JP7492676B2 - Method for estimating corrosion current density, method for estimating deterioration of steel material, and method for controlling anticorrosive current - Google Patents
Method for estimating corrosion current density, method for estimating deterioration of steel material, and method for controlling anticorrosive current Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 227
- 239000010959 steel Substances 0.000 title claims description 227
- 239000000463 material Substances 0.000 title claims description 195
- 230000007797 corrosion Effects 0.000 title claims description 164
- 238000005260 corrosion Methods 0.000 title claims description 164
- 238000000034 method Methods 0.000 title claims description 134
- 230000006866 deterioration Effects 0.000 title claims description 13
- 230000010287 polarization Effects 0.000 claims description 138
- 238000013213 extrapolation Methods 0.000 claims description 14
- 238000005259 measurement Methods 0.000 description 7
- 230000002787 reinforcement Effects 0.000 description 7
- 238000004210 cathodic protection Methods 0.000 description 5
- 230000001681 protective effect Effects 0.000 description 4
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 3
- 238000009434 installation Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 2
- -1 Iron ions Chemical class 0.000 description 2
- 239000010405 anode material Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 229910052801 chlorine Inorganic materials 0.000 description 2
- 239000000460 chlorine Substances 0.000 description 2
- 238000006731 degradation reaction Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 description 2
- 239000000523 sample Substances 0.000 description 2
- 239000004576 sand Substances 0.000 description 2
- 239000004575 stone Substances 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
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- VEMHQNXVHVAHDN-UHFFFAOYSA-J [Cu+2].[Cu+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O Chemical compound [Cu+2].[Cu+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O VEMHQNXVHVAHDN-UHFFFAOYSA-J 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- GTKRFUAGOKINCA-UHFFFAOYSA-M chlorosilver;silver Chemical class [Ag].[Ag]Cl GTKRFUAGOKINCA-UHFFFAOYSA-M 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
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Description
本発明は、コンクリート構造物に埋設された鋼材の腐食電流密度を推定するための腐食電流密度の推定方法、および、斯かる推定方法で得られる腐食電流密度の推定値に基づいて鋼材の劣化状態を推定する鋼材の劣化推定方法に関する。また、上記の腐食電流密度の推定値に基づいて防食電流を制御する防食電流の制御方法に関する。 The present invention relates to a corrosion current density estimation method for estimating the corrosion current density of a steel material buried in a concrete structure, and a steel deterioration estimation method for estimating the deterioration state of the steel material based on an estimated value of the corrosion current density obtained by the estimation method. It also relates to a corrosion protection current control method for controlling the corrosion protection current based on the estimated value of the corrosion current density.
コンクリート構造物に埋設されている鋼材は、表面に不動態皮膜が形成されているため、本来、腐食から保護されている。ところが、沿岸地域や凍結防止剤が頻繁に使用される地域などのように、塩素成分が多量に存在する環境下では、塩素成分が構造物中に侵入して鋼材表面の不動態皮膜を部分的に破壊する場合がある。そして、不動態皮膜が破壊された部分からは、鉄イオンが溶出するため、鋼材が腐食（酸化）することなる。 Steel materials embedded in concrete structures are essentially protected from corrosion by the formation of a passive film on their surface. However, in environments with large amounts of chlorine, such as coastal areas or areas where deicing agents are frequently used, the chlorine components can penetrate the structure and partially destroy the passive film on the steel surface. Iron ions are then eluted from the parts of the passive film that have been destroyed, causing the steel to corrode (oxidize).
上記のように、鋼材に部分的な腐食が生じることによって、鋼材には、腐食した領域（アノード部）と腐食していない領域（カソード部）とが形成される。このようなアノード部とカソード部との間には、電位差が生じており、アノード部からカソード部へ電子が流れることで腐食電流が発生し、アノード部からの鉄イオンの溶出（腐食）を更に進行させる要因となる。 As described above, partial corrosion of the steel material results in the formation of corroded areas (anodes) and non-corroded areas (cathodes) in the steel material. A potential difference occurs between these anodes and cathodes, and a corrosion current is generated when electrons flow from the anodes to the cathodes, which causes the elution (corrosion) of iron ions from the anodes to progress further.
このような腐食の進行を防止する方法としては、チタンなどの素材を用いて形成された陽極材から鋼材に対して電流（防食電流）を供給する電気防食方法が知られている。該電気防食方法は、鋼材に対して防食電流を供給することで、アノード部とカソード部との間に生じる電位差を解消し、腐食電流が発生するのを防止する方法である。 As a method for preventing the progression of such corrosion, a method of cathodic protection is known in which an electric current (corrosion protection current) is supplied to the steel material from an anode material formed from a material such as titanium. This cathodic protection method is a method in which a corrosion protection current is supplied to the steel material to eliminate the potential difference that occurs between the anode and cathode, thereby preventing the generation of a corrosion current.
斯かる電気防食方法では、供給する電流の管理（あるいは、陽極材と鋼材との間にかける電圧の管理）、つまりは防食電流量の管理が行われる。供給電流の管理は、電流を供給した際の鋼材の分極量や、供給電流を遮断した後の鋼材の復極量が所定の範囲となるように管理することで行われる。 In such an electrochemical protection method, the current supplied (or the voltage applied between the anode material and the steel material) is controlled, i.e., the amount of protective current is controlled. The current supplied is controlled by controlling the amount of polarization of the steel material when current is supplied and the amount of depolarization of the steel material after the supply current is cut off so that they are within a specified range.
上記のような電気防食方法において、効果的な防食効果を得るためには、コンクリート構造物に埋設された鋼材の腐食状態を定量的に推定することが重要である。鋼材の腐食状態を定量的に推定する方法としては、ターフェル外挿法を用いて腐食電流密度を推定し、該腐食電流密度の推定値に基づいて鋼材の腐食速度を推定する方法が知られている（特許文献１参照）。 In order to obtain an effective corrosion protection effect in the above-mentioned cathodic protection method, it is important to quantitatively estimate the corrosion state of the steel material embedded in the concrete structure. A method for quantitatively estimating the corrosion state of the steel material is known in which the corrosion current density is estimated using the Tafel extrapolation method, and the corrosion rate of the steel material is estimated based on the estimated corrosion current density (see Patent Document 1).
上記のように、ターフェル外挿法を用いて鋼材の腐食電流密度を推定する場合、鋼材の分極試験を行って分極曲線を作成し、該分極曲線にターフェル外挿法を適用する。分極試験では、鋼材に対して電流を供給する対極と照合電極とをコンクリート構造物の表面に設置し、対極から鋼材へ供給する電流の密度（以下では、「供給電流密度」とも記す）を変更しつつ鋼材の電位を測定し、各供給電流密度とこれに対する鋼材の電位とに基づいて分極曲線を作成する。このため、鋼材の所定箇所における腐食電流密度を推定する場合、推定箇所に実際に供給される電流の供給電流密度とこれに対する鋼材の電位とを把握することが、正確な推定を行う上で必要となる。 As described above, when estimating the corrosion current density of steel using the Tafel extrapolation method, a polarization test of the steel is performed to create a polarization curve, and the Tafel extrapolation method is applied to the polarization curve. In the polarization test, a counter electrode and a reference electrode that supply current to the steel are installed on the surface of a concrete structure, and the potential of the steel is measured while changing the density of the current supplied from the counter electrode to the steel (hereinafter also referred to as the "supply current density"), and a polarization curve is created based on each supply current density and the corresponding potential of the steel. Therefore, when estimating the corrosion current density at a specified location of the steel, it is necessary to know the supply current density of the current actually supplied to the estimated location and the corresponding potential of the steel in order to make an accurate estimation.
しかしながら、コンクリート構造物では、コンクリートのかぶり、コンクリートの電気抵抗率、鋼材の配筋状況等の影響によって、対極からの電流が拡散してしまい、鋼材における腐食電流密度の推定箇所に実際に供給される電流の供給電流密度を把握することは困難である。このため、コンクリート構造物に埋設された鋼材の腐食電流密度を、ターフェル外挿法を用いて定量的に推定することは困難と考えられていた。 However, in concrete structures, the current from the counter electrode diffuses due to the influence of the concrete cover, the electrical resistivity of the concrete, the reinforcement conditions of the steel material, etc., making it difficult to grasp the supply current density of the current actually supplied to the location in the steel material where the corrosion current density is to be estimated. For this reason, it was thought to be difficult to quantitatively estimate the corrosion current density of steel material buried in a concrete structure using the Tafel extrapolation method.
