Abstract:
Process for reinforcing a construction structure where, laid on one portion of said structure, is at least one portion of a reinforcement ( 10 ) of elongated shape comprising continuous fibers in the longitudinal direction of said reinforcement, which are combined with a polymer matrix, wherein said process comprises a step of removing the polymer matrix in one portion ( 20 ) of the reinforcement so as to release the fibers of the reinforcement in order to allow their rearrangement following their release from the polymer matrix. It is thus possible to optimize the binding configuration of the reinforcement with a portion of the structure to be reinforced.

Description:
This application claims priority to French Application No. 09 55462, filed on Aug. 3, 2009 in France, the contents of which is hereby incorporated by reference in its entirety as if fully set forth herein. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of reinforcing construction structures. 
     In this field, it is customary to bond reinforcements by means of suitable resins to portions of a structure to be reinforced. 
     BACKGROUND OF THE INVENTION 
     Initially made of metal sheets, such as used in the Lhermite process, these reinforcements have seen their composition evolve in the last few decades following the appearance of replacement materials for metal sheets. Reinforcements based on composites in the form of bonded plates (see, for example, document FR-A-2594871) or bonded fabrics (see, for example, document EP 0 799 951) are now commonly used. 
     Reinforcements based on composites have many advantages, in particular linked to their ease of use and to their ability to be applied to various surfaces. They improve, for example, very substantially, the dynamic behavior of the reinforced structure. 
     Use may advantageously be made of reinforcements of elongated shape comprising continuous fibers combined with a polymer matrix, manufactured for example by pultrusion or by extrusion and the cross section of which is substantially constant along a longitudinal direction. These reinforcements of elongated shape may advantageously be in lamellar form so as to provide a broad bonding surface area. These reinforcements are, for example, positioned on a face in tension of a structural element made of reinforced or prestressed concrete so as to enable a reinforcement in tension. These reinforcements may also have the shape of long cylinders commonly known as rods. 
     An example of a reinforcement in lamellar form is sold by the company Freyssinet under the commercial reference FOREVA® LFC. 
     By way of example, such elongated reinforcements in lamellar form may have a width of 50, 80, 100 or 150 mm and a thickness of 1.2 mm. 
     Still by way of example, reinforcements of elongated shape are constituted of carbon fibers impregnated by an epoxy matrix. Such reinforcements may be manufactured by pultrusion or by extrusion. 
     Such reinforcements of elongated shape, although very commonly used for reinforcing construction structures, nevertheless have certain drawbacks. In particular, it is observed that it is difficult to optimize the binding configuration of such reinforcements with a portion of the structure to be reinforced. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to propose a process for reinforcing a construction structure using such a reinforcement of elongated shape while making it possible to optimize the binding configuration with a portion of the structure to be reinforced. 
     The invention thus proposes a process for reinforcing a construction structure where, laid on one portion of said structure, is at least one portion of a reinforcement of elongated shape comprising continuous fibers in the longitudinal direction of said reinforcement, which are combined with a polymer matrix, where said process comprises a step of removing the polymer matrix in one portion of the reinforcement so as to release the fibers of the reinforcement in order to allow the rearrangement thereof following their release from the polymer matrix. 
     It is thus possible to use a reinforcement of elongated shape produced in a standard manner, the cost of which is advantageous, while rearranging some of the fibers which constitute it so as to optimize the binding configuration of the reinforcement with a portion of the structure to be reinforced. It is thus possible to take into account, for example, geometric variations of the structure and to preferentially reinforce certain zones of the structure, to distribute stresses between the reinforcement and certain zones of the structure in a controlled manner. 
     The expression “reinforcement of elongated shape” is understood to mean a reinforcement that extends along a longitudinal direction. 
     In general, but not necessarily, the cross section perpendicular to the longitudinal axis of said reinforcement is substantially constant over the entire length of said reinforcement. 
     According to various embodiments, the reinforcement of elongated shape is chosen from a reinforcement in lamellar form, a reinforcement in rod form, a pultruded elongated reinforcement, an extruded elongated reinforcement. 
     The expression “reinforcement in lamellar form” is understood to mean a reinforcement that extends along a longitudinal direction and the cross section of which, perpendicular to said longitudinal direction, has an elongated shape, with one dimension, designated the width, significantly greater than the other dimension, designated the thickness. By way of example, the width is greater than or equal to ten times the thickness, for example greater than or equal to twenty times the thickness, or even greater than or equal to forty times the thickness. 
