Repair methods for composite deteriorated concrete

Abstract

This invention provides a repair method for compositely deteriorated concrete that can effectively repair composite deterioration caused by both salt damage and alkali-silica reaction occurring simultaneously. [Solution] This is a method for repairing reinforced concrete that is undergoing combined deterioration due to salt damage and alkali-silica reaction, which involves applying an electrolyte solution for electrical treatment, followed by a dewatering treatment to release moisture from at least the electrical treatment area to the outside.

Description

Technical Field

[0001] The present invention relates to a method for repairing composite deteriorated concrete.

Background Art

[0002] Although there are various deterioration factors for concrete structures, typical deterioration factors include chloride attack and alkali-silica reaction. In marine structures, chloride ions penetrate into the reinforced concrete due to airborne salts, causing steel bars to rust. On roads in cold regions, chloride ions penetrate into the reinforced concrete by spraying deicing agents such as sodium chloride and potassium chloride. At this time, since Na ions and K ions penetrate into the reinforced concrete simultaneously with chloride ions, alkali-silica reaction (ASR) is often induced depending on the quality of the aggregates incorporated in the concrete. That is, in concrete structures under such environments, not only chloride attack alone but also composite deterioration with alkali-silica reaction is likely to occur.

[0003] In Patent Document 1, as a method for repairing a concrete structure made of reinforced concrete that has partially collapsed or has the potential to collapse due to chloride attack, a formwork is attached directly or with a gap on the outer surface, and a non-shrinking material composed of grout or mortar containing nitrite is filled between the formwork and the concrete structure, and the concrete structure is reinforced by the filled non-shrinking material and the formwork.

[0004] Also, in Patent Document 2, a method for repairing a concrete structure that combines lithium nitrite and an epoxy resin injection material with crack-following properties and applies it to a concrete structure that has undergone alkali-silica reaction to suppress crack closure and ASR has been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, Patent Document 1 describes a repair method for salt damage, and Patent Document 2 describes a repair method for alkali-silica reaction. No effective method is known for suppressing combined deterioration in which salt damage and alkali-silica reaction occur simultaneously.

[0007] Therefore, the present invention aims to provide a method for repairing composite deteriorated concrete that can effectively repair composite deterioration in which salt damage and alkali-silica reaction occur simultaneously. [Means for solving the problem]

[0008] The inventors of this invention conducted studies to solve the above problems and found that the present invention can solve them. That is, the present invention is as follows.

[0009] [1] A method for repairing reinforced concrete that is undergoing combined deterioration due to salt damage and alkali-silica reaction, comprising applying an electrolytic solution to the concrete, followed by a dewatering treatment to release moisture from at least the electrolytic treatment area to the outside. [2] The method for repairing composite deteriorated concrete according to [1], wherein the electrolyte solution is a lithium aqueous solution containing lithium. [3] The method for repairing composite deteriorated concrete according to [1] or [2], wherein the dewatering treatment is a treatment in which a Si-based surface impregnation material is applied to the energized treatment section. [4] The method for repairing composite deteriorated concrete according to [1] or [2], wherein the dewatering treatment is a treatment in which a reduced pressure treatment is applied to the energizing treatment unit. [5] A method for repairing composite deteriorated concrete according to any one of [1] to [4], wherein the energizing treatment is a treatment in which a direct current is passed between a steel material inside the reinforced concrete and an electrode installed on the concrete surface via the electrolyte solution. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for repairing composite deteriorated concrete that can effectively repair composite deterioration in which salt damage and alkali-silica reaction occur simultaneously. [Brief explanation of the drawing]

[0011] [Figure 1] This is an explanatory diagram illustrating the energization process according to this embodiment. [Modes for carrying out the invention]

[0012] The embodiments of the present invention (this embodiment) will be described in detail below. The repair method for composite deteriorated concrete according to this embodiment involves applying an electrolytic solution to reinforced concrete that is undergoing composite deterioration due to salt damage and alkali-silica reaction, followed by a dewatering treatment to release at least the moisture from the electrolytic treatment area to the outside.

