JP2004226135A

JP2004226135A - Method for evaluating corrosion rate of reinforcing bar

Info

Publication number: JP2004226135A
Application number: JP2003011803A
Authority: JP
Inventors: Hidenori Hamada; 秀則濱田; Toru Yamaji; 徹山路; Toshifumi Hirasaki; 敏史平崎; Kenichi Komure; 建一小牟禮
Original assignee: Sho Bond Corp; National Institute of Maritime Port and Aviation Technology
Current assignee: Sho Bond Corp; National Institute of Maritime Port and Aviation Technology
Priority date: 2003-01-21
Filing date: 2003-01-21
Publication date: 2004-08-12

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that polarization resistance acquired by the linear polarization resistance method has often contained environmental resistance in its resistance value. <P>SOLUTION: A potential sweep is performed at a potential of approximately ±10 mV with respect to the natural potential of a reinforcing bar at a speed, which indicates an environmental resistance (at which the potential is swept very fast), and a potential sweep is performed at a speed, which indicates the sum of the polarization resistance and the environmental resistance (at which the potential is swept very slowly). On the basis of the difference between the acquired sum of the polarization resistance and the environmental resistance and the acquired environmental resistance, the polarization resistance is determined to compute a corrosion current density. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、直線分極抵抗法を用いたコンクリート中の鉄筋の腐食速度の評価方法に関する。
【０００２】
【従来の技術】
コンクリート構造物の劣化問題が広く認識されるようになり、維持管理に対する関心も高まっている。一方、公共事業費の縮減が叫ばれる中、より効果的・経済的に維持管理を行う手段として、いわゆるＬＣＭ（ライフサイクルマネージメント）の考え方の確立が求められている。ＬＣＭを考慮する場合、構造物の将来的な劣化を予測し、それに応じた対策方法を選択する必要があるが、現段階で実際に劣化予測を行う手法は十分に確立されているとは言い難い。
【０００３】
劣化予測を行う際に最も重要な点として劣化速度の評価があり、特に塩害や中性化など、鉄筋腐食が問題となる劣化に対しては、鉄筋の腐食速度の評価が不可欠である。
【０００４】
鉄筋の腐食は電気化学的に進行するという事実から、その電気化学反応によって生じる腐食電流密度が鉄筋の腐食速度と直接的な関係を持つ。
【０００５】
腐食電流は鉄筋及び周辺のコンクリート内で収支するため、外部から腐食電流密度を直接計測することは非常に困難である。そこで、鉄筋を分極した時の電位・電流関係から腐食電流密度を推定する手法や、鉄筋を分極したときの分極抵抗から腐食電流密度を推定する方法が一般的である。
【０００６】
現在、コンクリート中にある鉄筋の腐食速度推定法として、分極曲線ターフェル外挿法、交流インピーダンス法、直線分極抵抗法が広く用いられているが、それぞれ一長一短があり、現時点で確実といえるものはない。したがって、より正確な鉄筋腐食速度評価法の確立が求められている。
【０００７】
本発明は、比較的簡易な計測である直線分極抵抗法によって環境抵抗、分極抵抗を個別に評価し、腐食速度を評価し得る測定方法である。
【０００８】
直線分極抵抗法は、鉄筋の自然電位から±１０ｍＶの範囲において、電位を掃引させたときに直線状に得られる電位・電流関係の傾きを分極抵抗とする方法であり、計測の簡易さと得られる値の取り扱いが簡易である利点がある。
【０００９】
【発明が解決しようとする課題】
しかしながら、得られる抵抗値に、分極抵抗以外のコンクリート抵抗、溶液抵抗などの環境抵抗を含み、これを分離できない課題がある。また、電位の掃引速度によって得られる抵抗値が大きく変化し、直線状の電位・電流関係が得られない場合もある。これらは、いずれもコンクリート中の鉄筋の特殊性によるものである。
【００１０】
【課題を解決するための手段】
本発明は、これらの課題を、直線分極抵抗法において、電位掃引速度の違いによって変化する抵抗値の違いを利用し、分極抵抗、環境抵抗を分離評価することで解決しようとするものである。
【００１１】
直線分極抵抗法では、鉄筋と参照電極から得られる鉄筋の自然電位に対し、±１０ｍＶ程度の範囲で電位を掃引し、そのときに得られる鉄筋と参照電極間の電位差変化、および鉄筋と対極間に流れる電流変化の関係から、鉄筋の腐食速度と密接な関係がある分極抵抗を得るものである。
【００１２】
本発明では、直線分極抵抗法において、環境抵抗が得られる非常に速い速度での電位掃引、および環境抵抗と分極抵抗の和が得られる非常に遅い速度での電位掃引を行い、得られた環境抵抗、および環境抵抗と分極抵抗の和との差から分極抵抗を求めて鉄筋の腐食速度を評価する方法を提供するものである。
【００１３】
【実施の形態】
まず、上述の直線分極抵抗法による問題点を検証するため、値が既知である市販の抵抗、コンデンサを用いて、表１の実験要因で図１の回路を組み、直線分極抵抗法による計測を行った。図１は鉄筋コンクリートを模擬的に表した、最も単純な等価回路モデルであり、Ｒ_ｓはコンクリート抵抗、Ｒ_ｐは分極抵抗、Ｃ_ｐは鉄筋表面の電気二重層によるコンデンサ成分を意味する。
【００１４】

