Concrete element for structural floor

Abstract

 A concrete element for constructing a structural floor has a prefabricated base slab (1) of concrete supporting the reinforcement (2) of the element, and a concrete slab (3) cast onto said base plate. The cast-on slab (3) consists of an upper layer (5) of concrete having a compressive strength of at least 30 MPa (after 28 days) and a density of at least 2,300 kg/m³, and of a lower layer (4) of lightweight aggregate concrete having a density of 600-800 kg/m³.

Description

[0001] The present invention relates to a concrete element for constructing a structural floor, said element comprising a prefabricated concrete base slab supporting the reinforcement of the element, and a concrete slab cast onto said base plate.

[0002] A known prefabricated concrete slab, so-called filigree slab, which, in accordance with the above, is used as a base slab in the construction of a structural floor, is mounted in position on the building site, whereupon a layer of concrete is cast upon it. The base slab supports a reinforcement projecting from the upper surface of the base slab for engaging with the cast-on slab. When the base slab is in position, also the reinforcement will be in position, and this means that the major part of the laborious reinforcement work has been done already in the factory. On casting of a structural floor, the filigree slab serves as a permanent shuttering, whereby the formwork is simplified considerably and striking is eliminated so that shorter building times are made possible. The construction of a structural floor by means of a concrete element which consists of a filigree slab and a cast-on concrete slab disposed thereon on the building site thus brings considerable advantages. In prior art constructions, the said cast-on slab consists of a layer of concrete, the thickness of the layer and the type of concrete being selected in dependence upon, inter alia, the span. The concrete must have a compressive strength sufficient to withstand the compression stress to which the concrete element will be subjected, for which reason there has been selected, according to prior art technique, a high-density concrete resistant to compression stress for the entire cast-on slab. For large spans, about 10 metres and more, the prior art technique therefore brings the disadvantage that the concrete element will sag because of its own heavy weight.

[0003] It therefore is the object of the present invention to provide a concrete element which is of the above- mentioned type and comprises a cast-on slab which has the requisite compressive strength but still is so light that, even with large spans, no appreciable sagging of the element will occur.

[0004] This object is achieved by means of a concrete element which is of the type mentioned above and which, according to the present invention, is characterised in that the cast-on slab comprises an upper layer of concrete having a compressive strength of at least 30 MPa (after 28 days) and a density of at least 2,300 kg/m³, and a lower layer of lightweight aggregate concrete having a density of 600-800 kg/m³.

[0005] The lightweight aggregate concrete of the lower layer preferably has a compressive strength of about 4 MPa (after 28 days) and a density of 650-750 kg/m³.

[0006] The lightweight aggregate concrete of the lower layer preferably consists of ready-mixed silica concrete containing an aggregate of polystyrene balls.

[0007] The invention will now be described in more detail, reference being made to the accompanying drawing which illustrates, partly in section, a concrete element according to the invention.

[0008] The concrete element shown in the drawing is intended to be used in the construction of a structural floor. The concrete element has a base slab 1 which consists of a so-called filigree slab of known type, i.e. a prefabricated concrete slab supporting the reinforcement 2 of the concrete element. In the embodiment illustrated, the reinforcement 2 consists of a reinforcing netting 2a and three reinforcing girders 2b extending in the longitudinal direction of the concrete element. The reinforcing girders 2b are connected to the reinforcing netting 2a and project from the upper surface of the base slab 1. When the base slab 1 is a prestressed concrete slab, as is required for longer spans, the reinforcement 2 may also comprise a number of prestressing wires (not shown) extending parallel to the girders 2b.

[0009] Furthermore, the concrete element has a cast-on slab 3 which consists of a lower layer 4 of lightweight aggregate concrete and an upper layer 5 of pressure resistant concrete. The two layers 4 and 5 are cast onto the prefabricated base slab 1 after this has been mounted in position on the building site.

[0010] The lightweight aggregate concrete of the lower layer 4 preferably is ready-mixed lightweight aggregate concrete containing cement, sand, lightweight aggregate in the form of polystyrene balls, and silica, and has a density of 600-800 kg/m³, preferably 650-750 kg/m³, and a compressive strength of about 4 MPa (after 28 days).

[0011] The concrete of the upper layer 5 preferably is a ready-mixed concrete having a compressive strength of at least 30 MPa (after 28 days) and a density of at least 2,300 kg/m ³

[0012] The concrete element according to the present invention thus consists of a known so-called filigree slab 1 and a cast-on slab 3 comprising two layers 4 and 5, whereby a partly prefabricated sandwich structure for constructing a structural floor is formed.

[0013] The compressive strength of the upper layer 5 is adapted to the maximum compression stress to which the cross-section of the cast-on slab may be subjected and which occurs in the upper part of the cross-section, i.e. in the upper layer 5. Since the compression stress is considerably lower in the underlying parts of the cross-section, a concrete having a considerably lower compressive strength and, thus, a lower density may be utilised in the lower layer 4. In this manner, the concrete element according to the present invention will be much lighter than prior art concrete elements of this type, and therefore the concrete element according to the invention can be utilised also with large spans without sagging.

[0014] In an embodiment intended for a span of about 10 metres, the concrete element according to the invention has a width of 1.2 metre and a length of about 10 metres, while the base slab 1, the lower layer 4 and the upper layer 5 have an approximate thickness of, respectively, 7 cm, 16 cm and 5 cm.

Claims

1. A concrete element for constructing a structural floor, said element comprising a prefabricated concrete base slab (1) supporting the reinforcement (2) of the element, and a concrete slab (3) cast onto said base plate, characterised in that the cast-on slab (3) comprises an upper layer (5) of concrete having a compressive strength of at least 30 MPa (after 28 days) and a density of at least 2,300 kg/m³, and a lower layer (4) of lightweight aggregate concrete having a density of 600-800 kg/m³.

2. A concrete element as claimed in claim 1, characterised in that the lightweight aggregate concrete of the lower layer (4) has a compressive strength of about 4 MPa (after 28 days).

3. A concrete element as claimed in claim 1 or 2, characterised in that the lightweight aggregate concrete of the lower layer (4) has a density of 650-750 _kg_/m³_.

4. A concrete element as claimed in any one of the preceding claims, characterised in that the lightweight aggregate concrete of the lower layer (4) is ready-mixed silica concrete.

5:. A concrete element as claimed in any one of the preceding claims, characterised in that the lightweight aggregate concrete of the lower layer (4) has an aggregate of polystyrene balls.

Drawing