METHOD FOR TREATMENT OF REINFORCED CONCRETE PRODUCTS

Description

METHOD FOR TREATMENT OF CEMENTITIOUS MATERIAL PRODUCTS ARMED ------ The present invention relates to a method for treat reinforced concrete artefacts. In In particular, the invention relates to a method for treat reinforced concrete artefacts, at the aim of protecting them and increasing their durability, which involves both an improvement in the properties mechanics of the cement matrix is ​​a improvement of corrosion resistance of steel bars. In the field of cementitious materials, it is known that problem of the degradation of reinforced concrete structures (i.e. cement-based mortars and concretes containing steel reinforcing bars inside), often due to corrosion of the reinforcing bars present inside. The deterioration of the reinforced concrete has a very negative impact heavy both economically and in terms of lives human. In particular, due to the carbonation of the concrete, a lowering of the pH may occur in the surrounding environment the reinforcing bars in steel, which determines the instability of the layer of magnetite which has a protective function (since (passivates steel) against corrosion of the bars. Furthermore, the presence of humidity and aggressive agents in contact with the bars determines at the same time generalized or localized corrosion phenomena that IC / A592790 can produce corrosion products (rust), which limit the safety and durability of the structure in reinforced concrete. Given the high economic and social impact of the degradation of reinforced cement mortars and concretes, often due to corrosion of the reinforcing bars present inside, several have been proposed methods for (1) reducing matrix porosity cement, increase its mechanical properties and durability, through the application of consolidants and to (2) re-alkalize the concrete, in order to reduce the risk of corrosion of the bars armor immersed in concrete. In this regard, different types of are known consolidants, i.e. liquid products to be applied on the cementitious product which then hardens once deeply penetrated, such as silicate sodium, ethyl silicate and nanosilica, which have the aim of reducing the porosity of the matrix cement and to increase its mechanical properties and durability. However, known consolidants act directly only on the cement matrix, while have no direct protective effect on the bars steel reinforcement and, therefore, reduce corrosion of the bars only indirectly. It is also known that possibility of reducing the presence of cracks in the concrete by electrodeposition of solutions of salts (such as ZnSO4 and MgCl2) which, falling into the cracks, they indirectly lead to a reduction in the likelihood of corrosion of the IC / A592790 reinforcing bars. At the same time, there are some methods to reduce the risk of corrosion of immersed reinforcing bars in concrete, i.e. the so-called re-methods alkalinization of concrete. These consist of in the application of an alkaline solution (e.g. sodium carbonate) which is made to migrate towards the reinforcing bar by applying a current cathode to the bar itself, with consequent creation of an alkaline environment near the bar. However, even in this case, the protective action on the bar it cannot be considered direct, in how alkaline an environment is created inside of the cement matrix which indirectly favors a partial protection of the bar. Furthermore, such methods are not able to increase at the same time the cohesion and the properties mechanics of the cement matrix. In light of the above, it appears clear that need to provide new methods for protection and the consequent increase in the durability of manufactured products made of reinforced concrete. The use of diammonium solutions is also known hydrogen phosphate (DAP), for the formation of phosphates of calcium, on different types of substrate, in especially for the conservation of natural stones, marbles, limestones, mortars and frescoes [1]. This method is has also been applied to cementitious substrates for improve the properties of historical cementitious artefacts and new [2,3], however these were substrates IC / A592790 non-reinforced concrete as they did not contain reinforcing bars steel inside. In this context the solution comes into play according to the present invention, which aims to provide an innovative method for improving the durability of reinforced concrete products. The method proposed according to the present invention It advantageously allows to simultaneously achieve two beneficial effects: (1) improve the properties mechanics of the cement matrix and (2) improve the corrosion resistance of steel reinforcement. The method according to the invention has, therefore, the aim to mitigate the problems related to the corrosion of the reinforcing bars thanks to the double effect of (1) improving matrix cohesion cement and, consequently, reduce its porosity, aspect that should slow down the transport of humidity and aggressive agents which are the cause of corrosion phenomena of the bars armor; and (2) protect the armor bar from generalized or localized corrosion phenomena by forming a phosphate layer. The double beneficial effect provided by the method according to the present