JP6239992B2 - Backfill for cathodic protection - Google Patents

Description

  The present invention relates to a backfill for an galvanic anode that is used for corrosion protection of reinforced concrete structures and the like.

  In reinforced concrete structures, corrosion occurs in the reinforcing bars due to internal penetration of oxygen, water, chloride ions and the like. The volume expansion of the corrosion product causes cracks in the concrete, which further accelerates the corrosion and causes a reduction in the cross section of the reinforcing bars, thereby ultimately reducing the performance such as the strength of the structure. For this reason, various means for preventing corrosion of reinforcing bars in concrete structures have been developed, and one of them is an anticorrosion method.

  As the anticorrosion method, there are a galvanic anode method and an external power supply method. In the galvanic anode method, a metal such as zinc or aluminum, which has an electrochemically low potential relative to steel (rebar), is attached to the surface of the concrete structure as a galvanic anode, and the potential difference between this metal and steel is determined. This is a system in which a battery is configured between the two and a direct current is supplied to the steel material. In the external power supply system, an electrode for anticorrosion is installed on the surface of a concrete structure or a groove cut on the surface, the reinforcing bar in the concrete structure is used as a cathode, and the electrode for anticorrosion is changed from the electrode for anticorrosion to the cathode using a DC power supply. This is a method of preventing corrosion by changing the potential of the cathode in the base direction by supplying a direct current.

  As one of the methods of applying the galvanic anode method to reinforced concrete structures, an anticorrosion backfill (hereinafter also simply referred to as backfill) layer is provided between the concrete and the anode to reduce the ground resistance of the anode. A method is known in which a sufficient amount of current is generated from the anode by reducing and improving the electrochemical characteristics. As the backfill, for example, a powdery or particulate mixture containing bentonite and magnesium chloride and kneaded with water to form a paste is conventionally used (see Patent Document 1). However, since the paste-like backfill needs to have a certain shape-retaining property, it has a problem that it is hard and has poor extensibility, cannot be uniformly spread and coated on the anode, and the amount used cannot be made constant. Furthermore, unskilled workers have problems such as spreading and unevenness in coating.

  Also known as backfill is a gel containing a water-soluble polymer and magnesium chloride (see Patent Document 2). Since such a gel-like backfill contains a water-soluble polymer, the gel-like backfill is excellent in fluidity, has a feature that it is easy to spread and apply a predetermined amount on the anode and is easy to construct. However, generally, when a gel-like backfill is installed on the concrete surface of a reinforced concrete structure, when the reinforced concrete structure is subjected to an external force such as vibration, the viscosity decreases due to thixotropy and may leak to the outside.

JP-A-2-83383 JP 2008-57015 A

  The present invention relates to an anticorrosion backfill that is easy to manufacture, excellent in workability and shape retention, and that exhibits practically sufficient performance for a galvanic anode material.

  The present invention is a backfill for cathodic protection containing a metal chloride salt, cement and water.

  According to the present invention, there is provided an anticorrosion backfill that is easy to manufacture, has excellent workability and shape retention, and exhibits practically sufficient performance for a galvanic anode material. The backfill for cathodic protection of the present invention is not only easy to manufacture, but also has excellent workability because the manufactured backfill can be easily spread and applied to the anode. Because it maintains its shape, it is difficult to leak to the outside during use, and it can exhibit the same or better performance as the conventional product for the galvanic anode material. Useful.

FIG. 1 is a cross-sectional view schematically showing one embodiment of an anticorrosive structure for a concrete structure provided with the anticorrosive backfill of the present invention. FIG. 2 is a graph showing temporal changes in the anode potential of the cathodic protection structures of the examples and comparative examples in the energization test. FIG. 3 is an explanatory diagram of the anodic polarization test. FIG. 4 is an anodic polarization curve of the cathodic protection structure of the example and the comparative example in the energization test.

