FR2757890A1 - COMPOSITE CONSTRUCTION ELEMENT WITH IMPROVED HIGH TEMPERATURE MECHANICAL RESISTANCE, AND ITS USE, AND FIRE-RESISTANT STRUCTURES MADE FROM SUCH ELEMENTS - Google Patents

Abstract

Disclosed is a construction element (1) including a panel (2) comprising at least one cementing substance in hydrated form, and a metal sheet (3) attached to at least one of the sides (2a, 2b) of said panel. The metal sheet (3) has a stiffness expressed by a modulus of elasticity E of at least 200,000 MPa, and/or a rupture break point level in traction R equal to at least 270 Mpa; said metal sheet (3) is directly or indirectly attached to one of the sides of said panel by a layer (4) of structural adhesive. The metal sheet (3) and the panel (3) together form a synergistic and relatively monolithic complex, in which they are structurally attached to one another.

Description

 The present invention relates to a composite construction element resistant mechanically to a relatively high temperature, more particularly suitable for the construction of partition elements or fire panels, it being understood that such construction elements have many other applications or uses, other than fire protection.

The use of materials capable of releasing water vapor during thermal stress, such as a fire, has been known for a long time. It is known, for example, to use hydraulic binders, and in particular plaster, in the form of plates comprising vaporizable water of crystallization, in construction elements such as fire walls, to delay heat transfer through of these during a fire. We know, for example by the French patent application
FR-A-2 502 215, combine with a polystyrene plate, a plasterboard and a metal sheet having practically no intrinsic rigidity, bonded or glued to the plasterboard, in order to obtain a resistant composite construction element fire. In such a composite construction element, the plaster serves to delay the thermal transfer to the polystyrene plate, which also delays the thermal degradation of the latter.

 However, all these fire structures, during the heating generated by a fire, quickly lose their cohesion due to the dehydration of the hydraulic binder of which they are made. They are thus weakened to the point of collapsing under the effect of their own weight or the slightest mechanical stress, and in particular a shock.

 This is the reason why, according to different national or international regulations or standards, fire test protocols for firewalls have been defined which, at the end of the test, provide for the application of mechanical stress, generally an impact, which must not result in the loss of the fire-resistant properties of the wall tested.

To solve this double problem of mechanical impact resistance and high temperature, it has been proposed, according to the European patent application
EP-A-0 654 566, a fire wall obtained by mounting or assembly, having a sandwich structure, comprising plasterboards screwed onto uprights profiled in sheet metal, covered with an intermediate layer of steel sheet, and additional plasterboard added to the outside of the intermediate sheet. The external plasterboards and the intermediate layer of sheet steel are assembled and mounted by quick-setting screws, which pass through all the other layers of the structure to be fixed in the profiled uprights of sheet metal.

In addition, the German utility model
DE-U-295 05 833.1 describes a fire wall obtained by mounting or assembly, comprising on either side of profiled uprights, steel sheets riveted on the latter, covered with one or more layers of sheets of plaster, which themselves are fixed by screwing in the metal sheets and profiles.

 However, due to the assembly between the plasterboard and the reinforcing sheets, the mechanical behavior of these fire walls, upon impact at the end of the fire test, is not satisfactory and indeed we observe significant falls of the plates due to their embrittlement by calcination, in particular at the point of application of the shock.

 On the other hand, in order to ensure the continuity of the reinforcement provided by the sheets, these must be assembled with a large overlap, which makes the design of the fire protection structure and its realization more difficult. Indeed, on the one hand the sheets necessarily have either a format or a pitch of assembly different from that of the plasterboards, and on the other hand their screwing is made difficult by their double thickness at the level of the overlaps.

 Still in the field of mechanical resistance at high temperature, sheaths and structural protection structures are more and more commonly constructed structures to provide ventilation with fresh air or smoke extraction in the event of fire, and fire protection of beams and columns for example.

