The invention concerns a concrete sandwich con¬ struction element, mainly for use in facades, consisting of two concrete plates which are interconnected and which have a layer of thermally insulating material between them. Depending on the requirements, it is necessary that this layer of material has sufficient strength and stiffness to transfer shearing forces be¬ tween the two plates. This is to produce a stressed-skin effect.

Concrete facade elements are well-known in the construction industry and have been widely used since the 1950 s. These elements are normally made up of a sandwich construction consisting of an outer plate of reinforced concrete with a thickness of typically 7 cm and an inner plate of reinforced concrete with a thick¬ ness of typically 10-15 cm. These two plates are inter¬ connected by means of steel bars. A layer of thermally insulating mineral fibre material, such as Rockwool, Glasuld (both of which are trade names) , or polystyrene is placed between the plates. The elements are factory- produced in steel moulds in which the reinforcement net for the outer plate is initially placed. The concrete is then cast into the bottom of the mould. In order to hold the outer and inner plates together, the reinforcement net is provided with steel anchoring braces which pro¬ trude through the concrete. After casting and vibration of the outer plate, the insulation is laid out and pressed down over the steel anchoring braces where these protrude. The reinforcement net for the inner plate is then laid out, and the plate is cast. Prior to the rein-

forcing and pouring of the concrete, formwork is carried out for the placing of window and door openings. This is struck and removed from the element after the curing of the concrete. The net weight of the element is approx. 500 kg/m2. Elements of this type can only be produced to order, due to the placement of window and door openings.

The outer plate has no loadbearing function, serving only as a climatic screen. The inner plate, which forms the inside wall, can be loadbearing and is dimensioned according to the specified static require¬ ments. The thermal insulation has no loadbearing or other static function.

The purpose of the invention has been to produce a concrete element of the type described above which is less expensive to manufacture and which, to a higher degree, fulfils the specified technical and functional requirements, including longevity. Moreover, with respect to transport and erection, the weight of the element is considerably less than that of a traditional concrete element so that the load on the main load¬ bearing system in high-rise construction is also re¬ duced.

In the following account of construction and dimen¬ sioning, behaviour, materials and production tech¬ niques, it will become evident that this has been achieved by the invention.

Construction and dimensioning are much simpler and plate thicknesses considerably reduced in comparison with traditional concrete elements. Thus, by making use of the stressed-skin effect, it is normally suffi¬ cient for the loadbearing or non-loadbearing inner plate to have a thickness of, for example 25 mm and the outer plate to have a thickness of, for example 15 mm as the plates are fibre reinforced. Likewise, it is not neces¬ sary to strengthen the plates by means of ribs or the like round the edges of the element or at window

openings, etc. In principle, the construction thus con¬ sists of two completely level, thin concrete plates interconnected by means of a correspondingly level intermediate layer of thermally insulating material, without the use of steel braces, ribs or other such devices which complicate production. The thickness of the insulation layer could, for example be 200 mm. The total thickness of the element could thus typically amount to 240 mm.

The static behaviour of stressed-skin elements differs essentially from traditional concrete sandwich elements. Fig. 2A depicts the erection, support, and loading of the traditional concrete sandwich element. In fig. 2B, the enlargement shows that the load is applied to the inner plate. Fig. 2C shows how failure occurs; the inner plate fractures without the insulation material or the outer plate having any influence on the loadbearing capacity.

Likewise, fig. 3A shows the erection, support, and loading of the element according to this invention. Fig. 3B, in a larger scale, shows that the load is applied to the inner plate, and fig. 3C shows that the element as a whole, buckles in a collapse situation (shown in exag¬ geration for the sake of elucidation) . In this way, as shown in a larger scale in fig. 3D, a shearing Z occurs between the outer and inner plates. As the insulation material has great shear strength as well as a high modulus of elasticity for shearing, it will lock shearing movements, thereby, to a certain extent, pre¬ venting buckling and thus failure. The locking of the

shearing movements will lead to tensile stress in the buckling plate. The crucial factor for collapse is not the shear strength of the insulation material, but the modulus of elasticity for shearing, on which the size of deflection, the moment arm, depends. At the exact moment it passes the critical value at which the stiffness of the element cannot cancel out the deflection, an accel¬ erating collapse starts. Calculations and tests per¬ formed at a recognised testing and research laboratory (the Norwegian Building Construction Research Institute in Oslo) show that the ultimate strength of a facade element with a 25 mm loaded inner plate is approx. 500-1500 Kn/m, depending on the type of mineral wool insulation used as the shear strength and modulus of elasticity increase with increasing density or fibre compactness, but this is also dependent on fibre structure (product) .

