EP0799951B1 - 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 of reinforcement of civil engineering structures with fibers bonded carbon, processes that are used to increase the resistance of civil engineering structures in particular when their mechanical characteristics have deteriorated due to aging.

In certain known processes of this type, factory prefabricated with composite material elements, made up of carbon fibers included in a matrix of synthetic resin, then these elements are used on building sites or public works by sticking them on 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 preservation 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 efforts which are taken up by the carbon fibers pass first by the glue by means of which the composite material is attached to the civil engineering structure and then by the matrix of synthetic resin, before being transmitted to the fibers of carbon: this multiplication of intermediate materials between the civil engineering structure and the carbon fibers affects the effectiveness of the reinforcement.

Furthermore, document US-A-5 308 430 describes a process of strengthening civil engineering structures in using carbon or other fibers which are coated with resin when applied to the structure.

But the fibers in question are all parallel to each other, so that strengthening as well achieved is effective only to resume 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 glued to a sheet flexible support.

Therefore, if it is necessary to overlay multiple layers of carbon fiber on the surface to reinforce, these layers are separated from each other by the flexible sheet of support material: a additional heterogeneity in the composite material of reinforcement, which decreases the ability of this material to properly transmit the efforts between the structure of civil engineering and carbon fibers.

Finally, the aforementioned document provides for using fibers that are initially stranded and then to flatten these strands by crushing in order to constitute flat strips of fibers: this manufacturing process presents the disadvantage of risking damaging the fibers during crushing the strands.

The object of the present invention is 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, le tissu de fibres de carbone se présentant sous la forme d'une bande qui s'étend selon une direction longitudinale, et les fibres de carbone de ce tissu formant d'une part des fils de chaíne sensiblement continus et parallèles à la direction longitudinale, et d'autre part des fils de trame transversaux.

To this end, the invention provides a method for reinforcing a civil engineering structure, consisting of gluing at least one layer of carbon fiber fabric to a surface to be reinforced belonging to said structure, this method 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, the carbon fiber fabric being in the form of a strip which extends in a longitudinal direction, and the carbon fibers of this fabric forming, on the one hand, substantially continuous warp threads parallel to the longitudinal direction, and, on the other hand, transverse weft threads.

Thanks to these provisions, it is possible to reinforce a surface of any shape, possibly curved or irregular, and there is no need to apply permanent pressure on the fiber fabric of carbon until the resin sets.

The reinforcement thus obtained is particularly efficient and reliable, in particular because the efforts to resume are transmitted from the civil engineering structure to carbon fibers through a matrix of unique and homogeneous resin, avoiding any layer of intermediate material between this matrix and the structure strengthen.

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

In addition, the use of carbon fibers under fabric shape, with warp threads and interwoven weft, ensures that the fibers of carbon keep a perfect cohesion during their setting which makes it very easy to implementation and high mechanical performance.

• la surface à renforcer est soumise à des efforts de traction, les fils de chaíne 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 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 detailed description following of one of its embodiments, given as non-limiting 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 setting work of the process according to the invention, used to reinforce or repair a reinforced concrete beam 1 supporting a floor 2 of building.

But of course, this app 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 sticking a fabric flexible 3 of carbon fibers on at least one surface of the civil engineering structure: the surface to be reinforced will be generally a surface subjected to tensile forces, in the occurrence the underside 4 of the beam 1, but it would also possible to reinforce in the same way a surface of the civil engineering structure which is subjected to efforts shear, for example the sides 5 of the beam 1 considered here, to 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 resin two-component epoxy consisting on the one hand of the resin base of mark "CECA XEP 3935 / A", and on the other hand by the hardener brand "CECA XEP 2919 / B", these two components being manufactured and marketed by CECA S.A., 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 ability to adhere to both the surface of the structure of civil engineering and on carbon fibers and which is able to plug possible cracks in the surface to strengthen 4.

This resin has, when applied to fluid state, viscosity at application temperature (i.e. usually at room temperature) included 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 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%.

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

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

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

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

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

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

Optionally, the amount of carbon fiber in the fabric 3 in a given direction can be modulated during the manufacture of this fabric, depending on the efforts to take up with carbon fibers.

When the strip 7 is applied to a surface to strengthen subject to tensile stress, the steering longitudinal X of this strip is preferably parallel to these tensile forces: this is how in the example shown in the drawings, the strip 7 is arranged in 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 carbon fiber fabric 3 is left bare, and one side covered by a flexible sheet 10 of synthetic material ("polyane") which is removably glued to the fabric 3 carbon fiber.

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

In addition, during the implementation of the strip of carbon fiber fabric, we only remove sheet 10 of flexible material only after the masking operation, so that this sheet 10 avoids any soiling or any damage carbon fiber fabric 3 when installing this tissue.

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

Indeed, experience shows that the constraints of shear between the strip 7 of fabric and the underlying structure to be reinforced are substantially zero in part band current 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, we see at each of said ends a very pronounced peak of shear stress.

In this case, the underlying structure to strengthen risk of cracking, especially when said structure is concrete.

On the contrary, because the ends 7a of the strip of fabric according to the invention are cut into points or at a bevel, the shear forces between the strip of tissue and the underlying structure are distributed under any the length of the tip, measured parallel to the longitudinal direction of the fabric strip. The result that the shear stresses reach values lower than when the ends of the fabric strip are rectangular, so that one can thus avoiding damage and in particular cracking of the underlying structure.

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

Claims (8)

1. Method for reinforcing a civil engineering structure (1), consisting of bonding at least one layer of carbon fibre fabric onto a surface to be reinforced (4) belonging to the said structure, this method comprising the following steps:

   a) preparing the surface to be reinforced (4)

   b) coating the 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 fibres and able to stop any cracks that may be present on the surface to be reinforced (4), this resin having, when it is 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 strength of between 5 and 100 Mpa with a shortening at break of between 0.5 and 10 %,

   c) and applying a dry flexible fabric (3), consisting of sized carbon fibres onto the layer of resin that is still in the fluid state, while exerting sufficient pressure on this fabric in order to impregnate it with resin and to equalise 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, the carbon fibre fabric (3) being in the form of a strip (7) which extends in a longitudinal direction (X) and the carbon fibres of this fabric forming on the one hand warp threads (8) that are substantially continuous and parallel to the longitudinal direction (X) and on the other hand transverse weft threads (9).
2. Method according to claim 1, wherein the surface to be reinforced (4) is subjected to tensile forces, the weft threads (8) of the carbon fibre fabric being disposed parallel to the said forces.
3. Method according to claim 2, wherein the strip (7) of carbon fibre fabric has at least one longitudinal end (7a) cut to a point.
4. Method according to claim 3, wherein the strip (7) of carbon fibre fabric has two longitudinal ends (7a) cut to a point.
5. Method according to any one of the preceding claims, wherein the carbon fibre fabric (3) has initially one bare face and one face covered with a detachable flexible sheet (10) made of synthetic material, the fabric (3) being applied to the resin film via its bare face, and the sheet (10) of synthetic material being removed from the fabric after this fabric has been impregnated with resin.
6. Method according to any one of the preceding claims, wherein the resin is thixotropic while it is in the fluid state.
7. Method according to any one of the preceding claims, wherein the resin does not contain any solvent.
8. Method according to any one of the preceding claims, wherein the civil engineering structure (1) consists of a material chosen from concrete, metal and wood.

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