WO2011045505A1

WO2011045505A1 - Reinforcing element made of a fibre‑cement composite and method of reinforcing reinforced concrete structures by such an element

Info

Publication number: WO2011045505A1
Application number: PCT/FR2010/052117
Authority: WO
Inventors: Emmanuel Ferrier; Amir Si-Larbi
Original assignee: Universite Claude Bernard Lyon I
Priority date: 2009-10-15
Filing date: 2010-10-07
Publication date: 2011-04-21
Also published as: FR2951483A1; FR2951483B1

Abstract

The invention relates to an element (1) for reinforcing a reinforced concrete structure, of the plate or beam type to be assembled by bonding or anchoring to a reinforced concrete structure (PB, DB) to be reinforced, characterized in that it is formed from at least one mineral matrix (2) comprising short fibres and from stiffening reinforcements (3), the stiffening reinforcements (3) being prestressed in the mineral matrix. The invention also relates to a method of reinforcing reinforced concrete structures using such a reinforcing element.

Description

Reinforcing element made of fiber cement composite and reinforcing method of reinforced concrete structures by such an element

Technical field of the invention

The present invention relates to the general field of civil engineering and construction of reinforced concrete structures.

The invention relates more particularly to a reinforcement element of concrete-reinforced structures, as well as a method of reinforcing such structures using such a reinforcing element.

State of the art Various techniques have already been proposed in the field of reinforcement of reinforced concrete structures and are currently exploited.

Among the most frequently used are the techniques of rehabilitation by shotcrete and strengthening techniques by external bonding or internal by engravure (so-called NSM technique) of composite plates or frames with organic matrices and glass or carbon fibers.

The techniques of rehabilitation by shotcrete are in the field of traditional civil engineering using conventional materials.

The resulting reinforced structures have the advantage of being brought into conformity with the possibility of rebuilding the section of reinforced concrete. It is a solution well adapted to particularly damaged structures.

Reinforcement techniques by external or internal bonding are aimed at increasing the bearing capacity of the structures by gluing on the tensioned faces of the beams thereof a carbon / epoxy or glass / epoxy composite sheet. Reinforcement products are easy to implement and mechanically efficient. This technique is replacing more and more at the first in operations of reinforcement and / or repair of structures.

The documents US 2002/110680, WO 03/053679 or EP 1 726 742 thus illustrate different reinforcement techniques by external or internal bonding.

However, in a majority of cases, these techniques have drawbacks related to the temperature resistance of the bonded sheets (fire problems), to the compatibility of the organic materials and ceramic materials used and also to the high cost, sometimes prohibitive. , of the product. In addition, the main disadvantage of these bonding reinforcement techniques is the insufficient profitability of the performance of the reinforcement plates, the ultimate strength of which is rarely approached during the rupture due to premature delamination on the one hand, and a lack of inertia particularly thin reinforcement plates on the other hand.

Description of the invention

The object of the present invention is to provide a new reinforcement technique reinforced concrete structures by bonding reinforcing elements that does not have the disadvantages of known techniques listed above.

A further object of the present invention is to provide a reinforcement technique capable of increasing the mechanical performance, in service and at break, of reinforced reinforced concrete structure.

An object of the present invention is also to propose a reinforcement technique requiring the implementation of a reduced amount of reinforcement materials, and if possible, at most similar to the quantities used in bonding reinforcement techniques known at this time. day. To achieve these various objectives, the present invention firstly proposes a reinforcing element of a reinforced concrete structure, of the plate or beam type to be assembled by bonding or anchoring to a reinforced concrete structure to be reinforced and which is characterized in that it consists at least of a mineral matrix comprising short fibers and stiffening reinforcements, the stiffening reinforcements being prestressed in the mineral matrix.

The inventors have demonstrated that it is possible to combine in a single reinforcing element a mineral matrix, short fibers and prestressing stiffening reinforcements, for example metal or composite, to obtain structure reinforcing elements meeting the objectives. above and thus to the expectations of users.

In particular, the reinforcing element of the invention has improved bending stiffness and / or ultimate load compared with CFRP bonding reinforcement solutions by virtue of increased inertia, especially provided by the mineral matrix, in which the frames are drowned. This increase in inertia compared to known reinforcing elements provides the reinforcing elements of the invention with a reduced crack opening, and hence, increased durability of the reinforced structure using such elements.