invention it is obtained by impregnating the artifact with a solution of a precursor phosphate (such as diammonium hydrogen phosphate, DAP, (NH ) HPO ), which can be applied for example 4 2 4 by compress, spray or brush. Within a few hours, the phosphate precursor solution penetrates progressively in the cement matrix up to IC / A592790 reach the steel reinforcing bar, usually positioned at a depth of 2-3 cm from the treated surface. As it penetrates the pores of the cement matrix, the solution reacts with it, forming new compounds based on calcium phosphates, which lead to an increase in cohesion and mechanical properties of the cement matrix. Subsequently, once the solution of phosphate precursor reached the armor bar, according to the method of the invention the formation of a phosphate layer on the surface of the reinforcing bar by a process electrochemical called electrodeposition, with consequent increase in the corrosion resistance of the bar itself. Therefore, the method according to the invention is configured as a technique to be applied on site directly on the surface of the reinforced concrete through various application methods such as compress, spray or brush. Once applied the product based on phosphate precursors on surface of the reinforced concrete to be protected, yes proceeds after a certain time to the process of electrodeposition on the reinforcing bar which in in the meantime she came into contact with the solution phosphate mentioned above. As mentioned above, the method of the invention It advantageously allows to simultaneously achieve the two effects mentioned above, that is, the improvement of mechanical properties of the cement matrix and IC / A592790 improvement of corrosion resistance of reinforcing bars. The method according to the present invention can advantageously be applied in the context of restoration and rehabilitation of existing buildings (also of historical-artistic interest, but not only) and of infrastructures (bridges, viaducts, etc.) in reinforced concrete that show problems of corrosion of the reinforcing bars embedded in the concrete. In addition to the "a posteriori" application, the method according to the present invention can also be applied "a priori", that is, to prevent degradation of reinforced concrete structures. Furthermore, the method of the present invention can can also be used on matrix composite materials cement containing dispersed steel fibers (instead of reinforcing bars). It is therefore the specific subject of this invention a method for treating an object or manufactured product in cement matrix (i.e. pastes, mortars or cement-based concretes) including its own inside at least one metal element (such as a steel bar, immersed in the matrix cementitious), said method comprising or being consisting of the following phases: a) put in contact at least a portion of the surface of said object or artifact with a solution comprising a phosphate precursor capable - 2- 3- to generate HPO , HPO , and / or PO ions, and leave 2 4 4 4 penetrate the solution into the said cement matrix to IC / A592790 the time needed for the said solution to reach - said at least one metallic element, said HPO ions, 2 4 2- 3- HPO and / or PO forming phosphate compounds by reacting with 4 4 cations present in said cement matrix, in said at least one metallic element and / or in said solution; b) put in contact a material anode metallic with the solution already in contact with said object, so that both said object and said anode are simultaneously in contact with the same solution; c) apply a potential difference between said anode and at least a portion of said element metallic, which acts as a cathode, present in said cement matrix, for example by means of a potentiostat, to obtain an electrodeposition of at least one layer of said phosphate compounds on the surface of said metal element. According to the present invention, said precursor phosphate is preferably able to generate ions 3- PO . According to the method of the present invention, the - 2- 3- HPO , HPO and / or PO ions present in the solution 2 4 4 4 used in phase a) generate said compounds phosphates reacting with cations present in said matrix, in said metal element and / or in said solution. For example, these phosphate compounds can be calcium phosphates (obtainable from the reaction - 2- 3- of HPO , HPO and / or PO ions with calcium ions 2 4 4 4 coming from the cement matrix itself and / or with calcium ions present in the solution itself), phosphates IC / A592790 - of iron (obtainable from the reaction of HPO ions, 2 4 2- 3- HPO or PO with iron present on said at least one 4 4 metallic element, for example iron present in possible rust of said metal element, and / or with iron ions present in the solution itself), both calcium phosphates or iron phosphates, or compounds phosphates containing other ions, such as ion ammonium. These phosphate compounds can vary in depending on the conditions of the treatment, for example 2+ whether or not Ca ions are supplied into the solution, whether organic additives are added or if it is the time in which the substance is allowed to penetrate has been varied solution in the matrix. As mentioned above, the so-called phase c) of applying