【００１５】
計測に際して、電位変化は、〔自然電位〕→〔−１０ｍＶ〕→〔＋１０ｍＶ〕→〔自然電位〕とした。なお、本測定システムは図１に示したように、作用極（Ｗ．Ｅ．）をＲ_ｐ、Ｃ_ｐ側に、参照電極（Ｒ．Ｅ．）と対極（Ｃ．Ｅ．）をＲ_ｓ側に接続することで、回路の自然電位を０としている。
【００１６】
得られた電位・電流関係の一例を図２に示す。同図はＲ_ｓ＝１ｋΩ、Ｒ_ｐ＝２ｋΩ、Ｃ_ｐ＝４７００μＦの場合の結果である。図２より、電位掃引速度が０．１ｍＶ／ｓのときの電位・電流関係は直線状であり、１ｍＶ／ｓのとき、膨らんだ形状となる。さらに掃引速度を１０ｍＶ／ｓとしたとき、０．１ｍＶ／ｓのときよりも傾きの小さい、直線状となる。このことより、電位掃引速度によって電位・電流関係が直線状にならない場合があること、ならびに電位掃引速度によって得られる抵抗値が変化することが再現できた。
【００１７】
つぎに、電位・電流関係において、要因を様々に変化させた時の、最も直線領域が得られやすい〔−１０ｍＶ〕→〔＋１０ｍＶ〕の範囲における直線領域の傾きと電位掃引速度との関係を調べた。その一例を図３に示す。同図より、得られる抵抗値は電位掃引速度が遅い時にはＲ_ｓ＋Ｒ_ｐとなり、掃引速度を速くするほどＲ_ｓに近づく結果となった。さらに、同図より、Ｒ_ｐが大きいほど、またＣ_ｐが大きいほどＲ_ｓが得られやすいことが判る。このことから直線分極抵抗法によってＲ_ｓ、Ｒ_ｐを分離評価できることが明かとなった。
【００１８】
また、直線分極抵抗法によって得られる抵抗値を理論的に解析した結果、直線分極抵抗法で得られる抵抗値は以下の式（１）で表されることを明らかにした。

これにより、非常に速く電位を掃引し、計測時間ｔが０に近い時はＲｓが得られ（式（２））、非常にゆっくりと電位を掃引し、計測時間ｔが充分大きい時はＲｐが得られる（式（３））ことを証明した。

