Salt-damaged concrete structure repairing method

Abstract

To provide a salt-damaged concrete repairing method that does not use polymer cement or polymer cement mortar and to provide a repairing method capable of increasing durability of salt damage repair portions.SOLUTION: The present invention provides a salt-damaged concrete structure repairing method in which a deteriorated part of a concrete structure exposed to salt is removed, the removed repair portions are then coated and impregnated with lithium nitrite, and then a cross-section repair material (excluding polymer cement or polymer cement mortar) obtained by blending cement materials that contain ground granulated blast furnace slag with an expansive agent, lithium nitrite, and fine aggregate is used, and a cross-section repair material for a salt-damaged concrete structure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for repairing concrete structures, particularly a method for repairing reinforced concrete structures deteriorated by chloride attack.

Background Art

[0002] Reinforced concrete structures deteriorate over time, and there are many cases where they deteriorate earlier than the service life of concrete. Typical deterioration phenomena and factors include carbonation, chloride attack, frost damage, chemical erosion, alkali-aggregate reaction, drying shrinkage, surface wear, poor construction, etc. In particular, in concrete structures such as quay walls and bridge piers, due to salts (chloride ions) such as seawater and sea sand, corrosion (rust) occurs in the reinforcing bars, and countermeasures against chloride attack that cause cracks, lifting, peeling, etc. in the concrete due to the corrosion expansion are important.

[0003] For the repair of concrete structures deteriorated by chloride attack, generally, the deteriorated part is removed (chiseled) until a sound concrete surface is exposed, and the chiseled part is filled back using a cement-based sectional repair material such as mortar. At this time, rust prevention treatment of the reinforcing bars and primer application are carried out if necessary.

[0004] For example, Patent Document 1 proposes a method in which after chiseling the concrete of the repaired part of a concrete structure, a nitrite aqueous solution is applied to the adhesion interface between the chiseled part and the sectional repair mortar and the entire surface of the exposed reinforcing bar, then a polymer cement mortar is applied, and then the section is repaired using the sectional repair mortar. Patent Document 2 proposes a mortar spraying method in which a mortar obtained by mixing a polymer cement, an aggregate, water, and a lithium nitrite solution is sprayed onto a predetermined location of a concrete structure using a mortar spraying nozzle. Patent Document 3 proposes a repair method using a polymer cement mortar containing a predetermined amount of nitrite, cement, polymer dispersion, expansion agent, fly ash, retarder, antifoaming agent, organic fiber, and fine aggregate.

[0005] However, as disclosed in Patent Documents 1, 2, and 3, in the conventional repair methods for chloride-damaged concrete, methods using polymer cement or polymer cement mortar have generally been common. In the case of polymer cement or polymer cement mortar, generally, a polymer for cement admixture (for example, styrene-butadiene copolymer) is blended in a larger amount (5% by weight or more based on cement, about 20 to 50 parts by weight based on 100 parts by weight of cement according to paragraph 0017 of Patent Document 1) than a cement admixture such as a water reducing agent. However, in the conventional methods, generally, the repair including rust removal of the reinforcing bars in chloride-damaged concrete or rust prevention treatment by applying a rust preventive for reinforcing bars is complicated, so a simple repair method has been demanded. Furthermore, recently, the problem of plastic (polymer) waste in the ocean has become prominent.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a repair method for chloride-damaged concrete that is easy to construct and does not use polymer cement or polymer cement mortar, and to provide a repair method capable of enhancing the durability of the chloride damage repair portion.

Means for Solving the Problems

[0008] As a result of various studies to solve the above problems, the present inventors have found that it is important as a measure against chloride damage to use cement mortar containing fine blast furnace slag powder as a cross-sectional repair material, and have reached the present invention.