In order to improve the loadbearing capacity of the element where, for instance, the stressed-skin effect of the insulation materials is too weak, a thicker inner plate can be used, or alternatively strengthening of the edges, such as those shown in figs. 1C and IF. The strengthening of the edges can be dimensioned and designed according to the static requirements.

The element used as flooring will be exposed to a strong moment, but not to the normal stress as when used as a facade element. In this case, the loadbearing capacity depends on the shear strength of the insulation material, while deflection depends on the modulus of elasticity for shearing. This will entail constant shearing stress in the insulation material - the oppo¬ site of the case where the element is used as a facade element - and corresponding tensile stress in the lower plate (ceiling) . Calculations and tests show that the construction can be used as a flooring element, e.g. in normal housing construction with spans of up to approx.

5-6 m with a deflection, with maximum loading, of no more than 1/500 of the span. Both tensile stress in the lower plate (ceiling plate) and shearing stress in the insulation are lower than the calculated values as well as lower than the values ascertained during material tests with a reasonable safety factor. At right angles to the loadbearing direction, the fibre rein¬ forcement effect in the plates will also work, and the shear strength and the modulus of elasticity for shearing of the insulation material will still be effec¬ tive, thus ensuring a cross reinforcement effect.

Local static elastic co-functioning between the plate and insulation under, e.g. the effect of impact, is important, due to the small plate thicknesses. The insulation functions as a supportive backing which pre¬ vents fracture in the plate. Fracture occurs if the plate is too stiff - which also depends on its thickness - and/or has too low a bending strength, i.e. the plate has been too weakly fibre reinforced.

Fracture precautions:

1) Elastic co-functioning between the plate and insulation material in order for the insulation material to support the plate, thus maintaining the deformation below breaking point.

2) High bending strength of the plate.

3) High modulus of elasticity for compression in the insulation material.

To achieve optimum impact resistance, the moduli of elasticity of the plate and the insulation material must be harmonised. Also, the plate must have a fibre rein¬ forcement which provides the necessary bending strength.

Element behaviour with respect to fire differs considerably from traditional concrete facade elements. The fire resistance (BS60)1 is due to the large heat capacity of concrete combined with good thermal conductivity. Therefore, during a fire test, the rise in temperature of a 150 mm concrete inner plate will only occur slowly and will not, within the 60-minute period, reach the critical limit of approx. 450°C at which the loadbearing capacity of concrete is destroyed.

With an inner plate concrete thickness of, for example approx. 25 mm, the temperature of the concrete, according to the invention, will reach approx. 920°C after a 60-minute fire test. By making the concrete material itself capable of resistance to fire, the fire- -resistant capabilities (BS60) for the construction as a whole can be achieved. Thus the element can endure high temperatures without loss of the calculated loadbearing capacity and without noticeable cracking or deformation. Regarding the technical mixing formula with respect to fire, see description below on materials for the inner plate. In terms of fire resistance, there is a free option regarding material thickness. The mineral wool fibres of the insulation material, which are embedded approx. 2 mm into the concrete, can endure approx. 1000°C, thus remaining intact during a fire.

The very high temperatures partially penetrate the insulation material and burn away the phenolic resin which serves as a proofing and strengthening agent in the insulation. However, the insulation still maintains enough of its strength to prevent a collapse.

The combined fire-resistant properties of the element construction, including form stability, is dependent not only on the fire-resistant properties at high temperatures of the concrete material itself, but also on the expansion and contraction of the concrete

material, which, through the stressed-skin function, brings about a curving of the element construction. With no movements of the concrete material there is no curving of the element. During a fire, it is therefore important for the stability of the construction and the loadbearing capacity that the deformation of the con¬ crete caused by temperature change is minimised.

This problem can be solved by the mixing formula, partially through the mixture ratio of cement and aggregate as cement contracts and aggregate expands during increased temperature in case of fire and par¬ tially through choice of cement and aggregate which together result in minimal combined deformation caused by temperature change in the cast concrete.

