Method for treating articles made of reinforced cementitious material

Abstract

The present invention relates to methods for treating articles made of reinforced cementitious material, with the aim of protecting them and increasing their durability, which brings about both an improvement in the mechanical properties of the cementitious matrix and an improvement in the corrosion resistance of the steel bars.

Description

[0001] METHOD FOR TREATING ARTICLES MADE OF REINFORCED

[0002] CEMENTITIOUS MATERIAL

[0003] The present invention relates to a method for treating articles made of reinforced cementitious material. In particular, the invention relates to a method for treating articles made of reinforced cementitious material with the aim of protecting them and increasing their durability, which simultaneously brings about both an improvement in the mechanical properties of the cementitious matrix and an improvement in the corrosion resistance of the steel bars.

[0004] In the field of cementitious materials, the problem of degradation of structures made of reinforced concrete (i.e. cement-based mortars and concretes containing steel reinforcement bars inside them) is well known, often due to the corrosion of the reinforcement bars present therein. The deterioration of reinforced concrete has a very heavy negative impact both in economic terms and in terms of human lives.

[0005] In particular, because of the carbonation of concrete, a lowering of the pH in the environment surrounding the steel reinforcement bars may occur, giving rise to instability of the magnetite layer which has a protective function (as it passivates the steel) against the corrosion of the bars. Furthermore, at the same time, the presence of humidity and aggressive agents in contact with the bars gives rise to generalised or localised corrosion phenomena that can produce corrosion products (rust), which limit the safety and durability of the reinforced concrete structure.

[0006] Given the high economic and social impact of the degradation of reinforced cementitious mortars and concretes, often due to the corrosion of the reinforcement bars present within them, various methods have been proposed to (1 ) reduce the porosity of the cementitious matrix and enhance its mechanical properties and durability through the application of consolidants, and to (2) re-alkalise the concrete, with the aim of reducing the risk of corrosion of the reinforcement bars embedded in the concrete.

[0007] In this regard, there are various types of known consolidants, i.e. liquid products to be applied on the cementitious article, which then harden once they have penetrated deeply; these include, for example, sodium silicate, ethyl silicate and nano-silica, which have the objective of reducing the porosity of the cementitious matrix and enhancing its mechanical properties and durability. However, the known consolidants act directly solely on the cementitious matrix, whereas they do not have a direct protective effect on the steel reinforcement bars and thus reduce the corrosion of the bars only indirectly. The possibility of reducing the presence of cracks in concrete by electrodeposition of salt solutions (such as, for example, ZnSO4 and MgCl2) which, by precipitating into the cracks, lead indirectly to a reduction in the likelihood of corrosion of the reinforcement bars, is also known.

[0008] At the same time, there exist several methods for reducing the risk of corrosion of the reinforcement bars embedded in concrete, i.e. so-called concrete re-alkalisation methods. They consist in the application of an alkaline solution (for example sodium carbonate), which is made to migrate towards the reinforcement bar by applying a cathode current to the bar itself, with the consequent creation of an alkaline environment in proximity to the bar. However, in this case as well, the protective action on the bar cannot be considered direct, since an alkaline environment is created within the cementitious matrix which indirectly favours a partial protection of the bar. Furthermore, such methods are not capable of simultaneously enhancing the cohesion and mechanical properties of the cementitious matrix.

[0009] In the light of the above, it appears evident that there is a need to provide novel methods for protecting and consequently increasing the durability of articles made of reinforced concrete.

[0010] The use of solutions of diammonium hydrogen phosphate (DAP) to form calcium phosphates on different types of substrates, in particular for the conservation of natural stone, marble, limestone, mortar and frescoes

[0001] , is also known. This method has also been applied to cementitious substrates to improve the properties of historical and new cementitious structures [2,3]; however, this involved non-reinforced cementitious substrates, as they did not contain steel bars within them.

