JPS6067681A - Corrosion-proof method of prestressed concrete - Google Patents

Abstract

PURPOSE:To prevent the lowering in the strength of a reinforcing steel material due to corrosion, by surrounding the surface of the reinforcing steel material in prestressed concrete by a corrosion-proof agent based on a synthetic resin emulsion and calcium nitrite. CONSTITUTION:As a corrosion-proof agent, a composition prepared by compounding 0.2-40pts.wt. of calcium nitrite with 100pts.wt. of the resin solid component of a synthetic resin emulsion is used and, pref., 0.2-40pts.wt. of calcium nitrite and 0.01-5pts.wt. of a volatile rest inhibitor are used. In this case, a vinyl acetate/ethylene copolymer emulsion is used as the synthetic resin emulsion and benzotriazole is used as the volatile rust inhibitor. This corrosion-proof agent is mixed in a cement composition in a ratio of 0.5-100pts.wt. to 100pts.wt. of said cement composition to form a slurry which is, in turn, adhered to the entire surface of a steel material to which tension force is applied and solidified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method for corrosion protection of prestressed concrete structures constructed using tensioned reinforced steel.

Prestressed concrete includes so-called britension-type prestressed concrete, in which tension is applied to the steel before the concrete is hardened, so-called boss-tensioned prestressed concrete, in which hardened concrete with perforated holes is adjusted and then hardened, and these two types. There is prestressed concrete in the middle area.

Conventionally, the steel shells used for these have not been subjected to anti-corrosion treatment, and sea sand has been used for the concrete, and the steel shells have been exposed to wind and rain at the edge of the beach where they are used. Paint can be applied to prevent these, but this [1]
The steel materials used for this purpose elongate as a result of being subjected to tensile stress, so the resin used in the paint must follow suit. In this respect, reaction-curing types such as epoxy resins are inappropriate, and water emulsions are preferred. However, synthetic resin emulsions generally contain various additives and residual monomers in addition to resin components. Additives include emulsifiers, thickeners, pH regulators, chain transfer agents, viscosity regulators, antifungal agents, antifreeze agents, film forming agents, etc.
Some are acidic, others contain halogen elements, and often corrode metal materials. Although the residual monomer varies depending on the type of resin, it may also be an organic acid, which also causes corrosion. Furthermore, when cement is mixed into the paint, cement curing retarders are used to ensure long-term use, but these are often organic acids and also induce corrosion.

On the other hand, the use of nitrite as a corrosion inhibitor for metals is known.

For example, Japanese Patent Publication No. 8 B-940 describes a method of rust-preventing concrete reinforcing bars and steel frames using sodium nitrite.1 However, since these are mixed with cement and used, they are exposed to harsh salts. However, if sodium nitrite is included in the nitrites, and if there is crosstalk with the synthetic resin emulsion product, the sulfate groups in the cement may and sodium ions react.

Generates sodium sulfate [7. Since the NazSO+ crystal particles are coarse, a so-called efflorescence phenomenon occurs in which white powder is formed on the surface of the cross-dried product, which is not preferable.

Therefore, we used calcium nitrite, which is a calcium compound close to the composition of concrete, without causing the efflorescence phenomenon.
We have discovered that blending a synthetic resin emulsion is effective in making the bond between steel and concrete 1 more dense, following the expansion and contraction of the steel, and retaining calcium nitrite, leading to the present invention. That is, the present invention is a method for preventing corrosion of iron fIrJtR material, which is characterized in that the surface of reinforced steel in prestressed concrete is surrounded by a synthetic resin emulsion and an anticorrosion agent mainly composed of calcium nitrite.

As the anticorrosive agent used in the present invention, calcium nitrite 02 to
A proportion of 40 parts by weight is preferred.

Furthermore, the anticorrosion agent is a resin solid content of synthetic resin emulsion of 10%.
0] containing 0.2 to 40 parts of calcium nitrite and 0.01 to 5 parts by weight of a volatile rust inhibitor per part of i (
preferable.

Examples of synthetic resin emulsions used in the invention include vinyl acetate, vinyl chloride, vinylidene chloride, styrene, ethylene, acrylic, nitrile, butadiene, bemeba, urethane, and epoxy. Examples include aqueous resin emulsions such as homopolymers of synthetic resins such as synthetic resins, alkyd-based resins, and copolymers of two or more types.