Fig. 14A shows an example of deformation due to

temperature change in concrete cast with normal white Portland cement and sand with chamotte (Leca, for example) . This produces quite moderate combined deforma¬ tion in the concrete due to temperature change which, by means of the cement/sand mixture ratio, can be con¬ trolled to approach zero at 950°C. This corresponds to a 60-minute fire test. Fig. 14B shows an example of con¬ crete with high alumina cement and chamotte sand (for example Leca sand) , each of which have minimal deforma¬ tion due to temperature change. Here, too, the deforma¬ tion can be controlled to approach zero at 950°C by means of the cement/sand mixture ratio. This mixture is particularly suitable in constructions with especial¬ ly strict fire requirements as the high alumina cement is only minimally weakened, approx. 20% at 950°C.

For a 2.5 m high and 0.24 m thick facade element, for example, the calculated maximal deflection during a fire test - the outward curve from the neutral recti¬ linear position - is in these two cases approx. 2 mm and 1.3 mm respectively, and the deflection of a 2 m high and 60 mm thick fire door element is approx. 4 mm and 3 mm respectively. However, for both types of element, there will be no deflection after a 60-minute fire test with a temperature of approx. 950°C.

To a certain extent, improved material properties are responsible for the high technological quality of the element construction, as defined in this invention.

Rockwool-batts (trade name) can, for example, find application as mineral fibre insulation material. These are manufactured with a low shear strength and a correspondingly low modulus of elasticity for shearing. However, after a process of lamination, i.e. the cutting up into laminae, which are turned at 90° and rejoined, the shear strength can be increased approx. eight times, while the modulus of elasticity for shearing can be increased approx. ten times, as shown in figs. 10-11. By

using batts, which are a standard product, the shear strength can thus reach approx. 100 kN/m2, the equi¬ valent of the weight of a 4.0 m thick concrete outer plate.

As shown in fig. 11, the improved strength pro¬ perties are due to the fact that, as a result of lamina¬ tion, the fibres lie in layers at right angles to the element plane and parallel with the loadbearing direc¬ tion. In these layers, the fibres are oriented in a direction at right angles to the element plane and with an angle of divergence of approx. 90°. At the point where the fibres cross, they are adhered by a drop of phenolic resin. In this way, at system of lattices is built up between the flanges (outer and inner plates) which affords great loadbearing capacity and stiffness as the modulus of elasticity for mineral wool fibres is approx. 1000 GPa. The ultimate tensile strength amounts to approx. 1200 MPa.

As an added strength resource, the batts can be supplied with an increased phenolic resin content, in which case the shear strength and modulus of elasticity for shearing can be increased to approx. twice as much. A further strength resource is for the laminae, during lamination, to be adhered with a polymer or similar material, or, for instance, with cement paste. Ribs are thus formed between the flanges (outer and inner plates) which are reinforced with the fibres of the insulation material, thus forming a lattice structure in the same plane as the rib. These ribs will strengthen the stressed-skin function and thus increase the loadbearing capacity and stiffness of the construction (fig. 13) .

The establishment of ribs can also include edge ribs at the edges of the element where the strength of the.plates with regard to impact stress would otherwise be low. This is especially important in terms of transport and erection. It also provides for the

environmental advantage of sealing in the mineral wool insulation.

Another strength resource aims at preventing shear rupture of the insulation material at the ends, i.e. the supports, if the element is used for flooring. The fracture is not due to fibre fracture, the tensile strength of which is three times that of steel, approx. 1200 MPa, but due to a breaking up of the fibre struc¬ ture. If, therefore, the structure is locked by bonding or adhesion of the fibres at the point where they cross, a considerable increase in the shear strength, tensile strength and compressive strength and the corresponding moduli of elasticity can been achieved. This structure locking can, for instance, be carried out with a bonding agent which penetrates the mineral wool so that the greatest possible number of fibre intersections can be fixed with the minimal amount of bonding agent, preferably an adhesive with a high modulus of elasticity.

This bonding process could, for example, be re¬ quested to be performed by the mineral wool manufacturer on ordering, in which case, for example a phenolic resin would be used as a bonding agent.

