AU2010201208A1

AU2010201208A1 - Tie bar conduit

Info

Publication number: AU2010201208A1
Application number: AU2010201208A
Authority: AU
Inventors: David Packer; Christopher John Taylor
Original assignee: BAULDERSTONE Pty Ltd
Current assignee: BAULDERSTONE Pty Ltd
Priority date: 2009-03-25
Filing date: 2010-03-25
Publication date: 2010-10-14

Description

P/00/01i1 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Tie bar conduit The following statement is a full description of this invention, including the best method of performing it known to us: 2 Tie Bar Conduit Field of the invention This invention relates to a conduit for receiving a tie bar used for joining together formwork for forming concrete structures. In particular, the conduit of the invention is of 5 the type that enables the tie bar to be removed from the concrete after the concrete has set. Background of the invention Conduits for receiving tie bars which hold together formwork panels used in the construction of concrete panels usually serve two purposes. Firstly they provide a 10 channels in which the tie bars are housed, and after the concrete is set the formwork can be stripped by removing the tie bars from the conduits to allow the panels to be peeled away from the formed concrete. Secondly, the conduits serve as spacers for spacing the formwork panels a predetermined distance apart from each other, the distance being defined by the length of the conduits. 15 Typically conduits have comprised a length of plastic tubing which is square cut to the required length and serves the aforementioned purposes reasonably satisfactorily. A cone shaped end cap is provided at opposite ends of the tubing which, after the concrete has set, is removed, resulting in a cone shaped recess in the concrete surrounding the tubing. This recess is typically filled with a special sealant after the 20 formwork has been stripped from the concrete. One problem, however, occurs due to the fact that concrete bonds very poorly to the plastic tubing. This results in the concrete surrounding the conduit to separate from the conduit as the concrete cures, creating a small annular water flow passage around the outside of the conduit. Since concrete is often exposed to the elements, if the conical 25 recess is not properly sealed, rainwater or other moisture will tend to percolate or travel along this annular flow passage into the interstices of the panel where it can come into contact with reinforcing in the panel.