According to one embodiment of the reinforcing element of the invention, the mineral matrix consists of at least one binder, sand, silica fume, water and a high water-reducing adjuvant. Preferably, the binder of the mineral matrix is chosen as a hydraulic cement.

The reinforcing element of the present invention thus advantageously has good compatibility with environmental criteria in view of the use of cement matrices to the detriment of organic matrices. According to one characteristic of the invention, the short fibers included in the mineral matrix of the proposed reinforcement element are fibers of metallic and / or organic and / or mineral and / or composite nature.

These fibers advantageously have a length of between 8 and 15 mm, and preferably of the order of 10 to 12 mm.

According to another particular and advantageous feature of the invention, the reinforcing armatures of the reinforcing element are reinforcements of a metallic and / or composite nature, and in particular made of steel and / or a polymer material reinforced with fiberglass and / or carbon fiber.

In an advantageous embodiment of the invention, the prestressing of reinforcing reinforcements of the reinforcements is applied before the casting of the mineral matrix around said reinforcements during the manufacture of the reinforcing elements and this prestressing is between 30% and 60% of the elastic limit of said armatures.

The reinforcing element of the invention thus offers, thanks to such a prestressing stiffening reinforcement, substantially improved performance compared to the composite-plate elements used in the current adhesive reinforcement techniques. In particular, the ultimate load supported by the reinforcing elements of the invention is at least 15% greater than that supported by carbon fiber reinforced polymer composite plates of the CFRP (Carbon Fiber Reinforced Polymer) type. Post-cracking stiffness is increased by 20%.

In addition, insofar as the reinforcements are embedded in the mineral matrix, they offer better fire resistance on the one hand and more generally external aggression, whether chemical or climatic, which improves the durability of the reinforcing element and therefore reinforcements operated using these materials.

In an advantageous embodiment of the reinforcement element of the invention, it has at its ends a beveled shape conferring a gradual decrease in thickness with a slope of 15 to 45 ° to the end. Such a geometry provides the reinforcing element of the invention with the advantage of delaying the delamination of the reinforcement plates, the particular geometry of the ends making it possible to limit the over-stressing at the ends.

The present invention also provides, according to a second object, a reinforcing method of reinforced concrete structures implementing at least one reinforcing element of the invention, as it has been presented previously. This method consists essentially in assembling by gluing on a reinforced concrete structure to reinforce a reinforcement element according to the invention, consisting of at least one mineral matrix, short fibers mixed in this matrix and reinforcement reinforcements, embedded and prestressed in this mineral matrix.

According to the method of the invention, the surfaces of the substrates to be bonded, that is to say of the reinforced concrete structure to be reinforced and of the reinforcement element, are prepared prior to bonding, by sanding or mechanical sanding.

Next, the two surfaces of the substrates to be assembled are preferably glued, which is then assembled by any means for applying the reinforcing element to the structure to be reinforced.

Still according to the method of the invention, the assembly of the reinforced concrete structure to be reinforced and the reinforcing element after bonding for a period of at least twelve hours are then maintained under pressure. Preferably, this pressure maintenance of the assembly can last at least 24 hours, and up to 48 hours.

According to various preferred features of the process of the invention:

an adhesive thickness of between 1 mm and 5 mm is applied to the surfaces of the substrates to be assembled before assembly;

the assembly is maintained under pressure after sizing until a final adhesive thickness of between 0.5 and 2 mm is obtained;

the substrates are adhered with a structural adhesive based on polyurethane, epoxy or a combination of these materials; - the reinforcing element (s) are optionally prestressed;

the mineral matrix of the reinforcing element (s) comprises cement;

the short fibers of the reinforcing element (s) are fibers of a metallic and / or composite nature and have a length of between 5 and 15 mm

The reinforcement element and the method of the present invention are both easy to implement, even in situ, and perfectly adapted to all construction industries, and in particular the building industry (individual houses, collective buildings). or industrial, freestanding floors, etc.), and to all markets for engineering structures (bridges, footbridges). Presentation of drawings

Other advantages and features of the invention will become clear from reading the description and examples, given purely by way of illustration and not limitation, which will follow.

Figure 1 shows in perspective a reinforcing element according to the invention, in the form of a flat.

Figure 2 shows a cross-sectional view of a reinforcing member of the invention applied under a reinforced concrete structure.

FIGS. 3A and 3B show two exemplary embodiments of reinforcement of reinforced concrete structures by the implementation of the reinforcing element of the invention.

