Method for reinforcing a civil engineering structure

Abstract

The invention relates to a method for reinforcing a civil engineering structure, comprising the following steps: - coating a surface of the structure with a first layer of resin in a fluid state, having a particle size distribution, termed first particle size distribution, - applying a layer of a dry woven fabric with a weight per unit area greater than or equal to 600 g / m2, termed high-grammage woven fabric, to the coated surface while the resin is still in the fluid state, by exerting on the woven fabric a pressure sufficient to impregnate it with resin, - coating the woven fabric with a second layer of resin, termed closure layer, in a fluid state, having a particle size distribution, termed second particle size distribution, which is less than or equal to the first particle size distribution.

Description

[0001] The invention relates to a method for reinforcing a civil engineering structure.

[0002] A first known surface reinforcement method consists of gluing steel sheet plates onto the concrete of the structure in addition to the reinforced concrete reinforcements, in particular in tensioned parts of said structure.

[0003] It is necessary to hold the plates in position on the surface by mechanical means, such as a clamping frame, in order to crush a film of glue on the one hand and to support the weight of the sheets during the polymerization of the resin on the other hand.

[0004] This technique has been widely used in construction, but over time it has revealed the major disadvantage of exposing the reinforcing sheets to the elements and requiring costly periodic maintenance to prevent corrosion.

[0005] In the 1990s, steel sheets were replaced by carbon fiber composite plates or strips, which offered the advantages of being insensitive to corrosion, being lightweight and having superior mechanical characteristics to the steel plates previously used.

[0006] The use of carbon fibers allows the development of another reinforcement process, consisting of coating a surface with resin in an area to be reinforced and then applying a strip of dry carbon fiber fabric to the coated surface, in order to manufacture the composite on the support itself. The video entitled "Structural Reinforcement - SikaWrap - Sika España" is available at the link https: / / www.youtube.com / watch?v=NBUwcC1Ponc (XP002779238) discloses such a strengthening method.

[0007] This process has undeniable advantages, such as its ability to reinforce by adding carbon fiber composites on non-flat surfaces as well as increased lightness and maneuverability.

[0008] However, only fabrics of low thickness (up to thicknesses of the order of 0.5 mm) and low dry weight (up to 500 g / m 2 < ) can be impregnated directly during their application to the support, which implies that the process is limited to lower reinforcement sections (or fiber densities).

[0009] One aim of the invention is to at least partially remedy these drawbacks.

[0010] To this end, the invention relates to a method for reinforcing a civil engineering structure, comprising the following steps: coating a surface of the structure with a first layer of resin in a fluid state, having a granulometry called the first granulometry, applying a layer of a dry fabric with a surface weight greater than or equal to 600g / m 2 <, called heavy weight, on the coated surface, the resin still being in the fluid state, by exerting sufficient pressure on the fabric to impregnate it with resin, coating the fabric with a second layer of resin, called the closing layer, in the fluid state having a granulometry called the second granulometry, less than or equal to the first granulometry, so as to constitute a composite reinforcement.

[0011] The resin, once polymerized, that is to say hardened, constitutes the matrix of the composite forming the reinforcement of the structure.

[0012] In other words, the resin has two functions since it allows the composite to be bonded and constitutes its matrix.

[0013] Thus, the method according to the present invention, by applying resins with calibrated granulometries, makes it possible to saturate (sufficiently impregnate) the dry fabric to form a composite, the first resin coating the support being sufficiently viscous to support the fabric's own weight, which makes it possible to reinforce the structure with a greater resistant section (fiber density), by using a dry fabric known as a high-grammage fabric (surface weight greater than 600g / m 2 < ).

[0014] According to another characteristic of the invention, the resin is in the form of a gel in a fluid state.

[0015] According to another characteristic of the invention, the fabric is composed of fibers having interstitial spaces, the first granulometry and the second granulometry being strictly less than the interstitial space, possibly zero (i.e. without added inert fillers).

[0016] According to another characteristic of the invention, the first particle size (intended for coating the support before laying the dry fabric) is less than or equal to 1 µm, preferably less than or equal to 0.1 µm.

[0017] According to another characteristic of the invention, granular elements of the resin comprise nanoparticles and / or silica.

[0018] According to another characteristic of the invention, the resin has a Brookfield viscosity at 23°C giving a shear rate of 15 to 25 Pa.s for a rotation speed of 1 s -1< and from 3 to 5 Pa.s for a rotation speed of 10 s -1< .

[0019] According to another characteristic of the invention, the resin comprises a thickening agent.

[0020] According to another characteristic of the invention, the resin has a zero particle size, that is to say without added inert fillers.

[0021] According to another characteristic of the invention, granular elements or inert fillers are added in a proportion of between 2% and 12%, preferably between 5% and 10% by mass.

[0022] Other characteristics and advantages of the invention will appear on reading the description which follows. This is purely illustrative and must be read in conjunction with the appended drawings in which: there Figure 1 illustrates a perspective view of an example of implementation of the method according to the invention; and the Figure 2 illustrates an arrangement of carbon fibers within a strip of fiber fabric of the example of the Figure 1 . Structural reinforcement

[0023] There Figure 1 shows a particular example of implementation of the method according to the invention, used to reinforce or repair a reinforced concrete beam 1 supporting a floor 2 of a building.

