FR2955858A1 - CONCRETE ELEMENT WITH SUPERHYDROPHOBIC SURFACE - Google Patents

Abstract

The invention relates to a concrete element comprising a superhydrophobic wall having a roughness Ra of 1 .mu.m to 10 .mu.m and having protuberances spaced two by two with an average interval of between 1 .mu.m and 40 .mu.m. Said concrete element has a critical pore diameter of less than 100 nm surface and includes portions flush with said wall more hydrophobic than concrete.

Description

The present invention relates to the field of concrete elements, in particular concrete elements of which at least one wall is visible. The walls of the concrete elements are likely to get dirty especially due to deposits of dissolved substances in the water flowing over the concrete elements. These deposits form traces that degrade the visual appearance of the walls of the concrete elements, which is undesirable when these walls are visible. To reduce the formation of traces, it is generally desirable that the visible walls of the concrete element be the least hydrophilic possible to prevent water adhesion. The risks of deposits of substances transported by water are thus reduced. It is generally considered that a wall is hydrophilic when the static contact angle of a drop of water disposed on the wall is less than 90 degrees and that the wall is hydrophobic when the static contact angle of a drop of water. distilled water disposed on the wall is greater than 90 degrees. The wall is said to be superhydrophobic when the static contact angle of a drop of distilled water disposed on the wall is greater than 130 degrees. To minimize the formation of deposits on the walls of a concrete element, it would be desirable for the walls of the concrete element to be superhydrophobic. However, the walls of a concrete element made by formwork or molding generally tend to be hydrophilic with, for example, a static contact angle between 10 and 50 degrees. There are coatings that can be applied to the walls of a concrete element to make these walls hydrophobic. However, the use of such coatings has several disadvantages. Indeed, if it is possible to obtain a hydrophobic wall by the application of a coating of a few hundred micrometers of fluoride-based paint type, it is generally not possible to achieve obtaining superhydrophobic walls . In addition, the cost of such coatings is high.

In addition, such coatings can change the visual appearance of the walls of the concrete element to which they are applied so that the use of coatings may not be compatible with the desired visual appearance of the walls (especially if wish to keep a visual "mineral").

The object of the present invention is therefore to propose a concrete element having a superhydrophobic wall obtained from the manufacture of the concrete element or obtained after application of a chemical compound which does not allow, if it were used alone, to to obtain a superhydrophobic wall. This object is achieved by the use of a concrete element, in particular for the field of construction, comprising a superhydrophobic wall having a roughness Ra of between 1 μm and 10 μm and having protuberances spaced two by two apart means ranging from 1 μm to 40 μm, said concrete member having a critical pore diameter of less than 100 nm surface and comprising portions flush with said wall more hydrophobic than concrete. Obtaining a concrete element having a superhydrophobic wall is due to the combination of four factors: a specific wall roughness in a given range, a mean deviation of the wall protuberances in a given range, a pore diameter surface criticism lower than a determined threshold and the presence of hydrophobic portions flush with at least a portion of the wall. By the term "hydraulic binder" is meant according to the present invention a powdery material which, mixed with water, forms a paste which sets and hardens as a result of reactions and hydration processes, and which after curing , retains its strength and stability even under water. By the term "concrete" is meant a mixture of hydraulic binder (for example cement), aggregates, water, possibly adjuvants, and possibly mineral additives, such as high performance concrete, concrete very high performance, self-compacting concrete, self-leveling concrete, self-compacting concrete, fiber concrete, ready-mix concrete or colored concrete. According to this definition, prestressed concrete is also meant. The term "concrete" includes mortars. In this specific case, the concrete comprises a mixture of hydraulic binder, sand, water and possibly additives and possibly mineral additions. The term "concrete" according to the invention denotes indistinctly fresh concrete or hardened concrete. By the term "high performance concrete" is meant a concrete with a compressive strength of 28 days at 50 to 100 MPa. By the term "ultra-high performance concrete" is meant a concrete whose compressive strength at 28 days is greater than 100 MPa, generally greater than 120 MPa. According to the invention the term "aggregates" refers to gravel, chippings and / or sand. By the term "Portland cement" is meant according to the invention a CEM I, CEM II, CEM III, CEM IV or CEM V cement according to the "Cement" NF EN 197-1 standard. According to the invention, the term "mineral additions" refers to a finely divided mineral material used in concrete to improve certain properties or to confer particular properties. These are, for example, fly ash (as defined in EN 450), silica fumes (as defined in EN 13263: 1998 or NF P 18-502), slags (such as as defined in standard NF P 18-506), calcareous additions (as defined in standard NF P 18-508) and siliceous additions (as defined in standard NF P 18-509). By the term "setting" is meant according to the present invention the transition to the solid state by chemical reaction of hydration of a hydraulic binder. The setting is usually followed by the hardening period. By the term "element for the field of construction" is meant according to the present invention any component of a construction 30 such as for example a floor, a screed, a foundation, a wall, a partition, a ceiling, a beam, worktop, pillar, bridge pier, cinderblock, pipe, post, cornice, road element (eg curb), tile, road surface, eg road , a plasterboard, an insulating element (acoustic and / or thermal).

