JP6027736B2 - Method for inhibiting corrosion of reinforcing bars embedded in existing reinforced concrete - Google Patents

Description

  The present invention relates to a method for inhibiting corrosion of reinforcing bars embedded in existing reinforced concrete.

  Durability due to aging of existing reinforced concrete (RC) or prestressed concrete (PC) structures (collectively concrete structures) has become a social problem. In particular, in the case of a concrete structure in the sea, in the vicinity of the coast, or in a place where a snow melting agent is sprayed, chloride ions enter the concrete, and the steel bars corrode and deteriorate. Therefore, repair and reinforcement are performed by various methods. If the damage is significant, the existing concrete structure may be destroyed and a new RC structure may be installed.

As a method for suppressing salt damage of existing concrete structures, the following construction methods are mainly adopted or proposed.
(1) Method of electrochemically discharging chloride ions that have entered concrete structures onto the concrete surface
(2) Method of repairing the cross section of a concrete structure with mortar containing lithium nitrite
(3) A method for extracting anions, etc. in concrete structures with a treatment agent containing an ion exchange resin

  Examples of the method classified as (1) include the method described in Patent Document 1. This method is a method in which a steel material inside a concrete structure is used as an internal electrode, an electrode installed on the surface of the concrete is used as a surface electrode, and a current is passed between the surface electrodes or between the surface electrode and the internal electrode.

  Examples of the method classified as (2) include the method described in Patent Document 2. In this method, after the concrete of the repaired part of the concrete structure is removed, a nitrite aqueous solution is applied to the adhesion interface between the removed part and the cross-sectional repair mortar, the exposed reinforcing steel surface, and nitrite is contained. This is a method of repairing the cross section with mortar.

  Examples of the method classified as (3) include the method described in Patent Document 3. In this method, a treatment agent comprising a mixture of an anion exchange resin, a cation exchange resin and a superabsorbent gel is applied to concrete to extract anions and cations contained in the concrete member.

JP-A-8-40784 JP 2003-120041 A JP 2003-27262 A Japanese Patent Laid-Open No. 2-279551 JP-A-9-86997

  Method (1) is an effective method for preventing corrosion of reinforcing steel in concrete structures. However, there is a problem that it is difficult to uniformly remove chloride ions from the concrete around the reinforcing bars. Moreover, since work such as electrode installation and energization becomes large, it is a problem that it is expensive.

The method (2) is effective in preventing corrosion of internal rebars because the passive film is regenerated by the reaction of nitrite ions (NO ₂ ⁻ ) and iron ions (Fe ₂ ⁺ ). However, when lithium nitrite is used as a nitrite, its toxicity and the price of lithium nitrite-containing mortar are extremely high.

  It is known that corrosion of reinforcing steel bars by salt water and snow melting agents is mainly the function of chloride ions. Therefore, it is effective to adsorb and remove chloride ions that corrode the reinforcing bars using a relatively inexpensive ion exchange resin as in the method (3). However, since the method of Patent Document 3 uses a superabsorbent gel as a treating agent, construction and handling are not easy, and a device for protecting the treating agent is required during extraction with the treating agent.

  Furthermore, as a method related to (3), for example, Patent Document 4 is characterized in that a coating material mainly composed of hydraulic cement and anion exchange resin is applied to a concrete surface containing a steel material. How to protect concrete is described. Further, Patent Document 5 describes a rust-proof mortar mainly composed of Portland cement and a chloride ion adsorbent (for example, calcium / aluminum composite hydroxide or synthetic zeolite), and concrete deteriorated due to reinforcement corrosion due to salt damage. It describes the repair of parts and the suppression of deterioration. Both are described as the prior art of Patent Document 3.

