WO2011095744A2

WO2011095744A2 - Concrete element having a superhydrophobic surface

Info

Publication number: WO2011095744A2
Application number: PCT/FR2011/050221
Authority: WO
Inventors: Matthieu Horgnies; Jeffrey Chen; Mélanie DYKMAN
Original assignee: Lafarge
Priority date: 2010-02-04
Filing date: 2011-02-03
Publication date: 2011-08-11
Also published as: WO2011095744A3; FR2955858A1; FR2955858B1

Abstract

The invention relates to a concrete element comprising a superhydrophobic wall having a roughness Ra of between 1 μm and 10 μm and protuberances spaced out two by two at an average interval of between 1 μm and 150 μm. Said concrete element has a surface critical pore diameter of less than 100 nm and has parts flush with the wall, that are more hydrophobic than the concrete.

Description

CONCRETE ELEMENT WITH SUPERHYDROPHOBIC SURFACE

The present invention relates to the field of concrete elements, including 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 are often of a substantial thickness (greater than 50 μιτι) and can modify the visual appearance of the walls of the concrete element to which they are applied so that the use of coatings can not be avoided. be compatible with the desired visual appearance of the walls (especially if one wishes to keep a visual appearance "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.

For this purpose, the present invention proposes a concrete element, in particular for the field of construction, comprising a superhydrophobic wall having a roughness Ra of between 1 μιτι and 10 μιτι and having protuberances spaced two by two apart from a mean interval. from 1 m to 150 μιτι, said concrete element 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.

The present invention also provides a method of manufacturing a concrete member, comprising the steps of:

-providing a mold in a more hydrophobic material than concrete, having a roughness Ra of 1 μιτι to 10 μιτι and hollows spaced two by two of an average range of 1 μιτι 150 μιτι;

pouring said concrete in the fresh state into the mold; and

-Remove said element of the mold after setting the concrete.

The present invention also provides a method of manufacturing a concrete member, comprising the steps of: -provide a mold;

pouring said concrete in the fresh state into the mold;

removing said element from the mold after setting the concrete;

on at least a portion of said element, to develop a layer comprising carbonates having a roughness Ra of

1 μιτι to 10 m and having protuberances spaced two by two with an average interval of 1 μιτι to 150 μιτι; and

at least partially covering said layer with a coating that is more hydrophobic than concrete.

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 greater than 50 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 cement of CEM I, CEM II, CEM III, CEM IV or CEM V according to the standard "Cement" NF EN 197-1.

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 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 constituent element of a construction such as for example a floor, a screed, a foundation, a wall, a partition, a ceiling, a beam , a work plan, a pillar, a bridge stack, a cinder block, a pipe, a post, a cornice, a road element (for example a curb), a tile, a covering, for example a 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 settings. 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 from 1 μιτι to 10 μιτι and having protuberances spaced two by two by an average interval of from 1 μιτι to 150 μιτι, 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 μιτι, preferably from 1 to 5 μιτι, advantageously from 1 to 3 μηη. According to an exemplary embodiment of the invention, the protuberances are spaced two by two by an average interval of from 10 m to 30 μm, preferably from 10 m to 20 μm.

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 μιτι, preferably less than 0.5 μιτι, still more preferably less than 0.2 μιτι.

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. They may be compounds having a higher concentration than in the core of the concrete element, for example fine elements such as silica fumes or calcareous filler materials.

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 Fiber Concretes" from the Road and Motorway 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 cement matrix, mention may be made of those described in patent applications EP-A-518777, EP-A-934915, WO-A-9501316, WO-A-9501317, WO-A-9928267, WO -A-9958468, WO-A-9923046, WO-A-0158826, WO2008 / 090481, WO2009 / 081277 to which it is returned for more details.

Examples of matrix are BPR, reactive powder concretes, while examples of UHPC 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 more for several hours, typically 90 ° C for 48 hours. The present invention also provides a method of manufacturing a concrete member, comprising the steps of:

pouring said concrete in the fresh state into the mold; and

-Remove said element of the mold after setting the concrete.

Preferably, the concrete results in a concrete element having a surface pore diameter of less than 100 nm. Advantageously, the filling of the mold is carried out flat.

