Galvanic anode for reinforced concrete structures with an electrolyte having a PH between 5.5 and 7.5

Abstract

The present application relates to a galvanic anode (100) for the protection of a steel reinforcement (200) of reinforced concrete structures. The galvanic anode (100) comprises: a first metal layer (1), a second metal layer (2) electrically connected to the first metal layer (1), an electrolyte (4) surrounding the first metal layer (1) and the second metal layer (2); the electrolyte (4) having a pH between 5.5 and 7.5 and the electrolyte (4) comprising an ion-conducting gel; a casing (6) contains the electrolyte (4); said casing being made of a material that allows for an ion exchange between the electrolyte (4) and the concrete suitable for surrounding the anode (100).

Description

[0001] GALVANIC ANODE FOR REINFORCED CONCRETE STRUCTURES WITH AN ELECTROLYTE HAVING A PH BETWEEN 5.5 AND 7.5

[0002] DESCRIPTION

[0003] The present invention relates to a galvanic anode for reinforced concrete structures.

[0004] As it is well known, a reinforced concrete structure comprises a steel reinforcement embedded in concrete. Such a reinforcement is in a state of passivity due to a thin film of oxides that is formed on the surface because of the high pH of the concrete. However, with the passing of time, external corrosive agents (such as carbonation and chlorides) lower the pH of the concrete and destroy the thin passivation film, initiating the corrosion process that results in the formation of rust. The resulting rust occupies a much larger volume than the original steel consumed by it. Therefore, the expansion of the reinforcement caused by rust results in splitting, delamination and cracking of the concrete with possible structural implications.

[0005] According to a report of the Federal Highway Administration, the cathodic protection of the reinforcement is the only rehabilitation technique capable of stopping corrosion in the reinforcements of the concrete structures contaminated by chloride regardless of its content.

[0006] The cathodic protection of a reinforcement is obtained by using impressed current systems, either by electrically connecting a sacrificial anode to the positive pole of a power supply, or with galvanic anodes generally made of zinc. Normally, galvanic anodes are preferred because they do not require external power sources, are easy to install and have a very low maintenance. The galvanic anodes are attached to the steel reinforcements by means of wires or metal connections. Once the galvanic anode is connected to the steel reinforcement and immersed in the cement matrix, the steel reinforcement becomes the cathode of a galvanic pile, whereas the anode will be the positive pole that will generate an electrical path for the movement of the electrons from the anode to the cathode in order to protect the steel. Usually, the anode includes a sacrificial zinc core that is immersed in a prefabricated cement mortar surrounding the zinc core. Predominantly, special mortars with a highly alkaline pH (pH> 14) are used, in which the cement mortar is composed of specially formulated alkalis. In other cases, the zinc core is surrounded by conducting mortars or electrolytes with different formulation.

[0007] Once installed, the zinc of the anode corrodes more than the reinforcement to which it is connected, thus controlling the galvanic corrosion control of the steel reinforcement adjacent to the anode.

[0008] The galvanic anodes are also used to minimize the ring effect (also known as incipient anode or halo effect) in the repairs of the reinforced concrete structures. Such an effect occurs when a reinforced concrete structure is repaired. The repair material creates a strongly cathodic area in the repair, which accelerates corrosion in the steel of the reinforcing bars immediately adjacent to the repair area, and is precisely known as halo effect because of the involvement of the area near the protected zone.

[0009] US2015 / 167178 discloses a galvanic anode according to the preamble of claim 1 .

[0010] The purpose of the present invention is to eliminate the drawbacks of the prior art by providing a galvanic anode for reinforced concrete structures that is reliable and able to generate a more effective and long-lasting protection.

[0011] Another purpose is to provide such a galvanic anode that is versatile and capable of operating without power supply, which produces an effect similar to that of the impressed current without the known drawbacks.

[0012] Another purpose is to provide such a galvanic anode that is easy to fabricate and install.

[0013] These purposes are achieved in accordance with the invention with the features of the appended independent claims.

[0014] Advantageous achievements of the invention appear from the dependent claims.

[0015] The galvanic anode according to the present invention is defined in claim Such an anode combines the high-level performance of an electrochemical treatment system similar to an impressed current for a polarization of the steel reinforcements, followed by a long-term galvanic protection, without the use of batteries or external power supplies. The impressed current is used to push away the corrosive agents in the steel reinforcement and to restore the alkalinity of the concrete in contact with the steel reinforcement.

