GB2400382A - Apparatus and method for casting concrete headwalls - Google Patents

Abstract

A mould for casting a concrete headwall is formed from plastics and defines the shape of the headwall ( e.g. sides 14, 26, rear wall 12, base 18 and pipe outlet 20) and an aperture for receiving concrete and an inner void for filling with concrete. This inner void may contain reinforcing rods 46 borne on supports 47, and ground anchors passing through the mould or a toe at its rear base may assist in securing the mould in place. Part of the mould may be removable to expose the concrete, and for re-use. Removable inserts may cater for different pipe diameters; the mould may be finished to resemble brick - or stone - work. A method of making the headwall by casting concrete in the mould is claimed, as is the product headwall.

Description

APPARATUS AND METHOD FOR CASTING CONCRETE HEADWALLS

This invention relates to apparatus and a method for casting concrete headwalls.

Background to the Invention

A concrete headwall (also known as a pipe outfall) is a common civil engineering structure used to support the end of a water or sewage pipe at the site of discharge. The headwall is typically formed of reinforced concrete and is located in a riverbank or alongside a ditch, stream or another such watercourse into which the pipe discharges.

Traditional concrete headwalls are heavily time consuming and labour intensive to construct, typically taking 15 days or longer. The traditional construction procedure involves assembling a mould in situ using wooden shutters (typically plywood boards), which is then filled with concrete. This assembly of the mould and the introduction of the concrete is done in two principal stages: firstly the base of the headwall is defined using shutters and then filled with concrete; and then secondly the vertical walls are prepared with further shutters and more concrete is added. Reinforcing steel may be added before the second stage if required. After the concrete has cured, the wooden shutters are then removed.

Traditionally, many defined stages need to be completed in order and in situ in order to complete the construction of the headwall. Numerous consultants, tradespeople and plant equipment are required, due to the nature of the reinforced concrete. The construction procedure is lengthy and requires skilled personnel, and is therefore expensive both in terms of time and employment costs. The overall construction procedure is typically as follows: Day 1: Dewater area (if applicable); excavate & lay blinding concrete (overnight cure) Day 2: Add reinforcing steel; assemble shutters to define the base and kicker of the headwall Day 3: Q.A. (quality assurance) check; place concrete into shutters; finish Day 4: Cure Day 5: Strip shutters; scabble kicker (i.e. expose aggregate in the concrete base, to enable subsequent vertical concrete sections to bind) Day 6: Add shutters to define the vertical walls of the headwall Day 7: Q.A. check; place concrete into shutters; finish Day 8: Cure Day 9: Cure Day 10: Strip shutters (i.e. remove all the wooden boards and props) Day 11: Cure Day 12: Cure Day 13: Cure Day 14: Cure Day 15: Backfill (with soil etc.) and grade (depending on site conditions and structural loading); add attachments (although in many cases resin or friction anchor fixings can only be applied once the concrete has cured for at least seven days) Day 16: Stop Prior to starting construction, a large quantity of plant and materials need to be delivered to the construction site. After the headwall has been completed many materials (including the shutters) then need to be taken away again. Both these stages of transportation add to the cost of the whole project.

It is desired to expedite and simplify the construction of a concrete headwall, and to reduce the associated costs (e.g. the labour and transport costs).

Once finished, a traditional concrete headwall may be regarded as aesthetically unpleasing, particularly if it is prominent in an otherwise green and pleasant location such as a riverbank.

The appearance of a traditional concrete headwall can often substantially deteriorate with time, as it is susceptible to weathering and erosion.

It is a general object of the present invention to overcome or at least mitigate at least some of the problems, shortcomings and disadvantages associated with traditional headwalls as identified above.

Summary of the Invention

According to a first aspect of the invention there is provided a mould for casting a concrete headwall, wherein the mould is formed from a plastics material and defines the shape of the headwall, and wherein the walls of the mould define an aperture for receiving concrete and an inner void for filling with concrete.

Such a mould may be prefabricated and supplied to the construction site ready for use, so that all that is essentially required for construction of the headwall is to prepare the site, place the mould into position, fit the water pipe and fill the mould with concrete. Fewer quality assurance checks and items of plant are required compared with the traditional headwall construction technique. Wooden shutters and the services of skilled carpenters are also no longer required. Using the mould, the time required to construct the headwall would typically be only one day or so. Thus the procedure for constructing the concrete headwall is facilitated and greatly expedited, and the associated costs can be reduced.

Since the mould remains in situ after being filled with concrete, the plastic provides a protective outer covering to the concrete, thereby mitigating the effects of weathering and erosion. The plastics material of the mould may be virtually any colour, e.g. different shades of green or brown. Thus the colour of the mould may be chosen to suit the surroundings of the installation site, to render the finished headwall aesthetically pleasing and visually unobtrusive. Alternatively the external surface of the mould may mimic existing construction techniques or materials. For example, the external surface may be moulded to give the impression of being made of brickwork or stonework.