According to an exemplary embodiment of the invention, the mold comprises silicone or polyurethane (flexible at room temperature). Advantageously, when the mold is made of silicone, it may not be necessary to use a demolding or stripping compound to facilitate removal of the concrete element 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, demonstrated a transfer of the roughness of the mold, in particular of silicone or polyurethane, to the wall of the concrete element. Therefore, by providing that the roughness of the mold is favorable to 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 1 μιτι to 10 μιτι. The inventors have, in fact, demonstrated an at least partial transfer of the irregularities of the 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. The method may furthermore comprise the preliminary step consisting in producing a treatment of the faces of the mold to obtain a roughness Ra of between 1 μιτι and 10 μιτι and hollows spaced two by two from an average interval of 1 m to 150 μιτι. The treatment can be sandblasting. Sandblasting can be achieved by spraying abrasive particles, for example sand, at high speed of the faces of the mold. By way of example, the abrasive particles may be projected on the faces of the mold at a pressure greater than 2 bars, for example about 3 bars.

The method may further include the prior steps of providing an additional mold;

performing a surface treatment of the additional mold to obtain a roughness Ra of from 1 μιτι to 10 μιτι and protuberances spaced two by two by an average interval of from 1 μιτι to 150 μιτι; and

-forming said mold, having a roughness Ra of 1 μιτι to 10 μιτι and hollows spaced two by two by an average interval of 1 μιτι to 150 μιτι, by casting said material more hydrophobic than the concrete in the additional mold and removing said mold.

The treatment of the faces of the additional mold can be achieved by sanding. It can be made by machining. It may further comprise a chemical etching of the faces of the additional mold, for example with nitric acid.

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:

- Coat the walls of the mold with the release composition;

- introduce the freshly prepared concrete into the mold; and

- Remove the piece from the mold after curing and possibly cure the concrete. The mold release 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, marketed by Wacker under the name SILRES BS29. The hydrophobic mixture may correspond to the demolding composition. The hydrophobic mixture may comprise a hydrophobic agent, for example more than 10% by weight, preferably more than 20% by weight, even more preferably more than 25% by weight of the hydrophobic agent, diluted in an organic solvent to facilitate its application.

The application of the layer of the hydrophobic mixture 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 diameter of critical pores of surface and the mean diameter of the entrance of open cavities (on the wall) of the concrete element insofar as at least some of the pores or cavities are plugged by the hydrophobic film. However, the inventors have demonstrated that the hydrophobic film does not modify or slightly the roughness Ra and the average distance between the protuberances of the wall of the concrete element.

-provide a mold;

pouring said concrete in the fresh state into the mold;

removing said element from the mold after setting the concrete; and

on at least a portion of said element, to develop a layer comprising carbonates, said layer having a roughness Ra of between 1 m and 10 μm and having protuberances spaced two by two by an average interval of from 1 μιτι to 150; μιτι, and a critical pore diameter of less than

100 nm; and

at least partially covering said layer with a mixture that is more hydrophobic than concrete.

By way of example, said layer has a thickness of between 2 and 10 μηη.

To grow at least a portion of said element a carbonate layer, the method may include the step of maintaining the concrete element in an enclosure containing carbon dioxide. The inventors have demonstrated that the growth of carbonate crystals on the surface of the concrete results in at least partial closure of the critical surface pores and 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 superhydrophobic wall, said wall having a roughness Ra of 1 μιτι to 10 μιτι and having protuberances spaced two by two from an average interval of 1 μιτι to 150 μιτι, said concrete element having a critical pore diameter of less than 100 nm surface 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 among which:

Figure 1 illustrates the principle of measuring a contact angle between a drop of water and a surface;

Figure 2 illustrates features of a surface of a concrete member; and

FIG. 3 represents 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 non-limiting examples. In the examples, the products and materials used are available from the following suppliers:

Product or material Supplier

(1) Lafarge Portland cement - France Val d'Azergues

(2) White Portland Cement Lafarge- France Le Teil

(3) Sand 0/4 mm Lafarge France

(St Bonnet Little Craz)

(4) Sand BE01 (D50 to 307 μηη) Sibelco France

(Career of SIFRACO BEDOIN)

(5) OMYA limestone filler

BETOCARB HP Orgon Filler limestone DURCAL 1 OMYA

Silica fumes MST SEPR (European Society of Refractory Products)

Optima 203 Chryso admixture

Ductal Adjuvant F2 Chryso

Solution SILRES BS29 Wacker

Ultra high performance concrete formulation

The formulation (1) of ultra-high performance concrete used to carry out the tests is described in Table 1 below:

Table 1: Formulation (1) of Ultra High Performance Concrete

non-fiber performance.