Vinyl acetate-ethylene copolymer emulsion and styrene-acrylic co-m6 emulsion both have good H contact properties with cement and concrete, and also have good adhesion of concrete to the coated crotch, and can be said to be the most preferred emulsions for this purpose.

Furthermore, a volatile rust preventive agent is effective as a second anticorrosive agent. That is, although calcium nitrite is intended to place iron in a passivating environment, its effectiveness decreases if the paint film peels off within the concrete. In this case, if a volatile rust preventive agent is present, C'J 8B will form a surface adsorption layer on the copper to prevent rust. In general, with prestressed concrete 1, shrinkage cracks are less likely to occur in the concrete, so the paint film is less likely to peel off due to external forces, or the anti-corrosion effect is complete when a water agent is used.

Particularly economically effective rust agents include benzotriazole, mercaptobenzotriazole and their potassium and sodium salts, dicyclohexylamine, cyclohexylaniline and their acid salts, such as nitrites.

In addition, triethanolamine, jetanolamine, aliphatic amines and their acid salts, and basic aluminum phosphate may also be used, although they are not major rust inhibitors.

As a specific means for applying it to prestressed concrete, in the case of the Pretensigon type, 05 to 100 parts by weight of the anticorrosive agent of the present invention is mixed with 100 parts by weight of a cement composition consisting of water, cement, and a cement retardant. , is applied to the entire surface of steel (often high-strength steel) and hardened.

This steel material is placed under tension in a formwork, and concrete is poured and hardened to form prestressed concrete.

In the case of the boss tension type, there is a hole that penetrates the hardened concrete (this hole is often made of a sheath), and a steel material (often high-strength steel) is passed through this hole and - tension is applied. Then, the gap between the steel material and the concrete is filled with cement milk consisting of water, cement, an expansion accelerator (golden kite aluminum powder), etc., but the present invention uses 0.5 parts of anticorrosion agent per 10 parts by weight of this cement milk. This can be carried out by filling up to 50 parts by weight of a mixed slurry.

Table 1 shows a mixture of synthetic resin Emension 100 heavy nail part adjusted to a solid content concentration of 45% and calcium nitrite for type 2 skin part, diluted 3 times with water and applied to a steel plate.
Apply the mortar at a ratio of 202/G and after 8 hours apply 20% mortar.
The tensile peel strength was measured after pouring to a thickness of 5 m and raising the beef indoors for 14 days. , this test can also determine the mixing compatibility of the emulsion and calcium nitrite.

Vinyl acetate-ethylene copolymer emulsion, styrene-
The acrylic copolymer emulsion showed particularly high adhesive strength.

It is true that adding calcium nitrite to an aqueous synthetic resin emulsion determines the rust prevention effect.

Therefore, the amount of legacy mixture is determined. The concentration of calcium nitrite mixed into aqueous or synthetic resin emulsions to provide rust prevention effects depends on the type and concentration of the emulsion, the type and concentration of the electrolyte, the residual monomer, the type and concentration of the pH 1 additive, and the material. j' and l depending on the composition of the metal.

Therefore, it is usually attached to JISA6205-1982! tf
In accordance with Book 4 I [Salt water immersion test for reinforcing bars], natural type t! occurs between the corresponding aqueous synthetic resin emulsion and a piece of metal that is the same as the metal material to be stored. ! It is determined by measuring the change in position Ilt over time. In other words, JIS 80 to 0
In accordance with Annex 1 of 5-1982, instead of the test salt water in 8.2.2, a solution prepared by adding calcium nitrite to the wood-based synthetic resin emulsion to a specified concentration was used to Use the same metal piece as the metal material to be stored instead,
The test shall be conducted in accordance with the test method of If the natural electrode potential after 7 days shifts to the "shell" side as shown in Figure 8 of Appendix 1, it is considered that the calcium nitrite concentration in the aqueous synthetic resin emulsion has a corrosion-preventing effect.

The concentration of calcium nitrite in the first test was o, l i
After that, increase or decrease as appropriate and repeat the test to find the appropriate value.

It is not economical to contain more calcium nitrite than is necessary for corrosion protection, and a large excess may cause the resin in the emulsion to aggregate, which is not preferable.