Figure 4 schematically illustrates the four-point bending test protocol established to evaluate the performance of the reinforcing member of the invention.

Figure 5 shows the load-displacement curves established during the comparative strength tests of various reinforced concrete structures reinforced according to methods of the prior art and the method of the invention; FIG. 6 represents the stiffness curves obtained during the comparative strength tests of various reinforcing reinforced concrete structures according to methods of the prior art and the method of the invention. Detailed description of the invention

According to a first object, the present invention provides a reinforcement element 1 of reinforced concrete structures. Such a reinforcing element 1 may in a preferred embodiment be in the form of a reinforcing plate or plate as shown in FIGS. 1 and 2. Such a reinforcing element 1 has a generally parallelepipedal general shape, except at its ends which have a particular beveled shape intended to limit the phenomena of delaminating shear stresses at the ends as will be described below.

Preferably, the dimensions of the reinforcing element 1 are between 60 and 150 mm in width and between 25 and 45 mm in thickness, the length of the plate 1 being able to extend between 1 and 5 m.

The reinforcing element 1 essentially consists, according to the invention, of a mineral matrix 2 comprising short fibers and in which stiffening reinforcements 3 are embedded. The mineral matrix 2 preferably comprises a cementitious binder.

Advantageously, the binder of the mineral matrix 2 is a cement and the composition of the matrix makes it possible to reduce the quantity of water at a Water / Cement ratio of 0.30, also comprising sand, silica fume, silica, water and a high water reducing adjuvant. This composition makes it possible to obtain compressive strengths at 28 days greater than 100 MPa and a bending tensile strength greater than 15 MPa. An example of a composition of a mineral matrix 2 of the reinforcement element of the invention is presented in Table 1 below: TABLE 1:

Advantageously, the matrix 2 of the reinforcing element 1 of the invention comprises short fibers of 10 to 12 mm. These short fibers may in particular be of a metallic, mineral, organic or composite nature or their combination. In the case of the composition given in Table 1, the short fibers are metallic allowing an increase in the tensile strength of the matrix and a ductile behavior.

The reinforcement element 1 of the invention finally comprises reinforcing reinforcements 3 embedded in the mineral matrix 2. These reinforcements 3 preferably extend over the entire length of the reinforcing element and may be of a metallic or composite nature. , or both. The reinforcements 3 may in particular be steel, polymer reinforced glass fiber or carbon, or their combination. Their diameter is advantageously between 6 and 12 mm, and they are positioned median in the thickness and the width of the matrix 2.

Tensile tensile moduli range from 40000 MPa for glass-fiber composites to 130000 MPa for carbon-fiber composites. Tensile strengths range from 1000 MPa, for glass fiber composites (FC), to 2300 MPa, for carbon fiber composites (FC). According to an advantageous embodiment of the reinforcement element of the invention, the reinforcements 3 may be prestressed before the casting of the die 2 to obtain an internally prestressed reinforcing member 1. Advantageously, the prestressing force is between 30% and 60% of the maximum strength of the composite reinforcement.

Finally, the geometry of the ends of the reinforcement element of the invention is specific to limit shear overloads (-50%) according to the calculation results resulting from an analytical formulation specific to the mechanics of bonded joints (B. Taljsten Sr. Res.Engr., Div.of Structural Engrg., Dept. Of Civ.Engrg., Luleâ Univ. Of Technol., S-971 87 Luleâ, Sweden; STRENGTHENING OF BEAMS BY PLATE BONDING, part of the Journal of Materials in Civil Engineering, Vol 9, No. 4, November, 1997) and is well-validated in the field of glue joints in the aerospace industry.

According to the invention, the shape of the ends of the reinforcing element

1 is beveled, and gives a gradual decrease in the thickness of the element 1 at its end, the last 15 cm, with a slope of 15 to 45 ° depending on the thickness of the element. The intensity of the shear stresses at the interface between reinforcement element 1 and reinforced support is decreased in a ratio of 2 to 3 by this specific geometry. The risk of detachment of the reinforcing element due to local overloads of shear is thus substantially reduced.

This is an advantage over traditional solutions and can not be implemented on composite and sealed reinforcement (NSM) solutions.