[0011] The solution according to the present invention fits into this context; it aims to provide an innovative method for improving the durability of articles made of reinforced concrete.

[0012] The method proposed according to the present invention advantageously enables two beneficial effects to be achieved simultaneously with a single treatment: (1 ) to improve the mechanical properties of the cementitious matrix (for example cohesion, surface hardness and abrasion resistance) and (2) to improve the corrosion resistance of the steel reinforcements.

[0013] The method according to the invention has the aim, therefore, of mitigating the problems related to the corrosion of the reinforcement bars thanks to the dual effect of (1 ) improving the cohesion of the cementitious matrix and, consequently, reducing its porosity, an aspect that is foreseen to slow down the transport of humidity and aggressive agents which are the cause of reinforcement bar corrosion phenomena; and (2) protecting the reinforcement bar from generalised or localised corrosion phenomena through the formation of a layer of phosphates.

[0014] The double beneficial effect provided by the method according to the present invention is obtained by impregnating the article with a solution of a phosphate precursor (such as, for example, diammonium hydrogen phosphate, DAP, (NH4)2HPO4), which may be applied, for example, by means of a wrapping, or by spray or brush application. In the space of a few hours, the solution of the phosphate precursor progressively penetrates into the cementitious matrix until reaching the steel reinforcement bar, usually positioned at a depth of 2-3 cm from the treated surface. While it penetrates into the pores of the cementitious matrix, the solution reacts with the latter, forming new mainly calcium phosphate-based compounds, and also magnesium phosphate-based ones, which lead to an enhancement of the cohesion and mechanical properties of the cementitious matrix. Subsequently, once the phosphate precursor solution has reached the reinforcement bar, according to the method of the invention, the formation of a phosphate layer is induced on the surface of the reinforcement bar by means of an electrochemical process called electrodeposition, with a consequent increase in the corrosion resistance of the bar itself.

[0015] Therefore, the method according to the invention represents a technique to be applied in situ, directly on the surface of the reinforced concrete, by means of various methods of application, such as, for example, by wrapping, or spray or brush application. Once the phosphate precursor-based product has been applied on the surface of the reinforced concrete to be protected, one proceeds, after a certain amount of time, to the process of electrodeposition onto the reinforcement bar, which in the meantime has come into contact with the abovementioned phosphate solution.

[0016] As stated above, the method of the invention advantageously enables the two aforesaid effects, i.e. the improvement of the mechanical properties of the cementitious matrix and improvement of the corrosion resistance of the reinforcement bars, to be achieved simultaneously.

[0017] The method according to the present invention can advantageously be applied in the context of rehabilitation and restoration of existing buildings (also of historical-artistic interest, but not only) and infrastructures (bridges, viaducts, etc.) made of reinforced concrete which show problems of corrosion of the reinforcement bars embedded in the concrete. In addition to “a posteriori” application, the method according to the present invention can also be applied “a priori”, i.e. to prevent the degradation of reinforced concrete structures.

[0018] Furthermore, the method of the present invention can also be used on composite materials with a cementitious matrix containing dispersed steel fibres (rather than reinforcement bars).

[0019] It is therefore a specific object of the present invention a method for treating an object or article 1 made up of a cementitious matrix 2 (i.e. cement-based pastes, mortars or concretes) and comprising within it at least one metal element 3 (such as, for example, a steel bar, embedded in the cementitious matrix), said method comprising or consisting of the following steps: a) placing at least a portion of the surface of said object or article 1 in contact with a solution 4 comprising a phosphate precursor capable of generating H2PO4 HPO42’ and / or PO43’ ions, and allowing the solution to penetrate into said cementitious matrix 2 for the time necessary in order for said solution 4 to reach said at least one metal element 3, said H2PO4 HPO42’ and / or PO43’ ions forming phosphate compounds 5 by reacting with cations present in said cementitious matrix 2, in said at least one metal element 3 and / or in said solution 4; b) placing an anode 6 made of metal material in contact with the solution 4 already in contact with said object 1 , so that both said object 1 and said anode 6 are simultaneously in contact with the same solution 4; c) applying a potential difference between said anode 6 and at least a portion of said metal element 3, which acts as a cathode, present in said cementitious matrix, for example by means of a potentiostat 7, in order to obtain an electrodeposition of at least one layer of said phosphate compounds 5 onto the surface of said metal element 3.

