WO2006001703A1

WO2006001703A1 - Reinforcement bars of composite material, surface pattern

Info

Publication number: WO2006001703A1
Application number: PCT/NO2005/000204
Authority: WO
Inventors: Arne Roger Hole; Rune Harald Gaarder
Original assignee: Exel Oyj
Priority date: 2004-06-23
Filing date: 2005-06-13
Publication date: 2006-01-05
Also published as: NO320965B1; NO20042649D0

Abstract

Reinforcing bar (8) of composite material, in particular intended to be used for the reinforcement of concrete, where the reinforcing bar (8), preferably of rectangular or square shape, may be formed in a forming process by pultruding, extrusion or moulding, or a combination of these, of continuous fibres and matrix (resin) in a one-line process or in combination with a second-line process and where the bar is made in the forming process with at least 50 % reinforcing fibres by weight and a matrix which impregnates the fibres through a bath, by spray injection or pressure. The surface of the reinforcing bar (8) is provided with a pattern in the form of a plurality of protrusions, whereby the angle (α) between the ground surface of the bar (8) and the flank of the individual protrusion is between 50° and 60°.

Description

Reinforcement bars of composite material, surface pattern

The present invention relates to reinforcing bars of composite material and in particular the surface pattern of such bars.

The reinforcing bar according to the invention may be formed in a forming process by pultruding, extrusion or moulding, or a combination of these, of continuous fibres and matrix (resin) in a one-line process or in combination with a second-line process. The bar is made in the forming process with at least 50% reinforcing fibres by weight and a matrix which impregnates the fibres through a bath, by spray injection or pressure.

Composite bars of the above type is used for the strengthening and stiffening of different products and constructions made of materials like metal, concrete, wood, plastics, stone, ceramic and combinations of these where sufficient bond between the bars and materials is required to achieve structural functionality and optimisation on slenderness, weight, size and cost. But this is often obtained on account of strength, stiffness or by becoming susceptible to oxidation such as steel and other metals causing problems with corrosion, discoloration and thereby loss of structural strength. In some cases where metals are used to strengthen or stiffening the products there are problems with elongation or variation in material physical behaviour that cause cracking or insufficient bond between the product's material and the strengthening elements, i.e. the reinforcing bars.

The reinforcing material according to the present invention is a continuous fibre and matrix composite often called FRP (Fibre Reinforced Polymer) which is being used in a variety of construction materials due to excellent and flexible physical material properties such as high specific strength, light weight, none or low electric conductivity, non-magnetic properties, high resistance against acids and chlorides or aggressive environments, as well as formability and shaping. As stated above, steel and metals in general are susceptible to oxidation which cause corrosion of and rust on ferrous metals due to hydroxides of iron and oxides from atmospheric oxygen in the presence of water. As long as the pH is maintained at high alkalinity (pH 12 - 14) and in combination with very good poured concrete quality, the steel keep passive leading. To low pH, low concrete quality, insufficient product quality, poor execution of work, or exposure to strong acid can cause penetration of the protecting concrete zone that should protect the steel reinforcement rebar, i.e. chlorine ions from salt contaminated aggregates, road salt, marine environmental, seawater, carbonisation, access to CO₂, access to oxygen, and moisture. Furthermore, conditions which may result in chemical deterioration of the concrete, i.e. by sulphate or acid attack, or mechanical deterioration of the concrete from freezing and thawing in a wet or moist condition, may in turn cause rust and corrosion of the steel reinforcement, cracking of the concrete and loss of structural strength. When the reinforcement start corroding (rusting), the ferrous oxide will expand and cracks are initiated in the concrete due to internal stresses caused by the rust. Concrete will fall off and the steel reinforcement bars will be exposed to the atmosphere and the environment that caused the corrosion process, the speed of the process will further increase and the structure will be loosing structural strength and may in worst case collapse. Controlling these parameters is difficult and substantial economical and structural problems for concrete structures is caused all over the world. Due to lack of other alternative strengthening materials, steel reinforcement bars often have been misused in concrete structures.

As stated above, composite reinforcement bars are previously known and have been used to a minor extent. Such known bars are, however, encumbered with a major disadvantage, namely that the bonding between the product's material (concrete) and the strengthening bar (FRP-bar) varies over the length of the bar. The fact that traditional bars are designed with a circular shape makes it difficult to provide the surface with the required roughness.

In the applicant's own WO 03/050364 is described a reinforcing composite bar where the bar is of a rectangular or preferably square shape with rounded corners, and where the bar under the manufacturing process is provided with a surface pattern or design comprising a multiplicity of depressions, dents or recesses formed in a texture.

With the present invention is provided a composite reinforcing bar with excellent bonding properties and where the required surface roughness is provided in a simple and cheap manner.

