PREFABRICATED STRUCTURAL ELEMENT, FLOOR STRUCTURE, AND METHOD FOR MAKING A FLOOR STRUCTURE

Abstract

 A prefabricated structural element (1) comprising an insulation material layer, a casting compound layer (3) and supporting bars (4, 4', 4") arranged in at least some grooves (6, 6') in the first surface of the insulation material layer (2). The floor structure according to the invention comprises first and second casting compound layers on top of the insulation material layer.

Description

Field of the invention

[0001] The invention relates to a prefabricated structural element, a floor structure, and a method for making a floor structure according to the appended independent claims.

Background of the invention

[0002] Cast floor structures comprise a thermal insulation material layer and a casting layer of a concrete mixture provided on top of it. Conventionally, the casting layer for a floor structure is made at the construction site. Layers of fresh concrete are typically thick and therefore require a long drying time.

Object and description of the invention

[0003] An object of the present invention is to reduce or even eliminate the above-mentioned problems present in prior art.

[0004] It is an object of this invention to provide a floor structure which allows the casting of a thinner casting compound layer in the floor structure on the construction site and thereby accelerates the drying times of cast floor structures. The object is particularly to present a floor structure in which it is possible to utilize prefabricated structural elements and thereby to accelerate the production of the floor structure.

[0005] The object of the invention is to provide a prefabricated structural element and a floor structure which can be used in ground-based floors, flooring structures, pile-supported floor slabs, as well as inverted ceiling structures.

[0006] To attain these purposes, the prefabricated structural element, floor structure, and method for producing a floor structure according to the invention are primarily characterized in what will be presented in the characterizing parts of the independent claims. The other, dependent claims will present some preferred embodiments of the invention.

[0007] Advantages of the invention are related to the prefabricated structural element, floor structure, and method for manufacturing the floor structure, even if this were not always mentioned separately.

[0008] A typical prefabricated structural element according to the invention comprises a planar lower surface, a planar upper surface, and side surfaces. The prefabricated structural element according to the invention comprises

• an insulation material layer formed of thermal insulation material having a compression strength of at least 50 kPa, and the insulation material layer comprises a first surface and a second surface, of which surfaces the first surface coming against a casting compound layer comprises grooves arranged in two directions throughout the area of the surface, the directions being substantially perpendicular to each other;
• a casting compound layer arranged on the first surface of the insulation material layer to form the planar upper surface of the structural element so that the surface area of the upper surface formed by the casting compound layer is smaller than the surface area of the insulation material layer, wherein at least two edges of the structural element comprise a planar brim formed of the insulation material layer underneath the casting compound layer and remaining exposed; and
• supporting bars arranged in at least some of the grooves on the first surface of the insulation material layer, the ends of the supporting bars extending beyond the side surface of the structural element formed by the insulation material layer.

[0009] A typical floor structure according to the invention comprises

• an insulation material layer comprising grooves on its surface;
• supporting bars arranged in at least some of the grooves on the surface of the insulation material layer;
• a first casting compound layer arranged on the surface of the insulation material layer;

and in which floor structure the insulation material layer, the first casting compound layer and the supporting bars are formed of prefabricated structural elements according to the invention so that the insulation material layers of the prefabricated structural elements are placed tightly against each other, and furthermore, the floor structure comprises a second casting compound layer formed of a second casting compound arranged on the surface of the first casting compound layer and in the recesses between the first casting compound layers in the prefabricated structural elements, forming a joint between the structural elements, wherein the compression strength and/or the hardness of the casting compound of the second casting compound layer is higher than that of the casting compound used in the first casting compound layer.

[0010] In a typical method according to the invention, a floor structure is made by

• arranging prefabricated structural elements according to the invention substantially throughout the area of the floor surface to be formed, wherein the insulation material layers of the structural elements are placed tightly against each other; and
• arranging second casting compound on the surface of the casting compound layer of the prefabricated structural elements for forming a second casting compound layer, and by arranging second casting compound in the recesses between the casting compound layers of the prefabricated structural elements for forming a joint between the structural elements, the compression strength and/or the hardness of the casting compound of the second casting compound layer is higher than that of the casting compound used in the first casting compound layer.