[0013] Here, reinforced concrete undergoing combined deterioration due to salt damage and alkali-silica reaction refers to reinforced concrete in which salt damage, in which chloride ions penetrate the interior of the reinforced concrete and cause the reinforcing steel to rust, and alkali-silica reaction, in which reactive components (e.g., reactive aggregates) react with sodium and potassium components, causing abnormal expansion of the concrete and resulting in cracking, are progressing in combination, or have already progressed in combination.

[0014] The repair method according to this embodiment involves applying an electrolytic solution to reinforced concrete that is undergoing complex deterioration. From the viewpoint of obtaining a good repair effect against complex deterioration, it is preferable that the electrolytic treatment involves passing a direct current through the electrolyte solution between the steel material inside the reinforced concrete and an electrode installed on the concrete surface.

[0015] Here, the electrolyte solution may be any solution that can penetrate into the concrete to reduce the electrical resistance of the concrete and facilitate the flow of electricity. Specifically, an aqueous solution in which various alkali metal salts and alkaline earth metal salts are dissolved in water as a solvent is preferably used. Examples of the alkali metal salts and alkaline earth metal salts include carbonates, nitrates, nitrites, sulfates, borates, hydroxides, chlorides, etc. of lithium, sodium, potassium, magnesium, calcium, etc. From the viewpoint of obtaining a good repair effect against composite deterioration, it is preferably a lithium aqueous solution containing lithium.

[0016] The electrode (external electrode) installed on the concrete surface is preferably one with excellent corrosion resistance. For example, a titanium mesh (for example, a titanium-based precious metal oxide coated product, roll width 120 cm ,

[0019] , , wire diameter longitudinal 0.87 × transverse 0.87 mm, mesh opening longitudinal direction 76 mm and transverse direction 34 mm) may be used.

[0017] When passing a direct current between the external electrode and the steel material (internal electrode) inside the reinforced concrete, the current is preferably 0.5 A / m 2 or more per unit concrete surface area, and more preferably 0.7 - 1.5 A / m 2 . The current is preferably passed continuously or intermittently.

[0018] An example of the energization treatment according to this embodiment will be described with reference to FIG. 1. As shown in FIG. 1, the electrode installed on the surface side of the concrete 10 is used as the external electrode (anode material) 20, and a steel material (not shown) embedded inside the concrete 10 is used as the internal electrode. The internal electrode, the electrolyte holding material 22 holding the electrolyte, the external electrode 20, and the protective substrate 24 are arranged in this order, and a direct current is passed between the external electrode 20 and the internal electrode. By providing the electrolyte holding material 22, the electrolyte permeability to the concrete is improved, and a stable voltage can be obtained quickly.

[0019] As shown in FIG. 1, an electrolyte holding member 22 that holds an electrolyte, an external electrode 20, and a protective substrate 24 are arranged in this order to form an electrode unit panel 26. For example, the protective substrate 24 is fixed on the outside by a plurality of crossbars 30.

[0020] Also, a water supply hose 34 as an electrolyte supply pipe is provided and fixed between two crossbars 30. An electrolyte supply port (not shown) is installed at an arbitrary position of the water supply hose 34. A recovery pipe (not shown) having an electrolyte recovery port for recovering the electrolyte from the water supply hose 34 is also provided as appropriate. That is, the electrolyte is continuously or intermittently supplied from the electrolyte supply port of the water supply hose 34 to the electrolyte holding member, and then the electrolyte is recovered by the recovery pipe (not shown).

[0021] It is preferable that the energization process is such that an electrolyte supply port is installed at an arbitrary position, an electrolyte recovery port is installed, and the electrolyte is continuously or intermittently supplied from the electrolyte supply port to the electrolyte holding member and the electrolyte is recovered from the electrolyte solution recovery port. With such a configuration, stable supply of the electrolyte is possible and the effect of the system can be more easily exerted.