Depending on the circumstances, when using the element as flooring, it can be advantageous to make the ribs with, for example a polymer adhesive with a con¬ siderably lower modulus of elasticity for shearing than cement paste. In this way, the modulus of elasticity for shearing of the ribs in a 1 m wide element approximately equals the modulus of elasticity for shearing of the mineral wool insulation. An elastic collaboration between the ribs and the insulation in the transference of shearing forces is thereby established. Thus, the loadbearing capacity is approximately doubled, provided that failure does not occur as tensile failure on the under-side of the element.

To prevent collapse of the rib itself, it can be advantageous to use an adhesive which slightly pene¬ trates - a few millimetres - into the insulation. This can, for instance, be achieved by atomizing by means of compressed air spraying or by using a foaming-up adhesive.

The connection between the insulation material and the outer and inner plates for the transference of shearing forces and tensile stresses is assured by fusion between the layers. This fusion is achieved by mechanical means, such as pressure, vibration, possibly ultrasound and possibly through an intermediate layer of cement paste. A vacuum can also be created in the insulation material to achieve the effect. The process of injecting the concrete or cement paste into the insu¬ lation material can be made more effective by using a super plastification agent and possibly a detergent.

By injecting the cement paste into the mineral wool insulation to a depth of, for example 2 mm, the already fibre reinforced concrete or cement paste will obtain an extra fibre reinforcement of approx. 2.5 vol.% with the use of an insulation material with a density of 75 kg/m3 and approx. 5 vol.% with a density of 145 kg/m3. The reinforcement effect for the concrete plate will also be optimally increased by this technique as the concentration of reinforcement will be highest at the plate surface, i.e the side facing the insulation. The total amount of fibres will be effective in reinforce¬ ment without loss of anchoring fibre length as the length of the fibres in the batts is reckoned to be infinite. The format ratio fibre length/fibre thickness ranges from approx. 102- .

With an approx. 200 mm insulation thickness, viable in a temperate climate, a U-value of approx. 0.20 W/m2K can be achieved. The density of the mineral wool can, for example be 70 kg/m3 as in standard concrete element

batts, or for example 140 kg/m3 as in standard terrain batts - depending on strength and fire requirements. If the thickness of the insulation layer is increased, both the insulation capacity and the stressed-skin effect, i.e. loadbearing capacity will be improved when the element is used as a facade. This is due to the fact that the insulation thickness, as a proportionality factor, is part of the calculation formula.

The outer and inner plates are made of concrete/cement mortar which is fibre reinforced with plastic fibres, such as polypropylene or a similar material, amongst other things out of consideration to fire resistance (see section below) . These fibres are cut into appropriate lengths, for example approx. 12 mm. The number of fibres that are mixed in is dependent on the static functional requirements, for instance 1, 2 or 3 vol.% (in relation to the total mortar volume). In this way, formation of cracks is prevented, and the material (the plates) incurs ductile rupture as opposed to brittle rupture, as would be the case without fibre reinforcement. Furthermore, the plates have an increased ultimate tensile strength which can be used in static calculations, contrary to the ultimate tensile strength of unreinforced mortar in connection with brittle rupture. In the latter case, the ultimate tensile strength cannot be used as even small impact stresses or temperature gradients will cause breaking stresses.

Mineral fibres for the reinforcement of concrete will also lead to an increase in tensile strength and can advantageously be used with plastic fibres which have the tensile strength of steel and a modulus of elasticity roughly on a level with that of concrete. Stress-strain curves (stress-strain relation) recorded during bending rupture tests, both on concrete exclusively reinforced with plastic fibres and on

concrete reinforced with a combination of plastic fibres and mineral fibres, show good ultimate tensile strengths, approx. 15-20 MPa, as well as ductile rupture with great internal work of fracture, i.e. plastic stress-strain relation.

Depending on the circumstances, a fibre cloth can also advantageously be used as fibre reinforcement. This is best placed near the surface of the plate, thus giving optimum reinforcement effect in connection with the bending moment in the concrete plate itself. It is advantageous to use reinforcement fibres with small fibre thicknesses, e.g. 5-10 mm x 10-3, as this provides high fibre surface area thus giving corre¬ spondingly good adhesion to the cement matrix and thereby greater reinforcement effect. The format ratio (fibre length/- fibre thickness) should be as high as possible as this defines the extent to which the tensile strength of the fibres is utilized. With a low format ratio, the fibre strength is not utilized as well, as on rupture the fibres are pulled out. The optimum format ratio is thus dependent on the fibre adhesion to the cement matrix and is calculated accordingly. In terms of mixing, the shorter the fibre length,the lesser the problems.