  Hereinafter, the backfill for cathodic protection of the present invention will be described. In FIG. 1, as an example of using the backfill of the present invention for cathodic protection by a galvanic anode method of a reinforced concrete structure, a concrete structure having a backfill 12 which is an embodiment of the backfill of the present invention is shown. An anticorrosion structure 10 is shown. As shown in FIG. 1, the anticorrosion structure 10 is interposed between the electrode 11 and the concrete structure 20, and an electrode 11 for an anticorrosion that sends an anticorrosion current to the steel material 21 (rebar) in the reinforced concrete structure 20. The backfill 12 is disposed, and electrical connection means is formed by connecting lead wires 13 extending from the electrode 11 and the steel material 21 in a connection box 14. The reference electrode 17 is installed in the vicinity of the steel material 21 in the concrete structure 20, and the lead wire 13 connected to the reference electrode 17 is drawn to the connection box 14, thereby measuring the potential of the steel material 21. Monitoring is possible.

  The electrode 11 is a plate-like object made of a metal having an electrochemically low potential with respect to the steel material 21 in the concrete structure 20, such as zinc or aluminum, and is fixed by a fixture 15 such as an anchor bolt or a rivet. It is fixed on the surface of the concrete structure 20. In the space where the backfill 12 is not disposed between the electrode 11 and the surface of the concrete structure 20 (installation surface of the electrode 11), a cushioning material such as epoxy resin, silicon resin, foamed polyethylene, and foamed polyurethane is provided. The buffer layer 16 is formed by filling.

  The cathodic protection structure 10 can lower the electric potential of the cathodic protection electrode 11 for a long period of time in the cathodic protection of the concrete structure 20 and release hydrogen gas generated when the cathodic protection electrode 11 is dissolved in water to the outside. It has air permeability and has the advantage that the electromotive force (potential difference between the electrode 11 and the steel material 21) required for cathodic protection increases due to the development of such excellent energization performance and air permeability. Sustain efficiency. Such an effect of the anticorrosion structure 10 largely depends on the performance of the backfill 12. The backfill 12 contains at least a metal chloride salt, cement, and water. The thickness of the backfill 12 is preferably 3 to 20 mm, more preferably 5 to 15 mm.

  The metal chloride salt contained in the backfill of the present invention only has the effect of reducing the resistivity and keeping the surface of the anode (electrode 11 in the anticorrosion structure 10) active and maintaining a low potential. There is also hygroscopicity. Examples of the metal chloride salt having such an action include magnesium chloride, sodium chloride, calcium chloride, potassium chloride, and lithium chloride. In the present invention, one or more of these are selected and used. can do. Among these, magnesium chloride is particularly preferably used in the present invention because it has a high potential lowering effect. The content of the metal chloride salt is preferably 15 to 30% by mass, more preferably 20 to 26% by mass in the backfill of the present invention.

  One of the main features of the backfill of the present invention is that it contains cement. Cement has the property of losing fluidity after the lapse of time when water is added and kneaded, and has the property of changing the backfill of the present invention including this to paste or clay and maintaining its shape. The backfill of the present invention containing cement is easy to manufacture because it can be obtained simply by mixing various components (metal chloride, cement, water, etc.), and after manufacture, it can be easily spread and applied to the anode. Therefore, it is excellent in workability and, after construction, has a feature that it is difficult to leak outside during use because it maintains sufficient shape retention.

  As the cement used in the present invention, various portland cements such as normal, moderately hot and sulfate-resistant; various mixed cements obtained by mixing these portland cements with blast furnace slag, fly ash or silica (blast furnace cement, fly ash cement, silica cement) In the present invention, one of these can be used alone or two or more can be used in combination. However, early strength / super early strength Portland cement and alumina cement generate a large amount of heat due to heat of hydration, so it is preferable to avoid using them in the present invention. The cement content is preferably 6 to 16% by mass, more preferably 8 to 14% by mass in the backfill of the present invention. If the cement content is too low, the backfill may become weak and shape retention may be reduced, and the backfill may leak to the outside. If the cement content is too high, other components of the backfill It may be difficult to uniformly disperse, and the ease of manufacture and workability may be reduced.