[0020] According to one embodiment of the present invention, said solution 4 comprising a phosphate precursor capable of generating H2PO4; HPO42’ and / or PO43’ ions is not seawater.

[0021] According to the present invention, said phosphate precursor is preferably capable of generating PO43’ ions.

[0022] According to the method of the present invention, the H2PO4 HPO42’ and / or PO43' ions present in the solution 4 used in step a) generate said phosphate compounds 5 by reacting with cations present in said matrix 2, in said metal element 3 and / or in said solution 4. For example, said phosphate compounds 5 can be one or more types among the following phosphates: calcium phosphates (obtainable from the reaction of the H2PO4; HPCM2’ and / or PO43’ ions with calcium ions originating from the cementitious matrix and / or with calcium ions present in the solution itself), iron phosphates (obtainable from the reaction of the H2PO4 HPO42’ or PO43' ions with the iron present on said at least one metal element 3, for example iron present in any rust of said metal element, and / or with iron ions present in the solution itself), both calcium phosphates and iron phosphates, phosphate compounds containing other ions, such as, for example, magnesium ions (magnesium phosphates) and / or ammonium ions (ammonium phosphates), mixed phosphates, such as, for example, magnesium ammonium phosphates (i.e. a mineral called struvite). Said phosphate compounds 5 may vary according to the treatment conditions, for example whether or not Ca2+ions are provided in the solution, whether organic additives are added, whether the pH of the solution is varied or whether the time for which the solution is allowed to penetrate into the matrix is varied.

[0023] As stated above, said step c) of applying a potential difference between said anode 6 and at least a portion of said metal element 3 can be carried out by means of a potentiostat 7. In particular, in said step c) said at least a portion of said metal element 3, in order that it may act as a cathode (or, in a preliminary step, as an anode, as described further below), must be made accessible in order to be connected to an electrode. Therefore, it is possible, for example, to remove a portion of said cementitious matrix 2 to expose said at least a portion of the metal element 3.

[0024] According to the method of the present invention, said applied potential difference is a (fixed) value which can be selected in the range of -0.5V to -3.5V, preferably -1V to -2V, more preferably -1V, relative to a reference electrode.

[0025] According to the present invention, said at least one metal element 3 can be selected from a steel reinforcement bar and steel fibres, preferably a steel reinforcement bar. Therefore, according to the present invention, said object or article 1 made of a cementitious matrix 2 is preferably an object or article made of reinforced concrete, that is, an object or article made of a cementitious matrix 2 comprising at least one steel reinforcement bar within it. Preferably, said cementitious matrix 2 is not based on magnesium phosphate (so-called magnesium phosphate cements). In particular, the presence of phosphates in the starting cementitious sublayer (as in the case of magnesium phosphate cement) is not necessary, since the phosphates are added from the outside according to the method of the invention. According to the invention, the cementitious matrix 2 is preferably Portland cement (CEM I according to standards EN 197-1 and EN 197- 5; CEM ll-CEM VI according to standards EN 197-1 and EN 197-5) with the possible addition of supplementary cementitious materials. According to the present invention, phosphate precursor means an inorganic or organic compound, preferably inorganic, preferably a phosphate salt, such as, for example, an orthophosphate or a pyrophosphate, comprising the element P and capable of generating H2PO4 HPO42’ and / or PO43’ ions in said solution.