[0016] Further features of the invention will become clearer from the following detailed description, which refers to a purely illustrative and therefore nonlimiting embodiment, illustrated in the appended drawings, wherein:

[0017] Fig. 1 is a longitudinal sectional view of a galvanic anode according to the invention;

[0018] Fig. 2 is a perspective view of the galvanic anode arranged on a reinforcement of a concrete structure;

[0019] Fig. 3 is an exploded sectional view that illustrates the various components of a preferred embodiment of the anode according to the invention;

[0020] Fig. 4 is a perspective view that illustrates the anode of Fig. 3 in assembled condition, wherein some layers are sectioned;

[0021] Fig. 5 is a graph illustrating a diffraction test performed on a sample containing only nano-clay and a sample containing nano-clay and conducting paste;

[0022] Fig. 6 is a graph illustrating the electrical potential of four different anodes, in relation to time; and

[0023] Fig. 7 is a graph illustrating the electrical potential of five different anodes in relation to time.

[0024] With the aid of the Figures, the galvanic anode according to the invention, which is comprehensively indicated with the reference numeral 100, is described.

[0025] With reference to Fig. 1 , the anode (100) comprises:

[0026] - a first metal layer (1 ),

[0027] - a second metal layer (2) connected to the first metal layer (1 ), and - an electrolyte (4) surrounding the first metal layer (1 ) and the second metal layer (2).

[0028] The first metal layer (1 ) comprises a first sacrificial metal (10) that is more electro-chemically negative than the steel that is commonly used in concrete reinforcements. By way of example the first sacrificial metal (10) can be Zinc. The first metal layer (1 ) may consist of a zinc bar or plate, or it may be a multilayer comprising multiple layers of zinc plates. The first metal layer (1 ) has a thickness (S1 ) of approximately 1 - 40 mm.

[0029] The second metal layer (2) includes a second sacrificial metal (20) that is more electro-chemically negative than the first sacrificial metal (10). By way of example, the second sacrificial metal (20) may be Magnesium. The second sacrificial metal (20) is electrically connected to the first sacrificial metal (10).

[0030] The second metal layer (2) is superimposed on the first metal layer (1 ), for example, the second metal layer (2) is welded to the first metal layer (1 ). The second metal layer (2) is smaller in size than the first metal layer (1 ).

[0031] The first metal layer (1 ) has a length (L1 ) that can vary from 2 cm to 1 m. The second metal layer (2) has a length (L2) that can vary from 1 cm to 95 cm. The ratio of the length (L2) of the second metal layer (2) to the length (L1 ) of the first metal layer is 0.1 -0.95. The second metal layer (2) is arranged centrally to the length of the first metal layer (1 ).

[0032] The second metal layer (2) has a thickness (S2). The ratio of the thickness (S2) of the second metal layer (2) to the thickness (S1 ) of the first metal layer is 0.1 -0.6.

[0033] Advantageously, the galvanic anode (100) also comprises a third metal layer (3) that is not electrically connected to the first metal layer (1 ) and to the second metal layer (2).

[0034] However, the third metal layer (3) is totally surrounded by the electrolyte (4). In fact, a portion of the electrolyte (4) separates the second metallic layer (2) from the third metallic layer (3).

[0035] The third metal layer (3) comprises a third sacrificial metal (30) that is more electro-chemically negative than the steel that is commonly used in the concrete reinforcements, but less electro-chemically negative than the second metal layer (2). The third metal layer (3) can be of the same metal as the first metal layer (1 ). For example, the third metal layer (3) can be a zinc plate.

[0036] The third metal layer has a thickness (S3) that is thin compared to the thickness (S2) of the second metal layer. The thickness (S3) of the third metal layer can be approximately 50 to 150 pm.

[0037] The third metal layer (3) can have an omega-shaped longitudinal section in such a way to completely surround the second metal layer (2).

[0038] The electrolyte (4) comprises an ion-conducting gel (40) with a pH between 5.5 and 7.5. The use of an electrolyte with a pH comprised between 5.5 and 7.5 is a novelty in the field of galvanic anodes because the galvanic anodes of the prior art are usually embedded in alkaline cement mortars with pH > 14.