[0009] That is, the present invention is a method for repairing a chloride-damaged concrete structure, which comprises chiseling a deteriorated part of a concrete structure exposed to chloride damage, applying and impregnating lithium nitrite to the chiseled repair part, and then adding an expansive agent, lithium nitrite and fine aggregate to a cement material containing fine blast furnace slag powder, and using a cross-sectional repair material (excluding polymer cement or polymer cement mortar). Further, the present invention is a method for repairing a chloride-damaged concrete structure, which comprises chiseling a deteriorated part of a concrete structure exposed to chloride damage until at least part of the reinforcing bars are exposed, applying no rust preventive for the reinforcing bars, applying and impregnating lithium nitrite to the chiseled repair part, and then adding an expansive agent, lithium nitrite and fine aggregate to a cement material containing fine blast furnace slag powder, and using a cross-sectional repair material (excluding polymer cement or polymer cement mortar). Further, the present invention is a cross-sectional repair material used in a method for repairing a chloride-damaged concrete structure, which is obtained by blending an expansive agent, lithium nitrite and fine aggregate with a cement material containing fine blast furnace slag powder (excluding polymer cement or polymer cement mortar), wherein the cross-sectional repair material contains 2.0 to 10.0% by weight of fine blast furnace slag powder, the Blaine specific surface area of the fine blast furnace slag powder is 3,000 to 8,000 cm 2 / g, and 3.0 to 5.0% by weight of an expansive agent and 0.1 to 3.0% by weight of lithium nitrite in solid content are blended.

Advantages of the Invention

[0010] According to the repair method of the present invention, the construction is simple, the chloride-damaged concrete structure can be appropriately repaired without using polymer cement or polymer cement mortar, the durability can be maintained for a long period of time, and the chloride damage deterioration phenomenon of the concrete structure can be suppressed.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0012] The repair method for chloride-damaged concrete structures of the present invention is applicable to concrete structures exposed to chloride damage, such as quay walls, bridge piers, etc., mainly concrete structures used in the ocean. In particular, it is effective for the following chloride-damaged concrete structures when the chloride ion concentration is 10 kg / m 3 It is effective for the following chloride-damaged concrete structures.

[0013] In the repair method of the present invention, a cross-section repair material (excluding polymer cement or polymer cement mortar) in which an expansion material, lithium nitrite, and fine aggregate are blended with a cement material containing blast furnace slag fine powder is used. The repair method of the present invention is characterized by not using polymer cement or polymer cement mortar containing a polymer admixture as an essential component.

[0014] Steel slag generated as a by-product in the steel manufacturing process is roughly classified into blast furnace slag and steelmaking slag. In the present invention, blast furnace slag is used. Blast furnace slag refers to a material obtained by melting and separating components other than iron contained in iron ore in a blast furnace for producing molten pig iron together with ash in by-products such as limestone and coke. Blast furnace slag is classified into slowly cooled slag and granulated slag according to its cooling method, and preferably granulated slag. Granulated slag is obtained by rapidly cooling the molten slag, such as by injecting pressurized water. It is desirable that the cross-section repair material of the present invention contains 2.0 to 10.0% by weight of fine blast furnace slag powder. By blending a predetermined amount of fine blast furnace slag powder, chloride ions can be fixed and the intrusion of chloride ions from the outside can be suppressed, so that the deterioration of concrete can be suppressed. The blending amount of the fine blast furnace slag powder is more preferably 3.0 to 8.0% by weight. It is desirable that the Blaine specific surface area of the fine blast furnace slag powder is 3,000 to 8,000 cm 2 / g. When it is less than 3,000 cm 2 / g, the initial strength and the effect of suppressing chloride ions become small. When it exceeds 8,000 cm 2 / g, cracks due to autogenous shrinkage are likely to occur. More preferably, it is 3,500 cm 2 / g or more and 6,500 cm 2 / g or less.

[0015] In the cross-section repair material of the present invention, the mixing ratio of the cement material containing fine blast furnace slag powder and the fine aggregate is usually in the range of 100 to 400 parts by weight of the fine aggregate with respect to 100 parts by weight of the cement material. The amount of water is preferably about 15 to 20% by weight with respect to the cross-section repair material.

[0016] In the cement material containing fine blast furnace slag powder, general-purpose Portland cement, early-strength Portland cement, etc. can be used as the cement. As the fine aggregate, in addition to natural sand and silica sand, limestone fine aggregate, artificial lightweight aggregate, blast furnace slag fine aggregate, recycled aggregate, etc. can also be used. Fibers can also be used if necessary.