 Plates based on hydrated hydraulic binder, and in particular plaster-based plates are frequently used in this field, and the prior art proposes systems for assembling these plates by means of a sub-construction forming a reinforcing or supporting metal framework. These systems are not entirely satisfactory, because they are long and difficult to assemble on the one hand, and because they require on the other hand numerous devices for hanging on the surrounding walls and ceilings, in particular when are made horizontally.

 At the end of this inventory of the state of the art, there is therefore a need for a construction element having in itself good mechanical strength (static and / or dynamic), up to a relatively high temperature, and can therefore be implemented in a traditional way, such as a simple plasterboard for example.

 This is the object of the present invention.

 In accordance with this object, the invention provides a composite construction element comprising a plate constituted by at least one hydraulic binder in hydrated form, and a metal sheet linked directly or indirectly to at least one of the faces of said plate.

The composite building element is characterized in that, on the one hand, the metal sheet is rigid enough to substantially maintain its flat conformation on edge, and the metal sheet is structurally linked to one of the faces of said plate, by a layer of adhesive having the property of synergistically complexing the hydraulic binder plate and the metal sheet.

 When it is not complexed with the plate, the metal sheet must be sufficiently rigid to substantially maintain its flat conformation on edge. This characteristic means that this sheet has the consistency of a sheet, when it is a metallic sheet of steel, and differs, in particular in terms of thickness, from a thin sheet or film, such as be used as a vapor barrier. This metal sheet has for example a thickness at least equal to 0.1 mm, and preferably between 0.1 and 0.5 mm, and in particular between 0.1 and 0.3 mm. This metal sheet has for example mechanical properties which can be expressed by an elastic modulus E of at least 200,000 MPa, and / or a tensile breaking stress R at least equal to 270 MPa.

 The length and width of the metal sheet can be substantially equal to the length and width of the plate, or shorter than those of the plate, for example 10 mm shorter, depending on the desired overlap.

 The metal sheet can be of any kind, provided that it meets the criteria of rigidity and / or thickness defined above. It can be a pure metal, or an alloy of metals. Preferably, the metal sheet is made of steel, and more preferably comprises an anti-corrosion coating, on one and / or the other of its faces, and for example, is galvanized steel. In this case, the metal sheet is made of mild galvanized steel, according to standards NF A36.321 and ISO 3575, of current quality. Preferably, the anticorrosion zinc coating is present on both sides of the metal sheet, and is classified at least Z100, that is to say comprises at least 100 g / m2 of zinc (i.e. 50 g / m2 per face ). The surface of the zinc anti-corrosion coating may show normal (N) or faded (M) flowering.

 In order to obtain a composite element according to the present invention, it is necessary to use an adhesive having the property of synergistically complexing the hydraulic binder plate and the metal sheet, in order to bind them structurally. The synergy considered according to the present invention consists in significantly increasing any mechanical property of the plate / metal sheet complex, compared to the same mechanical property of the plate / metal sheet assembly, all other things being equal. A significant example of this synergy will be given below. All the traditional adhesives tested by the Applicant do not exhibit this synergistic property; thus relatively flexible, or semi-rigid adhesives, of the rubber or neoprene type are not suitable for complexing the plate and the metal sheet.

 Preferably, the adhesive (s) are structural. Such adhesives are generally known, and are preferably curable and / or crosslinkable. The term “structural adhesive” is intended to mean an adhesive having in the solid state an increased mechanical resistance to dynamic and static stresses; for example, epoxy resins, and some polyurethanes are structural adhesives.

 Preferably, the adhesives considered by the present invention are fire resistant, in the sense that they retain most of their mechanical resistance up to a temperature of the order of 140 C. And by way of example, in the state liquid, they have a flash point greater than 200 "C.

 The adhesives considered by the present invention, which are generally also free of solvents, make it possible to obtain a rigid composite construction element, substantially monolithic, due to the rigid bond established by virtue of the adhesive between the metal foil and the plate of the hydrated hydraulic binder.

