Cathodic protection backfill

Abstract

To provide a cathodic protection backfill that is less prone to electrolyte dissipation even when installed in a high-resistance environment, does not hinder the dissipation of gases generated from electrodes used in conjunction, and has excellent cathodic protection performance and ease of installation. [Solution] The cathodic protection backfill of the present invention is provided near an electrode 14 that passes a corrosion protection current through an embedded metal material 13, and includes an electrolyte and a retaining material that holds the electrolyte. The electrolyte contains an electrolyte and a solvent, and has a viscosity V1 (25°C, 3 rpm) measured by a B-type viscometer of 300 to 109,000 mPa·s, a viscosity V2 (25°C, 100 rpm) measured by a B-type viscometer of 200 to 6,000 mPa·s, and a thixotropy index (V1 / V2) of 1.3 to 19.0.

Description

Technical Field

[0001] The present invention relates to an anticorrosive backfill used for the electrocorrosion prevention of metal materials embedded in concrete, soil, etc.

Background Art

[0002] When electrocorroding metal materials such as steel materials in a high-resistance environment such as in concrete or soil by the flowing current anode method or the external power source method, if an anode is simply installed around the metal material, due to the high electrical resistance of the surrounding environment of the anode, in the flowing current anode method, the corrosion prevention current generated at the anode decreases, and in the external power source method, inconveniences such as an increase in the applied voltage occur, and a sufficient corrosion prevention effect cannot be obtained. Therefore, in electrocorrosion prevention for metal materials in a high-resistance environment, for the purpose of reducing the electrical resistance of the surrounding environment of the anode, a composition called backfill, which includes an electrolytic solution and a holding material for the electrolytic solution, may be installed near the anode.

[0003] For the backfill to stably exhibit its effect, it is important that the holding amount of the electrolytic solution in the backfill is maintained. If this decreases, the electrical resistance of the backfill increases, and there is a risk of deterioration of the electrocorrosion prevention system, such as the corrosion prevention current becoming difficult to flow. However, the environment where the backfill is installed is often drier than inside the backfill, and due to the difference in the moisture content inside and outside such a backfill, there is a problem that the electrolytic solution inside the backfill dissipates into the surrounding environment. Also, when such dissipation of the electrolytic solution occurs, there is also a risk that the electrolytic solution leaking from the backfill contacts the metal material to be protected against corrosion and promotes corrosion.

[0004] As a method for solving the problem of dissipation of the electrolytic solution in such a backfill, a method of reducing the fluidity of the electrolytic solution by blending a thickening agent into the electrolytic solution to gel it is known. As the thickening agent, Patent Document 1 describes using a water-soluble polymer such as polyvinyl alcohol, and Patent Document 2 describes using a water-absorbing resin that forms a gel state when mixed with an alkaline aqueous solution.

[0005] Patent Document 3 describes a corrosion prevention method for underground pipes penetrating reinforced concrete structures, which includes the steps of forming a drilled hole in the concrete wall and soil near the penetration, installing an electrode inside the drilled hole, and then injecting a conductive filler containing bentonite powder and a water-soluble thickener. Xanthan gum is described as a specific example of the water-soluble thickener. As described above, by adding a water-soluble thickener to the conductive filler, a high thickening effect can be imparted to the conductive filler, and it is said that the filling and sealing of drilled holes provided in the horizontal or diagonal direction can be performed efficiently (see

[0034] and

[0036] of Patent Document 3). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-57015 [Patent Document 2] Japanese Patent Publication No. 2008-127678 [Patent Document 3] Japanese Patent Publication No. 2008-202116 [Overview of the project] [Problems that the invention aims to solve]

[0007] As mentioned above, the problem of electrolyte dissipation in the backfill can be solved by reducing the fluidity of the electrolyte, such as by gelling it, but it has been found that this can create new problems. Specifically, when the cathodic protection system, including the metal material to be protected (cathode), anode, and backfill, is in operation (while the protective current is being generated), gases such as oxygen and hydrogen are generated from the anode. These gases permeate the backfill, which is placed on top of the anode, and dissipate into the surrounding environment. However, if the electrolyte in the backfill is gelled, the gases cannot permeate the backfill, and the gases, having nowhere to go, remain between the anode and the backfill, forming a gas reservoir. This can result in problems such as a reduction in the effective area of ​​the anode and physical damage to the backfill. Furthermore, reducing the fluidity of the electrolyte in the backfill makes it difficult to fill the electrolyte, which may reduce the workability when installing the backfill.

[0008] The object of the present invention is to provide a cathodic protection backfill that can overcome the shortcomings of the prior art, and more specifically, to provide a cathodic protection backfill that is less prone to electrolyte dissipation even when installed in a high-resistance environment, does not hinder the dissipation of gases generated from electrodes used in combination, and has excellent cathodic protection performance and ease of installation. [Means for solving the problem]

[0009] The inventors of the present invention have conducted various studies to achieve both the prevention of electrolyte dissipation and the promotion of the dissipation of gases (hereinafter also referred to as "electrode gases") generated from electrodes such as anodes used in combination with the cathodic protection backfill. As a result, they have found that imparting thixotropy to the electrolyte is effective, and as a result of further studies, they have found that adjusting the thixotropy index of the electrolyte to a specific range is effective (first finding). When electrode gases are generated during the operation of the cathodic protection system, pressure (gas pressure) caused by the electrode gases acts on the backfill adjacent to the anode. A specific electrolyte with a thixotropy index within a specific range has a high viscosity equivalent to or greater than that of corn syrup and poor fluidity in a static state when not subjected to gas pressure. However, when subjected to an external force from a static state, the viscosity decreases over time and fluidity improves, and when the external force disappears, the viscosity increases over time and returns to the high viscosity and low fluidity of the static state. Therefore, when an electrochemical corrosion protection system, including a backfill containing a specific electrolyte, is in operation, the specific electrolyte has poor fluidity and is therefore less likely to dissipate into the surrounding environment when no electrode gas is generated. However, when electrode gas is generated and gas pressure acts on the specific electrolyte, the viscosity of the specific electrolyte decreases to a degree that allows electrode gas to permeate, thus promoting the dissipation of electrode gas into the surrounding environment.