[0026] According to the present invention, said phosphate precursor can be selected from ammonium phosphate (NH4)sPO4, diammonium hydrogen phosphate (DAP, (NH4)2HPO4), ammonium dihydrogen phosphate (NH4H2PO4), potassium phosphate (K3PO4), dipotassium hydrogen phosphate (K2HPO4), potassium dihydrogen phosphate (KH2PO4), sodium phosphate (NasPO4), disodium hydrogen phosphate (Na2HPO4), and sodium dihydrogen phosphate (NaH2PO4), preferably diammonium hydrogen phosphate.

[0027] According to the present invention, said solution 4 can be an aqueous solution.

[0028] According to the present invention, said solution 4 preferably has an initial pH value from 8 to 13, more preferably (particularly when said phosphate precursor is diammonium hydrogen phosphate) from 8 to 9. These values refer to the initial pH of the solution, i.e. before the reaction is made to take place, since, given a certain starting pH of the solution, this pH will change gradually as the reaction with the substrate (which can have a pH between 10 and 12.5, depending on the age and state of conservation of the article, as well as the depth from the surface) is taking place. Furthermore, according to the present invention, said step a) can be conducted by wrapping 8 the outer surface of the object with a material, such as, for example, cellulose pulp, impregnated with said solution 4, or by spray application of said solution 4 on the outer surface of said object 1 or by application with a brush on the outer surface of said object 1 or by immersion of said object 1 in said solution 4, preferably by wrapping 8.

[0029] Preferably, according to the present invention, after said object has been impregnated with said solution 4, an impermeable coating, for example a plastic film, is applied on the outer surface of the object to prevent the evaporation of the solution, which can be removed once step a) has ended.

[0030] According to the present invention, when said object or article 1 has been placed in contact with said solution 4 by means of a wrapping 8 for the time necessary in order for said solution 4 to reach said at least one metal element 3, said step b) can be carried out by placing the anode 6 made of metal material in contact with the wrapping impregnated with solution placed in contact with the object 1 made of a cementitious matrix.

[0031] According to the present invention, in said step a) the solution 4 is allowed to penetrate into the cementitious matrix 2 for a suitable time, which may be determined by the person skilled in the art based on the size and conditions of the object to be treated, in particular the depth at which said metal element 3 is located. For example, the solution can be allowed to penetrate for a time ranging from 6 hours to 7 days, preferably from 24 hours to 48 hours, more preferably for 24 hours.

[0032] The anode 6 made of metal material according to the method of the invention can be a metal grid, for example a steel grid, a metal bar or a metal plate.

[0033] According to the method of the present invention, the concentration of the phosphate precursor in the solution 4 can range from 0.1 M to the saturation concentration, preferably from 0.1 M to 2 M, more preferably 1 M.

[0034] The solution 4 used in the method of the present invention can further comprise a compound that is a source of calcium ions (Ca2+), such as, for example, a compound selected from CaCl2, Ca(NOs)2, and Ca(OH)2, preferably CaCl2.

[0035] The ions freed from the calcium ion source compound added to said solution 4 favour and accelerate the formation of calcium phosphates, which would otherwise be formed only by the calcium ions present in the cementitious sublayer, which, however, is poorly soluble and thus provides few calcium ions. The advantageous effect of adding calcium ions directly into the solution is therefore to enable the formation of a larger quantity of calcium phosphates in a shorter time, compared to the case wherein no calcium ion source is added into the solution.

[0036] In particular, said calcium ion source compound can be present in a calcium ion source compound: phosphate precursor molar ratio ranging from 1 : 1000 to 10:6, preferably 1 :1000.

[0037] Furthermore, said solution 4 can further comprise one or more compounds selected from ethanol, isopropanol, acetone, and / or hydrogen peroxide, preferably ethanol. In particular, said one or more compounds can be present in the solution in a percentage ranging 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.

[0038] According to some preferred embodiments of the method according to the present invention, the solution 4 of step a) can for example comprise:

[0039] - 0.1 M DAP + 0.1 mM CaCl2 in 10vol% ethanol,

[0040] - 1 M DAP+ 1 mM CaCl2, or

[0041] - 2 M DAP + 2 mM CaCI2.

