EP0799951A1 - Method for reinforcing building constructions by means of glued carbon fibres - Google Patents

Abstract

The method consists of sticking a layer of carbon fibre cloth onto a structure reinforcing surface (4). Firstly the reinforcing surface is prepared and then coated with an epoxy resin layer in the fluid state. A dry flexible cloth (3), constituted from carbon fibres, is placed onto the resin layer still in the fluid state. A sufficient pressure is exerted on the cloth to impregnate the resin and equalise the resin film. The carbon fibre cloth has the shape of a band (7) which extends in a longitudinal direction (X). The carbon fibres form a continuous wire chain parallel to the longitudinal direction and a transverse wire weft.

Description

The present invention relates to methods for reinforcing civil engineering structures using bonded carbon fibers, methods which are used to increase the resistance of civil engineering structures, especially when their mechanical characteristics have deteriorated due to aging.

In certain known processes of this type, composite material elements are prefabricated in the factory, consisting of carbon fibers included in a synthetic resin matrix, then these elements are used on building sites or public works by bonding them to the surfaces to be reinforced.

• il peut s'agir d'un matériau rigide qui se présente sous forme de plaques planes, auquel cas le procédé n'est applicable que pour renforcer une surface parfaitement plane, et il est nécessaire de maintenir les plaques de matériau composite en appui contre cette surface jusqu'à ce qu'elles soient définitivement collées sur ladite surface,
• le matériau composite peut également être maintenu dans un état plastique par une conservation à très basse température qui bloque la polymérisation de sa matrice de résine, ce qui permet l'application dudit matériau sur des surfaces non planes : mais la conservation à très basse température rend l'utilisation de ce matériau composite extrêmement lourde, et ce mode de conservation exclut même l'utilisation d'un tel matériau sur de petits chantiers, qui ne peuvent être dotés que d'un équipement léger.

Depending on the case, the carbon fiber composite material prepared in the factory may have different consistencies:

• it may be a rigid material which is in the form of flat plates, in which case the method is only applicable to reinforce a perfectly flat surface, and it is necessary to keep the plates of composite material in abutment against this surface until they are permanently bonded to said surface,
• the composite material can also be maintained in a plastic state by a conservation at very low temperature which blocks the polymerization of its resin matrix, which allows the application of said material on non-planar surfaces: but the conservation at very low temperature makes the use of this extremely heavy composite material, and this method of conservation even excludes the use of such a material on small sites, which can only be equipped with light equipment.

In addition, in all cases, the forces which are taken up by the carbon fibers pass first through the adhesive by means of which the composite material is attached to the civil engineering structure, then by the synthetic resin matrix, before being transmitted to the carbon fibers: this multiplication of intermediate materials between the civil engineering structure and the carbon fibers harms the effectiveness of the reinforcement.

Furthermore, document US-A-5 308 430 describes a method for reinforcing civil engineering structures by means of carbon fibers or the like which are coated with resin at the time of their application to the structure.

But the fibers in question are all parallel to each other, so that the reinforcement thus produced is effective only to take up efforts in one direction.

In addition, in order to maintain a certain cohesion between these fibers before their implementation, it is necessary that said fibers are bonded to a flexible support sheet.

Consequently, if it is necessary to superimpose several layers of carbon fibers on the surface to be reinforced, these layers are separated from one another by the flexible sheet of support material: an additional heterogeneity is thus introduced into the composite reinforcement material, this which reduces the ability of this material to properly transmit the stresses between the civil engineering structure and the carbon fibers.

Finally, the aforementioned document provides for using fibers which are initially in the form of strands, then for flattening these strands by crushing in order to constitute flat strips of fibers: this manufacturing process has the drawback of risking damaging the fibers during the crushing of the strands.

The present invention aims in particular to overcome these various drawbacks.

