The present invention relates to formers and methods of casting bodies, particularly concrete bodies.

It is known to manufacture concrete slabs and similar structures with internal cavities so as to reduce overall weight, and facilitate transportation to a construction site, and to produce a corresponding saving in the amount of concrete required in production. In fact, the saving in concrete can be as high as 65%. Furthermore, if the cavities are properly designed, they do not weaken the concrete slab. On the contrary, the reduction in net slab weight resulting from the omission of material enhances the load-bearing capability of the slab compared to a traditional slab span of similar thickness. Among other things this latter property permits the construction of lighter structures with wider spans and/or thinner floors and/or a greater number of floors on a given site area, all of which are important issues in concrete design and construction work.

In the past, the cavities in concrete slabs have been provided using plastic balls which are individually positioned and secured in a steel reinforcement matrix, prior to casting the concrete. This system requires accurate positioning of the balls within the reinforcement matrix, and therefore requires skill, and is time-consuming and increases manufacturing costs. Further, it is not economically practical to cast the concrete manually in situ, since apart from the skilled labour required, this would also involve transportation of the plastic balls, which are bulky, as well as the concrete materials and steel reinforcement matrix.

Therefore, automated centralised manufacture is used, and the finished concrete slabs are transported to the site where they are to be installed.

It is therefore an object of the invention to address these problems of the prior art and provide a method of making cast bodies (such as concrete structures) with internal cavities which are simpler and cheaper to manufacture, which can be manufactured in situ, and which still possess the desired property of a greatly improved net-weight to load-bearing ratio as described above.

According to the invention an array of multiple interconnected chambers is provided around which a body can be cast, e. g. a cast-concrete slab. Preferably, these chambers are interconnected by spacers which preferably provide communication between the chambers.

Preferably, the chambers are generally spherical and are positioned in a common plane.

Preferably, the multiple interconnected chambers are defined by a former around which the body is cast.

The former may be rigid and preferably comprises two portions which are assembled together to form the chambers and spacers between them. These two portions may be held together by snap-fit connections. Preferably, these two portions are designed so that they can be stacked in a compact manner ready for use. For example, they may be of the same general form so that concavities in one can seat in concavities in the other, or one can be reversed in the other so that the concavities form the chambers therebetween.

Preferably, a rigid former is composed of polyolefin. Preferably, the polyolefin comprises polypropylene or polyethylene, or a combination thereof. Both polypropylene and polyethylene are biodegradable materials, and therefore more environmentally acceptable materials than many alternative plastics. Further, there is no toxic waste produced during the polyolefin manufacturing process.

Alternatively, the former may be an inflated sealed structure, and used in its inflated form during the casting of the body (e. g. a concrete slab). Alternatively, the former may be inflated and cured, to create a rigid structure, and then used in the casting of the body.

Alternatively, the former may be inflated at the site of use and kept inflated during the casting process, while the casting material (e. g. concrete) sets. The former may comprise two superimposed sheets heat sealed along appropriate join lines to form the chambers and spacers, and with excess material removed, typically by laser.

Preferably, the former is provided with a plurality of spacer studs. These spacer studs serve to space the chambers of the former from the exterior walls of the cast body. The spacer studs may extend from the chamber, or alternatively, may extend from the spacers, or the junction between the spacers and the chambers. Preferably, the spacer studs are tapered.

Preferably, the spacer studs are hollow. This allows any condensation which forms in the chambers and spacers either during the casting process or during subsequent use, to drain to the exterior of the cast body. Further, the diameter of the spacer studs at the external wall of the cast body is of a suitably small diameter so as not to compromise the load-bearing strength of the cast body.

The spacer studs may be integral with the former, or alternatively, may be removable after the casting material has set, leaving only small drainage holes in the exterior wall of the cast body. These holes may be left, or alternatively, the holes may be filled with a suitable filler material.

During the casting process, the former and preferably also a reinforcement matrix are placed inside a mould. Preferably, the mould is a rigid mould, and may be composed of polyolefin. The polyolefin may comprise polypropylene or polyethylene, or a combination thereof. Preferably, this external mould is an integrated part of the rigid former.

It is a major advantage over the prior art that the chamber-interconnections and stud-holes provided by the present invention allow for the convenient subsequent incorporation of cables, pipes, ducts and/or other technical installations within the cast body.

The invention will now be described, by way of example only, with reference to the attached figures in which: Figure 1 shows a horizontal cross-section of an inflatable former according to a first embodiment of the present invention; and Figure 2 shows a vertical cross-section of an inflatable former according to figure 1.

Figure 3 shows a vertical cross-section of an inflatable former according to figure 2 surrounded by a concrete casting; and Figure 4 shows a vertical cross-section of an inflatable former according to figure 2 with associated reinforcement matrix; and Figure 5 shows a vertical cross-section of an inflatable former according to figure 3 with associated reinforcement matrix; and Figure 6 shows a horizontal cross-section of an inflatable former according to figure 1 surrounded by a concrete casting and associated reinforcement matrix; and Figure 7 shows a vertical cross-section of a rigid former surrounded by a rigid liner for containing the poured concrete as it sets.

Figures 1 to 4 show a former 10 in cross-section, comprising multiple chambers 20 interconnected by spacers 30. The chambers 20, are generally spherical and are arranged such that the chambers 20 are positioned in a single plane and each chamber 20 is interconnected, via spacers 30, with each immediately adjacent chamber 20. The former comprises two sheets which are sealed together in the pattern of the chambers 20 and spacers 30, and the excess sheet material removed.

The former is then force-inflated, and the sheet material is cured whilst in the force-inflated state, resulting in a rigid former which can then be transported to the site of concrete casting.

In an alternative embodiment, the former is formed from two separate, but inter-connectable portions. These portions have the same profile, and are formed by press-moulding to produce rigid stackable former portions. These stackable portions take up less space for transportation to the site of concrete casting. Once at the site, two of jthe stackable former portions are assembled together with respective concavities in each aligned mouth-to-mouth to form the chambers 20 and spacers therebetween.

Figures 4,5 and 6 show the associated reinforcement matrix 40 on which the former 10 is positioned.

Once the former 10 is in position in association with the reinforcement matrix 40, the concrete is cast around the matrix 40 and former 10, to form a concrete slab, incorporating the former 10.

A further embodiment of the present invention is shown in figure 7. In this embodiment, the rigid former 10 is provided with a plurality of tapered spacer studs 50 extending from the chambers 20 of the former 10. These spacer studs 50 are hollow and allow any condensation which forms in the chambers 20 and spacers 30 to drain from the cast concrete structure.

In an alternative embodiment, the spacer studs are not tapered, and are removably attached to the chambers of the former. This allows the removal of the spacer studs after the casting of the concrete structure. The resultant hole in the wall of the cast concrete structure may be left, or plugged, or may be filled with a suitable filler material.

The chambers 20 and spacers 30 of the former 10 can be accessed via the hollow spacer studs 50, or the resultant hole when the spacer studs 50 are removed. This allows subsequent incorporation of pipes, cables and ducts into the internal cavities of the concrete slab after the casting process is complete.

Further, figure 7 shows a rigid mould 60. During the concrete casting process, the former 10 and reinforcement matrix 40 (not shown) are placed inside the mould 60. The walls of the mould may be re-inforced by placing wooden supports against their exterior sides 80, before pouring the concrete mixture into the mould 60. The mould 60 can then be removed after the concrete has set. Alternatively, the mould 60 may be left in place, and the cast concrete structure used in combination with its surrounding polyolefin mould 60.