The second method of determining the minimum amount of calcium nitrite mixed using hinyl acetate-ethylene copolymer emulsion.
Shown in the table. It can be seen that the rust prevention property can be exhibited when the addition amount is approximately 0.1:gi% or more, that is, approximately 0.2:fi% or more in terms of resin solid content, but the corrosion rate tends to be somewhat high and the zero value is the limit. be. The upper limit is also related to the environment in which it is used, but if it is added to the upper limit, the strength of the coating film generally decreases. Therefore, it varies depending on the emulsion, and although it is difficult to determine in general, when using it as milk with cement added, the maximum weight is 40% in terms of resin solid content, and when using it alone as a coating film, it is It is preferably 10% by weight or less, and more preferably about 5 to 70% by weight as a coating film. Table 8 shows that under even more severe conditions, the coating was applied to a copper rod, which was not air-dried for 6 hours, then smoked for 5 hours at 50°C, and immersed in 3% saline solution.
This shows that the effect has been confirmed. 0 This clearly shows the effect of the present invention, but it can also be seen that the volatile rust preventive agent enhances this effect.゛A: Mercaptobenzotriazole sodium salt B dicyclohexylamine (no rust) *l Manufactured by Sumitomo Chemical - Sumiriki Flex *2 Manufactured by Chuo Rika Kogyo - Rikabond *B Manufactured by Naugatac - Laticrete *4 Daicel Chemical - Cevian - A ×5 It is also clear from the tests made by Shiraki Exlan Ordinary Portland cement 100 parts Vinyl acetate-ethylene copolymer emulsion (resin solid content 47%) 10 parts Methyl cellulose 0.5 parts Water 45 parts There are two types: one containing calcium nitrate and one containing 0.5% benzotriazole, and one without. After dipping each piano wire with a wire diameter of 29 mm in the cement milk, drying it in the air for 60 minutes, and then surrounding it for 120 minutes.
Dry in air at 0°C for 714 hours to prepare a coating film.

This was wired in the longitudinal direction of a 4 am x 4α x 16- plastic mold. The wiring method is 4, llW x 4
．． Drill 4 holes each with a diameter of 8 mm in the center of the inside of the plastic from the edge of the plastic, making 4 holes in total at both ends.
I ran the piano wire through the book.

After putting this piano wire under slight tension, the water/cement ratio is 0.
．． 65. Toyoura standard sand/cemen H mortar was poured.

The amount of water used according to JIS A6205 varies depending on the density of the concrete used, but it is generally effective if it is 0.01% by weight or more for emulsion solid public use, but preferably 0.05%. With the above, we can expect even better effects. The maximum amount is determined by economics and solubility. Therefore, from an economic standpoint, the upper limit is about 5%, preferably 2% or less.

The purpose of using it in addition to cement and concrete is to increase the thickness of the coating film, improve Il/i@ properties, and improve mechanical strength and adhesion with surrounding concrete. This is particularly effective for boss-tensioned prestressed coccycrete because the surrounding area is hardened by watertight concrete containing resin. Although the mixing of resins into cement is not particularly new, the novelty of the present invention lies in its combination with rust-inhibiting substances. The best method is to determine the mixing ratio of resin from a company where calcium nitrite effectively exhibits rust prevention properties in concrete.

Table 5 shows the rusting status obtained by immersing a copper plate for one week in a cement extract solution, which is assumed to have dissolved 1.56% of common salt into the free water present in cement and concrete. (A 1.55% solution was used because the rusting power of common salt is generally optimal between 1% and 8%.) Table 5 *Cement extract at 20°C and neutralized solution by blowing CO2 gas It can be seen that 0.1% or more of calcium nitrite is required to ensure long-term rust prevention performance until the cement is neutralized. As mentioned above, the required amount of calcium nitrite per resin solid content is 0.2 to 20 Mm% (external number), so the required amount of resin emulsion (solid content equivalent) for concrete or mortar is 6 (li amount). % to 0.5 times.

Practical emulsions are about 50% solids by weight, so the required amount is between about 100% and about 1% by weight.

Considering the case where the salt content is low, even the case of 0.5% by weight is effective. In addition, the maximum amount of cement milk for pouring in case of prestressed concrete and when it is included in the concrete structure is 50 kg.
Even if it is reduced to 1%, the effect will not decrease and it will be economical.