[0017] The cross-section repair material of the present invention preferably contains 3.0 to 5.0% by weight of an expansion material and 0.1 to 3.0% by weight of lithium nitrite in solid content in cement mortar. When the solid content of lithium nitrite is less than 0.1% by weight, the rust prevention effect is not fully exerted. When it exceeds 3.0% by weight, there is a concern that cracks may occur due to an increase in the shrinkage amount, and the cost also becomes high, which is uneconomical. More preferably, it is 0.5 to 2.0% by weight. The total amount of cement / fine aggregate / slag powder / expansion material is 100 wt%, and lithium nitrite is an external number and a solid content. The expansion material is an inorganic admixture that compensates for dry shrinkage and reduces cracking. Examples of the expansion material include calcium sulfoaluminate-based, quicklime-based, and composite-based including calcium sulfoaluminate-based and quicklime-based. When it is less than 3.0% by weight, the expansion amount is insufficient and there is a risk of cracking. When it exceeds 5.0% by weight, there is a concern that the expansion becomes excessive. More preferably, it is 4.0% by weight or less. Lithium nitrite is, for example, blended as a 30 to 50% aqueous solution.

[0018] In the repair method of the present invention, as a cross-section repair material, other cement admixtures (agents) can be blended in a cement material containing blast furnace slag powder together with an expansion material, lithium nitrite, and fine aggregate within a range that does not inhibit the effects of the present invention. Examples of the admixtures (agents) that can be blended include AE agents, water reducers, fluidizing agents, segregation reducing agents, surfactants, hardening regulators, rust preventives, waterproof agents, fly ash, silica fume, rapid hardening materials, shrinkage reducing agents, defoaming agents, and the like.

[0019] The repair method of the present invention is applied to the repair of deteriorated parts of chloride-damaged concrete structures. The repair of the deteriorated part typically involves removing (chiseling) the deteriorated part of the concrete structure exposed to chloride, applying and impregnating lithium nitrite to the chiseled repair part. Then, using the cross-section repair material of the present invention, the chiseled part is filled or coated to restore it. If necessary, surface coating is performed to complete the repair. In particular, the repair method of the present invention chisels the deteriorated part of the concrete structure exposed to salt damage. However, after chiseling, it is not necessarily required that the reinforcing bars be exposed. There is no need to perform chiseling treatment until all the reinforcing bars are exposed. It is sufficient to perform chiseling treatment until the reinforcing bars are partially (about half) exposed. If necessary, rust generated on the exposed reinforcing bars may be removed, and there is no need to apply a rust preventive material for reinforcing bars to the exposed reinforcing bars (see Fig. 1). Therefore, the chiseling amount can be reduced, the construction period can be shortened, and the treatment with a rust preventive material for reinforcing bars can be omitted, so the construction is simple.

Example

[0020] Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to the following examples.

[0021] The concrete for salt damage test used in the examples and the raw materials for adjusting the concrete cross-section repair material are shown below. (1) Concrete for salt damage test; Ordinary Portland cement (manufactured by Nippon Steel Cement Co., Ltd.) NaCl: Sodium chloride special grade (manufactured by Kanto Chemical Co., Inc.) Fine aggregate: Crushed sand (maximum size 5 mm) Coarse aggregate: Crushed stone (maximum size 15 mm, 20 mm) Water / Cement (W / C) = 55 wt% Fine aggregate / aggregate = 46.5 vol% (2) Concrete cross-section repair material (cement mortar); Ordinary Portland cement (manufactured by Nippon Steel Cement Co., Ltd.) Fine aggregate 1: Tohoku silica sand No. 5 (manufactured by Hokuriku Sangyo Co., Ltd.) Fine aggregate 2: Standard sand for cement strength (manufactured by the Cement Association) Ground granulated blast-furnace slag (Blaine specific surface area 3,970 cm 2 / g, manufactured by Nippon Steel Cement Co., Ltd.) Expansion material: DENKA CSA#20 (manufactured by DENKA Co., Ltd.) Lithium nitrite (LiNO2) 40% aqueous solution (manufactured by Honso Chemical Co., Ltd.)

[0022] Examples 1 to 8, Comparative Examples 1 to 8 The above raw materials were blended at the ratios (weight %) shown in each table and kneaded to prepare cement mortar as a concrete cross-section repair material. However, the total amount of cement / fine aggregate / slag micro powder / expansion material was set to 100 wt%, and lithium nitrite (LiNO2) was an external number and a solid content. Before using the cross-section repair material, the LiNO2 to be applied and impregnated to the chiseled repair area was the application amount (300 g / m 2 ) of a 40% aqueous solution.