• a) préparer la surface à renforcer,
• b) enduire ladite surface à renforcer d'une couche de résine époxy à l'état fluide, capable d'adhérer sur la structure de génie civil et sur les fibres de carbone et apte à boucher d'éventuelles fissures présentées par la surface à renforcer, cette résine présentant, lorsqu'elle est appliquée à l'état fluide, une viscosité comprise entre 1 000 et 100 000 mPa.s, et cette résine ayant par ailleurs, une fois durcie, une résistance à la rupture en traction comprise entre 5 et 100 MPa avec un allongement à la rupture compris entre 0,5 et 10 %, et une résistance à la rupture en compression comprise entre 5 et 100 MPa avec un raccourcissement à la rupture compris entre 0,5 et 10 %,
• c) et appliquer un tissu souple sec, constitué de fibres de carbone ensimées, sur la couche de résine encore à l'état fluide, en exerçant sur ce tissu une pression suffisante pour l'imprégner de résine et pour égaliser le film de résine, le tissu présentant, dans au moins une direction, une résistance à la rupture supérieure à 1 500 MPa et un module élastique compris entre 200 et 400 GPa.

To this end, the invention provides a method for reinforcing a civil engineering structure, consisting in bonding at least one layer of carbon fiber fabric to a surface to be reinforced belonging to said structure, this process comprising the following steps:

• a) prepare the surface to be reinforced,
• b) coating said surface to be reinforced with a layer of epoxy resin in the fluid state, capable of adhering to the civil engineering structure and to the carbon fibers and capable of plugging any cracks presented by the surface to be reinforced. , this resin having, when applied in the fluid state, a viscosity of between 1,000 and 100,000 mPa.s, and this resin having moreover, once hardened, a tensile strength of between 5 and 100 MPa with an elongation at break of between 0.5 and 10%, and a compressive breaking strength of between 5 and 100 MPa with a shortening at break of between 0.5 and 10%,
• c) and apply a dry flexible fabric, consisting of sized carbon fibers, to the layer of resin still in the fluid state, by exerting on this fabric sufficient pressure to impregnate it with resin and to equalize the resin film, the fabric having, in at least one direction, a breaking strength greater than 1,500 MPa and an elastic modulus of between 200 and 400 GPa.

Thanks to these provisions, it is possible to reinforce any surface of any shape, possibly curved or irregular, and it is not necessary to apply permanent pressure to the carbon fiber fabric until the resin sets.

The reinforcement thus obtained is particularly effective and reliable, in particular because the forces to be taken up are transmitted from the civil engineering structure to the carbon fibers by means of a single and homogeneous resin matrix, avoiding any layer of material. intermediary between this matrix and the structure to be reinforced.

Furthermore, the method according to the invention also contributes to reducing the bending stresses in the resin.

In addition, the use of carbon fibers in the form of fabric, having interwoven warp and weft threads, makes it possible to guarantee that the carbon fibers keep perfect cohesion during their implementation, which allows both great ease of implementation and high mechanical performance.

• le tissu de fibres de carbone se présente sous la forme d'une bande qui s'étend selon une direction longitudinale, les fibres de carbone de ce tissu formant d'une part des fils de chaîne sensiblement continus et parallèles à la direction longitudinale, et d'autre part des fils de trame transversaux ;
• la surface à renforcer est soumise à des efforts de traction, les fils de chaîne du tissu de fibres de carbone étant disposés parallèlement auxdits efforts ;
• la bande de tissu de fibres de carbone présente au moins une extrémité longitudinale découpée en pointe ;
• la bande de tissu de fibres de carbone présente deux extrémités longitudinales découpées en pointe ;
• le tissu de fibres de carbone comporte initialement une face nue et une face recouverte d'une feuille souple amovible en matériau synthétique, le tissu étant appliqué sur le film de résine par l'intermédiaire de sa face nue, et la feuille de matériau synthétique étant enlevée du tissu après imprégnation de ce tissu par la résine ;
• la résine peut être thixotrope lorsqu'elle est à l'état fluide ;
• la résine ne comprend aucun solvant ;
• la structure de génie civil est constituée d'un matériau choisi parmi le béton, le métal et le bois.