そこで、本発明は、コンクリート構造物に埋設された鋼材の腐食電流密度を、ターフェル外挿法を用いて比較的正確に推定することができる腐食電流密度の推定方法、および、腐食電流密度の推定値に基づいて鋼材の劣化を比較的正確に推定することができる鋼材の劣化推定方法を提供することを課題とする。また、腐食電流密度の推定方法で得られる腐食電流密度の推定値に基づいて防食電流を制御する防食電流の制御方法を提供することを課題とする。 The present invention aims to provide a corrosion current density estimation method that can relatively accurately estimate the corrosion current density of steel embedded in a concrete structure using the Tafel extrapolation method, and a steel deterioration estimation method that can relatively accurately estimate the deterioration of the steel based on the estimated corrosion current density. It also aims to provide a corrosion protection current control method that controls the corrosion protection current based on the estimated corrosion current density obtained by the corrosion current density estimation method.
本発明に係る腐食電流密度の推定方法は、コンクリート構造物に埋設された鋼材の腐食電流密度を推定するための腐食電流密度の推定方法であって、鋼材における腐食電流密度を推定する箇所に達するようにコンクリート構造物に形成された削孔内に照合電極が挿入され、該削孔内で照合電極と鋼材とが接触するように配置されると共に、該照合電極と鋼材とが電気的に接続されており、鋼材に電流を供給するための対極がコンクリート構造物の表面に設置されると共に、該対極と鋼材とが電源装置を介して電気的に接続されており、対極から鋼材に印加電流を供給していない状態から鋼材に印加電流を供給して鋼材をカソード分極させると共に、照合電極に基づいて測定される鋼材電位から求まる鋼材の分極量が所定値となるまで分極量が増加するように鋼材へ供給する印加電流を増加させ、任意の複数の分極量のそれぞれが得られる際の鋼材電位を照合電極に基づいて測定するカソード分極工程と、対極から鋼材に印加電流を供給していない状態から鋼材に印加電流を供給して鋼材をアノード分極させると共に、照合電極に基づいて測定される鋼材電位から求まる鋼材の分極量が所定値となるまで分極量が増加するように鋼材へ供給する印加電流を増加させ、任意の複数の分極量のそれぞれが得られる際の鋼材電位を照合電極に基づいて測定するアノード分極工程と、ＦＥＭ解析を用いてコンクリート構造物のＦＥＭ解析モデルを作成する工程と、鋼材の自然電位と対極の自然電位とコンクリート構造物の電気抵抗率とをＦＥＭ解析の境界条件として用いると共に、ＦＥＭ解析モデルにおける鋼材の腐食電流密度の推定箇所の印加電圧を変更し、ＦＥＭ解析モデルにおける鋼材の腐食電流密度の推定箇所のモデル印加電流をカソード分極工程およびアノード分極工程における各分極量が得られた際の印加電流と一致させるフィッティング工程と、フィッティング工程後、カソード分極工程およびアノード分極工程における各分極量が得られた際の印加電流と鋼材の自然電位と対極の自然電位とコンクリート構造物の電気抵抗率とを境界条件としてＦＥＭ解析を行い、ＦＥＭ解析モデルにおける鋼材の腐食電流密度の推定箇所で各分極量が得られる際のモデル印加電流を求めると共に、各分極量が得られる際のモデル印加電流それぞれをコンクリート構造物における鋼材の腐食電流密度の推定箇所の表面積で除することでＦＥＭ解析モデルにおける各分極量が得られる際のモデル電流密度を算出する工程と、カソード分極工程およびアノード分極工程における各分極量が得られる際の鋼材電位と、ＦＥＭ解析モデルにおける各分極量が得られる際のモデル電流密度とを用いて分極曲線を作成し、該分極曲線からターフェル外挿法により腐食電流密度を求める工程とを備える。 The corrosion current density estimation method according to the present invention is a corrosion current density estimation method for estimating the corrosion current density of steel material buried in a concrete structure, in which a reference electrode is inserted into a drilled hole formed in the concrete structure so as to reach a location in the steel material where the corrosion current density is to be estimated, the reference electrode and the steel material are arranged in the drilled hole so as to come into contact with each other, and the reference electrode and the steel material are electrically connected, a counter electrode for supplying a current to the steel material is installed on the surface of the concrete structure, and the counter electrode and the steel material are electrically connected via a power supply device, and an applied current is supplied to the steel material from a state in which no applied current is supplied from the counter electrode to the steel material, thereby cathodically polarizing the steel material, a cathodic polarization process in which an applied current is increased so that the polarization amount of the steel material determined from the steel material potential measured based on the reference electrode increases until the polarization amount of the steel material reaches a predetermined value, and the steel material potential when each of the arbitrary multiple polarization amounts is measured based on the reference electrode; an anodic polarization process in which an applied current is supplied to the steel material from a state in which no applied current is supplied to the steel material from the counter electrode to anodically polarize the steel material, and an applied current is increased so that the polarization amount of the steel material determined from the steel material potential measured based on the reference electrode increases until the polarization amount of the steel material determined from the steel material potential measured based on the reference electrode reaches a predetermined value, and the steel material potential when each of the arbitrary multiple polarization amounts is measured based on the reference electrode; a fitting step of using the natural potential of the steel material, the natural potential of the counter electrode, and the electrical resistivity of the concrete structure as boundary conditions for the FEM analysis, changing the applied voltage at the location in the FEM analysis model where the corrosion current density of the steel material is estimated, and matching the model applied current at the location in the FEM analysis model where the corrosion current density of the steel material is estimated with the applied current when each polarization amount is obtained in the cathodic polarization step and the anodic polarization step; and The method includes a process of performing FEM analysis as a boundary condition, determining the model applied current when each polarization amount is obtained at the estimated location of the corrosion current density of the steel in the FEM analysis model, and calculating the model current density when each polarization amount is obtained in the FEM analysis model by dividing each model applied current when each polarization amount is obtained by the surface area of the estimated location of the corrosion current density of the steel in the concrete structure, and a process of creating a polarization curve using the steel potential when each polarization amount is obtained in the cathodic polarization process and the anodic polarization process, and the model current density when each polarization amount is obtained in the FEM analysis model, and determining the corrosion current density from the polarization curve by Tafel extrapolation.
斯かる構成によれば、ＦＥＭ解析を行うことで、アノード分極工程およびカソード分極工程における各分極量が得られる際のモデル電流密度を得ることができ、該モデル電流密度は、実際のコンクリート構造物における照合電極を設置した位置（鋼材の腐食電流密度の推定箇所）の電流密度の推定値となる。これにより、斯かるモデル電流密度と、カソード分極工程およびアノード分極工程における各分極量が得られる際の鋼材電位とに基づいて分極曲線を作成し、ターフェル外挿法によって分極曲線から腐食電流密度を求めることで、実際のコンクリート構造物における照合電極を設置した位置（鋼材の腐食電流密度の推定箇所）の腐食電流密度を比較的正確に推定することができる。 According to this configuration, by performing FEM analysis, a model current density can be obtained when each polarization amount in the anodic polarization process and the cathodic polarization process is obtained, and the model current density is an estimate of the current density at the position where the reference electrode is installed in the actual concrete structure (the location where the corrosion current density of the steel is estimated). As a result, a polarization curve is created based on the model current density and the steel potential when each polarization amount in the cathodic polarization process and the anodic polarization process is obtained, and the corrosion current density is obtained from the polarization curve by Tafel extrapolation, so that the corrosion current density at the position where the reference electrode is installed in the actual concrete structure (the location where the corrosion current density of the steel is estimated) can be estimated relatively accurately.
本発明に係る鋼材の劣化推定方法は、上記の腐食電流密度の推定方法で求められる腐食電流密度に基づいて鋼材の腐食速度を算出する工程と、前記腐食速度に基づいて所定の材齢のコンクリート構造物に埋設された鋼材の減少量を算出する工程とを備える。 The method for estimating the deterioration of steel according to the present invention includes a step of calculating the corrosion rate of the steel based on the corrosion current density obtained by the above-mentioned corrosion current density estimation method, and a step of calculating the amount of reduction in the steel embedded in a concrete structure of a specified material age based on the corrosion rate.