[0011] The floor structure according to the invention is based on a structure in which two casting compounds with different properties are used. The first casting compound layer is provided on the surface of an insulation material layer, and the second casting compound is provided on the surface of this casting compound layer and in the joints between the prefabricated structural elements. In an advantageous embodiment of the invention, the floor structure comprises two casting compound layers provided on top of each other on a surface of the thermal insulation material. In the solution according to the invention, the thermal insulation material layer and the first casting compound layer on the surface of it are provided in a prefabricated structural element, wherein on the building site it will suffice to fill in the joints between the prefabricated structural elements and to cast a thin uniform second casting compound layer on the surface of the structural elements placed next to each other. The second casting compound layer to be formed at the building site and having a higher compression strength and/or hardness is considerably thinner than the first casting compound layer ready in the prefabricated structural elements. Therefore, the floor structure can be made quickly, and long drying times are no longer required at the building site, but the first casting compound layer requiring a longer drying time is already provided in the prefabricated structural elements. The different properties of the casting compound layers guarantee sufficient strength and quick drying of the structure.

[0012] The prefabricated structural element according to the invention comprises a layer of insulation material typically formed of a single solid board of thermal insulation material. According to an embodiment, the insulation material layer can be formed of two or more insulation material boards placed tightly next to each other. Typically, the insulation material boards to be placed tightly against each other comprise a tongue and a groove or other corresponding shapes on their side surfaces to enable their engagement to each other. The insulation material layer comprises a first planar surface and a second planar surface. The insulation material layer forms the side surfaces of the lower part of the structural element. The supporting bars and the first casting compound layer are arranged on the first planar surface of the insulation material layer. Typically, the second planar surface of the insulation material layer constitutes the lower surface of the prefabricated structural element. In an advantageous embodiment of the invention, the insulation material layer is formed of one or more grooved boards of thermal insulation material, whereby the board(s) comprise(s) grooves on the first surface that will come against the casting compound layer, the grooves being oriented in two directions substantially perpendicular to each other, forming a chequered grooving on the surface of the board. Typically, the first surface of the insulation material layer comprises grooves in the length and width directions of the board, whereby the grooves constitute a grooving in the length and width directions on the planar surface of the insulation material layer. Typically, the first surface of the insulation material layer that will come against the casting compound layer comprises grooves throughout the planar surface area of the board, typically in the length and width directions of the board throughout the planar surface area of the board.

[0013] Supporting bars for reinforcing the structure are arranged in at least some of the grooves on the surface of the insulation material layer. In an advantageous embodiment of the invention, the first surface of the insulation material layer that will face the casting compound layer comprises grooves in the length and width directions of the structural element, whereby supporting bars are arranged in at least some of the grooves on the surface of the insulation material layer, in the length and width directions of the structural element. In an embodiment of the invention, supporting bars are arranged in all the grooves on the surface of the thermal insulation material. The spacing between the grooves on the planar surface of the insulation material board (measured center-to-center) may vary; typically, the spacing between grooves may be about 50 to 600 mm. The spacing between the grooves may be different in the width direction and the length direction of the board. In a structural element according to the invention, grooves are arranged at intervals of about 300 mm (measured center-to-center) in the length and width directions of the structural element; this is an advantageous solution to provide sufficient strength when supporting bars are provided in all the grooves. The spacing between the grooves may also vary depending on the use of the structural elements and the material used in the insulation boards. Furthermore, the number of grooves in the width and length directions of the structural element may vary. The width of the groove may also vary, depending on the properties required. Typically, the width of the grooves is about 40 to 60 mm. Similarly, the depth of the grooves may vary; typically, the depth of the grooves is about 40 to 60 mm.

[0014] In the prefabricated structural element according to the invention, the supporting bars are arranged in the grooves on the first surface of the insulation material layer in such a way that the ends of the supporting bars extend beyond the side surface of the structural element formed by the insulation material layer. Typically, the supporting bars are arranged in the grooves in the length and width directions of the structural element. In a prefabricated structural element according to the invention, the ends of the supporting bars may extend from 20 to 500 mm, or typically from 50 to 200 mm or from 20 to 100 mm, beyond the side surface of the structural element formed by the insulation material layer. These ends of supporting bars extending beyond the side surface of the structural element make it possible to fasten the structural elements to each other in the floor structure and simultaneously secure the strength of the floor made of prefabricated structural elements throughout the area of the floor structure, including the joints of the structural elements. If the insulation material layer is formed of several boards of thermal insulation material, the supporting bars may be arranged in the grooves to partly overlap at the joints of the boards of thermal insulation material, to make a strong structure. These joints will be embedded in the first casting compound layer.