[0042] According to the present invention, said step c) can be carried out for a time ranging from 1 minute to 12 hours, preferably from 1 hour to 12 hours, more preferably from 1 hour to 6 hours, for example from 1 hour to 3 hours.

[0043] According to the present invention, the method of the invention can be carried out applying one of the following conditions:

[0044] - solution of step a): 1 M DAP + 1 mM CaCl2; electrodeposition conditions (step c)): for 3 h at -1 V;

[0045] - solution of step a): 1 M DAP + 1 mM CaCl2; electrodeposition conditions (step c)): for 6 h at -1 V;

[0046] - solution of step a): 1 M DAP + 1 mM CaCl2; electrodeposition conditions (step c)): for 1 h at -2 V.

[0047] The potential difference applied in said step c) according to the present invention can be applied in a continuous or pulsed mode.

[0048] According to one embodiment of the present invention, said steps a), b) and c) are cyclically repeated two or more times. In particular, according to a preferred embodiment, said steps a), b) and c) are repeated twice consecutively for two treatment cycles and wherein in the first treatment cycle step a) provides for placing said object or article 1 in contact with a solution 4 comprising the phosphate precursor and not comprising a calcium ion source compound, so as to enable the potential formation of iron phosphates and the deposition thereof onto the surface of the metal element 3 during step c), and in the second treatment cycle step a) provides for placing said object or article 1 in contact with a solution 4 comprising the phosphate precursor and a calcium ion source compound, so as to enable the formation of calcium phosphates that will be deposited over the iron phosphates during the electrodeposition step c).

[0049] Therefore, according to the present invention, steps a), b) and c) can be cyclically repeated to further improve the durability and mechanical characteristics of the object or article 1 . Therefore, said object 1 can be impregnated with a solution 4 as defined above and subjected to electrodeposition more than once consecutively. As in the embodiment described above, the solution 4 with which the object is impregnated in step a), which again comprises a phosphate precursor, can vary in its composition at every treatment cycle. Similarly, according to the present invention, when steps a), b) and c) are repeated more than once, every electrodeposition treatment cycle carried out in step c) can be carried out with a different voltage from the previous cycle.

[0050] Furthermore, the method of the present invention can further comprise the following steps performed before said steps a), b) and c): a1 ) placing at least a portion of the surface of said object or article 1 in contact with a solution 4 comprising a phosphate precursor capable of generating H2PO4 HPO42’ and / or PO43’ ions and not comprising a calcium ion source, and allowing the solution to penetrate into said cementitious matrix 2, so as to enable the formation of iron phosphates, for the time necessary in order for said solution 4 to reach said at least one metal element 3; b1 ) placing a cathode made of metal material in contact with the solution 4 already in contact with said object 1 , so that both said object 1 and said cathode are simultaneously in contact with the same solution 4; and c1 ) applying a potential difference between said cathode and at least a portion of said metal element 3, which acts as an anode, present in said cementitious matrix, for example by means of a potentiostat 7, to obtain an electrodeposition of at least one layer of said iron phosphates onto the surface of said metal element 3.

[0051] Said steps a1 ), b1 ) and c1 ) are consecutive, i.e. said step b1 ) is carried out following said step a1 ) and said step c1 ) is carried out following said step b1 ).

[0052] According to the present invention, the reversal of the configuration provided for in steps a1 ), b1 ) and c1 ), wherein the metal element 3 acts as an anode rather than a cathode, can favour the formation of iron phosphates as the main species of phosphate compounds and, therefore, during step c1 ) there will be a deposition of a layer of phosphate compounds mainly comprising iron phosphates, prior to the application, via one or more cycles, of steps a), b) and c) wherein the metal element 3 acts as a cathode.