  According to the description of Patent Document 3, by using the superabsorbent gel, the moisture retained by the superabsorbent gel exerts the ion exchange ability of the anion exchange resin and the cation exchange resin, and from the concrete. Anion and cation extraction can be performed more rapidly. On the other hand, when hydraulic cement or Portland cement is used as a medium, it is presumed that there is no effect as much as using a superabsorbent gel. However, the method of Patent Document 3 requires construction for holding the treatment agent composed of the superabsorbent gel during the repair period, and is not a simple method.

  Therefore, the object of the present invention is to provide a relatively simple construction method and excellent chemical safety with respect to reinforcing bars embedded in concrete in existing reinforced concrete structures exposed to salt water such as seawater and snow melting agents. An object of the present invention is to provide a new method for inhibiting corrosion using an inexpensive material.

  As a result of diligent research to solve the above problems, after repairing the concrete in the repaired part, mortar containing a strongly basic anion exchange resin was used as a repair material to repair the cross-section, thereby embedding it in existing reinforced concrete. The present invention has been completed by finding that the corrosion of the formed reinforcing bars can be suppressed.

  The present invention is a method for inhibiting corrosion of a reinforcing bar embedded in an existing reinforced concrete, wherein at least a part of the concrete on the surface of the existing reinforced concrete that has caused salt damage or may cause salt damage is suspended, The present invention relates to the corrosion inhibiting method, characterized in that at least a part of the suspended portion is filled with a mortar containing a strongly basic anion exchange resin to repair the cross section.

According to the present invention, by suspending the concrete on the surface of the existing reinforced concrete structure that caused salt damage and repairing the cross section with a mortar containing a strongly basic anion exchange resin, the free water contained in the mortar for cross section repair, The chloride ions impregnated in the existing concrete around the internal reinforcing bars are adsorbed on the strongly basic anion exchange resin, whereby the concentration of chloride ions around the reinforcing bars can be lowered. At the same time, desorption of OH 2 ⁻ ions from the ion exchange resin is expected to increase the alkali ion concentration (pH) around the reinforcing bars and make it difficult to corrode.

  Strongly basic anion exchange resin retains most of the ability to adsorb chloride ions when the cross-section repair mortar is cured, so it adsorbs chloride ions that enter from the outside of the concrete structure. By gradually adsorbing chloride ions contained in existing concrete nearby, it is possible to protect internal reinforcing bars from corrosion over a long period of time. Further, as described above, the alkali ion concentration (pH) around the reinforcing bars is increased, and the corrosion prevention environment is maintained.

A schematic description of the method of the present invention is shown. A schematic description of the method of the examples is shown.

  The present invention is a method for inhibiting corrosion of reinforcing bars embedded in existing reinforced concrete. The method for inhibiting corrosion according to the present invention removes at least a part of the concrete on the surface of the existing reinforced concrete that has caused salt damage or may cause salt damage, and at least a part of the removed part is strongly basic. The cross-section is repaired by applying a mortar containing an anion exchange resin.

  The reinforced concrete to be subjected to the method of the present invention is an existing reinforced concrete that has caused salt damage or salt damage. For example, although it is a reinforced concrete structure exposed to salt water such as seawater or a snow melting agent, it is not particularly limited. Furthermore, the method of the present invention is also effective for a reinforced concrete structure that has been neutralized with an acidic gas such as carbon dioxide.

  In the method of the present invention, at least a part of the concrete on the surface of the existing reinforced concrete is removed. There are no particular restrictions on the portion of the reinforced concrete surface to be suspended, but the entire reinforced concrete structure may be suspended in consideration of the damage caused by salt damage of the reinforced concrete structure or the expected damage caused by salt damage. Alternatively, it is possible to partially remove portions where damage due to salt damage is significant. More specifically, the surface of the concrete surface is conspicuous, the part that is likely to peel off with just a light tapping accounts for almost half of the total area, or the rust juice of the internal rebar is transmitted to the surface It is preferable that the surface where there are many spots is to be picked up. Especially for reinforced concrete structures that have been in service for several decades, there are various `` location environments '' such as the surface facing the sea, the surface facing the opposite side of the sea, and the piers built in the mountains. ”Depending on the surface, the progress of deterioration differs for each surface. Therefore, in consideration of the surface condition of the concrete as described above, for example, a part of the outer surface of the concrete, for example, only a part of the quadrangular prism, and a part of the surface are suspended. There are cases where When suspending a plurality of outer surfaces of concrete, from the viewpoint of maintaining the strength of the concrete structure, it is preferable to suspend and apply mortar to each outer surface step by step.