[0023] Test Example 1 (Example 1, Comparative Examples 1 to 3) <Rusting situation of chloride ion-containing concrete> As shown in Figure 2, a deformed steel bar with a diameter of φ16 mm was fixed at the center of a 100×100×400 mm steel formwork, and concrete for chloride ion concentration 6 kg / m 3 for the chloride attack test was placed. Then, it was demolded in 2 days and sealed and cured at 20°C until the age of 28 days to prepare a concrete specimen for the chloride attack test. The central part of the cured specimen was chiseled out with a size of 100 mm in length, 100 mm in width, and about 50 mm in depth, and half of the cross-section of the steel bar embedded in the chloride attack test concrete was exposed. Next, a 40% aqueous solution of LiNO2 was impregnated and applied at 300 g / m 2 to the chiseled surface and the part where the steel bar was exposed. After 24 hours, the concrete cross-section repair material adjusted at the blending ratio in Table 1 was applied, demolded after 1 day, and sealed and cured at 20°C until the age of 7 days. After that, it was cured for 112 days in an accelerated environment of 40°C and 90% RH, and the rust prevention situation (rusting) of the steel bar taken out by disassembling the chloride damaged concrete was visually confirmed. The judgment criteria are as follows. ○ Rusting area of the steel bar after disassembly less than 20% △ Rusting area of the steel bar after disassembly 20% or more and less than 40% × Rusting area of the steel bar after disassembly 40% or more The results are shown in Table 1.

[0024]

Table 1

[0025] Test Example 2 (Examples 2 to 4) <Macrocell corrosion situation> As shown in Fig. 3, split steel bars were fabricated and fixed at the center of the specimen for measuring macrocell corrosion current. The split steel bars were made by using φ9 mm steel bars and adhering steel bars with a length of 6 cm at both ends and a length of 3 cm × 5 bars inside at intervals of 1 cm with epoxy resin. The steel bars used were of two types: non-corroded steel bars and galvanically corroded steel bars. The non-corroded steel bars were cut to a length of 32 cm and immersed in a 10% aqueous solution of ammonium citrate at 60 °C for about 6 hours to remove the black skin. The galvanically corroded steel bars were fixed at the center of a 100 × 100 × 400 mm steel formwork with non-galvanically corroded steel bars, and mortar with a chloride ion concentration of Cl-10 kg / m 3 and a W / material of 12.5 wt% of cement: fine aggregate 2 = 1:3 was prepared. After being sealed and cured for 7 days, it was immersed in a 3 wt% aqueous sodium chloride solution and energized for 14 days, and then the mortar was disassembled and taken out. Next, using non-corroded steel bars and galvanically corroded steel bars, lead wires were soldered to the ends of the steel bars and then adhered with epoxy resin. The pre-treated steel bars were fixed at the center of a 100 × 100 × 300 mm steel formwork and installed in the formwork so that 1.5 cm protruded from both ends. The chloride ion concentration was 0, 5, 10 kg / m 3 to cast concrete for chloride attack test, and after 1 day, the repair surface was chiseled, and 300 g / m of a 40% aqueous solution of LiNO2 was applied and impregnated. 2 Thereafter, a concrete cross-section repair material adjusted at the mixing ratio shown in Table 2 was cast in a size of 100 × 100 × 150 mm to prepare a specimen for measuring macrocell corrosion current, and sealed curing was carried out until the age of 28 days. After the sealed curing, curing was carried out in an accelerated environment of 40 °C and 90% RH, and the corrosion currents of A1 and A2 were measured 6 months after the accelerated curing. From the measured corrosion currents, the macrocell corrosion current density in the steel bars was calculated from the following formula (1).

Equation

[0026]

