Description

COMPOSITE ROD REINFORCED BY A BRAIDED STRUCTURE WITH AXIAL REINFORCEMENT AND

PRODUCTION TECHNIQUE THEREOF

FIELD OF THE INVENTION

[1] The present invention refers to a composite rod reinforced by braided textile structures with axial reinforcement to replace steel on the reinforcement of concrete structures, allowing their monitoring, and production process thereof. The said production process consists on the simultaneous production of the braided structure and insertion of the axial reinforcement, comprising by high performance fibres and with conductive characteristics previously imbibed in a polymeric matrix.

[2] Hence, the present invention is applicable to the reinforcement of general concrete elements, with more emphasis on concrete elements subjected to aggressive environmental conditions, such as seaside environment.

BACKGROUND OF THE INVENTION

[3] Decades have passed since composite materials have been used for the first time in structural projects. The main purpose leans on the countless advantages that composite materials offer, namely, low weight associated to high stiffness and mechanical resistance, high moulding versatility according to the project necessities, high potential on costs efficiency (initial and maintenance costs), among others. Besides all these advantages, composite materials present high thermal and corrosion resistance that, when combined with the mechanical properties, origin composite materials extremely resistant used instead of conventional materials.

[4] In the scope of technical applications of textile materials, one of the areas that has raised more interest in the past years is their application on the reinforcement of matrixes, such as polymers, resulting on the textile reinforced composite materials.

[5] The application of textile materials on the reinforcement of polymeric matrixes, in the form of fibres, threads or fabric, has experienced significant developments in the past years, not only at industrial level but also at a technical- scientific level, due to their unique properties.

[6] Particularly in the construction industry, it can be verified that steel reinforced concrete structures are subjected to the action of aggressive agents that, due to physical and chemical actions, diminish the mechanical resistance of the structures during their service life, compromising their behaviour and durability. One of the main problems affecting steel reinforced concrete structures is the steel armour corrosion.

[7] Steel corrosion occurs due to carbonation or to the chloride ions action. Armour corrosion jeopardizes the performance of the reinforced concrete elements, leading to attain the Service Limit State or the Ultimate Limit State.

[8] In this type of application, composite materials appear as a suitable alternative to

conventional materials, minimizing the corrosion effects of armours.

[9] There are already documented processes where fibres are impregnated in resins to reinforce concrete structures. Document JP2001247636: Resin composition for fiber reinforcement, fiber-reinforced resin and method for reinforcing and repairing concrete structure using resin composition for fiber reinforcement, of 9 ^th March 2000, publishes a resin composition and the methodology of resin application to reinforce and repair concrete structures using fibres.

[10] On the other hand, specific fibres impregnated in resins allowing the reinforcement of plastic rods have already been described, as published in JP7026661: FRP bar and manufacture thereof of 13 ^th July 1993, disclosing the production procedure of plastic rods reinforced with carbon fibres, by braiding carbon fibres with carbon axial reinforcement. The production procedure comprehends two steps: the first one consists in the impregnation of the reinforcement fibres; the second step consists on the impregnation of the braided structure.

[11] Another solution to concrete reinforcement is presented on the document

JP2000240218: Concrete reinforcement member, of 22 ^nd February 1999, which discloses an element to reinforce and monitor concrete through an optical fibre with a protective film.

[12] Document RU2249085: Rod for concrete structures reinforcement and plant for its production, 3 ^rd December 2002, discloses a rod formed by fibre rovings impregnated in a polymeric matrix and its production procedure, by pultrusion, comprehending bobbins to supply the fibre rovings, tension disposals for the fibre rovings, heating cameras, resin bath, pulverization cameras and cutting mechanisms.

[13] The present invention differs from the ones presented on the production technique and on the materials used. The polymeric matrix used can be of any type physically and chemically compatible with the fibres to be used and with the production process. The braided structure fibres and its axial reinforcement can be of any type compatible with the production process, according to the properties required for the rod to be produced. The axial reinforcement fibres to be used will allow the monitoring of the rod's tensile status and consequently of the structure in which it is integrated, being any type of piezoelectric or piezoresistant fibres, thus meaning conductive or semi- conductive fibres. In piezoelectric and piezoresistant fibres, charge or electric power exchange varies with tensile or compression forces applied.

[14] The application of fibres with these features allows identifying the rod's tensile status and consequently the tensile status applied on the concrete structure. The ability to monitor the rod's tensile status and structure it is inserted in, allows the constant assessment of the structure's behaviour throughout its service life, enabling the previous identification of eventual end of life and supplying indispensable technical data for the correct reinforcement of the structures.

BRIEF DESCRIPTION OF THE FIGURES

[15] Fig. 1: Schematic representation of the composite rod reinforced by a braided textile structure, with axial reinforcement, and its production procedure.

Fig. 2: Schematic representation of an example of a composite rod according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[16] The present invention refers to a composite rod reinforced by a braided textile structure, with axial reinforcement, based on the concept of multifunctional structures, where different types of fibres are used in different parts of the rod, according to mechanical and physical requirements. These rods allow a rational distribution of the several types of fibre used, optimizing their use, guarantying the required performance and contributing to reduce the costs associated with the rod production.