[0015] The supporting bars used in the invention may be any supporting bars suitable for the purpose. In an embodiment according to the invention, the supporting bars are ribbed reinforcement bars, prefabricated meshes made of ribbed bars, or other conventional products used for reinforcement. In another advantageous embodiment of the invention, the supporting bars are supporting bars comprising glass fibre, advantageously polymer bars or the like reinforced with glass fibre, or prefabricated meshes formed thereof. Supporting bars comprising glass fibre, such as polymer bars reinforced with glass fibre, enable a solution which has a lighter weight and is more ecological than ribbed reinforcement bars but which still secures a firm and strong floor structure.

[0016] The thermal insulation material used in the floor structure according to the invention may be any thermal insulation material that is suitable for the purpose and has a sufficient compression strength. The compression strength of the thermal insulation material to be used should be at least 50 kPa (according to the standard EN 826); typically, the compression strength is between 50 and 200 kPa and most typically between 100 and 700 kPa. In an advantageous embodiment of the invention, the thermal insulation material is extruded polystyrene (XPS), expanded polystyrene (EPS), polyurethane (PIR/PUR), phenolic foam, or PVC foam. In an advantageous embodiment of the invention, a insulation material layer is formed of extruded polystyrene (XPS). The thermal insulation material to be used is selected according to the properties required of the floor structure to be built. The thermal insulation material is typically insulation board formed of a thermal insulation material.

[0017] The casting compound layer in the prefabricated structural element is arranged on the first surface of the insulation material layer to form the planar upper surface of the structural element so that the surface area of the upper surface of the casting compound layer is smaller than the surface area of the insulation material layer, whereby at least two edges of the structural element are provided with a planar brim formed by the insulation material layer underneath the casting compound layer and remaining exposed. In an advantageous embodiment of the invention, the casting compound layer is surrounded by a planar brim formed by the insulation material layer under the casting compound layer at all edges of the structural element; in other words, the brim encircles the structural element. In this way, the casting compound layer does not cover the whole insulation material layer but part of the insulation material layer remains exposed in the edges of the structural element. In a typical embodiment of the invention, the width of the planar brim formed by the insulation material layer around the casting compound layer is substantially equal to the length of the ends of the supporting bars extending beyond the side surface of the structural element formed by the insulation material layer. Thus, when two structural elements are placed next to each other, the ends of the supporting bars are placed on top of the planar brim formed by the insulation material of the adjacent structural element. In this way, the joints of the prefabricated structural elements become strong, when the supporting bars substantially overlap at the joints, and the reinforcement becomes uniform throughout the floor surface to be made.

[0018] In the prefabricated structural element according to the invention, the first casting compound layer is typically formed of a concrete mixture or a ceramic based mixture. The concrete mixture may be any concrete that is suitable for the purpose and comprises a binding agent. The concrete may be fibre-reinforced concrete, porous concrete, or the like. Alternatively, the casting compound layer formed on the insulation material layer may be formed of a ceramic based casting mixture or compound suitable for the purpose. For example, the casting compound may comprise magnesium phosphate cement which is fast drying. In the structure according to the invention, it is possible to use a reduced amount of casting compound for obtaining sufficient strength, because the casting compound layer is formed on top of the grooved layer of thermal insulation material, and furthermore, a second thin casting compound layer is formed on top of the cast layer at the installation site. Because a reduced amount of casting compound is sufficient, the casting compound layer can be formed of a casting compound that is more expensive and dries faster than a conventional concrete, without excessively increasing the price of the structural element. The structural element according to the invention makes it possible to build a floor structure in a cost-effective way. The first casting compound layer may also comprise reinforcement layers, such as reinforcing fibre matting or the like. The fibre matting can be made of glass fibres, carbon fibres or other material having a good tensile strength.