By the term "contact angle" or "wetting angle" is meant the angle formed between a liquid / vapor interface and a solid surface. By the term "roughness" is meant the irregularities of the order of one micrometer of a surface which are defined by comparison with a reference surface, and are classified in two categories: asperities or "peaks" or "protuberances" , and cavities or "hollows". The roughness of a given surface can be determined by measuring a number of parameters. In the remainder of the description, the parameter Ra, as defined by standards NF E 05-015 and ISO 4287, corresponding to the arithmetic average of all the ordinates of the profile within a base length ( in our examples, the latter was set at 12.5 mm). By the term "wall of the concrete element" is meant both a wall of a bare concrete element and the wall of an assembly comprising a concrete body covered, possibly only partially, with a layer of a material other than concrete and having a thickness less than one millimeter. By the expression "portions flush with said wall more hydrophobic than concrete" is meant more hydrophobic than the wall of a concrete element whose composition would be perfectly uniform. The expression "mean diameter of entry of open cavities on said wall" means the average diameter of the cavities and depressions, including possibly pores, which open on the wall, the diameters being measured at the wall. By the term "critical surface pore diameter" is meant the inlet diameter of the largest pores opening on the wall. The critical surface pore diameter is preferably measured via the pore size distribution curve obtained by mercury porosimetry. The invention relates to a concrete element comprising a superhydrophobic wall having a roughness Ra of 1 μm to 10 μm and having protuberances spaced two by two by an average interval of between 1 μm and 40 μm, said concrete element having a diameter of critical surface pores less than 100 nm and comprising portions flush with said wall more hydrophobic than concrete. According to an exemplary embodiment of the invention, the roughness Ra is from 1 to 7 μm, preferably from 1 to 5 μm, advantageously from 1 to 3 μm. According to an exemplary embodiment of the invention, the protuberances are spaced two by two by an average interval of from 10 .mu.m to 30 .mu.m, preferably from 10 .mu.m to 20 .mu.m. According to an exemplary embodiment of the invention, the diameter of critical surface pores (English breakthrough radius) is less than 50 nm, preferably less than 20 nm. The diameter of critical surface pores can be measured by mercury porosimetry. According to an exemplary embodiment of the invention, the wall comprises open cavities on said wall and the average inlet diameter of the open cavities on said wall is less than 1 μm, preferably less than 0.5 μm, and even more preferably less than 0.2 .mu.m. According to an exemplary embodiment of the invention, the surface porosity of the concrete element is less than or equal to 10%, preferably less than or equal to 9%. Surface porosity can be measured by mercury porosimetry. The nature of the portions flush with said wall and more hydrophobic than concrete depends on the method of manufacturing the concrete element. According to an exemplary embodiment of the invention, the portions correspond to a chemical compound deposited on the concrete body of the concrete element. Advantageously, the portions then comprise silicone. According to another embodiment of the invention, the portions belong to the surface layer of the concrete element. Advantageously, the portions then comprise silica fume at a concentration higher than the average concentration of the silica fume concrete. According to an exemplary embodiment of the invention, said element is a high performance concrete, preferably an ultra high performance concrete, for example a fiber ultra high performance concrete. Ultra high performance fibered concretes are concretes with a cement matrix containing fibers. It is referred to the document entitled "Ultra-High Performance Boundary Concretes" of the Roads and Highways Technical Studies Department (Setra) and the French Association of Civil Engineering (AFGC). The fibers are metallic, organic, or a mixture. The binder dosage is high (the E / C ratio is low, generally the E / C ratio is at most about 0.3). The amount of fiber is generally low, for example between 1 and 8% by volume. The cementitious matrix may comprise cement (Portland), a pozzolanic reaction element (in particular silica fumes) and a fine sand. For example, the cement matrix may comprise Portland cement; fine sand; a silica-type element; - possibly quartz flour; the quantities being variable and the dimensions of the various elements being chosen between the micron or submicron range and the millimeter, with a maximum dimension not exceeding in general 5 mm; and a superplasticizer being added in general with the mixing water. By way of example of a cementitious matrix, mention may be made of those described in patent applications EP-A-518777, EP-A-934915, WO-A-9501316, WO-A-9501317 and WO-A-9928267. WO-A-9958468, WO-A-9923046, WO-A-0158826, WO2008 / 090481, WO2009 / 081277 to which it is referred for more details. Examples of matrix are BPRs, reactive powder concretes, while examples of UHPCs are BSI concrete from Eiffage, Ductal® from Lafarge, Cimax® from Italcementi and BCV from Vicat. A thermal treatment can be implemented on these concretes. For example, the heat treatment comprises, after the hydraulic setting, heating at a temperature of 60 ° C or higher for several hours, typically 90 ° C for 48 hours. The invention also relates to a method of manufacturing a concrete element as defined above, comprising the steps of providing a mold, casting said concrete in the fresh state and removing said element from the mold after the taking concrete. Advantageously, the filling of the mold is carried out flat. According to an exemplary embodiment of the invention, the mold is made of a more hydrophobic material than concrete. According to an exemplary embodiment of the invention, the mold comprises silicone. Advantageously, when the mold is silicone, it may not be necessary to use a mold release or form release composition to facilitate removal of the concrete member from the mold. The inventors have demonstrated that the use of a silicone mold could lead, when a concrete is introduced into the mold, to a modification of the surface composition of the concrete. The inventors have, moreover, highlighted a transfer of the roughness of the silicone mold to the wall of the concrete element. Therefore, by providing that the roughness of the silicone mold is favorable for obtaining a superhydrophobic wall, the concrete element obtained by molding in a silicone mold is adapted to obtain a superhydrophobic wall. Preferably, the mold has a roughness Ra of from 1 μm to 10 μm. The inventors have, in turn, demonstrated an at least partial transfer of the irregularities of the silicone mold to the wall of the concrete element. Therefore, by providing that the irregularities of the silicone mold are favorable for obtaining a superhydrophobic wall, the concrete element obtained by molding in a silicone mold is adapted to obtain a superhydrophobic wall. According to an exemplary embodiment of the invention, the method further comprises the step of disposing a demolding composition in the silicone mold before filling the mold with the fresh concrete.