【００１９】
以下、図４に示す鉄筋２が埋設されているモルタル試験体１について、分極抵抗を算出して腐食電流密度まで計算した実施例を説明する。ここでモルタル試験体１はφ５０×９６ｍｍ、鉄筋はφ９ｍｍである。
【００２０】
計測方法は、図５に示すように、鉄筋２を計測器３の作用極と接続し、コンクリート表面に参照電極４および対極５を設置し、これらを計測器３に接続する。計測器３は３電極方式のポテンシオスタットを用いた。
【００２１】
これらについて、直線分極抵抗法で計測を行った。
【００２２】
非常に速い電位掃引速度（環境抵抗を示す速度）として５０ｍＶ／ｓ、非常に遅い電位掃引速度（分極抵抗と環境抵抗の和を示す速度）として０．０５ｍＶ／ｓを選択した。電位の変化は、〔自然電位〕→〔−１０ｍＶ〕→〔＋１０ｍＶ〕→〔自然電位〕とした。
【００２３】
まずはじめに、鉄筋の自然電位を測定した。その結果は−０．８２４Ｖであった。
【００２４】
つぎに非常に速い電位掃引速度５０ｍＶ／ｓで、自然電位（−０．８２４Ｖ）→−１０ｍＶ（−０．８３４ｍＶ）→＋１０ｍＶ（０．８１４ｍＶ）→自然電位の範囲で計測を行った（図６の５０ｍＶ／ｓの図）。
【００２５】
理論式の検証から、時間が０に近い時、得られる抵抗は環境抵抗Ｒ_ｓとなることがわかっているため、図６の▲１▼部分の傾き（△Ｅ／△Ｉ）を環境抵抗Ｒ_ｓとした。そのときの結果は、Ｒ_ｓ＝２７８Ω・・・（４）である。
【００２６】
それから非常に遅い電位掃引速度０．０５ｍＶ／ｓで、自然電位（−０．８２４Ｖ）→−１０ｍＶ（−０．８３４ｍＶ）→＋１０ｍＶ（０．８１４ｍＶ）→自然電位の範囲で計測を行った（図６の０．０５ｍＶ／ｓの図）。
【００２７】
理論式の検証から、時間が０が非常に大きい時、得られる抵抗は環境抵抗Ｒ_ｓ＋分極抵抗Ｒ_ｐとなることがわかっているため、図６の▲２▼部分の傾きをＲ_ｓ＋Ｒ_ｐとした。そのときの結果は、Ｒ_ｓ＋Ｒ_ｐ＝８８７２Ω・・・（５）である。
【００２８】
（５）−（４）より、
（Ｒ_ｓ＋Ｒ_ｐ）−Ｒ_ｓ＝Ｒ_ｐ＝８８７２Ω−２７８Ω＝８５９４Ω・・・（６）
であり、（６）式より分極抵抗Ｒ_ｐは８５９４Ωとなる。
【００２９】
ここで、鉄筋の表面積Ａは、２８．１１３ｃｍ^２であったので、単位面積あたりの分極抵抗は、Ｒ_ｐ’＝８５９４×２８．１１３＝２４１６０３Ω・ｃｍ^２・・・（３）
となる（抵抗は面積に反比例するため、単位面積あたりの抵抗値は、得られた抵抗と面積の積となる）。
【００３０】
腐食電流密度Ｉｃｏｒｒは、一般的に以下の式で表される。
Ｉｃｏｒｒ＝Ｋ／Ｒ_ｐ’・・・（４）（ここでＫは定数０．０２６Ｖ）
【００３１】
（４）式に（３）を代入すると、
Ｉｃｏｒｒ＝０．０２６Ｖ／２４１６０３Ωｃｍ^２＝１．０７×１０^‐ ^７Ａ／ｃｍ^２＝０．１０７μＡ
が得られ、これが鉄筋の腐食速度と密接な関係がある腐食電流密度になる。
【００３２】
なお、本手法を実構造物に適用する場合、図７に示すように、構造物の一部で鉄筋を露出させて作用極を接続し、コンクリート表面から参照電極４と対極５を押し当てる形となり、計測の方法は前述のように、まず鉄筋の自然電位を測定した後、自然電位から±１０ｍＶ程度の範囲で非常に速く、次いで非常に遅く電位を掃引することで、環境抵抗、および環境抵抗と分極抵抗の和を測定し、分極抵抗を算出する。
【００３３】
【発明の効果】
本発明は、上述のようにしてなるので、つぎの効果を有する。
【００３４】
すなわち、非常に速く電位を掃引したとき、電位・電流関係は直線状となり、このときの電位・電流の傾きが環境抵抗を示し、非常にゆっくりと電位を掃引したとき、電位・電流関係は曲線状となり、このときの電位・電流関係の直線部分の傾きは、分極抵抗と環境抵抗の和を示すので、この２回の計測値の差から容易に分極抵抗を単独で得ることができる。
【００３５】
したがって、既述したような、直接分極抵抗の利点を維持しつつ、その欠点を排除して、分極抵抗を求めることができ、腐食電流密度が算出でき、これをもとに鉄筋の腐食速度を評価することができる。
【図面の簡単な説明】
【図１】鉄筋コンクリートを模擬的に表した等価回路図である。
【図２】電位掃引速度の変化に伴う電位・電流関係の変化を示す図で、（Ａ）は電位掃引速度が０．１ｍＶ／ｓ、（Ｂ）は電位掃引速度が１ｍＶ／ｓ、（Ｃ）は電位掃引速度が１０ｍＶ／ｓのときの図である。
【図３】抵抗値と電位掃引速度の関係図で、（Ａ）はＣ_ｐ＝１０００μＦ、（Ｂ）はＣ_ｐ＝４７００μＦ、（Ｃ）はＣ_ｐ＝９４００μＦのときの図である。
【図４】実施例に使用したモルタル試験体を示す斜視図である。
【図５】実施例の計測方法の概略図である。
【図６】実施例において、速度の変化に伴う電位・電流関係の変化を示す図である。
【図７】実構造物に本発明を適用した概略図である。
【符号の説明】
１モルタル試験体
２鉄筋
３計測器
４参照電極
５対極[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for evaluating the corrosion rate of reinforcing steel in concrete using the linear polarization resistance method.
[0002]
[Prior art]
The problem of deterioration of concrete structures has been widely recognized, and interest in maintenance has been increasing. On the other hand, as reductions in public works expenses are called for, there is a need to establish a concept of so-called LCM (life cycle management) as a means for more effective and economical maintenance. When considering LCM, it is necessary to predict the future deterioration of a structure and select a countermeasure method according to it. However, it is said that the method of actually performing deterioration prediction at this stage is not well established. hard.
[0003]
The most important point when performing deterioration prediction is the evaluation of the deterioration rate. In particular, evaluation of the corrosion rate of the reinforcing steel is indispensable for the deterioration in which the corrosion of the reinforcing steel is a problem such as salt damage and neutralization.
[0004]
Due to the fact that rebar corrosion progresses electrochemically, the corrosion current density generated by the electrochemical reaction is directly related to the rebar corrosion rate.
[0005]
It is very difficult to directly measure the corrosion current density from the outside because the corrosion current balances in the reinforcing steel and surrounding concrete. Therefore, a method of estimating the corrosion current density from the potential-current relationship when the rebar is polarized, and a method of estimating the corrosion current density from the polarization resistance when the rebar is polarized are generally used.