  Further, the water content is preferably 15 to 30% by mass, more preferably 20 to 28% by mass in the backfill of the present invention. If the water content is too low, it will be difficult to uniformly disperse other components of the backfill, and there is a risk that manufacturability and workability will be reduced. If the water content is too high, the backfill will be lost. There is a risk that the backfill will leak out.

  In addition to the above components (metal chloride salt, cement and water), the backfill of the present invention may further contain bentonite. Bentonite has a high water retention property and a property of reducing ground resistance, and can impart high water retention property and viscosity to the backfill of the present invention including the bentonite. Bentonite includes calcium type and sodium type, and both can be used in the present invention, but sodium type bentonite having higher water absorption / swellability than calcium type is advantageous. This sodium-type bentonite is bentonite in which alkali metals such as sodium ions and potassium ions are adsorbed between layers of montmorillonite sheet-like crystals. The content of bentonite is preferably 35 to 50% by mass, more preferably 40 to 46% by mass in the backfill of the present invention. If the content of bentonite is too small, the water retention of the backfill may be insufficient, and if the content of bentonite is too large, the surface of the backfill may become soft and may be easily washed away. .

  If necessary, the backfill of the present invention may further contain one or more metal sulfates such as magnesium sulfate, calcium sulfate and sodium sulfate; metal nitrates such as magnesium nitrate, calcium nitrate and lithium nitrate. It may be included.

  The resistivity of the backfill of the present invention is preferably 10 to 100 Ω · cm, more preferably 10 to 20 Ω · cm. When the resistivity of the backfill is within such a specific range, an effect of stabilizing the potential of the electrode for anticorrosion for a long time is exhibited. The backfill whose composition is as described above may have a resistivity within such a specific range.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such embodiments.

[Example 1]
Bentonite and cement were mixed with a mixer to prepare mixed powder A. Bentonite 250 mesh manufactured by Hoyo Bentonite Mining Co., Ltd. was used as the bentonite, and ordinary Portland cement manufactured by Tokuyama Co., Ltd. was used as the cement. Separately, water was added to magnesium chloride (hexahydrate) and stirred to prepare an aqueous magnesium chloride solution B. And mixed powder A and magnesium chloride aqueous solution B were knead | mixed with the mixer, and the target backfill was prepared. The content of each component in the backfill of Example 1 thus obtained is as follows. Bentonite 43% by mass, magnesium chloride (hexahydrate) 23% by mass, cement 11% by mass, water 23% by mass.

[Comparative Example 1]
Water was added to the conventionally used bentonite backfill mixed powder and kneaded to prepare the backfill of Comparative Example 1. Bentonite 250 mesh manufactured by Hoyo Bentonite Mining Co., Ltd. was used as the bentonite. The content of each component in the backfill of Comparative Example 1 thus obtained is as follows. Bentonite 32% by mass, magnesium chloride (hexahydrate) 19% by mass, gypsum 9% by mass, water 40% by mass.

<Evaluation of workability (application time and application unevenness)>
As the anode plate, six zinc anode plates having a rectangular shape in a plan view of 500 × 1000 mm and a thickness of 1 mm were used. A backfill to be evaluated was applied to the entire surface of each of the six zinc anode plates so that the thickness after application was 10 mm to form a backfill layer. The time (coating time) required to apply the backfill on one surface of all six anode plates was measured. Moreover, the surface state (presence / absence of coating unevenness) of each backfill layer was visually evaluated.

  The application time of the backfill is about 10 minutes in Example 1 containing cement and about 30 minutes in Comparative Example 1 not containing cement. Example 1 compares the application time due to appropriate fluidity during application. It was shortened to about 1/3 of Example 1. In addition, in the visual observation of the surface of the backfill layer, Example 1 was satisfactory without coating unevenness, but Comparative Example 1 produced some coating unevenness and the contrast of coating unevenness was conspicuous, and the surface state was favorable. It wasn't.