[0039] Such an ion-conducting gel (40) may be a gel that is commonly used for medical use for the application of ECG electrodes to the skin or for an ultrasound scan or ultrasound application.

[0040] Three medical gel compositions that are commonly found on the market are given below.

[0041] ELECTROMEDICAL CONDUCTING GEL FOR ECG:

[0042] 1. Deionized water (60-85%): main solvent, essential for electrical conduction.

[0043] 2. Glycerin (5-10%): wetting agent that contributes to the consistency of the gel.

[0044] 3. Carbomer (1 -2%): thickening agent that imparts viscosity to the gel.

[0045] 4. Sodium chloride (NaCI) (0.3-2%): electrolytic salt used to adjust the electrical conductivity of the gel and stabilize the PH between 5.5 and 7.5.

[0046] 5. Hydroxyethyl cellulose (0.5-1%): stabilizing agent that stabilizes the formula and improves consistency.

[0047] CONDUCTING GEL FOR MEDICAL ULTRASOUND EQUIPMENT:

[0048] 1 . Distilled water (85-90%): main solvent for gel formulation.

[0049] 2. Glycerin (6-8%) : wetting agent that contributes to the consistency of the gel.

[0050] 3. Carbomer (1 -2%): thickening agent that imparts viscosity to the gel. 4. Sodium chloride (NaCI) (0.3-0.5%): electrolytic salt used to adjust the electrical conductivity of the gel and stabilize the PH between 5.5 and 7.5

[0051] 5. Hydroxyethyl cellulose (1 -2%): additive that improves the consistency of the gel and the stability.

[0052] 6. Phenoxyethanol (0.5-1 %): preservative that protects the gel from bacterial contamination and prolongs the life of the product.

[0053] 7. Methylparaben (0.1 -0.2%): antimicrobial preservative that helps to prevent the growth of microorganisms.

[0054] 8. Ethanol (1 -3%): auxiliary solvent that helps to improve the spreading of the gel and accelerate evaporation.

[0055] MEDICAL ULTRASOUND GEL

[0056] 1 . Water: the main component of the gel is water, which forms the base of the product. Water serves to maintain viscosity and the ability to conduct sound waves.

[0057] 2. Glycerin: glycerin is used to give a viscous consistency to the gel.

[0058] 3. Carboxymethylcellulose (CMC): this substance is a polymer derived from cellulose and serves as a thickening agent, giving a viscoelastic consistency to the gel.

[0059] 4. Salts: salts, such as sodium chloride, are added to balance the osmolarity of the gel and improve its ability to conduct sound waves. These salts help to prevent dehydration of the gel and maintain good acoustic conductivity.

[0060] 5. Preservatives: to prevent the gel from deteriorating and becoming a favorable environment for the growth of bacteria or fungi, preservatives such as methylparaben and propylparaben are added. They prevent the microbiological contamination of the gel during use.

[0061] 6. Miscellaneous additives: the gel may sometimes contain small amounts of other substances to improve its characteristics, such as fragrances to reduce the odor or coloring agents to distinguish it more easily (often blue or green in color).

[0062] In any case, the ion-conducting gel (40) comprises;

[0063] - water, - a wetting agent, such as glycerin,

[0064] - a thickening agent, such as for example carbomer or CMC, and

[0065] - an electrolytic salt, such as for example sodium chloride, which is added into the composition to achieve a pH comprised between 5.5 and 7.5.

[0066] The applicant carried out several tests with the three aforementioned types of gel available on the market, and the results turned out to be surprising and very similar to each other. In fact, all the gels that were tested comprises electrolytic salts that provide activating electrolytes and thus an ionic conductivity characteristic of the gel. Such an ionic conductivity characteristic of the gel was shown to be sufficient to activate the sacrificial anode. The fact that the gel includes additives is completely irrelevant to the ionic conductivity characteristic because the additives only serve only to make the gel usable for medical uses applied to the human body.

[0067] In addition to the ion-conducting gel (40), the electrolyte (4) may also include an ion-conducting paste (41 ) that coats the ion-conducting gel (40).