[0006]
At present, polarization curve Tafel extrapolation, AC impedance method, and linear polarization resistance method are widely used as methods for estimating the corrosion rate of reinforcing steel in concrete, but each has advantages and disadvantages, and there is no reliable method at this time. . Therefore, establishment of a more accurate method of evaluating the corrosion rate of reinforcing steel is required.
[0007]
The present invention is a measurement method capable of individually evaluating environmental resistance and polarization resistance by a linear polarization resistance method which is a relatively simple measurement, and evaluating a corrosion rate.
[0008]
The linear polarization resistance method is a method in which the gradient of the potential-current relationship obtained linearly when the potential is swept within the range of ± 10 mV from the spontaneous potential of the reinforcing bar is used as the polarization resistance, and simplicity of measurement can be obtained. There is an advantage that handling of values is simple.
[0009]
[Problems to be solved by the invention]
However, the obtained resistance value includes environmental resistance such as concrete resistance and solution resistance other than polarization resistance, and there is a problem that these resistances cannot be separated. In addition, the resistance value obtained by the potential sweep speed changes greatly, and a linear potential-current relationship may not be obtained. These are all due to the specificity of the reinforcing steel in concrete.
[0010]
[Means for Solving the Problems]
The present invention intends to solve these problems by separating and evaluating polarization resistance and environmental resistance in a linear polarization resistance method by utilizing a difference in resistance value that changes according to a difference in potential sweep speed.
[0011]
In the linear polarization resistance method, the potential is swept within a range of about ± 10 mV with respect to the spontaneous potential of the reinforcing bar obtained from the reinforcing bar and the reference electrode, and the potential difference between the reinforcing bar and the reference electrode obtained at that time is changed. A polarization resistance closely related to the corrosion rate of the reinforcing bar is obtained from the relationship of the change in the current flowing through the steel.
[0012]
In the present invention, in the linear polarization resistance method, a potential sweep is performed at a very high speed at which environmental resistance is obtained, and a potential sweep is performed at a very low speed at which the sum of environmental resistance and polarization resistance is obtained. It is an object of the present invention to provide a method for evaluating a corrosion rate of a reinforcing bar by obtaining a polarization resistance from a resistance and a difference between an environmental resistance and a sum of a polarization resistance.
[0013]
Embodiment
First, in order to verify the problem with the linear polarization resistance method described above, the circuit shown in FIG. 1 was assembled using commercially available resistors and capacitors whose values are known, using the experimental factors shown in Table 1, and measurement was performed using the linear polarization resistance method. went. 1 showing the reinforced concrete simulatively, the simplest equivalent circuit model, R _s is concrete resistance, R _p is the polarization resistance, C _p denotes a capacitor component by electric double layer rebar surface.
[0014]