More specifically, according to an exemplary embodiment, the method comprises the following steps: - coating the walls of the mold with the demolding composition; - Introduce the freshly prepared concrete in the mold and - Remove the piece of the mold after hardening and possibly cure 15 of the concrete. The demolding composition may comprise one or more compounds selected from a stabilizer, a dispersant, a surfactant, a preservative, a solvent, a thickener and a thixotropic agent, including one or more compounds selected from a water repellant and a pigment. According to an exemplary embodiment, the method further comprises the step of at least partially covering said element with a layer of a more hydrophobic mixture than concrete, hereinafter referred to as a hydrophobic mixture. It may be an aqueous solution of silane, siloxane and synthetic resins sold by Wacker under the name SILRES BS29. The hydrophobic mixture may correspond to the demolding composition. The application of the hydrophobic mixture layer can be carried out directly on the concrete element after demolding or, when the hydrophobic mixture corresponds to the demolding composition, the application of the hydrophobic mixture can be carried out on the mold. The application may be carried out by means known per se, for example by application with a brush, cloth, or roller, by dipping or by spraying, the latter mode of application being preferred.

The amount of hydrophobic mixture to be applied is chosen to be sufficient to form a more or less continuous film over the entire outer surface of the concrete member. The thickness of the formed film is generally less than 5 micrometers. As an indication, it is generally sufficient to apply 5 to 15 g / m 2 of a mixture having a viscosity of about 50 mPa.s. The inventors have demonstrated that the film of the hydrophobic mixture causes a decrease in the surface critical pore diameter and in the mean diameter of the entrance of open cavities (on the wall) of the concrete element to the extent that at least some pores or cavities are clogged by the hydrophobic film. However, the inventors have demonstrated that the hydrophobic film does not change or slightly the roughness Ra and the average gap between the protuberances of the wall of the concrete element. According to an exemplary embodiment, the method further comprises the step of growing on at least a portion of said element a layer of carbonates. To do this, the method may include the step of holding the concrete element in an enclosure containing carbon dioxide. The inventors have demonstrated that the growth of the carbonate crystals on the surface of the concrete results in the closure, at least in part, of the critical pores of surfaces and of the open cavities on the wall of the concrete element. In addition, the growth of the carbonate crystals results in the appearance of a roughness Ra and a mean deviation of the surface protuberances of the concrete element adapted to obtain a superhydrophobic wall. The invention also relates to the use of a wall of a concrete element as a superhydrophobic wall, said wall having a roughness Ra of between 1 .mu.m and 10 .mu.m and having protuberances spaced two by two apart from an average interval of 1 μm to 40 μm, said concrete member having a critical pore diameter of less than 100 nm surfaces and comprising portions flush with said wall more hydrophobic than concrete. The invention will be described in more detail by means of the following examples, given in a non-limiting manner, in relation to the figures in which: FIG. 1 illustrates the principle of measuring a contact angle between a drop of water and a area ; Figure 2 illustrates features of a surface of a concrete member; and Figure 3 shows evolution curves of mercury volumes absorbed by two samples as a function of the pore inlet diameter of the samples. EXAMPLES The present invention is illustrated by the following nonlimiting examples. In the examples, the products and materials used are available from the following suppliers: Product or material Supplier (1) Lafarge-France Val d'Azergues Portland Cement (2) Lafarge-France White Portland Cement Tell (3) Sand 0/4 mm Lafarge France (St Bonnet Little Craz) (4) Sand BE01 (D50 at 307 pm) Sibelco France (Career of SIFRACO BEDOIN) (5) Filler limestone OMYA BETOCARB HP Orgon (6) Filler limestone DURCAL 1 OMYA (7) Smoke Silica MST SEPR (European Society of Refractory Products) (8) Optima 203 Chryso Additive (9) Ductal Adjuvant F2 Chryso (10) SILRES Solution BS29 Wacker Ultra High Performance Concrete Formulation (1) Ultra High Performance Concrete Formulation (1) The following is used in Table 1: Formulation (1) of Ultra High Performance Concrete Component Proportion (% by weight based on the weight of the composition) Portland White Cement Lafarge 31.0 Teil Wire 1 limestone DURCAL 1 9.3 Silica fumes MST 6.8 Sand BEOI 44.4 Tempering water 7.1 Ductal adjuvant F2 1.4 The water / cement ratio is 0.26. It is an ultra high performance non-fiber concrete. Ultra-High Performance Concrete Preparation Method The ultra-high performance concrete according to the formulation (1) is made by means of a RAYNERI type mixer. The whole operation is carried out at 20 ° C. The method of preparation comprises the following steps: • At T = 0 seconds: put the cement, calcareous fillers, silica fumes and sand in the mixing bowl and knead for 7 minutes (15 revolutions / min); • At T = 7 minutes: add water and half of the adjuvant mass and knead for 1 minute (15 rpm); • At T = 8 minutes: Add the remaining adjuvant and knead for 1 minute (15 rpm); • At T = 9 minutes: knead for 8 minutes (50 rpm) and • AT = 17 minutes: knead for 1 minute (15 rpm). • From T = 18 minutes: pour the concrete flat in the mold or molds provided for this purpose.

