Evaluation method for rebar corrosion, electrochemical treatment method

Abstract

To provide a method for evaluating reinforcing bar corrosion that can relatively easily confirm the repair effect of electrochemical treatment. A method for evaluating rebar corrosion involves measuring the natural potential before and after electrochemical treatment.

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating rebar corrosion and an electrochemical treatment method. [Background technology]

[0002] Traditionally, reinforced concrete has generally been used to construct civil engineering structures such as roads and railways, specifically bridge substructures, bridge girders, underground structures such as tunnels or semi-underground structures, and culverts. Reinforced concrete is widely used as a structural material because it is possible to create composite structures with both compressive and tensile strength by combining concrete, which has high compressive strength, with reinforcing bars, which have high tensile strength. Structures using reinforced concrete are known as PC structures, and many concrete structures also contain PC steel (PC wires, PC bars, PC strands, etc.) placed within the concrete.

[0003] Concrete has high environmental resistance, and since concrete itself is strongly alkaline with a pH of 12 to 12.5, it has been thought that reinforcing bars placed inside concrete form a passive film on their surface, preventing them from corroding.

[0004] However, in recent years, deterioration of reinforced concrete structures due to salt damage and alkali-aggregate reaction (ASR) has become a social problem. Here, "salt damage" refers to a deterioration phenomenon that occurs when seawater splashes onto the surface of concrete structures in coastal areas, and the salt penetrates the concrete due to the adsorption phenomenon of the concrete and concentration gradients, reaching the reinforcing bars, where chloride ions destroy the passive film on the reinforcing bars, initiating corrosion. Furthermore, in past concrete structures, sea sand was sometimes used as fine aggregate, and if it was used without sufficient salt removal, large amounts of chlorides would be present in the concrete, which in some cases destroyed the passive film on the reinforcing bars and initiated corrosion. In addition, alkali-aggregate reaction (ASR) is a deterioration phenomenon in which alkali silica gel, formed by a chemical reaction between alkali metals in concrete and substances contained in the aggregate, expands due to moisture that penetrates into the concrete, causing cracks. If the above-mentioned deterioration phenomenon of reinforced concrete progresses, the durability of the composite structure will be greatly reduced.

[0005] Therefore, as a method for treating deteriorated reinforced concrete, in addition to methods that involve destruction of the structure, such as chipping off the deteriorated parts and backfilling them with concrete or mortar, construction methods that use electrochemical methods to treat the structure without destroying it have been proposed and implemented.

[0006] For example, Patent Document 1 proposes a method for electrochemically treating reinforced concrete, in which external electrodes are arranged on one side of a plate-like body, and a large number of electrode unit panels are prepared, with the entire area where the external electrodes are arranged being covered with an electrolyte solution holding material made of a fibrous sheet; the electrode unit panels are arranged side by side on the concrete surface to be treated, and liquid-tightness is ensured in the joints and outer periphery between adjacent electrode unit panels; electrolyte solution supply ports are provided at desired locations, and electrolyte solution recovery ports are provided; electrolyte solution is continuously or intermittently supplied between the electrode unit panels and the concrete surface from the electrolyte solution supply ports, and the electrolyte solution is recovered from the electrolyte solution recovery ports. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6586000 Summary of the Invention [Problem to be solved by the invention]

[0008] Regarding the above-mentioned electrochemical treatment for repairing reinforced concrete, a non-destructive testing method is required that can relatively easily confirm the effectiveness of the treatment.

[0009] In view of the above, an object of the present invention is to provide a method for evaluating reinforcing bar corrosion that allows the repair effect of electrochemical treatment to be confirmed relatively easily. [Means for solving the problem]

[0010] As a result of intensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by measuring the spontaneous potential before and after electrochemical treatment, and have thus completed the present invention.