[17] The present invention is characterized in that it presents in its triaxil braiding production technique, a vat (B) coupled to the braiding machine (A), allowing the impregnation of the axial reinforcement fibres in the polymeric matrix, immediately before the braiding production.

[18] This composite rod performs two simultaneous functions, reinforcement and monitoring, contributing to the minimization of the reinforced concrete structures degradation.

[19] The 'multifunctional structure' concept of the invention, includes the existence of different parts of the rod with different types of fibres, is possible due to the technology used for the rod production.

[20] This technology, braiding, allows the braid production with several geometries, namely different braiding angles function of the number of bobbins used, the position of the former ring of the braiding point and the drawing rate. If the number of bobbins used, the position of the former ring of the braiding point and the draw rate are properly programmed, the braiding angle and diameter can be controlled. The direction of braiding is flexible, and may be horizontal, vertical, from the bottom to top or in reverse.

[21] When an axial reinforcement is required in the braided structure , a system of axial reinforcement fibres may be introduced, thus producing a triaxial structure fibre- oriented at zero degrees in relation to the rotational axis of the braiding equipment.

[22] The braiding comprises a group of fibres which are usually divided along de braiding machine in a symmetric way, thus conceiving a braiding element presenting half of the fibres in one angle and the other half in the symmetrical angle. So being, the triaxial structure is conceived with braiding fibres, with two symmetrical angles and with the axial reinforcement fibres.

[23] If a thicker structure is necessary, several layers may be braided, one above the other or the quantity of fibres in longitudinal reinforcement may be increased, thus producing a thicker braided element - this procedure is called 'overbraiding'.

[24] In practical terms, the insertion of different types of fibre is made through the braiding machine (A) bobbins and through the supply of axial reinforcement fibres.

[25] To produce a composite rod, simultaneously to the production of the braided structure, the previous impregnation of the axial reinforcement fibers system, oriented at zero degrees in relation to the rotational axis of the braiding equipment, takes place.

[26] There are two features presented by the composite rod: reinforcement of concrete elements and monitoring of stress-strain stages of the reinforced concrete element.

[27] On the composite rods reinforced by braided structures with axial reinforcement, three different components may be pointed out.

[28] Hence, there is component (1), which comprises the braided structure, which is responsible for the maintenance of the correct position of the axial reinforcement fibres and, due to the ability to produce ribbed braided structures, for the propitious conditions to maximize adherence tensions between the rod and the surrounding concrete.

[29] Component (2) consists on the braided structure comprises axial reinforcement fibres of the braided structure which is responsible for the mechanical behaviour of the rod. This component is also responsible for the conductive properties of the composite rod.

[30] Component (3) comprises the polymeric matrix and is responsible for the correct distribution of stresses between the different elements that constitute the axial reinforced braided structure.

[31] According to the schematic representation of the production (Fig. 1), the production process of the rod occurs in a single step.

[32] The ribbed braided structure is produced through the use of bobbins with fibre rovings with different linear densities and the braiding's resin impregnation process occurs through the previous impregnation of the axial reinforcement fibres. Therefore, when the resin is confined to the web of the braided structure, it tends to involve the braided structure fibres and the impregnation occurs from the inside out of the structure guarantying the total impregnation of the axial reinforced braided structure, avoiding discontinuities on the material to be produced.

[33] Hence, simultaneously to the production of the braided structure in the braiding machine (A), the impregnation of the axial reinforcement fibres occurs immediately before their introduction in the system, through the use of a vat (B) coupled to the braiding machine.

[34] The vat (B), coupled to the braiding machine and containing the polymeric matrix, is responsible for the simultaneous impregnation to the triaxial braiding process, endowing the production process of a single step.

[35] The composite rod thus produced may present several modifications regarding geometry and the type of fibre used in the braided structure, the type of fibre used in the axial reinforcement of the braided structure and to the type of polymeric matrix

used to be reinforced by the axial reinforced braided structure.

[36] It what concerns the Relatively to the braided structure geometry, the rods may be produced with several braiding angles, diameters and rib configurations, through the use of different numbers of bobbins with several fibre rovings with different linear densities. The braided structure may also be produced with several types of fibre. The fibre used as axial reinforcement of the braided structure can be of several types as well as the polymeric matrix to be reinforced.

[37] The definition and implementation of these parameters allow the production of several types of composite rods reinforced by braided structures with axial reinforcement, maximizing the rational use of materials regarding the specifications of the concrete structure to reinforce.

[38] In a preferred embodiment, the rod according to the invention comprises: braided structure (1) produced with eight bobbins of polyester fibre (two of them comprising 4 yarns); axial reinforcement of the braided structure (2) in glass fibre, carbon fibre, polyethylene fibre, sisal fibre or simultaneous use of different types of fibres; and a polymeric matrix (3) such as vinyl ester resin.

[39] Table 1 - Axial reinforced braided structure (type of fibre, linear density and number of roving s/filaments used) and polymeric matrix.

[40] Table 2 - Mechanical properties of composite rods reinforced by braided structure with axial reinforcement.