     By way of example, the thickness of such a reinforcement in lamellar form is greater than or equal to 0.5 mm, for example greater than or equal to 1 mm, in particular less than or equal to 5 mm. By way of example, the width of such a reinforcement is greater than or equal to 10 mm, for example greater than or equal to 50 mm and in general less than or equal to 500 mm, or even less than or equal to 200 mm. 
     By way of example, the length of such a reinforcement is greater than or equal to ten times its width; in particular it is greater than or equal to one meter and measures, for example, several meters. 
     The term “rod” is understood to mean a reinforcement of elongated shape, the cross section of which, perpendicular to the longitudinal direction, has the shape of a circle or of an ellipse. The largest dimension of this cross section is, for example, between 1 cm and 10 cm. 
     The cross section of elongated shape of a reinforcement of elongated shape is, for example, substantially constant over the entire length of the reinforcement. 
     A reinforcement of elongated shape is, in general, a straight reinforcement. It is also possible for the reinforcement of elongated shape to be curved or arched in the longitudinal direction, in general with a large radius of curvature. It is also possible to envision reinforcements of elongated shape with sinuosities in the longitudinal direction, provided, for example, in order to adapt to the geometry of a portion of the structure to be reinforced. 
     The reinforcement of elongated shape comprises continuous fibers, in general in continuity of material over the whole of the length of the reinforcement, combined with a polymer matrix. 
     Numerous fibers may be used for manufacturing such reinforcements such as, non-limitingly, carbon fibers, mineral fibers, such as for example glass fibers or basalt fibers, polymer fibers such as for example aramid fibers (known, for example, under the trade name KEVLAR®). 
     The fibers are generally positioned unidirectionally in the longitudinal direction of the reinforcement. It is also possible to manufacture reinforcements of elongated shape with fibers arranged in the form of woven fabrics, where a portion of the fibers is positioned in the longitudinal direction of the reinforcement and the other portion in a transverse direction. 
     The polymer matrix may be essentially constituted of a thermosetting polymer, such as for example an epoxy resin, or of a thermoplastic polymer. 
     Preferably, such a reinforcement is obtained by industrial techniques of composite production, such as for example pultrusion, extrusion or molding. 
     According to one embodiment, the polymer matrix is essentially constituted of a thermosetting polymer and the removal thereof is obtained by pyrolysis. The temperature conditions of the pyrolysis are determined so as to remove the thermosetting polymer while preserving the fibers, and especially their mechanical properties. 
     By way of example, the fibers are carbon fibers and the pyrolysis temperature is between 800° C. and 1500° C. The pyrolysis may be obtained, for example, by placing the portion of the reinforcement, where it is desired to remove the polymer matrix, in a furnace brought to the desired temperature, or according to another embodiment by directing a blowpipe toward this portion of the reinforcement. 
     According to one embodiment, a portion of the reinforcement of elongated shape is cooled so as to limit the heat transfer due to the pyrolysis. Such cooling may, for example, be obtained by clamping a portion of the reinforcement of elongated shape in a cooled part or by spraying with a cold gas. 
     According to another embodiment, the step of removing the polymer matrix is obtained by selective chemical dissolution of the matrix. 
     According to various embodiments which may be combined together in accordance with all the combinations that can be envisioned:
         a portion of the reinforcement where the polymer matrix has been removed is positioned at one end of said reinforcement;   a portion of the reinforcement where the polymer matrix has been removed is positioned between the ends of said reinforcement;   the rearrangement of the fibers released from the polymer matrix consists in positioning and bonding these fibers to a portion of the structure to be reinforced; the fibers may then be positioned over the structure in all the desired directions and distributed judiciously in order to improve the binding with the structure in a desired portion of the latter; according to various embodiments, the fibers released are positioned in the form of a fan, some of the fibers are positioned going backwards relative to the direction they emerged in, they are positioned in the form of a spindle, they are positioned in the form of a “button”; this results in a local increase of the bonding surface area and/or the presence of a supplementary anchoring means; according to one embodiment, a portion of the structure is reinforced with two reinforcements of elongated shape that each comprise fibers released from their polymer matrix in one portion of each of the reinforcements and where the fibers of these reinforcement portions, released from their polymer matrix, are arranged by superposing them one on top of the other and they are bonded to the portion of the structure to be reinforced;   the rearrangement of the fibers released from the polymer matrix consists in positioning these fibers in a cavity; the fibers may be bonded or sealed into the cavity; the cavity may be a through-cavity and it is possible to make the fibers pass through the cavity and to make them reemerge in order, for example, to then bond them; the through-cavity may, for example, be part of an anchoring element which is added onto the structure to be reinforced;   the fibers of the reinforcement, released from the polymer matrix, are positioned in the form of a loop in a hole of an anchoring element.       

