In the casting of concrete walls and floors, shut¬ tering panels are used in the formwork structure. Con- ventionally, these shuttering panels consist of wood or plywood and are mounted in a frame which in most cases, especially if the shuttering panels are to be used repeatedly, is made of metal. For ergonomic reasons, the frames are often made of aluminium. Such shuttering panels are superior to many other types of panels, inter alia because of their low weight. Regardless of whether the frames are made of aluminium or some other metal, these prior art shuttering panels suffer from the disad¬ vantage that it is difficult to achieve satisfactory con- tact between abutting panels. If the joints are not tight, excess material may build up on the finished sur¬ face. The prior art shuttering panels with frames of e.g. metal are, further, disadvantageous in that the support¬ ing beams extending on the back of the wood or plywood sheet to impart bending rigidity to the structure must be located comparatively close to one another, frequently at a centre distance of 20-30 cm. This increases the weight of the shuttering panel, which is highly undesirable. Moreover, the prior art formworks are disadvantageous in that they are not insulated. In winter, it may frequently be necessary to insulate the formwork or supply heat to set the concrete in a satisfactory way. In summer, it may at times be necessary to insulate the formwork if satis¬ factory setting requires that the concrete be cooled. Swiss Patent Specification 514,764 discloses a shut¬ tering panel which consists of a laminated structure with two opposing wall-forming sheets and an intermediate cel¬ lular-plastic layer connected to the wall sheets. If such a structure were to be used as shuttering panel, the cel- lular-plastic layer might easily be damaged by stones and

other solid particles which may penetrate into the joint between the abutting edges of the shuttering panels.

German Patent Specification DE-C-3,429,303 discloses a shuttering panel having a circumferential frame with transverse stiffening beams for supporting the shuttering panel proper. This shuttering panel suffers from the dis¬ advantage that it is difficult to achieve satisfactory contact in the joint between abutting shuttering panels. _. German Offenlegungsschrift DE-A-1,684,359 discloses a similar shuttering panel, the edge portions of which are formed by the webs of U-sections, which also in this case makes it difficult to achieve satisfactory contact in the joint between _. abutting panels.

German Offenlegungsschrift DE-A-2,618,366 discloses a shuttering panel whose edges are protected by sturdy sec¬ tional elements of wear-resisting and oil-resisting rubber or plastic. However, this structure is not insulated and requires the use of a massive shuttering panel or a metal section with yielding edge protection members. This struc- ture is unsuitable for insulated shuttering panels.

One object of the invention is to provide a new type of shuttering panel which makes it easier to achieve tightness in the joints between abutting shuttering- panels in a formwork structure. Another object is to provide a shuttering panel of less weight than prior art shuttering panels, but of sufficient bending rigidity. A further object is to provide a shuttering panel which is insu¬ lated. Yet another object is to provide an insulated shut¬ tering panel of low weight, but of high bending rigidity. These and other objects of the invention are achieved by the shuttering panel as defined in claim 1. The sub- claims state especially preferred embodiments of the invention.

The invention will be described in more detail below, reference being had to the accompanying drawings of two preferred embodiments of the inventive shuttering panel.

In the drawings,

Fig. 1 is a perspective view of an embodiment of an inventive shuttering panel,

Fig. 2 is a section of a joint between two abutting shuttering panels in a formwork, taken approximately along line II-II in Fig. 1,

Fig. 3 shows a detail forming part of the inventive shuttering panel,

Fig. 4 is a perspective view of another embodiment of the inventive shuttering panel, and

Fig. 5 is a partly exploded view of the shuttering panel in Fig. 4.

The shuttering panel in Figs 1-3 has two thin oppos¬ ing sheets 10, 11 which preferably consist of plywood but also may be ma.de of other material. If made of plywood, the sheets may have a thickness of 4-15 mm. If.made of metal, e.g. aluminium, the sheets may have a thickness of about 1-2 mm. The desired thickness depends on the intended use of the shuttering panel and is easily deter- mined by the expert in the field. In general, it is safe to assume that a shuttering panel for floors may have thinner sheets 10, 11 than a shuttering panel for walls.