Ultra-high performance concrete preparation method

The ultra high performance concrete according to the formulation (1) is produced by means of a RAYNERI type kneader. The whole operation is carried out at 20 ° C. The method of preparation includes 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 rpm); • 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: mix for 8 minutes (50 rpm);

• AT = 17 minutes: mix for 1 minute (15 rpm); and

• From T = 18 minutes: pour the concrete flat in the mold or molds provided for this purpose.

Mortar formulation

The formulation (2) of mortar used to carry out the tests is described in Table 2 below:

Table 2: Mortar formulation (2)

Lafarge Portland Cement is a cement CEM I 52.5 PMES.

Mortar preparation method

The mortar according to the formulation (2) is produced by means of a Perrier type kneader. 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 stirring (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 first hydrophobic mixture to a face of a concrete sample

After stripping the concrete sample, a first hydrophobic mixture is applied to one side of the sample. The first 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 / m ² . The layer thickness obtained is then less than 5 μιτι.

Method of applying a second hydrophobic mixture to one face of a concrete sample

After stripping the concrete sample, a second hydrophobic mixture is applied to one side of the sample. The second hydrophobic mixture applied comprises from 5 to 15% by weight of polyalkylalkoxysilane diluted in an organic solvent (of the white-spirit type). The second hydrophobic mixture is applied by spraying. The final amount applied is approximately 100 g / m ² . It is then expected 4 hours at 20 ° C to dry the second hydrophobic mixture.

Aging process for 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%. 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%.

Wet aging method 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 consists of placing the sample to be cleaned in an enclosure and projecting ultraviolet rays of the sample onto the measuring face of the sample. 254 nm wavelength to dissociate the organic compounds present on the 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 (H ₂ O, CO, CO ₂ ) which are removed from the speaker 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 is the interface liquid / gas 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.

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%. There is a drop of water 14 having a volume of 2.5 μί on the surface 10 of the sample 12. The angle measurement is performed by an optical method, for example using a shape analysis device (English Drop Shape Analysis), for example the device DSA 100 marketed by Kruss. 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, an effect microscope high-resolution field (FEI 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 over a thickness of approximately 1 μιτι is obtained.

Method for 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 μιτι.

Method for measuring the surface porosity and the diameter of critical surface pores of the concrete sample (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.

p ₌ Jcos6 ₍₁₎ r

P is the mercury pressure (Pa),

y is the surface tension of the liquid (N / m),

Θ 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 depending on the pore inlet diameter, expressed in μιτι or nm. The critical pore diameter, or critical diameter, of the surface of the sample corresponds to the inlet diameter of the largest pores leading to the test. 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 sold by MITUTOYO under the name SURFTEST SJ-201 M. The average roughness parameter (Ra) is measured 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 average gap between the protuberances on a wall of the concrete sample

A section of the sample is made through the wall considered. 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 point on the further away from the protuberance 18 relative to a reference line), determining the deviations D1, D2, D3 between the vertices of each pair of adjacent protuberances 18 and determining 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) was prepared. A polyvinyl chloride (PVC) mold was used. The concrete was 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. A face of the concrete element called measuring face has been selected.

The inlet diameter of the open cavities on the measuring face is 0.1 to 10 μιτι. The roughness Ra of the measuring face is 0.4 μιτι (+/- 0.1 μιτι). The surface porosity of the concrete element is about 8%. The critical pore diameter of the measuring face is about 0.015 μιτι. FIG. 3 represents the curve of evolution of the incremental volume, used during the realization of 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 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 measuring face, measured according to the method described above, is 12 degrees (+/- 3 degrees). The measurement face is therefore hydrophilic.