In addition, the depth to be rubbed is within a range that does not cause problems in use and service in terms of load resistance and strength characteristics of the reinforced concrete structure, considering the corrosion inhibition effect of the reinforcing bars after applying the method of the present invention. And it is preferable to suspend to the depth where the amount of chloride in concrete exceeds the amount of rusting chloride (for example, 1.2 to 2.4 kg / m ³ ). Therefore, when the salt is strongly damaged by salt, it is preferable to lift up to a position closer to the reinforcing bar inside the concrete, and most preferably to the part where the reinforcing bar inside the reinforced concrete is exposed.

  In the present invention, at least a part of the concrete on the surface of the existing reinforced concrete is removed, and at least a part of the removed part is coated with a mortar containing a strongly basic anion exchange resin to the concrete part. There is an advantage that the contained chloride can be removed and the chloride existing in the concrete near the reinforcing bar can be effectively removed.

  Next, a mortar containing a strongly basic anion exchange resin is applied to at least a part of the suspended portion. Preferably, a mortar containing a strongly basic anion exchange resin is applied so that the suspended portion can be almost filled. In the present invention, chloride ions that have infiltrated into the reinforced concrete are adsorbed and removed from the concrete that has caused salt damage by the strong basic anion exchange resin. Thereby, the progress of corrosion of the reinforcing bars by chloride ions is suppressed. The portion where the mortar containing the strongly basic anion exchange resin is applied is preferably in contact with the concrete that caused salt damage in order to adsorb and remove chloride ions from the concrete that caused salt damage. There is no particular limitation on the portion to be removed, and it can be appropriately determined in consideration of the degree of salt damage of the existing reinforced concrete and the portion that has received salt damage. For example, if the part close to the concrete surface is damaged by salt, but is not damaged by the salt near the reinforcing bar and halfway between the reinforcing bar and the surface, it will be damaged by the salt between the reinforcing bar and the surface. It is possible to rub off the concrete portion and apply a mortar containing a strongly basic anion exchange resin to the stranded portion. If salt damage has occurred not only near the concrete surface but also in the vicinity of the reinforcing bar, remove the concrete from the surface to the vicinity of the reinforcing bar or until the outermost reinforcing bar is exposed. A mortar containing a strongly basic anion exchange resin can be applied to the part. However, the mortar containing strong basic anion exchange resin is in contact with the reinforcing bar because chloride ions are adsorbed to the mortar containing strong basic anion exchange resin and chloride ions are present near the reinforcing bar. More preferably not. From this point of view, the concrete is suspended until the outermost reinforcing bars are exposed, and mortar containing no strongly basic anion exchange resin is applied. A mortar containing can also be applied. In order to prevent the penetration of chloride ions by seawater and snow melting agent from the outside, a mortar containing a strongly basic anion exchange resin may be applied in the vicinity of the surface after cross-sectional repair.

  However, for effective adsorption removal of chloride ions from concrete by strong basic anion exchange resin, water must coexist in the dispersion medium of strong basic anion exchange resin to promote ionization of chloride. There is. Therefore, in the present invention, mortar is used as a dispersion medium for the strongly basic anion exchange resin. The mortar is composed of cement, sand, and water. Even during and after curing, the mortar contains water until it is dried, which is advantageous for promoting adsorption and removal of the chloride ions.