3 Concrete structures and panels are usually reinforced with steel reinforcing. Typically concrete structures are formed by first placing the reinforcing in position, then erecting the formwork panels around the reinforcing, and thereafter pouring concrete into the space between the formwork panels. Frequently the reinforcing bars are in contact with 5 the tie bar conduits prior to the concrete being poured. When the concrete has set, and the aforementioned water migration into the panel occurs along the interface between the conduits and the concrete, that water comes into contact with the reinforcing bars which are then subjected to rusting. This can, and does, compromise the strength of the reinforcing which can in turn lead to failure of the structure. Contractors attempt to 10 ensure that reinforcing bars do not contact the conduits, but that is not always possible to achieve. One way of reducing the problem is to take the trouble to ensure that the gap between the conduits and the concrete is properly sealed. Whilst this action will to a large extent solve the problem, the sealing of each tie bar hole is a time consuming and labour 15 intensive exercise and can be dangerous, since the tie bar holes are often located at elevated positions on the concrete structure. Also, quality assurance is not always possible, given the large numbers of tie bar holes in a typical large-scale concrete structure. Reference to any prior art in the specification is not, and should not be taken as, an 20 acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. Summary of the invention 25 According to an aspect of the invention there is provided a tie bar conduit for use with formwork to form a concrete panel, said conduit comprising: an elongate tubular body formed of a high strength plastic material and defining an internal passage for receiving a tie bar therethrough and having an external surface; 4 annular end flanges formed on the ends of the tubular body; wherein the external surface has a ribbed, threaded or corrugated configuration to increase the length of the water flow path from the outer face of a concrete panel along said external surface to reinforcement embedded within the concrete panel in use and 5 the end of the conduit has a lip formed thereon such that the tie bar is spaced from the internal surface of the passage during insertion and removal of the tie bar. Further there is provided for the conduit to include a pair of inner annular flanges inwards of the end flanges. The inner flanges may be spaced from the end flanges by a distance of between about 30 mm and 50 mm. The diameter of the internal passage 10 may be between about 30 mm and 50 mm. Optionally the external surface may be of a rough or abrasive texture to enhance the bond between the concrete and the conduit. The threads, corrugations or ribs may be of generally rectangular form in cross-section, having a height of between about 3 mm and 8 mm, and a width of between about 3 mm 15 and 8 mm. The length of the conduit may be selected to accord with the thickness of the panel to be formed using the conduit. According to another aspect of the invention there is provided a tie bar conduit comprising an elongate tubular body formed of a high strength plastic material, annular end flanges formed on the ends of the tubular body; and a moisture barrier means on 20 the outer surface of the body, inwards of the respective ends of the body, said moisture barrier means being adapted to be embedded within concrete in use to form a moisture barrier when so embedded to at least substantially prevent the ingress of moisture along the outer surface of the body into the interstices of the concrete. The moisture barrier means may comprise a pair of annular seals that in use absorb water. 25 The conduit may be formed from at least three components, including a pair of end components, and a central spacer component, the three components adapted to be coaxially joined together to form said tie bar conduit, the length of the central spacer component being selected to accord with the required length of conduit. Optionally the 5 components may be sealed together to ensure the conduit is fluid impervious along its length. These and further features of the invention will be made apparent from the description of an embodiment of the invention given below by way of example. In the description 5 reference is made to the accompanying drawings but the specific features shown in the drawings should not be construed as limiting on the invention. As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps. 1o Brief description of the drawings / figures Embodiments of the invention are described below with reference to the Figures, in which: Figure 1 shows a cross-sectional side view of an embodiment of the invention in use as part of a tie bar assembly; 15 Figure 2 shows a plan view of the conduit shown in Figure 1; Figure 3 shows a cross-sectional side view of the conduit along line A-A of Figure 2; Figure 4 shows a plan view of a conduit having sealing rings; and Figure 5 shows a cross-sectional side view of the conduit of Figure 4 along line A-A. Detailed description of the embodiments 20 As shown in the drawings, a tie bar conduit 10 has a hollow tubular body having ends 12 and 14 and an inner passage 16. The inner passage 16 is sized to receive a threaded tie bar 18 which extends out of both ends of the conduit as shown. The tie bar has a length sufficient to pass through formwork plates 20, vertical support struts 22, and cross braces 24. The tie bar 18 has squared ends 19 to enable the bar to be 6 gripped by a spanner. Spherical nuts 26 which bear against anchor plates 28 hold the two sides of the formwork together, and can be used to adjust the distance that the two formwork sides are apart from each other. A concrete panel to be formed between the two plates 20 will have a width defined by 5 the distance the two plates are apart from each other. This distance is the same as the length of the conduit, that is, the conduit is specifically selected to be the same as the intended width of the concrete panel to be formed. Reinforcing 30 is located midway between the plates 20, and the reinforcing will be embedded within the concrete in known manner. Once the formwork has been assembled as indicated in figure 1, 10 concrete is poured into the gap 32 between the plates 20, and thereafter allowed to set. Once set, one of the nuts 26 will be removed from the tie bar, and the tie bar will then be removed from the conduit 10, after which the formwork can be stripped. Turning to figures 2 and 3, the conduit is shown having an annular flange 34 on each of the ends 12 and 14. In use the plates 20 will bear against the outer face of the flanges 15 34, so that when each plate is hard up against the respective flange 34 the width of the concrete panel to be formed between the plates will be the same as the length of the conduit 10. This ensures that a precisely dimensioned panel will be formed using the conduit as a spacer. It is envisaged that the flanges 34 will have smooth outer end face 35 and a diameter approximately twice that of the intemal diameter of the conduit. Thus 20 if the internal diameter is 50 mm (to accommodate a 26.5 mm threaded tie bar), the diameter of the flanges 34 may be 100 mm. Other configurations are of course possible, for example, the tie bar may have a diameter in the range of 12mm to 20mm, the internal diameter of the conduit and the diameter of the flanges being changed appropriately. 25 It will be noted that the outer surface 36 of the conduit has a series of ribs or corrugations 38 thereon along the length of the conduit. These ribs 38 serve to extend the length of the flow path along which moisture will need to travel from the outer surface of the concrete panel into the centre of the panel. As mentioned above, a narrow annular passage around the conduit may be a flow path for moisture into the 30 interstices of the panel. By forming the ribs or corrugations on the surface of the conduit 7 the length of this flow path is increased significantly, thereby ensuring that there is a far greater resistance to moisture travel along this flow path, which should considerably reduce the problems referred to above. The ribs 38 preferably are of nearly square or rectangular cross sectional shape, as 5 shown. This is advantageous because moisture tends to resist travel around sharp corners, and the corners on the ribs will thus serve to further resist the ingress of moisture into the interstices of the panel. A pair of inner flanges 44 are formed approximately 40 mm inwards from the end flanges 34. The inner flanges, once again, form a significant extension to the length of 10 the flow passage along the outer surface of the conduit. The inner flanges 44 may have a diameter the same as or similar to the diameter of the end flanges 34. The inner flanges taper towards the radially outer edge thereof to facilitate formation of the conduit in an injection mould during manufacture. In the embodiment, reinforcing is approximately 75 mm from the face of the panel so as to provide sufficient concrete 15 cover for the reinforcing, and the inner flanges are located a distance less than 75 mm, thus ensuring that the moisture flow path is of significant length prior to coming into contact with the reinforcing 30. Typically, concrete cover to reinforcing is between 40mm and 100mm. In the embodiment shown, for forming a concrete panel of 350 mm thickness, the flow 20 path from the face of the panel to the reinforcing will be approximately 200 mm whereas, were the outer surface of the conduit to be smooth, the flow path would be approximately 75 mm long. It is envisaged that the outer surface 36 of the conduit will have a rough textured finish. The textured finish may be similar to that of course sandpaper, for example. The rough 25 textured finish will have the effect of ensuring the concrete bonds well to the conduit, thus reducing the gap between the concrete and the conduit. This will further reduce the capacity of moisture to travel along the flow path into the interstices of the concrete panel.