The epoxy resins can be of known type, liquid or solid at ordinary temperature, depending on the length of molecular chain chosen, and hardenable cold or hot. Generally, they react with acidic or basic polyfunctional bodies called "hardeners", to give hard and infusible products. Such hardeners are for example - aliphatic, cycloaliphatic and
aromatics (e.g. polyethylene polyamines,
N-amino ethyl piperazine, and xylene diamine - phthalic anhydrides and its derivatives, anhydride
dodecylsuccinique, and pyroméllitique dianhydride - polyphenols, for example novolacs - amino resins, polyamides, etc.

 As regards the polyurethanes capable of being used as a structural adhesive in a composite element according to the invention, it is possible to use those obtained for example by combination of one or more di- or polyisocyanates with one or more polyalcohols. By way of example, mention may be made of di-, tri- and polymeric, aliphatic or aromatic isocyanates, for example toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymethylene polyphenyl isocyanate (PAPI) , or that resulting from the action of TDI on trimethylolpropane. As regards the polyols, mention will be made, by way of example, of diols and triols, based on polyethers, polyesters, or a combination of the two.

 The adhesive, which is generally, but not necessarily, in the form of a mixture of the components described above, can be applied to one or both sides of the plate, after preparation of the surface thereof, for example by dusting and degreasing.

The metal sheet can then be pressed onto the face (s) of the plate, glued.

 In a particular embodiment of the invention, the composite construction element comprises two metal sheets, each linked by a layer of adhesive respectively to the two opposite faces of the plate.

 The plate consists of at least one hydraulic binder in hydrated form. This hydraulic binder can be for example a cement, a concrete, or a plaster, or even a mixture of hydraulic binders. Preferably the hydraulic binder is a plaster.

 In a preferred variant of the invention, the plate comprises, between a core of hydraulic binder in hydrated form and the layer of adhesive, a facing, in particular of cardboard or a veil of organic or inorganic fibers. This facing adheres on its internal face to the hydraulic binder in hydrated form, and is linked on its external face to the metal sheet by the adhesive layer. Preferably, the adhesion of the facing to the hydraulic binder is obtained by interface crystallization.

If the facing is made of cardboard, its adhesion to the hydraulic binder is advantageously reinforced by gelatinization. If the facing is a veil of fibers, it is preferably made of glass fibers, woven or not.

 Furthermore, the plate may have zones of variable density, for example layers of variable density, and / or be reinforced or reinforced.

 More particularly advantageously, building elements according to the invention have anyway, at room temperature and outside their fire protection applications, on the one hand a very good flexural strength, and on the other hand a very good puncture resistance.

 The first property allows them to overcome the mechanical limitations of traditional plates based on hydraulic binders, for example plaster, and to compare themselves to other construction elements, such as panels based on wood, or fibers and particles, to be used in new applications such as dry floors, or ceilings, or sails working for the bracing of wooden or metal structures.

 The second property allows them to hang heavy loads, with screws or nails for example, or to be assembled reliably on a frame, or between them.

 Another object of the present invention is the use of such elements in the construction of fire protection structures, in particular fire walls, ventilation or smoke extraction ducts, technical ducts, and fire protection structures. structure.

 Preferably, the fire wall comprises a first layer of elements or panels according to the invention, fixed to a frame, all oriented along a dimension, for example longitudinal, of the panel, and a second layer of elements or panels according to the invention, fixed to the first layer, for example all oriented according to another dimension, for example transverse, of the panel.