A cellular-plastic layer 19 of low volume weight and* comparatively high shear modulus is provided between the two sheets. The layer 19 is connected to the sheets 10, 11 across their opposing face sides, preferably by using an adhesive. The volume weight of the cellular-plastic layer

₃ may be 20-50 kg/cm . Preferably, the cells of the cel¬ lular-plastic layer are closed, since the shear modulus then becomes much higher than if the cells are open. With open cells, the shear modulus is usually about the square of the density, but with closed cells, it is generally about the cube of the density. At present, it is preferred that the cellular-plastic layer consists of an extruded, expanded polystyrene sheet which may have a thickness of 8-9 cm, so that the total thickness of the shuttering

panel is about 10 cm. A suitable glue is used to inter¬ connect the three layers across their face sides.

To reinforce the corners, corner or angle elements 12 are provided which are recessed into the side edges of the shuttering panel to give a smooth surface. These corner elements may be made of metal, rigid plastic, ceramics or, preferably, rubber. The corner elements 12 have inwardly projecting supporting members 13, 14 which, in the embodi¬ ment shown, have the form of internal flanges, but which may consist of inwardly projecting pins or the like. After assembly, these supporting members are in contact with the inside of the sheets 10, 11 to support these and prevent them from being pressed towards each other within the cor¬ ner regions. Further, the corner elements protect the cor- ners and prevent other damage thereto.

The circumferential edge portions of the shuttering panel are coated with a layer 15 of resilient plastic or rubber material. This layer, which is thin and may have a thickness of e.g. 1 or 3 mm, preferably consists of rub- ber. It covers the entire circumferential edge of the shuttering panel and preferably extends a short distance on to the face sides of the shuttering panel, as intimated in Figs 1 and 2. The protective layer 15 serves five dif- - ferent purposes. Firstly, it constitutes a yielding mecha- nical protection for the edge portions of the shuttering panel. Secondly, it prevents moisture from penetrating into the laminate, the glue and the cellular-plastic layer, thereby reducing the risk of swelling and delamina- tion. Thirdly, it acts as a highly efficient sealing strip in the joints between abutting shuttering panels because a high surface pressure arises in the joints between the sheets 10 and 11 of abutting shuttering panels. Fourthly, it serves as a yielding protection for the cellular-plas¬ tic layer if gravel or other foreign material should stick to the edges of the shuttering panel. Lastly, it functions as a release agent making it more difficult for concrete and cement to stick to the edges of the shuttering panel

or, in any case, making it easier to remove them. Thus, the protective layer 15 should be thin so as to yield to pressure from any solid particles in the joints between abutting shuttering panels. In this manner, any solid par- tides are absorbed in the joint because the protective layer 15 is deformed and produces depressions in the cel¬ lular-plastic layer 19 without any risk of this being worn off.

As is apparent from Fig. 2, the inventive shuttering panels can be supported directly by stringers 16 when used for the construction of floors, and there is no need of any joists or frame structures. Thus, a centre distance of 120-150 cm may be sufficient for the shuttering panels according to the invention. As can be seen in Fig. 1, both face sides of the shuttering panel may be formed with holes 17 in the vici¬ nity of the corners. In known manner, these holes may serve as mounting holes not only for keeping together abutting shuttering panels when these have been positioned in the formwork, but also for fixing the shuttering panels to the stringers. The holes 17 as well as holes 18 in the edges of the shuttering panel can, furthermore, be used when stripping the form from the hardened concrete.

The embodiment in Figs 4 and 5 differs from that in Figs 1-3 mainly in the design of the protective layers for the edges and the corner elements.