Such moulds may be supplied in a range of sizes and configurations to suit a variety of applications.

Preferably the walls of the mould are formed and configured to provide integral structural reinforcement to the mould, e.g. by incorporating plastic ribs on the inner surfaces of the mould walls or by increasing the thickness of the plastic walls in the appropriate places.

Thus, in some low load situations (e.g. smaller headwalls) it is possible simply to fill the mould with concrete without requiring steel reinforcements.

Preferably the walls of the mould are formed and configured to receive and provide support for a plurality of reinforcing members within the inner void. Particularly preferably the inner surfaces of the walls of the mould comprise a plurality of protrusions, said protrusions being integrally formed with the walls of the mould and configured to receive and provide support for said reinforcing members. The protrusions may function both as spacers and supports for the reinforcing members. One or more of the protrusions may comprise a recess shaped to receive a reinforcing member, e.g. using a snap fit arrangement.

Particularly preferably the mould further comprises a plurality of reinforcing members within the inner void, ready for installation. These reinforcing members are typically steel rods or tangs, and are preferably held in place by the spacers or other features integral with the inner surfaces of the mould walls.

Preferably the mould is formed and configured to receive and provide support for one or more ground anchors, which may comprise metallic rods that are at least partly encapsulated with a plastics material. In use, the mould may comprise one or more such ground anchors.

In one embodiment the mould further comprises a toe region shaped to key into the ground to enhance the stability of the mould and the resultant headwall. Preferably, in the toe region of the mould, the walls of the mould include apertures through which concrete can emerge during filling of the mould. This further enhances the stability of the resultant headwall in the surrounding ground.

Preferably the walls of the mould comprise one or more grout check holes, to provide an indication in use that concrete correctly fills the mould. Grout check holes provide a ready visual means for installation personnel to ensure that adequate compaction of the concrete is taking place within the mould during casting.

Preferably the mould comprises one or more holes for receiving a vibrating poker, which also aids compaction of the concrete during casting.

The mould may comprise a plurality of apertures for receiving concrete. Using a plurality of apertures, particularly in moulds for larger headwalls, further assists in improving the integrity of the cast concrete within the mould, and reduces occurrences of voids within the resultant headwall.

Preferably the mould has substantially curved internal edges, which also give rise to improved concrete compaction during casting.

Preferably the mould further comprises one or more plastic caps for clipping over or otherwise covering holes or apertures in the mould. The caps seal the concrete within the mould and prevent ingress of water or chemicals, which could lead to the erosion and weakening of the concrete. The caps also improve the overall aesthetic appeal of the finished headwall, since the internal concrete is hidden from view.

The mould may be formed and configured to receive one or more attachments selected from a group comprising: a pipe guard or grille; a flap or nonreturn valve for the water pipe; a step iron; a hand rail. Other possible attachments will be known to those skilled in the art.

The mould may further comprise these attachments ready for installation.

Preferably a hole is provided through the mould for receiving a pipe, said hole being defined by a first aperture in a first wall of the mould and a second aperture in a second wall of the mould, the first and second walls being mutually opposing and the first and second apertures being mutually aligned and shaped to receive the pipe.

Particularly preferably the first aperture is substantially the size of the external diameter of the pipe, and the second aperture is substantially the size of the internal diameter of the pipe, such that the pipe passes through the first aperture but does not pass through the second aperture. The walls of the mould around either aperture may be formed and configured to provide support for the pipe - in a preferred embodiment, this support formation is provided around the second aperture, to hold the end of the pipe securely against the inner surface of the second wall of the mould.

In one embodiment, the walls of the mould comprise a plurality of selectively removable regions, the selectively removable regions corresponding to a range of pipe cross-sectional shapes or sizes such that, in use, by the removal of an appropriate region or regions, the mould can receive a pipe having one of a corresponding range of crosssectional shapes or sizes. For example, a plurality of concentric circular removable regions may be provided, corresponding to different pipe diameters, and the appropriate regions may be punched out to accommodate a given pipe.

The mould may further comprise compressible foam around the interior walls of the mould, the foam being such that it is compressed by concrete introduced during casting, and subsequently expands during contraction of the concrete, thereby mitigating the formation of voids between the concrete and the mould.

The mould may further comprise one or more detachable parts to enable exposure of the concrete after casting, e.g. to enable the concrete to be inspected, or to leave the finished headwall with a concrete appearance if desired.

According to a second aspect of the invention there is provided a concrete headwall comprising at least part of a mould in accordance with the first aspect of the invention. That is to say, after casting, at least part of the mould remains in place as an integral part of the concrete headwall, together with external attachments if desired and internal reinforcements (if used) within the concrete itself. It is envisaged that, in the majority of cases, the entire mould would be left in place after casting, to provide an outer covering to the concrete.