EXAMPLE 2

A concrete having the formulation (1) was prepared. A steel mold was used. The concrete was poured into the mold using a mixture of ECO2 oil and SILRES BS29 product in proportions of 80% / 20% as form release composition. 0.25 g of the form release composition was placed in the mold. The sample obtained by molding corresponds to a parallelepiped having 100 mm width, 10 mm height and 150 mm length. A face of the concrete element called measuring face has been selected.

The inlet diameter of the open cavities on the measuring face is 0.1 to 10 μιτι. The roughness Ra of the measuring face is 0.8 μιτι (+/- 0.3 μιτι). The surface porosity of the concrete element is about 8%. The critical pore diameter of the measuring face is about 0.015 μιτι. The wetting angle of a drop of water on the measuring face is 1 19 degrees (+/- 2 degrees). The measuring face is therefore hydrophobic, but not superhydrophobic.

EXAMPLE 3

A concrete having the formulation (1) was prepared. A polyurethane mold was used. The concrete was poured into the mold using the SILRES BS29 product as a release composition. 0.25 g of the form release composition was placed 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. A face of the concrete element called measuring face has been selected.

The inlet diameters of the open cavities on the measurement face vary from 0.1 to 10 μιτι. The roughness Ra of the measuring face is 0.9 μιτι (+/- 0.2 μιτι). The surface porosity of the concrete element is about 8%. The critical pore diameter of the measuring face is about 0.015 μιτι. The wetting angle of a drop of water on the measuring face is 1 18 degrees (+/- 4 degrees). The measuring face is therefore hydrophobic, but not superhydrophobic.

EXAMPLE 4

A concrete having the formulation (1) was prepared. The polyurethane mold which was previously sandblasted was used. Sandblasting was carried out by spraying a powder of corundum (diameter 5 μιτι) on the surface of the mold under a pressure of 3 bars. The concrete was poured into the mold without using form release composition. The sample obtained by molding corresponds to a parallelepiped having 150 mm in width, 10 mm in height and 150 mm in length. A face of the concrete element called measuring face has been selected.

The wetting angle of a drop of water on the measuring face, measured according to the method described above, is 5 degrees (+/- 5 degrees). The measurement face is therefore hydrophilic.

EXAMPLE 5

A concrete having the formulation (1) was prepared. The polyvinyl chloride mold was used. The concrete was poured into the mold without using a form release composition. The sample obtained by molding corresponds to a parallelepiped having 150 mm in width, 10 mm in height and 150 mm in length. One face of the concrete element, called measuring face, was covered with the second hydrophobic mixture as described above.

The wetting angle of a drop of water on the measurement face, measured according to the method described above, is 130 degrees (+/- 3 degrees). The measuring face is therefore hydrophobic, but not superhydrophobic.

EXAMPLE 6

A mortar having the formulation (2) was prepared. A silicone mold was used. The concrete was poured into the mold without formwork compound. The sample obtained by molding corresponds to a parallelepiped having 200 mm in width, 10 mm in height and 300 mm in length. A face of the concrete element called measuring face has been selected.

The inlet diameters of the cavities open on the measuring face vary from 1 to 10 μιτι. The roughness Ra of the measuring face is 1, 6 μιτι (+/- 0.4 μιτι). The average distance between the protuberances of the measuring face is 10 to 30 μιτι. The surface porosity of the concrete element is about 15%. The critical pore diameter of the measuring face is approximately 0.32 μιτι. FIG. 3 represents the evolution curve 20 of the incremental volume, used during the realization of 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 7

A mortar having the formulation (2) was prepared. A silicone mold was used. The concrete was poured into the mold using the SILRES BS29 product as a release composition. 1.0 g of the form release composition was placed 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. A face of the concrete element called measuring face has been selected.

The inlet diameters of the cavities open on the measuring face vary from 1 to 10 μιτι. The roughness Ra of the measuring face is 1, 7 μιτι (+/- 0.5 μιτι). The average distance between the protuberances of the measuring face is 10 to 30 μιτι. The surface porosity of the concrete element is about 15%. The critical pore diameter of the measuring face is approximately 0.32 μιτι. 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 8 to 15 which follow are examples for which a superhydrophobic surface is obtained.