[0068] In such a case, the ion-conducting paste (40) includes:

[0069] - a water-based acrylic binder having a weight percentage of 5 to 40 percent of the total weight of the ion-conducting paste;

[0070] - a hydrochloric acid in 10% solution having a weight percentage from 5% to 15% of the total weight of the ion-conducting paste;

[0071] - an inert filler material, such as mica, having a weight percentage from 30 to 60 percent of the total weight of the ion-conducting paste;

[0072] - additives (activators, stabilizers, electrolytic salts) having a weight percentage of 1 to 10 percent of the total weight of the ion-conducting paste; and

[0073] - deionized water (remaining).

[0074] Advantageously, the ion-conducting paste (41 ) comprises clay nanoparticles. The clay nanoparticles are in the form of a fine powder with a particle size of less than ten nanometers, so that they amalgamate uniformly in the ion-conducting paste (41 ). The clay nanoparticles are present in the ion-conducting paste (41 ) in a weight percentage between 1 and 10 to the total weight of the ion-conducting paste.

[0075] The galvanic anode (100) includes a casing (6) that contains the electrolyte (4). The casing (6) may include a bag made of a breathable fabric, such as cotton, to allow an ion exchange between the electrolyte (4) and the concrete that will surround the galvanic anode (100).

[0076] The galvanic anode (100) also includes conducting bands (5) that are connected to the first metal layer (1 ) and come out of the casing (6) that contains the electrolyte (4) to be connected to the reinforcements to be protected.

[0077] With reference to Fig. 2, the galvanic anode (100) installed on a reinforcement (200) of a reinforced concrete structure is illustrated.

[0078] The reinforcement (200) comprises a plurality of steel bars (201 ) connected together. The anode (100) includes the electrical connection bands (5) that are welded to the first metal layer (1 ) of the anode and protrude outwardly to be connected to a bar (201 ) of the reinforcement.

[0079] The anode (100) comprises two electrical connection bands (5) that protrude from two opposite ends of the anode. The electrical connection bands (5) are made of an electrically conducting material, such as galvanized steel.

[0080] Each electrical connection band (5) includes a Z-shaped bracket (50) to support the anode (100) spaced from the bar (201 ) of the reinforcement. The bracket (50) has a base (51 ) with a plurality of holes (52) suitable to accommodate fastening means for attachment to the bar (201 ) of the reinforcement. In such a way, an electrical connection is defined between the galvanic anode (100) and the bar of the reinforcement (200), together with a circuit in which electric current flows.

[0081] With reference to Figs. 3 and 4, a preferred embodiment of the galvanic anode (100) is described.

[0082] The first metal layer (1 ) is a multilayer comprising a plurality of plates that are welded together. Two plates (1 a, 1 b) are shown in the example in the figure. The second metal layer (2) is welded onto the first plate (1 a) of the first metal layer (1 ). Advantageously, the galvanic anode (100) may include an additional second layer (2') welded on the second plate (1 b) of the first layer. Said additional second metal layer (2') is made of a more electro-chemically negative sacrificial metal than the first sacrificial metal of the first metal layer (1 )-

[0083] The conducting bands (5) are welded between the two plates (1 a, 1 b) of the first layer (1 ).

[0084] A first layer of ion-conducting gel (40a) is applied on the first band (1 a) of the first metal layer (1 ) so as to cover the second metal layer (2). A second layer of ion-conducting gel (40b) is applied on the second plate (1 b) of the first metal layer so as to cover the additional second metal layer (2').

[0085] The third metal layer (3) is disposed on the first layer of ion- conducting gel (40a). A third layer of ion-conducting gel (40c) is applied so as to cover and separate the third metal layer (3) from the first two metal layers (1 , 2) that are welded together.

[0086] A first layer of ion-conducting paste (41 a) is applied on the third layer of ion-conducting gel (40c). A second layer of ion-conducting paste (41 b) is applied on the second layer of ion-conducting gel (40b). The first and second layer of ion-conducting paste (41 a, 41 b) contain clay nanoparticles.

[0087] Hereinafter, the working principle of the galvanic anode (100) according to the invention is described.

[0088] The galvanic anode (100) is applied to the reinforcement (200) of a reinforced concrete structure to protect the steel of the bars (201 ) of the reinforcement. This generates an electrical potential difference between the galvanic anode (100) and the steel reinforcement (200). Such a potential difference causes a current to flow through an electrical connection between the various bars (201 ) of the reinforcement and ions to flow through the concrete around the reinforcement (200) to an extent sufficient to prevent or reduce the corrosion of the steel reinforcement, while causing the corrosion of the sacrificial metals (10, 20, 30) of the anode (100). It should be considered that during the operation of the galvanic anode (100), oxidation products may be deposited on the surface of the sacrificial metals (10, 20, 30) of the anode as the anode is consumed. If the corrosion products are not removed from the surfaces of the metal layers (1 , 2, 3) of the anode, the corrosion products cause a situation that is known as passivation of the anode, preventing an electrochemical reaction and blocking the flow of ions through the electrolyte (4) of the anode.