Anchoring of the fibres to the cement matrix can be assured/improved with a low water/cement ratio, but also by adding an adhesive, such as a polymer (e.g. epoxy or acrylic resins) to the concrete/mortar.

Permeability to water vapour can, with advantage, be greatest in the outer plate to prevent condensation - depending on the climate - and this can be regulated by the water/cement ratio, in which case this must be highest for the outer plate, for example approx. 0.4. If the figure is higher than 0.4, there is capillary water in the concrete/mortar, and, as such, there is no guarantee for frost resistance. It is advantageous to

use white cement which is low alkali and sulphate-resistant, but grey cement can also be used as well as dyes, pigments, and surface structure can be achieved by using a profiled mould bottom. To achieve a good flow and prevent air pockets, it can be advantageous to use a plastification agent and possibly an air-entraining agent. In order to speed up the hardening process to enable a 24-hour production cycle, it can be advantageous to use an accelerator/hardening with heat application.

To avoid absorption of water from rain, for example, and the consequentially damaging chemical reactions in the concrete and fibres, it is possible, in order to ensure longevity, to impregnate the outer surface with a hydrophobic penetrant. This penetrates a few millimetres into the concrete, thus repelling water without noticeably reducing the permeability of water vapour.

The inner plate, which is possibly loadbearing, must have

1) high fire-resistant capacity

2) high strength

3) high resistance to water vapour diffusion.

Point 1 is achieved by the mixing formula for concrete/- cement mortar which is characterised by a water/cement ratio of approx. 0.25-0.35 and a microsilica content of approx. 20-25% in relation to the amount of cement. This causes a reduction in the Ca(OH)2 content, which normally accounts for 50% of freshly hardened cement, to approx. 1/10. Similarly, the liberation of chemically bound water is impeded and thereby also the destruction of the binding properties of the cement during a fire with temperatures exceeding approx. 450°C.

Reinforcement fibres of plastic, such as

polypropylene or the like of, e.g. 12 mm in length, which correspond to a minimum of approx. 0.5% of the total weight, are used. During a fire, the plastic fumes and water vapour (partly from the chemically bound water, partly from the hygroscopically bound water in the cement gel and partly from possible capillary water) are drained out through the micro-canal system which the plastic fibres have left in the concrete. During heat exposure, the plastic fibres are broken down from the exposed surface of the element and inwards, thus letting the vapours escape without shattering of the concrete. Tests have shown that the concrete can withstand over 1000°C without mentionable loss of strength. In addi¬ tion, mineral reinforcement fibres can be used, such as Rockwool s, as they have a stabilising effect on the concrete so that during and after a fire, the concrete thus remains even and level.

Points 2 and 3 can be achieved as described above. In addition, it can be advantageous to use sand of good quality with an ideally continuous grade curve (i.e. optimum ratio between the amount of coarse grades and fine grades to minimalise the interstice percentage) . This enables good flow, strength, density and securing of the reinforcement fibres.

As aggregate, naturally found sand and stone can be used, but also materials of other origin can conceivably be used, for example clinker or other calcinated materials.

Other types of cement can wholly or partially be used as an alternative to Portland cement in the outer and/or inner plates, for example high alumina cement which is highly fireresistant.

According to this invention, the production tech¬ nique of element construction opens up many new pro¬ spects in comparison with the traditional concrete facade element. There are, for example, no activities

which interrupt production, such as the positioning of the reinforcement grid when pouring the outer plate, the placing of steel braces in the concrete of the outer plate in order to anchor the inner plate, the placing of formwork for window openings and the fitting of insula¬ tion around these, the positioning of the reinforcement grid for pouring the inner plate, recesses for edge strengthening (increased plate thickness) , and the plac¬ ing of special reinforcements in these, and the pos¬ sible placing of electrical and plumbing/heating instal¬ lations. It is thus possible to bring about the estab¬ lishment of continuous production with the use of, for instance extrusion production machinery, as shown in figs. 8A-B and discussed below in connection with the explanation of the drawings. It is also possible to practise stationary piece-by-piece production as used with traditional elements.

In connection with continuous production, a con¬ tinuous length of ready-laminated insulation slab (batts) can flow into the extrusion production machinery, as shown in fig. 8A, having been laminated in a machine, the function sequence of which could be as shown in figs. 9A-E.