EXAMPLE 8

A concrete having the formulation (1) was prepared. A silicone mold without a form release composition in which the concrete was poured was used. 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 before treatment is about 8%. The critical pore diameter of the measuring face is before treatment of approximately

T _ièttr SBDMP has _pr s

d _el mou _g e

0.015 μηη. A face of the concrete element called measuring face has been selected. _{At dtt} n _g ee conac

The tr ₍₎ e _de _gr following saitements were applied to the face of measurement:

Treatment No. 1: no treatment on the measuring face;

D _{iè dt} am ee _r _p o _r es

-treatment # 2: Sample aging process in concrete i _idt c _rq uese

carbon dioxide previously described for one week; and

f ₍₎ su _r ace _μηι

treatment No. 3: UV-ozone cleaning process as described above.

P o _r _{ied dt} dare

Measurements of the diameter of critical surface pores, the porosity f _è su _r ace a _pr s

after treatment, the inlet diameter of the open cavities, the mean difference

(% _{) i tttr} aemen

between the protrusions, roughness and wetting angle of the concrete sample were performed on D _{iè ETT} am _r _r e een measuring face according to the methods described above. The results of the _Diet are cavs measures are summarized in Table (3): _{() t} ove _r es _μηι

Table 3 E _tt ca _r _are mo _r e

Formulation (1) - Silicone mold - - No mold release composition _lbét _pr es or _r ances

_{()μηι() Μηι}

E

ZI

03 this

.0

^'C 3 o this no less than 1143 or less than or less than Between 10 and 30 1, 6

(+/- 3) equal to 0.015 equal to 8 0.1 (+/- 0.3) No. 2 141 Less than or less than or less than 10 to 30 1, 6

(+/- 5) equal to 0.015 equal to 8 0.1 (+/- 0.3) No. 3 140 less than or less than or less than 10 to 30 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 previously described. The inventors have thus demonstrated that the grains present on the surface of the measuring face of the concrete sample according to the formulation (1) demolded with a silicone mold were composed mainly of fine particles (silica fumes, calcareous fillers. ..).

EXAMPLE 9

A concrete having the formulation (1) was prepared. The silicone mold which was previously sandblasted was used. Sandblasting was carried out by spraying a powder of corundum (diameter 5 μιτι) on the surface of the mold under a pressure of 3 bars. The concrete was poured into the mold without using a form release composition. The sample obtained by molding corresponds to a parallelepiped having 200 mm in width, 10 mm in height and 300 mm in length. A face of the concrete element called measuring face has been selected.

The following treatments have been applied to the measurement face:

Treatment No. 4: no treatment on the measuring face;

Treatment No. 5: Cover the measurement face of the second hydrophobic mixture as described above.

The wetting angle of a drop of water on the measurement face, measured according to the process described above, for treatment No. 4, is 148 degrees (+/- 3 degrees) and for treatment No. 5 , is 165 degrees (+/- 5 degrees). The measurement face is therefore superhydrophobic.

EXAMPLE 10

A concrete having the formulation (1) was prepared. The flexible polyurethane mold which has been sandblasted beforehand was used. Sandblasting was carried out by spraying a powder of corundum (diameter 5 μιτι) on the surface of the mold under a pressure of 3 bars. The concrete was poured into the mold without using a form release 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 the face of measured, was covered with the second hydrophobic mixture as described previously.

The wetting angle of a drop of water on the measurement face, measured according to the method described above, is 157 degrees (+/- 1 degree). The measurement face is therefore superhydrophobic.

EXAMPLE 11

A concrete having the formulation (1) was prepared. A silicone mold was used. The concrete was poured into the mold using the SILRES BS29 product as a release composition. 1.0 g of the form release composition was placed 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 were performed on the measurement face:

Treatment No. 6: no treatment of the measuring face; and

Treatment No. 7: method of aging the concrete sample described above for a week.