The invention will be better understood by referring to the following description of the preferred embodiments of the present invention, given as an indication, and accompanied by the accompanying drawings, in which - Figure 1 represents an exploded perspective view
of a preferred embodiment of an element of
composite construction according to the present invention - Figure 2 shows a sectional view along the line
II-II of Figure 1 of the same construction element
composite - Figure 3 shows a sectional view of the same type as
in Figure 2, but shows a variant
of the composite element according to the present invention - Figure 4 shows a vertical sectional view of a
assembly of composite building elements according to
Figure 1, forming a fire wall - Figure 5 shows a perspective view of a
fire wall constructed from elements of
composite construction according to Figure 1 - Figure 6 shows a comparison graph of the
heat transfer of different elements of
construction according to the invention and the prior art - Figure 7 shows a cross-sectional view
a dynamometer and a building element
composite according to Figure 1, illustrating a test at
the removal of a screw - Figure 8 shows a cross-sectional view
a duct (for ventilation or smoke extraction), obtained at
from a building element according to Figure 1 - Figure 9 shows a cross-sectional view
a fire protection work, obtained at
starting from a building element according to Figure 1,
around a beam.

 In accordance with Figures 1 and 2, the element 1 of composite construction is in the form of a thin and rigid panel, comprising a plate 2 formed by plaster, that is to say capable of releasing vapor from water by dehydration during its heating.

The element 1 comprises on one of its two main faces 2b a sheet of galvanized steel, or sheet 3 of 0.1 to 0.5 mm thick covering a large part of said face, or according to Figure 3 , two sheets of galvanized steel 3, 5, or sheets covering its two opposite faces 2a, 2b respectively. The bonding of the steel sheet 3 to the plate 2 is provided structurally by a layer of structural adhesive 4, for example an epoxy resin, having in the liquid state a flash point greater than or equal to 200 "C, and preferably non-flammable at least up to 140 "C.

 Figures 4 and 5 show a fire wall or partition constructed from composite building elements according to the invention. In general, the partition consists of a light frame 8 made of metal profiles for example, sandwiched between two partitions each consisting of a double layer 9 and 7 of composite building elements according to the invention. The rear wall is not illustrated in Figures 4 and 5 to facilitate understanding of the structure. Each building element is formed, for example, of a plasterboard 15 mm thick between two cardboard facings, on the back of which is bonded, by means of the layer of structural adhesive 4, a steel sheet. 3 galvanized 0.25 mm thick, the same format as plasterboard 2; and each element is fixed to the frame 8 by screwing 10, 10a, (cf. Fig 4), the screws 10 of the second layer 9 passing through the first 7, and the joints 11, îîa between the elements of the two layers being offset to avoid overlapping. The elements of the first layer 7 are arranged relative to the elements 1 of the second layer, and relative to the frame 8, so that the metal sheets 3 of the first layer are in contact with the frame, and the sheets 3 of the second layer are placed between the plates 2 of the two layers 7 and 9 respectively.

 So as to compare fire-resistant structures assembled with known construction elements (applications DE-U-295 05 833.1 and EP-A-0 654 566), with a structure based on elements according to the invention, according to the example described with reference to Figures 4 and 5, fire resistance tests were carried out for a period of 90 minutes, at the end of which three successive shocks of 3000 Joules are applied to the side of the structure not exposed to fire.

 The main difference between the two structures compared according to this test is that the metal sheets are, according to the prior art independent and distinct from the plasterboards of the two layers respectively, on each side of the framework, and according to the invention structurally linked with the structural adhesive, to the plasterboards of the same two layers respectively.

Following the three shocks of 3000 Joules, we observe - for the partition according to the invention, on the side exposed to fire
the fall of a few pieces of layer plates
exterior 9 and no plasterboard drop from the
inner layer 7, while art structures
previous under the same test conditions are
prone to falling plasterboard very
important which affect the two layers - for the partition according to the invention, on the side not exposed to
fire which receives shocks, a slight depression of the
facing of the exterior plasterboard, in line with
shocks, surrounded by a more or less continuous crack in the
same facing, while the structures of art
anterior are subject to a more marked depression,
with significant breaks in the facing of the plates
exterior plaster, which may cause falls
partial plaster - for the partition according to the invention, a deformation
low residual of the bulkhead, the
frame profiles themselves being slightly deformed,
while the structures of the prior art are
subject to strong deformation, with twisting and
profile crushing - for the partition according to the invention, little or not
thermal elevation of the impacted area on
the side not exposed to fire, while the structures of
prior art are subject to an elevation of
rapid temperature of this area within minutes which
follow the shocks.