a potential difference between said anode and at least one portion of said metallic element may be carried out through a potentiostat. In particular, in said phase c) said at least a portion of said metallic element, so that it acts as a cathode (or, in a preliminary phase, from anode as described below), must be made accessible in order to be connected to an electrode. Therefore, it is possible for example remove a portion of said cement matrix for expose said at least one portion of the element metallic. According to the second method of this invention, said potential difference can be variable from -0.5V to -3.5V, preferably from -1V to - 2V, more preferably -1V, relative to an electrode of reference. IC / A592790 According to the present invention, said element metal can be chosen from a reinforcing bar made of steel and steel fibres, preferably one steel reinforcing bar. Therefore, according to the present invention, said object or artifact in cement matrix is ​​preferably an object or reinforced concrete product, i.e. an object or product in cement matrix including its own inside at least one steel reinforcing bar. According to the present invention, for precursor phosphate means a compound, inorganic or organic, preferably inorganic, preferably a phosphate salt, such as an orthophosphate or a pyrophosphate, comprising the element P and capable of - 2- 3- generate HPO , HPO and / or PO ions in said solution. 2 4 4 4 According to the present invention, said precursor phosphate can be chosen from ammonium phosphate (NH ) PO , diammonium hydrogen phosphate (DAP, (NH ) HPO ), 4 3 4 4 2 4 ammonium dihydrogen phosphate (NH HPO ), diphosphate 4 2 4 potassium (K PO ), dipotassium hydrogen phosphate (K HPO ), 3 4 2 4 potassium dihydrogen phosphate (KH ₂PO₄), sodium phosphate (Na PO ), disodium hydrogen phosphate (Na HPO ), sodium 3 4 2 4 dihydrogen phosphate (NaHPO ), preferably diammonium 2 4 hydrogen phosphate. According to the present invention, said solution It can be an aqueous solution. Furthermore, according to the present invention, said phase a) can be carried out by compressing the external surface of the object with a material, such as for example cellulose pulp, impregnated with said IC / A592790 solution, or by spray application of said solution on the external surface of said object or by applying it with a brush on the external surface of said object or by means immersion of said object in said solution, preferably by means of a compress. Preferably, according to the present invention, after having impregnated said object with said solution a waterproof coating is applied, for example a plastic film, on the surface external part of the object to prevent evaporation of the solution, which can be removed once finished phase a). According to the present invention, when said object or artifact has been brought into contact with said solution by compress for the necessary time in order for said solution to reach said at least one metallic element, said phase b) can be conducted by putting the anode made of metallic material in contact with the solution-impregnated poultice put in contact with the object in cement matrix. According to the present invention, in said step a) the solution is allowed to penetrate inside the cement matrix for an appropriate, assessable time by the expert in the field based on the size and conditions of the object to be treated, in particular the depth at which the said metallic element is found. for example, you can let the solution penetrate for a time varying from 6 hours to 7 days, preferably from 24 hours to 48 hours, more preferably for 24 hours. IC / A592790 The anode made of metallic material according to the method of the invention may be a metal grid, for example example a steel grid, a metal bar or a metal plate. According to the method of the present invention, the concentration of the phosphate precursor in the solution can vary from 0.1 M up to the concentration of saturation, preferably 0.1 M to 2 M, plus preferably 1 M. The solution used in the method of this invention may further comprise a compound 2+ source of calcium ions (Ca ), such as a compound chosen from CaCl, Ca(NO), Ca(OH), 2 3 2 2 preferably CaCl . The ions released from the ion-source compound calcium added to the said solution promotes and accelerate the formation of calcium phosphates, which otherwise they would only form from calcium ions present in the cement substrate, which however is little soluble and therefore provides few calcium ions. The effect advantage of adding calcium ions directly in the solution is, therefore, that of allow the formation of a greater quantity of calcium phosphates in a shorter time, compared to the case in which no ion source is added calcium in the solution. In particular, said ion source compound calcium can be present in a molar ratio calcium ion source compound: phosphate precursor from 1:1000 to 10:6, preferably 1:1000. IC / A592790 Furthermore, this solution may include further one or more compounds selected from ethanol, isopropanol, acetone, and / or hydrogen peroxide, preferably ethanol. In particular, said one or more compounds may be present in the solution in a percentage varying from 0.1 to 30 vol%. The addition