[0010] The present invention (first invention) is based on the first findings described above and is an electrochemical backfill provided near an electrochemical electrode that passes an electrochemical current through an embedded metal material, comprising an electrolyte and a retaining material that holds the electrolyte, wherein the electrolyte contains an electrolyte and a solvent, and has a viscosity V1 of 300 to 109,000 mPa·s, a viscosity V2 of 200 to 6,000 mPa·s, and a thixotropy index of 1.3 to 19.0 as measured by the method described below.

[0011] Furthermore, the inventors have found (second finding) that by using an electrolyte in a cathodic protection backfill where the retention rate and electrolytic voltage, measured by the following method, are within a specific range, it is possible to achieve both prevention of electrolyte dissipation and promotion of electrode gas dissipation.

[0012] The present invention (second invention) is based on the second findings described above and is an electrochemical corrosion protection backfill provided near an electrochemical corrosion protection electrode that passes an electrochemical corrosion protection current through an embedded metal material, comprising an electrolyte and a retaining material that holds the electrolyte, wherein the electrolyte contains an electrolyte and a solvent, and the retention rate measured by the method described below is 10% or more, and the electrolytic voltage is 2.0 to 5.0 V.

[0013] Furthermore, the present invention (third invention) is an electrochemical corrosion protection backfill provided near an electrochemical corrosion protection electrode that passes an electrochemical corrosion protection current through an embedded metal material, having a laminated structure of a plurality of functional layers, each of which comprises an electrolyte and a retaining material that holds the electrolyte, and the functional layer closest to the environment surrounding the metal material is the electrochemical corrosion protection backfill of the present invention (first or second invention). [Effects of the Invention]

[0014] According to the present invention, a cathodic protection backfill is provided that is less prone to electrolyte dissipation even when installed in a high-resistance environment, does not hinder the dissipation of gases generated from electrodes used in combination, and has excellent cathodic protection performance and ease of installation. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a diagram showing an example of the application of one embodiment of the cathodic protection backfill of the present invention to a concrete structure, and is a schematic cross-sectional view showing a cross section along the thickness direction of the backfill. [Figure 2] Figure 2 shows the viscosity measurement results of an example of the electrolyte contained in the backfill of the present invention using a type B viscometer, and is a graph that substitutes a diagram to show the relationship between the rotation speed of the rotor of the type B viscometer and the viscosity of the electrolyte. [Figure 3]FIG. 3 is a view showing an application example of the electric corrosion prevention backfill of the present invention to a concrete structure in another embodiment, and is a cross-sectional view schematically showing a cross-section along the thickness direction of the backfill. [Figure 4] FIG. 4 shows the measurement results of the viscosity of the electrolytic solution in the backfill of the example and the comparative example by a B-type viscometer, and is a graph substituting for a drawing showing the relationship between the rotational speed of the rotor of the B-type viscometer and the viscosity of the electrolytic solution. [Figure 5] FIG. 5 is a graph substituting for a drawing showing the change over time of the electrolytic voltage when the electrolytic solution is electrolyzed. [Figure 6] FIG. 6 is a graph substituting for a drawing showing the change over time of the anode potential in the energization test for the electric corrosion prevention structure using the backfill of the example or the comparative example. [Figure 7] FIG. 7 is a graph substituting for a drawing showing the change over time of the voltage (hereinafter, also referred to as "inter-electrode voltage") applied between the anode and the metal material (corrosion prevention target) in the energization test for the electric corrosion prevention structure using the backfill of the example or the comparative example.

Mode for Carrying Out the Invention

[0016] The electric corrosion prevention backfill of the present invention (hereinafter, also simply referred to as "backfill") is provided in the vicinity of an electric corrosion prevention electrode that passes a corrosion prevention current through an embedded metal material (corrosion prevention target). The type of metal constituting the metal material to be corrosion-prevented is not particularly limited, but typically, it is iron or an alloy of iron. Further, the environment around the metal material to be corrosion-prevented (the location where the metal material to be corrosion-prevented is embedded) is also not particularly limited, and for example, it can be in concrete or in soil. As described above, both in concrete and in soil are high-resistance environments with relatively high electrical resistance. As an application example of the backfill of the present invention, a concrete structure including concrete and a metal material (corrosion prevention target) embedded in the concrete can be mentioned.

[0017] Figure 1 shows backfill 1, which is one embodiment of the backfill of the present invention. Backfill 1 is applied to cathodic protection of a concrete structure 11 using a galvanic anode method, and together with the concrete structure 11, constitutes a cathodic protection structure 10. The concrete structure 11 is composed of concrete 12 and a metal material 13 embedded in the concrete 12. The concrete structure 11 is typically a reinforced concrete structure, in which case the metal material 13 is reinforcing steel. The concrete structure 11 can be, for example, a bridge, a bridge girder, a bridge pier, a box culvert, a retaining wall, a pier, a revetment, etc. In the present invention, concrete refers collectively to cement paste, cement mortar, and cement concrete.