 On the other hand, the applicant has observed that a composite construction element according to the invention makes it possible to extend the dehydration level corresponding to the vaporization of the water of crystallization of the hydraulic binder, which has the beneficial effect of delaying the rise in temperature on the face of the same element not exposed to fire, and thus reinforce its fire resistance.

Still in a comparative manner between the general prior art and the invention, FIG. 6 shows the difference in temperature kinetics of the unexposed face (upper curves) to fire and of the interface between the two layers (curves bottom), when each structure is subjected on the other face to a temperature rise "conventional fire", according to the temperature / time law T-T0 = 345.log (8t + 1), with t in minutes, TO initial temperature in "C, T temperature at time t in" C (see standard ISO 834). In this case, the plates used are plasterboard 15 mm thick, of the prior art, called GKF15 (plate standardized in Germany), and the metal sheet is a steel sheet of 0.25 mm. The curves in white squares and circles relate to a structure with two composite elements according to the invention, superimposed as shown in
Figure 5, and the black square and round curves to a structure with two superimposed plasterboards, without metal sheets. The circles refer to the side not exposed to fire, and the squares to the interface between the two layers. For the structure according to the invention, there is an elongation of the vaporization level, both at the interface between the two layers, and on the face not exposed to fire, and a lower slope of temperature rise is observed after the vaporization level, on the side not exposed to fire, which saves time from 10% to 15% to reach a temperature between 140 "C and 1800C, conventionally corresponding to the upper limit of the fire rating classification.

 In terms of mechanical behavior, it was mentioned above that the resistance to dynamic stresses, in the form of shock for example, are very significantly improved, with a composite construction element according to the invention, even after prolonged exposure to fire.

 When cold, while a 15 mm thick cardboard coated plasterboard is cracked or punctured by a 240 Joule impact, this same plate structurally bound to a 0.25 mm thick steel sheet will not be cracked or perforated only under a shock of the order of 1000 Joules.

Similarly, in static bending stress, carried out according to the specifications of the French standard
NFP 72-302, the breaking load of a plasterboard coated with 15 mm cardboard can reach 80 to 90 daN in the long direction and 35 to 40 daN in the transverse direction. This same plasterboard linked by a rigid adhesive plane based on polyurethane or epoxy resin for example, to a steel sheet 0.25 mm thick sees its breaking strengths brought to 330 daN in the long direction and crosswise if the metal foil is located on the stretched part of the test piece. The same sheet added without adhesive on the same plate brings the resistance to flexural rupture to a value of the order of 110 daN. This demonstrates in particular the synergy between plate and metal sheet, obtained according to the invention.

 It can therefore be seen that not only are the tensile strengths multiplied by a factor at least equal to 3, but also that the well-known difference between the long and cross direction resistances of plasterboard coated with cardboard, due to the oriented behavior thereof, is removed by the presence of the thin metal sheet according to the invention.

 The rigidity and the synergistic nature of the adhesive bonding the plate and the metal foil are determining factors for obtaining the increase in mechanical performance mentioned above.

 Thus the same plasterboards of 15 mm linked to the same metal sheet of 0.25 mm thick, but by a flexible adhesive of neoprene type, see their bending strength increase only by a factor of 1, 1 to 1.2, instead of a factor greater than 3, in accordance with the invention. This improvement in flexural strengths by rigid bonding of a 0.25 mm steel sheet is verified on plasterboards of thickness other than 15 mm: thus a 12.5 mm plasterboard modified in accordance with l he invention saw its breaking strength go from 65 daN to 200 daN, and a 23 mm plate went from 140 daN to 500 daN.

 It was also verified that the flexural strengths remained significantly improved according to the invention, after exposure of the flexural specimen for one hour and a half at 140 "C., Thus, the flexural test carried out according to the specifications of the French standard NF P 702-302 on a 15 mm plasterboard coated with cardboard after this heat treatment, gives a breaking load of 78 daN in the long direction and 35 daN in the cross direction, while this same plate, bonded with a rigid adhesive based polyurethane to a steel sheet of 0.25 mm, provides tensile strengths of the order of 280 daN in the long direction and in the transverse direction.