[0019] In the structural element according to the invention, the thickness of the insulation material layer and the first casting compound layer may vary, depending on the materials and the use. Typically, the thickness of the insulation material layer of the structural element is between 50 and 500 mm or 80 and 300 mm, measured between the planar surfaces of the layer. In an embodiment of the invention, the thickness of the first casting compound layer of the structural element is from 10 to 250 mm or from 10 to 200 mm, measured between the planar surface of the insulation material layer and the planar surface of the casting compound layer. If the insulation material layer comprises grooves, the casting compound layer also fills in the grooves in the insulation material layer, typically having a depth of from 40 to 60 mm. In this way, the adhesive strength of the casting compound layer to the insulation material layer can be considerably increased, and furthermore, the supporting bars required for reinforcing the structure can be arranged in the grooves.

[0020] In a floor structure according to an advantageous embodiment of the invention, the insulation material layer, the supporting bars for reinforcing the structure, and the first casting compound layer are provided in the structure by using prefabricated structural elements which are placed tightly against each other so that the insulation material layers of the prefabricated structural elements are placed against each other. The second casting compound is arranged to fill in the recesses between the casting compound layers of the prefabricated structural elements in the floor structure, thereby forming the joints between the structural elements. At the joints between the structural elements, the second casting compound is supplied on top of the planar brim formed by the thermal insulation material layer of the structural elements, and the supporting bars on top of the structural elements placed next to each other are embedded in the second casting compound at the joint. On top of the casting compound layer forming the upper surface of the prefabricated structural elements, a second layer of the second casting compound may be cast as well. In an advantageous embodiment of the invention, the second casting compound constitutes the joints between the prefabricated structural elements as well as the second casting compound layer, so-called surface layer, for the floor structure. The second casting compound is used as a joint sealing compound and a surface covering compound. The compression strength and/or hardness of the second casting compound used in the invention is greater than the compression strength and/or hardness of the first casting compound used in the first casting compound layer of the prefabricated structural elements. In a typical floor structure according to the invention, the ends of supporting bars of two adjacent structural elements are placed substantially against each other in a joint between the two adjacent structural elements, filled with the second casting compound.

[0021] In an advantageous embodiment according to the invention, the insulation material layers of the prefabricated structural elements comprise tongues and grooves or other corresponding shapes on the side surfaces, allowing the placement of the insulation material layers of the structural elements tightly against each other. In a particularly advantageous embodiment, the side surface of the insulation material layer is provided with a locking tongue and groove or a corresponding structure to keep the structural elements tightly engaged so that no gap can be formed between the insulation material layers of the adjacent structural elements when the second casting compound layer is formed for the floor structure, and/or the joint between the structural elements is filled in with the second casting compound. The locking tongue and groove prevent the structural elements from being separated from each other, possibly by pressure of the second casting compound, and the thermal insulation material layer of the floor structure thus remains continuous throughout the area of the floor structure.

[0022] At the building site, the casting compound layer of the prefabricated structural element may be covered by a thin layer of the second casting compound, consisting of a casting compound having a higher compression strength and/or hardness than the prefabricated first casting compound layer. Thus, only a thin fast-drying casting compound layer is cast at the building site, and the drying time of the floor structure can be significantly reduced. In a typical floor structure according to the invention, the second casting compound is a casting compound having a drying shrinkage < 0.1 mm/m and a compression strength > 30 MPa. Typically, the drying shrinkage of the second casting compound is zero or almost zero. The compression strength of the second casting compound may vary, depending on the material used. In an advantageous embodiment of the invention, the second casting compound comprises magnesium phosphate cement based casting compound. In an embodiment, the first and second casting compound layers may both comprise magnesium phosphate cement as a binding agent, but the casting compound of the first casting compound layer may further comprise inorganic material, such as sand.

[0023] The second casting compound layer is typically considerably thinner than the first casting compound layer. In an embodiment of the invention, the thickness of the second casting compound layer is from 1 to 10 mm or from 2 to 10 mm, measured between the planar surfaces of the casting compound layer; that is, between the top surface of the casting compound layer and the planar lower surface coming against the first casting compound layer.