斯かる構成によれば、腐食電流密度の推定方法で求められる腐食電流密度に基づいて鋼材の腐食速度を算出することで、比較的正確な鋼材の腐食速度を得ることができる。このため、所定の材齢のコンクリート構造物に埋設された鋼材の減少量を比較的正確に推定することができる。 With this configuration, a relatively accurate corrosion rate of steel can be obtained by calculating the corrosion rate of the steel based on the corrosion current density obtained by the corrosion current density estimation method. Therefore, the reduction amount of steel embedded in a concrete structure of a specified material age can be estimated relatively accurately.
本発明に係る防食電流の制御方法は、上記の腐食電流密度の推定方法で求められる腐食電流密度に基づいて鋼材に供給する防食電流を制御する。 The method for controlling the corrosion protection current according to the present invention controls the corrosion protection current supplied to the steel material based on the corrosion current density obtained by the above-mentioned corrosion current density estimation method.
斯かる構成によれば、上記の腐食電流密度の推定方法によって、照合電極を設置した位置（鋼材における腐食電流密度の推定箇所）における腐食電流密度を比較的正確に推定することができるため、該腐食電流密度に基づいて鋼材に供給する防食電流を制御することで、より効果的な電気防食を行うことができる。 With this configuration, the corrosion current density at the position where the reference electrode is installed (the location where the corrosion current density in the steel material is estimated) can be estimated relatively accurately by the above-mentioned corrosion current density estimation method, and more effective cathodic protection can be performed by controlling the anticorrosive current supplied to the steel material based on the corrosion current density.
本発明によれば、コンクリート構造物に埋設された鋼材の腐食電流密度を、ターフェル外挿法を用いて比較的正確に推定することができる。 According to the present invention, the corrosion current density of steel embedded in a concrete structure can be estimated relatively accurately using the Tafel extrapolation method.
以下、本発明の一実施形態について、図１を参照しながら説明する。
なお、以下の図面において同一または相当する部分には同一の参照符号を付しその説明は繰り返さない。
Hereinafter, one embodiment of the present invention will be described with reference to FIG.
In the following drawings, the same or corresponding parts are given the same reference symbols and their descriptions will not be repeated.
本実施形態に係る腐食電流密度の推定方法は、図１に示すように、コンクリート構造物Ｘに埋設された鋼材（鉄筋等）Ｘ１の腐食電流密度を推定するものである。本実施形態に係る腐食電流密度の推定方法では、照合電極１と対極２とが使用される。また、本実施形態に係る腐食電流密度の推定方法では、照合電極１と鋼材Ｘ１とに電気的に連結されるマルチメーター３と、対極２と鋼材Ｘ１とに電気的に連結される電源装置４とが使用される。 As shown in FIG. 1, the corrosion current density estimation method according to this embodiment estimates the corrosion current density of steel material (rebar, etc.) X1 embedded in a concrete structure X. In the corrosion current density estimation method according to this embodiment, a reference electrode 1 and a counter electrode 2 are used. In addition, the corrosion current density estimation method according to this embodiment uses a multimeter 3 electrically connected to the reference electrode 1 and the steel material X1, and a power supply device 4 electrically connected to the counter electrode 2 and the steel material X1.
照合電極１は、鋼材Ｘ１の電位を測定する際の基準となるものである。具体的には、照合電極１と鋼材Ｘ１との間の電位差が鋼材の電位として測定される。照合電極１としては、一般的に用いられるものを使用することができ、例えば、飽和銀塩化銀照合電極、銅硫酸銅照合電極、鉛照合電極、または二酸化マンガン照合電極等を用いることができる。 The reference electrode 1 serves as a reference for measuring the potential of the steel material X1. Specifically, the potential difference between the reference electrode 1 and the steel material X1 is measured as the potential of the steel material. As the reference electrode 1, a commonly used electrode can be used, such as a saturated silver-silver chloride reference electrode, a copper-copper sulfate reference electrode, a lead reference electrode, or a manganese dioxide reference electrode.
対極２は、鋼材Ｘ１に印加電流を供給し、鋼材Ｘ１を分極させるように構成されている。対極２としては、特に限定されるものではなく、例えば、環状、板状、棒状、または、帯状に形成されたものを用いることができる。対極２を形成する素材としては、特に限定されるものではなく、チタン製のもの等を用いることができる。 The counter electrode 2 is configured to supply an applied current to the steel material X1 to polarize the steel material X1. The counter electrode 2 is not particularly limited, and may be formed, for example, in a ring, plate, rod, or strip shape. The material from which the counter electrode 2 is formed is not particularly limited, and may be made of titanium, etc.
マルチメーター３は、照合電極１に基づいて測定される鋼材Ｘ１の自然電位、直流電位（Ｉｎｓｔａｎｔｏｆｆ電位：通電時の真の鋼材電位）、直流分極量を受信して表示するように構成されている。 The multimeter 3 is configured to receive and display the natural potential, DC potential (instant off potential: the true steel potential when current is applied), and DC polarization of the steel material X1 measured based on the reference electrode 1.
電源装置４は、対極２から鋼材Ｘ１へ向けてコンクリート構造物Ｘ内を直流電流が流れるように、対極２と鋼材Ｘ１との間に電位差を生じさせるように（電圧を調節可能に）構成されている。 The power supply unit 4 is configured to generate a potential difference between the counter electrode 2 and the steel material X1 (to adjust the voltage) so that a direct current flows from the counter electrode 2 to the steel material X1 within the concrete structure X.
＜対極および照合電極の設置＞
本実施形態に係る腐食電流密度の推定方法では、鋼材Ｘ１における腐食電流密度を推定する箇所に達するようにコンクリート構造物Ｘに形成された削孔Ｘ２内に電解質（具体的には、導電性ゲル等）を充填し、更に該削孔内に照合電極１を挿入する。そして、該削孔Ｘ２内で照合電極１と鋼材Ｘ１とを接触させる（具体的には、電解質を介して電気的に接触させる）。また、照合電極１と鋼材Ｘ１とを電気的に（具体的には、マルチメーター３を介して電気的に）接続する。
<Installation of counter and reference electrodes>
In the method for estimating corrosion current density according to the present embodiment, an electrolyte (specifically, a conductive gel or the like) is filled into a drilled hole X2 formed in a concrete structure X so as to reach a location in a steel material X1 where the corrosion current density is to be estimated, and a reference electrode 1 is inserted into the drilled hole. Then, the reference electrode 1 and the steel material X1 are brought into contact with each other in the drilled hole X2 (specifically, electrically contacted via the electrolyte). The reference electrode 1 and the steel material X1 are also electrically connected (specifically, electrically connected via a multimeter 3).
また、対極２と鋼材Ｘ１とを電源装置４を介して電気的に接続する。具体的には、コンクリート構造物Ｘの表面に接するように対極２を設置すると共に、該対極２と鋼材Ｘ１とを電源装置４を介して電気的に接続する。また、コンクリート構造物Ｘの削孔Ｘ２の近傍で削孔Ｘ２を囲むように対極２を設置する。本実施形態では、対極２は、環状に形成されているため、対極２の内側に削孔Ｘ２が位置するように、対極２を設置する。 The counter electrode 2 and the steel material X1 are electrically connected via a power supply 4. Specifically, the counter electrode 2 is installed so as to be in contact with the surface of the concrete structure X, and the counter electrode 2 and the steel material X1 are electrically connected via a power supply 4. The counter electrode 2 is installed so as to surround the drilled hole X2 in the concrete structure X near the drilled hole X2. In this embodiment, the counter electrode 2 is formed in a ring shape, and therefore the counter electrode 2 is installed so that the drilled hole X2 is located inside the counter electrode 2.
本実施形態に係る腐食電流密度の推定方法では、対極２の自然電位と鋼材Ｘ１の自然電圧とを測定することが好ましい。対極２の自然電位を測定する際には、対極２と照合電極１とをマルチメーター３に接続し、電流の印加前に、照合電極１を基準に自然電位を測定する。また、鋼材Ｘ１の自然電圧を測定する際には、鋼材Ｘ１と照合電極１とをマルチメーター３に接続し、電流の印加前に、照合電極１を基準に自然電位を測定する。 In the corrosion current density estimation method according to this embodiment, it is preferable to measure the natural potential of the counter electrode 2 and the natural voltage of the steel material X1. When measuring the natural potential of the counter electrode 2, the counter electrode 2 and the reference electrode 1 are connected to a multimeter 3, and the natural potential is measured with reference to the reference electrode 1 before applying a current. When measuring the natural voltage of the steel material X1, the steel material X1 and the reference electrode 1 are connected to a multimeter 3, and the natural potential is measured with reference to the reference electrode 1 before applying a current.