 These results imply that not only the layer of adhesive must be as rigid as possible as mentioned above, but also that this layer can preferentially (but not exclusively) withstand temperatures of at least 140 "C.

 It has also been shown that the elements in accordance with the invention ensure a resistance of the screws to tearing off, significantly greater than that obtained with the plasterboards of the prior art.

 FIG. 7 shows the device used to measure the tear resistance of a screw 10 fixed in a plasterboard of the prior art, compared to a composite construction element 12 according to the invention, by means of a traction device fitted with a dynamometer 13. The tearing off of a screw known as "small threads" occurs at 26 daN for a 15 mm plasterboard of the prior art, and at 86 daN for this same 15 mm plate structurally bonded according to the invention to a 0.25 mm steel sheet. Likewise, a so-called "coarse thread" screw is torn off respectively at 61 daN or 105 daN, depending on whether the plate belongs to the prior art or relates to the invention.

 This increase in the strength of the screws allows the attachment of substantially heavier objects on the partitions or ceilings made with construction elements according to the invention, without the addition of specific reinforcements which are generally difficult to implement and often unsightly.

 This improvement in the strength of the screws in the elements according to the invention also makes it possible to ensure a reliable connection by simple screwing between two superimposed elements.

In addition, we can take advantage of the fact that an element or panel according to the invention, consisting of a plasterboard coated with cardboard, structurally bonded to a metal sheet of 0.2 to 0.4 mm on one of its faces, can be easily folded without complete rupture of the panel after having cut the cardboard side not covered with the metal sheet according to the chosen rupture or folding line, and this in order to constitute a section profile in
L, in U, or formed as a polygon.

The combination of the two properties mentioned above (resistance to screwing and folding without breaking) allows the production of ducts and fire protection ducts for smoke extraction and ventilation, as illustrated in
Figure 8, or fire protection of structural elements such as beams and columns (see Figure 9).

In such an application, the plate of the composite element formed has notches going up to the metal sheet 3, to form edges of a polygonal envelope; the external face of the metal sheet is oriented towards the outside, towards the pre-existing structure of the work; the free edges of element 1 at least are fixed together and / or to the pre-existing structure, and the continuity of fire protection, in the angles opened by folding, is ensured by stuffing 14 with a fire-resistant binder, in particular based on plaster.

 The sheath shown in FIG. 8 is obtained by superposition of composite elements according to the invention, cut out, one internal and the other external, metal sheet against metal sheet, and joined together tests of alternating horizontal stresses, reproducing the forces generated by the wind on the constructions, demonstrate not only an improved resistance with reduced deformations compared to plasterboard the prior art, but also an insensitivity to fatigue after several thousand cycles, which is not the case. case of plasterboard of the prior art which no longer make a mechanical contribution to the stability of the structure after a few tens of cycles.

 Another advantage of the use of composite construction elements in accordance with the invention is the reduction of the risks linked to electromagnetic disturbances or radiation to which electrical networks are subjected, or generated by them when they are installed in railways. cables made with plasterboard of the prior art.

 In fact, electromagnetic compatibility (EMC), which is the ability of an electrical appliance or system to function satisfactorily without producing intolerable disturbances for its environment, becomes a major concern in buildings, especially in so-called "smart" buildings. The cause stems from the massive use of electronics in recent years, which has profoundly changed the electromagnetic environment.

It has resulted, on the one hand, in the multiplication of "polluting" transmitters (televisions, computers, household appliances) and, on the other hand, devices with a high concentration of components sensitive to disturbances. To minimize EMC problems, it is important to physically separate high current cables from low current cables, and use continuous metal supports. The most effective supports are the metal elements made of solid and enveloping sheet metal, which the elements according to the invention make it possible to easily produce using the folding technique mentioned above, after cutting the cardboard face of the panel, that is to say say that not covered with the metal sheet, and folding.