A face of the concrete element called measuring face has been selected. Surface area pore diameter measurements, post-treatment porosity, open cavity inlet diameter, average protrusion spacing, roughness and wetting angle of the concrete sample were performed on the measurement face according to the methods described above. The results of the measurements are collated in the following table (4):

T _i è _ttr aemen ap _rs

dice _the mouage Table 4

Formulation (1) - Silicone mold - With mold release composition

At _the ngee conac

( _{) d} eeg _rs

E

ZI

03

D _i è _dt am _r ee po ^r es ce

.0 f ^d _t _ii c _rq uese surace ^'c 3

o ( ⁾ _μ η ^ι D3

Z3 No. 6,143 Less than or Less than or Less than 10 to 30 2, 1 f P ⁱ ^{d d} o ^r o ^c o ^r ace

(+/- 4) equal to 0.015 equal to 8 0, 1 (+/- 0.2) è ^{i ttt} ap ^r s ^r aemen

No. 7 144 Less than or Less than or Less than 10 to 30 2, 1

⁽ % ⁾

(+/- 2) equal to 0.015 equal to 8 0, 1 (+/- 0.2)

For each treatment, analyzed D ⁱ th ^of e ^tt e ^r eam ^r een chemical elements on the surface of the sample measuring face é é ^di ^t your cavsé performed according to the method described above. The inventors have thus set ^{() t} ove ^r es ^μηι evidence that the grains present at the surface of the measurement face of the SAMPLES E ^tt because average ^r concrete formulation according to (1) removed from the mold with a silicone mold and ^lB e ^t ^r or ^r PHEA ancesient mainly composed of fine particles (silica fume, fillers calcai ⁽⁾ r ^μηι e ...).

EXAMPLE 12

A concrete having the formulation (1) was prepared. A mold made of polyvinyl chloride, wood, polyurethane, polyoxymethylene, steel or silicone was used interchangeably. The concrete was 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. A face of the concrete element called measuring face has been selected.

The following treatment was performed on the measurement face:

Treatment No. 8: 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 hydrophobic mixture 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 were performed on the measurement face according to the methods described above. The results of the measurements are summarized in the following table (5):

Table 5

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 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 13

A first concrete having the formulation (1) was prepared. A silicone mold without a release composition was used in which the first concrete was poured. The piece obtained by molding has the shape of a mold. The internal faces of the mold made with the first concrete were covered with the second hydrophobic mixture as described above.

A second concrete having the formulation (1) was prepared. The concrete mold in which the second concrete was cast was used without form release composition. The second concrete sample obtained by the second molding corresponds to a parallelepiped having 200 mm width, 10 mm height and 300 mm length. One face of the element made with the second concrete called measurement face was selected.

The wetting angle of a drop of water on the measuring face, measured according to the method described above, is 148 degrees (+/- 4 degrees). The measurement face is therefore superhydrophobic.

EXAMPLE 14

A steel mold was prepared by carrying out a microstructuring treatment of the internal walls of the steel mold so that they comprise studs that are a few micrometers high, a few micrometers wide and spaced a few tens of micrometers apart. This microstructuring was carried out by machining and nitric acid etching of the steel mold.

A silicone mold was then prepared by directly casting the liquid silicone into the microstructured steel mold. The silicone was allowed to cure and then the silicone part was removed from the mold. The texture of the walls of the steel mold (in particular the regularly spaced micrometer pads) is transferred onto the walls of the silicone mold.

A concrete having the formulation (1) was prepared. The microstructured silicone mold was used. The concrete was poured into the mold without using a form release composition. A face of the concrete element called measuring face has been selected.

The following treatments were performed on the measurement face:

Treatment No. 9: no treatment of the measuring face; and

Treatment No. 10: Cover the measuring face of the second hydrophobic mixture as described above.

The following measurements were made on the steel mold before microstructuring treatment, on the steel mold after microstructuring treatment, on the silicone mold and on the measuring faces for which treatments 9 and 10 were applied: average gap between the protuberances for the concrete elements and the steel mold, average deviation between the cavities for the silicone mold, roughness, sample wetting angle in concrete. The results of the measurements are collated in the following table (6):

Table 6

EXAMPLE 15

A mortar having the formulation (2) was prepared. A silicone mold is used. The mortar was 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 was selected.