本実施形態に係る腐食電流密度の推定方法では、コンクリート構造物の電気抵抗率を測定することが好ましい。コンクリート構造物の電気抵抗率は、４点電極法（４プローブ法）により測定することができる。 In the method for estimating corrosion current density according to this embodiment, it is preferable to measure the electrical resistivity of the concrete structure. The electrical resistivity of the concrete structure can be measured by the four-point electrode method (four-probe method).
＜カソード分極工程＞
本実施形態に係る腐食電流密度の推定方法では、対極２から鋼材Ｘ１に印加電流を供給していない状態から鋼材Ｘ１に印加電流を供給して鋼材Ｘ１をカソード分極させるカソード分極工程を行う。該カソード分極工程では、照合電極１に基づいて測定される鋼材電位から求まる鋼材Ｘ１の分極量が所定値となるまで分極量が増加するように鋼材Ｘ１へ供給する印加電流を所定の掃印速度で増加させ、任意の複数の分極量のそれぞれが得られる際の電流値、電圧値および鋼材電位を照合電極１に基づいて測定する。なお、カソード分極工程を後述のアノード分極工程後に行う場合には、アノード分極工程後、５分間以上電流印加を停止させ、再度自然電位からカソード分極させる。
<Cathode polarization process>
In the method for estimating a corrosion current density according to this embodiment, a cathodic polarization step is performed in which a current is supplied to the steel material X1 from a state in which no current is supplied to the steel material X1 from the counter electrode 2, thereby cathodically polarizing the steel material X1. In the cathodic polarization step, the current supplied to the steel material X1 is increased at a predetermined sweep speed so that the polarization amount of the steel material X1 determined from the steel material potential measured based on the reference electrode 1 increases until the polarization amount becomes a predetermined value, and the current value, voltage value and steel material potential when each of a plurality of arbitrary polarization amounts is obtained are measured based on the reference electrode 1. Note that, when the cathodic polarization step is performed after the anodic polarization step described below, the current application is stopped for 5 minutes or more after the anodic polarization step, and the steel material is cathodically polarized again from the natural potential.
＜アノード分極工程＞
本実施形態に係る腐食電流密度の推定方法では、対極２から鋼材Ｘ１に印加電流を供給していない状態から鋼材Ｘ１に印加電流を供給して鋼材Ｘ１をアノード分極させるアノード分極工程を行う。該アノード分極工程では、照合電極１に基づいて測定される鋼材電位から求まる鋼材Ｘ１の分極量が所定値となるまで分極量が増加するように鋼材Ｘ１へ供給する印加電流を所定の掃印速度で増加させ、任意の複数の分極量のそれぞれが得られる際の電流値、電圧値および鋼材電位を照合電極１に基づいて測定する。なお、アノード分極工程をカソード分極工程後に行う場合には、カソード分極工程後、５分間以上電流印加を停止させ、再度自然電位からアノード分極させる。
<Anode polarization process>
In the method for estimating a corrosion current density according to this embodiment, an anodic polarization step is performed in which an applied current is supplied to the steel material X1 from a state in which no applied current is supplied to the steel material X1 from the counter electrode 2, thereby anodically polarizing the steel material X1. In the anodic polarization step, the applied current supplied to the steel material X1 is increased at a predetermined sweep speed so that the polarization amount of the steel material X1 determined from the steel material potential measured based on the reference electrode 1 increases until it reaches a predetermined value, and the current value, voltage value and steel material potential when each of a plurality of arbitrary polarization amounts is obtained are measured based on the reference electrode 1. Note that, when the anodic polarization step is performed after the cathodic polarization step, the application of current is stopped for 5 minutes or more after the cathodic polarization step, and the steel material is again anodically polarized from the natural potential.
＜ＦＥＭ解析モデルを作成する工程＞
本実施形態に係る腐食電流密度の推定方法では、ＦＥＭ解析を用いてコンクリート構造物のＦＥＭ解析モデルを作成する。該ＦＥＭ解析モデルの作成は、コンクリート構造物Ｘの配筋状況（具体的には、鋼材の配置間隔、コンクリートのかぶり厚み、鋼材径）を境界条件として行うことができる。配筋状況は、電磁波レーダー法並びに電磁誘導法を用いて測定したものであってもよく、コンクリート構造物Ｘの設計情報（設計図等）から得たものであってもよい。
<Process for creating FEM analysis model>
In the method for estimating corrosion current density according to the present embodiment, an FEM analysis model of a concrete structure is created using FEM analysis. The FEM analysis model can be created using the reinforcement state of the concrete structure X (specifically, the interval between steel members, the concrete cover thickness, and the diameter of the steel members) as boundary conditions. The reinforcement state may be measured using an electromagnetic radar method and an electromagnetic induction method, or may be obtained from design information (design drawings, etc.) of the concrete structure X.
＜フィッティング工程＞
本実施形態に係る腐食電流密度の推定方法では、鋼材Ｘ１の自然電位と対極２の自然電位とコンクリート構造物Ｘの電気抵抗率とをＦＥＭ解析の境界条件として用いると共に、ＦＥＭ解析モデルにおける鋼材Ｘ１の腐食電流密度の推定箇所の印加電圧を変更し、ＦＥＭ解析モデルにおける鋼材Ｘ１の腐食電流密度の推定箇所のモデル印加電流をカソード分極工程およびアノード分極工程における各分極量が得られた際の印加電流と一致させる工程を行う（フィッティング工程）。
<Fitting process>
In the method for estimating the corrosion current density according to this embodiment, the natural potential of the steel material X1, the natural potential of the counter electrode 2, and the electrical resistivity of the concrete structure X are used as boundary conditions for the FEM analysis, and a process is performed in which the applied voltage at the estimation point of the corrosion current density of the steel material X1 in the FEM analysis model is changed and the model applied current at the estimation point of the corrosion current density of the steel material X1 in the FEM analysis model is made to match the applied current when each polarization amount was obtained in the cathodic polarization process and the anodic polarization process (fitting process).
＜モデル電流密度を算出する工程＞
本実施形態に係る腐食電流密度の推定方法では、フィッティング工程後、カソード分極工程およびアノード分極工程における各分極量が得られる際の印加電流と鋼材Ｘ１の自然電位と対極２の自然電位とコンクリート構造物Ｘの電気抵抗率とを境界条件としてＦＥＭ解析を行い、ＦＥＭ解析モデルにおける鋼材Ｘ１の腐食電流密度の推定箇所で各分極量が得られる際のモデル印加電流を求めると共に、各分極量が得られる際のモデル印加電流のそれぞれをコンクリート構造物における鋼材の腐食電流密度の推定箇所の表面積で除することでＦＥＭ解析モデルにおける各分極量が得られる際のモデル電流密度を算出する工程を行う。
<Step of calculating model current density>
In the method for estimating the corrosion current density according to this embodiment, after the fitting step, an FEM analysis is performed using the applied current when each polarization amount is obtained in the cathodic polarization step and the anodic polarization step, the natural potential of the steel material X1, the natural potential of the counter electrode 2, and the electrical resistivity of the concrete structure X as boundary conditions, to determine the model applied current when each polarization amount is obtained at the estimation point of the corrosion current density of the steel material X1 in the FEM analysis model, and to calculate the model current density when each polarization amount is obtained in the FEM analysis model by dividing each of the model applied currents when each polarization amount is obtained by the surface area of the estimation point of the corrosion current density of the steel material in the concrete structure.