An important part of the production sequence is the mixture of the concrete/mortar, and the particular thing about this is the mixing in of up to 3 vol.% of fibres, for example 12 mm long plastic fibres plus possibly mineral fibres. This is not possible with the usual mixing machinery without lumps forming in the finished mixture. The mixing technique to be used aims to dis¬ perse the fibres in two stages: firstly, air dispersal and secondly, further dispersal in mixing the mortar.

With the use of compressed air, the preceding air dispersal can be achieved by the blowing apart of the pre-cut fibres (in lengths of, for example 12 mm) to cause a volume increase, like a feathery mass, after

which they are put into the mixing machine. Alternative¬ ly the fibres can be cut in a supplementary machine in connection with the mixing machine after which they are blown into the mixing chamber where they float down like snow.

The further dispersal throughout the mortar in the mixing machine is achieved by means of one or more stirrers, depending on the size of the mixer, either gear- or motor-driven. An example of a stirrer of this kind is shown in figs. 12A-D. The stirrer should be high-speed with, for example 1000-1400 r.p.m. to ensure that plenty of mixing energy is applied per unit of volume. This may cause a temperature rise in the finished mixture, possibly up to 40°C. To prevent the mixing in of air in the mortar, the mixing chamber should be deeper than usual, and the stirrer should be placed well down in the mortar volume.

The mixed-in fibres will be oriented in random directions in the concrete/mortar volume, meaning low reinforcement effect. This can be improved if the fibres can be given the same direction, parallel to the plane of the plate and, to a certain degree, concentrated near the surfaces of the plate. This can be done by placing rectifiers in the form of plates and/or ribs in the feeding duct and nozzle of the extruder.

The mixture-pouring process can alternatively be undertaken by spray casting with, for example a spray gun which can either be manually or mechanically operated. Due to the spreading, there should be screens along the edges to intercept the material which fails to strike the mould. The problem of establishing an even, level surface on the sprayed out concrete is solved by rolling/stopping so that in the case of a subsequent laying of insulation, optimum contact can be achieved.

The traditional concrete facade element, built as a sandwich construction has a number of poor

characteristics:

1. Short life span of typically approx. 20-30 years, the major cause of which is corrosion of the reinforcing steel, largely due to carbonation and micro- -cracks, and increased by dampness when exposed to frost.

2. Great weight, typically 450-550 kg/m2, which is disadvantageous and causes increased transport and erection costs. Furthermore, it is also disadvantageous in connection with loading of the loadbearing structure.

3. Poor ability to "breathe" (permeability for water vapour, 02, C02 and other gases) which causes poor indoor atmospheric conditions exacerbating allergies and breathing difficulties for the occupants.

4. Poor insulating ability; U-value approx. 0.35 W/m2K as a thicker layer of insulation will increase the already large construction thickness of 32-35 cm and result in a disproportionate cost increase, due to the edge ribs, window openings, and steel braces between the outer and inner plates. There are furthermore thermal bridges in the form of steel braces and edge reinforce¬ ments.

The innovation of this invention lies in the fact that, in connection with the stressed-skin effect, a design and dimensioning, fibre-reinforcement and mixing formula are all used, and these, along with the produc¬ tion techniques described, permit the following charac¬ teristics:

1. Long life span as there are no steel reinforce¬ ments or braces and no micro-cracks. The latter is due to the high degree of fibre reinforcement and the use of thin plate thicknesses. The fibre reinforcement has an almost unlimited life span, approx. 100-200 years

(confirmed during polypropylene fibre tests at the Danish State Building Research Institute) .

2. Low weight, typically approx. 100 kg/m2, which makes for lower transport and erection costs and minimal loading of the loadbearing structure.

3. Good ability to "breathe", approximately five times better than traditional concrete facade elements as the thickness of the concrete amounts to approximate¬ ly one fifth of traditional elements. Resistance to water vapour diffusion is proportional to thickness. This leads to a good internal atmosphere - as with a brick wall.

4. Good insulating ability. A typical insulation thickness of 200 mm leads to a U-value of approx. 0.20 W/m2K and not necessarily any thermal bridges. A greater insulation thickness provides a higher stressed-skin effect which in turn results in an improved loadbearing capacity. Furthermore, the extra insulation thickness is less expensive than the original thickness as the lamination costs are independent of the insulation thickness.