[0011] [1] A method for evaluating rebar corrosion by measuring the natural potential before and after electrochemical treatment. [2] The method for evaluating rebar corrosion described in [1] above, in which the natural potential is measured 24 hours after the electrochemical treatment. [3] The method for evaluating rebar corrosion according to [1] or [2] above, wherein the natural potential is measured 14 days after the electrochemical treatment. [4] The method for evaluating reinforcing bar corrosion according to any one of the above [1] to [3], wherein the natural potential is measured one month after the electrochemical treatment. [5] The method for evaluating reinforcing bar corrosion according to any one of [1] to [4] above, wherein a copper sulfate electrode selected from the group consisting of a manganese dioxide electrode, a saturated copper sulfate electrode, a saturated calomel electrode, a saturated silver chloride electrode, and a lead electrode is used as a reference electrode in measuring the natural potential. [6] The method for evaluating rebar corrosion according to any one of [1] to [5] above, wherein the natural potential is measured at 10 or more points per concrete structure. [7] An electrochemical treatment method using the method for evaluating reinforcing bar corrosion according to any one of [1] to [6] above. [8] The electrochemical treatment method according to [7] above, wherein the natural potential 24 hours after the electrochemical treatment is −500 mV or less as a saturated copper sulfate electrode value. [9] The electrochemical treatment method according to [7] or [8] above, wherein the natural potential 14 days after the electrochemical treatment is higher than −500 mV as a saturated copper sulfate electrode value.

[10] The electrochemical treatment method according to any one of [7] to [9] above, wherein at each measurement point, the natural potential one month after the electrochemical treatment is higher than the natural potential 14 days after the electrochemical treatment.

[11] The electrochemical treatment method according to any one of the above [7] to

[10] , wherein the difference between the natural potential before the electrochemical treatment and the natural potential 24 hours after the electrochemical treatment is 150 mV or more as a saturated copper sulfate electrode value. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a method for evaluating reinforcing bar corrosion that allows the repair effect of electrochemical treatment to be confirmed relatively easily. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing an example of reinforced concrete evaluated by the rebar corrosion evaluation method of the present invention. FIG. [Figure 2] 1 is a diagram showing an embodiment of an electrochemical treatment method of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention (the present embodiment) will be described in detail, but the present invention is not limited to this embodiment.

[0015] [Method for evaluating rebar corrosion] The method for evaluating rebar corrosion according to this embodiment is a method for measuring the natural potential before and after electrochemical treatment. In the present invention, electrochemical treatment refers to a process for repairing concrete by using a rebar embedded in the concrete as an internal electrode and an external electrode installed outside the concrete and passing an electric current through the electrode. This process includes a "desalting method" for removing salt from the concrete, a "re-alkalinization method" for restoring the alkalinity of neutralized concrete, an "electrodeposition method" for densifying the concrete surface with an electrodeposit, and a "cathodic protection method" for reducing the corrosion rate of steel.

[0016] The natural-cell potential measurement method for the rebar corrosion evaluation method of this invention can be performed in accordance with the method specified in the Japan Society of Civil Engineers standard JSCE-E 601-2018, "Method for Measuring Natural-Cell Potential in Concrete Structures." The rebars are connected to the potentiometer at a single point if the rebars in the concrete are electrically continuous with each other; otherwise, one point is used for each continuous group. The concrete surface that will be in contact with the reference electrode is preferably pre-wetted, and measurements are preferably performed within 30 minutes of spraying water on the concrete surface. Furthermore, the measurement position on the concrete surface is preferably directly above the rebars.

[0017] The reference electrode used in measuring the natural potential is usually a wet sponge wrapped around the tip and placed in contact with the concrete surface. Any of the following types of reference electrodes can be used: manganese dioxide electrode, saturated copper sulfate electrode, saturated calomel electrode, saturated silver chloride electrode, or lead electrode.

[0018] The environment for measuring the spontaneous potential is preferably one in which the temperature is 10 to 40° C., more preferably 20 to 30° C. The humidity is preferably 60 to 95% RH, more preferably 65 to 80% RH.

[0019] The rebar corrosion evaluation method of the present invention can be performed by referring to ASTM C876-91 "Standard Test Method for Half-Cell Potentials of Uncoated Reinforcing Steel in Concrete" established by the American Society for Testing and Materials. The evaluation criteria for rebar corrosion in the present invention are shown in Table 1 below. Note that the evaluation criteria listed in Table 1 below are based on a copper sulfate reference electrode. However, when using other reference electrodes, the values ​​measured with various reference electrodes can be converted to values ​​measured with a copper sulfate reference electrode using the conversion formula described in JSCE-E 601-2018 "Method for Measuring Natural Potential in Concrete Structures" for evaluation.