The invention is characterized in that the surface of the reinforcing bar is provided with a pattern in the form of a plurality of protrusions, whereby the angle, (α), between the basic surface of the bar and the flank of the individual protrusion is between 50° and 60°, as defined in the attached independent claim 1.

Dependent claims 2 - 10 define preferred embodyments of the invention.

The invention will be further described in the following by way of example and with reference to the drawings where,

Fig. 1 shows a schematic view of an apparatus by which a reinforcing bar according to the present invention may be manufactured,

Fig. 2 shows partly in perspective an example of a tool element according to the present invention by which the pattern on the surface of a reinforcing bar is made,

Fig. 3 a, b shows, in larger scale, an example of a tool according to the present invention with segments intended to be provided on endless conveyers as shown as shown in Fig. 1 , and where Fig. 3 a shows segment provided in a distance from the bar, and Fig. 3b shows the segments provided in contact with the bar,

Figs. 4 - 6 shows three-dimensional depictions of patterns with protrusions of different design,

Fig. 7 shows two-dimensional drawing with descriptions of geometry of a pattern with protrusions shown in Fig. 5,

Fig. 8 shows, in larger scale, the design of an individual protrusion in the form a cam, in cross section,

Fig. 9 shows the curves of the normal and shears strain relative to the angel of the flank of the cam. The present invention relates as stated above to a method for the manufacturing of reinforcing bars 8 of composite material, in particular intended to be used for the reinforcement and strengthening of concrete. The reinforcing bar 8, preferably being of rectangular or square shape, may be formed in a forming process by pultruding, extrusion or moulding, or a combination of these, of continuous fibres and matrix (resin) in a one-line process or in combination with a second-line process, as shown in Fig 1 , where the bar is made from fibres 2 which are drawn through a unit 1 where the matrix material is provided, and further through a forming and heating unit 3 and unit 4, including heating means (not further shown) where the bar 8 is formed, hardened or partly hardened. The bar is preferably made in the forming process on a continuous basis with at least 50% reinforcing fibres by weight and with a matrix (resin mixture) which impregnates the fibres through a bath, by spray injection or pressure. The temperature inside unit 3 shall be between 90-250 ⁰C and the temperature inside unit 4 shall be between 120-250 ⁰C.

By one method of production of reinforcing bars according to the present invention, the surface of the reinforcing bar 8, after being hardened or essentially being hardened, is provided with or coated with a resin or adhesive whereby a pattern in the form of a plurality of protrusions is provided or imprinted in the adhesive on the surface of the bar 8 by means of a tool 5, as shown in Fig. 2, with grooves or recesses 6 corresponding to the design of the wanted shape of the protrusions. It is of vital importance that the tool 5 is pressed against the surface of the reinforcing bar until the adhesive is hardened or essentially hardened.

The tool as shown in Fig. 2 may be provided on endless conveyors 9, in an imprinting and heatingunit 4 (see Fig. 1) on each side of the reinforcing bar being produced, whereby the reinforcing bar is pulled between the conveyors 9 such that the tools 5 are pressed against the surface of the bar 8 by means of the conveyors. Preferably, the tools 5 when being provided on endless conveyors 9, may be in the form of individual segments 7, as is shown in Fig 3 a, b and Fig. 4 and Fig. 5, being made from aluminium or other metals, special high temperature resistant polymer materials, or ceramic materials. The tools 5 are as stated above pressed against the surface of the bar until the adhesive or resin is hardened, and the tool is then removed or retracted from the bar. To reduce sticking or avoid that the tool is sticking to the surface of reinforcing bar after hardening of the adhesive, the surface of the tool may be provided with a non-sticking coating such as Teflon®.

As is shown in Fig. 3 the segments 7 may be in the form of angularly shaped elements with the required or wanted patterns provided on each arm 10, 11 of the element. The two elements 7 may each be provided on diametrically placed conveyors 9, whereby the elements, when making the pattern on a reinforcing bar, are forced against the surface of the reinforcing bar 8. An option may be to supply the adhesive initially on the surface of the tool 5, whereby the adhesive is provided on to the surface of the reinforcing bar 8 and the pattern is formed in one operation by pressing the tool against the reinforcing bar.

It should be stressed that the pattern formed on a reinforcing bar as described above by initially providing a resin on the surface and then forming the pattern by a pressing tool against the surface of the bar is just an option. The pattern may as well be formed under the forming of the bar as such, without using additional resin, for instance by pressing a tool against the surface under the hardening operation of the bar.

Fig. 4 - 6 shows patterns with different designs of protrusions being formed on the surface of a reinforcing bar 8 according to the invention. As is shown in Figs. 4 - 6 the protrusions may be in the form of semi spherical knobs 12, they may be in the form semi oval cams 13, or they may be in the form of cams 14 with a length covering the total or basically the total width of one side of the bar 8, or if the bar is of circular shape, being continuous around the bar.