     According to one embodiment, the rearrangement of the fibers released from the polymer matrix of the reinforcement consists in positioning these fibers in a mold and in mixing them with a polymer matrix in order to form, by molding, a reinforcement portion of different shape to the initial shape of the reinforcement of elongated shape; a composite reinforcement portion is then reconstructed, having a shape different to the initial shape of the reinforcement. According to one example relating to this embodiment, the polymer matrix used for this molding is of similar or even identical composition to that of the initial polymer matrix of the reinforcement of elongated shape. This portion of the reinforcement may be bonded or sealed with the structure according to the desired configurations. According to various variants of this embodiment:
         the shape of the portion formed by molding has a more compact cross section than the initial cross section of the reinforcement of elongated shape;   the portion formed by molding is inserted into a portion of the structure to be reinforced and bound to this portion of the structure;   the binding of the portion formed by molding into the portion of the structure to be reinforced takes place according to one of the methods chosen from the list constituted of bonding, of pouring a mortar between the portion formed by molding and the portion of the structure in which it is inserted, of the insertion of the portion formed by molding during the fabrication, for example by pouring, of the portion of the structure to be reinforced;   the shape of the portion formed by molding is more flared than the initial shape of the reinforcement of elongated shape; according to one embodiment, the flared part formed by molding is bonded to a portion of the structure to be reinforced.       

     The present invention also targets a construction structure reinforced by a reinforcement bonded to at least one portion of said structure wherein the reinforcement comprises a portion of elongated shape comprising continuous fibers in the longitudinal direction of said reinforcement, combined with a polymer matrix, and a portion where fibers in continuity of material with the fibers of the portion of elongated shape are arranged in a different geometry from the fibers of the portion of elongated shape, for example bonded directly to a portion of the construction structure or, for example, positioned in a polymer matrix along a cross section different from that of the portion of elongated shape. 
     It goes without saying that all the features described above in relation to the process according to the invention find their application in the structure according to the invention and may be combined in order to illustrate various embodiments of a structure according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other particularities and advantages of the present invention will appear from the description below of non-limiting exemplary embodiments, with reference to the appended drawings in which: 
         FIG. 1  represents a schematic view of a device for removing the polymer matrix from a reinforcement of elongated shape; 
         FIGS. 2 to 6  illustrate various arrangements according to the invention, of fibers released from the polymer matrix and bonded to a portion of a structure to be reinforced; 
         FIG. 7  represents a schematic view of a device for molding a portion of reinforcement according to the invention; 
         FIGS. 8 to 10  illustrate various reinforcements obtained according to the invention comprising a molded reinforcement portion; 
         FIG. 11  illustrates one mode of reinforcing a structure. 
     
    
    
     For reasons of clarity, the dimensions of the various elements represented in these figures are not necessarily in proportion to their actual dimensions. In these figures, identical references correspond to identical elements. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  represents a schematic view of a device for reducing the polymer matrix of a reinforcement of elongated shape  10 , for example in lamellar form. The latter is introduced into a furnace  41  brought to a temperature suitable for leading to the pyrolysis of the polymer matrix of the reinforcement  10  while preserving the continuous fibers which are part of this reinforcement. In order to limit the zone of the reinforcement where the polymer matrix is removed, cooled parts  42  contact the reinforcement  10  near the furnace  41  and thus prevent the heat from transferring beyond a desired zone. The cooled parts  42  comprise, for example, cavities  43  in which a cold fluid  44  flows. 
     After having removed the polymer matrix with the above device, or any other suitable method, the fibers are rearranged in order to optimize the binding of the reinforcement  10  with a portion of the structure to be reinforced (not represented as such). 
     According to the embodiment from  FIG. 2 , the reinforcement  10  in the lamellar form has an initial width L 1 . The fibers are released from the polymer matrix in a zone  20  located at one end of the reinforcement  10  and positioned substantially in a fan so as to make it possible to obtain a great expansion of the fibers and a greater contact area for one and the same length as with the initial reinforcement in lamellar form. The width L 2  over which the fibers released from the matrix may extend may be, for example, five to ten times greater than L 1 . The fibers released from the matrix are bonded to a portion of the structure to be reinforced. 