[0018] As shown in Figure 1, the cathodic protection structure 10 comprises a concrete structure 11, an electrode 14 positioned outside the concrete structure 11 and supplying a corrosion protection current to the metal material 13, a reference electrode 15 positioned near the metal material 13 within the concrete 12 and measuring the potential of the metal material 13, and connecting means for electrically connecting each part. The connecting means is configured by connecting lead wires 16 extending from the metal material 13, the electrode 14, and the reference electrode 15 within a connection box 17.

[0019] The electrode 14 is a plate-like object made of a metal that has an electrochemically low potential relative to the metal material 13 in the concrete 12, and is fixed to the surface of the concrete 12 by fasteners 18 such as anchor bolts and rivets. The electrode 14 can be any material commonly used as a sacrificial anode or galvanic anode, without any particular limitations, such as aluminum or its alloys, zinc or its alloys, magnesium or its alloys, etc.

[0020] As shown in Figure 1, the backfill 1 is interposed between the electrode 14 and the concrete 12 of the concrete structure 11, and is a component of the cathodic protection structure 10. A cushioning material 19 made of resin, such as urethane resin, is placed between the electrode 14 and the concrete 12 around the backfill 1. The thickness of the backfill 1 is not particularly limited, but is usually about 10 mm.

[0021] The backfill of the present invention comprises an electrolyte and a retaining material for holding the electrolyte. The electrolyte contains at least an electrolyte and a solvent.

[0022] The backfill of the present invention includes the first and second inventions. The backfill of the first invention is characterized in that the electrolyte contained therein is thixotropic. The backfill of the second invention is characterized in that the retention rate and electrolytic voltage of the electrolyte contained therein are, respectively, within a specific range. Unless otherwise specified, "the present invention" as used herein includes the first and second inventions.

[0023] The backfill of the first invention will be described below. The electrolyte contained in the backfill of the first invention has a viscosity V1 of 300 to 109,000 mPa·s, a viscosity V2 of 200 to 6,000 mPa·s, and a thixotropy index (hereinafter also referred to as "TI value") of 1.3 to 19.0, as measured by the method described below. Thixotropy is the property that viscosity gradually decreases when subjected to continuous shear stress, and gradually increases when the shear stress disappears and the substance comes to rest. The TI value is an indicator of thixotropy; the closer the TI value is to 1, the closer the electrolyte is to a Newtonian fluid (a fluid whose viscosity does not change with the applied force), and the larger the TI value, the higher the thixotropy of the electrolyte, meaning it is close to a solid state when no external force is acting, and tends to become close to a liquid state when an external force is applied.

[0024] <Method for measuring viscosity V1 and V2 and thixotropy index (TI value)> The viscosity of the substance to be measured (electrolyte) is measured using a B-type viscometer under two conditions, Condition 1 and Condition 2, as described below. The viscosity under Condition 1 is denoted as V1, and the viscosity under Condition 2 as V2. The ratio of viscosity V1 to viscosity V2 (V1 / V2) is calculated and used as the thixotropy index of the substance to be measured. Condition 1: Temperature of the object being measured: 25°C, rotation speed: 3 rpm Condition 2: Temperature of the object being measured: 25°C, rotation speed: 100 rpm

[0025] Viscosity V1 can be determined by adjusting the temperature of the electrolyte to be measured to 25°C, placing the rotor of a type B viscometer into the electrolyte, and measuring the viscosity 60 seconds after the rotor starts rotating at a rotation speed of 3 rpm. Viscosity V2 can be determined by adjusting the temperature of the electrolyte to be measured to 25°C, placing the rotor of a type B viscometer into the electrolyte, and measuring the viscosity 30 seconds after the rotor starts rotating at a rotation speed of 100 rpm. For the B-type viscometer, for example, the "TVB-10M" manufactured by Toki Sangyo Co., Ltd. can be used. For the rotor, M1 to M4 rotors can be used. Furthermore, in order to measure the viscosity of the electrolyte contained in the backfill, it is necessary to remove the electrolyte from the backfill. This can be done by squeezing the retaining material that holds the electrolyte, or by using a suction means such as a suction pump to suck the electrolyte from the retaining material.

[0026] Figure 2 shows the relationship between the rotation speed of the rotor of a B-type viscometer and the viscosity of an example of an electrolyte contained in a backfill of the first invention, as measured by a B-type viscometer. The electrolyte shown in Figure 2 has a viscosity of approximately 140 Pa·s when the rotation speed is close to zero and almost no external force is acting on it, which is a high viscosity equivalent to or greater than that of general corn syrup. However, the viscosity decreases as the rotation speed increases, with a viscosity of 28 Pa·s (28,000 mPa·s) at a rotation speed of 3 rpm and a viscosity of 2 Pa·s (2,000 mPa·s) at a rotation speed of 100 rpm, which is about the same viscosity as egg white. The electrolyte shown in Figure 2 is thixotropic, and its TI value is in the range of 1.3 to 19.0.