The reinforcing element 1 of the present invention provides a particularly effective and advantageous solution for reinforcement of reinforced concrete structures. As shown in FIGS. 3A and 3B, the reinforcing element 1 can be used alone to reinforce, for example, a reinforced concrete beam PB (FIG. 3A) by longitudinal gluing under the beam of a reinforcing element 1, or by combination of several reinforcing elements 1 bonded parallel to each other under a reinforced concrete slab DB (FIG. 3B).

Reinforcement operations of reinforced concrete structures consist in assembling the reinforcing element 1 under the reinforcement reinforced concrete structure by bonding, as shown in FIGS. 3A and 3B. This bonding assembly is advantageously with a structural adhesive 4 based on polyurethane, epoxy or a combination of these materials.

Preferably, it is necessary to prepare the surfaces to be bonded both of the structure to be reinforced and the reinforcement element or elements used to carry out the reinforcing operation. This preparation of the bonding surfaces consists in particular in a sanding or mechanical sandblasting of said surfaces in order to clean them and facilitate the setting of the glue which is then applied, by any known means, in particular a spatula, on two surfaces of the substrates to be assembled.

In order to obtain a satisfactory strength assembly, an adhesive thickness of between 1 mm and 5 mm is preferably applied to the two surfaces of the substrates to be assembled. The thickness of the glue layer depends in particular on its viscosity. However, in any case, the amount of structural adhesive used according to the process of the invention should be about 2 Kg per unit area of bonding.

Once the glue has been applied, the glued surfaces are applied to one another by pressure of the reinforcing element or elements implemented on the surface of the reinforcing concrete structure previously glued. Advantageously, it is then maintained under pressure, before the end of the DPU (practical duration of use) of the glue, the assembly of the reinforced concrete structure to reinforce and reinforcement element (s) for a duration of at least twelve hours and up to 48 hours, advantageously for 24 hours. Preferably, the pressurization is carried out until all the excess glue has been rejected, so as to obtain a final adhesive thickness varying from 0.3 to 3 mm, preferably from 0.5 to 2 mm . In order to validate the intrinsic performances of the reinforcement element 1 of the invention and the reinforced structures according to the method of the invention, the inventors have carried out various comparative mechanical tests whose nature and the results are reported below.

Four reinforcing plates in accordance with the invention were made up of a high-performance fibered cementitious matrix 2 (UHPC) in accordance with the composition given in Table 1, which will subsequently be presented in the following tables of results as the composition F6mod.

In order to test the performance of the cementitious matrix itself, four 4 X 4 X 16 type concrete specimens formed from this matrix were subjected to a three-point bending test to measure the bending tensile strength. The average resistance obtained is 25.5 MPa.

Subsequently, ten reinforced concrete girders protected against shear failure were made, one (P8) called "control" devoid of reinforcement and the others reinforced in the lower part by different reinforcing elements according to the present invention, formed of a parallelepipedal plate of composite short-cement fibers, glued between the supports of the beam, and in which are embedded centrally rods of composite glass or carbon fibers forming reinforcements stiffening 3.

In order to compare the performance of the reinforcement obtained according to the invention with respect to existing reinforcement methods, two other reinforced concrete beams, identical to those reinforced using short-cement fiber composite plates according to the invention. have been reinforced, one by bonding one carbon plate (P6) and the other (P7) by means of two carbon rods glued in two grooves on the concrete according to the NSM procedure (Near Surface Mounted).

Several combinations of reinforcement were tested, the variants between each beam PI to P12 tested holding cementitious matrix formulations reinforcing plates 1 (also called reinforcement plates), the dimensions of the sections of said plates, the type of reinforcement ( CF P carbon or GFRP glass), prestressing possibly applied to reinforcements and geometry of the ends of the reinforcing plates. The different combinations are referenced in Table 2.

Table 2:

A 4-point bend test described in FIG. 4 was carried out on the beams P1 to P12 thus prepared in order to test the different reinforcement configurations. This test consists of stressing the beams statically and monotonically at four different points of application A1 to A4 until they break. The loading of the beam is carried out by applying a force F applied to the points A2 and A3. The arrow of the beam in the middle under the application of the force F is measured by a displacement sensor C. The adopted instrumentation continuously collects the applied force and the arrow mid-span. The results of these bending tests are reported in Table 3 below and in Figure 5.

Table 3:

These results allow us to draw the following conclusions.

The performance of the beams reinforced by reinforcement plates in accordance with the invention (P1-P6 and P9-P12), comprising a fiber-cement composite mineral matrix are systematically and very significantly improved compared to those of the control beam (P8). whether they are ultimate loads (up to 63% gain) or that they relate to service behavior characterized by significantly higher rigidity and a substantially deferred degradation level.