However, the mould may be constructed such that one or more parts of it may be removed after casting, if it is desired for the finished headwall to have a conventional concrete appearance. The parts of the mould that are detached (e.g. the front and top sections) may then be reused in the construction of another headwall.

Preferably the concrete headwall comprises pump mix concrete, particularly preferably containing aggregate particles 10 mm in diameter.

According to a third aspect of the invention there is provided a method of casting a concrete headwall using a mould in accordance with the first aspect of the invention, the method comprising the steps of: positioning the mould in the construction site; fitting a pipe to the mould such that outflow from the pipe will pass through the headwall; and filling the mould with concrete. As mentioned above, this method is substantially quicker and easier than the traditional method, and does not require expensive tradesmen to be contracted for the fabrication of a wooden mould using shutters.

The method may further comprise inserting reinforcing members into the mould, and/or pushing one or more ground anchors through the mould and into the ground below, before filling the mould with concrete.

If ground anchors are used, preferably the method further comprises adding a sealant bead around the interface between the ground anchors and the mould wall, before filling the mould with concrete. This sealant bead prevents ingress of water or chemicals through the holes in the mould through which the ground anchors pass, thereby protecting the concrete within.

The method may further comprise attaching attachments to the mould, before filling the mould with concrete. The attachments, examples of which have been given above, are thus cast as an integral part of the headwall.

The method may also comprise operating a vibrating poker to compact the concrete within the mould, and afterwards covering any holes or apertures in the mould with caps or patches.

Preferably the step of filling the mould with concrete comprises filling the mould with pump mix concrete containing aggregate particles 10 mm in diameter. Preferably the entire mould is filled with concrete in a single filling operation.

The method may further comprise detaching part of the mould to expose concrete cast within.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example, and with reference to the drawings in which: Figure 1 illustrates a plan view of a plastic mould for casting a concrete headwall, located in situ on a riverbank; Figure 2 illustrates a front view of the mould of Figure 1; Figure 3 illustrates a side view of the mould of Figure 1; Figure 4 illustrates a vertical cross section through part of a mould; Figure 5 shows a vertical cross section through another part of the mould (or an alternative mould) incorporating a ground anchor; Figure 6 shows a horizontal cross section through part of a mould having a symmetrical profile when viewed from above; Figures 7 and 8 show horizontal cross sections through alternative moulds having asymmetrical profiles; Figure 9 shows a horizontal cross section through the region of the mould adapted to receive a pipe; Figure 10 illustrates a side view of a mould in situ incorporating ground anchors, with a region partially cut away to indicate the internal structure of the mould; Figure 11 illustrates a side view of an alternative mould incorporating an anchoring toe; Figure 12 illustrates a front view of a mould with a region partially cut away to indicate the internal structure; and Figure 13 illustrates a rear view of a mould with a region partially cut away to indicate the internal structure.

Consistent numbering of equivalent components is used throughout the drawings.

Detailed Description of Preferred Embodiments

The present embodiments represent the best ways known to the applicant of putting the invention into practice. However they are not the only ways in which this can be achieved.

The plastic moulds for casting concrete headwalls are made in a factory and supplied to the construction site ready for use. Each mould is typically manufactured in two or more parts that are assembled in the factory. The mould may be produced by vat forming, injection moulding or rotation moulding. Vat forming involves placing plastic sheets over a hot bed and then dropping them over a mould to form the required mould product. Rotation moulding is a technique in which plastic is introduced into a mould which is then spun on all three axes at a high temperature, such that molten plastic is spun to the outside of the mould to form of the required product.

Figures 1, 2 and 3 illustrate plan, front and side views respectively of a plastic mould 10 for casting a concrete headwall. (In use, the mould is filled with concrete, such that the finished headwall will also have the appearance of the mould of Figures 1, 2 and 3.) The mould 10, which is substantially hollow in order to receive concrete, comprises a base part 18, a back 12 and side walls 14, 16. The back includes a hole 20 into which a pipe is fitted. The mould is placed by a river 22 or similar watercourse, into which liquid emerging from the pipe will flow.

As mentioned above, such moulds may be formed in two parts in the factory. Typically, all of the top and front faces of the mould are formed as a first moulding, and all the back and bottom faces are formed as a second moulding. The two parts of the mould are then brought together and joined in the factory, before delivery to the construction site.

Figure 4 shows a vertical cross sectional view through a vertical region 40 of the mould, for example side wall 14 of the overall mould as shown in the earlier Figures. The mould 42 comprises a first mould wall 43 and an opposing mould wall 44. If required by the size and intended loading of the headwall, a reinforcing cage comprising an array of reinforcing members 41, 46, 47 (typically steel rods) may be mounted in the cavity between the opposing mould walls 43, 44. Some reinforcing members 47 extend between the opposing mould walls, whilst other reinforcing members 41, 46 extend vertically. (Members 41 and 46 may be formed from a continuous rod bent as shown in the Figure.) The reinforcing cage is prefabricated and preinstalled in the mould in the factory.