of one or more of these compounds to the solution advantageously improves the reactivity of the phosphate ions. According to some preferred embodiments of the method according to the present invention, the solution of phase a) may for example include: − 0.1 M DAP + 0.1mM CaCl in 10vol% ethanol, − 1M DAP+ 1mM CaCl , or − 2M DAP + 2mM CaCl . According to the present invention, said phase c) can be conducted for a variable time from 1 minute to 6 hours, preferably 1 hour to 6 hours, plus preferably 1 hour to 3 hours. According to the present invention, the method of the invention can be conducted by applying a of the following conditions: − solution of phase a): 1M DAP + 1mM CaCl ; Electroplating conditions (phase c): for 3 h at -1 V; − solution of phase a): 1M DAP + 1mM CaCl ; Electroplating conditions (phase c): for 6 h at -1 V; − solution of phase a): 1M DAP + 1mM CaCl ; Electroplating conditions (phase c): for 1 h IC / A592790 at -2 V. The potential difference applied in said phase c) according to the present invention can be applied in continuous or pulsed mode. According to one embodiment hereof invention, said phases a), b) and c) are repeated two or several times cyclically. In particular, according to a preferred embodiment, said phases a), b) and c) are repeated twice consecutively for two treatment cycles and in which in the first cycle of treatment phase a) involves putting into contact said object or artifact with a solution including the phosphate precursor and not including a compound that is a source of calcium ions, so that allow the possible formation of iron phosphates and their deposition on the surface of the element metallic during phase c), and in the second cycle of treatment phase a) involves putting into contact said object or artifact with a solution comprising the phosphate precursor and a compound source of calcium ions, so as to allow the formation of calcium phosphates which will be deposited above the iron phosphates during phase c) of electrodeposition. Therefore, according to the present invention, the phases a), b) and c) can be repeated cyclically for further improve durability and mechanical characteristics of the object or artifact. So, the said object can be impregnated with a solution as defined above and subjected to IC / A592790 electrodeposition more than once consecutively. As in the embodiment described above, the solution with which it is impregnated the object in phase a), which always includes a phosphate precursor, can vary in its composition at each treatment cycle. Similarly, according to the present invention, when steps a), b) and c) are repeated more than once, at each cycle of electrodeposition treatment carried out in phase c) can be conducted with a different voltage compared to the previous cycle. Furthermore, the method of the present invention can further understand the following steps performed prior to said phases a), b) and c) a1) put in contact at least a portion of the surface of said object or artifact with a solution comprising a phosphate precursor capable - 2- 3- to generate HPO , HPO and / or PO ions and not 2 4 4 4 comprising a source of calcium ions, and leave penetrate the solution into the said cement matrix, in so as to allow the formation of iron phosphates, for the time necessary for said solution to be implemented reaches said at least one metallic element; b1) put in contact a cathode material metallic with the solution already in contact with said object, so that both said object and said cathode are simultaneously in contact with the same solution; and c1) apply a potential difference between said cathode and at least a portion of said element IC / A592790 metallic, which acts as an anode, present in said cement matrix, for example by means of a potentiostat, to obtain an electrodeposition of at least one layer of said iron phosphates on the surface of said metal element. According to the present invention, the inversion of configuration envisaged by phases a1), b1) and c1), in where the metal element acts as an anode instead of cathode can promote the formation of iron phosphates as the main species of phosphate compounds and, therefore, during phase c1) there will be the deposition of a layer of phosphate compounds comprising mainly iron phosphates, before applying, through one or more cycles, phases a), b) and c) in which the metal element acts as a cathode. The present invention will now be described, illustrative but not limiting title, according to its own preferred form of embodiment, with particular reference to the examples and figures in the drawings attachments, in which: - Figure 1 shows an application scheme of the method of invention to a real structure in reinforced concrete; - Figure 2 shows a schematic of the samples of cement mortar reinforced with steel bars used in the examples; - Figure 3 shows the setup used in the Examples 1 and 2 for solution electrodeposition of DAP on the steel bar; - Figure 4 shows the setup used in the IC / A592790 Examples 1 and 2 for the accelerated corrosion test of the steel bar; - Figure 5 shows a comparison between the curves of anodic polarization in 3.5 wt% NaCl of non-samples treated (A) and treated under conditions 1M, 3h, -1V (B) and 1M, 