  The strong base anion exchange resin is not limited as long as it is an anion exchange resin having a strong basic anion exchange group showing strong basicity as an ion exchange group. The degree of polymerization, shape, and the like are not particularly limited, and the shape of the resin may be a gel shape or a porous shape. The “strongly basic anion exchange resin” of the present invention can be obtained, for example, by chloromethylating a styrene and divinylbenzene copolymer, followed by amination. Examples of strongly basic anion exchange groups include quaternary ammonium groups such as trimethylammonium group, triethylammonium group, tributylammonium group, dimethylhydroxyethylammonium group, dimethylhydroxypropylammonium group, methyldihydroxyethylammonium group, and the like. Examples thereof include a trisulfonium group and a phosphonium group. The strongly basic anion exchange resin may be OH type or Cl type. In the case of Cl type, it may be used after regenerating and washing with sodium hydroxide or the like to form OH type. In addition, when it changes from Cl type to OH type, it swells about 20%, and the particle size becomes large correspondingly.

  Representative examples of the strongly basic anion exchange resin include, for example, Amberjet 4002 (manufactured by Rohm and Haas Japan), Amberjet 4010 (manufactured by Rohm and Haas Japan), and Amberjet 4400 (Rohm). And an anion exchange resin containing a quaternary ammonium group such as & Haas Japan).

  The ion exchange capacity of the strongly basic anion exchange resin is not particularly limited, but it is preferably as high as possible from the viewpoint that more chloride ions can be captured. However, considering the balance with cost, the ion exchange capacity is suitably in the range of, for example, 2 to 5 meq / g. However, it is not intended to be limited to this range.

  The diameter of the strongly basic anion exchange resin is not particularly limited, and for example, a range of 0.1 to 1.0 mm is appropriate at the time of mixing with mortar. If it is 0.1 mm or more, when mixed in mortar, it can be easily mixed without floating as a powder. If it is 1.0 mm or less, the ion-exchange resin does not become a foreign substance in the mortar, and the mechanical properties of the concrete part whose cross-section has been repaired are not lowered to the extent that hinders practical use. The strongly basic anion exchange resin may be a mixture of ion exchange resins having different diameters or average diameters. The strongly basic anion exchange resin may be granular or may be in the form of a powder pulverized by an appropriate means. The diameter of the strongly basic anion exchange resin hardly changes before and after mixing with the mortar and immediately after the repair is completed.

  The mixing amount (volume ratio) of the strongly basic anion exchange resin mixed with the mortar can be appropriately determined in consideration of the type of strong basic anion exchange resin to be used and the degree of salt damage of the concrete to be treated. it can. For example, the volume ratio with respect to the mortar can be, for example, in the range of 0.1 to 5.0%. If it is 0.1% or more, a predetermined anticorrosive effect is obtained. If it is 5.0% or less, dispersion for mixing the strongly basic anion exchange resin into the mortar can be easily performed, and construction for repairing the mortar can be easily performed.

  The cement used for the mortar in the present invention is not particularly limited as long as it is a hydraulic cement capable of forming a cured body by reaction with water. Examples of the hydraulic cement include Portland cement, blast furnace cement, fly ash cement, and alumina cement. Portland cement and alumina cement may be mixed with admixtures such as blast furnace slag and fly ash. Polymer cement is also applicable.

Although strongly basic anion exchange resins have the ability to adsorb chloride ions, the order of adsorption capacity for ion exchange resins is SO ₄ ²⁻ > NO ₃ ⁻ > Cl 2 ⁻ . Ordinary cement contains about 5% by weight of SO ₄ ^2- as gypsum (CaSO ₄ .2H ₂ O). Gypsum Cl solubility in water ^- (NaCl, CaCl ₂₎ lower. Therefore, in the short term, there are few sulfate ions derived from gypsum, and the ion exchange resin exhibits an adsorbing ability for chloride ions without being disturbed by sulfate ions. However, in the long term, the ion exchange resin adsorbs SO ₄ ^2- and the chloride ions are liberated, which may corrode the internal rebar.