Preinstallation of the reinforcing cage is achieved by placing the cage between the two parts of the mould during assembly of the mould in the factory. For example, the cage may be located in a first part of the mould and then the second part of the mould may be brought into place and joined to the first part, thereby enclosing the reinforcing cage.

The mould walls 43, 44 are formed and configured to provide secure support for the reinforcing members 41, 46, 47. In preferred embodiments, this support is provided by a plurality of regions 45 integrally moulded in, and protruding from, the inner surfaces of the mould walls. The protruding regions 45 serve both as supports and spacers for the reinforcing cage. Each protruding region 45 may be incorporate a recess shaped to receive a bar of the reinforcing cage. The recesses may be further shaped such that the reinforcing bars 47 are clipped into the recesses (i.e. using a snap fit technique) or alternatively the bars may be held in place by a friction fit or adhesive.

Between the opposing mould walls 43, 44 and around the reinforcing cage is a hollow cavity or void 48 which is filled with concrete during construction of the headwall. The support and spacer regions 45 of the mould walls hold the reinforcing cage in an appropriate position relative to the mould walls 43, 44 such that adequate concrete coverage occurs around the cage and throughout the mould. In Figure 4, the level of concrete after the mould has been filled is indicated by the dotted line 49.

The arrangement of the reinforcing cage within the base part 18 of the mould is illustrated in the cut away regions of Figures 12 and 13.

The mould may be reinforced further by the incorporation of plastic ribs inside the mould.

These ribs may be moulded as an integral part of the inner surfaces of the mould walls. To provide further strengthening, the thickness of the mould walls may be increased as necessary, and different steel reinforcing cages may be employed depending on the size of the headwall, its location and structural loading requirements.

External surface finish and appearance of the mould Since the mould remains in situ after being filled with concrete, the plastic provides a protective outer covering to the internal concrete, thereby mitigating the effects of weathering and erosion. The plastics material of the mould may be virtually any colour, e.g. shades of green or brown, to suit the surroundings of the installation site and to render the finished headwall aesthetically pleasing and visually unobtrusive. Alternatively the external surface of the mould may mimic existing construction techniques or materials. For example, the external surface may be moulded to give the impression of being made of brickwork or stonework.

Grout check holes In Figure 4, a grout check hole 50 is shown in one wall 43 of the mould. During casting of the headwall, the grout check hole 50 provides visible verification to installation personnel that the concrete is correctly filling the mould in the region of the grout check hole. Several such holes are provided for this purpose around the mould.

Ground anchors To enhance the stability of the mould during construction, and also the stability of the finished headwall, ground anchors may be used to anchor the mould to the ground below. A ground anchor is a steel rod that is driven into the ground through the base 18 and/or walls 12, 14, 16 of the mould. The length, cross section and number of rods that are used will depend on the size and location of the headwall. The mould incorporates holes in appropriate places in its base through which the ground anchor rods are driven into the ground.

This ability to use ground anchor rods in the construction of a concrete headwall is a direct consequence and benefit arising from the use of the plastic mould of the present invention.

Traditional headwalls formed using wooden shutters would not have used such ground anchors, and instead would have relied on the provision of a toe in the base of the headwall to enhance the stability of the structure. (Such toes are discussed in greater detail below, with reference to Figure 11.) As shown in Figure 5, when installed a ground anchor 52 may extend through substantially the entire height of the mould 42, as well as penetrating the ground below via holes in the base of the mould. To aid in the positioning of the ground anchors, the plastic mould preferably includes strategically placed ground anchor guides 51, which may be integrally formed with the mould. Within the mould, the ground anchors 52 pass between the reinforcing steel rods 41, 46. The ground anchors are installed before concrete is introduced to the mould. When concrete is added, the length of each ground anchor within the mould is encapsulated in concrete. This firmly secures the ground anchor to the headwall and mould, and also provides further reinforcement to the concrete itself.

Preferably the ground anchor rods for use with the present plastic moulds are at least partly plastic coated. The rods may be entirely plastic coated, or alternatively the plastic coating may only cover the part of each rod that penetrates the ground, from the ground-penetrating tip up to the base of the mould. Then, by applying a sealant (e.g. silicone rubber) bead around the interface between the rod and the base of the plastic mould prior to the introduction of concrete, the mould may be rendered watertight to prevent water ingress into the mould from below. This thereby prevents the internal concrete from being attacked by water etc. during service.