Mortar formulation The mortar formulation (2) used to carry out the tests is described in Table 2 below: Table 2: Mortar formulation (2) Component Proportion (% by weight relative to the mass of the composition) Portland cement Lafarge Val 23.9 of Azergues Filler limestone BETOCARB HP 12.3 Sand 0/4 51.9 Pre-wetting water 0.011 Tempering water 11.9 Adjuvant Optima 203 0.0026 The ratio of water to cement / cement is 0.496.

Lafarge Portland cement is a CEM 152.5 PMES cement. Method of preparation of the mortar The mortar according to the formulation (2) is produced by means of a Perrier type mixer. The whole operation is carried out at 20 ° C. The method of preparation includes the following steps: • Put the sands in a mixing bowl; • At T = 0 seconds: start mixing (140 rpm) and simultaneously add the dampening water in 30 seconds, then continue mixing (140 rpm) for up to 60 seconds; • AT = 1 minute: stop mixing and let stand for 4 minutes; • At T = 5 minutes: add the hydraulic binder; • At T = 6 minutes: mix for 1 minute (140 rpm) • At T = 7 minutes: add the mixing water in 30 seconds (while mixing (140 rpm)); • At T = 7 minutes and 30 seconds: knead for 2 minutes (140 rpm); and • From T = 9 minutes and 30 seconds pour the concrete flat in the mold or molds provided for this purpose. Method of applying a hydrophobic mixture to one face of a concrete sample After the concrete sample is stripped, a hydrophobic mixture is applied to one side of the sample. The hydrophobic mixture applied is an aqueous solution of silane, siloxane and synthetic resins, marketed by Wacker under the name SILRES BS29. This solution comprises about 70% water and 30% of a mixture of silane, siloxane and synthetic resins. The solution is applied with a brush so as to completely cover the treated surface with a weight of 15 g / m2.

The layer thickness obtained is then less than 5 μm. Aging process of a carbon dioxide concrete sample After demolding a concrete sample, the sample is stored for 7 days in an enclosure in which the temperature is 20 ° C and the relative humidity is 50 ° C. %. Then the concrete sample is stored, for the desired duration, in a carbonation chamber in which is maintained an atmosphere containing 50% carbon dioxide and the relative humidity is 65%. Process for wet aging of a concrete sample The process is carried out by means of a water condensation chamber, for example the chamber developed by Q-Lab Corporation under the name QCT. The QCT water condensation chamber allows accelerated simulation of damage caused by a hot and humid atmosphere on a concrete sample. In general, the sample to be tested is arranged to form a part of the wall of a chamber of the condensation chamber QCT. The angle of inclination of the sample is 15 °. Distilled water is heated to generate water vapor. The vapor fills the chamber to obtain an atmosphere having a relative humidity of 100% and a temperature of 38 ° C ± 2 ° C. The sample includes a portion in the chamber and a portion exposed to the ambient atmosphere. The difference in temperature causes the condensation of water vapor on the sample. As the condensation occurs continuously, a water runoff is obtained on the face of the sample oriented in the QCT chamber. UV-Ozone Cleaning Process The method involves placing the sample to be cleaned in an enclosure and projecting ultraviolet rays of 254 nm wavelength on the measuring face of the sample to dissociate the organic compounds present in the sample. 'sample. Simultaneously, a second range of ultraviolet rays having a wavelength of 185 nm produces a large amount of ozone in the chamber by interaction with the oxygen molecules present in the atmosphere of the chamber. The oxidants thus formed (ozone, hydroxyl radicals) make it possible to ensure perfect oxidation of the surface of the sample: the contaminants are then transformed into volatile species (H2O, CO, CO2) which are evacuated from the enclosure via the use of a pump. The duration of the process is 20 minutes. Method of measuring a wetting or contact angle FIG. 1 illustrates the principle of measuring a wetting angle between a solid surface 10 of a concrete sample 12 and a drop 14 of a liquid deposited on the surface 10. The reference 16 denotes the liquid / gas interface between the drop 14 and the ambient air. FIG. 1 is a section on a plane perpendicular to the surface 10. In the section plane, the wetting angle α corresponds to the angle, measured from inside the liquid drop 14, between the surface 10 and the tangent T at the interface 16 at the point of intersection between the solid 10 and the interface 16. In order to measure the wetting angle, the sample 12 is placed in a room at a temperature of 20 ° C. and a relative humidity of 50%. A drop of water 14 having a volume of 2.5 μL is placed on the surface 10 of the sample 12. The measurement of the angle is carried out by an optical method, for example using a shape analysis device. (English Drop Shape Analysis), for example the device DSA 100 marketed by Krüss. The measurements are repeated five times and the value of the contact angle measured between the drop of water and the support is equal to the average of these five measurements. Method of chemical analysis of the surface elements of a concrete sample The measurement surface of the concrete sample is observed by scanning electron microscopy (SEM). For this, a high-resolution field effect microscope (FEG Quanta 400 from FEI Company) is used with an acceleration voltage of 15 keV with a current intensity of 1 nA. Images are acquired after covering the sample with a thin chromium-based metal layer. A semi-quantitative chemical analysis is performed by an EDS (Energy Dispersive Spectroscopy) analyzer coupled to the scanning electron microscope. Quantification of the chemical elements (calcium, silicon, iron, etc.) contained in the surface layer of the sample to a thickness of about 1 μm is obtained. Method of Measuring the Average Inlet Diameter of the Open Cavities at the Surface of the Concrete Sample The wall of the sample is observed by scanning electron microscopy (SEM). For this, a high-resolution field effect microscope (FEG Quanta 400 from FEI Company) is used with an acceleration voltage of 15 keV with a current intensity of 1 nA. Images are acquired after covering the sample with a thin chromium-based metal layer.