8 The end 12 of the conduit, which in use will be at the outer side of the formwork, has an inwardly-directed lip 46 formed thereon which serves as a spacer or guide for the tie bar 18. Typically the tie bar 18 is inserted into and removed from the conduit 12 from the outer side of the formwork, and the lip 46 serves to space the tie bar from the surface of 5 the passage 16 during insertion and removal, thus ensuring that this surface is not damaged. Damage could cause the rupturing of the conduit which in turn would allow the ingress of moisture into the interstices of the concrete panel from the passage 16. It is envisaged that the internal diameter of the lip 46 is about 1 mm larger than the external diameter of the tie bar with which the conduit is to be used. The lip 46 is 10 relatively thin so that on rotation of the tie bar into or out of the conduit the lip could be damaged somewhat without creating difficulty in inserting or removal of the tie bar. It is envisaged that the conduit will be formed of a high strength plastic material such as PVC, Nylon, UPC Grade U, or like material. This should ensure that the conduit lasts the life of the concrete panel without degrading or cracking. Materials of the 15 aforementioned type should have a lifespan of 100 years or more. The conduit need not be formed as a single unitary construction, as shown in the drawings. For example, it would be possible to form the conduit in say three components, that is a pair of end components, and a central spacer component. The components will, it is envisaged, fit together in an axially aligned end-to-end 20 arrangement. The length of the spacer will be selected to accord with the desired length of conduit. Thus, for example, where the panel is to be say 300 mm wide, the two end components may each be say 100 long, and the central component also 100 mm long, so that the overall length when the three components are joined together would be 300 mm. Those two end components could be used with a spacer component of 50 mm 25 long to form a conduit of 250 mm. A cooperatively stepped connection arrangement on the ends of the spacer and the corresponding end components will ensure the internal surface of the conduit is smooth. A suitable adhesive or other bonding agent will ensure the connection between the end components and the spacer will not inadvertently come apart, and will be fluid impervious.