Fig. 7 shows a two-dimensional sketch of a pattern with individual cams as is shown in perspective in Fig. 5. The letter "cl" and "ct" represents the distance between the cams in longitudinal and transverse direction of the bar length, "a" represents the length of each cam, "h" represents the height of each cam, "b" represents the width of each cam, and "r" represents the radii of curvature for eiipsoidical shape of the cam, "R" represents the radii of curvature for the arc of the circle segment that defines the height of each cam, "r"' represents the hollow key between the bar surface and the cam, "h"' represents the height of the cut spherical segment. To obtain good bonding properties between the bar and the concrete, tests have proven that the cam height "h" should be 0,03 - 0,06 of the bar diameter or bar tickness, however minimum 0,4 and maximum 1 ,2 mm, the width "b" should be between 0,8 - 1 ,25 of "h", the length "a" of the cams should be 1 ,0 - 1 ,2 of the width "b", and the distance "ct" between the cams (from centre to centre) in transverse direction should be 1 ,2 - 2,0 of the width "b" and in the distance "cl" between the cams (from centre to centre) in longitudinal direction should be 1 ,2 - 2,0 of the length "a". The spherical segment cams can be cut at a height "h"' and should be between 0,8-0,9 of "h". Further the relative cam area projected in the longitudinal direction or in the transverse direction should be 0,1 - 0,25 and the ground are of the cam should be 0,4 - 0,6.

The crucial design of the protrusions according to the invention is, however, the angel, "α" between the bar surface and the flank of the protrusion (cam or knob etc.) as is shown in Fig. 7 and Fig. 8. In particular on reinforcing bars made of composite material (polymer and fibre), the strength of the protrusions in the area between the protrusion and the bar surface, i.e. the ground section area, the materials ability to withstand stress or strain due to bending is rather poor since the protrusions may contain minor or small amounts of fibres. On the other hand, the protrusions may withstand high shear forces, and based on calculations and tests it is fund that the angel, α, should preferably be between 50° - 60°. Optimally, the angel, α, should be about 53°. Fig. 9 shows, based on calculations, curves of the normal, σ, and shear strain, T, in the ground section area between a protrusion and the surface of a bar relative to the flank angel, α. As is shown by the black, dotted line in Fig. 9, the shear strain is close to zero with a flank angel, α, at 53°, and between 50° and 60° the shear strain is rather low. Another important feature of the invention is the design of the concave moulding curvature between the surface of the bar and the individual protrusion, which should be concave or fluted with a radii "r".

Claims

1. Reinforcing bar (8) of composite material, in particular intended to be used for the reinforcement of concrete, where the reinforcing bar (8), preferably of rectangular or square shape, may be formed in a forming process by pultruding, extrusion or moulding, or a combination of these, of continuous fibres and matrix (resin) in a one-line process or in combination with a second-line process and where the bar is made in the forming process with at least 50% reinforcing fibres by weight and a matrix which impregnates the fibres through a bath, by spray injection or pressure characterised in that the surface of the reinforcing bar (8) is provided with a pattern in the form of a plurality of protrusions, whereby the angle (α) between the basic surface of the bar (8) and the flank of the individual protrusion is between 50° and 60°.

2. A bar in accordance with claim 1 , characterised in that the angel (α) between the basic surface of the bar (8) and the flank of the individual protrusion is 53°.

3. A bar in accordance with claims 1 and 2, characterised in that the protrusions are in the form of knobs or cams with semi-spherical or semi- eliptoidal shape.

4. A bar in accordance with claim 1 - 3, characterised in that the cam height (h) should be 0,03 - 0,06 of the bar diameter or bar thickness, but as minimum 0,4 and maximum 1 ,2 mm.

5. A bar in accordance with claims 1 -3 characterised in that the width (b) should be between 0,8 - 1 ,25 of the height (h).

6. A bar in accordance with claim 1 - 3, characterised in that the length (a) of the cams should be 1 ,0 - 1 ,2 of the width (b).

7. Bar in accordance with claims 1 - 3, characterised in that distance (ct) between the cams (from centre to centre) in both directions should be 1,0 -2,0 of the width (b)

8. Bar in accordance with claims 1 -3, characterised in that distance (cl) between the cams (from centre to centre) in both directions should be 1,0 -2,0 of the width (a)

9. Bar in accordance with claims 1 - 3, characterised in that the hight (h¹) for cutted cams hould be 0,8-0,9 of the cam hight (h)

10. Bar in accordance with claims 1 - 3, characterised in that the relative cam area projected in the longitudinal direction or in the transverse direction should be 0,1 - 0,25 mm², and the relative ground area of the cam should be between 0,4 - 0,6.