The present invention relates to a composite wall panel with outer sides of concrete and with intermediate insulating material.

Small houses, as well as houses with several stories, and industrial buildings are now generally built with walls made of prefabricated panels.

Wall panels made of reinforced concrete, now in use, usually consist of two, at least five centimetres thick reinforced concrete layers with intermediate insulating material. A layer thickness of at least five centimetres is required for the concrete to give sufficient protection of the reinforcement, since if the reinforcing steel starts to rust, it will expand and may break the concrete layers. Concrete panels with a thickness of five centimetres are comparatively heavy; the density is about 2.4, and the panels therefore have to be mechanically connected to each other. One object of the invention is to produce wall panels, which are less heavy and have better thermal and sound isolating properties than previously known wall panels. The wall panels according to the invention also become more easy to handle than the previously known panels.

According to the invention, the wall panels are produced from two thin panels of concrete reinforced with oriented fibres and intermediate insulating material, preferably of mineral wool. The concrete sides are fixed by the steel fibres at the intermediate insulating material layer, forming a sandwich construction. The comparatively thin concrete sides and the intermediate, comparatively thick insulating material provide a very good sound-proofing and thermal insulation.

The panels according to the invention thus consist of two thin fibre concrete panels with intermediate insulating material, such as mineral wool or cellular plastic. In partition walls and in so called "joint spacing elements" the panels need not be structural elements, but instead the inherent strength of the thin concrete panels is quite sufficient, and the elements thus will be light. For

structural elements, the bracing only are made of fibre concrete, which fact, however, need not increase the weight of the panels with more than 20 - 22 kg/m ² .

The invention is characterized in that very thin fibre concrete panels are cast together with intermediate insulating material into strengthwise cooperating and very light wall panels, and in that a mixture of steel fibres and plastic fibres in the concrete attach to the insulating layer, when the form is vibrated. The mixture of oriented steel fibres and plastic fibres enhances the resistance of the concrete panels against blows and gives a more ductile rupture. The plastic fibres, preferably polypropylene, prevent micro cracks from forming in the panels and prevent the steel fibres from sedimentation when vibrating the casting form. In the outer panels of facing wall panels, the plastic fibres are the only reinforcement in the outmost 5 millimetres, which are kept free of steel fibres in order to prevent rust outbursts. The invention also comprises a new method of quick and economical orientation of the fibres in the desired directions without any slow manual processing.

The strength of the final products can be varied within wide limits depending on the intended use by the fact that larger or smaller fibre amounts quickly can change into orientations in different directions so that the desired properties are best obtained. The properties can also be varied in different ways by using different blends of different kinds of fibres.

According to the present invention the fibres are oriented in a concrete panel by vibrating the concrete material during the casting. The fibres are mixed into the concrete mass by stirring, and by performing the vibration according to the invention, during the casting the fibres will orient in the direction of the movement of the mass. By performing the orientation so that e.g. 40 % of the fibres are brought to orient themselves in about the direction of movement of the mass, and part thereof, e.g. 20 %, in the cross direction, with the remaining fibres scattered in different directions, a high strength in all directions is

obtained with the highest strength in the longitudinal direction, a good unity and a minium of crack formation, is obtained. The mixing conditions and the orientation are adjusted to the intended use, so that the properties of the final product always will be at the optimum, and the dimensioning and the consumption of material can thereby be kept at a minimum. We have found that suitable amounts of steel fibres are between 1 and 1.5 % by volume, and of plastic fibres, 0.1 - 1 % by volume, preferably between 0.2 and 0.5 % by volume.

Different fibres will act in different ways so that steel fibres, especially coarser fibres, are oriented much easier than plastic fibres, which fact also can be used in order to obtain an optimum orientation by mixing different fibres in suitable ratios. With a mixture of steel fibres and plastic fibres, the reinforcement in the longitudinal direction will thus to the greater part be comprised of steel fibres, while the plastic fibres will dominate in the cross direction. Short plastic fibres lay themselves preferably more easy in the longitudinal direction of the mass, while long plastic fibres are more affected by different flows and turbulence in the mass and are therefore not as easy oriented in the longitudinal direction as are the short fibres.

Suitable sizes of the steel fibres are a length of 25 - 40 millimetres and a diameter 0.3 - 0.4 millimetres, and suitable sizes of the plastic fibres are a length of 6 - 12 millimetres and a diameter of 35 - 200 microns. The sizes are approximate, and can be allowed to vary depending on the manufacture technique, and so can the form of the fibres. The plastic fibres may for example be square or ribbon formed. The fibre concrete advantageously contains 300 - 400 kg/m ³ of cement with a particle size < 5, preferably < 3 millimetres, and 1.2 - 1.5 % by volume of steel fibres and 0.2 - 1.0 % by volume of polypropylene fibres. The invention is described more in detail below through an example directed to the casting of a concrete panel according to the invention with reference to the accompanying Fig. 1.

A concrete mass was formed with a particle size < 3

millimetres and a cement content of 400 kg/m ³ and an addition of 1.2 % by volume of steel fibres having a length of 25 millimetres and a diameter of 0.3 millimetres, and 0.3 % by volume of polypropylene fibres having a length of 6 millimetres and a diameter of 35 - 200 microns.