[0020] [Table 1]

[0021] The rebar corrosion evaluation method of the present invention measures the natural potential at multiple points for each electrically continuous rebar, determines the natural potential classification according to the above evaluation criteria at each measurement point, and calculates the proportion of each classification to the total number of measurement points. The lower limit of the number of measurement points is preferably 10 or more for each electrically continuous rebar, more preferably 20 or more, and even more preferably 30 or more. Furthermore, it is preferable to measure the natural potential at 10 or more points per concrete structure, more preferably 20 or more, and even more preferably 30 or more. Measuring the natural potential at or above the lower limit improves the accuracy of the evaluation. The upper limit of the number of measurement points is preferably 80 or less for each electrically continuous rebar, more preferably 50 or less, and even more preferably 40 or less. Furthermore, it is preferable to measure the natural potential at 80 or less points per concrete structure, more preferably 50 or less, and even more preferably 40 or less. Measuring the natural potential at or below the upper limit improves the efficiency of measuring the natural potential of the rebar.

[0022] In the method for evaluating rebar corrosion of the present invention, if the proportion of category B (-350 mV≦E<-200 mV) above is 50% or more or the proportion of category C (E<-350 mV) above is 1% or more for the natural potential (E) measured before electrochemical treatment, it is determined that corrosion exists, and the proportion of each of the above categories is calculated for the natural potential (E) measured after electrochemical treatment, and the results of the electrochemical treatment are evaluated.

[0023] In the rebar corrosion evaluation method of the present invention, it is preferable to measure the natural potential 24 hours after the electrochemical treatment. When the ratio of the above-mentioned category C is 99% or more for the natural potential measured 24 hours after the electrochemical treatment, it can be determined that the electrochemical treatment has been completed, and the treatment results can be quickly evaluated. Measuring the natural potential 24 hours after the electrochemical treatment improves the efficiency and accuracy of confirming the completion of the electrochemical treatment.

[0024] In the method for evaluating rebar corrosion of the present invention, it is preferable to measure the natural potential 14 days after the electrochemical treatment. When the natural potential measured 14 days after the electrochemical treatment is such that the proportion of the above-mentioned category A is 5% or more, or the proportion of the above-mentioned category B is 30% or more and the proportion of the above-mentioned category C is 70% or less, it can be determined that the electrochemical treatment has been completed, and the treatment results can be quickly evaluated.

[0025] In the method for evaluating rebar corrosion of the present invention, it is preferable to measure the natural potential one month after the electrochemical treatment. When the natural potential measured one month after the electrochemical treatment is such that the ratio of the above-mentioned section A is 99% or more, or the ratio of the above-mentioned section B is 25% or less and the ratio of the above-mentioned section C is 10% or less, it can be determined that the electrochemical treatment has been completed, and the treatment results can be quickly evaluated.

[0026] [Electrochemical treatment method] The electrochemical treatment method according to this embodiment is an electrochemical treatment method that uses the reinforcing bar corrosion evaluation method of the present invention.

[0027] In the electrochemical treatment method of the present invention, the natural potential 24 hours after the electrochemical treatment is preferably −500 mV or less as a saturated copper sulfate electrode value. Furthermore, it is preferable that the proportion of the natural potential (E) 24 hours after the electrochemical treatment that falls in the aforementioned category C (E<−350 mV) is 99% or more.

[0028] In the electrochemical treatment method of the present invention, the natural potential 14 days after the electrochemical treatment is preferably higher than −500 mV as a saturated copper sulfate electrode value. Furthermore, it is preferable that the proportion of the aforementioned category B in the natural potential (E) 14 days after the electrochemical treatment is 1% or more.

[0029] In the electrochemical treatment method of the present invention, at each measurement point, the natural potential one month after the electrochemical treatment is preferably higher than the natural potential 14 days after the electrochemical treatment, more preferably by 100 mV or more. Furthermore, it is preferable that the proportion of the aforementioned category B in the natural potential (E) one month after the electrochemical treatment is 10% or more.

[0030] In the electrochemical treatment method of the present invention, the difference between the natural potential before the electrochemical treatment and the natural potential 24 hours after the electrochemical treatment is preferably 150 mV or more, and more preferably 200 mV or more, as the saturated copper sulfate electrode value.

[0031] The electrochemical treatment method of the present invention can be carried out as a desalination method, a re-alkalization method, an electrodeposition method, or an electrolytic protection method, and can be suitably used for concrete structures using reinforcing bars, such as bridges. [Example]

[0032] The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention.