In preferred embodiments, recourse may also be had to one and / or the other of the following arrangements:

• the carbon fiber fabric is in the form of a band which extends in a longitudinal direction, the carbon fibers of this fabric forming on the one hand warp threads substantially continuous and parallel to the longitudinal direction, and on the other hand transverse weft son;
• the surface to be reinforced is subjected to tensile stresses, the warp threads of the carbon fiber fabric being arranged parallel to said stresses;
• the strip of carbon fiber fabric has at least one longitudinal end cut into a point;
• the strip of carbon fiber fabric has two longitudinal ends cut into a point;
• the carbon fiber fabric initially has a bare face and a face covered with a removable flexible sheet of synthetic material, the fabric being applied to the resin film via its bare face, and the sheet of synthetic material being removed from the fabric after impregnation of this fabric with the resin;
• the resin can be thixotropic when it is in the fluid state;
• the resin does not include any solvent;
• the civil engineering structure is made of a material chosen from concrete, metal and wood.

Other characteristics and advantages of the invention will appear during the following detailed description of one of its embodiments, given by way of nonlimiting example, with reference to the accompanying drawings.

• la figure 1 est une vue en perspective illustrant un exemple de mise en oeuvre du procédé selon l'invention,
• la figure 2 illustre la disposition des fibres de carbone au sein de la bande de tissu de fibres de carbone utilisée dans l'exemple de la figure 1,
• et la figure 3 montre la bande de tissu de fibres de carbone de la figure 2, revêtue d'une feuille protectrice amovible.

In the drawings:

• FIG. 1 is a perspective view illustrating an example of implementation of the method according to the invention,
• FIG. 2 illustrates the arrangement of the carbon fibers within the strip of carbon fiber fabric used in the example of FIG. 1,
• and Figure 3 shows the strip of carbon fiber fabric of Figure 2, coated with a removable protective sheet.

Figure 1 shows a particular example of implementation of the method according to the invention, used to strengthen or repair a reinforced concrete beam 1 supporting a building floor 2.

But of course, this application is not limiting, and the invention can be used to reinforce any civil engineering structure, in particular concrete, metal (especially steel) or wood.

This reinforcement is obtained by bonding a flexible fabric 3 of carbon fibers to at least one surface of the civil engineering structure: the surface to be reinforced will generally be a surface subjected to tensile forces, in this case the underside 4 of the beam 1, but it would also be possible to reinforce in the same way a surface of the structure of civil engineering which is subjected to shearing forces, for example the sides 5 of the beam 1 considered here, at the right of the supports 6 of this beam.

• la surface à renforcer 4 de la structure de génie civil est nettoyée, le cas échéant sablée et dégraissée, ou encore cette surface peut subir toute autre préparation mécanique ou chimique visant à assurer la durabilité du renforcement,
• cette surface est enduite d'un film mince de résine à l'état fluide,
• on applique ensuite le tissu de fibres, sec, sur le film de résine encore à l'état fluide,
• ce tissu est marouflé, c'est-à-dire pressé contre la surface à réparer, avec une pression suffisante pour égaliser l'épaisseur de la résine entre cette surface à réparer et le tissu, et pour imprégner ce tissu avec la résine,
• et le cas échéant, on procède à nouvelles applications de résine et de tissu s'il est nécessaire d'utiliser plusieurs couches de tissu superposées, éventuellement avec des dimensions de tissu différentes.