[0022] The diameter of the electrolyte supply port of the water supply hose 34 is preferably 0.5 to 1.0 mm, and more preferably 0.6 to 0.8 mm. By being 0.5 to 1.0 mm, the electrolyte can be stably supplied to the unit panel. Also, the interval between the electrolyte supply port and the adjacent electrolyte supply port is preferably 10 to 35 mm, and more preferably 15 to 30 mm. By the interval being 10 to 35 mm, the electrolyte can be uniformly supplied to the electrode unit panel 26.

[0023] In a plurality of electrolyte supply pipes (water supply hoses 34) having electrolyte supply ports, the distance W between one electrolyte supply pipe and other electrolyte supply pipes installed parallel to it is preferably 300 to 600 mm. A distance of 300 to 600 mm allows the electrolyte to be sufficiently distributed to the electrolyte retaining material while preventing leakage due to an excessive amount of electrolyte. A distance W of 400 to 500 mm is more preferable.

[0024] Furthermore, it is preferable that multiple electrolyte supply tubes are covered on the outside with a resin sheet. This allows the electrolyte solution to penetrate the concrete uniformly, enabling stable electrical treatment. As the resin sheet, for example, corrugated plastic (made of polypropylene) can be used.

[0025] The electrode unit panel 26 may be mounted, for example, using a panel fixing bracket described in Japanese Patent Publication No. 6586000, or by other known means.

[0026] Furthermore, when arranging the electrode unit panels 26 in a grid pattern, a predetermined gap may be provided between adjacent electrode unit panels 26, and the connecting member described in Japanese Patent No. 6586000 may be placed in this gap (joint) to ensure liquid tightness.

[0027] Preferably, the water supply hose 34 and the recovery pipe are connected to the outside by hoses or the like. That is, the electrolyte solution is pumped into the water supply hose 34 from an electrolyte solution tank (not shown). Preferably, the electrolyte recovered in the recovery pipe is pumped back into the electrolyte solution tank via an electrolyte solution separation tank (a tank that separates air from the electrolyte solution) and an element.

[0028] After the energizing treatment described above, a dehydration treatment is performed to release at least the moisture from the energized area to the outside. Although the energizing treatment provides a repair effect against complex deterioration, after this treatment, the electrolyte solution may absorb a large amount of moisture into the reinforced concrete due to electrophoresis. This moisture can cause further deterioration, such as re-corrosion of the steel or alkali-silica reaction. Therefore, in this embodiment, a dehydration treatment is performed to remove this moisture.

[0029] As for the dehydration treatment, from the viewpoint of making the dehydration effect more effective, it is preferable to apply a Si-based surface impregnation material to the energized section (surface coating treatment), and / or to apply a reduced pressure treatment to at least the energized section (reduced pressure treatment).

[0030] While epoxy resins and the like can be used as impregnating materials for surface coating, it is preferable to use Si-based surface impregnating materials from the viewpoint of obtaining a better repair effect through a high dehydration effect.

[0031] In surface coating treatments, the Si-based surface impregnating material is preferably a surface impregnating material containing one of the following: silane-based, siloxane-based, or silane-siloxysane-based. For example, materials mainly composed of alkoxysilane, silane oligomer, alkylalkoxysilane, alkylalkoxysilane containing an amino group, or polysiloxane can be used. Materials containing 60% by mass or more, preferably 75% by mass or more, of these in an alcohol-based medium can also be used.

[0032] More specifically, examples include BASF Pozzolith's "ProtectSil" (product name), Kajima Renovate's "Magical Repeller" (product name), and Daido Paint's "AquaSeal" (product name). These can be used in any form, such as liquid or paste.

[0033] The method for applying the surface impregnating material is not limited to any method that allows for uniform application; conventional application methods such as brushes, rollers, and trowels can be arbitrarily selected. The application amount and number of applications can be set appropriately according to the structure, but the application amount is 200 to 1000 ml / m². 2 It is preferable to keep the concentration to around 400-800 ml / m². 2 It is preferable to apply the coating in an average of three or more coats on vertical surfaces and an average of two or more coats on horizontal surfaces, with a minimum interval between coats allowing for touch-drying time (e.g., 20 minutes or more).