[0024] The floor structure according to the invention is formed by using prefabricated structural elements and arranging the structural elements tightly against each other substantially throughout the area of the floor surface to be formed in such a way that the insulation material layers of the structural elements are placed against each other. Second casting compound is provided in the recesses between the prefabricated structural elements (between the first layers of casting compound), to make strong joints between the structural elements. At the building site, a second casting compound layer is arranged on the surface of the first casting compound layer, which second casting compound layer is formed of a casting compound having a higher compression strength, and the recess between the first casting compound layers of the adjacent structural elements is also filled with the second casting compound constituting the second casting compound layer of the structure. Consequently, at the building site, casting compound of the second casting compound layer is arranged in the joints between the structural elements and used for forming a thin uniform surface layer for the floor structure. Further, the surface formed by the second casting compound layer can be coated with a coating suitable for the purpose.

[0025] In the floor structure according to the invention, the function of the first casting compound layer is to provide the structure with the required strength. The function of the second casting compound is primarily to act as a joint sealing compound between the structural elements and as a coating for the floor structure.

[0026] In an embodiment of the invention, the brim formed by the insulation material layer at the edge of the structural elements is larger at the supporting bars than in other parts of the structural element. In this way, a wider joint can be formed of the second casting compound at the supporting bars. Typically, the supporting bars are also placed in a groove in the insulation material layer, whereby second casting compound is provided down to the bottom of the groove at the brim. The second casting compound used for the floor structure typically has good adhesive strength to the supporting bars, to make the floor structure strong at the joints as well.

[0027] Heating cables or heating pipes may also be arranged in recesses between the first casting compound layers of prefabricated structural elements at the building site, before the casting of the second casting compound layer. In this way, a floor structure comprising heating cables or heating pipes can also be easily and rapidly implemented with the prefabricated structural elements according to the invention.

[0028] Prefabricated structural elements according to the invention can be made in different sizes. The insulation material boards used for the prefabricated structural elements and the floor structure according to the invention are typically provided in the size of 600 x 1200 mm or 600 x 2400 mm or 1200 x 2400 mm. The grooves and the supporting bars in the insulation material layer are typically arranged at intervals of 300 mm (measured center-to-center) in the length and width directions of the structural element, whereby the structural element comprises at least two supporting bars in the width direction of the structural element. The prefabricated structural elements may be provided in the size of the above-mentioned insulation material boards, or they may be considerably larger, such as 2400 x 5000 mm, 2500 x 5000 mm, 2400 x 10 000 mm or 2500 x 10 000 mm. Prefabricated structural elements may be compiled into larger elements and, if necessary, pre-coated with a second casting compound layer, whereby only the joints between the elements have to be filled with second casting compound at the building site.

[0029] The floor structure according to the invention may be used in all kinds of cast floor structures, such as ground-based floors, pile-supported floor slabs, and flooring structures. Furthermore, the floor structure according to the invention may be used in inverted ceiling structures whose structure corresponds to a ceiling structure.

Brief description of the drawings

[0030] In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1a

shows the structure of a prefabricated structural element according to an embodiment of the invention, seen from above;

Fig. 1b

shows a prefabricated structural element according to an embodiment of the invention, in a cross-sectional view;

Fig. 2

shows a floor structure according to an embodiment of the invention, seen from above;

Fig. 3

shows a joint between structural elements according to an embodiment of the invention, in a cross-sectional view; and

Fig. 4

shows a joint between structural elements according to an embodiment of the invention, in a cross-sectional view at supporting bars.