Table 2

[0027] Test Example 3 (Example 5, Comparative Examples 4, 5, 6) <Salt water immersion test (apparent diffusion coefficient)> It was in accordance with the Concrete Standard Specification of the Japan Society of Civil Engineers, "Test Method for Apparent Diffusion Coefficient of Chloride Ions in Concrete by Immersion (JSCE-G 572-2018)". Concrete cross-section repair materials adjusted at the mixing ratios shown in Table 3 were used to prepare specimens with a diameter of φ100×200 mm. The specimens were demolded after 1 day of sealed curing and then cured in water for 21 days. After that, they were cut at a position 50 mm from both end faces of the specimens, and the central part with a size of φ100×100 mm was used as the specimen for evaluation. These specimens were dried for about 12 hours (20°C, 60% RH), and the surfaces other than the penetration surface were coated with epoxy. After coating, they were left for 4 days (20°C, 60% RH) and cured in water until the age of 28 days. Then, they were immersed in a 10 wt% sodium chloride aqueous solution at a temperature of 20°C ± 2°C for 200 days so that the entire uncoated release surface was constantly in contact with the solution, and the apparent diffusion coefficient was determined. The judgment criteria are as follows. 〇 Apparent diffusion coefficient (cm 2 / year) Less than 0.250 △ Apparent diffusion coefficient (cm 2 / year) 0.250 or more and less than 0.350 × Apparent diffusion coefficient (cm 2 / year) 0.350 or more The results are shown in Table 3.

[0028]

Table 3

[0029] Test Example 4 (Examples 6 to 8, Comparative Example 7) <Drying shrinkage, cracking situation> The shrinkage amount was measured in accordance with the NEXCO test method, Part 4, Structural Relationship Test Method (July 2020), "Dimensional Change Rate Test Dial Gauge Method". Using the concrete section repair material adjusted at the mixing ratio shown in Table 4, specimens were prepared using a 40×40×160 mm steel formwork, demolded after 2 days, cured at 20°C and 60% RH for 26 days, and then the shrinkage amount was measured. As shown in Fig. 4, for the cracking, the central part of the concrete with a length of 900 mm, width of 1600 mm, and depth of 500 mm was cut out to a size of 700 mm in length, 1000 mm in width, and 100 mm in depth. A formwork was installed on the surface with decorative plywood, and the concrete section repair material adjusted at the mixing ratio shown in Table 4 was filled. After curing in the formwork for 7 days after filling, the formwork was removed and the occurrence of cracking was confirmed. The judgment criteria are as follows. ○ Drying shrinkage (×10 -6 ) - less than 900, no cracking × Drying shrinkage (×10 -6 ) - more than 900, cracking present The results are shown in Table 4.

[0030]

Table 4

Industrial Applicability

[0031] The present invention can be widely used as a repair method for concrete structures, particularly as a repair method for marine reinforced concrete structures such as quay walls and bridge piers deteriorated by salt damage.

Claims

1. After chiseling the deteriorated part of a concrete structure exposed to salt damage, applying and impregnating lithium nitrite to the chiseled repair area, and then using a cross-section repair material (excluding polymer cement or polymer cement mortar) prepared by blending an expansion agent, lithium nitrite, and fine aggregate into a cementitious material containing blast furnace slag fine powder for repairing the salt-damaged concrete structure.

2. The cross-section repair material contains 2.0 to 10.0% by weight of fine blast furnace slag powder, and the Blaine specific surface area of the fine blast furnace slag powder is 3,000 to 8,000 cm ２ 2 / g. The repair method for a chloride-damaged concrete structure according to claim 1.

3. The repair method for a salt-damaged concrete structure according to Claim 1, wherein the cross-section repair material is prepared by blending 3.0 to 5.0% by weight of an expansion agent and 0.1 to 3.0% by weight of lithium nitrite in solid content.

4. After chiseling the deteriorated part of a concrete structure exposed to salt damage until at least part of the reinforcing bars are exposed, without applying a rust preventive for the reinforcing bars, applying and impregnating lithium nitrite to the chiseled repair area, and then using a cross-section repair material (excluding polymer cement or polymer cement mortar) prepared by blending an expansion agent, lithium nitrite, and fine aggregate into a cementitious material containing blast furnace slag fine powder for repairing the salt-damaged concrete structure.

5. A cross-section repair material used in a repair method for a chloride-damaged concrete structure, which is a cementitious material containing fine blast furnace slag powder blended with an expansive agent, lithium nitrite and fine aggregate (excluding polymer cement or polymer cement mortar), and the cross-section repair material contains 2.0 to 10.0% by weight of fine blast furnace slag powder, and the Blaine specific surface area of the fine blast furnace slag powder is 3,000 to 8,000 cm ２ / g, and is characterized in that 3.0 to 5.0% by weight of an expansive agent and 0.1 to 3.0% by weight of lithium nitrite in solid content are blended. A cross-section repair material for a chloride-damaged concrete structure.

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