The following treatment has been applied to the measurement face:

treatment No. 1 1: aging method of the carbon dioxide concrete sample described above for 7 days, followed by a method of wet aging for 10 days, followed by the application of the SILRES BS29 hydrophobic mixture on the measuring face.

Surface pore diameter measurements, post-treatment porosity, open cavity inlet diameter, average protrusion spacing, roughness and wetting angle of the concrete sample were performed on the measurement face according to the methods described above. The results of the measurements are collated in the following table (7):

Table 7

EXAMPLE 16

A mortar having the formulation (2) was prepared. The silicone mold was used. The mortar was poured into the mold using the SILRES BS29 product as form release composition. 1.0 g of the form release composition was placed 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%. A face of the concrete element called measuring face has been selected.

The following treatment was performed on the measurement face:

Treatment No. 12: aging method of the carbon dioxide concrete sample described above for 7 days, followed by wet aging for 10 days, followed by the application of the SILRES BS29 hydrophobic mixture on the measuring face.

Surface pore diameter measurements, post-treatment porosity, open cavity inlet diameter, average protrusion spacing, roughness and wetting angle of the concrete sample were performed on the measurement face according to the methods described above. The results of the measurements are collated in the following table (8):

Table 8

Claims

Concrete element (12) having a superhydrophobic wall (10) having a roughness Ra of 1 μιτι to 10 m and having protuberances (18) spaced two by two by an average interval of from 1 m to 150 μιτι, 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.

Concrete element according to claim 1, wherein the roughness Ra is from 1 to 7 μιτι.

Concrete element according to claim 1 or 2, wherein the protuberances (18) are spaced two by two by an average interval of 10 m to 30 μιτι.

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 open cavities on said wall (10) is less than 1 μιτι.

The concrete element of any one of claims 1 to 4, wherein said portions comprise silicone.

Concrete element according to any one of claims 1 to 5, having a surface porosity, measured by mercury porosimetry, less than or equal to 10%.

7. A method of manufacturing a concrete element according to one of claims 1 to 6, comprising the following steps: -providing a mold of a more hydrophobic material than concrete, having a roughness Ra of 1 μιτι to 10 μιτι and recesses (18) spaced two by two of an average range of 1 μιτι 150 μιτι;

pouring said concrete in the fresh state into the mold; and

-Remove said element of the mold after setting the concrete.

The method of claim 7, wherein the mold comprises silicone.

The method of claim 7 or 8, further comprising the step of at least partially coating said member with a more hydrophobic blend than the concrete. 10. Method according to one of claims 7 to 9, comprising the prior step of performing a face treatment of the mold to obtain a roughness Ra of 1 μιτι to 10 μηη and hollows spaced two by two of an interval average of 1 μιτι to 150 μηη.

1 1. The method of claim 10, wherein the treatment is sanding.

12. Method according to one of claims 7 to 9, comprising the following preliminary steps:

-provide an additional mold;

performing a surface treatment of the additional mold to obtain a roughness Ra of from 1 μιτι to 10 μηη and protuberances spaced two by two by an average interval of from 1 μιτι to 150 μιτι; and -forming said mold, having a roughness Ra of 1 μιτι to 10 m and hollows spaced two by two of an average interval of 1 μιτι to 150 m, by casting said material more hydrophobic than the concrete in the additional mold and removing said mold.

13. A method of manufacturing a concrete element according to one of claims 1 to 6, comprising the following steps:

-provide a mold;

pouring said concrete in the fresh state into the mold;

removing said element from the mold after setting the concrete; on at least a portion of said element, to develop a layer comprising carbonates, said layer having a roughness Ra of between 1 m and 10 μm and having protuberances spaced two by two by an average interval of from 1 μιτι to 150; μιτι, and a surface pore diameter of less than 100 nm; and

14. Use of a wall (10) of a concrete element (12) as superhydrophobic wall, said wall having a roughness Ra of 1 μιτι to 10 m and having protuberances (18) spaced two by two from one an average interval of 1 m to 150 μιτι, said concrete element having a critical surface pore diameter of less than 100 nm and comprising portions flush with said wall more hydrophobic than concrete.