Figure 6 illustrates a plan cross-sectional view of a mould showing the positions of four ground anchors 52. This Figure also indicates further details of the configuration of the steel reinforcing cage within the mould. The cage comprises a plurality of cross-members 47 extending between the opposing walls 43, 44, and also horizontal members 60, 62 extending around the inside of the mould. Vertical reinforcements 41, 46 (as introduced with reference to Figure 4) are also used, although these are not shown in Figure 6.

Different ground types require different types of ground anchor rods. For example, with gravel soils, the ground anchor rods may incorporate a helical coil or a screw thread to enable them to be twisted into the ground (like a drill bit). With clay or fine gravel, the ground anchor rods may be smooth and are simply pushed into the earth. When fixing into rock strata, on the other hand, holes are pre-drilled into the rock to accommodate the ground anchor rods. The rods are then inserted into the holes and are resin anchored in place.

Although the ground anchor rods may in principle be pre-installed in the mould in the factory, they would more commonly be supplied separately from the mould. They would then be driven through the mould and into the ground on site. This provides the benefit that the mould effectively acts as a guide for the positioning of the ground anchors during installation.

However, alternatively, the ground anchor rods can be inserted into the ground separately from the mould, and then the mould can be lowered into place over the rods.

Symmetric and asymmetric moulds and headwalls Although the mould shown in Figure 6 is symmetrical when viewed from above, in some applications asymmetrical headwalls are preferable. Examples are shown in Figures 7 and 8, which have equivalent features to the mould of Figure 6. With a headwall cast using the mould of Figure 6, when in service, water flowing through an attached pipe and out of the headwall would leave the headwall in substantially equal amounts towards the top and bottom of Figure 6, as indicated by the arrows 64, 66. However, with the moulds of Figures 7 and 8, the water would flow preferentially towards the top of each Figure, as indicated by arrows 70 and 80. Thus, asymmetric headwalls can be used to control the direction of outflow. With the moulds of Figures 7 and 8, a splay could be provided on the right-angled internal corner of the mould, in regions 72 and 82, to prevent a build up of silt or debris in this corner of the headwall when in service.

Fitting the pipe to the mould Figure 9 illustrates, in plan cross section, one possible configuration of the back 12 of the mould, around the hole 20 for receiving the water pipe. The pipe is shown in cross section as two pipe walls 90, 92, and the direction of flow of water along the pipe is indicated by the arrow 91. Typically, a 600 mm length of pipe would be inserted into the mould, also in the direction of the arrow 91.

The hole in the mould wall 43 though which the pipe first passes is substantially equal in size to the outside diameter of the pipe, thereby enabling the pipe to pass into the mould. In this embodiment, the hole in the second mould wall 44 is substantially equal in size to the internal diameter of the pipe, so that the pipe abuts the second wall 44 from within the mould, but does not pass through this wall. An annular moulding 98 may be provided on the inside of the second wall 44 to support and retain the end of the pipe.

To prevent ingress of water into the inside of the mould, seals (e.g. Orings or beads of sealant) may be provided around the pipe, at the interfaces between the pipe and wall regions 94, 96 and 98.

The pipe is fitted to the mould before the mould is filled with concrete.

Preferably, a range of moulds are manufactured to cater for pipes of different specified diameters. However, in an alternative embodiment, to enable a variety of pipe sizes to be accommodated by a single mould, the walls 43, 44 of the mould may comprise a plurality of selectively removable regions, e.g. regions that may be punched out or otherwise detached as required. These selectively removable regions correspond to a range of pipe cross- sectional shapes or sizes such that, by the removal of an appropriate region or regions, holes can be produced in the mouldwalls to accommodate the pipe in question. For example, a plurality of concentric circular removable regions may be provided, corresponding to different pipe diameters. A variety of pipe shapes (e.g. non-circular in cross section) may also be accommodated by providing appropriately shaped removable regions in the mould walls.

Enhancinn the stability of the mould and the finished headwall IS Figures 10 and 11 illustrate two alternative techniques for enhancing the stability of the mould and the resultant headwall. Figure 10 illustrates further the principle of ground anchoring that has already been introduced above. Here, ground anchor rods 100 and 102 extend into the ground 104 beneath the mould. Through the cutaway region of the illustration at the top of wall 12, the top part 52 of the ground anchor 100 can be seen passing through the array of reinforcing rods 46, 47. This figure also shows a typical arrangement of six grout check holes 50 in the side wall 16 of the mould.

Figure 11, on the other hand, shows a plastic mould incorporating a toe 110. With traditional headwalls cast using wooden shutters, a toe 110 is usually incorporated in the headwall to provide stability. With the present plastic moulds, a toe is generally not necessary to ensure the stability of the mould and the finished headwall, particularly if ground anchor rods are used. However, the present moulds may incorporate a toe if required, and this may be of benefit in certain applications in which ground anchor rods cannot be used (e.g. because they would foul some other underground installation beneath the headwall). In use, the toe 110 anchors the mould and the finished headwall by keying in to an excavation 105 in the ground below. This excavation 105, which would need to be excavated separately, is of a corresponding shape to the toe 110. The toe is an integral part of the mould, and is filled with concrete during casting. The mould wall in the toe 110 may incorporate open regions 112 through which concrete can pass during casting, which further aids the anchoring of the headwall in the ground.