＜腐食電流密度（推定値）を求める工程＞
本実施形態に係る腐食電流密度の推定方法では、カソード分極工程およびアノード分極工程における各分極量が得られる際の鋼材電位と、ＦＥＭ解析モデルにおける各分極量が得られる際のモデル電流密度とを用いて分極曲線を作成し、該分極曲線からターフェル外挿法により腐食電流密度を求める工程を行う。具体的には、各分極曲線におけるターフェル勾配およびターフェル直線を求め、ターフェル直線同士の交点における腐食電流密度を求める。斯かる腐食電流密度は、照合電極１を設置した位置（鋼材Ｘ１における腐食電流密度の推定箇所）における腐食電流密度の推定値となる。
<Step of determining corrosion current density (estimated value)>
In the method for estimating the corrosion current density according to the present embodiment, a polarization curve is created using the steel material potential when each polarization amount is obtained in the cathodic polarization process and the anodic polarization process, and the model current density when each polarization amount is obtained in the FEM analysis model, and the corrosion current density is calculated from the polarization curve by Tafel extrapolation. Specifically, the Tafel gradient and Tafel line are calculated for each polarization curve, and the corrosion current density at the intersection of the Tafel lines is calculated. Such a corrosion current density is an estimated value of the corrosion current density at the position where the reference electrode 1 is installed (the location where the corrosion current density is estimated in the steel material X1).
＜鋼材の劣化推定方法＞
上記のように構成される腐食電流密度の推定方法で得られる腐食電流密度は、鋼材Ｘ１の劣化状態を推定する鋼材の劣化推定方法で用いることができる。
<Method for estimating steel deterioration>
The corrosion current density obtained by the corrosion current density estimation method configured as described above can be used in a steel degradation estimation method for estimating the degradation state of the steel material X1.
＜腐食速度（推定値）を算出する工程＞
本実施形態に係る鋼材の劣化推定方法では、上記の腐食電流密度の推定方法で得られる腐食電流密度（推定値）に基づいて鋼材Ｘ１の腐食速度の推定値を算出する。具体的には、鋼材Ｘ１の腐食速度（推定値）は、ファラデーの第二法則に基づいて、上記の腐食電流密度の推定方法で得られる腐食電流密度（推定値）から算出することができる。該腐食速度（推定値）は、鋼材Ｘ１の単位表面積において単位時間当たりに減少する鋼材Ｘ１の質量の推定値である。
<Step of calculating corrosion rate (estimated value)>
In the method for estimating deterioration of a steel material according to this embodiment, an estimated value of the corrosion rate of the steel material X1 is calculated based on the corrosion current density (estimated value) obtained by the above-mentioned method for estimating the corrosion current density. Specifically, the corrosion rate (estimated value) of the steel material X1 can be calculated from the corrosion current density (estimated value) obtained by the above-mentioned method for estimating the corrosion current density based on Faraday's second law. The corrosion rate (estimated value) is an estimated value of the mass of the steel material X1 that decreases per unit time in a unit surface area of the steel material X1.
＜鋼材の減少量（推定値）を算出する工程＞
本実施形態に係る鋼材の劣化推定方法では、上記の腐食速度（推定値）に基づいて所定の材齢のコンクリート構造物Ｘに埋設された鋼材Ｘ１の減少量の推定値を算出する。具体的には、鋼材Ｘ１における照合電極１を設置した位置（鋼材Ｘ１における腐食電流密度の推定箇所）の表面積とコンクリート構造物Ｘの材齢と腐食速度（推定値）とに基づいて鋼材Ｘ１の減少量の推定値を算出する。
<Step of calculating the amount of reduction (estimated value) of steel material>
In the method for estimating deterioration of steel material according to this embodiment, an estimated value of the reduction amount of steel material X1 embedded in a concrete structure X of a predetermined material age is calculated based on the above-mentioned corrosion rate (estimated value). Specifically, the estimated value of the reduction amount of steel material X1 is calculated based on the surface area of the position where the reference electrode 1 is installed in the steel material X1 (the location where the corrosion current density in the steel material X1 is estimated) and the material age and corrosion rate (estimated value) of the concrete structure X.
＜防食電流の制御方法＞
上記のように構成される腐食電流密度の推定方法で得られる腐食電流密度（推定値）は、鋼材Ｘ１の電気防食を行う際に、防食電流を制御するために用いることができる。具体的には、上記のように構成される腐食電流密度の推定方法で得られる腐食電流密度（推定値）に対応した電流密度で防食電流を鋼材Ｘ１に供給することで、鋼材Ｘ１に流れる腐食電流が消失または低減し、これによって鋼材Ｘ１の腐食が抑制される。このため、上記の腐食電流密度の推定方法で得られる腐食電流密度（推定値）に対応した電流密度となるように防食電流の供給を制御することで、効果的な電気防食を行うことができる。
<Method of controlling anticorrosive current>
The corrosion current density (estimated value) obtained by the corrosion current density estimation method configured as described above can be used to control the protective current when performing electrochemical protection of the steel material X1. Specifically, by supplying the steel material X1 with a protective current at a current density corresponding to the corrosion current density (estimated value) obtained by the corrosion current density estimation method configured as described above, the corrosion current flowing through the steel material X1 disappears or is reduced, thereby suppressing corrosion of the steel material X1. Therefore, by controlling the supply of protective current so as to obtain a current density corresponding to the corrosion current density (estimated value) obtained by the corrosion current density estimation method described above, effective electrochemical protection can be performed.
以上のように、本発明に係る腐食電流密度の推定方法、鋼材の劣化推定方法、および、防食電流の制御方法は、コンクリート構造物に埋設された鋼材の腐食電流密度を、ターフェル外挿法を用いて比較的正確に推定することができる。 As described above, the corrosion current density estimation method, steel deterioration estimation method, and anticorrosive current control method according to the present invention can estimate the corrosion current density of steel buried in a concrete structure relatively accurately using the Tafel extrapolation method.
即ち、ＦＥＭ解析を行うことで、アノード分極工程およびカソード分極工程における各分極量が得られる際のモデル電流密度を得ることができ、該モデル電流密度は、実際のコンクリート構造物Ｘにおける照合電極１を設置した位置（鋼材Ｘ１の腐食電流密度の推定箇所）の電流密度の推定値となる。これにより、斯かるモデル電流密度と、カソード分極工程およびアノード分極工程における各分極量が得られる際の鋼材Ｘ１の電位とに基づいて分極曲線を作成し、ターフェル外挿法によって分極曲線から腐食電流密度を求めることで、実際のコンクリート構造物Ｘにおける照合電極１を設置した位置（鋼材Ｘ１の腐食電流密度の推定箇所）の腐食電流密度を比較的正確に推定することができる。 That is, by performing FEM analysis, a model current density can be obtained when each polarization amount in the anodic polarization process and the cathodic polarization process is obtained, and the model current density is an estimate of the current density at the position where the reference electrode 1 is installed in the actual concrete structure X (the location where the corrosion current density of the steel material X1 is estimated). As a result, a polarization curve is created based on the model current density and the potential of the steel material X1 when each polarization amount in the cathodic polarization process and the anodic polarization process is obtained, and the corrosion current density is obtained from the polarization curve by Tafel extrapolation, so that the corrosion current density at the position where the reference electrode 1 is installed in the actual concrete structure X (the location where the corrosion current density of the steel material X1 is estimated) can be estimated relatively accurately.
また、上記の腐食電流密度の推定方法で求められる腐食電流密度に基づいて鋼材Ｘ１の腐食速度を算出することで、比較的正確な鋼材Ｘ１の腐食速度を得ることができる。このため、所定の材齢のコンクリート構造物Ｘに埋設された鋼材Ｘ１の減少量を比較的正確に推定することができる。 In addition, by calculating the corrosion rate of the steel material X1 based on the corrosion current density obtained by the above-mentioned corrosion current density estimation method, a relatively accurate corrosion rate of the steel material X1 can be obtained. Therefore, the amount of reduction in the steel material X1 embedded in the concrete structure X of a specified material age can be estimated relatively accurately.
また、上記の腐食電流密度の推定方法によって、照合電極１を設置した位置（鋼材Ｘ１における腐食電流密度の推定箇所）における腐食電流密度を比較的正確に推定することができるため、該腐食電流密度に基づいて鋼材Ｘ１に供給する防食電流を制御することで、より効果的な電気防食を行うことができる。 In addition, the above-mentioned corrosion current density estimation method allows for relatively accurate estimation of the corrosion current density at the position where the reference electrode 1 is installed (the location where the corrosion current density in the steel material X1 is estimated), so that more effective electrical protection can be achieved by controlling the anticorrosive current supplied to the steel material X1 based on the corrosion current density.