The acquired images are analyzed, for example by computer, in order to determine the average input diameter of the open cavities on the surface. By way of example, the method consists in determining the contours of the open cavities at the surface by an analysis of the contrast of the image and in determining for each contour the circle which corresponds best to the contour of the open cavity according to a criterion of optimization. The inlet diameter of the open cavity corresponds to the diameter of the circle obtained. The average inlet diameter of the cavities open at the surface corresponds to the average of the diameters of the circles obtained. Preferably, when determining the contours of the open cavities, it may not be taken into account the cavities opening on the wall whose input diameter is less than 0.1 pm. Method for Measuring Surface Porosity and Surface Pore Diameter of Concrete Sample Porosimetry (Mercury Porosimetry) An Autopore III mercury porosimeter was used. The analyzed concrete samples are in the form of small parallelepipedic blocks of a typical size of a few millimeters to 1 cm side and they are dried beforehand at 45 ° C for 8 h. One face of the block corresponds to the face to be tested. The other faces of the block are covered with a waterproof layer, for example an epoxy resin layer. The mercury is brought into contact with a sample and pressure is exerted on the sample to penetrate the mercury in the pores of the sample by the face to be tested. The volume of mercury entering the pores of the sample under the action of the pressure is measured, by a capacitive system, as a function of the pressure applied to the sample. The Washburn equation (1) makes it possible to relate the pressure to the pore diameter. Porosity calculations are based on the equation that expresses the penetration of a non-wetting liquid (mercury) into the pores of a porous material. The calculation is made considering that the wetting angle of the mercury is of the order of 130 ° (on glass as on most solids) and the surface tension is equal to 480 mN / m at 20 ° C. ù ycos8 (1) r P is the mercury pressure (Pa), y is the surface tension of the liquid (N / m), 8 is the contact angle between the solid and the liquid. r is the inlet diameter of the pore.

From the evolution curve of the volume having penetrated the pores of the sample as a function of the pressure exerted on the mercury and of the Washburn equation, it is possible to determine the pore diameter distribution which is generally expressed in terms of percentage or mL / mm 2 as a function of the pore inlet diameter, expressed as {gamma or nm. The critical pore diameter, or critical diameter, of the sample surface corresponds to the inlet diameter of the largest number of pores opening onto the face to be tested. The surface porosity is determined from the comparison of the volume of the concrete sample and the volume of mercury which has entered the sample by the face to be tested. It is expressed as a percentage by volume of voids in the concrete sample. It represents the porosity accessible via the face to be tested. Method for Measuring the Roughness Ra on the Surface of the Concrete Sample The measurement is carried out with a probe rugosimeter marketed by MITUTOYO under the name SURFTEST SJ-201 M. The average roughness parameter (Ra) is measured at five times over a distance of 12.5 mm and the roughness value Ra is equal to the average of these five measurements. Method for Measuring the Mean Distance Between the Protuberances on a Wall of the Concrete Sample A section of the sample is made through the wall in question. The section of the sample is observed by scanning electron microscopy (SEM). For this, a high-resolution field effect microscope (FEG Quanta 400 from FEI Company) is used with an acceleration voltage of 15 keV with a current intensity of 1 nA. The images are acquired after covering the sample with a thin chromium-based metal layer. FIG. 2 illustrates the principle of measuring the average gap between the surface protuberances of a superhydrophobic concrete sample 12 and represents a schematic sectional view of the sample 12. The inventors have shown that the surface of the Superhydrophobic sample 12 comprises protuberances 18 distributed substantially evenly. The average deviation between two adjacent protuberances is determined from the analysis, for example by computer, of the section of the sample 12.