[0033] Using concrete 10 with the composition shown in Table 2 below and reinforcing bars 12 with a diameter of 13 mm, rectangular column specimens 14 (100 mm x 100 mm x 400 mm, 30 mm cover) were prepared as shown in Figures 1(A) and (B) and subjected to sealed curing for 28 days. Following this, based on JCI-SC3 "Accelerated Corrosion Test Method for Reinforcing Steel Bars in Salt-Containing Concrete - Dry-Wet Cycling Method," the following steps (1) to (3) were performed as one cycle, with up to 20 cycles: (1) Saltwater environment: Immersion in 3% saline at 20°C for 1 day; (2) Humid environment: Temperature 65°C, 95% relative humidity for 2 days; and (3) Dry environment: Temperature 18°C, 40% relative humidity for 4 days. The natural potential of the reinforcing bars was then measured before energization. Measurements were made at 15 points, and a saturated copper sulfate electrode was used as the reference electrode for natural potential measurements.

[0034] [Table 2]

[0035] 2(A) and (B), a 5 mm-thick electrolyte solution-retaining material (nonwoven fabric) 22 soaked in an electrolyte solution was placed on the underside of a rectangular column specimen 14, followed by an anode material (titanium mesh) 21. Epoxy resin (manufactured by Konishi Corporation, product name Bond Quick Mender) was applied to the side of the rectangular column specimen 14 below the reinforcing bar 12, and then heated to form an epoxy resin coating 36. The reinforcing bar 12 served as the internal electrode, and the titanium mesh 21 served as the external electrode, allowing a direct current to be passed between them. The current was applied using a constant current method (a constant current value was applied using a DC power supply), the voltage required to apply the specified current was measured, and the change in voltage over time was recorded and saved using a data logger. The current applied to the concrete was 1 A / m per concrete surface area. 2 The subjects were then given electricity for eight weeks. The electrolyte was 0.18 mol / L lithium carbonate (Li2CO3), which was impregnated into a nonwoven fabric of polypropylene Hazmat Pig absorbent (MSD-015, manufactured by New Pig Corporation) to prepare an electrolyte solution holding material. The natural potential of the reinforcing bar after the energization treatment was measured at the same measurement points as before the energization for the specified times shown in Table 3, using a saturated copper sulfate electrode as a reference electrode.

[0036] [Table 3] [Industrial Applicability]

[0037] The method for evaluating reinforcing bar corrosion of the present invention can be suitably used for electrochemical treatment methods such as desalination methods, re-alkalization methods, electrodeposition methods, and cathodic protection methods. [Explanation of symbols]

[0038] 10. Concrete 12 Reinforced concrete 14 Square column specimen 21 Anode material 22 Electrolyte solution holding material 36 Epoxy resin coating

Claims

1. A method for evaluating rebar corrosion by measuring the natural potential before and after electrochemical treatment.

2. The method for evaluating reinforcing bar corrosion according to claim 1, wherein the natural potential is measured 24 hours after the electrochemical treatment.

3. The method for evaluating reinforcing bar corrosion according to claim 1 or 2, wherein the natural potential is measured 14 days after the electrochemical treatment.

4. 3. The method for evaluating reinforcing bar corrosion according to claim 1, wherein the spontaneous potential is measured one month after the electrochemical treatment.

5. 3. The method for evaluating reinforcing bar corrosion according to claim 1, wherein the reference electrode used in measuring the natural potential is one of a manganese dioxide electrode, a saturated copper sulfate electrode, a saturated calomel electrode, a saturated silver chloride electrode, and a lead electrode.

6. 3. The method for evaluating rebar corrosion according to claim 1, wherein the natural potential is measured at 10 or more points per concrete structure.

7. An electrochemical treatment method using the reinforcing bar corrosion evaluation method according to claim 1.

8. 8. The electrochemical treatment method according to claim 7, wherein the natural potential 24 hours after the electrochemical treatment is −500 mV or less as a saturated copper sulfate electrode value.

9. 9. The electrochemical treatment method according to claim 7, wherein the natural potential 14 days after the electrochemical treatment is higher than −500 mV as a saturated copper sulfate electrode value.

10. 9. The electrochemical treatment method according to claim 7, wherein the natural potential one month after the electrochemical treatment is higher than the natural potential 14 days after the electrochemical treatment at each measurement point.

11. 9. The electrochemical treatment method according to claim 7, wherein the difference between the natural potential before the electrochemical treatment and the natural potential 24 hours after the electrochemical treatment is 150 mV or more in terms of saturated copper sulfate electrode value.

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