In addition, compared to conventional prior solutions (P6, P7) the reinforcing plates according to the invention are significantly more efficient than the carbon dish (P6), with a substantially increased ultimate load (up to 17%) . This ultimate load remains moreover of the same order (2% difference) than the P7 beam reinforced by the NSM technique.

As for the post-cracking stiffness and plasticization of passive metal reinforcement, it is increased (+ 20%) vis-à-vis the two traditional solutions, thus reinforcing the interest of the present invention especially in the case of in-service behavior (Figure 6).

It is also significant to note that the rate of work (deformation and stress) of the rods of carbon in the reinforcement plates of the invention is significantly increased (between 10% and 30%) with regard to CFRP type solutions (carbon plate ) or NSM which suggests the possibility of optimization and consequently a gain of material and its corollary in terms of price.

The use of mechanical anchoring and / or a modification of the geometry of the ends of the dishes also provides an improvement in the performance of the beams, particularly in terms of ultimate load.

The invention is not limited to the examples described and shown because various modifications can be made without departing from its scope.

Claims

1 - Element (1) for reinforcing a reinforced concrete structure, of the plate or beam type to be assembled by bonding or anchoring to a reinforced concrete structure (PB, DB), characterized in that it is constituted by less than one mineral matrix (2) comprising short fibers and stiffening reinforcements (3), the stiffening reinforcements (3) being prestressed in the mineral matrix.

2 - reinforcing element (1) according to claim 1, characterized in that the mineral matrix (2) consists of at least one binder, sand, silica fume, water and a high reducing adjuvant of water.

3 - reinforcing element (1) according to claim 2, characterized in that the binder of the mineral matrix is a hydraulic cement.

4 - reinforcing element (1) according to one of claims 1 to

3, characterized in that the short fibers included in the mineral matrix are fibers of a metallic and / or organic and / or mineral and / or composite nature.

5 - reinforcing element (1) according to one of claims 1 to

4, characterized in that the short fibers included in the mineral matrix have a length of between 8 and 15 mm.

6 - reinforcing element (1) according to one of claims 1 to

5, characterized in that the reinforcing plates (3) are reinforcements of a metallic and / or composite nature.

7 - reinforcing element (1) according to claim 6, characterized in that the reinforcing reinforcements (3) consist of steel and / or a polymer material reinforced with glass fibers and / or carbon.

8 - Reinforcement element (1) according to one of claims 1, characterized in that the preload of the stiffening reinforcement is between 30% and 60% of the elastic limit of said reinforcements. 9 - reinforcing element (1) according to one of claims 1 to 8, characterized in that its ends have a beveled shape conferring a gradual decrease in thickness with a slope of 15 to 45 ° to the end.

10 - Reinforcing method of a reinforced concrete structure, characterized in that it is assembled by gluing on a reinforced concrete structure to reinforce at least one reinforcing element (1) comprising a mineral matrix (2) comprising fibers short and stiffening armatures (3), said stiffening armatures being prestressed in the mineral matrix.

11 - Process according to claim 10, characterized in that the surfaces of the substrates to be bonded are prepared before bonding by sanding or mechanical sanding.

12 - Process according to claim 11, characterized in that one glues the two surfaces of the substrates to be assembled.

13 - Method according to one of claims 11 to 13, characterized in that one maintains under pressure the assembly of the reinforced concrete structure to reinforce and the reinforcing element after gluing for a period of at least twelve o'clock.

14 - Method according to one of claims 10 to 13, characterized in that one applies a glue thickness (4) of between 1 mm and 5 mm on the surfaces of the substrates to be assembled before assembly.

15 - Process according to claims 13 and 14, characterized in that the pressure is maintained under pressure after sizing to obtain a thickness of adhesive (4) final between 0.5 and 2 mm.

16 - Method according to one of claims 10 to 15, characterized in that the surfaces to be glued are glued with a structural adhesive (4) based on polyurethane, epoxy or a combination of these materials.

17 - Method according to one of claims 10 to 16, characterized in that the mineral matrix (2) of the element (s) of reinforcement comprises a hydraulic binder. 18 - Process according to one of claims 10 to 17, characterized in that the short fibers of the reinforcing element (s) are fibers of a metallic and / or composite nature and have a length of between 5 and 15 mm.