なお、本発明に係る腐食電流密度の推定方法、鋼材の劣化推定方法、および、防食電流の制御方法は、上記実施形態に限定されるものではなく、本発明の要旨を逸脱しない範囲で種々の変更が可能である。また、上記した複数の実施形態の構成や方法等を任意に採用して組み合わせてもよく（１つの実施形態に係る構成や方法等を他の実施形態に係る構成や方法等に適用してもよく）、さらに、下記する各種の変更例に係る構成や方法等を任意に選択して、上記した実施形態に係る構成や方法等に採用してもよいことは勿論である。 The corrosion current density estimation method, steel deterioration estimation method, and anticorrosion current control method according to the present invention are not limited to the above-mentioned embodiments, and various modifications are possible without departing from the gist of the present invention. In addition, the configurations and methods of the above-mentioned embodiments may be arbitrarily adopted and combined (the configurations and methods of one embodiment may be applied to the configurations and methods of other embodiments), and further, the configurations and methods of the various modified examples described below may be arbitrarily selected and adopted in the configurations and methods of the above-mentioned embodiments.
例えば、上記実施形態では、対極２が環状に形成され、内側に照合電極１が配置されるように構成されているが、これに限定されるものではなく、例えば、複数の対極２を照合電極１の周囲に配置するように構成されてもよい。 For example, in the above embodiment, the counter electrode 2 is formed in a ring shape and the reference electrode 1 is arranged inside, but this is not limited to this, and for example, multiple counter electrodes 2 may be arranged around the reference electrode 1.
また、上記実施形態において、カソード分極工程を行った後、アノード分極工程を行ってもよく、アノード分極工程を行った後、カソード分極工程を行ってもよい。 In addition, in the above embodiment, the anode polarization process may be performed after the cathode polarization process, or the cathode polarization process may be performed after the anode polarization process.
次に、実施例および比較例を挙げて本発明についてさらに具体的に説明する。 Next, the present invention will be explained in more detail with reference to examples and comparative examples.
＜使用材料＞
・セメント：普通ポルトランドセメント（密度３．１５ｇ／ｃｍ３，比表面積３３００ｃｍ２／ｇ、住友大阪セメント社製）
・鋼材：主筋Ｄ３２、配力筋Ｄ１６
・細骨材：茨城県産陸砂（表乾密度２．６０ｇ／ｃｍ３）と栃木県産砕砂（表乾密度２．６８ｇ／ｃｍ３）の混合砂
・粗骨材：茨城県産砕石（表乾密度２．６５ｇ／ｃｍ３）と栃木県産石灰砕石（表乾密度２．７０ｇ／ｃｍ３）の混合砕石
<Materials used>
Cement: Ordinary Portland cement (density 3.15 g/cm 3 , specific surface area 3300 cm 2 /g, manufactured by Sumitomo Osaka Cement Co., Ltd.)
Steel: Main bar D32, distribution bar D16
Fine aggregate: a mixture of land sand produced in Ibaraki Prefecture (surface dry density 2.60 g/cm 3 ) and crushed sand produced in Tochigi Prefecture (surface dry density 2.68 g/cm 3 ). Coarse aggregate: a mixture of crushed stone produced in Ibaraki Prefecture (surface dry density 2.65 g/cm 3 ) and limestone crushed stone produced in Tochigi Prefecture (surface dry density 2.70 g/cm 3 ).
＜コンクリート構造物の作製＞
上記の材料を用いて下記表１の配合で、上記実施形態と同様のコンクリート構造物Ｘを作成した。コンクリート構造物Ｘのサイズは、９０ｃｍ×７０ｃｍ×２０ｃｍとした。また、コンクリート構造物Ｘに埋設された鋼材Ｘ１は、主筋Ｄ３２を８ｃｍピッチ、配力筋Ｄ１６を３３．５ｃｍピッチ、かぶり５ｃｍとした。
<Creating concrete structures>
Using the above materials, a concrete structure X similar to the above embodiment was created with the mix ratio shown in Table 1 below. The size of the concrete structure X was 90 cm x 70 cm x 20 cm. The steel material X1 embedded in the concrete structure X had main reinforcement D32 at an 8 cm pitch, distribution reinforcement D16 at a 33.5 cm pitch, and a cover of 5 cm.
＜コンクリート構造物の配筋状況の測定＞
上記のコンクリート構造物Ｘを脱型して３ヶ月経過した時点（材齢３ヶ月）で、コンクリート構造物Ｘの配筋状況を上記実施形態の方法で測定した。
<Measurement of reinforcement in concrete structures>
Three months after the concrete structure X was demolded (material age: 3 months), the reinforcement state of the concrete structure X was measured by the method of the above embodiment.
＜コンクリート構造物の電気抵抗率の測定＞
材齢３ヶ月のコンクリート構造物Ｘの電気抵抗率を４点電極法（４プローブ法）で測定した。コンクリート構造物の電気抵抗率は、８．０７ｋΩ・ｃｍであった。
<Measurement of electrical resistivity of concrete structures>
The electrical resistivity of the concrete structure X, which was 3 months old, was measured by the four-point electrode method (four-probe method). The electrical resistivity of the concrete structure X was 8.07 kΩ·cm.
＜照合電極と対極の設置＞
上記実施形態と同様に、鋼材Ｘ１における腐食電流密度の推定箇所でコンクリート構造物Ｘを削孔し、鋼材Ｘ１に達する削孔Ｘ２（φ３０ｍｍ）を形成した。そして、斯かる削孔Ｘ２内に露出した鋼材Ｘ１の周囲に導電性のクリームを塗布すると共に、上記実施形態と同様の照合電極１を削孔Ｘ２に挿入し、該照合電極１を鋼材Ｘ１と接触させた状態で設置した。
また、上記実施形態のように、環状の対極２（チタンメッシュ対極）の内側に削孔Ｘ２が位置するように、対極２をコンクリート構造物Ｘの表面に設置した。
そして、鋼材Ｘ１と対極２とを電源装置４（北斗電工社製 ポテンショ／ガルバノスタット）を介して電気的に接続し、鋼材Ｘ１と照合電極１とをマルチメーター３（製品名：ＴＹ７２０、横河計測社製）を介して電気的に接続した。
<Installation of reference electrode and counter electrode>
As in the above embodiment, the concrete structure X was drilled at the location where the corrosion current density of the steel material X1 was estimated, and a drilled hole X2 (φ30 mm) was formed that reached the steel material X1. Then, a conductive cream was applied to the periphery of the steel material X1 exposed in the drilled hole X2, and the reference electrode 1 similar to the above embodiment was inserted into the drilled hole X2 and placed in a state where the reference electrode 1 was in contact with the steel material X1.
As in the above embodiment, the counter electrode 2 (titanium mesh counter electrode) was placed on the surface of the concrete structure X so that the drilled hole X2 was located inside the annular counter electrode 2 .
Then, the steel material X1 and the counter electrode 2 were electrically connected via a power supply 4 (potentio/galvanostat manufactured by Hokuto Denko Corporation), and the steel material X1 and the reference electrode 1 were electrically connected via a multimeter 3 (product name: TY720, manufactured by Yokogawa Measurement Co., Ltd.).
＜対極２及び鋼材Ｘ１における自然電位及び自然電圧の測定＞
上記実施形態と同様の方法で、対極２および鋼材Ｘ１の自然電位、対極２および鋼材Ｘ１の自然電圧を測定した。測定結果については、下記表３に示す。
<Measurement of natural potential and natural voltage of counter electrode 2 and steel material X1>
The natural potential of the counter electrode 2 and the steel material X1, and the natural voltage of the counter electrode 2 and the steel material X1 were measured in the same manner as in the above embodiment. The measurement results are shown in Table 3 below.
＜カソード分極工程＞
上記実施形態と同様の方法でカソード分極工程を行った。具体的には、対極２から鋼材Ｘ１へ印加電流を供給していない状態（印加電流が０ｍＡの状態）から２００ｍＶまで分極量が増加するように掃印速度４０ｍＶ／ｍｉｎで印加電流を増加させ、各分極量が得られた際の鋼材電位を照合電極に基づいて測定した。分極量、印加電圧、印加電流、および、鋼材電位の測定結果については、下記表２に示す。
<Cathode polarization process>
The cathodic polarization step was carried out in the same manner as in the above embodiment. Specifically, the applied current was increased at a sweep speed of 40 mV/min so that the polarization amount increased from a state where no current was supplied from the counter electrode 2 to the steel material X1 (a state where the applied current was 0 mA) to 200 mV, and the steel material potential when each polarization amount was obtained was measured based on the reference electrode. The measurement results of the polarization amount, applied voltage, applied current, and steel material potential are shown in Table 2 below.