[0027] The backfill of the first invention has an electrolyte viscosity V1 of 300 to 109,000 mPa·s and a viscosity V2 of 200 to 6,000 mPa·s, and the TI value calculated as V1 / V2 is in the range of 1.3 to 19.0. Therefore, it is possible to achieve both the prevention of electrolyte dissipation and the promotion of electrode gas dissipation as described above, and can exhibit stable corrosion protection performance over a long period of time. For example, in the cathodic protection structure 10 shown in Figure 1, when no corrosion protection current flows from the electrode 14 to the metal material 13, the electrolyte in the backfill 1 is in a static state, highly viscous, and has poor fluidity, thus preventing the electrolyte from dissipating into the concrete 12. Furthermore, when a corrosion protection current flows from the electrode 14 to the metal material 13, gases such as oxygen gas are generated from the electrode 14. Since the static electrolyte is not permeable to these gases, a gas reservoir may form between the electrode 14 and the backfill 1, potentially leading to problems such as a reduction in the effective area of ​​the electrode 14 and physical damage to the backfill 1. However, since the TI value of the electrolyte in the backfill 1 is in the range of 1.3 to 19.0 when the viscosities V1 and V2 are within the specified range, the viscosity of the electrolyte in the backfill 1 decreases as it is continuously subjected to the external force (gas pressure) caused by the generation of the gas, and eventually it becomes permeable to the gas. Therefore, the gas generated from the electrode 14 dissipates into the external space through the backfill 1 (the holding material that retains the electrolyte), preventing the formation of a gas reservoir between the electrode 14 and the backfill 1. Furthermore, while installing a backfill typically requires tasks such as applying the electrolyte to the retaining material, impregnating the retaining material into the electrolyte, and degassing the backfill, the electrolyte contained in the backfill of the first invention has a TI value in the range of 1.3 to 19.0 when viscosities V1 and V2 are within the specified range. Therefore, when external force is applied to the electrolyte during these operations, the viscosity decreases appropriately, allowing these operations to be carried out smoothly. Consequently, the backfill of the first invention offers excellent workability during installation.

[0028] Assuming that viscosities V1 and V2 are within the specified range, if the TI value of the electrolyte in the backfill is less than 1.3, the electrolyte may dissipate into the surrounding environment of the backfill. If the TI value of the electrolyte in the backfill exceeds 19.0, the backfill may hinder the dissipation of gases generated from electrodes such as the anode. In either case, sufficient corrosion protection cannot be obtained. The TI value of the electrolyte in the backfill is preferably 1.4 to 19.0, more preferably 5.0 to 19.0.

[0029] From the viewpoint of ensuring that the effects resulting from the electrolyte's TI value being within the specified range are achieved more reliably, the viscosity V1 of the electrolyte is preferably 1,000 to 109,000 mPa·s, more preferably 2,500 to 109,000 mPa·s, and the viscosity V2 of the electrolyte is preferably 600 to 6,000 mPa·s, more preferably 1,000 to 6,000 mPa·s, assuming that the viscosity V2 is smaller than the viscosity V1.

[0030] The following describes the backfill of the second invention. The electrolyte contained in the backfill of the second invention has a retention rate of 10% or more and an electrolytic voltage of 2.0 to 5.0V, as measured by the following method. The aforementioned retention rate is an indicator of the dissipation of the electrolyte from the backfill. It is the rate of change in mass of the retaining material before and after contact between the retaining material holding the electrolyte and the highly absorbent diatomaceous earth board. A higher retention rate indicates that the electrolyte is less likely to dissipate from the backfill. The electrolysis voltage is an indicator of the gas diffusivity of the electrolyte, and is the so-called bath voltage. The smaller the value of the electrolysis voltage, the higher the gas diffusivity of the electrolyte, and the easier it is for the electrode gas generated in the electrolyte to dissipate from the backfill. When gas is generated from the electrode in the electrolyte, bubbles are generated on the surface of the electrode. If the gas diffusivity of the electrolyte is high, the bubbles detach from the surface of the electrode and move to near the liquid surface of the electrolyte, and do not remain on the surface of the electrode. However, if the gas diffusivity of the electrolyte is low, the bubbles do not detach from the surface of the electrode and remain near the point of generation. If many gas bubbles accumulate on the surface of the electrode during electrolysis, the effective area of ​​the electrode decreases, and the electrolysis voltage increases.

[0031] If the electrolyte retention rate of the backfill is less than 10%, there is a risk that the electrolyte will dissipate into the surrounding environment. Furthermore, if the electrolysis voltage of the electrolyte in the backfill exceeds 5.0V, the dissipation of gases generated from electrodes such as the anode may be inhibited. The electrolyte retention rate of the backfill is preferably 20% or more, more preferably 60% or more, and ideally 100%. The electrolytic voltage of the backfill electrolyte is preferably 2.0 to 5.0 V, more preferably 2.0 to 4.0 V. The retention rate and electrolysis voltage can be adjusted by appropriately adjusting the composition, viscosity, and other characteristics of the electrolyte. The electrolyte contained in the backfill of the first invention (an electrolyte in which viscosity V1 and V2 and TI value are within the specified range) may have a retention rate of 10% or more and an electrolysis voltage of 2.0 to 5.0V.

[0032] <Method for measuring retention rate> A measurement sample is prepared by holding the electrolyte to be measured in a flat holding material. After measuring the mass (M0) of the measurement sample, the measurement sample is placed on a flat diatomaceous earth plate and left to stand for 14 days with a load of 1 kPa applied to the measurement sample. After the standing period, the mass (M1) of the measurement sample is measured, and the retention rate is calculated using the following formula (1). Retention rate (%)=(M1 / M0)×100...(1)

[0033] <Method for measuring electrolytic voltage> The electrolyte to be measured was measured at a temperature of 25°C and a current density of 1 mA / cm². 2 Electrolysis is performed under conditions of an electrolysis time of 5 hours, and the voltage between the cathode and anode (bath voltage) is measured.