Detailed description of the invention

[0031] Figure 1 a shows the structure of a prefabricated structural element 1 according to an embodiment of the invention, seen from above. Figure 1b shows a prefabricated structural element 1 according to an embodiment of the invention, in a cross-sectional view. The prefabricated structural element 1 comprises a planar lower surface, a planar upper surface, and side surfaces. The prefabricated structural element 1 is formed of an insulation material layer 2 which comprises a first surface and a second surface; and a first casting compound layer 3 arranged on the first surface of the insulation material layer 2 to form a planar upper surface of the structural element in such a way that the surface area of the upper surface formed by the casting compound layer 3 is smaller than the surface area of the insulation material layer 2, whereby the casting compound layer 3 of the structural element 1 is surrounded by a planar brim 5 formed by the insulation material layer 2. Furthermore, the prefabricated structural element 1 comprises supporting bars 4, 4', 4" arranged in grooves 6, 6' on the first surface of the insulation material layer 2, typically extending in the length and width directions of the structural element 1. In Fig. 1a, the supporting bars are arranged in the grooves 6, 6' on the surface of the insulation material layer 2 in such a way that the ends 4a, 4b of the supporting bars extend beyond the side surface of the structural element 1 formed by the insulation material layer 2. In Fig. 1a, a planar brim 5 formed by the insulation material layer encircles the whole structural element 1, and more of the insulation material layer 2 is exposed at the supporting bars 4, 4', 4" than in other parts of the brim 5.

[0032] Figure 2 illustrates a floor structure 10 formed of prefabricated structural elements 1, 1', 1" according to the invention, seen from above. In the floor structure 10, prefabricated structural elements 1, 1', 1" are arranged next to each other so that the insulation material layers of the prefabricated structural elements are placed tightly against each other and form a uniform surface. Second casting compound is arranged in the joints 8 between the casting compound layers of the prefabricated structural elements. Further, a second casting compound layer is advantageously formed of the second casting compound onto the surface of the prefabricated structural elements. Figures 3 and 4 show more detailed views of the floor structure 10 and a joint 8 between prefabricated structural elements, that is, a recess between the first casting compound layers 3 of the prefabricated structural elements, where second casting compound is arranged.

[0033] Figure 3 shows a joint 8 between prefabricated structural elements, filled with second casting compound, in a cross-sectional view at a brim section without a supporting bar. Figure 4 shows a joint 8 between prefabricated structural elements in a cross-sectional view at a section where the ends 4a, 4b of supporting bars overlap on a planar brim 5 formed by the insulation material layer 2 at the joint 8 of the structural elements. In the floor structure 10 shown by Figs. 3 and 4, the insulation material layers 2 of two prefabricated structural elements 1, 1' are connected to each other by means of a locking tongue and groove 9 at the joint between the structural elements. A second casting compound layer 7 is applied to the top surface of the first casting compound layer 3. Some of the casting compound forming the second casting compound layer 7 is also arranged in the recess between the casting compound layers 3 of the structural elements to form a joint 8 between the elements so that the second casting compound fills the space between the first casting compound layers 3. Figure 4 illustrates the recess between the casting compound layers 3 of the structural elements, in which second casting compound is arranged to form the joint 8 between the structural elements and in which the ends 4a, 4b of supporting bars are overlapping and are embedded in the second casting compound 7. In the floor structures shown in Figs. 3 and 4, the second casting compound layer 7 constitutes the upper surface layer of the floor structure 10, and the insulation material layer 2 of the structural elements 1, 1' constitutes the lower surface of the floor structure. The supporting bar 4 is arranged in the groove on the surface of the insulation material layer 2 and embedded in the first casting compound layer 3.

Claims

1. A prefabricated structural element (3) comprising a planar lower surface, a planar upper surface, and side surfaces, characterized in that the structural element comprises

- an insulation material layer (2) formed of a thermal insulation material having a compression strength of at least 50 kPa, and the insulation material layer (2) comprises a first surface and a second surface, of which surfaces the first surface coming against a casting compound layer comprises grooves (6, 6') oriented in two directions throughout the area of the surface, the directions being substantially perpendicular to each other;

- a casting compound layer (3) arranged on the first surface of the insulation material layer (2) to form the planar upper surface of the structural element so that the surface area of the upper surface formed by the casting compound layer (3) is smaller than the surface area of the insulation material layer (2), wherein at least two edges of the structural element (1) comprise a planar brim (5) formed of the insulation material layer (2) underneath the casting compound layer (3) and remaining exposed; and

- supporting bars (4, 4', 4") arranged in at least some of the grooves (6, 6') in the first surface of the insulation material layer (2), the ends (4a, 4b) of the supporting bars extending beyond the side surface of the structural element (1) formed by the insulation material layer (2).