[0015]
At the time of measurement, the potential change was [natural potential] → [−10 mV] → [+10 mV] → [natural potential]. In this measurement system, as shown in FIG. 1, the working electrode (WE) is R _p , the reference electrode (RE) and the counter electrode (CE) are R _s on the C _p side. Side, the natural potential of the circuit is set to zero.
[0016]
FIG. 2 shows an example of the obtained potential-current relationship. The figure is the result of the case of _{_{R s = 1kΩ, R p =}} 2kΩ, C p = 4700μF. As shown in FIG. 2, the potential-current relationship is linear when the potential sweep speed is 0.1 mV / s, and expands when the potential sweep speed is 1 mV / s. Further, when the sweep speed is set to 10 mV / s, it becomes a straight line having a smaller inclination than when the sweep speed is set to 0.1 mV / s. From this, it was possible to reproduce that the potential-current relationship may not be linear depending on the potential sweep speed, and that the resistance obtained by the potential sweep speed changes.
[0017]
Next, the relationship between the gradient of the linear region and the potential sweep speed in the range of [−10 mV] → [+10 mV] where the linear region is most easily obtained when the factors are variously changed in the potential / current relationship is examined. Was. An example is shown in FIG. As shown in the figure, the obtained resistance value is R _s + R _p when the potential sweep speed is low, and the resistance value approaches R _s as the sweep speed increases. Furthermore, from the figure, the more R _p is large, also C _p the larger R _s It can be seen easily obtained. From this, it became clear that R _s and R _p can be separately evaluated by the linear polarization resistance method.
[0018]
Moreover, as a result of theoretically analyzing the resistance value obtained by the linear polarization resistance method, it was clarified that the resistance value obtained by the linear polarization resistance method was represented by the following equation (1).