     According to one variant represented in  FIG. 3 , the fibers released from the matrix are positioned in a zone  21 , partly backwards with respect to the direction from which they emerge from the reinforcement in lamellar form where the matrix is retained. 
     According to another variant, represented in  FIG. 4 , the reinforcement of elongated shape is a rod of circular cross section. The fibers are released from the matrix in one reinforcement zone located between two ends of this reinforcement and in one other, a reinforcement zone located at the end of said reinforcement. The fibers released between two ends are between an upstream portion  31  and a downstream portion  32  of the rod. The fibers released at the end are located beyond the downstream portion  32  of the rod. These fibers are rearranged in the form of “buttons”  35 ,  36 . The button  35  is formed by bringing the upstream portion  31  and downstream portion  32  closer together so as to form, for example, a ball or a flat cylinder. The button  36  is formed by rearranging the fibers released in the form of a ball or of a flat cylinder. It is noted that the fibers in zones  35 ,  36  could also adopt the shape of a spindle. 
     According to another variant, represented in  FIGS. 5   a  and  5   b , a reinforcement in lamellar form is positioned on a structure  45 . The fibers of this reinforcement are released from the polymer matrix in a zone  22 , located between an upstream reinforcement portion  11  and a downstream reinforcement portion  12 . These reinforcement portions may be bonded to the surface of the structure  45 . 
     The fibers from zone  22  are arranged as a spindle at the surface of the structure  45 . A hole  46  is made in the structure  45  so as to receive a rod  41 . The rod  41  may be held in the hole  46  by bonding, by introduction of a grout or any other suitable means. 
     The rod  41  is introduced into the hole  46  after having passed through the spindle-shaped fibers  22  of the reinforcement in lamellar form. 
     The fibers located at one end of this rod  41  are previously released from the polymer matrix. 
     These fibers  42 , located at one end of the polymer rod opposite the end of the rod which is placed in the hole  46 , are then positioned on top of the fibers  22  of the reinforcement in lamellar form. The fibers  22  and  42  are then firmly attached together, for example by bonding. It goes without saying that the fibers  42  may extend beyond the fibers  22 , and be positioned, for example, on the upstream portion  11  and downstream portion  12  of the reinforcement in lamellar form, and also at the surface of the structure  45 . 
     According to another variant represented in  FIG. 6 , two reinforcement zones  23 ,  24  where the fibers are released from their polymer matrix and located respectively between two ends  13 ,  14  and  15 ,  16  of these two reinforcements, are superposed. The released and superposed fibers are bonded to a portion of the structure to be reinforced thus making it possible to increase the strength of the bond in the crossover zone of the two reinforcements. 
     Tests have been carried out in accordance with one embodiment where use is made of a reinforcement in lamellar form of the FOREVA® LFC type, of width L 1 =50 mm, having a thickness of 1.2 mm and that is constituted of carbon fibers and of epoxy resin. It is determined that such a reinforcement makes it possible to take up a load over one portion of a concrete structure of the order of 2.5 tonnes when it is bonded to concrete over a length of 100 mm. It is determined that the bonding of a reinforcement to a portion of concrete structure, as illustrated in  FIG. 2 , where the fibers have been released from the matrix over a length of 100 mm and where L 2 =2L 1 , makes it possible to substantially double the load taken up by the reinforcement. 
     According to other embodiments, illustrated in  FIGS. 7 to 10 , the rearrangement of the fibers released from the polymer matrix of the reinforcement consists in positioning these fibers in a mold and in mixing them with a polymer matrix in order to form, by molding, a reinforcement portion  25 ,  26 ,  27 ,  28 ,  29  having a shape different from the initial shape of the reinforcement of elongated shape, for example in lamellar form,  17 ,  18 ,  19 . It is also possible to envision forming a reinforcement portion by mixing fibers released from the initial polymer matrix with a polymer matrix by any other forming method, other than molding, suitable for the manufacture or a composite portion, such as for example extrusion or pultrusion. 
       FIG. 7  represents a schematic view of a molding device  50  comprising a portion  51  that makes it possible to support a reinforcement in lamellar form  17  and a portion  52  comprising a cavity  53  into which the fibers of said reinforcement, previously released from the polymer matrix, are introduced. These fibers are placed in the cavity  53  and mixed with a polymer resin, for example having a composition similar to that of the polymer matrix of the reinforcement. 
     In the example represented, the cavity  53  is of substantially rectangular cross section; generally, its cross section and its shape are chosen so as to obtain the desired shape of the reinforcement portion having a shape different from the initial shape of the reinforcement of elongated shape. 