[0034] To elaborate on the method for measuring the retention rate, any material capable of absorbing and retaining electrolyte can be used as the retaining material, such as melamine foam. A commercially available melamine foam suitable for use as a retaining material is BASF's "Basotect." The amount of electrolyte to be retained by the retaining material (electrolyte retention amount) is 50-120 g per unit area (1 square decimeter) of the retaining material, i.e., 50-120 g / dm². 2 The method for retaining the electrolyte in the retaining material is not particularly limited; for example, methods include immersing the retaining material in the electrolyte or applying the electrolyte to the retaining material. As the diatomaceous earth board, for example, Fujiwara Chemical Co., Ltd.'s "NEW Foot Dry Bath Mat" can be used. Applying a load of 1 kPa to the measurement sample can be done, for example, by placing a weight on top of the measurement sample.

[0035] To elaborate on the method for measuring the electrolytic voltage, the electrolysis of the electrolyte can be carried out according to conventional methods. Typically, this is done by immersing the cathode and anode in an electrolyte at 25°C, connecting both electrodes to an external power source, and applying a voltage between the electrodes using the external power source. The time during which this voltage is applied (energization time) is the "electrolysis time." The cathode and anode are made of the same material. The material and shape of the cathode and anode are not particularly limited, provided that they are suitable for use as electrodes.

[0036] With regard to the first invention, from the viewpoint of reliably adjusting the viscosity V1 and V2 of the electrolyte and the TI value to the specified range, and with regard to the second invention, from the viewpoint of reliably adjusting the retention rate of the electrolyte and the electrolysis voltage to the specified range, it is preferable that the electrolyte further contains, in addition to the electrolyte and solvent, one or more thickening agents selected from xanthan gum, carrageenan, pectin, and carboxymethylcellulose. Among these thickening agents, xanthan gum is particularly preferred because it can achieve a higher level of both preventing the dissipation of the electrolyte and promoting the dissipation of the electrode gas.

[0037] The amount of thickener in the electrolyte (or the total amount if the electrolyte contains two or more types of thickeners) is preferably 0.25 to 3% by mass, more preferably 0.75 to 3% by mass, relative to the total mass of the electrolyte. If the amount of thickener is too low, its use is not very meaningful, and if the amount of thickener is too high, the electrochemical reaction on the anode necessary to supply the corrosion protection current may be inhibited.

[0038] The electrolyte contained in the electrolyte solution can be any electrolyte conventionally used in this type of backfill without any particular limitations. Preferred electrolytes in the present invention include acetates such as magnesium acetate, lithium acetate, sodium acetate, and potassium acetate; chlorides such as magnesium chloride, lithium chloride, sodium chloride, and calcium chloride; and nitrates such as magnesium nitrate, lithium nitrate, and potassium nitrate. One of these deliquescent salts can be used alone or in combination of two or more. Among these deliquescent salts, acetates are particularly preferred, and magnesium acetate is especially preferred because its performance can be further improved when combined with a thickener such as xanthan gum.

[0039] The electrolyte content in the electrolyte solution (or the total content if the electrolyte solution contains two or more types of electrolytes) is preferably 5 to 70% by mass, more preferably 15 to 50% by mass, relative to the total mass of the electrolyte solution.

[0040] The solvent used in this type of backfill can be used without any particular restrictions as the solvent in the electrolyte. Typically, the electrolyte is an aqueous electrolyte solution containing water as the solvent.

[0041] In this invention, preferred solvents include water and a mixture of water and a polyhydric alcohol (aqueous solution of polyhydric alcohol). By using an aqueous solution of polyhydric alcohol as the solvent for the electrolyte, the effects of having the electrolyte's TI value within the specified range can be further improved. In particular, when magnesium acetate is used as the electrolyte, using an aqueous solution of polyhydric alcohol as the solvent for the electrolyte eliminates the low deliquescence, which is a drawback of magnesium acetate, and makes it possible to impart high water retention to the backfill, thereby more effectively preventing the evaporation of the electrolyte from the backfill. Examples of polyhydric alcohols include glycerin, polyethylene glycol, polypropylene alcohol, polyglycerin, ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,2-pentanediol, 1,2-hexanediol, maltitol, and sorbitol. These can be used individually or in combination of two or more. Among these polyhydric alcohols, glycerin is particularly preferred because it can maintain a high level of water retention in the backfill over a long period of time. The proportion of polyhydric alcohol in the total mass of the aqueous solution of polyhydric alcohol is preferably 1 to 60% by mass, more preferably 10 to 50% by mass, with the remainder being water.

[0042] As a retaining material for holding the electrolyte, any material conventionally used in this type of backfill can be used without particular limitation. Examples include sheet-like retaining materials such as cellulose fiber aggregates, melamine foam, urethane foam, and HIPE foam; and powder-like retaining materials such as bentonite and perlite. One of these can be used alone or in combination of two or more. The HIPE foam is obtained by encapsulating an aqueous phase consisting of an aqueous liquid such as water in a high proportion within an organic phase containing vinyl monomers, a crosslinking agent, an emulsifier, a polymerization initiator, etc., to form a water-in-oil high internal phase emulsion (HIPE), and then polymerizing the organic phase in the emulsion. The HIPE foam has a buoyant structure in which numerous bubbles exist within the polymer of vinyl monomers, and also has a continuous buoyant structure in which numerous pores are formed that connect the bubbles.

[0043] In the backfill of the present invention, the amount of electrolyte held per unit area (1 square decimeter) of the retaining material cannot be determined definitively as it varies depending on the type and thickness of the retaining material, but is generally preferably 50 to 200 g / dm 2 Comfortable 50-120g / dm 2 That is the case.