To implement the reinforcement method according to the invention, the procedure is as follows:

• the surface to be reinforced 4 of the civil engineering structure is cleaned, if necessary sanded and degreased, or this surface can undergo any other mechanical or chemical preparation aimed at ensuring the durability of the reinforcement,
• this surface is coated with a thin film of resin in the fluid state,
• the dry fiber fabric is then applied to the resin film still in the fluid state,
• this fabric is mounted, that is to say pressed against the surface to be repaired, with sufficient pressure to equalize the thickness of the resin between this surface to be repaired and the fabric, and to impregnate this fabric with the resin,
• and if necessary, new resin and fabric applications are made if it is necessary to use several superimposed layers of fabric, possibly with different fabric dimensions.

The resin used may for example be the two-component epoxy resin constituted on the one hand by the base resin of the brand "CECA XEP 3935 / A", and on the other hand by the hardener of the brand "CECA XEP 2919 / B" , these two components being manufactured and marketed by CECA SA, 12 place de l'Iris, La Défense 2, Cédex 54, 92062 PARIS LA DEFENSE (FRANCE).

More generally, the resin used may be a thermoplastic or thermosetting resin, flame retardant or not, resistant to ultraviolet rays or not, which has the capacity to adhere both to the surface of the civil engineering structure and to the fibers of carbon and which is capable of plugging any cracks in the surface to be reinforced 4.

This resin has, when applied in the fluid state, a viscosity at the application temperature (that is to say in general at room temperature) of between 1,000 and 100,000 mPa.s.

• une résistance au cisaillement compatible avec celle du matériau constituant la structure de génie civil,
• une résistance à la rupture en traction comprise entre 5 et 100 MPa, avec un allongement à la rupture compris entre 0,5 et 10 %,
• et une résistance à la rupture en compression comprise entre 5 et 100 MPa, avec un raccourcissement à la rupture compris entre 0,5 et 10 %.

This resin, a hardened liver, presents:

• a shear strength compatible with that of the material constituting the civil engineering structure,
• a tensile breaking strength between 5 and 100 MPa, with an elongation at break included between 0.5 and 10%,
• and a compressive breaking strength of between 5 and 100 MPa, with a shortening at break of between 0.5 and 10%.

Preferably, the resin is thixotropic when it is in the fluid state, and it does not contain any solvent.

Advantageously, a resin is used which polymerizes at room temperature.

In addition, it will be noted that the same resin can be used whatever the material of the civil engineering structure (concrete, metal, wood).

The fabric 3 of carbon fibers, for its part, is preferably in the form of a flexible strip 7 (see FIG. 2) which extends in a longitudinal direction X and which is generally stored in the form of a roll.

This strip 7 consists of sized carbon fibers which form, on the one hand, substantially continuous warp threads 8 extending in the longitudinal direction X, and on the other hand, weft threads 9 (possibly of different size from the threads of chain) extending in a transverse direction Y parallel to the width of the strip 7 (or possibly in oblong directions).

The carbon fibers constituting the fabric have a tensile strength which is greater than 1,500 MPa, and an elastic modulus of between 200 and 400 GPa.

Optionally, the quantity of carbon fibers in the fabric 3 in a given direction can be modulated during the manufacture of this fabric, depending on the forces to be taken up by the carbon fibers.

When the strip 7 is applied to a surface to be reinforced subjected to tensile stresses, the longitudinal direction X of this strip is preferably parallel to these tensile stresses: this is how, in the example shown in the drawings, the strip 7 is arranged parallel to the length of the beam 1.

Advantageously, as shown in FIG. 3, the strip 7 may initially have a face on which the fabric 3 of carbon fibers is left bare, and a face covered by a flexible sheet 10 of synthetic material ("polyane") which is glued removably on the fabric 3 of carbon fibers.

In this case, the strip 7 is preferably wound with the flexible sheet 10 directed towards the outside of the roll, so as to protect the carbon fibers during the storage of said strip.

In addition, during the implementation of the carbon fiber fabric strip, the sheet 10 of flexible material is not removed until after the masking operation, so that this sheet 10 avoids any soiling or any damage. carbon fiber fabric 3 during the installation of this fabric.