1h, -2V (C); - Figure 6 shows a comparison between the values ​​of Knoop surface hardness of treated and untreated samples treaties; - Figure 7 shows a comparison between the values ​​of loss of abraded material from treated and untreated samples treaties; - Figure 8 shows a comparison between the values ​​of the dynamic elastic modulus of treated and untreated samples treaties. EXAMPLE 1. Example of application of the method according to the present invention on mortar samples reinforced concrete. Cylindrical samples of cement mortar (ratio water / cement = 0.5) with a diameter of 5 cm and a height of 10 cm, containing a carbon steel bar in the center of 10 mm diameter (Figure 2), were treated in the following way. First, on the lateral surface of each specimen a thick compress was applied to the cylindrical about 1 cm of cellulose pulp and a solution aqueous solution containing 1M DAP + 1mM CaCl. The compress is was covered with waterproof plastic film to prevent evaporation of the solution. After 24 hours, the sample was placed in a container of IC / A592790 glass and inside the pack a metal plate (Figure 3). The steel bar and the metal plate are were then connected to a potentiostat, so such that the bar acted as a cathode and the plate as anode. A potential of -1 V was then applied compared to the reference electrode (electrode saturated calomel, SCE, also in contact with the compress) for 3 hours. At the end, the film and the poultice was removed, the sample was rinsed with water and left to dry. After the treatment, the improvement of the corrosion rate by placing each sample in the same container with a surrounding cylindrical steel grid and 200 were poured mL of a 3.5 wt% aqueous NaCl solution simulate sea water. A test was then performed anode polarization test, connecting the bar steel and the grid to a potentiostat, so that that the bar this time acted as an anode and the cathode grid (Figure 4). It was then performed the test, which consisted in varying the potential from -0.2V to +1.0V with respect to the potential at open circuit, recording the current corresponding. Considering the average of 3 replicates for condition, compared to the untreated reference i samples treated with 1 M DAP+1 mM CaCl at -1 V for 3 h they showed a reduction in the circulating current in the system (and therefore an improvement in resistance IC / A592790 (corrosion) by 28% (Figure 5). On the same cylindrical samples were then tests were carried out to determine the improvement of the properties of the cement mortar following the treatment: (i) Knoop surface hardness tests, or resistance to penetration by an indenter on the treated surface, (ii) resistance tests abrasion, in terms of material loss for action of metal spheres kept in rotary motion on the surface of the sample for a certain time, (iii) dynamic elastic modulus tests, calculated by measuring the speed of an ultrasonic pulse passing through the cylindrical sample through a diameter (in the area without the steel bar). Considering the average of 3 replicates for condition, compared to the untreated reference i samples treated with 1 M DAP+1mMCaCl at -1 V for 3 h show an increase in Knoop surface hardness of 75% (Figure 6), a 57% decrease in material lost by surface abrasion (Figure 7) and an increase in the dynamic elastic modulus of 5% (Figure 8). EXAMPLE 2. Example of application of the method according to the present invention on mortar samples reinforced concrete. Compared to example 1, the samples were treated with an aqueous solution containing 1 M DAP+1 mM CaCl with a similar procedure, but reducing the time of electrodeposition from 3 hours to 1 hour and varying the potential from -1 V to -2 V with respect to the electrode IC / A592790 reference. Considering the average of 3 replicates for condition, compared to the untreated reference i samples treated with 1 M DAP+1 mM CaCl at -2 V for 1 h they showed a reduction in the circulating current in the system (and therefore an improvement in resistance (corrosion) by 22% (Figure 4), an increase in Knoop surface hardness of 78% (Figure 5), a 61% reduction in material lost through abrasion surface (Figure 6) and an increase in the modulus dynamic elasticity of 11% (Figure 7). Bibliography [1] Sassoni E., Hydroxyapatite and Other Calcium Phosphates for the Conservation of Cultural Heritage: A Review, Materials 11 (2018) 557, DOI: 10.3390 / ma11040557 [2] Sassoni E., Franzoni E., Lime and cement mortar consolidation by ammonium phosphate. With- struction and Building Materials 245 (2020) 118409, DOI: 10.1016 / j.conbuildmat.2020.118409 [3]Pasco H., Naidu S., Lothenbach B., Sassoni E., Enhancement of surface properties of cementitious materials by phosphate treatments, Cement and Concrete Composites 141 (2023) 105124, DOI: 10.1016 / j.cemconcomp.2023.105124 Barzanò & Zanardo Roma SpA IC / A592790

Claims

