A concrete hollow-core slab and a method of creating a lowered region in a non-cured concrete hollow-core slab

Abstract

A concrete hollow-core slab (1) comprises an upper layer (3) which has an upper surface (4) and a lower surface (5), a lower layer (6) which has an upper surface (7) and a lower surface (8) and at least two ribs (9) which interconnect the upper layer (3) and the lower layer (6), hence forming an elongate channel (10) between the ribs (9), the upper surface (7) of the lower layer (6) and the lower surface (5) of the upper layer (3). The concrete hollow-core slab (1) has a lowered region (2) which has an upper surface (11) at a lower level than the lower surface (5) of the upper layer (3). A transition portion (12) located at a higher level than the lowered region (2) at a transition between the lowered region (2) and the upper layer (3) in longitudinal direction of the channel (10) interconnects the lowered region (2) and at least a portion of the ribs (9) adjacent to the transition portion (12). The transition portion (12), the ribs (9), the lowered region (2), the upper layer (3) and the lower layer (6) are made in one piece.

Description

[0001] The present invention relates to a concrete hollow-core slab, comprising an upper layer which has an upper surface and a lower surface, a lower layer which has an upper surface and a lower surface and at least two ribs which interconnect the upper layer and the lower layer, hence forming an elongate channel between the ribs, the upper surface of the lower layer and the lower surface of the upper layer, wherein the concrete hollow-core slab has a lowered region which has an upper surface at a lower level than the lower surface of the upper layer

[0002] Such a concrete hollow-core slab is known in the prior art. The known concrete hollow-core slab can be applied in a building to form a floor field together with other concrete hollow-core slabs. The concrete hollow-core slabs may span between supports at opposite end portions of the respective slabs. The upper surface of the upper layer may form a support for a walking floor and the lower surface of the lower layer may form a ceiling. The lowered region is intended for placing thereon elements which are to be accommodated in the floor, such as sewer drains, ventilating ducts, or the like. The residual space remaining after the placement of the element in question can be filled up again with granular filler or similar material, for example concrete, gravel, sand or the like. Since the lowered region may reduce resistance against structural forces the known concrete hollow-core slab must have a relatively thick lower layer.

[0003] An object of the invention is to provide a light-weight and high-strength concrete hollow-core slab including a lowered region.

[0004] This object is accomplished with the concrete hollow-core slab according to the invention, wherein a transition portion located at a higher level than the lowered region between the lowered region and the upper layer in longitudinal direction of the channel interconnects the lowered region and at least a portion of the ribs adjacent to the transition portion, wherein the transition portion, the ribs, the lowered region, the upper layer and the lower layer are made in one piece.

[0005] Due to the invention the transition portion, the adjacent ribs and the lowered region are continuous and made of the same material. The lowered region and the lower layer are also continuous. If the lowered region is adjacent to the ribs they are also continuous. Since the transition portion is integral with the lowered region and the adjacent ribs above the lowered region the concrete hollow-core slab according to the invention provides a relatively high structural strength, such as bending strength and shear strength. This allows to provide a relatively thin lower layer of the concrete hollow-core slab, which means that the resulting concrete hollow-core slab has a relatively low weight. It is noted that the transition portion projects from the upper surface of the lowered region. Furthermore, the concrete hollow-core slab may have more than two ribs resulting in a plurality of parallel channels.

[0006] The lowered region may form a continuous material without channels. The lowered region may be compacted, for example, to achieve a high structural strength. The transition portion may at least partly close the channel.

[0007] The lowered region may have a lower surface which coincides with the lower surface of the lower layer of the concrete hollow-core slab. The upper surface of the lowered region may be substantially flat, for example parallel to the upper surface of the upper layer.

[0008] Preferably, the transition portion interconnects the lowered region and the ribs such that it closes the channel, since after installing the concrete hollow-core slab in a building, placing elements in a space above the lowered region and filling a remaining space with a liquid filler, for example a granular filler such as concrete, gravel, sand or the like, the filler does not flow away through the channel.

[0009] The transition portion may also interconnect the lowered region and the upper layer. This improves the bending strength of the concrete hollow-core slab further. In this case the transition portion, the upper layer, the lowered region and at least a portion of the ribs are continuous and made of the same material.

[0010] The lowered region may be elongated and extend in transverse direction of the longitudinal direction of the channel.

[0011] The lowered region may extend over the entire width of the concrete hollow-core slab.

[0012] The transition portion may have an inclined frontal surface which borders a space above the lowered region, which inclined frontal surface may have an angle between 210° and 270°, for example, with respect to the upper surface of the upper layer. This may create a gradual transition at the transition between the lowered region and the upper layer in longitudinal direction of the channel.

[0013] In an embodiment the lowered region is located at a distance from opposite ends of the concrete hollow-core slab in longitudinal direction of the channel, for example halfway the concrete hollow-core slab in its longitudinal direction.

[0014] In a particular embodiment the transition portion is a first transition portion and the concrete hollow-core slab comprises a second transition portion at another transition between the lowered region and the upper layer which is located opposite to the first transition portion and preferably similar to the first transition portion.

[0015] The upper surface of the lowered region may lie at a higher level than the upper surface of the lower layer, for example more than 100%, 200% or 250% higher than the upper surface of the lower layer as measured from the lower surface of the lower layer.

[0016] In the event that the transition portion has an inclined frontal surface, the transition portion may have a thickness which substantially equals the distance between the upper surface and the lower surface of the upper layer. The upper layer and the transition portion may form a substantially continuous layer.