[0089] By making the corrosion products soluble, the anode can continue to operate as intended. The solubility of the corrosion products is ensured by the electrolyte (4) of the anode. The electrolyte (4) provides a mechanism for removing the corrosion products from the surface of the sacrificial metals (10, 20, 30) of the anode, and also provides an ion path for the ions to flow from the steel reinforcement (200) to the anode (100).

[0090] In contrast to the use of a cement electrolyte with a pH >14, as in the case of other anodes that are currently available on the market, the galvanic anode (100) uses an electrolyte (4) comprising an ion-conducting gel (40) with a pH comprised between 5.5 and 7.5. Also the ion-conducting paste (41 ) has a pH comprised between 5.5 and 7.5

[0091] The clay nanoparticles contained in the ion-conducting paste (41 ) contribute to improve the adsorption effect of the corrosion products.

[0092] Due to the electrolyte (4), the oxidation reactions on the surfaces of the metal layers (1 , 2, 3) of the anode cause a further decrease in the alkalinity of the electrolyte. In such a case, the decrease in alkalinity of the electrolyte not only prevents the passivation of the surfaces of the metal layers (1 , 2, 3) of the anode, but also increases the amount of oxidation products of the anode absorbed by the clay nanoparticles of the electrolyte (4).

[0093] The galvanic anode (100) has an electrolyte (4) comprising an ionconducting paste (41 ) with clay nanolayers for the encapsulation of the anodic oxidation products, using the cation exchange mechanism with controlled release properties from the spaces between the interlayers of the clay nanoparticles. The galvanic anode (100) is mainly aimed at limiting the adsorption of the oxidation products in different parts of the clay nanolayers, except for the interlayers. In such a way, the oxidation products are mainly adsorbed by the interlayers of the clay nanoparticles, and the maximum amount of release of the oxidation products is achieved from the interlayers of clay nanoparticles.

[0094] Fig. 5 is a graph illustrating the result of two diffraction tests performed with a sample 3 comprising only nano-clay and a sample 5 comprising nanoclay inside an ion-conducting paste. The abscissa indicates the position 2Thetha which is the diffusion angle and is measured in degrees. The ordinate indicates the diffraction intensity (counts per second).

[0095] The intensity of the highest peak is considered to be 100, and the intensities of the other peaks are normalized with respect to the intensity of the highest peak.

[0096] Such a graph in Fig. 5 shows the effect of the clay nanoparticles on the adsorption of the corrosion products. A low-angle X-ray diffraction test was performed on samples 3 and 5. The shift of the dispersion peak to lower degrees (from 6.1935 to 6.1227) in sample 5 compared with sample 3 indicates an increase in the distance between the clay nanoparticles, which occurs due to the absorption of ions (corrosion products) in the electrolyte of the galvanic anode according to the invention.

[0097] The operation of the galvanic anode (100) is developed in three stages.

[0098] The first stage uses the third metal layer (3) composed of a thin plate of sacrificial metal (30) (with a thickness of approximately 30 to 150 pm) to adjust the activation time of the second metal layer (2), which is more electronegative than the first metal layer (1 ) and the third metal layer (3).

[0099] In the second stage, the second metal layer (2) will produce an increase in the electromotive force to allow the polarization of the reinforcement (200).

[0100] In the third phase, the first metal layer (1 ), which is typically zinc, will provide a control current typical of the galvanic systems to maintain a protective state on the reinforcement, preventing the corrosion of the reinforcement.

[0101] The galvanic anode (100) comprises the third metal layer (3), which is not electrically connected to the other two metal layers (1 , 2). The function of the third metal layer (3) is to protect the second metal layer (2) for a period of time usually coinciding with the cure time (approximately one month) of the concrete of the reinforced concrete structure.

[0102] The consumption of the third metal layer (3) enables the full activation of the second metal layer (2) only when the chemical-physical reactions of the concrete hydration process have settled down.