5. The loadbearing capacity is high in relation to the quantity of material or net weight. Maximum load¬ bearing capacity is no less than that of a traditional concrete facade element as the inner plate can be dimen- sionally designed for various needs, for instance 150 mm.

6. High fire resistance ability (BS60 or BS120) with an inner plate of only 25 mm and an outer plate of only 15 mm as the concrete material itself has been made fire-resistant (unlike traditional concrete elements) which means that thickness of the concrete in terms of fire resistance does not have to be taken into consider¬ ation.

7. High sound insulation as sound bridges between the outer and inner plate can be avoided and with the

mineral wool insulation functioning as a sound absor¬ bent.

8. Apart from being used as a facade element, load¬ bearing or non-loadbearing, the construction can also be used as a flooring or roofing element with a span of approx. 5-6 m, as an interior wall, loadbearing or non— loadbearing partition wall or sound insulating/fire— resistant party wall, as a door or gate, fire-resistant or non-fire-resistant. In addition, it can be used in the shipbuilding industry as fire-resistant walling, panelling, doors, gates, etc.

9. Uncomplicated production techniques as there is no steel reinforcement and no steel braces to hold the two plates together, no edge strengthening of the plates, etc. Also, there is no formwork for window or door openings as these 2 Danish fire classification: fire-resistant for 60 and 120 minutes respectively, can be cut at a later point in time than during the actual production process, thus allowing production to stock. The activities mentioned above, as in a traditional concrete element, interrupt the flow of production, but the invention, as described, allows for the establish¬ ment of the following:

10. Continuous production contrary to that applying to traditional concrete elements, and

11. Low production costs, approx. 2/3 of the costs of traditional concrete elements.

Thus, it is evident that this invention represents an epoch-making new construction.

In the following, this invention is illustrated by more concrete examples, as shown in figs. 1A-1F, 2A-2C, 3A-3D, 4A-4B, 5A-5F, 6A-6C, 7A-7D, 8A-8B, 9A-9E, 10-11, 12A-12B, 13 and 14A-14B.

The drawings in figs. 1A-1C show a facade element, as described in this invention, seen from the front, in a vertical section and in a horizontal section. (2)

indicates the outer plate of the element, (4) the inner plate, (6) possible strengthening of the inner plate along the vertical edge, (8) insulation, and (10) assembly bolt which is concreted into the edge strengthening. The outer plate is 15 mm thick and cast with white cement with a possible water-repellant sur¬ face treatment. The insulation is, for example laminated Rockwool element batts. The inner plate is 25 mm thick. The physical properties are as follows: U-value approx. 0.20 W/m2K, BS60, ultimate strength with linear loading 50,000 kg/m (with industry terrain batts of 145 kg/m3 approx. 100,000 kg/m), good sound insulation, net weight of approx. 100 kg/m2 and no thermal bridges. The drawings in figs. ID-IE show an enlarged picture of the vertical and horizontal sections respectively where the edge strengthening (6) and assembly bolt (10) are shown more clearly.

The drawings in figs. 2A-2C show the typical placing of the traditional concrete element at the sup¬ ports, loading and the failure situation in fig. 2C, as discussed in the section on static behaviour.

The drawings in figs. 3A-3D show the corresponding pictures for the element according to this invention.

The drawing in fig. 4A shows a cross section of the external wall of a building constructed with facade elements of the kind according to this invention. (12) indicates the element, (14) a load distributing wall plate and (16) the roof construction as a whole, (18) and (20) indicate a normal foundation and floor con¬ struction. The drawing in fig. 4B shows an example of a horizontal section at the corner of the building. The joints (22) between the elements are, for example filled with polyurethane foam or possibly mineral wool covered on the outside with a rubber strip or plastic sealant and on the inside with a mortar joint or the equivalent.

The drawing in fig. 5A shows part of a high-rise

building facade and in fig. 5B a corresponding vertical section of the facade where (12) indicates the element, (26) the loadbearing concrete beams in the facade and (28) a traditional concrete floor. Fig. 5C shows the corresponding horizontal section of the facade.