[0053] The present invention will now be described by way of non-limiting illustration according to a preferred embodiment thereof, with particular reference to the examples and figures of the appended drawings, in which:

[0054] - Figure 1 shows a diagram of the application of the method of the invention to a real reinforced concrete structure; in particular, the figure shows the object 1 consisting of a cementitious matrix 2 and a steel reinforcement bar as the metal element 3; the object 1 is covered with a wrapping 8 soaked in a solution 4 based on phosphates, which provide PO43’ ions, and a metal grid is placed in contact as an anode 6 with said wrapping 8; the anode 6 and a part of the steel reinforcement bar, which acts as the cathode, are connected to a potentiostat 7 with which a potential difference is applied to favour the electrodeposition of new phosphate minerals 5, which have formed in said cementitious matrix 2, onto the surface of said steel reinforcement bar (metal element 3);

[0055] - Figure 2 shows a diagram, in particular a perspective (A) and a section (B), of the samples of cementitious mortar (cylinder of cementitious mortar) reinforced with a steel bar used in the examples;

[0056] - Figure 3 shows the setup used in Examples 1 and 2 for the electrodeposition of the DAP solution onto the steel bar;

[0057] - Figure 4 shows the setup used in Examples 1 and 2 for the accelerated corrosion test on the steel reinforcement bar;

[0058] - Figure 5 shows a comparison between the curves of anodic polarisation, in NaCI 3.5 wt%, of untreated samples (A) and samples treated under conditions of 1 M, 3h, -1 V (B) and 1 M, 1 h, -2V (C);

[0059] - Figure 6 shows a comparison between the Knoop surface hardness values of treated and untreated samples;

[0060] - Figure 7 shows a comparison between the values regarding the loss of material abraded from treated and untreated samples;

[0061] - Figure 8 shows a comparison between the values of the dynamic elastic modulus of treated and untreated samples.

[0062] EXAMPLE 1. Example of application of the method according to the present invention on samples of reinforced cementitious mortar.

[0063] Cylindrical samples of cementitious mortar (water / cement ratio = 0.5) with a diameter of 5 cm and height of 10 cm, containing a carbon steel reinforcement bar with a diameter of 10 mm at the centre (Figure 2), were treated in the following manner.

[0064] First, a wrapping 8 of cellulose pulp and a DAP solution was applied on the lateral surface of every cylindrical test sample. In particular, the wrapping was about 1 cm thick, consisting of cellulose pulp with an aqueous solution containing 1 M DAP + 1 mM CaCl2. The wrapping 8 was covered with a waterproof plastic film to prevent evaporation of the solution. After 24 hours, the sample was placed in a glass receptacle 9 and a metal plate was placed inside the wrapping as an anode 6 (Figure 3).

[0065] The steel bar and metal plate were then connected to a potentiostat 7, so that the bar would act as a cathode and the plate as an anode. A potential of -1 V relative to the reference electrode (saturated calomel electrode, SCE, also in contact with the wrapping) was then applied for 3 hours. At the end, the film and wrapping 8 were removed, and the sample was rinsed with water and allowed to dry.

[0066] After the treatment, the improvement in the corrosion rate was checked by placing every sample in the same receptacle with a steel cylindrical grid around it and 200 mL of an aqueous solution 11 of NaCI at 3.5 wt% were poured in to simulate seawater. An anodic polarisation test was then carried out by connecting the steel reinforcement bar and the metal grid to a potentiostat, so that this time the bar acted as an anode and the grid as a cathode 10 (Figure 4). The test was then carried out; it consisted in varying the potential from -0.2V to +1.0V relative to the open circuit potential and recording the corresponding current.

[0067] Considering the mean of 3 replicates per condition, compared to the untreated reference, the samples treated with 1 M DAP+1 mM CaCl2 at -1 V for 3 h showed a 28% reduction in the current circulating in the system (and hence an improvement in corrosion resistance) (Figure 5).