[0103] Immediately after the installation of the galvanic anode (100) and the pouring of concrete on the reinforcement (200), the high alkalinity of the concrete and the presence of accelerating factors (moisture, high pH, low resistivity) in the concrete curing stage immediately activate the second metal layer (2) made of magnesium, rapidly resulting in the power increase provided by the second metal layer.

[0104] Then, such a second magnesium metal layer is consumed, activating an intense power booster for the polarization of the reinforcement steel bars, in a relatively short time interval, whereas the first zinc metal layer will operate to maintain a protective condition of the reinforcement bars.

[0105] A further objective of the galvanic anode (100) is to regulate the consumption of the second metal layer (2), which may be activated at the end of the curing phase of the concrete, to provide a polarization of the reinforcement in a more effective and long-lasting way.

[0106] In the galvanic anode (100), the third metal layer (3) is not electrically connected to the other metal layers (1 , 2), but performs its sacrificial function independently during the curing period of the concrete.

[0107] At the end of the curing period of the concrete, with a stable concrete and having completed the chemical-physical reactions of the curing process, the second metal layer (2) will begin to activate, but due to the lower presence of moisture and the other accelerating factors and especially in the presence of a stable concrete, the power delivery will be less instantaneous and more regular, allowing a lower consumption of the second metal layer (2) and consequently the advantage of a longer durability of the galvanic anode (100) over time.

[0108] Fig. 6 illustrates the electrical potentials of four different anodes 1 , 2, 3, 4, in relation to time. Anode 1 comprises only one metal layer of zinc immersed in an electrolyte with ion-conducting gel with pH from 5.5 to 7.5.

[0109] Anode 2 comprises a first metal layer of zinc connected to a second metal layer of magnesium and immersed in an electrolyte with ion-conducting gel with pH from 5.5 to 7.5. As shown in the graph of Anode 2, the second metal layer of magnesium is immediately activated, giving a high potential in the first two months of the anode life.

[0110] Anode 3 comprises a magnesium plate placed inside two zinc layers. In such a case, the effect of the magnesium does not exist.

[0111] Anode 4 comprised a magnesium plate that is not electrically connected to the first metal layer of zinc. In such a case, the magnesium is ineffective.

[0112] The graph in Fig. 6 shows that the galvanic anode (100) according to the invention works only if there is an electrical connection between the first zinc layer and the second magnesium layer and if the second magnesium layer is directly exposed to the electrolyte. In such a case, the second magnesium layer provides a very high initial electrical potential difference, it being depleted in a shorter time.

[0113] Fig. 7 illustrates the electrical potentials of five different anodes 5, 6, 7, 8, 9, in relation to time.

[0114] Anode 5 comprises only one metal layer of zinc immersed in an electrolyte with an ion-conducting gel with pH from 5.5 to 7.5.

[0115] Anode 6 comprises a second metal layer of magnesium electrically connected to a first metal layer of zinc, and a third metal layer comprising a thin zinc plate not connected to the other two layers. The three metal layers are immersed in an electrolyte with an ion-conducting gel with a pH of 5.5 to 7.5. Anode 7 comprises a magnesium plate placed inside two main layers of zinc.

[0116] Anode 8 is the same anode as Anode 6, but with a different amount of magnesium.

[0117] Anode 9 comprises a magnesium plate that is not electrically connected to the first zinc metal layer.

[0118] The graph in Fig. 7 shows that the initial protection provided by the presence of the third metal layer comprising the thin zinc plate prevents a rapid and immediate consumption of the magnesium. In fact, the potential of anodes 6 and 8 follows the trend of the potential of anode 5 for about a month and then, as the magnesium is activated, the potential of anodes 6 and 8 becomes more negative (about -1.2-1 .3 V), showing a smoother and longer-lasting curve compared with anode 2 in the graph of Fig. 6.

[0119] Equivalent variations and modifications may be made to the present embodiment of the invention, within the reach of a person skilled in the art, but still within the scope of the invention as expressed by the appended claims.