Therefore, Portland cement can also be used as the cement used in the mortar. However, from the viewpoint of long life, a cement that does not substantially contain sulfate that has substantially no possibility of releasing SO ₄ ² − from cement immediately after water injection is selected. The cement substantially free of sulfate means that a material containing sulfate is not used as a raw material of the cement, and cement containing sulfate as an impurity inevitably mixed in the cement in production of the cement, The present invention includes a cement substantially free of sulfate. Specific examples of cement substantially free of sulfate include alumina cement and magnesia cement. However, in the case of alumina cement, there is a possibility that the compressive strength of the hardened body is lowered. In such a case, it is preferable to use blast furnace slag together. Portland cement includes ordinary cement, early-strength cement, medium heat cement, low heat cement, sulfate resistant cement and the like. For cross-section repair mortar, it may be preferable to use early-strength cement.

  The mortar for cross-sectional repair is a mortar in which moderate water is added to a mixture of strongly basic ion exchange resin, cement and aggregate sand. When the sand which is aggregate is river sand or sea sand which does not contain chloride, it is preferable to use the sand washed with water. The particle diameter of the sand as the aggregate may be similar to or different from the particle diameter of the strongly basic ion exchange resin. In consideration of the mixing at the time of mortar preparation and the ease of construction for cross-sectional repair, the sand for mortar for cross-sectional repair is not particularly limited as long as it is normally used. The average particle diameter of the sand that is an aggregate is not particularly limited, but can be, for example, in the range of 0.15 to 5 mm.

  The content of the strongly basic ion exchange resin in the mortar is as described above, but the content of cement, the content of sand as an aggregate, and the content of water are as follows. Considering mortar fluidity, workability, and strength after hardening, the sand / cement mass ratio is preferably in the range of 0.8 to 2.5, and the water / cement mass ratio is preferably 0.15 to 0.5.

  In addition to the above components, the mortar for cross-sectional repair in the present invention adds reinforcing short fibers, a water-curable resin, a water reducing agent, a fluidizing agent, a thickening agent, a setting retarding agent, a setting accelerator, an expansion agent, and the like. You can also In particular, the reinforcing short fibers are important for improving the workability of the cross-sectional repair mortar itself, suppressing cracking, and preventing the penetration of chloride ions from the outside.

  As a method for preparing a mortar containing a strongly basic ion exchange resin, after mixing cement, aggregate (sand) and ion exchange resin in a dry state, an appropriate amount of water may be added and mixed. An ion exchange resin may be added and mixed separately when the repair mortar and an appropriate amount of water are kneaded. Examples of the mixer include, but are not limited to, a forced biaxial kneading mixer, a tilting mixer, a pan mixer, and a hand mixer. Before mixing with water, it is more preferable to mix the cement, aggregate (sand), and ion exchange resin in a dry state because the ion exchange resin can be more uniformly dispersed in the mortar.

The method of the present invention will be further described with reference to FIG.
A shows an existing reinforced concrete structure. It is a concrete structure that is damaged by salt and has reinforcing bars inside. In B, the concrete on the outside of the reinforcing bars on the surface of the concrete structure which has been damaged by salt is picked up. In B, the concrete on all the surfaces of the concrete structure is suspended until the reinforcing bars are exposed. In C, the cross-section is repaired by applying the mortar for cross-section repair to the portion where the concrete is suspended. In FIG. 1, the surface on the right side of the drawing is removed. From the standpoint of maintaining the safety of the entire structure when the surface on the left side of the drawing, the surface on the near side, and the surface on the back side are both suspended and the surface is restored, It is preferable to carry out sequentially.

