GB2193679A - Concrete pipes - Google Patents

Abstract

A reinforced cast concrete pipe (10) has a collar (12) which is located lowermost in the mould during casting, and a water bar (15) which extends continuously around the collar to prevent seepage of water or other liquid along the concrete/collar interface (14). The water bar is of elongate cross-section to present opposing surfaces to be gripped by the concrete with a locking or bonding effect. The water bar is angled to the horizontal to encourage the upward flow of air during casting and prevent entrapment of air pockets under the water bar. <IMAGE>

Description

SPECIFICATION Concrete pipes This invention relates to a concrete pipe of the kind which is cast with the axis of the pipe in a vertical plane, having a projecting collar anchored to one end of the pipe, which collar is located lowermost in the mould during casting, and which is provided with water bar means where the collar is contiguous with the pipe and a concrete/collar interface is formed, the water bar means extending continuously around the collar to prevent seepage of water or other liquid along the interface.

One consideration in making cast concrete products is the shrinkage effect of the concrete as it hardens. In making pipes of the kind described above, what tends to happen is that the shrinkage of the concrete causes the pipe to separate from the collar at the concretejcollar interface. Indeed, the water bar in these pipes is needed for preventing seepage of water or other liquid along the path created by this separation. Water bars in conventional pipes with steel collars are just simple round or rectangular steel strips which are welded round the collar. However, the water bars in these conventional pipes have little ability to counter the effect of shrinkage of the concrete or improve the watertightness of the collar joint.

The present invention provides a concrete pipe of the kind which is cast with the axis of the pipe in a vertical plane, having a projecting collar anchored to one end of the pipe, which collar is located lowermost in the mould during casting, and which is provided with water bar means where the collar is contiguous with the pipe and a concrete/collar interface is formed, the water bar means extending continuously around the collar to prevent seepage of water or other liquid along the interface, in which the water bar means has an elongate cross-section and is arranged extending away from the collar into the concrete, the water bar means presenting opposing surfaces to be gripped by the concrete with a locking or bonding effect, and in which the lower of the two opposing surfaces, as considered when the pipe is being cast, is shaped so that it extends away from the collar higher than or progressively higher than the horizontal whereby to encourage the upward flow of air during the casting process and prevent the entrapment of air pockets under the water bar means.

In the preferred embodiment, the lower of the two opposing surfaces is frusto-conical, slanting upwardly away from the collar, and the water bar means conveniently comprises a flange of rectangular cross-section.

The pipe may be a so-called jacking pipe and include reinforcement, such as a steel cage.

The collar on the pipe will usually be an external sleeve for engagement by a spigotted end of the next pipe in a butt joint, with an elastomeric ring to form a flexible joint. The collar will usually be of steel.

The water bar means is preferably spaced adjacent to the upper end of the collar where a greater body of concrete is defined between the water bar means, the collar and the potential shrinkage fracture plane of the concrete. This helps to improve the resistance of the finished structure to fracture, which would lead to loss of watertightness.

The collar is preferably anchored to the end of the pipe by means of a plurality of lugs which extend away from the collar into the concrete, the lugs being connected both to the collar and to the water bar means. In the preferred embodiment, the water bar means is provided in a plurality of sections, each section extending between adjacent lugs and being attached continuously both to the lugs and the collar helping to form a strong, integrated structure, and providing convenience and economy of fabrication.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a sectional view showing a detail of a concrete pipe according to the invention.

In Figure 1 there is seen part of one end of a concrete pipe 10. In this case, the pipe 10 is a so-called jacking pipe which is reinforced by means of a steel cage 11. Of course, the pipe 10 may have no reinforcement or be reinforced by other means such as fibre rovings.

On the end of the pipe 10 there is anchored a collar 12. The collar 12 here is of mild steel, but other materials, e.g. plastics may be used.

With the collar 12, the pipe 10 can be buttjointed to a spigotted end of the.next pipe, usually with an elastomeric ring to form a flexible joint. The collar 12 is anchored on the end of the pipe 10 by means of a plurality of lugs 13 attached to the inside of the collar and extending into the concrete. The lugs 13 here are conveniently of mild steel and are welded to the collar 12. The pipe 10 shown in figure 1 is made in a vertical casting process in which the collar 12 is situated at the bottom of the mould, i.e, with the pipe oriented as shown in Figure 1.

The water bar for the pipe 10 shown in Figure 1 is provided at the interface 14 in the form of a flange 15 extending from its root at the collar 12 into the concrete. The flange 15 here is conveniently of steel and is attached at its root to the collar 12 by welding. For convenience and economy of fabrication, the flange 15 is provided in a plurality of sections, each fitting between adjacent lugs 13 and each being attached with a continuous weld 18 to both the collar and the lugs 13. The result is a strong, integrated structure.