Thereby, the potential is swept very quickly, and Rs is obtained when the measurement time t is close to 0 (Equation (2)), and the potential is swept very slowly, and when the measurement time t is sufficiently large, Rp is obtained. It was proved that (formula (3)) was obtained.

[0019]
Hereinafter, an example of calculating the polarization resistance and calculating the corrosion current density of the mortar specimen 1 in which the reinforcing bar 2 is embedded shown in FIG. 4 will be described. Here, the mortar specimen 1 is φ50 × 96 mm, and the rebar is φ9 mm.
[0020]
In the measuring method, as shown in FIG. 5, the reinforcing bar 2 is connected to the working electrode of the measuring device 3, the reference electrode 4 and the counter electrode 5 are installed on the concrete surface, and these are connected to the measuring device 3. The measuring device 3 used a three-electrode type potentiostat.
[0021]
These were measured by the linear polarization resistance method.
[0022]
50 mV / s was selected as a very fast potential sweeping speed (speed indicating environmental resistance) and 0.05 mV / s as a very slow potential sweeping speed (speed indicating the sum of polarization resistance and environmental resistance). The change of the potential was [natural potential] → [−10 mV] → [+10 mV] → [natural potential].
[0023]
First, the spontaneous potential of the reinforcing bar was measured. The result was -0.824V.
[0024]
Next, at a very high potential sweep speed of 50 mV / s, measurement was performed in the range of natural potential (−0.824 V) → −10 mV (−0.834 mV) → + 10 mV (0.814 mV) → natural potential (FIG. 6). 50 mV / s diagram).
[0025]
When close to the verification of the theoretical equation, the time is 0, the resistance obtained is found to be environmental resistance R _s, environmental resistance slope (△ E / △ I) of ▲ 1 ▼ portion of FIG 6 R _s . The result at that time is R _s = 278Ω (4).
[0026]
Then, at a very low potential sweep rate of 0.05 mV / s, measurement was performed in the range of natural potential (−0.824 V) → −10 mV (−0.834 mV) → + 10 mV (0.814 mV) → natural potential (FIG. 6, 0.05 mV / s).
[0027]
The verification of the theoretical formula, when time is very large 0, the resistance obtained is found to be environmental resistance R _{s +} polarization resistance R _p, the tilt of the ▲ 2 ▼ portion of FIG 6 R _{s +} R _p . The result at that time is R _s + R _p = 8872Ω (5).
[0028]
From (5)-(4),
_{_{_{_{(R s + R p) -R}}}} s = R p = 8872Ω-278Ω = 8594Ω ··· (6)
, And the becomes 8594Ω polarization resistance _{R p} from equation (6).
[0029]
Here, the surface area A of the rebar, so was 28.113Cm ^2, polarization resistance per unit _{area, R p '= 8594 × 28.113} = 241603Ω · cm 2 ··· (3)
(Since the resistance is inversely proportional to the area, the resistance value per unit area is the product of the obtained resistance and the area).
[0030]
The corrosion current density Icorr is generally represented by the following equation.
Icorr = K / R _p ′ (4) (where K is a constant of 0.026 V)
[0031]
Substituting (3) into equation (4) gives
^{Icorr = 0.026V / 241603Ωcm 2 = 1.07} × 10 - 7 A / cm 2 = 0.107μA
Which results in a corrosion current density that is closely related to the corrosion rate of the rebar.
[0032]
When this method is applied to a real structure, as shown in FIG. 7, a part of the structure exposes a reinforcing bar, connects the working electrode, and presses the reference electrode 4 and the counter electrode 5 from the concrete surface. As described above, the measurement method is to first measure the spontaneous potential of the reinforcing bar, and then sweep the potential very quickly within a range of about ± 10 mV from the spontaneous potential, and then very slowly, thereby obtaining environmental resistance and environmental resistance. The sum of the resistance and the polarization resistance is measured, and the polarization resistance is calculated.
[0033]
【The invention's effect】
Since the present invention is configured as described above, it has the following effects.
[0034]
That is, when the potential is swept very quickly, the relationship between the potential and the current becomes linear, and the slope of the potential and current at this time indicates the environmental resistance. Since the slope of the linear portion of the potential-current relationship at this time indicates the sum of the polarization resistance and the environmental resistance, the polarization resistance can be easily obtained independently from the difference between the two measured values.
[0035]
Therefore, while maintaining the advantages of direct polarization resistance as described above, the disadvantages can be eliminated and the polarization resistance can be obtained, the corrosion current density can be calculated, and the corrosion rate of the reinforcing steel can be calculated based on this. Can be evaluated.
[Brief description of the drawings]
FIG. 1 is an equivalent circuit diagram schematically showing reinforced concrete.
FIGS. 2A and 2B are diagrams showing a change in a potential-current relationship with a change in a potential sweep speed. FIG. 2A shows a potential sweep speed of 0.1 mV / s, FIG. 2B shows a potential sweep speed of 1 mV / s, and FIG. () Is a diagram when the potential sweep speed is 10 mV / s.
[3] in relation diagram of the resistance value and the potential sweep rate, (A) is _C p = _1000μF, (B) is _C p = _{4700μF, (C)} is a diagram when the _C p = _9400μF.
FIG. 4 is a perspective view showing a mortar specimen used in the examples.
FIG. 5 is a schematic diagram of a measurement method according to an embodiment.
FIG. 6 is a diagram showing a change in a potential-current relationship with a change in speed in the example.
FIG. 7 is a schematic diagram in which the present invention is applied to an actual structure.
[Explanation of symbols]
1 Mortar specimen 2 Reinforcing bar 3 Measuring instrument 4 Reference electrode 5 Counter electrode

Claims

The potential sweep is performed at a very high speed at which the environmental resistance is obtained at a potential of about ± 10 mV with respect to the spontaneous potential of the reinforcing bar, and at the very low speed at which the sum of the polarization resistance and the environmental resistance is obtained. A method for evaluating the corrosion rate of a reinforcing bar, comprising performing a potential sweep, and obtaining a polarization resistance from the obtained environmental resistance and a difference between the polarization resistance and the sum of the environmental resistances.