By way of example, the method consists in determining the contour of the surface 10 by an image contrast analysis, in determining the vertex of each protuberance 18 on the contour (which may correspond to the furthest point of the protrusion 18 relative to a reference line), to determine the differences D1, D2, D3 between the vertices of each pair of adjacent protuberances 18 and to determine the average deviation. Examples 1 to 5 which follow are reference examples for which no superhydrophobic wall is obtained. EXAMPLE 1 A concrete having the formulation (1) is prepared. A polyvinyl chloride (PVC) mold is used. The concrete is poured into the PVC mold without using a form release compound. The sample obtained by molding corresponds to a parallelepiped having 100 mm in width, 10 mm in height and 150 mm in length. One side of the concrete element called measuring face is selected.

The inlet diameter of the open cavities on the measuring face is 0.1 to 10 μm. The roughness Ra of the measuring face is 0.4 μm (+/- 0.1 μm). The surface porosity of the concrete element is about 8%. The critical pore diameter of the measurement face is about 0.015 μm. FIG. 3 represents the evolution curve of the incremental volume, used during the realization of the porosimetry of the measurement surface, as a function of the pore inlet diameter opening on the measuring face. The critical diameter corresponds to the diameter of the maximum point 12 of the curve 10. The measuring face is very smooth so that it is not possible to highlight a particular texture. The wetting angle of a drop of water on the measurement face, measured according to the method described above, is 12 degrees (+ 1-3 degrees). The measurement face is therefore hydrophilic. EXAMPLE 2 A concrete having the formulation (1) is prepared. A steel mold is used. The concrete is poured into the mold using as a release composition a mixture of ECO2 oil and SILRES BS29 product in the proportions 80% / 20%. 0.25 g of the form release composition is available in the mold. The sample obtained by molding corresponds to a parallelepiped having 100 mm in width, 10 mm in height and 150 mm in length. One side of the concrete element called measuring face is selected. The inlet diameter of the open cavities on the measuring face is 0.1 to 10 μm. The roughness Ra of the measuring face is 0.8 μm (+/- 0.3 μm). The surface porosity of the concrete element is about 8%. The critical pore diameter of the measurement face is about 0.015 μm. The wetting angle of a drop of water on the measurement face is 119 degrees (+/- 2 degrees). The measuring face is therefore hydrophobic, but not superhydrophobic. EXAMPLE 3 A concrete having the formulation (1) is prepared. A polyurethane mold is used. The concrete is poured into the mold using the SILRES BS29 product as a release compound. 0.25 g of the form release composition is available in the mold. The sample obtained by molding corresponds to a parallelepiped having 100 mm in width, 10 mm in height and 150 mm in length. One side of the concrete element called measuring face is selected. The inlet diameters of the open cavities on the measuring face range from 0.1 to 10 μm. The roughness Ra of the measuring face is 0.9 μm (+/- 0.2 μm). The surface porosity of the concrete element is about 8%. The critical pore diameter of the measurement face is about 0.015 μm. The wetting angle of a drop of water on the measuring face is 118 degrees (+/- 4 degrees). The measuring face is therefore hydrophobic, but not superhydrophobic.

EXAMPLE 4 A mortar having the formulation (2) is prepared. A silicone mold is used. The concrete is poured into the mold without formwork composition. The sample obtained by molding corresponds to a parallelepiped having 200 mm in width, 10 mm in height and 300 mm in length. One side of the concrete element called measuring face is selected. The inlet diameters of the open cavities on the measuring face vary from 1 to 10 μm. The roughness Ra of the measuring face is 1.6 μm (+/- 0.4 μm). The average distance between the protuberances of the measurement face is 10 to 30 μm. The surface porosity of the concrete element is about 15%.

The critical pore diameter of the measurement face is about 0.32 μm. FIG. 3 represents the evolution curve 20 of the incremental volume, used when carrying out the porosimetry of the measuring surface, as a function of the pore inlet diameter opening on the measuring face. The critical diameter corresponds to the diameter of the maximum point 22 of the curve 20.

The wetting angle of a drop of water on the measuring face is 15 degrees (+/- 3 degrees). The measurement face is therefore hydrophilic. EXAMPLE 5 A mortar having the formulation (2) is prepared. A silicone mold is used. The concrete is poured into the mold using the SILRES BS29 product as a release compound. 1.0 g of the form release composition is available in the mold. The sample obtained by molding corresponds to a parallelepiped having 200 mm in width, 10 mm in height and 300 mm in length. One side of the concrete element called measuring face is selected. The inlet diameters of the open cavities on the measuring face vary from 1 to 10 μm. The roughness Ra of the measuring face is 1.7 μm (+/- 0.5 μm). The average distance between the protuberances of the measurement face is 10 to 30 μm. The surface porosity of the concrete element is about 15%.