[0044] The backfill of the present invention can be manufactured according to conventional methods. A method for manufacturing the backfill typically comprises a first step of preparing an electrolyte and a second step of holding the electrolyte prepared in the first step in a retaining material, and the backfill of the present invention is obtained by carrying out the second step. Regarding the first step described above, when preparing the electrolyte, the solvent may be heated in order to completely dissolve the electrolyte and the thickener in the solvent. When the electrolyte contains a polyhydric alcohol such as glycerin, the electrolyte is typically prepared by dissolving the electrolyte and the thickener in the solvent and then adding the polyhydric alcohol to the solvent. Another method for preparing the electrolyte is to first disperse the thickener in a polyhydric alcohol, and then add the electrolyte and solvent to the polyhydric alcohol. This alternative preparation method suppresses the inconvenience of the thickener forming clumps, and makes it possible to prepare the electrolyte efficiently. With respect to the second step, the method for retaining the electrolyte in the retaining material is not particularly limited, and typically the electrolyte is applied to the retaining material or the retaining material is immersed in the electrolyte to impregnate it. It is preferable that the electrolyte is uniformly distributed throughout the retaining material.

[0045] Figure 3 shows another embodiment of the backfill of the present invention. The other embodiments described later will primarily describe configurations that differ from the backfill 1 described above, while similar configurations will be denoted by the same reference numerals and their descriptions will be omitted. Configurations not specifically described in the embodiments described later will be appropriately covered by the description of backfill 1.

[0046] The backfill 1A constituting the cathodic protection structure 10A shown in Figure 3 has a laminated structure (specifically, a two-layer structure) of multiple functional layers 2 and 3, each containing an electrolyte and a retaining material that holds the electrolyte. Of the multiple functional layers 2 and 3, the functional layer 3 closest to the surrounding environment (concrete 12 in the illustrated form) of the metal material 13 to be protected from corrosion consists of the cathodic protection backfill of the present invention described above. That is, the functional layer 3 has an electrolyte with a viscosity V1 of 300 to 109,000 mPa·s, a viscosity V2 of 200 to 6,000 mPa·s, a TI value of 1.3 to 19.0, and / or a retention rate of 10% or more of the electrolyte, and an electrolytic voltage of 2.0 to 5.0 V. On the other hand, the configuration of the functional layer 2 is not particularly limited. For example, the functional layer 2 may have a configuration similar to that of the functional layer 3 of the first invention, and the TI value of the electrolyte may be in the range of 1.3 to 19.0, or it may not have thixotropy. The configuration of the functional layer 2 can be the same as that of a conventionally known backfill.

[0047] Backfill 1A having such a layered structure also provides the same effect as backfill 1 with a single-layer structure. If the functional layer 2 has a TI value of the electrolyte contained therein outside the range of 1.3 to 19.0, or a retention rate of less than 10%, or an electrolytic voltage outside the range of 2.0 to 5.0V, and has the same configuration as conventionally known backfills, that is, if the electrolyte in the functional layer 2 is low viscosity and relatively fluid, there is a concern that the electrolyte may leak out and dissipate into the concrete 12. However, in the cathodic protection structure 10A, a functional layer 3 is interposed between the functional layer 2 and the concrete 12, where the viscosity V1 of the electrolyte is 300 to 109,000 mPa·s, the viscosity V2 is 200 to 6,000 mPa·s, and the TI value is in the range of 1.3 to 19.0, or where the retention rate of the electrolyte is 10% or more and the electrolytic voltage is 2.0 to 5.0V, thus eliminating such concerns. Furthermore, if the electrolyte in the functional layer 2 is low viscosity and relatively fluid, the functional layer 2 is permeable to the gas generated from the electrode 14. Therefore, in the cathodic protection structure 10A, the dissipation of the gas is promoted, and gas accumulation is less likely to form between the electrode 14 and the backfill 1A.

[0048] The present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. For example, while the backfills 1 and 1A in the above embodiment were for cathodic protection of concrete structures using a galvanic anode method, the cathodic protection method to which the present invention can be applied is not particularly limited, and can be applied, for example, to cathodic protection using an external power supply method. Furthermore, the present invention encompasses embodiments that include features of both the first and second inventions. That is, the present invention may be "a cathodic protection backfill provided near a cathodic protection electrode that passes a corrosion protection current through an embedded metal material, comprising an electrolyte and a retaining material that holds the electrolyte, wherein the electrolyte contains an electrolyte and a solvent, and has a viscosity V1 of 300 to 109,000 mPa·s, a viscosity V2 of 200 to 6,000 mPa·s, a thixotropy index of 1.3 to 19.0 (having the features of the first invention), and has a retention rate of 10% or more and an electrolytic voltage of 2.0 to 5.0 V (having the features of the second invention)." [Examples]

[0049] [Preparation of electrolyte solution] Electrolytes A-T and Z1-Z2, containing electrolytes and solvents, were prepared. For each electrolyte, viscosity V1, V2, and TI values, as well as retention rate and electrolysis voltage, were measured using the method described above, and gas diffusivity was evaluated using the method described below. These results, along with the composition of each electrolyte, are shown in Tables 1-2 below.

