Method for mounting a lifting anchor in a concrete hollow core slab and a bag for use in such a method

Technical field of the invention

The present invention relates to concrete hollow core slabs and their production.

Background of the invention

Concrete hollow core slabs are widely used for especially flooring, and roofing in buildings. The advantage of concrete hollow core slabs compared to conventional reinforced concrete slabs are their significantly lower weight. Slabs in prestressed concrete are usually produced in lengths of up to 200 meters. The process involves extruding wet concrete along with prestressed steel wires from a moving mold. The continuous slab is then cut to required lengths by a large diamond circular saw. Anchors are often incorporated into the concrete to be able to lift the slaps. However, it is difficult to establish to what extent the anchoring of the anchor meets the established safety requirements.

FI20185462A1 discloses a method of attaching a lifting member to a hole plate, in which method a hole is made in the hole plate, which is in communication with the cavity in the hole plate for inserting a square-shaped flexible net in the cavity through the hole. The net is positioned so that there is formed a space delimited by the net in the cavity, and concrete is cast into the space delimited by the net through the hole. Then a lifting member for the hole plate is mounted in the hole and the space delimited by the net before or after the casting of the concrete. When using such a square-shaped bag, the bag will not unfold the same way every time, and the concrete introduced into said bag will often only distribute to one side of the channel rather than to both. Hence, a solution is needed that insures a safe lift of a hollow core slab without danger of dropping it during the lifting operation. Description of the invention

It is an object of the present invention to overcome the above-mentioned problems.

One aspect relates to a method for mounting a lifting anchor in a concrete hollow core slab, comprising the steps of: a) Providing a hollow core slab with at least one cavity extending longitudinally or transversely across the slab; b) Forming a channel, of a size suitable for receiving a part of a lifting anchor, from one of the two opposing side faces of said slap and into said cavity; c) Inserting a bag with an open end and a closed end into said channel such that its open end flanks the walls of said channel and its closed end is positioned within said cavity; d) Pouring a castable material into said bag, thereby filling said channel and a part of said cavity; and e) Before hardening or curing of said castable material, positioning the insert of a lifting anchor into said castable material.

In the present context, the term "hollow-core slab" refers to a structural element incorporating at least one cavity extending longitudinally or transversely across the slab. The cavity is advantageously void (free air space) or it can be filled to some degree with e.g. a porous material. The essential characteristic required from the porous material is that it must not present any substantial resistance to air compression or expansion.

The channel may be formed while the hollow-core slab material is uncured/unhardened, or partly cured/hardened, or after the hollow-core slab material has completely cured/hardened. The channel may e.g., be formed by indentation or drilling. When the channel is formed into the cavity within the hollow-core slab, the bag may be inserted.

In the present context, the term "lifting anchor" should be broadly construed to encompass any such device for lifting the slab, including a coupler adapted for receiving a lifting anchor.

In the present context, the term “castable material” should be broadly construed to encompass materials such as cement, mortar, concrete, ceramics, thermoset plastics, and thermoplastics. Preferably, the castable material comprises cement, such as concrete, e.g., fiber reinforced concrete.

In one or more embodiments, the bag comprises a collar attached to its opening, said collar being adapted for preventing said opening from falling into the cavity.

In one or more embodiments, the method further comprises the step of: f) removing the collar from the bag by cutting, tearing, or the like. As the concrete hollow core slab is used for defining a building surface, it is preferred that it is smooth. Therefore, the collar should preferably be removed after the castable material has hardened or cured. For the collar to be easily removed from the remaining bag material, the bag may preferably be made from a woven or non- woven textile, where the treads are made from a material that can easily be cut or torn. Alternatively, the bag comprises a tear line where the material is weakened or a tear seal.

In one or more embodiments, the collar is a ring or a cross, e.g., made from metal or plastic. The ring or cross may have a diameter larger than the formed channel, such that it may rest on the face of the hollow core slab.

In one or more embodiments, the bag is porous, thereby allowing a part of the castable material to escape therefrom. This configuration secures that the castable material, e.g., cement or concrete, to react with the concrete of the slab, thereby securing the bag to the cavity walls of the hollow core slab. Preferably, the porous bag has an average pore size within the range of 0.5-5 mm, such as within the range of 1-4 mm, e.g., within the range of 2-3 mm. This allows a little of the castable material to reach the outer surface of the bag, and at the same time secure that the bag will not empty before the castable material will harden or cure.

For all embodiments of the method of the present invention, the bag is T-shaped with two closed ends and a single opening. In the present context, the term “T- shaped bag” should be interpreted to mean a bag having a cross section with a shape, which is similar to a capital T. This configuration will secure the filled bag within the cavity on both sides of the channel. Hence, the two closed ends of the T-shaped bag are preferably of equal length.

A second aspect relates to a bag for use in the production of concrete hollow core slabs, the bag being T-shaped with two closed ends and a single opening.

A third aspect relates to a T-shaped bag with two closed ends and a single opening.

A fourth aspect relates to a hollow core slab produced by the method according to the present invention.

In one or more embodiments, the bag further comprises a collar attached to the opening.

It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention. Brief description of the figures

Figure 1 shows a perspective view of a part of a hollow core slab, where channels have already been formed into the longitudinal cavities;

Figure 2 is a cross-sectional view of Figure 1 ;

Figure 3 shows a perspective view of a bag according to the present invention;

Figure 4 shows a cross-sectional view of a part of a hollow core slab, where a bag according to the present invention has been inserted into a longitudinal cavity through a channel; and

Figure 5 shows a cross-sectional view of a part of a hollow core slab, where a bag according to the present invention has been inserted into a longitudinal cavity through a channel.

Detailed description of the invention

Figure 1 shows a part of a hollow core slab 10 with four longitudinal cavities 12.

A channel 14 has been formed into each of two cavities 12. Figure 2 gives a better view of the channel 14 formed in a side face of the slap 10 and into a cavity 12. Figure 3 shows a bag 100 according to the present invention. The bag is T-shaped with two closed ends 110 and a single opening 120. The bag also comprises a collar in the form of a ring 130 attached to its opening 120. The bag is preferably made from a porous material with an average pore size within the range of 0.5-5 mm, thereby allowing a part of the added castable material to escape therefrom.

Figure 4 shows a cross-sectional view of a part of a hollow core slab 10, where a bag 100 according to the present invention has been inserted into a longitudinal cavity 12. The bag has already been filled with added castable material, and an insert of a lifting anchor 200 has been mounted therein. Figure 5 shows a cross-sectional view of a part of a hollow core slab 10, where the T-shape of the bag according to the present invention is better seen within the cavity 12.

References

10 Hollow core slab

12 Cavity

14 Channel

100 Bag

110 Closed end

120 Open end

130 Ring

200 Lifting anchor