The critical pore diameter of the measurement face is about 0.32 μm. The wetting angle of a drop of water on the measuring face is 87 degrees (+/- 3 degrees). The measuring face is therefore hydrophobic, but not superhydrophobic. Examples 6 to 10 which follow are examples for which a superhydrophobic surface is obtained. EXAMPLE 6 A concrete having the formulation (1) is prepared. A silicone mold is used without formwork compound in which the concrete is poured. The sample obtained by molding corresponds to a parallelepiped having a width of 200 mm, a height of 10 mm and a length of 300 mm. The surface porosity of the concrete element before treatment is about 8%. The critical pore diameter of the measuring face is approximately 0.015 μm before treatment. One side of the concrete element called measuring face is selected. The following treatments are applied to the measuring face: treatment No. 1: no treatment on the measurement face; Treatment No. 2: aging method of the carbon dioxide concrete sample described above for a week; and treatment No. 3: UV-ozone cleaning method as described above. Surface area pore diameter measurements, post-treatment porosity, open cavity inlet diameter, average protrusion spacing, roughness and wetting angle of the concrete sample are performed on the measuring face according to the methods described above. The results of the measurements are summarized in the following table (3). Table 3 Formulation (1) Silicone mold - No release composition CD a) a? 1 = that (/ i OE ~ C ~ 3 3 ~ + co o -8 a) E cl) L ui 1 = Ç, cn CD -0 3 .0 a); _ o aaio a ~ v EN yci .0. D o os a) 0 F- -o <0 o co a Ô ow? LL No. 1,143 Less than or Less than or Less than 10 to 1.6 (+/- 3) equal to 0.015 equal to 8 0.1 (+/- 0.3) No. 2,141 Lower or lower or lower at From 10 to 1.6 (+ 1-5) equal to 0.015 equal to 8 0.1 (+/- 0.3) No. 3 140 lower or lower or lower than From 10 to 1.6 (+ / -2) equal to 0.015 equal to 8 0.1 (+/- 0.3) For each treatment, a chemical analysis of the elements on the surface of the measuring face of the sample was carried out according to the method described above. The inventors have thus demonstrated that the grains present on the surface of the measurement face of the concrete sample according to the formulation (1) demoulded with a silicone mold were composed mainly of silica fumes.

EXAMPLE 7 A concrete having the formulation (1) is prepared. A silicone mold is used. The concrete is poured into the mold using the SILRES BS29 product as a release compound. 1.0 g of the form release composition is available in the mold. The sample obtained by molding corresponds to a parallelepiped having 200 mm in width, 10 mm in height and 300 mm in length. The following treatments are carried out on the measuring face: treatment no. 4: no treatment of the measurement face and treatment no. 5: aging method of the concrete sample described above for a week. One side of the concrete element called measuring face is selected. Surface area pore diameter measurements, post-treatment porosity, open cavity inlet diameter, average protrusion spacing, roughness and wetting angle of the concrete sample are performed on the measuring face according to the methods described above. The results of the measurements are summarized in the following table (4). Table 4 Formulation (1) - Silicone mold - With release composition c. ~ T /) Û O O Q) N .. ~ O. O Q) ~. Q) O -n N E E fd O O Q) b CO N U QQ)) u Q) N f (u) O Q) a) O in ù m. ù>>> NO NO NO NO NO NO NO NO NO NO NO NO>>>>))))))))))))))))))))))))))))))) 0 Q 0 U 3 N. ~ -Oo W `. No. 4,143 Less than or less than 10 to 30,1,1 (+ 1-4) equal to 0,015 equal to 8 0,1 (+/- 0,2) No. 5,144 Less than or less than or less than From 10 to 30 2.1 (+/- 2) equal to 0.015 equal to 8 0.1 (+/- 0.2) For each treatment, a chemical analysis of the elements on the surface of the measuring face of the sample was carried out according to the method described above. The inventors have thus demonstrated that the grains present on the surface of the measurement face of the concrete sample according to the formulation (1) demoulded with a silicone mold were composed mainly of silica fumes. EXAMPLE 8 A concrete having the formulation (1) is prepared. A mold made of polyvinyl chloride, wood, polyurethane, polyoxymethylene, steel or silicone is used interchangeably. The concrete is poured into the mold without using a form release composition. The sample obtained by molding corresponds to a parallelepiped having 100 mm in width, 10 mm in height and 150 mm in length. One side of the concrete element called measuring face is selected.

The following treatment is carried out on the measuring face: treatment No. 6: aging method of the carbon dioxide concrete sample described above for 7 days, then wet aging method for 10 days, followed by the application SILRES BS29 hydrophobic mixture on the measuring face.