＜アノード分極工程＞
上記のカソード分極工程後、５分以上の時間を空けて、上記実施形態と同様の方法でアノード分極工程を行った。具体的には、対極２から鋼材Ｘ１へ印加電流を供給していない状態（印加電流が０ｍＡの状態）から２００ｍＶまで分極量が増加するように掃印速度４０ｍＶ／ｍｉｎで印加電流を増加させ、各分極量が得られた際の鋼材電位を照合電極に基づいて測定した。分極量、印加電圧、印加電流、および、鋼材電位の測定結果については、下記表２に示す。
<Anode polarization process>
After the above-mentioned cathodic polarization step, an anodic polarization step was performed in the same manner as in the above-mentioned embodiment after a time of 5 minutes or more. Specifically, the applied current was increased at a sweep speed of 40 mV/min so that the polarization amount increased from a state where no applied current was supplied from the counter electrode 2 to the steel material X1 (a state where the applied current was 0 mA) to 200 mV, and the steel material potential when each polarization amount was obtained was measured based on the reference electrode. The measurement results of the polarization amount, applied voltage, applied current, and steel material potential are shown in Table 2 below.
＜ＦＥＭ解析モデルを作成する工程＞
上記で作成したコンクリート構造物Ｘの情報に基づいて、ＦＥＭ解析モデルを作成した。ＦＥＭ解析モデルの大きさは、照合電極１を設置した位置から３００ｍｍ以上の大きさとした。
<Process for creating FEM analysis model>
An FEM analysis model was created based on the above-created information of the concrete structure X. The size of the FEM analysis model was set to be 300 mm or more from the position where the reference electrode 1 was installed.
＜フィッティング工程＞
上記実施形態と同様に、フィッティング工程を行い、ＦＥＭ解析モデルにおける鋼材Ｘ１の腐食電流密度の推定箇所のモデル印加電流をカソード分極工程およびアノード分極工程における各分極量が得られた際の印加電流と一致させる。
<Fitting process>
As in the above embodiment, a fitting process is performed to match the model applied current at the location in the FEM analysis model where the corrosion current density of steel X1 is estimated with the applied current when each polarization amount is obtained in the cathodic polarization process and the anodic polarization process.
＜モデル電流密度を算出する工程＞
フィッティング工程後、カソード分極工程およびアノード分極工程における各分極量が得られた際の印加電流と鋼材Ｘ１の自然電位と対極２の自然電位とコンクリート構造物Ｘの電気抵抗率とを境界条件としてＦＥＭ解析を行い、ＦＥＭ解析モデルにおける鋼材Ｘ１の腐食電流密度の推定箇所で各分極量が得られる際のモデル印加電流を求めた。
また、該各分極量が得られる際のモデル印加電流それぞれをコンクリート構造物Ｘにおける鋼材Ｘ１の腐食電流密度の推定箇所の表面積で除することでＦＥＭ解析モデルにおける各分極量が得られる際のモデル電流密度を算出した。
鋼材Ｘ１における腐食電流密度の推定箇所の表面積、モデル印加電流、モデル電流密度については、下記表４に示す。
<Step of calculating model current density>
After the fitting process, an FEM analysis was performed using the applied current when each polarization amount was obtained in the cathodic polarization process and the anodic polarization process, the natural potential of the steel material X1, the natural potential of the counter electrode 2, and the electrical resistivity of the concrete structure X as boundary conditions, and a model applied current when each polarization amount was obtained at the estimated location of the corrosion current density of the steel material X1 in the FEM analysis model was determined.
In addition, the model applied current when each polarization amount was obtained was divided by the surface area of the estimated location of the corrosion current density of the steel material X1 in the concrete structure X to calculate the model current density when each polarization amount was obtained in the FEM analysis model.
The surface area, model applied current, and model current density of the location in steel material X1 where the corrosion current density is estimated are shown in Table 4 below.
＜腐食電流密度（推定値）を求める工程＞
カソード分極工程およびアノード分極工程における各分極量が得られた際の鋼材電位と、ＦＥＭ解析モデルにおける各分極量が得られる際のモデル電流密度とを用いてカソード分極の分極曲線とアノード分極の分極曲線とを作成した。
そして、各分極曲線からターフェル外挿法によりＦＥＭ解析モデルにおける腐食電流密度を求めた。具体的には、各分極曲線におけるターフェル勾配およびターフェル直線を求め、ターフェル直線同士の交点におけるモデル電流密度を腐食電流密度として求めた。
斯かる腐食電流密度は、実際のコンクリート構造物Ｘにおいて、照合電極１を設置した位置（鋼材Ｘ１における腐食電流密度の推定箇所）の腐食電流密度の推定値となる。
各分極曲線およびターフェル直線については、図２に示す。
また、腐食電流密度（推定値）については、下記表５に示す。
<Step of determining corrosion current density (estimated value)>
A polarization curve for cathodic polarization and a polarization curve for anodic polarization were created using the steel material potential when each polarization amount was obtained in the cathodic polarization process and the anodic polarization process, and the model current density when each polarization amount was obtained in the FEM analysis model.
Then, the corrosion current density in the FEM analysis model was calculated from each polarization curve by Tafel extrapolation. Specifically, the Tafel slope and Tafel line of each polarization curve were calculated, and the model current density at the intersection of the Tafel lines was calculated as the corrosion current density.
Such a corrosion current density is an estimated value of the corrosion current density at the position where the reference electrode 1 is installed in the actual concrete structure X (the location where the corrosion current density is estimated in the steel material X1).
The polarization curves and Tafel lines are shown in FIG.
The corrosion current density (estimated value) is shown in Table 5 below.
＜腐食速度（推定値）を算出する工程＞
ファラデーの第二法則に基づいて上記の腐食電流密度（推定値）から鋼材の腐食速度（推定値）を算出した。該腐食速度（推定値）は、鋼材Ｘ１の単位表面積において単位時間当たりに腐食する（減少する）鋼材Ｘ１の質量（推定値）である。
また、腐食速度（推定値）については、下記表５に示す。
<Step of calculating corrosion rate (estimated value)>
The corrosion rate (estimated value) of the steel material was calculated from the above corrosion current density (estimated value) based on Faraday's second law. The corrosion rate (estimated value) is the mass (estimated value) of the steel material X1 corroded (reduced) per unit time in a unit surface area of the steel material X1.
The corrosion rates (estimated values) are shown in Table 5 below.
＜鋼材の減少量（推定値）を算出する工程＞
上記の腐食速度（推定値）に基づいて、材齢３ヶ月のコンクリート構造物Ｘにおける鋼材Ｘ１の減少量の推定値を算出した。具体的には、鋼材Ｘ１における照合電極１を設置した位置（削孔Ｘ２に露出した部分）の表面積とコンクリート構造物Ｘの材齢と腐食速度（推定値）とに基づいて鋼材Ｘ１の減少量（推定値）を算出した。
鋼材Ｘ１の減少量（推定値）は下記表５に示す。
<Step of calculating the amount of reduction (estimated value) of steel material>
Based on the above corrosion rate (estimated value), an estimated value of the reduction in the steel material X1 in the 3-month-old concrete structure X was calculated. Specifically, the reduction in the steel material X1 (estimated value) was calculated based on the surface area of the position (exposed in the drilled hole X2) where the reference electrode 1 was installed in the steel material X1, the age of the concrete structure X, and the corrosion rate (estimated value).
The reduction amount (estimated value) of steel material X1 is shown in Table 5 below.
＜鋼材の減少量（実測値）の測定＞
コンクリート構造物Ｘを解体し、削孔Ｘ２内に露出した鋼材Ｘ１の質量を測定した。そして、該鋼材Ｘ１におけるコンクリート構造物Ｘを作製する前に測定した質量との差を算出し、鋼材Ｘ１の減少量（実測値）を得た。
鋼材Ｘ１の減少量（実測値）は下記表５に示す。
<Measurement of steel material loss (actual value)>
The concrete structure X was dismantled, and the mass of the steel material X1 exposed in the drilled hole X2 was measured. The difference between the mass of the steel material X1 measured before the concrete structure X was fabricated and the mass of the steel material X1 measured before the concrete structure X was fabricated was calculated to obtain the reduction amount (actual value) of the steel material X1.