[0034] As for the depressurization process, for example, as shown in Figure 1, a through-hole is made in the transparent resin substrate, and excess water and trapped air in the concrete are removed by suction using a vacuum pump or the like through a suction pipe.

[0035] In any of the above dewatering treatments, it is preferable to first clean the surface to be treated by removing oil, dirt, dust, etc. using a high-pressure washer, wire brush, nonwoven abrasive material, etc., before performing the dewatering treatment. Furthermore, it is preferable to perform the treatment on a sufficiently dry surface, for example, with a surface moisture content of 8% or less.

[0036] Examples of concrete structures to which the repair method for composite deteriorated concrete applies include buildings such as condominiums and office buildings, tunnels, precast concrete structures, bridges, bridge piers, abutments, piers, railings, undersides of deck slabs, balconies, chimneys, concrete poles, tanks, slope frames, embankments, and concrete pipes, where the natural potential is in the corrosive range according to ASTM's criteria, and where cracks appear, gel seepage is observed, or expansion occurs. [Examples]

[0037] The present invention will be described in more detail below based on examples, but the present invention is not limited thereto.

[0038] [Example 1] (Preparation of salt damage test specimens) Using concrete with the mix shown in Table 1 below and 13mm diameter reinforcing bars, rectangular prism specimens measuring 100mm (length) x 100mm (width) x 400mm (depth) with a 30mm cover were prepared. After preparation, salt damage test specimens were prepared by repeatedly drying (20°C, 60% humidity) and wetting (30°C, 95% or higher humidity) every other day for 28 days.

[0039] [Table 1]

[0040] ·Materials used C: Standard Portland cement (commercially available) W: Water (tap water) S: Fine aggregate (reactive aggregate that produces ASR; S1: non-reactive fine aggregate (crushed sand from Ichiba, Anan City, Tokushima Prefecture) and S2: reactive fine aggregate (crushed andesite sand from Hokkaido) mixed in a mass ratio of 5:5) G: Coarse aggregate (reactive aggregate that produces ASR; G1: non-reactive coarse aggregate (crushed stone from Osaka, Itano-cho, Tokushima Prefecture) and G2: reactive coarse aggregate (crushed andesite from Hokkaido) mixed in a mass ratio of 5:5) When preparing the test specimens, the concrete was treated with a Cl concentration of 8 kg / m³. 3 NaCl (industrial grade, commercially available) is added to achieve this result.

[0041] (Electrification process) Epoxy resin (manufactured by Konishi Co., Ltd., product name Bond Quick Mender) was applied to the sides of the salt-damaged test specimen, excluding the top surface and the measurement window area provided on one side, and then heated to create an epoxy resin coating.

[0042] Subsequently, a 5mm thick electrolyte solution holding material was placed on the top surface of the salt-damaged specimen, and the anode material (external electrode: titanium mesh) was placed on top of it. Reinforcing bars were used as internal electrodes, and a direct current was passed between them and the external electrodes.

[0043] Furthermore, a 1.3% by mass saturated lithium carbonate aqueous solution was used as the electrolyte, and this was impregnated into a nonwoven fabric made of polypropylene Hazmat Pig absorbent (MSD-015, manufactured by New Pig Corporation) to create an electrolyte solution retaining material that holds the electrolyte.

[0044] The following conditions were used for the power-on process. • Current density and temperature during energization: 1.5 A / m 2 ,30℃ • Power supply period: 8 weeks

[0045] (Dehydration process) After the energizing process, the anode material is removed, and a Si-based surface impregnation material is applied to the top surface to a thickness of 600 ml / m². 2 The coating was applied in this manner. The Si-based surface impregnation material used was "Magical Repeller" (product name) manufactured by Kajima Renovate.

[0046] (Measurement of natural potential, polarization resistance, and concrete resistance) After dehydration, the specimens were stored in an accelerated ASR environment (95% RH, 40°C) and underwent expansion measurements and electrochemical monitoring (spontaneous potential, polarization resistance, concrete resistance) every two weeks for 100 days. The day before measurement, the specimens were moved to a constant temperature room at 20°C while still in a moist state, and after measurement (100 days later), they were left undisturbed in air (20°C, 60% RH) for 24 hours.