Attachments to the mould Headwalls often have various other features that traditionally are attached to the headwall after casting and curing are complete. These attachments may include: À a pipe guard or grille (fixed over the outlet of the pipe, to prevent animals and children etc. from entering the pipe) À a flap or non-return valve for the water pipe À step irons (essentially forming a ladder up the side of the headwall) À hand rails With the present moulds, however, the above attachments would generally be added as required to the mould prior to casting. The attachments would either be factory fitted, or the mould would have preformed holes and guides so that the attachments can be attached to the mould on site prior to (or just after) filling with concrete. Preferably the attachments comprise rods or pins that pass through the walls of the mould and extend into the inner void, such that they are trapped in the concrete and become an integral part of the finished headwall.

Concrete and casting considerations The preferred concrete used for filling the plastic mould is very fluid pump mix concrete containing aggregate particles 10 mm in diameter (rather than the more conventional 20 mm diameter aggregate particles). 10 mm aggregate particles are sufficiently small to enable the mould to be filled effectively. It is possible to fill the mould using less fluid concrete with larger aggregate, but improved results are obtained using pump mix concrete.

In most cases, concrete is introduced to the mould through one or more apertures in the top edge. However, in some cases it is possible that some internal regions of the mould have complex shapes, and a potential problem is that the concrete would not be adequately compacted throughout the mould. Poorly compacted concrete would lead to much lower structural strength of the finished headwall.

To address this potential problem, the present plastic moulds have a number of design features to ensure that poor compaction of the concrete does not occur. These features include: À Grout check holes in the mould, providing a visible indication that the concrete has filled a particular section of the mould.

À In some cases detachable mould wall panels may also (or alternatively) be provided to expose the internal concrete, to enable it to be checked.

Additional concrete may be added if necessary, and then the panel is replaced (e.g. clipped back into place).

À Vibrating poker holes, through which a suitably sized vibrating poker may be inserted into the mould to assist the compaction of the concrete during casting. The mould wall may again incorporate removable panels for this purpose, which may be replaced after the vibrating poker has been used.

À Additional concrete placing holes - in larger moulds, it may be necessary to have additional holes in the top face of the base 18 of the mould, through which concrete may also be introduced.

À Forming the mould such that all the internal edges and corners of the mould are curved, thereby making it easier for the concrete to fill the entire of the mould, right up to the edges and corners. This is preferable over square edged internal mould surfaces.

When casting the headwall, the entire plastic mould is preferably filled in a single operation, e.g. with a single continuous pour. This is to be contrasted with the traditional technique, in which some concrete is cast, then left to cure before further concrete can be added.

Sealino the mould One potential problem that has been considered is the possibility of water or chemical ingress into the finished headwall, for example, via a grout check hole or a vibrating poker hole in the mould wall. There may possibly be voids in places between the mould wall and the cast concrete, due to contraction of the concrete during casting and debonding of the concrete from the mould wall. If, in service, water were to enter the mould and make its way into such a void, the water could freeze and expand and consequently crack the surface of the concrete. Over time, such a cycle could threaten the structural integrity of the unit.

Therefore, after filling with concrete, it is desirable to seal the mould in order to prevent ingress of water or chemicals, to prevent attack of the concrete over time. As described above, the mould may incorporate a number of grout check holes and/or vibrating poker holes, and these can readily be sealed using pre-prepared caps that are clipped or otherwise secured into position over the pre-formed holes. The apertures in the mould through which the concrete was poured may also be sealed in such a manner. The caps may be sealed with a suitable adhesive, solvent or sealant (as would be selected by a person skilled in the art) to create a water/chemical resistant unit. As an alternative to caps, patches could be applied over the holes and sealed into place. Sealing the holes also improves the aesthetic appearance of the finished headwall.

Headwalls for low load applications For low load applications (typically with smaller headwalls) it is possible to omit the steel reinforcements from inside the mould and still provide adequate reinforcement of the headwall by the use of any of the following, or a combination thereof: À reinforcing ribs integrally moulded with the plastic mould, typically on the internal surfaces of the mould walls; À an interior plastic reinforcing cage, which may be integrally formed with the mould walls, or inserted separately; À increased wall thickness of the mould in regions requiring reinforcement; À a specialized concrete mix such as a composite of glass fibres and concrete, or steel fibres and concrete.

Even in low load applications, concrete would still be used to fill the mould in order to give the resultant headwall the required mass and stability.