Claims

CLAIMS1. Galvanic anode (100) for protection of a steel reinforcement (200) of reinforced concrete structures; said galvanic anode (100) comprising:- a first metal layer (1 ) comprising a first sacrificial metal (10) that is more electrochemically negative than the steel that is commonly used in the reinforcement,- a second metal layer (2) electrically connected to the first metal layer (1 ); said second metal layer (2) comprising a second sacrificial metal (20) that is more electrochemically negative than the first sacrificial metal (10) of the first metal layer,- an electrolyte (4) surrounding said first metal layer (1 ) and second metal layer (2);- a casing (6) containing said electrolyte (4); said casing being made of a material that allows for an ion exchange between the electrolyte (4) and the concrete suitable for surrounding the galvanic anode (100), and- conducting bands (5) made of an electrically conducting material, connected to said first metal layer (1 ) and coming out of the casing (6) in order to be connected to said reinforcement (200), characterized in that said electrolyte (4) comprises an ion-conducting gel (40) comprising water, a wetting agent, a thickening agent and an electrolytic salt and said ionconducting gel (40) has a pH comprised between 5.5 and 7.5.

2. The galvanic anode (100) according to claim 1 , wherein said electrolyte (4) comprises an ion-conducting paste (41 ) that coats said ionconducting gel (40); said ion-conducting paste having a pH comprised between 5.5 and 7.5.

3. The galvanic anode (100) according to claim 2, wherein said electrolyte (4) comprises clay nanoparticles contained in said ion-conducting paste (41 ).

4. The galvanic anode (100) according to claim 3, wherein said clay nanoparticles are in the form of a fine powder having a particle size of less than10 nanometers and are mixed in the ion-conducting paste (41 ) of the electrolyte.

5. The galvanic anode (100) according to claim 3 or 4, wherein said clay nanoparticles are present in the ion-conducting paste (41 ) in a weight percentage comprised between 1 and 10 relative to the total weight of the ionconducting paste.

6. The galvanic anode (100) according to any one of the preceding claims, wherein said first sacrificial metal (10) is zinc and said second sacrificial metal (20) is magnesium.

7. The galvanic anode (100) according to any one of the preceding claims, wherein said second metal layer (2) is superimposed on said first metal layer (1 ).

8. The galvanic anode (100) according to any one of the preceding claims, wherein the second metal layer (2) is smaller in size than the first metal layer (1 ).

9. The galvanic anode (100) according to any one of the preceding claims, wherein the first metal layer (1 ) is a multilayer comprising a plurality of metal plates (1 a, 1 b) that are welded together.

10. The galvanic anode (100) according to any one of the preceding claims, further comprising an additional second layer (2') electrically connected to the first metal layer (1 ); said additional second metal layer (2') being made of a sacrificial metal that is more electrochemically negative than the first sacrificial metal of the first metal layer.

11. The galvanic anode (100) according to any one of the preceding claims, further comprising a third metal layer (3) not electrically connected to the first metal layer (1 ) and to the second metal layer (2); said third metal layer (3) being immersed and completely surrounded by the electrolyte (4); said third metal layer (3) comprising a third sacrificial metal (30) that is more electrochemically negative than the steel used in the reinforcement (200), but less electrochemically negative than the second metal layer (2).

12. The galvanic anode (100) according to claim 9, wherein said third metal layer (3) comprises a plate having a thickness (S3) comprised between 30 and 150 pm.

13. The galvanic anode (100) according to claim 1 1 or 12, wherein said first metal layer (1 ) is a multilayer comprising a plurality of plates (1 a, 1 b) that are welded together; the second metal layer (2) is welded to a first plate (1 a) of the first metal layer (1 ); the conducting bands (5) are welded between two plates (1 a, 1 b) of the first metal layer (1 ); a first layer of ion-conducting gel (40a) is applied on the first plate (1 a) of the first metal layer (1 ) so as to cover the second metal layer (2); a second layer of ion-conducting gel (40b) is applied on a face of the first metal layer (1 ) opposite to that where the first layer of ion-conducting gel (40a) is applied, the third metal layer (3) is disposed on the first layer of ion-conducting gel (40a); a third layer of ion-conducting gel (40c) is applied on the first layer of ion-conducting gel (40a) so as to cover and separate the third metal layer (3) from the first two metal layers (1 , 2) that are welded together; a first layer of ion-conducting paste (41 a) is applied on the third layer of ion-conducting gel (40c); a second layer of ion-conducting paste (41 b) is applied on the second layer of ion-conducting gel (40b); the first layer and the second layer of ion-conducting paste (41 a, 41 b) contain clay nanoparticles.

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