Furthermore, during the implementation of the strip 7 of carbon fiber fabric, the ends 7a of this strip (or at least one longitudinal end 7a) can advantageously be cut into a point, as shown in FIG. 1, so as to better distribute the shear stresses exerted in the resin between the civil engineering structure and the carbon fiber fabric.

In fact, experience shows that the shear stresses between the strip 7 of fabric and the underlying structure to be reinforced are substantially zero in the running part of the strip, but are concentrated at the ends of said strip.

When said ends of the strip are straight lines perpendicular to the longitudinal direction of the strip of fabric, there is at each of said ends a very pronounced peak in shear stress.

In this case, the underlying structure to be reinforced risks being cracked, especially when said structure is concrete.

On the contrary, since the ends 7a of the strip of fabric according to the invention are cut into points or bevels, the shear forces between the strip of fabric and the underlying structure are distributed over the entire length of the tip , measured parallel to the longitudinal direction of the fabric strip. As a result, the shear stresses reach lower maximum values than when the ends of the fabric strip are rectangular, so that damage and in particular the cracking of the underlying structure can be avoided.

The remarkable efficiency of the reinforcement method according to the invention could be verified in particular during a simple bending rupture test, carried out on two identical reinforced concrete beams, only one of which had been reinforced by bonding a fabric. of carbon fibers on its underside, according to the method described above: the effort required to break the unreinforced beam was 1.5 tonnes, while the effort required to break the fiber reinforced beam of carbon was 4 tonnes.

Claims (9)

Method for reinforcing a structure (1) of civil engineering, consisting in sticking at least one layer of carbon fiber fabric on a surface to be reinforced (4) belonging to said structure, this method comprising the following steps: a) prepare the surface to be reinforced (4), b) coating said surface (4) with a layer of epoxy resin in the fluid state, capable of adhering to the civil engineering structure and to the carbon fibers and capable of plugging any cracks presented by the surface to reinforce (4), this resin having, when applied in the fluid state, a viscosity of between 1,000 and 100,000 mPa.s, and this resin having moreover, once cured, a resistance to rupture in tensile strength between 5 and 100 MPa with elongation at break between 0.5 and 10%, and tensile strength in compression between 5 and 100 MPa with shortening at break between 0.5 and 10% , c) and apply a dry flexible fabric (3), consisting of sized carbon fibers, on the resin layer still in the fluid state, by exerting on this fabric sufficient pressure to impregnate it with resin and to equalize the film of resin, the fabric having, in at least one direction, a breaking strength greater than 1,500 MPa and an elastic modulus between 200 and 400 GPa. Method according to claim 1, in which the fabric (3) of carbon fibers is in the form of a strip (7) which extends in a longitudinal direction (X), the carbon fibers of this fabric forming 'a part of the warp son (8) substantially continuous and parallel to the longitudinal direction, and secondly the weft son (9) transverse. The method of claim 2, wherein the the surface to be reinforced (4) is subjected to tensile stresses, the warp threads (8) of the carbon fiber fabric being arranged parallel to said stresses. The method of claim 3, wherein the strip (7) of carbon fiber fabric has at least one longitudinal end (7a) cut into a point. The method of claim 4, wherein the strip (7) of carbon fiber fabric has two longitudinal ends (7a) cut into a point. Method according to any one of the preceding claims, in which the fabric (3) of carbon fibers initially comprises a bare face and a face covered with a removable flexible sheet (10) of synthetic material, the fabric (3) being applied. on the resin film via its bare face, and the sheet (10) of synthetic material being removed from the fabric after impregnation of this fabric with the resin. A method according to any one of the preceding claims, wherein the resin is thixotropic when in the fluid state. A method according to any one of the preceding claims, in which the resin does not comprise any solvent. Method according to any one of the preceding claims, in which the civil engineering structure (1) consists of a material chosen from concrete, metal and wood.

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