Claims (19)

 1 / Construction element (1) comprising a plate (2) constituted by at least one hydraulic binder in hydrated form, and a metal sheet (3) linked directly or indirectly to at least one of the faces (2a, 2b) of said plate , characterized in that it stinks - the metal sheet (3) is sufficiently rigid to  keep its conformation substantially on edge  plane - and this metal sheet (3) is linked, so  structural, to one of the faces of said plate, by a  layer (4) of an adhesive having the property of complexing  synergistically the hydraulic binder plate and  the metal sheet.  2 / building element according to claim 1, characterized in that the adhesive is a structural adhesive.  3 / building element according to claim 2, characterized in that the adhesive is fire resistant, in the sense that it retains most of its mechanical strength up to a temperature of about 140 "C.  4 / composite construction element (1) according to claim 1, characterized in that the hydraulic binder in hydrated form is a plaster.  5 / building element (1) according to claim 1, characterized in that it comprises two metal sheets (3, 5), each linked by a layer of adhesive respectively to the two opposite faces (2a, 2b) of the plate (2).  6 / building element (1) according to any one of the preceding claims, characterized in that the metal sheet (3, 5) has a thickness at least equal to 0.1 mm, and preferably between 0.1 and 0 , 5 mm, in particular between 0.1 and 0.3 mm.  7 / building element (1) according to any one of the preceding claims, characterized in that the metal sheet (3, 5) is made of steel.  8 / building element (1) according to any one of the preceding claims, characterized in that the metal sheet (3, 5) has an anti-corrosion coating, on at least its outer face.  9 / building element (1) according to any one of the preceding claims, characterized in that the adhesive is a curable structural adhesive, for example an epoxy resin or a polyurethane.  10 / building element (1) according to any one of the preceding claims, characterized in that the plate (2) comprises, between a core of hydraulic binder in hydrated form and the layer (4) of adhesive, a facing, in particular in cardboard or a veil of organic or inorganic fibers, said facing adhering on its internal face to the hydraulic binder in hydrated form, and being linked on its external face to the metal sheet by said layer of adhesive.  11 / building element (1) according to claim 10, characterized in that the facing adheres to the hydraulic binder by interface crystallization.  12 / Building element (1) according to claim 10 or claim 11, characterized in that the facing is made of cardboard, and adheres to the hydraulic binder, moreover by gelatinization.  13 / building element (1) according to any one of claims 10 and 11, characterized in that the facing is a veil of glass fibers, woven or not.  14 / building element (1) according to any one of the preceding claims, characterized in that the plate has zones of variable density, and / or is reinforced.  15 / Use of a building element according to any one of the preceding claims, for the construction of fire protection structures, in particular fire walls, ventilation or smoke extraction ducts, technical ducts, structural protection works .  16 / Fire barrier wall (6), characterized in that it comprises a first layer (7) of elements according to any one of claims 1 to 14, fixed to a frame (8), all oriented in one dimension of said element, and a second layer (9) of elements according to any one of claims 1 to 12, fixed against the first layer (7), for example all oriented according to another dimension of said element.  17 / Fire protection structure, characterized in that it consists of at least one composite construction element according to any one of claims 1 to 14, at least one composite element having at least a slot notching the plate up to the metal sheet (3), to form at least one edge of a polygonal envelope, the external face of the metal sheet being oriented towards the outside, the free edges of said element (1) at less being fixed together and / or to the structure of the structure, the continuity of the structure, in the angles opened by the folding, being ensured by a packing (14) with a binder resistant to fire, in particular based on plaster.  18 / Use of a building element according to any one of claims 1 to 14, for the construction of protective structures against radiation or electromagnetic disturbances.  19 / Use of a building element according to any one of claims 1 to 14, for the construction of sails working for the bracing, or for hanging heavy loads, or dry floors, or ceilings.