[0050] Regarding the measurement method for retention rate, a flat melamine foam plate (BASF's "Basotect") with a rectangular shape in plan view (54 mm long, 54 mm wide) and a thickness of 12 mm was used as the electrolyte retention material, and a flat diatomaceous earth plate (Fujiwara Chemical Co., Ltd.'s "NEW Ashikan Bath Mat") with a rectangular shape in plan view (70 mm long, 70 mm wide) and a thickness of 9 mm was used as the diatomaceous earth plate. The retention material was immersed in the electrolyte to be measured, and the electrolyte was distributed throughout the entire retention material. The electrolyte retention rate per unit area of ​​the retention material was 108 g / dm². 2 The board was held in place in this manner. Furthermore, a holding material containing an electrolyte solution was placed on one side (top surface) of the diatomaceous earth board so that the entire surface of the holding material facing the diatomaceous earth board (bottom surface) was in contact with the holding material, and a weight was placed on top of the holding material so that a load of 1 kPa was applied to the entire holding material.

[0051] Regarding the method for measuring electrolytic voltage, linear electrodes with a diameter of 1.6 mm and a length of 100 mm were used as electrodes (cathode and anode). The surface of the electrode portion of the linear electrode, which was made of platinum-plated titanium, was covered with Teflon® tape. The Teflon® tape was peeled off from each end of the linear electrode in the longitudinal direction for a length of 10 mm, exposing the electrode portion. Two electrodes were immersed in 100 mL of the electrolyte to be measured, with a distance of 20 mm between the two electrodes, and electrolysis was performed.

[0052] <Method for evaluating gas diffusivity> In the above-described method for measuring electrolytic voltage, the anode and cathode were visually observed 5 hours after the start of electrolysis (just before the end of the test) and evaluated according to the following evaluation criteria. Oxygen gas or oxygen gas and chlorine gas were generated from the anode, and hydrogen gas was generated from the cathode.

[0053] (Evaluation criteria for gas diffusivity) • Evaluation A: Five hours after the start of electrolysis, bubbles had detached from the electrode surface at both the anode and cathode. These detached bubbles rose to the surface of the electrolyte and escaped from the electrolyte, indicating good gas diffusion. Evaluation B: Five hours after the start of electrolysis, bubbles were observed on the surface of at least one of the anode and cathode, and no detached bubbles were visible on the surface of the electrolyte, indicating poor gas diffusion.

[0054] [Table 1]

[0055] [Table 2]

[0056] Figure 4 shows the relationship between the rotor speed of the B-type viscometer and the viscosity of electrolytes A-T and Z1-Z2, based on viscosity measurements using a B-type viscometer. As shown in Tables 1 and 2, electrolytes A-T all have a viscosity V1 of 300-109,000 mPa·s, a viscosity V2 of 200-6,000 mPa·s, and a TI value of 1.3-19.0. As shown in Figure 4, in viscosity measurements using a B-type viscometer at a temperature of 25°C, the viscosity decreases as the rotor speed increases in the range of 3-100 rpm. In contrast, as shown in Tables 1 and 2, the viscosity V1 and V2 and TI values ​​of electrolytes Z1 and Z2 are outside the specified range, and as shown in Figure 4, in the viscosity measurements, they exhibit different properties from electrolytes A-T in the range of 3-100 rpm.

[0057] Figure 5 shows the electrolytic voltages of electrolyte A and electrolyte Z2 measured by the method described above. In electrolyte Z2, the electrolytic voltage rose sharply from about 1300 seconds after the start of electrolysis, reaching 12V at 1500 seconds, whereas in electrolyte A, no significant increase in electrolytic voltage was observed even after 18000 seconds from the start of electrolysis, and the electrolytic voltage remained stable for a long period of time. Electrolyte Z2 had poor gas diffusivity, and many gas bubbles accumulated on the electrode surface during electrolysis, whereas electrolyte A had excellent gas diffusivity, and during electrolysis, gas bubbles detached from the electrode surface, rose to the liquid surface of the electrolyte, and escaped outside. Therefore, in order to ensure the cathodic protection performance of the backfill, it is important to impart gas diffusivity to the electrolyte contained therein, and to do so, it is effective to adjust the viscosity V1 and V2 and TI value of the electrolyte to within the specified range.

[0058] [Example 1 and Comparative Example 1] Commercially available soft polyurethane foam (kitchen sponge) was used as the electrolyte holder, and the electrolyte was held in the holder to create a backfill. In each backfill, the amount of electrolyte held per unit area of ​​the holder was 40 g / dm². 2 The electrolytes used in each backfill were as follows: Example 1: Electrolyte A ·Comparative example 1: Electrolyte Z1

[0059] [Example 2 and Comparative Example 2] Instead of using flexible polyurethane foam as a retaining material, melamine foam (BASF's "Basotect G+") was used, and the electrolyte retention capacity per unit area is 108 g / dm². 2 Except for the above, the backfill was prepared in the same manner as in Example 1 and Comparative Example 1.

[0060] [Example Test] For each example and comparative example, an energization test was conducted on the backfill using the method described below, and the anode potential and inter-electrode voltage were measured accordingly.

[0061] <Power-on test> An electrochemical corrosion protection structure similar in basic configuration to the electrochemical corrosion protection structure 10 shown in Figure 1 was fabricated. In the fabricated electrochemical corrosion protection structure, referring to Figure 1, the backfill to be measured was used as backfill 1, steel was used as the metal material to be protected 13, and a zinc anode was used as the electrode 14. The steel material and zinc anode were connected to a DC power supply, a constant current was applied, and the anode current density was 125 mA / m². 2 An energization test was performed under the following conditions. Three samples were prepared for the backfill of Example 1 and Comparative Example 1, and two samples were prepared for the backfill of Example 2 and Comparative Example 2. The arithmetic mean of the anode potential and inter-electrode voltage of these two or three samples was used as the anode potential and inter-electrode voltage for the respective example and comparative example.

