possible to supply lithium nitrite continuously and without loss to a concrete hardened product that is expected to deteriorate,
It has a great effect on suppressing salt damage of hardened concrete and deterioration due to alkali-aggregate reaction.

Front page continuation (72) Inventor Tadashi Naito 3-7 Kanda Nishikicho, Chiyoda-ku, Tokyo 1 (72) Inventor Takahiro Hori 722 Tsuboicho, Funabashi-shi, Chiba 1 Nissan Chemical Industries, Ltd. Central Research Institute (72) Invention Person Yuji Nakamura 722-1, Tsuboi-cho, Funabashi, Chiba Prefecture, Central Research Laboratory, Nissan Chemical Industries, Ltd. (72) Inventor Higashi ▲ Akira ▼ 2-40 Acacia, Uchinada-cho, Kawakita-gun, Ishikawa Prefecture Yoichi Inuzuka Komatsu-shi, Ishikawa Prefecture 715, Karumi-cho (56) Reference JP-A-1-103970 (JP, A)

Claims (5)

[Claims] 1. The surface of hardened concrete is coated with cement paste, mortar or concrete, which is obtained by blending 1 to 25% by weight of lithium nitrite and 0.1 to 15% by weight of polypropylene with respect to cement (based on dry weight). A method for preventing deterioration of hardened concrete, which comprises: 2. The surface of hardened concrete is mixed with cement (based on dry weight) in an amount of 1 to 25% by weight of lithium nitrite, 0.1 to 5% by weight of polypropylene, and 0.5 to 10% by weight of asphalt. Cement paste,
A method for preventing deterioration of hardened concrete, characterized by coating with mortar or concrete. 3. The surface of the hardened concrete is based on the total weight of the coating, 1-25% by weight of lithium nitrite, 0.5-10% by weight of asphalt, 0.1-5% by weight of polypropylene and 1-25% by weight of acrylic resin. %, A method for preventing deterioration of hardened concrete, characterized by coating with a paint consisting of an aqueous dispersion containing 100%. 4. A deterioration preventing composition comprising lithium nitrite and polypropylene in a weight ratio of (1-25) / (1-15) to an uncured concrete composition in an amount of 0.05-8% by weight (in concrete). The ratio of the solid content of the composition for preventing deterioration based on the weight of cement) is added, and the method prevents deterioration of hardened concrete. 5. Lithium nitrite, polypropylene and asphalt (1 to 25) in an uncured concrete composition.
The composition for preventing deterioration, which is included in a weight ratio of / (1 to 15) / (0.5 to 10), is blended in an amount of 0.05 to 8% by weight (a ratio of solid contents of the deterioration preventing composition based on the weight of cement in concrete). A method to prevent deterioration of the characteristic hardened concrete.