The shuttering panel in Figs 4 and 5 also comprises two thin opposing sheets 10, 11 which preferably consist of plywood, but may be of other material. The thickness and the design may be identical to those in the embodiment of Figs 1-3. Also in this case, a cellular-plastic layer 19 is provided between the two sheets and is connected thereto by a suitable glue.

In the embodiment in Figs 4 and 5, the corner rein- forcements are rubber elements 20 extending arcuately into the corners of the shuttering panel. The arcuate in-turned portion of the element 20 comprises stepped surfaces 21 on

which edge portions 22 of the sheets 10, 11 rest after assembly. To make room for the corner elements 20, an arcuate portion is thus cut off at the corners of the sheets 10, 11. There is a corresponding arcuate cut-out in the cellular-plastic layer .19 but, in order to expose the edge portions 22 of the sheets 10, 11, the cellular-plas¬ tic layer portion removed from the corner is larger than for the wall sheets.

The holes 17, 18 in the embodiment in Figs 1-3 are, in the embodiment in Figs 4 and 5, formed in the corner elements 20. This improves the strength of the structure.

The embodiment in Figs 4 and 5 comprises a protective layer 23 in the form of a thin sectional element of plas¬ tic or rubber. This sectional element has projections 24 to be inserted between the cellular-plastic layer 19 and the sheets 10, 11. If required, grooves can be milled in the boundary area between the sheets 10, 11 and the cel¬ lular-plastic layer where the projections 24 are to be inserted. Like the protective layer 15 in Figs 1-3, the • layer 23 is not thicker than e.g. 1 or 2 mm to acquire the same function and properties as the layer in Figs 1-3'. As indicated in the drawing, the protective layer 23 may be formed with a low ridge at its outer edges opposite to the sheets 10, 11 to further increase the contact pressure in the joint between abutting shuttering panels.

To enable recessing, the corner elements 20 are pro¬ vided with stepped surfaces 25 and 26 for accommodating the edge covers 23 and their projections 24.

The shuttering panels according to the invention are highly advantageous in that they have low weight but still sufficient bending rigidity to be used for concreting. Another advantage is that the edges and corners of the laminated panels are sealed with an elastic material in the form of the plastic or elastomeric layer 15, 23 which mechanically protects the core of soft cellular-plastic material. Since this layer 15, 23 consists of an elastic material, its tendency to crack is slight or nonexistent.

The layer protects the edges and corners of the laminate from penetration of liquid and from mechanical damage by impacts. Above all, this layer increases the tightness in the joints between abutting shuttering panels. Owing to its elasticity, it can yield without being damaged if solid particles, e.g. small stones, enter between abutting shuttering panels, while maintaining the tightness there¬ between. Yet another advantage of the layer 15, 23 is that its adhesion to the concrete is very low, so that it pro- tects the shuttering panel from the adhesion of mortar, cement mortar and concrete.

Further, the inventive shuttering panels are highly advantageous in that they insulate against heat and cold, thereby enabling concreting under difficult climatic con- ditions.

The drawings illustrate the preferred embodiments of the inventive shuttering panel which comprises two oppos¬ ing wall-forming sheets 10, 11 and an intermediate cel¬ lular-plastic layer 19. If the bending rigidity needs to be further increased, and if a certain increase in weight is acceptable, the laminate or sandwich construction may be composed of- two outer-wall-forming sheets, one or more intermediate-wall-forming sheets and a corresponding num- - ber of cellular-plastic layers, e.g. three sheets and two cellular-plastic layers. In this case, these layers are interconnected across their face sides, preferably by gluing.

To further increase the bending rigidity, spacers may be arranged between the various rigid sheets of the sand- wich construction. Such spacers should be placed at a dis¬ tance from the edges of the shuttering panel, since the cellular material should extend to these and be coated with the protective layer of plastic or elastomeric mate¬ rial. The spacers may have the shape of pins or strips and be mechanically connected to the sheets and glued to the cellular material.