[0062] Figure 6 shows the change in anode potential over time during an energizing test for the cathodic protection structure using the backfill of Example 1 or Comparative Example 1. In Example 1, the viscosity V1 of the electrolyte A contained in the backfill was in the range of 300 to 109,000 mPa·s, the viscosity V2 was in the range of 200 to 6,000 mPa·s, and the TI value was in the range of 1.3 to 19.0. Therefore, compared to Comparative Example 1, which did not meet these conditions, the anode potential remained stable in a relatively low range. Stability in a relatively low range of anode potential suppresses anode deterioration and contributes to extending the lifespan of the cathodic protection structure. In the backfill of Comparative Example 1, the electrolyte retention rate was low, and the phenomenon of electrolyte dissipation into the surrounding environment (concrete) was observed during the energizing test. In contrast, the backfill of Example 1 had a high retention rate, and such a phenomenon was hardly observed. Therefore, it is inferred that the viscosity V1 and V2 and TI value of the electrolyte being within the specified range increased the retention rate of the backfill containing them, and as a result, the anode potential was stable.

[0063] Figure 7 shows the change in inter-electrode voltage over time during an energization test for the cathodic protection structure using backfill in Example 2 or Comparative Example 2. In Example 2, the viscosity V1 of the electrolyte A contained in the backfill was in the range of 300 to 109,000 mPa·s, the viscosity V2 was in the range of 200 to 6,000 mPa·s, and the TI value was in the range of 1.3 to 19.0. Therefore, compared to Comparative Example 2, which did not meet these conditions, the inter-electrode voltage remained stable in a relatively low range. Stability in a relatively low range of inter-electrode voltage contributes to the high performance of the cathodic protection system. [Explanation of symbols]

[0064] 1.1A backfill 2,3 Functional Layers 10,10A Cathodic Protection Structure 11. Concrete structures 12 Concrete 13 Metal materials 14. Electrodes for cathodic protection 15 Reference electrode 16 Lead wires 17. Junction Box 18 Fixtures 19. Buffer material

Claims

1. A cathodic protection backfill provided near an electrochemical electrode that passes a corrosion protection current through an embedded metal material, It comprises an electrolyte and a retaining material that holds the electrolyte, The aforementioned electrolyte is a backfill for cathodic protection, containing an electrolyte and a solvent, and having a viscosity V1 of 300 to 109,000 mPa·s, a viscosity V2 of 200 to 6,000 mPa·s, and a thixotropy index of 1.3 to 19.0, as measured by the method described below. <Method for measuring viscosity V1 and V2 and thixotropy index> The viscosity of the sample to be measured is measured using a B-type viscometer under two conditions, 1 and 2, as described below. The viscosity under condition 1 is denoted as V1, and the viscosity under condition 2 as V2. The ratio of viscosity V1 to viscosity V2 (V1 / V2) is calculated and used as the thixotropy index of the sample. Condition 1: Temperature of the object to be measured: 25°C, rotation speed: 3 rpm Condition 2: Temperature of the object being measured: 25°C, rotation speed: 100 rpm

2. A cathodic protection backfill provided near an electrochemical electrode that passes a corrosion protection current through an embedded metal material, It comprises an electrolyte and a retaining material that holds the electrolyte, The aforementioned electrolyte is a cathodic protection backfill containing an electrolyte and a solvent, with a retention rate of 10% or more and an electrolytic voltage of 2.0 to 5.0 V, as measured by the method described below. <Method for measuring retention rate> A measurement sample is prepared by holding the electrolyte to be measured in a flat holding material. After measuring the mass (M0) of the measurement sample, the measurement sample is placed on a flat diatomaceous earth plate and left to stand for 14 days with a load of 1 kPa applied to it. After the aforementioned standing period, the mass (M1) of the measurement sample is measured, and the retention rate is calculated using the following formula (1). Retention rate (%) = (M1 / M0) x 100...(1) <Method for measuring electrolytic voltage> The electrolyte to be measured was measured at a temperature of 25°C and a current density of 1 mA / cm². ２ Electrolysis is performed under conditions of an electrolysis time of 5 hours, and the voltage between the cathode and anode is measured.

3. The cathodic protection bagfill according to claim 1 or 2, wherein the electrolyte contains one or more thickeners selected from xanthan gum, carrageenan, pectin, and carboxymethylcellulose.

4. The cathodic protection backfill according to claim 3, wherein the content of the thickener in the electrolyte is 0.25 to 3% by mass.

5. The cathodic protection bag fill according to claim 1 or 2, wherein the electrolyte is one or more selected from acetates, chlorides, and nitrates.

6. The cathodic protection backfill according to claim 1 or 2, wherein the solvent is water or a mixture of water and a polyhydric alcohol.

7. The cathodic protection backfill according to claim 1 or 2, wherein the retaining material is one or more selected from cellulose fiber aggregate, melamine foam, urethane foam, HIPE foam, bentonite, and perlite.

8. The aforementioned metal material is embedded in the concrete of a concrete structure or in the soil, as described in claim 1 or 2, for cathodic protection backfill.

9. A cathodic protection backfill provided near an electrochemical electrode that passes a corrosion protection current through an embedded metal material, It has a laminated structure of multiple functional layers, Each of the aforementioned functional layers includes an electrolyte and a retaining material that holds the electrolyte. A cathodic protection backfill, wherein, among the plurality of functional layers, the functional layer closest to the environment surrounding the metal material is made of the cathodic protection backfill described in claim 1 or 2.

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