<Anode performance test (measurement of anode potential and calculation of generated electricity)>
As the concrete structure, reinforced concrete (100 × 200 × 300 mm) having rebars with a diameter of φ13 mm arranged in a lattice pattern and having a cover thickness of 37 mm and a pitch of 100 mm inside is evaluated. The surface of this reinforced concrete is evaluated. An aluminum anode plate (1 × 180 × 280 mm) was fixed through a 10 mm-thick backfill layer made of the target backfill, and an anticorrosion structure of a concrete structure having the structure shown in FIG. 1 was produced. Using the prepared anticorrosion structure, constant current electrolysis at 10 mA / m ² was performed using the reinforcing bar in the reinforced concrete as a counter electrode. A reference electrode was embedded in reinforced concrete using an MMO electrode, and the anode potential was measured over time. The result is shown in FIG. Further, the mass of the aluminum anode plate before and after the start of energization was measured, and the amount of generated electricity was calculated from the amount of decrease in the mass.

  As shown in FIG. 2, the anode potential in the case of using the backfill of Example 1 has a smaller variation width than the backfill of Comparative Example 1, and maintains stable anode performance even during long-term use. It was. From this, it can be seen that the inclusion of cement in the backfill is effective not only for the backfill workability but also for improving the electrical performance, particularly for the long-term stability of the anode potential.

  Further, the amount of electricity generated when the backfill of Example 1 was used was 762 A · hr / kg, and the amount of electricity generated when the backfill of Comparative Example 1 was used was 389 A · hr / kg. It can be seen that Example 1 has a larger value of generated electricity than that of Comparative Example 1, and has excellent anode performance.

<Anode polarization test>
FIG. 3 shows an apparatus configuration of the anodic polarization test. A counter electrode 51 made of hollow cylindrical stainless steel having a diameter of 90 mm and a height of 130 mm is disposed in a hollow portion of the hollow cylindrical test tank 50, and a backfill 52 having fluidity to be evaluated is formed in the hollow portion of the counter electrode 51. Further, a rod-like zinc anode 53 of 99.995% by mass or more of zinc was embedded in the center portion of the test tank 50 in the backfill 52 so that one end portion in the longitudinal direction protruded from the backfill 52. In the rod-shaped zinc anode 53, only a rectangular portion with a surface area of 20.1 cm ² near the other end in the longitudinal direction is a zinc exposed portion 53A, and the other end in the longitudinal direction of the exposed portion 53A is rubber. It is covered with a cap 54 and one end side in the longitudinal direction is covered with a vinyl tape 55. Further, a reference electrode 56 made of a silver / silver chloride electrode was embedded in the backfill 52 in the vicinity of the zinc anode 53 (exposed portion 53A). A potential sweep device 57, a potentiostat 58, and a recorder 59 were arranged outside the test tank 50, and these were connected to each part in the test tank 50 with lead wires.
The anodic polarization test was performed under the condition of a sweep rate of 20 mV / min after 1 hour had passed since the backfill 52 was poured into the counter electrode 51. In addition, the anode polarization test is performed by preventing the diffusion of moisture by covering the outer surface of the backfill 52 to be evaluated with a wrap (non-breathable resin film), and without covering the outer surface with a wrap. The test was carried out under two conditions. The result is shown in FIG.

As shown in FIG. 4, when the backfill of Example 1 was used, for a current value exceeding 30 mA / m ² (per anode area), which is the maximum current density normally used in cathodic protection. However, the anode potential was low and constant as compared with the case of using the backfill of Comparative Example 1, and the anode performance was good. For this reason, the inclusion of cement in the backfill is effective not only for the backfill workability but also for improving the electrical performance, especially for increasing the electromotive force (potential difference between the anode and steel) required for anticorrosion. It can be seen that it is.

10 Electro-corrosion-proof structure 11 Electro-corrosion-proof electrode (galvanic anode)
12 Backfill 13 Lead wire 14 Connection box 15 Fixture 16 Buffer layer 17 Reference electrode 20 Concrete structure 21 Steel material (rebar)

Claims (1)

Containing metal chloride salt, cement and water , the metal chloride salt is magnesium chloride,
Furthermore, it contains 35 to 50% by mass of bentonite, 15 to 30% by mass of magnesium chloride, 6 to 16% by mass of cement, and 15 to 30% by mass of water . Backfill.

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