Optional detachable Darts of the mould Parts of the mould may be detachable, to enable exposure of the concrete after casting has been completed. These detachable parts may be provided for inspection of the concrete (e.g. to verify the quality of the concrete immediately after casting, or for subsequent checks on the structural integrity of the concrete). In such cases, the detachable parts would be replaced (e.g. clipped back onto the rest of the mould) after the concrete has been inspected.

Alternatively, parts of the mould may be detached and removed to leave the finished l 0 headwall with a traditional concrete outward appearance if so desired. In particular, the front and top sections of the mould may be detachable for this purpose. The removed mould parts may subsequently be reused in the construction of another headwall.

Tvoical installation schedule IS A typical installation schedule for a concrete headwall using a plastic mould as described herein is as follows: Day 1: Dewater area (if applicable); excavate; lift mould into position; set up pipe; fill mould with concrete; backfill with soil and grade (if required, depending on site conditions and structural loading) Day 2: Stop This is dramatically quicker than the equivalent schedule for the installation of traditional headwalls as previously presented herein.

Casting of other civil engineering structures and the use of a bonding agent Plastic moulds could be used for casting concrete civil engineering structures other than headwalls, with the mould remaining in situ to provide an outer coating to the concrete.

However, for many structural applications, it would be necessary to apply a bonding agent (e.g. one that is epoxy based) to the inside of the plastic mould, in order to ensure adequate bonding of the concrete to the mould wall, and thereby provide sufficient strength to the finished structure.

In the case of concrete headwalls, however, it has been found that a plastic mould as described herein may be used without the need for any bonding agent. This is because concrete headwalls only need to bear relatively low loads (essentially only those of the pipe and the surrounding earth). If, as a consequence of using no bonding agent, some debonding occurs between the concrete and the headwall mould, then this does not present a problem. With headwalls, such debonding does not cause any significant loss of structural integrity, and the aesthetic qualities of the unit are not compromised (provided the mould is designed and manufactured correctly).

Furthermore, if some bonding occurs between the concrete and the headwall mould, then provided the unit is sealed as described above, there will be no risk of water entering the voids caused by debonding and attacking the concrete.

Foam lining to mitinate the formation of voids between the mould and the concrete If, for a particular application, it is desired to mitigate the formation of voids between the mould and the concrete, then a compressible foam may be applied to the inner surfaces of the mould. A bonding agent need not be used. The foam is selected such that it is able to be compressed by the concrete when wet. As the concrete sets and contracts, the foam expands with the retracting concrete. Accordingly, the foam remains in contact with the concrete, and prevents or at least mitigates the formation of voids between the concrete and the mould. This technique is applicable to the casting of concrete headwalls using plastic moulds and, in principle, to other civil engineering applications in which concrete is cast in moulds. It is particularly applicable to applications in which the mould is left to form an integral part of the finished article, as is the case with the present concrete headwalls.

Summary

Prefabricated plastic moulds are provided for casting concrete headwalls and pipe ouffalls (into streams, rivers, ditches etc.). The mould is supplied to the construction site ready to use, and is filled with concrete in situ. The mould remains an integral part of the finished headwall.

The following are variables dependent on the pipe size, structural loading and site conditions: À size À shape À mould wall thickness À quantity of steel reinforcement (if any) À ground anchoring À attachments (e.g. flap valves, flow control products, pipe guards, steps, safety hand rails) À colour and external surface finish Use of such moulds enables a saving in cost, time and skills to be made, together with an improved quality of the finished product, when compared to traditional headwalls.

Claims (41)

1. A mould for casting a concrete headwall, wherein the mould is formed from a plastics material and defines the shape of the headwall, and wherein the walls of the mould define an aperture for receiving concrete and an inner void for filling with concrete.

2. A mould as claimed in Claim 1, wherein the walls of the mould are formed and configured to provide integral structural reinforcement to the mould.

3. A mould as claimed in either preceding Claim, wherein the walls of the mould are formed and configured to receive and provide support for a plurality of reinforcing members within the inner void.

4. A mould as claimed in Claim 3, wherein the inner surfaces of the walls of the mould comprise a plurality of protrusions, said protrusions being integrally formed with the walls of the mould and configured to receive and provide support for said reinforcing members.

5. A mould as claimed in Claim 4, wherein one or more of the protrusions comprise a recess shaped to receive a reinforcing member.

6. A mould as claimed in Claim 5, wherein said recess is shaped to receive a reinforcing member in a snap fit arrangement.

7. A mould as claimed in any preceding Claim, further comprising a plurality of reinforcing members within the inner void.

8. A mould as claimed in any preceding Claim, wherein the mould is formed and configured to receive and provide support for one or more ground anchors.

9. A mould as claimed in any preceding Claim, further comprising one or more ground anchors.

10. A mould as claimed in Claim 9, wherein the ground anchors comprise metallic rods that are at least partly encapsulated with a plastics material.