[0068] Tests were then performed on the same cylindrical samples to determine the improvement in the properties of the cementitious mortar following the treatment: (i) Knoop surface hardness tests, i.e. tests on the resistance to the penetration of an indenter on the treated surface, (ii) tests on abrasion resistance, in terms of loss of material due to the action of metal balls kept in rotational motion over the surface of the sample for a certain amount of time, and (iii) tests on the dynamic elastic modulus, calculated by measuring the velocity of an ultrasonic pulse passing through the sample across a diameter (in the area without the steel bar).

[0069] Considering the mean of 3 replicates per condition, compared to the untreated reference, the samples treated with 1 M DAP+1 mM CaCl2 at -1 V for 3 h showed a 75% increase in Knoop surface hardness (Figure 6), a 57% decrease in the material lost due to surface abrasion (Figure 7) and a 5% increase in the dynamic elastic modulus (Figure 8).

[0070] EXAMPLE 2. Example of application of the method according to the present invention on samples of reinforced cementitious mortar.

[0071] Compared to example 1 , the samples were treated with an aqueous solution containing 1 M DAP+1 mM CaCl2 with a similar procedure, but the electrodeposition time was reduced from 3 hours to 1 hour and the potential was varied from -1 V to - 2 V relative to the reference electrode.

[0072] Considering the mean of 3 replicates per condition, compared to the untreated reference, the samples treated with 1 M DAP+1 mM CaCl2 at -2 V for 1 h showed a 22% reduction in the current circulating in the system (and hence an improvement in the corrosion resistance) (Figure 4), a 78% increase in Knoop surface hardness (Figure 5), a 61 % decrease in the material lost due to surface abrasion (Figure 6) and an 11 % increase in the dynamic elastic modulus (Figure 7).

[0073] References

[0074]

[0001] Sassoni E., Hydroxyapatite and Other Calcium Phosphates for the Conservation of Cultural Heritage: A Review, Materials 11 (2018) 557, DOI: 10.3390 / ma11040557

[0075] [2] Sassoni E., Franzoni E., Lime and cement mortar consolidation by ammonium phosphate. Construction and Building Materials 245 (2020) 118409, DOI: 10.1016 / j.conbuildmat.2020.118409

[0076] [3]Pasco H., Naidu S., Lothenbach B., Sassoni E., Enhancement of surface properties of cementitious materials by phosphate treatments, Cement and

[0077] Concrete Composites 141 (2023) 105124, DOI:

[0078] 10.1016 / j.cemconcomp.2023.105124

Claims

CLAIMS1 ) A method for treating an object (1 ) made of a cementitious matrix (2) comprising within it at least one metal element (3), said method comprising or consisting of the following steps: a) placing at least a portion of the surface of said object (1 ) in contact with a solution (4) comprising a phosphate precursor capable of generating H2PO4; HPO42’ and / or PO43’ ions, and allowing the solution (4) to penetrate into said cementitious matrix (2) for the time necessary in order for said solution (4) to reach said at least one metal element (3), said H2PO4; HPO42’ and / or PO43’ ions forming phosphate compounds (5) by reacting with cations present in said cementitious matrix (2), in said at least one metal element (3) and / or in said solution (4); b) placing an anode (6) made of a metal material in contact with the solution (4) in contact with said object (1 ), so that both said object (1 ) and said anode (6) are in contact with the same solution (4); c) applying a potential difference between said anode (6) and at least a portion of said metal element (3), which acts as a cathode, in order to obtain an electrodeposition of at least one layer of said phosphate compounds (5) onto the surface of said metal element (3).2) The method according to claim 1 , wherein said potential difference is a value selected in the range from -0.5V to -3.5V, preferably from -1V to -2V, more preferably -1V, relative to a reference electrode.3) The method according to any one of the preceding claims, wherein said at least one metal element (3) is selected between a steel reinforcement bar and steel fibres, preferably a steel reinforcement bar.4) The method according to any one of the preceding claims, wherein said phosphate precursor is selected from ammonium phosphate (NH4)sPO4, diammonium hydrogen phosphate (DAP, (NH4)2HPO4), ammonium dihydrogen phosphate (NH4H2PO4), potassium phosphate (K3PO4), dipotassium hydrogen phosphate (K2HPO4), potassium dihydrogen phosphate (KH2PO4), sodium phosphate (NasPO4), disodium hydrogen phosphate (Na2HPO4), and sodium dihydrogen phosphate (NaH2PO4), preferably diammonium hydrogen phosphate.5) The method according to any one of the preceding claims, wherein said solution (4) is an aqueous solution.6) The method according to any one of the preceding claims, wherein saidsolution (4) has an initial pH value from 8 to 13, preferably from 8 to 9.7) The method according to any one of the preceding claims, wherein said step a) is carried out by wrapping (8) the outer surface of the object with a material impregnated with said solution (4), or by spray application of said solution (4) on the outer surface of said object (1 ) or by application with a brush on the outer surface of said object (1 ) or by immersion of said object (1 ) in said solution (4), preferably by wrapping (8).8) The method according to any one of the preceding claims, wherein said anode (6) made of metal material is a metal grid, for example a steel grid, a metal bar or a metal plate.9) The method according to any one of the preceding claims, wherein the concentration of the phosphate precursor in the solution ranges from 0.1 M to the saturation concentration, preferably from 0.1 M to 2 M, more preferably 1 M.10) The method according to any one of the preceding claims, wherein said solution (4) further comprises a calcium ion source compound, such as, for example, a compound selected from CaCl2, Ca(NOs)2, and Ca(OH)2, preferably CaCl2.11 ) The method according to the preceding claim, wherein said calcium ion source compound is present in a calcium ion source compound: phosphate precursor molar ratio from 1 : 1000 to 10:6, preferably 1 : 1000.12) The method according to any one of the preceding claims, wherein said solution (4) further comprises one or more compounds selected from ethanol, isopropanol, acetone, and / or hydrogen peroxide, preferably ethanol.13) The method according to the preceding claim wherein said one or more compounds are present in the solution in a percentage ranging from 0.1 to 30 vol%.14) The method according to any one of the preceding claims, wherein said step c) is carried out for a time ranging from 1 minute to 12 hours, preferably from 1 hour to 12 hours, more preferably da 1 hour to 6 hours.15) The method according to any one of the preceding claims, wherein said potential difference in said step c) is applied in a continuous or pulsed mode.16) The method according to any one of the preceding claims, wherein said steps a), b) and c) are repeated two or more times.17) The method according to the preceding claim, wherein said steps a), b) and c) are repeated twice for two treatment cycles and wherein in the first treatment cycle step a) provides for placing said object (1 ) in contact with a solution (4)comprising the phosphate precursor and not comprising a calcium ion source compound, and in the second treatment cycle step a) provides for placing said object (1 ) in contact with a solution (4) comprising the phosphate precursor and a calcium ion source compound.18) The method according to any one of the preceding claims, wherein said method further comprises the following steps performed before said steps a), b) and c): a1 ) placing at least a portion of the surface of said object (1 ) in contact with a solution (4) comprising a phosphate precursor capable of generating H2PO4; HPO42’ and / or PO43’ ions and not comprising a calcium ion source, and allowing the solution (4) to penetrate into said cementitious matrix (2), so as to enable the formation of iron phosphates, for the time necessary in order for said solution (4) to reach said at least one metal element (3); b1 ) following said step a1 ), placing a cathode made of metal material in contact with the solution (4) in contact with said object, so that both said object and said cathode are in contact with the same solution; and c1 ) following said step b1 ), applying a potential difference between said cathode and at least a portion of said metal element (3), which acts as an anode, to obtain an electrodeposition of at least one layer of said iron phosphates onto the surface of said metal element (3).

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