     After molding with the device  50 , a reinforcement is obtained, represented in  FIG. 8 , comprising a portion in lamellar form having a width L 1  and a thickness e 1 , and an intermediate zone  25  of length D where the fibers converge toward a parallelepipedal portion  26  of width L 3  and of thickness e 3 . In this embodiment, L 3  is substantially equal to e 3 . 
     The parallelepipedal portion  26  may advantageously then be placed in a cavity of the structure to be reinforced and be sealed therein, for example by bonding or by introduction of a mortar. The portion  17  in lamellar form may be bonded to another portion of the structure to be reinforced. 
     According to a variant represented in  FIG. 9 , the parallelepipedal portion  28  is inclined in a plane different from that of the portion  18  in lamellar form. It is thus advantageously possible to anchor this parallelepipedal portion  28  in a cavity inclined relative to an axis of reinforcement, so as, for example, to reinforce a beam over its length. 
     According to another embodiment represented in  FIG. 10 , the fibers previously released from the polymer matrix have been placed in a mold comprising a trapezoidal cavity that makes it possible to obtain a portion  29  where the fibers spread out in a direction perpendicular to the longitudinal direction so that this portion  29  is flatter and wider than the portion  19  in lamellar form. By way of example, the maximum width L 4  of this portion  29  is around two times greater than the width L 1  of the portion in lamellar form and its minimum thickness e 4  is two times smaller than the thickness e 1  of the portion in lamellar form. Such a widened portion  29  may be bonded to a portion of the structure to be reinforced so as to increase the load uptake in this portion of the structure. 
     It goes without saying that similar rearrangements may be obtained with reinforcements in rod form, or that have any other elongated shape.  FIG. 11  illustrates a schematic view of a method of reinforcement of a construction structure. 
     The structure comprises a buried portion  60  constituted of a foundation footing surmounted by a semi-buried wall  62 . A slab  63  is attached to the wall  62 . The wall  62  is surmounted by a wall  61  which emerges from the ground. By way of example, the foundation footing, the semi-buried wall and the slab are made of reinforced concrete and the wall  61  is made of masonry. 
     A vertical axis has been represented as a dotted line. By convention, it is said that this line limits the outer face of the walls  62  and  61  and that the opposite face of these walls is an internal face. 
     In the structure represented, the level of the slab  63  is below the external level of the ground so much so that the face  67  of the semi-buried wall  62  is accessible whereas the opposite face of this wall is buried. The portion of the semi-buried wall  62  located underneath the level of the slab  63  is completely buried, as is the foundation footing. 
     In order to reinforce this structure, a cavity  64  has been hollowed out at a slant in the wall  62  and the foundation footing. In the example represented, the cavity  64  is substantially cylindrical and may measure several meters in length and have a diameter of around a few tens of centimeters. 
     Placed in the cavity  64  next is an anchoring element  70  which comprises one end  71  through which rovings of reinforcing yarns may be threaded. The anchoring element  70  is sealed, for example with a grout of cement or mortar, or concrete by filling the cavity  64 . A reinforcement of elongated shape  80  is placed on the internal face  66  of the wall  61  and the internal face of the wall  62 . This reinforcement may be in lamellar form. It may comprise unidirectional fibers or a woven fabric of fibers. 
     The fibers of this reinforcement are previously released from their polymer matrix at one end, situated beyond the zone  81 . They are then positioned so that one portion of the fibers forms a roving. This roving is threaded into the end  71  of the anchoring element  70  before the latter is completely positioned in the cavity  64 , and therefore before it is sealed. The roving of reinforcing yarns forms a loop that passes through said cavity  64  and the roving reemerges from the cavity  64 . After positioning then sealing of the anchoring element  70  in the cavity  64 , the roving of reinforcing yarns is positioned, for example as a fan at the internal surface  67  of the wall  62  and/or on the reinforcement  80 . The yarns thus positioned are firmly attached, for example by bonding to the structure. The embodiments described in the patent application published under the reference FR 2 918 689 can be used within the context of the present invention, where a reinforcement of elongated shape is positioned on a portion of a structure and where a roving of reinforcing yarns is formed from said reinforcement by release from the polymer matrix. 
     It is thus possible to use the process according to the invention for reinforcing construction structures according to numerous configurations. 
     The invention is not limited to the embodiment types exemplified and should be interpreted in a manner that is nonlimiting and that encompasses any equivalent embodiment.