[0024] But of course, this application is not limiting, and the invention can be used to reinforce any civil engineering structure, in particular in concrete, metal (especially steel) or wood.

[0025] This reinforcement is obtained by gluing a flexible fabric 3 of fibers onto at least one surface of the civil engineering structure: the structural zone to be reinforced will generally be an area 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 an area of ​​the civil engineering structure which is subjected to shear forces (these stresses inducing so-called main tensile stresses), for example by gluing a flexible fabric onto the sides 5 of the beam 1 considered here, at the supports 6 of this beam.

[0026] As it emerges from the Figure 2, the fiber fabric 3 is preferably in the form of a flexible strip 7 which extends in a longitudinal direction X and which is generally stored in the form of a roll.

[0027] This band 7 is made up of fibers, some of which, referenced 8, extend in the longitudinal direction X, and others called weft fibers, referenced 9, (possibly of a different thickness from the fibers 8) extending in a transverse direction Y parallel to the width of the band 7 (or possibly in an oblique direction).

[0028] Each fiber 8, 9 is composed of filaments separated from each other by interstitial spaces 10.

[0029] For example, the diameter of the filaments is between 5 µm and 7 µm and that of the interstitial spaces is of the order of 2 µm.

[0030] The fibers are, for example, carbon or glass, aramid, or even basalt.

[0031] When the strip 7 is applied to a surface adjacent to an area to be reinforced subjected to tensile forces, the longitudinal direction X of this strip is preferably parallel to these tensile forces: thus in the example shown in the drawings, the strip 7 is arranged parallel to the length of the beam 1. Reinforcement process

[0032] First, surface 4 of the civil engineering structure to be reinforced is cleaned, if necessary sandblasted and degreased, or this surface may undergo any other mechanical or chemical preparation aimed at ensuring the durability of the reinforcement. In particular, a so-called primer coating may be applied beforehand to this surface.

[0033] Then, surface 4 is coated with a thin film of resin in a fluid state, as will be detailed later.

[0034] Then, the dry fiber fabric 7 is applied to the resin film while it is still in a fluid state.

[0035] The fabric 7 is pressed, that is, pressed against the application surface, with sufficient pressure to equalize the thickness of the resin between the surface 4 and the fabric, and to impregnate the fabric with the resin.

[0036] The marouflage is carried out using, for example, a pressure roller and / or a spatula.

[0037] The fabric 7 is then coated with a second layer of resin.

[0038] If necessary, new resin and fabric applications are made if it is necessary to use several layers of fabric superimposed, possibly with different fabric dimensions.

[0039] Preferably, the fabric 7 is of high grammage, that is to say of surface weight greater than 600g / m 2 < , the particular advantage of high grammage fabrics being to offer a greater thickness (a resistant section) for equal surface area, to avoid or limit the need to superimpose several layers of fabric.

[0040] In practice, the layers of superimposed reinforcing fabric are assigned a regulatory reduction coefficient relating to their mechanical performance. Resin application steps

[0041] As already mentioned, the application of resin is done in two stages.

[0042] In a first step, the surface 4 is coated with a first layer of resin provided with inert granular elements having a granulometry called the first granulometry.

[0043] By particle size, we mean the maximum size of inert fillers present in the resin.

[0044] Zero particle size means that the resin is free of fillers.

[0045] The dry fiber fabric 7 is then applied to the resin film, which is still in a fluid state. The fabric 7 is laminated so that it is well impregnated with resin. In a second step, the fabric is then coated with a second layer of resin, called the closing layer, provided with granular elements having a granulometry called the second granulometry, less than or equal to the first granulometry, possibly zero (without inert fillers).

[0046] The resin used is a fluid epoxy system intended for the stratification and coating of porous supports such as concrete or wood and suitable for the construction or reinforcement of composite structures.

[0047] This resin is, for example, a two-component epoxy resin combining a base resin on the one hand, and a hardening agent on the other, mixed during application.

[0048] The base resin has a density of around 1.10 and a viscosity of between 1.0 and 1.5 Pa.s at 23°C.

[0049] The hardening agent has a density close to 1.0 and a viscosity between 0.05 and 0.25 Pa.s at 23°C.

[0050] The resin / hardener mixture when free of thickening agent, in a dosage ratio of 100 / 30 by mass, has a viscosity of between 0.5 and 1.5 Pa.s at 23°C.

[0051] To meet application constraints, it is advantageous to use a resin with a thixotropic character (i.e. having a higher viscosity at rest). This character is obtained either by adding a liquid rheo-thickening agent, or by adding inert fillers or by combining the two.

[0052] 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 carbon fibers and which is capable of filling any cracks in the surface to be reinforced 4.

[0053] Preferably, the resin is thixotropic when in a fluid state, and it does not include a solvent.

[0054] Preferably, the resin is a gel in a fluid state.

[0055] Advantageously, a resin is used which polymerizes at room temperature.