Bost tensi compressor is used for stress concrete. In case 4, the thickness of the layer surrounding the piano wire exceeds the range of the paint film, so its public rust resistance is ensured, so the amount of emulsion for cement and concrete (
(solid content equivalent) can be reduced to 2.J11% considering economic efficiency.

Setting retarders include gluconic acid, mineral acid, textrin, sugar, etc., and expansion accelerators include aluminum powder. , the present invention will be described below with examples.
As will be explained more specifically, the present invention is not limited to these examples, and can be applied in a variety of ways.

Examples 1 to 4 and Comparative Examples 1 to 2 Using the anticorrosive cement 1 composition shown in the 6th section, a corrosion test was carried out.

A piano wire with a wire diameter of 2.9 fl was immersed in the cement composition, dried in air for 2 hours, and then dried at 120 DEG C. for 10 minutes to harden the coating. This is 160 pieces x 2
Wiring was carried out in the longitudinal direction of the 000 m L formwork. The wiring method is to drill 4 holes each with a diameter of 8 mm from the end of the 160 x 160 m in the center of the inside of the 20 pieces, making a total of 8 holes at both ends.
I ran the piano wire through the book. After slightly tensioning this piano wire, the water/cement ratio is 0.40, and the unit cement amount is 450.
Pf/-r, unit coarse aggregate ff1l120/d, unit fine aggregate! 1680I! I poured f7ri concrete. Rod-shaped vibrator after pouring concrete
The piano wire was compacted for 1 hour and then steam-cured for 1 Ohr at normal pressure, and then a tension of 800 Pf was applied to the piano wire, and after being left as it was for 2 weeks, the stress was removed. The ends of the piano wire were then cut and painted with epoxy resin, including the mortar ends. The test specimen obtained in this way was JIS A62
The wire was immersed in a salt solution specified in 2005-8.2 at the age of 28 days, and after 12 months, the piano wire was opened and the piano wire was taken out and its condition was observed. The results are shown in Table 7.

Table 7 Examples 5i 1 to 5 all showed excellent anticorrosion effects. In Comparative Example 1, localized rust occurred due to an insufficient amount of rust preventive agent, and in Comparative Example 2, the amount of calcium nitrite was too large for the emulsion, causing the emulsion to coagulate. This is due to rust not being formed.

Examples 5 to 8 Corrosion tests were conducted using the cement compositions containing anticorrosive agents shown in Table 8.

16 (L + a + mouth x 2000 fin formwork 160 x 16
28 tar from the end of the parrot to the center of the inside of the 20 parrot
Install the steel pipes e. through 4 locations. This formwork was then filled with a water/cement ratio of 0.40. Unit cement 450Kp/
y+f, unit coarse aggregate amount 1120/g, unit fine aggregate wind 6
80 ~ / so concrete was poured. After compacting with a rod vibrator for 8 hours and curing at normal pressure for 1 Ohr, the W4 tube was pulled out and a hole was made. After leaving it as it was for 2 weeks, a 1'6 m If PC steel rod was passed through the hole and a tension of 8ooXP was applied to fix the end.

Thereafter, the mixture shown in Table 8 was injected into the gap between the person and the PCfi4 rod. The edges of the mortar and exposed metal parts were then painted with epoxy resin. The test specimen obtained in this way is
A6205.8.2
Immersed in 8 days, removed and opened after 12 months, PCw4
I took out the stick and observed its condition.

Paste the results in Table 9. Table 9

Claims (3)

[Claims] (1) A method for preventing corrosion of reinforced steel, which is characterized by surrounding the surface of reinforced steel in prestressed concrete with a synthetic resin emulsion and an anticorrosive agent containing calcium nitrite as its main ingredients. (2) Resin solid content of synthetic resin emulsion in which the anticorrosive agent is 10
The method according to claim 1, wherein the ratio of calcium nitrite is 0.2 to 40 parts per 0 parts. (3) Resin solid content of synthetic resin emulsion with anti-corrosion agent: 10
2. The method according to claim 1, comprising 0.2 to 40 parts by weight of calcium nitrite and 0.2 to 40 parts by weight of a volatile rust inhibitor per 0 parts by weight.