In a laying-out carriage for the casting of panels of fibre concrete, 300 litres of the fibre concrete mixture was filled into the container 2. The out-flowing amount was controlled with the damper 3, whereby, and especially if the concrete mass has a high viscosity and the fibre content is high, a variable vibrator 4 on the container could be used in order to facilitate the flowing-out of the mass. In the container a slowly rotating screw could also be arranged, in order to keep the mass homogenous. The concrete did flow with guidance of guide rails 8 down onto an output feeder 5 with variable inclination and provided with a variable vibrator 6, and from this down onto the casting table 7. The thickness of the cast panel was controlled with the wiper 10. The flow over the output feeder 5 and the guide rails 8 orients the fibres, whereby the length of the output feeder also affects the degree of orientation. The flow velocity may be increased or reduced by changing the inclination angle of the output feeder, as is shown with the dashed lines of the output feeder 12 and the wiper 13, whereby the height of the casting table 7 can be changed correspondingly.

Because the guide rails 8 control the flow along the output feeder plane the degree of orientation is increased. The flow velocity and the vibration effect are variable and are controlled with control means.

The degree of orientation increases at lower flow velocity and higher vibration effect.

The longitudinal movement of the laying-out carriage can be varied continuously from 0 to 17.4 m/min and its cross movement between 0.75 and 3.0 m/min. The cross movement is used in casting of concrete panels being wider than the output feeder in order to lay out an even layer over the whole surface of the casting table.

The more coarse and heavy fibres, such as steel fibres,

are oriented more easy than the thinner and lighter plastic fibres, such as polypropylene fibres, which demand a longer orientation distance, i.e. a longer output feeder or smaller inclination of the output feeder. The most suitable degree of orientation has to be tested out empirically and is affected by the consistency of the concrete, the fibre concentration, the type of fibres used and the composition of said fibre mixtures.

Using the present invention, thin panels of concrete can be produced with as good properties as the earlier eternite panels, and also panels with better properties than those most frequently used today, that is the plaster panels which are fragile and sensitive to moisture. Further, thicker panels, 5 centimetres or more, can be produced for use as partition walls, alone, or for outer walls and structural wall elements.

Other products can be manufactured with fibres oriented in the same way, such as machine foundations and similar constructions. The mass from the output feeder is thereby allowed to run down into a form so arranged that the product will have the exact dimensions and with insertions for holes, notches etc., so that only a small or no supplementary work is required.

The outer panels of the wall panel according to the invention are manufactured according to the above described method and with the means for the orientation of the fibres, and will be described more in detail with an example and with reference to Fig. 2.

In a form, the intended inner panel 20 was cast with a thickness of 15 millimetres and with a reinforcement of 1.2 % by volume of steel fibres and 0.3 % by volume of polypropylene fibres. The casting and reinforcement of the panel and the orientation of the fibres took place in the manner described above. Insulating material 21 was place on the panel, consisting of 20 centimetres of mineral wool, and on the insulating material the outer panel 22, 23 was cast, with a thickness of 2 centimetres, whereby firstly, a 1.5 centimetres thick layer 22 was cast in the same way as the inner panel, and thereupon an upper, 5 millimetres thick

layer 23 was cast, containing only polypropylene fibres as a reinforcement. In order to compress the concrete to a certain extent, and to increase the adherence to the mineral wool, the form was vibrated during the casting. The panel could be stripped from the form the day after the casting, and the concrete panels exhibited a very god adherence to the insulating material.

The above disclosed fibres, 1.0 - 1.5 % by volume of steel fibres with a length of 25 - 40 millimetres and a diameter of 0.3 - 0.4 millimetres, and 0.2 - 0.5 % by volume of polypropylene fibres with a length of 6 - 12 millimetres and a diameter of 35 - 200 microns, gave good results. However, dimensions and amounts outside these ranges could well be used, such as other particle sizes in the concrete. Normally, a particle size < 5 millimetres and preferably < 3 millimetres is used in the concrete. An insulation with 10 to 30 centimetres of mineral wool or thinner insulation with cellular plastic is suitable, and preferably 20 centimetres of mineral wool is sufficient and economically most advantageous for most walls.

In order to get a measure of the adherence between the fibre concrete and the insulating material, a property which is essential for the function of the panel as a structural element, especially in view of wind load, the shear load was investigated. The mean shear load was with a mineral wool insulation, 28 kPa. The characteristic strength according to BBK (Conditions for concrete constructions, Stockholm 1979, Band 1, page 52) becomes fk = 23 kPa.

A wall panel with the width of 2.4 meters and the height of 3.0 metres was loaded with a pressure force of 114 kN, corresponding to 3 times the normal load in an actual case. No important deformations could be observed under the influence of the load, and the break load thus lie substantially higher. The fibre reinforcement makes it suitable also to substitute conventional concrete for high strength concrete with a compressive strength of 80 to 120 MPa.

At bending testing the bending moment was 14.6 kNm/m. In comparison thereto, the bending moment at normal wind load is

0.36 kNm/m, i.e. 1/40 of the bending moment at the test. This stiffness of the element depends on that the outer panel and the inner panel cooperates through shear stresses in the insulating material. The maximum shear stress at the test load can be calculated to 158 kPa, which is substantially higher than the values obtained in clean shear tests according to the above. Fire and load tests have also been performed, and the panels were shown to have a separating and structural function for 120 minutes, corresponding to fire class 120 A.