[0056] Furthermore, it should be noted that the same resin can be used regardless of the material of the civil engineering structure (concrete, metal, wood).

[0057] The application of the resin with granular elements of two different granulometries ensures both sufficient viscosity for good adhesion to the support and good hold of the dry fabric (including when applied to a ceiling) while having a sufficiently small granulometries to allow good impregnation of the fabric.

[0058] The application of the resin with the first granulometry, higher than the second granulometry, makes it possible to obtain the desired viscosity, the granular elements (i.e. inert fillers) giving it a satisfactory consistency to adhere to the support and maintain the weight of the fabric.

[0059] During marouflage, the resin migrates into the interstices of the filaments. The resin penetrates the interstitial spaces of the fabric, despite the presence of granular elements.

[0060] The application on the laminated fabric of a closing layer of resin with the second granulometry, low or even zero, ensures that the resin can penetrate deeply and at least as much as the first layer applied to the support.

[0061] Thus, the application of the first layer on the support on the one hand, of the second layer of resin, called closing, on the laminated fabric, makes it possible to obtain a correctly saturated (or impregnated) composite for bonding to the support on the one hand and constitution of the matrix of the composite on the other hand.

[0062] As already indicated, it is therefore possible to use a dry fabric with a high grammage, i.e. with a surface weight greater than or equal to 600g / m 2< , or even strictly greater than 600g / m 2< , and even greater than or equal to 700g / m 2< , up to 1500g / m 2< .

[0063] Preferably, the resin obtained after mixing the components (base resin and hardener) has a Brookfield viscosity at 23°C giving a shear rate of 15 to 25 Pa.s for a rotation speed of 1 s -1< and from 3 to 5 Pa.s for a rotation speed of 10 s -1< according to a Brookfield plane / striated plane rheometer measurement.

[0064] As already indicated, the first granulometry is strictly less than the interstitial space.

[0065] Moreover, the second grain size is smaller than the first, or even zero.

[0066] For example, the first particle size is less than or equal to 1 µm, preferably less than or equal to 0.1 µm.

[0067] In most cases, and particularly in cases of zero particle size, the resin may contain a thickening agent such as a liquid additive, having a rheo-thickening character. Mixing is carried out separately for the hardener on the one hand and for the resin on the other hand, using a high-turbulence deflocculation mixer.

[0068] In the case of a non-zero particle size, granular elements such as inert fillers are used to thicken the resin (and hardener). As described above, the mixing is carried out separately for the hardener on the one hand and for the resin on the other, using a high-turbulence deflocculation mixer. These mixtures are carried out in the workshop or factory, so that only the mixing of the base resin and the hardener is carried out at the application site, using a simple mixer.

[0069] Granular elements are very fine particles such as nanoparticles or, less expensively, filler elements with very fine granulometry such as silica, for example pyrogenic and hydrophilic with a maximum granulometry ranging from 0.04 to 0.99µm.

[0070] Advantageously, the granular elements or inert fillers are added in a proportion of between 2% and 12%, preferably between 5% and 10% by mass, for the base resin, as for the hardener.

[0071] This produces a resin that can remain on the ceiling over significant thicknesses (0.7 to 0.9 mm) without running.

[0072] Advantageously, the granular elements have dimensions less than 0.06µm, i.e. approximately 30 times smaller than the interstitial space.

[0073] With the resin thus formulated in gel form according to the present invention, the low pressure of manual marouflage is sufficient to migrate the resin into the filamentary interstices and makes it possible to obtain a saturation rate of the order of 75% for a fabric of 1200g / m 2< .

Claims

1. A method for reinforcing a civil engineering structure, the method comprising: - coating a surface of the structure with a first layer of resin in a fluid state, having a particle size referred to as the first particle size, - with the resin still in the fluid state, applying a layer of dry fabric with an areal weight greater than or equal to 600 g / m2, referred to as a high grammage fabric, to the coated surface, while applying to the fabric sufficient pressure to impregnate it with resin, - coating the fabric with a second layer of resin, referred to as sealed resin, in the fluid state and having a particle size referred to as the second particle size, less than or equal to the first particle size.

2. The method as claimed in the preceding claim, wherein the resin is in the form of a gel in the fluid state.

3. The method as claimed in any one of the preceding claims, wherein the resin contains a thickener.

4. The method as claimed in any one of the preceding claims, wherein the fabric comprises fibers having interstices, the first particle size and the second particle size being strictly smaller than the interstices, or even zero.

5. The method as claimed in any one of the preceding claims, wherein the particle size of the first layer of resin is less than or equal to 1 µm, preferably less than or equal to 0.1 µm.

6. The method as claimed in any one of the preceding claims, wherein granular elements of the resin comprise nanoparticles and / or silica.

7. The method as claimed in any one of the preceding claims, wherein the resin has a Brookfield viscosity at 23°C giving a shear rate of 15 to 25 Pa.s for a rotational speed of 1 s-1 and of 3 to 5 Pa.s for a rotational speed of 10 s-1.

8. The method as claimed in the preceding claims, wherein inert granular elements or fillers are added in a proportion comprised between 2% and 12%, preferably between 5% and 10% by weight.

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