9 Figure 4 shows an embodiment of the conduit 10 having an additional sealant applied to the exterior surface 36 of the conduit at one or more locations. In the depicted arrangement the sealant 50, 53 is applied to the conduit just inwardly of the end flanges 34. The sealant may also be applied at locations 51 and 52, ie in contact with the 5 flanges 44 on the face of the flange closest to the respective ends 12, 14. The sealants 50, 51, 52, 53 may each form a ring substantially filling a groove defined by a rib 38 and an adjacent flange 34, 44. An example of a suitable sealant is Leakmaster LV-1, which is a polyurethane water-swelling sealant that may, for example, be applied using a caulking gun. The sealant preferably has capacity to absorb water. 10 For example, the Leakmaster LV-1 polyurethane may swell up to approximately twice its original volume as a result of water absorption. The sealants 50, 51, 52, 53 thus provide a moisture barrier that assists in limiting ingress of water into the interior of the panel. There may be variations to the preferred embodiments without departing from the scope 15 of the invention. For example, the configuration of the outer surface of the conduit may differ from that described herein. It would be possible, for example, to have other forms of ribs, and other more effective forms of seal. The seal arrangement may, for example, be flexible, or made of a material different from the conduit. A softer plastic material is specifically envisaged. 20 In this specification reference is made to the construction of concrete panels. Of course the invention can be used with the construction of virtually any formed concrete structure, and thus the term "panel" should be construed broadly. Also, the term "concrete" is intended to cover any cementitious material with which the invention might be used. 25 It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. A tie bar conduit for use with formwork to form a concrete panel, said conduit comprising: an elongate tubular body formed of a high strength plastic material and defining 5 an internal passage for receiving a tie bar therethrough and having an external surface; annular end flanges formed on the ends of the tubular body; wherein the external surface has a ribbed, threaded or corrugated configuration to increase the length of a water flow path from an outer face of the concrete panel along 0 said external surface to reinforcement embedded within the concrete panel in use, and at least one end of the internal passage of the conduit has an inwardly-directed annular flange formed thereon such that the tie bar is spaced from an internal surface of the internal passage during insertion and removal of the tie bar.

2. The conduit of claim 1, wherein the conduit includes a pair of inner annular 15 flanges extending from the external surface and located inward of the end flanges.

3. The conduit of claim 2, wherein the inner flanges are spaced from the end flanges by a distance of between about 30 mm and 50 mm.

4. The conduit of any one of the preceding claims, wherein the diameter of the internal passage is between about 30 mm and 50 mm. 20

5. The conduit of any one of the preceding claims, wherein the inwardly-directed annular flange of the internal passage ensures the tie bar is centrally located in the passage.

6. The conduit of any one of the preceding claims, wherein the threads, corrugations or ribs have a generally rectangular form in cross section. 11

7. The conduit of any one of the preceding claims, wherein the external surface has a rough or abrasive texture to enhance the bond between the concrete and the conduit.

8. The conduit of any one of the preceding claims, wherein the threads, corrugations, or ribs have a height of between about 3 mm and 8 mm, and a width of 5 between about 3 mm and 8 mm.

9. The conduit of any one of the preceding claims, wherein a length of the conduit is selected to accord with a thickness of the panel to be formed using the conduit.

10. A tie bar conduit comprising: an elongate tubular body formed of a high strength plastic material defining an 10 internal passage for receiving a tie bar and having an outer surface; annular end flanges formed on the ends of the tubular body; a plurality of ribs to increase a length of a water-flow path from the annular end flanges along the outer surface; and moisture barrier means on the outer surface of the body, inwards of the 15 respective end flanges, said moisture barrier means being adapted to be embedded within concrete in use to form a moisture barrier when so embedded to at least substantially prevent the ingress of moisture along the outer surface of the body into the concrete,

11. The tie bar conduit of claim 10 wherein the moisture barrier means comprises at 20 least one pair of annular seals formed of a polyurethane material that in use absorbs water.

12. The conduit of claim 11, wherein the conduit is formed from at least three components, including: a pair of end components, and 12 a central spacer component, wherein the three components are adapted to be coaxially joined together to form said tie bar conduit, the length of the central spacer component being selected to accord with the required length of conduit. 5

13. The conduit of claim 12, wherein the components are sealed together to ensure the conduit is fluid impervious along its length.