[0047] Here, the natural potential, polarization resistance, and concrete resistance were measured using a corrosion monitor 7635 (manufactured by Toho Giken Co., Ltd.). A saturated silver chloride electrode (Ag / AgCl) was used as the reference electrode, and a titanium mesh was used as the counter electrode. The values ​​were measured as the average values ​​over the entire length of the reinforcing bars in the specimen. The natural potential is preferably high in the range of -0.1 to 2V, the polarization resistance is preferably high in the range of 130 to 150kΩ, and the concrete resistance is preferably high in the range of 3.5 to 8kΩ. The polarization resistance was determined using the square wave current polarization method, based on the difference in impedance values ​​at applied currents of 10 μA and frequencies of 800 Hz and 0.1 Hz. The concrete resistance was determined as the impedance value on the high-frequency side (800 Hz). The polarization curve was calculated by changing the potential by ±800 mV from the natural potential at a sweep speed of 2.8 mV / sec so that the sweep time was approximately 5 minutes, and the relationship between potential and current during this period was measured. The results are shown in the table below.

[0048] (Measurement of expansion rate) The day before measuring the concrete expansion coefficient, the specimens were moved to a constant temperature room at 20°C, and the change in concrete length was measured using a contact gauge. The concrete expansion coefficient was calculated using the measurement taken immediately after curing as the origin. A smaller concrete expansion coefficient is preferable.

[0049] [Example 2] Except for using a commercially available moisture-resistant epoxy resin instead of a Si-based surface impregnation material for the dewatering treatment, the same procedure as in Example 1 was used to measure the natural potential, polarization resistance, and concrete resistance. The results are shown in the table below.

[0050] [Comparative Example] The same energizing treatment as in Example 1 was performed, except that the dewatering treatment was omitted. The natural potential, polarization resistance, and concrete resistance were measured in the same manner as in Example 1. The results are shown in the table below.

[0051] [Table 2]

[0052] In the examples, concrete expansion was suppressed in response to ASR, and the natural potential and polarization resistance were evaluated as not corroding in response to salt damage. Furthermore, it was confirmed that cracking was suppressed by visual inspection of the test specimens. In particular, Example 1, which used a Si-based surface impregnation material, showed better results. [Industrial applicability]

[0053] The present invention's method for repairing composite deteriorated concrete can be suitably used for structures where composite deterioration is progressing or has already progressed, such as buildings like condominiums and office buildings, tunnels, precast structures, bridges, bridge piers, abutments, piers, railings, undersides of deck slabs, balconies, chimneys, concrete poles, tanks, slope frames, embankments, concrete pipes, etc. [Explanation of Symbols]

[0054] 10 Concrete 12 Reinforcing bars 14 prism specimens 20 External electrode 21. Anode material (titanium mesh) 22 Electrolyte retention material 24 Protective board 26 Electrode Unit Panel 30 wooden beams 34 Water supply hose

Claims

1. A method for repairing reinforced concrete that is undergoing combined deterioration due to salt damage and alkali-silica reaction, comprising applying an electrolyte solution for electrical treatment, followed by a dewatering treatment to release moisture from at least the electrical treatment area to the outside.

2. The method for repairing composite deteriorated concrete according to claim 1, wherein the electrolyte solution is a lithium aqueous solution containing lithium.

3. The method for repairing composite deteriorated concrete according to claim 1, wherein the dewatering treatment is a treatment in which a Si-based surface impregnation material is applied to the energized treatment section.

4. The method for repairing composite deteriorated concrete according to claim 1, wherein the dewatering treatment is a treatment in which a depressurization treatment is applied to the energizing treatment unit.

5. The method for repairing composite deteriorated concrete according to any one of claims 1 to 4, wherein the energizing process is a process of passing a direct current through the electrolyte solution between a steel material inside the reinforced concrete and an electrode installed on the concrete surface.

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