CLAIMS 1) Method for treating an object in a cement matrix comprising at least one metallic element therein, said method comprising or consisting of the following steps: a) putting in contact at least a portion of the surface of said object with a solution comprising a phosphate precursor capable of generating H2PO4-, HPO42- and / or PO43- ions, and allowing the solution to penetrate into said cement matrix for the time necessary for said solution to reach said at least one metallic element, said H2PO4-, HPO42- and / or PO43- ions forming phosphate compounds by reacting with cations present in said cement matrix, in said at least one metallic element and / or in said solution; b) putting in contact a metallic anode with the solution in contact with said object, so that both said object and said anode are in contact with the same solution;c) applying a potential difference between said anode and at least a portion of said metallic element, which acts as a cathode, to obtain an electrodeposition of at least one layer of said phosphate compounds on the surface of said metallic element.; 2) Method according to claim 1, wherein said potential difference is variable from -0.5V to 3.5V, preferably from -1V to -2V, more preferably -1V, with respect to a reference electrode. 3) Method according to any of the IC / A592790 Barzanò & Zanardo - 21 preceding claims, wherein said metal element is selected from a steel reinforcing bar and steel fibres, preferably a steel reinforcing bar. 4) Method according to any of the preceding claims, wherein said phosphate precursor is selected from ammonium phosphate (NH4)3PO4, diammonium hydrogen phosphate (DAP, (NH4HHPO4), ammonium dihydrogen phosphate (NH4H2PO4), potassium phosphate (K3PO4), dipotassium hydrogen phosphate (K2HPO4), potassium dihydrogen phosphate (KH2PO4), sodium phosphate (Na3PO4), disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), preferably diammonium hydrogen phosphate. 5) Method according to any of the preceding claims, wherein said solution is an aqueous solution. 6) A method according to any of the preceding claims, wherein said step a) is carried out by packing the external surface of the object with a material impregnated with said solution, or by spraying said solution onto the external surface of said object, or by applying it with a brush onto the external surface of said object, or by immersing said object in said solution, preferably by packing. 7) Method according to any of the preceding claims, wherein said anode made of metallic material is a metallic grid, for example IC / A592790 Barzanò & Zanardo - 22 a steel grid, a metallic bar or a metallic plate. 8) Method according to any of the preceding claims, wherein the concentration of the phosphate precursor in the solution varies from 0.1 M up to the saturation concentration, preferably from 0.1 M to 2 M, more preferably 1 M. 9) Method according to any of the preceding claims, wherein said solution further comprises a calcium ion source compound, such as a compound selected from CaCl2, Ca(NO3)2, Ca(OH)2, preferably CaCl2. 10) Method according to the preceding claim, wherein said calcium ion source compound is present in a molar ratio calcium ion source compound: phosphate precursor from 1:1000 to 10:6, preferably 1:1000. 11) A method according to any of the preceding claims, wherein said solution further comprises one or more compounds selected from ethanol, isopropanol, acetone, and / or hydrogen peroxide, preferably ethanol. 12) Method according to the preceding claim wherein said one or more compounds are present in the solution in a percentage varying from 0.1 to 30 vol%. 13) Method according to any of the preceding claims, wherein said step c) is carried out for a time varying from 1 minute to 6 hours, preferably from 1 hour to 6 hours, more preferably IC / A592790 Barzanò & Zanardo - 23 from 1 hour to 3 hours. 14) Method according to any of the preceding claims, wherein said potential difference in said step c) is applied in continuous or pulsed mode. 15) Method according to any of the preceding claims, wherein said steps a), b) and c) are repeated two or more times. 16) Method according to claim 15 wherein said steps a), b) and c) are repeated twice for two treatment cycles and wherein in the first treatment cycle step a) involves contacting said object with a solution comprising the phosphate precursor and not comprising a calcium ion source compound, and in the second treatment cycle step a) involves contacting said object with a solution comprising the phosphate precursor and a calcium ion source compound. 17) A method according to any preceding claim, wherein said method further comprises the following steps performed prior to said steps a), b) and c) a1) contacting at least a portion of the surface of said object with a solution comprising a phosphate precursor capable of generating H2PO4-, HPO42- and / or PO43- ions and not comprising a source of calcium ions, and allowing the solution to penetrate into said cement matrix, so as to allow the formation of iron phosphates, for the time necessary for said solution to reach said at least one metallic element; IC / A592790 Barzanò & Zanardo - 24 b1) contacting a cathode made of metallic material with the solution in contact with said object, so that both said object and said cathode are in contact with the same solution;and c1) applying a potential difference between said cathode and at least a portion of said metallic element, which acts as an anode, to obtain an electrodeposition of at least one layer of said iron phosphates on the surface of said metallic element.;