11. A mould as claimed in any preceding Claim further comprising a toe region shaped to key into the ground to enhance the stability of the mould and the resultant headwall.

12. A mould as claimed Claim 11 wherein, in the toe region of the mould, the walls of the mould include apertures through which concrete can emerge during filling of the mould.

13. A mould as claimed in any preceding Claim, wherein the walls of the mould comprise one or more grout check holes, to provide an indication in use that concrete correctly fills the mould.

14. A mould as claimed in any preceding Claim, wherein the mould comprises one or more holes for receiving a vibrating poker.

15. A mould as claimed in any preceding Claim, wherein the mould comprises a plurality of apertures for receiving concrete.

16. A mould as claimed in any preceding Claim having substantially curved internal edges.

17. A mould as claimed in any preceding Claim, further comprising one or more plastic caps for clipping over or otherwise covering holes or apertures in the mould.

18. A mould as claimed in any preceding Claim, wherein the mould is formed and configured to receive one or more attachments selected from a group comprising: a pipe guard or grille; a flap or non-return valve for the water pipe; a step iron; a hand rail.

19. A mould as claimed in any preceding Claim, further comprising one or more attachments selected from a group comprising: a pipe guard or grille; a flap or non- return valve for the water pipe; a step iron; a hand rail.

20. A mould as claimed in any preceding Claim having a hole through the mould for receiving a pipe, said hole being defined by a first aperture in a first wall of the mould and a second aperture in a second wall of the mould, the first and second walls being mutually opposing and the first and second apertures being mutually aligned and shaped to receive the pipe.

21. A mould as claimed in Claim 20, wherein the first aperture is substantially the size of the external diameter of the pipe, and the second aperture is substantially the size of the internal diameter of the pipe, such that the pipe passes through the first aperture but does not pass through the second aperture.

22. A mould as claimed in Claim 20 or Claim 21, wherein the walls of the mould around either aperture are formed and configured to provide support for the pipe.

23. A mould as claimed in any of Claims 20 to 22, wherein the walls of the mould comprise a plurality of selectively removable regions, the selectively removable regions corresponding to a range of pipe crosssectional shapes or sizes such that, in use, by the removal of an appropriate region or regions, the mould can receive a pipe having one of a corresponding range of cross-sectional shapes or sizes.

24. A mould as claimed in any preceding Claim, further comprising compressible foam around the interior walls of the mould, the foam being such that it is compressed by concrete introduced during casting, and subsequently expands during contraction of the concrete, thereby mitigating the formation of voids between the concrete and the mould.

25. A mould as claimed in any preceding Claim, further comprising one or more detachable parts to enable exposure of the concrete after casting.

26. A concrete headwall comprising at least part of a mould as claimed in any preceding Claim.

27. A concrete headwall as claimed in Claim 26, comprising pump mix concrete.

28. A concrete headwall as claimed in Claim 27, wherein the concrete comprises aggregate particles 10 mm in diameter.

29. A method of casting a concrete headwall using a mould as claimed in any of Claims 1 to 25, the method comprising the steps of: positioning the mould in the construction site; fitting a pipe to the mould such that outflow from the pipe will pass through the headwall; and filling the mould with concrete.

30. A method as claimed in Claim 29, further comprising inserting reinforcing members l 5 into the mould before filling the mould with concrete.

31. A method as claimed in Claim 29 or Claim 30, further comprising pushing one or more ground anchors through the mould and into the ground below, before filling the mould with concrete.

32. A method as claimed in Claim 31, further comprising adding a sealant bead around the interface between the ground anchors and the mould wall, before filling the mould with concrete.

33. A method as claimed in any of Claims 29 to 32, further comprising attaching attachments to the mould, before filling the mould with concrete.

34. A method as claimed in any of Claims 29 to 33, further comprising operating a vibrating poker to compact the concrete within the mould.

35. A method as claimed in any of Claims 29 to 34, further comprising covering any holes or apertures in the mould with caps or patches.

36. A method as claimed in any of Claims 29 to 35, wherein the step of filling the mould with concrete comprises filling the mould with pump mix concrete containing aggregate particles 10 mm in diameter.

37. A method as claimed in any of Claims 29 to 36, wherein the entire mould is filled with 1 S concrete in a single filling operation.

38. A method as claimed in any of Claims 29 to 37, further comprising detaching part of the mould to expose concrete cast within.

39. A mould for casting a concrete headwall substantially as herein described with reference to and as illustrated in any combination of the accompanying drawings.

40. A concrete headwall comprising a mould substantially as herein described with reference to and as illustrated in any combination of the accompanying drawings.

41. A method of casting a concrete headwall substantially as herein described with reference to and as illustrated in any combination of the accompanying drawings.