The flange 15 has an elongate cross-sec tion, which in this case is rectangular, and presents a pair of opposing surfaces 16 and 17. The longitudinal dimension of the crosssection of the flange 15 is several times greater than the lateral dimension, the preferred ratio being typically 5:1. The surface area of the two opposing surfaces 16 and 17 takes up a substantial proportion of the total surface area of the flange 15 which is embedded in concrete. In the specific example mentioned, 10/11 of the total surface area is taken up by the opposing surfaces 16 and 17.

The purpose of this is to make use of a known property of concrete, which is that when two opposing surfaces are embedded in concrete, a locking or bonding effect is achieved because the opposing surfaces are actually gripped by the concrete. Here, a substantial proportion of the surface area of the flange 15 is taken up by the two opposing surfaces 16 and 17, so the locking or bonding effect is considerable when compared with a conventional round or square water bar, for example. It will be appreciated that the inner surface 19 of the flange 15 does not contribute towards the locking or bonding effect because this has no opposing counterpart embedded in the concrete. The water bar, therefore, is designed with an elongate cross-section so that the embedded surface area not given up to the two opposing surfaces, and thus not contributing to the locking or bonding effect, is kept small.

Also, as will be seen in Figure 1, the flange 15 is arranged to extend away from the collar 12 at an upward slant. The lower opposing surface 17 of the flange 15 therefore has the contour of a frustrum of a cone. The purpose of this is to encourage the upward flow of air during the casting process, after the concrete has been poured and whilst it is being compacted by vibration. There is therefore little risk of the entrapment of pockets of air under the flange 15. The entrapment of air pockets is a flaw common to conventional water bar designs; it is undesirable because it means there is effectively less opposing surface area embedded in concrete, which means there is less of a locking or bonding effect and the joint is weaker and less watertight.

It is of course possible to deviate from the slanting rectangular-sectioned water bar design described above. It is not essential for the opposing surfaces to be parailel, for example, or planar. Nor is it essential that the two surfaces are alike. To encourage the upward flow of air during casting, however, it is important that the lower of the two opposing surfaces is shaped to extend from its root at the collar higher than (e.g slanting upwardly) or progressively higher than (e.g curving upwardly) the horizontal.

The water bar in the pipe 10 shown in Figure 1 is located adjacent to, but not at the upper end of the collar 12. The reason for being adjacent can be understood from a consideration of the potential mode of shrinkage failure of the concrete. Dotted line 20 indicates the potential fracture plane. It will be seen that between the collar 12, the water bar 15 and the potential fracture plane 20 there is a relatively substantial body of concrete 21. The volume of this body of concrete 21 is sufficiently large to be'able to contain a significant amount of relatively large sized aggregate. This means that the body of concrete is effective to contribute towards the strength of the structure and resist failure along the potential fracture plane 20. If a water bar similar to the flange 15 were to be located further down the collar 12, it will be seen that there would be a far less substantial body of concrete 21 below the potential fracture plane 20 to resist fracture. On the other hand, if the flange 15 were to be located right at the end of the collar 12, the joint between the flange and collar would be exposed to the corrosive conditions which surround the pipe in use.

The angle of slant of the water bar 15 and anchoring lugs may typically be 37 to the horizontal base of the casting. The collar 12 shown in Figure 1 has a chamfered lower end and a plain upper end to its bore. The lower chamfered end is to facilitate butt-jointing to the next pipe. The upper end may also have a chamfer.

Claims (7)

1. A concrete pipe of the kind which is cast with the axis of the pipe in a vertical plane, having a projecting collar anchored to one end of the pipe, which collar is located lowermost in the mould during casting, and which is provided with water bar means where the collar is contiguous with the pipe and a concrete/collar interface is formed, the water bar means extending continuously around the collar to prevent seepage of water or other liquid along the interface, in which the water bar means has an elongate cross-section and is arranged extending away from the collar into the concrete, the water bar means presenting opposing surfaces to be gripped by the concrete with a locking or bonding effect, and in which the lower of the two opposing surfaces, as considered when the pipe is being cast, is shaped so that it extends away from the collar higher than or progressively higher than the horizontal whereby to encourage the upward flow of air during the casting process and prevent the entrapment of air pockets under the water bar means.

2. A concrete pipe as claimed in claim 1 wherein the lower of the two opposing surfaces is frusto-conical, slanting upwardly away from the collar.

3. A concrete pipe as claimed in claim 1 or claim 2 wherein the water bar means comprises a flange of rectangular cross-section.

4. A concrete pipe as claimed in claim 1, claim 2 or claim 3 wherein the water bar means is spaced adjacent to the upper end of the collar where a greater body of concrete is defined between the collar, the water bar means and the potential fracture plane of the pipe.

5. A concrete pipe as claimed in any preceding claim wherein the collar is anchored to the end of the pipe by means of a plurality of lugs extending away from the collar into the concrete, the lugs being connected both to the collar and to the water bar means

6. A concrete pipe as claimed in claim 5 wherein the water bar means is provided in a plurality of sections, each section extending between adjacent lugs and being attached continuously both to the lugs and to the collar.

7. A concrete pipe substantially as hereinbefore described with reference to the accompanying drawings.