2. A prefabricated structural element according to claim 1, characterized in that the thermal insulation material is extruded polystyrene (XPS), expanded polystyrene (EPS), polyurethane (PIR/PUR), phenolic foam, or PVC foam.

3. A prefabricated structural element according to claim 1 or 2, characterized in that the casting compound layer (3) is surrounded by the planar brim (5) formed by the insulation material layer (2) at all edges of the structural element (1).

4. A prefabricated structural element according to any of the preceding claims, characterized in that the first surface of the insulation material layer comprises grooves (6, 6') in the length and width directions of the structural element.

5. A prefabricated structural element according to any of the preceding claims, characterized in that the ends (4a, 4b) of the supporting bars extend from 20 to 500 mm, typically about from 50 to 200 mm beyond the side surface of the structural element (1) formed by the insulation material layer (2).

6. A prefabricated structural element according to any of the preceding claims, characterized in that the width of the planar brim (5) formed by the insulation material layer (2) around the casting compound layer (3) is substantially equal to the length of the ends (4a, 4b) of the supporting bars extending beyond the side surface of the structural element (1) formed by the insulation material layer (2).

7. A prefabricated structural element according to any of the preceding claims, characterized in that the casting compound layer (3) is formed of a concrete mixture or a ceramic based mixture.

8. A prefabricated structural element according to any of the preceding claims, characterized in that the supporting bars (4, 4', 4") are supporting bars comprising glass fibre, advantageously polymer bars reinforced with glass fibre.

9. A floor structure (10) comprising

- an insulation material layer (2) comprising grooves (6, 6') on its surface;

- supporting bars (4, 4', 4") arranged in at least some of the grooves (6, 6') on the surface of the insulation material layer (2);

- a first casting compound layer (3) arranged on the surface of the insulation material layer (2);

characterized in that the insulation material layer (2), the first casting compound layer (3) and the supporting bars (4, 4', 4") in the floor structure are formed of prefabricated structural elements (1) according to any of the preceding claims 1 to 8 in such a way that the insulation material layers (2) of the prefabricated structural elements (1) are placed tightly against each other; and
furthermore, the floor structure (10) comprises a second casting compound layer (7) formed of a second casting compound arranged on the surface of the first casting compound layer (3) and in the recesses between the first casting compound layers (3) of the prefabricated structural elements, forming a joint (8) between the structural elements, wherein the compression strength and/or the hardness of the casting compound of the second casting compound layer (7) is higher than that of the casting compound used in the first casting compound layer (3).

10. The floor structure according to claim 9, characterized in that

- the thickness of the first casting compound layer (3) is from 10 to 250 mm, measured between the planar surfaces of the casting compound layer; and

- the thickness of the second casting compound layer (7) is from 1 to 10 mm, measured between the planar surfaces of the casting compound layer.

11. The floor structure according to claim 9 or 10, characterized in that the second casting compound is a casting compound having a drying shrinkage < 0.1 mm/m and a compression strength > 30 MPa.

12. The floor structure according to any of the preceding claims 9 to 11, characterized in that the casting compound of the second casting compound layer comprises a magnesium phosphate cement based casting compound.

13. The floor structure according to any of the preceding claims 9 to 12, characterized in that the ends (4a, 4b) of supporting bars in two adjacent prefabricated structural elements (1) are placed substantially against each other in the joint (8) between the two adjacent structural elements (1).

14. The floor structure according to any of the preceding claims 9 to 13, characterized in that heating cables or heating pipes are arranged in recesses between the first casting compound layers (3) of prefabricated structural elements.

15. A method for making a floor structure (10), characterized in that the floor structure is made by

- arranging prefabricated structural elements according to any of the preceding claims 1 to 8 substantially throughout the area of the floor surface to be formed, wherein the insulation material layers (2) of the structural elements (1) are placed tightly against each other; and

- arranging second casting compound on the surface of the casting compound layer (3) of the prefabricated structural elements (1), for forming a second casting compound layer (7), and arranging second casting compound in the recesses between the casting compound layers (3) of the prefabricated structural elements (1), for forming a joint (8) between the structural elements, the compression strength and/or the hardness of the casting compound of the second casting compound layer (7) is higher than that of the casting compound used in the first casting compound layer (3).

Drawing