Surface area pore diameter measurements, post-treatment porosity, open cavity inlet diameter, average protrusion spacing, roughness and wetting angle of the concrete sample are performed on the measuring face according to the methods described above. The results of the measurements are summarized in the following table (5):

Table 5 Formulation (1) - No Release Compound U) BN u) Û a) .o - a ~ E co o U) ô C .. U v CQE o C co (~ C rn (DE 1 U) ~, ° -a -oa .r 0 'a) o E 1: 3, e) Q Û o o o)) N N NE NE NE NE NE E E E ((((((( _ i O 1- cE> w? LL H -V O O U L O N O a. UD -D on ° 6 137 less than or near to less than From 1 to 5 (+/- 2) equal to 0.1 0 0.1 (+ 1-0.5) Chemical analysis of the surface elements of the measuring face of the sample was carried out according to the method described above. The inventors have demonstrated that the surfaces of the sample aged in the climatic chamber were covered with a layer of calcium carbonates (whose protuberances are regularly spaced), itself at least partially covered with the hydrophobic mixture SILRES BS29 . EXAMPLE 9 A mortar having the formulation (2) is prepared. A silicone mold is used. The mortar is poured into the mold without the use of a form release composition. The sample obtained by molding corresponds to a parallelepiped having 100 mm in width, 10 mm in height and 150 mm in length. The surface porosity of the concrete element prior to treatment is about 15%. One side of the mortar element called measuring face is selected. The following treatment is applied to the measuring face-treatment No. 7 aging method of the carbon dioxide concrete sample described above for 7 days, followed by a wet aging process for 10 days, followed by the application of the mixture. hydrophobic SILRES BS29 on the measuring face.

Surface area pore diameter measurements, post-treatment porosity, open cavity inlet diameter, average protrusion spacing, roughness and wetting angle of the concrete sample are performed on the measuring face according to the methods described above. The results of the measurements are summarized in the following table (6). Table 6 Formulation (2) - Silicone Mold - No Release Compound a) a) a) O o o t `c c c c ~. (a) (a) (a) (a) (a) (a) (a) (a) (a) (a) (o) a) NONE co. U 6 E • O ~~ E-V <E E. O Q. a) U v) oac ~ D vow 3 3 ..., n ° 7 141 lower close to lower than From 10 to 30 1.6 (+ / -2) at 0.1 0 0.1 (+/- 0.4) EXAMPLE 10 A mortar having the formulation (2) is prepared. The silicone mold is used. The mortar is poured into the mold using the SILRES BS29 product as form release composition. 1.0 g of the form release composition is available in the mold. The sample obtained by molding corresponds to a parallelepiped having 200 mm in width, 10 mm in height and 300 mm in length. The surface porosity of the concrete element prior to treatment is about 15%. One side of the concrete element called measuring face is selected. The following treatment is carried out on the measuring face: treatment No. 8: aging method of the carbon dioxide concrete sample described above for 7 days, then wet aging method for 10 days, followed by the application SILRES BS29 hydrophobic mixture on the measuring face.

Surface area pore diameter measurements, post-treatment porosity, open cavity inlet diameter, average protrusion spacing, roughness and wetting angle of the concrete sample are performed on the measuring face according to the methods described above. The results of the measurements are collated in the following table (7): Table 7 Formulation (2) - Silicone mold - With demolding composition a) N ~ + NQ) NN, O vo `C = -a) crs QOC .- . a) COCN ^ U) NC fQ E -0 0 E a) a) U) Q) .0 o: te .0 NN u, OQ) Q) ù NO 4) E 0 u) -a) 8 u) N E) A)))))))))))))))))))) E E E E E E E E E E E E E E E E E E E E 139 139 139 139 139 139 139 139 139 139 139 139 139 139 , 7 (+/- 4) at 0.1 0 0.1 (+/- 0.5)

Claims (14)

REVENDICATIONS1. A concrete element (12) having a superhydrophobic wall (10) having a roughness Ra of from 1 μm to 10 μm and having protuberances (18) spaced two by two by an average interval of from 1 μm to 40 μm, said element concrete having a critical surface pore diameter of less than 100 nm and further comprising portions flush with said wall more hydrophobic than concrete. The concrete element of claim 1, wherein the roughness Ra is from 1 to 7 μm. The concrete element of claim 1 or 2, wherein the protuberances (18) are spaced two by two by an average range of from 10 μm to 30 μm. 4. Concrete element according to any one of claims 1 to 3, wherein said wall (10) comprises cavities open on said wall and wherein the average diameter of the cavities open on said wall (10) is less than 1 pm The concrete element of any one of claims 1 to 4, wherein said portions comprise silicone. The concrete element of any one of claims 1 to 4, wherein said portions comprise silica fume. 7. Concrete element according to any one of claims 1 to 6, having a surface porosity, measured by mercury porosimetry, less than or equal to 10%. 8. A method of manufacturing a concrete element according to one of claims 1 to 7, comprising the steps of: -provider a mold; pouring said concrete in the fresh state into the mold; and -drawing said mold element after setting the concrete. 9. The method of claim 8, wherein the mold is of a more hydrophobic material than concrete. The method of claim 9, wherein the mold comprises silicone. 11. A process according to any one of claims 8 to 10, wherein the mold has a roughness Ra of from 1 μm to 10 μm. The method of any one of claims 8 to 11, further comprising the step of. at least partially covering said element with a more hydrophobic mixture than the concrete. The method of claim 8, further comprising the step of growing on at least a portion of said element a layer comprising carbonates. 25 14. Use of a wall (10) of a concrete element (12) as a superhydrophobic wall, said wall having a roughness Ra of 1 μm to 10 μm and having protuberances (18) spaced two by two from one another. an average range of from 1 μm to 40 μm, said concrete member having a critical surface pore diameter of less than 100 nm and having portions thereof flush with said wall more hydrophobic than concrete.