By holding in this state, at least chloride ions present in the concrete near the reinforcing bar diffuse into the mortar for cross-sectional repair, and ion exchange is performed in the strongly basic ion exchange resin contained in the mortar. By this ion exchange, hydroxide ions (OH ⁻ ) possessed by the ion exchange resin are released from the strongly basic ion exchange resin into the mortar, and this hydroxide ion is considered to diffuse into the concrete near the reinforcing bar. (D). Furthermore, the chloride ions present in the part sandwiched between the reinforcing bars also adsorb to the ion exchange resin instead of the hydroxide ions desorbed from the ion exchange resin due to the adsorption performance of the ion exchange resin (outside of the reinforcing bar). Move to). In addition, the reaction formula of chloride ion adsorption by ion exchange resin is represented by the following formula, for example.
_{R-CH 2 N (CH 3} ) OH + Cl - → R-CH 2 N (CH 3) Cl + OH -

  After the cross-sectional repair by mortar coating for C cross-sectional repair, as shown by D, mortar coating and surface coating can be usually applied on the coated cross-sectional repair mortar.

  In order to prevent the invasion of chloride ions from the surface of the reinforced concrete structure after cross-section repair in this way, a method that has already been applied, such as coating with normal mortar containing short fibers and further coating with resin, is used in combination. It is desirable. In addition, it is desirable that the surface coating is periodically updated.

  Even in the case of a reinforced concrete structure repaired by the method of the present invention, when the ion exchange resin is completely adsorbed by chloride ions over the long term, the anticorrosion effect of the internal rebar is lost. Therefore, it is possible to protect the reinforcing bar from corrosion over a long period of time by re-attaching the mortar on the reinforcing bar surface and repairing it using the same method as described above.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1

  As shown in FIG. 2, first, a mortar containing a high-strength Portland cement containing sodium chloride was placed in a rectangular mold having a height, a width and a height of 10 cm, respectively. This was wet-cured for 14 days, and then mortar containing an early strong Portland cement containing a strongly basic anion exchange resin was added by 2 cm in thickness. For example, as the strongly basic anion exchange resin used in the mortar continuously placed in Test No. 4, Amberjet 4002 (Rohm and Haas Japan, OH type, average particle size of 0.50 to 0.50) 0.80 mm) was used. The mortar was prepared by previously mixing 30 g of strongly basic anion exchange resin, 5860 g of early strong Portland cement and 12560 g of sand (average particle size 1.2 mm), and mixing 2930 g of water with this mixture to prepare 10 liters of mortar. .

  Two days after the additional casting, the added mortar portion was cut and separated, pulverized, and then the total chloride ion was quantified according to JIS A 1154 “Test method for chloride ions contained in hardened concrete”. Are shown in Table 1. Thus, a large amount of chloride was quantified in the mortar to which the strongly basic anion exchange resin was added. That is, the strongly basic anion exchange resin adsorbs the chloride ions in the concrete first placed. That is, it is shown that chloride ions existing in the vicinity of the reinforcing bar of the existing concrete structure subjected to salt damage move to the cross-section repair material containing the strongly basic anion exchange resin, and the corrosion of the reinforcing bar can be prevented.

  By suspending the concrete on the surface of existing reinforced concrete structures damaged by salt damage and repairing the cross section with mortar containing a strongly basic anion exchange resin, chloride ions existing in the vicinity of the reinforcing bars or newly penetrated chloride ions are removed. Because it can be adsorbed, it can protect the internal reinforcing bars from corrosion. As a result, it is possible to suppress the corrosion of the reinforcing bars embedded in the reinforced concrete structure exposed to salt water such as seawater or a snow melting agent for a long period of time and extend the life of the concrete structure.

Claims (1)

A method for inhibiting corrosion of reinforcing steel embedded in existing reinforced concrete, wherein the concrete on the surface of the existing reinforced concrete that has caused salt damage or may cause salt damage is suspended until the reinforcing bars are exposed, At least a portion of the removed portion is filled with a mortar that does not contain a strong basic anion exchange resin in contact with the reinforcing bar, and then the OH type strong basic anion so as not to contact the exposed reinforcing bar. The mortar containing the exchange resin is filled to repair the cross section , and the mortar containing the strong base anion exchange resin is mixed with cement, aggregate, and the strong base anion exchange resin in a dry state, The method for inhibiting corrosion is characterized by adding and mixing .