The drawing in fig. 5D shows, in an enlarged ver¬ tical section, an example of an element joint and the assembly to the loadbearing concrete beam with a bearing bracket (24) , which is attached to the facade beam and designed as shown in fig. 5F. This enables it to embrace the corners of four elements which meet where the vertical and horizontal joints cross. (12) indicates the element, (26) the loadbearing concrete facade beam and (28) the floor. Fig. 5E shows a horizontal section with the joint (22) and bearing bracket (24) .

The drawing in fig. 6A shows a perspective picture of box houses built together in two storeys in which the walls, floors, and ceilings are made up of elements according to this invention. Fig. 6B shows a cross-sec¬ tion through the building, and fig. 6C shows an enlarged cross-section of the joints between floor and facade and between facade and roof.

The drawings in figs. 7A-7D show a sketch in prin¬ ciple illustrating the production sequence with, for example stationary extrusion machinery and mobile moulds. Fig. 7A illustrates the situation shortly after production start in the morning where a mould (34) is on its way through the extrusion machinery (32) . (36) is a filled-up mould on its way to the hardening chamber (38) . Fig. 7C is the corresponding vertical section which shows that the moulds, after arriving in the hardening chamber, are stacked in piles from the bottom.

Fig. 7B illustrates the situation later in the day and shows an almost full hardening chamber. The follow¬ ing morning, the moulds are transported by travelling crane, as illustrated in fig. 7D, to striking of the

moulds (40) , and the elements go into storage while the moulds are prepared for a new batch, as production takes place over a 24-hour cycle.

The drawing in figs. 8A-8B shows a sketch in prin¬ ciple of an example of a stationary extrusion machine. Fig. 8A depicts a perspective picture of the machinery and fig. 8B the corresponding plan picture. (34) indi¬ cates the filled concrete mould, (42) the empty concrete mould, (44) the concrete/mortar container, (46) the extrusion arm and nozzle and (48) the vibrator beam, (50) the cement paste sprayer, (52) continuous length of laminated insulation material, (54) possible unit for the laying of fibre fabric saturated in cement paste (number and placing according to need) . The machinery is stationary, the moulds travelling at a speed of approx. 13 mm/second. The mould lengths can, for example be 16,8 m, the struck element having the same length which, after storage can be cut up in shape to order. The draw¬ ings in figs. 9A-9E show a sketch in principle illu¬ strating an example of the production sequence of a machine for the laminating of the insulation material of mineral fibres into slab form (batts) . Fig. 9A shows the cutting up of the insulation slab in breadths cor¬ responding to the thickness of the insulation layer in the construction according to the invention. Fig. 9B shows the cut-up strips being rotated 90° to the posi¬ tion in fig. 9C where they are brought closer together in position for adhesion. Fig. 9D shows a bonding agent being applied from spray nozzles (56) after which the strips are pressed together to create 9E the ready— manufactured units of laminated insulation material which can be combined with other corresponding units to a format suitable for the actual production.

The drawings in fig. 10 show the structures of normal Rockwool concrete element batts. The grooves of the surface A of the batt (not shown in the figure) are

parallel with the end surface C. The sides are indicated by B. On the sub-drawings 10A-10C, the structural picture of the fibres becomes evident with an indication of fibre direction spreading, shown by means of arrows. In fig. IOC, only the fibre ends appear as this is a cross section at right angles to the fibres.

The drawing in fig. 11 shows the cutting up of the batts into laminae. This can be done by X-cutting, as indicated, i.e. a structure as manufactured, with low shear strength. X-cutting involves a stratification of the batts. With a Y-cutting, the shear strength and modulus of elasticity for shearing is five times better than with X-cutting. Z-cutting provides an even better shear strength and modulus of elasticity for shearing, i.e. eight times better than X-cutting. The structure is shown in figs. 11A-11C. P indicates the shearing forces.

The drawings in figs. 12A-12D show a sketch in principle illustrating an example of the design and mounting of a stirrer for fibre dispersal in the con¬ crete mixing machine. Fig. 12A shows a horizontal picture of the mixing chamber. (57) indicates the side and bottom scrapers, (58) indicates the electric motors for the stirrers (62) , (59) indicates the bracket for the electric motors, (60) indicates the middle column of the mixing chamber, and (61) indicates the sides of the mixing chamber. Fig. 12B shows a vertical section in the mixing chamber. The stirrers (62) are coupled to the driving shaft of the electric motors. Fig. 12C shows a section through the bracket (59) which is screwed on to the middle column (60) . Fig 12D shows the stirrer (62) .