The reduction amount (actual measured value) of steel material X1 is shown in Table 5 below.
＜まとめ＞
上記のように、カソード分極工程およびアノード分極工程で得られるデータを用いてＦＥＭ解析を行い、図２に示す分極曲線を作成し、ターフェル外挿法を用いることで、鋼材Ｘ１の腐食電流密度を推定することができる。
そして、斯かる腐食電流密度の推定値に基づいて算出される鋼材Ｘ１の腐食速度から、鋼材Ｘ１の減少量を推定することができる。ここで、表５を見ると、鋼材Ｘ１の減少量の推定値は、実測値と同等であることが認められる。つまり、本発明に係る腐食電流密度の推定方法によって、腐食電流密度を比較的正確に推定することができる。また、本発明に係る鋼材の劣化推定方法によって、鋼材の劣化（鋼材の減少量）を比較的正確に推定することができる。また、本発明に係る防食電流の制御方法によって、腐食電流密度の推定値に対応する防食電流を鋼材に供給することで、鋼材の電気防食を効果的に行うことができる。
<Summary>
As described above, the FEM analysis is performed using the data obtained in the cathodic polarization step and the anodic polarization step, the polarization curve shown in FIG. 2 is created, and the corrosion current density of the steel material X1 can be estimated by using the Tafel extrapolation method.
The amount of reduction in steel material X1 can be estimated from the corrosion rate of steel material X1 calculated based on the estimated value of the corrosion current density. Here, looking at Table 5, it is recognized that the estimated value of the amount of reduction in steel material X1 is equivalent to the actual measured value. In other words, the corrosion current density can be estimated relatively accurately by the method for estimating corrosion current density according to the present invention. Furthermore, the deterioration of steel material (amount of reduction in steel material) can be estimated relatively accurately by the method for controlling anticorrosion current according to the present invention. Furthermore, cathodic protection of steel material can be effectively performed by supplying anticorrosion current corresponding to the estimated value of corrosion current density to the steel material.
１…照合電極、２…対極、３…マルチメーター、４…電源装置、Ｘ…コンクリート構造物、Ｘ１…鋼材、Ｘ２…削孔 1...Reference electrode, 2...Counter electrode, 3...Multimeter, 4...Power supply, X...Concrete structure, X1...Steel material, X2...Drilling
Claims (3)
鋼材における腐食電流密度を推定する箇所に達するようにコンクリート構造物に形成された削孔内に照合電極が挿入され、該削孔内で照合電極と鋼材とが電気的に接触するように配置され、該照合電極と鋼材とが電気的に接続されており、
鋼材に電流を供給するための対極がコンクリート構造物の表面に設置されると共に、該対極と鋼材とが電源装置を介して電気的に接続されており、
対極から鋼材に印加電流を供給していない状態から鋼材に印加電流を供給して鋼材をカソード分極させると共に、照合電極に基づいて測定される鋼材電位から求まる鋼材の分極量が所定値となるまで分極量が増加するように鋼材へ供給する印加電流を増加させ、任意の複数の分極量のそれぞれが得られる際の鋼材電位を照合電極に基づいて測定するカソード分極工程と、
対極から鋼材に印加電流を供給していない状態から鋼材に印加電流を供給して鋼材をアノード分極させると共に、照合電極に基づいて測定される鋼材電位から求まる鋼材の分極量が所定値となるまで分極量が増加するように鋼材へ供給する印加電流を増加させ、任意の複数の分極量のそれぞれが得られる際の鋼材電位を照合電極に基づいて測定するアノード分極工程と、
ＦＥＭ解析を用いてコンクリート構造物のＦＥＭ解析モデルを作成する工程と、
鋼材の自然電位と対極の自然電位とコンクリート構造物の電気抵抗率とをＦＥＭ解析の境界条件として用いると共に、ＦＥＭ解析モデルにおける鋼材の腐食電流密度の推定箇所の印加電圧を変更し、ＦＥＭ解析モデルにおける鋼材の腐食電流密度の推定箇所のモデル印加電流をカソード分極工程およびアノード分極工程における各分極量が得られた際の印加電流と一致させるフィッティング工程と、
フィッティング工程後、カソード分極工程およびアノード分極工程における各分極量が得られた際の印加電流と鋼材の自然電位と対極の自然電位とコンクリート構造物の電気抵抗率とを境界条件としてＦＥＭ解析を行い、ＦＥＭ解析モデルにおける鋼材の腐食電流密度の推定箇所で各分極量が得られる際の鋼材のモデル印加電流を求めると共に、各分極量が得られる際の鋼材のモデル印加電流それぞれをコンクリート構造物における鋼材の腐食電流密度の推定箇所の表面積で除することでＦＥＭ解析モデルにおける各分極量が得られる際のモデル電流密度を算出する工程と、
カソード分極工程およびアノード分極工程における各分極量が得られる際の鋼材電位と、ＦＥＭ解析モデルにおける各分極量が得られる際のモデル電流密度とを用いて分極曲線を作成し、該分極曲線からターフェル外挿法により腐食電流密度を求める工程と、
を備える腐食電流密度の推定方法。 A corrosion current density estimation method for estimating a corrosion current density of a steel material buried in a concrete structure, comprising:
a reference electrode is inserted into a drilled hole formed in the concrete structure so as to reach a location where the corrosion current density in the steel material is to be estimated, the reference electrode is arranged in the drilled hole so as to be in electrical contact with the steel material , and the reference electrode and the steel material are electrically connected;
A counter electrode for supplying a current to the steel material is installed on the surface of the concrete structure, and the counter electrode and the steel material are electrically connected via a power supply device;
a cathodic polarization process in which a current is supplied to the steel material from a state in which no current is supplied to the steel material from a counter electrode, and the current supplied to the steel material is increased so that the polarization amount of the steel material determined from the steel material potential measured based on the reference electrode increases until the polarization amount of the steel material reaches a predetermined value, and the steel material potential when each of a plurality of arbitrary polarization amounts is obtained is measured based on the reference electrode;
an anodic polarization process in which an applied current is supplied to the steel material from a state in which no applied current is supplied to the steel material from a counter electrode, and the applied current supplied to the steel material is increased so that the polarization amount of the steel material determined from the steel material potential measured based on the reference electrode increases until the polarization amount of the steel material reaches a predetermined value, and the steel material potential when each of any plurality of polarization amounts is obtained is measured based on the reference electrode;
creating an FEM analysis model of the concrete structure using FEM analysis;
a fitting process in which the natural potential of the steel material, the natural potential of the counter electrode, and the electrical resistivity of the concrete structure are used as boundary conditions for the FEM analysis, and the applied voltage at the estimation location of the corrosion current density of the steel material in the FEM analysis model is changed to match the model applied current at the estimation location of the corrosion current density of the steel material in the FEM analysis model with the applied current when each polarization amount was obtained in the cathodic polarization process and the anodic polarization process;
a process of performing FEM analysis using the applied current when each polarization amount in the cathodic polarization process and the anodic polarization process is obtained, the natural potential of the steel, the natural potential of the counter electrode, and the electrical resistivity of the concrete structure as boundary conditions, determining a model applied current of the steel when each polarization amount is obtained at an estimated location of the corrosion current density of the steel in the FEM analysis model, and calculating a model current density when each polarization amount in the FEM analysis model is obtained by dividing each model applied current of the steel when each polarization amount is obtained by a surface area of the estimated location of the corrosion current density of the steel in the concrete structure;
a step of creating a polarization curve using a steel material potential when each polarization amount is obtained in the cathodic polarization step and the anodic polarization step and a model current density when each polarization amount is obtained in the FEM analysis model, and determining a corrosion current density from the polarization curve by Tafel extrapolation;
A method for estimating a corrosion current density comprising:
前記腐食速度に基づいて所定の材齢のコンクリート構造物に埋設された鋼材の減少量を算出する工程とを備える、
コンクリート構造物に埋設された鋼材の劣化推定方法。 A step of calculating a corrosion rate of a steel material based on the corrosion current density obtained by the method for estimating corrosion current density according to claim 1;
and calculating a reduction amount of a steel material embedded in a concrete structure of a predetermined age based on the corrosion rate.
A method for estimating deterioration of steel materials embedded in concrete structures.
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