[0017] Thicknesses of the upper layer and the lower layer may be substantially the same.

[0018] An upper side of the concrete hollow-core slab may be provided with an elongate slot which extends in longitudinal direction of the channel and ends in a space above the lowered region. The bottom of the elongate slot may extend at substantially the same height as the upper surface of the lowered region. The material below the elongate slot may be compacted and may be integral with the lowered region.

[0019] The invention is also related to a method of creating a lowered region in a non-cured concrete hollow-core slab including an upper layer which has an upper surface and a lower surface, a lower layer which has an upper surface and a lower surface and at least two ribs which interconnect the upper layer and the lower layer, hence forming a channel between the ribs, the upper surface of the lower layer and the lower surface of the upper layer, wherein at an intended location of a lowered region a pushing element is inserted into the non-cured concrete hollow-core slab in a direction from the upper layer towards the lower layer to a level between the lower surface of the upper layer and the upper surface of the lower layer and subsequently moved with respect to the non-cured concrete hollow-core slab in a pushing direction, which is in longitudinal direction of the channel, over a predetermined distance such that concrete of the upper layer and at least a portion of the ribs adjacent to the pushing element is moved towards the lower layer and in the pushing direction.

[0020] During moving the pushing element in the pushing direction concrete of the upper layer and at least a portion of the ribs will partially drop down into the channel and partially pushed forwardly. Consequently, a lowered region as described above will arise below the pushing element and a transition portion as described above will arise between the pushing element and a non-deformed remainder of the non-cured concrete hollow core slab. The transition portion which is developed during moving the pushing element in the pushing direction may be pushed against the non-deformed adjacent upper layer and ribs. It is noted that a non-cured concrete hollow-core slab is a 'fresh' or 'green' concrete product of which the concrete is still not cured and still deformable. It may be made through extrusion or slipforming, for example.

[0021] After creating the lowered region the resulting product may be cured in order to form a concrete hollow-core slab which can be applied in a building.

[0022] Preferably, the pushing element is vibrated at least up and down when moved in the pushing direction, since this appears to provide a proper interconnection of the lowered region, the transition portion and at least the ribs. It is also possible that the pushing element is vibrated in three orthogonal directions when moved in the pushing direction.

[0023] The pushing element may be elongated and its longitudinal direction may be transverse with respect to the longitudinal direction of the channel.

[0024] The invention will hereafter be elucidated with reference to very schematic drawings showing embodiments of the invention by way of example. Fig. 1 is a perspective view of a part of an embodiment of a concrete hollow-core slab according to the invention. Fig. 2 is a similar view as Fig. 1, but showing a section along the line II-II in Fig. 1. Fig. 3 is a similar view as Fig. 2, but showing an alternative embodiment. Fig. 4 is a sectional view along a channel of a non-cured concrete hollow-core slab, illustrating an embodiment of a method of creating a lowered region in a non-cured concrete hollow-core slab 1 according to the invention. Fig. 5 is a similar view as Fig. 4, illustrating a next step of the method. Fig. 6 is a similar view as Fig. 2, but showing another alternative embodiment. Fig. 7 is a similar view as Fig. 3, but showing another alternative embodiment. Fig. 8 is an enlarged cross-sectional view of a part of the embodiment as shown in Fig. 7.

[0025] Figs. 1 and 2 show an embodiment of an elongate concrete hollow-core slab 1 according to the invention. The concrete hollow-core slab 1 can be applied in a building in order to form a floor together with other concrete hollow-core slabs in a well-known manner. Opposite end portions of the concrete hollow-core slab 1 in its longitudinal direction may rest on walls of the building. The concrete hollow-core slab 1 has a lowered region 2 at a distance from its opposite ends in its longitudinal direction, but in an alternative embodiment the lowered region 2 may form an end portion of the concrete hollow-core slab 1. The lowered region 2 is intended for receiving elements thereon which are to be accommodated in the floor, such as sewer drains, ventilating ducts, etc. The residual space remaining after the placement of the element in question can be filled up again with a granular filler or similar material, for example concrete, gravel, sand or the like.

[0026] Outside the lowered region 2 the concrete hollow-core slab 1 resembles a traditional concrete hollow-core slab. It has an upper layer 3 which has an upper surface 4 and a lower surface 5 and a lower layer 6 which has an upper surface 7 and a lower surface 8. In the embodiment as shown the thickness of the upper layer 3 is substantially the same as the thickness of the lower layer 6, but this may be different in an alternative embodiment. Furthermore, the concrete hollow-core slab 1 has a plurality of parallel ribs 9 which interconnect the upper layer 3 and the lower layer 6, hence forming elongate channels 10. Each channel 10 is bordered by a pair of neighbouring ribs 9, the upper surface 7 of the lower layer 6 and the lower surface 5 of the upper layer 3. The lower layer 6 may be provided with reinforcement bars (not shown) which extend in longitudinal direction of the concrete hollow-core slab 1.

[0027] In the embodiment as shown in Figs. 1 and 2 the lowered region 2 is elongated and extends perpendicularly with respect to the longitudinal direction of the concrete hollow-core slab 1. It is also conceivable that the longitudinal direction of the lowered region 2 has a different angle with respect to the longitudinal direction of the concrete hollow-core slab 1, for example diagonal. Fig. 1 shows that the lowered region 2 extends over the entire width of the concrete hollow-core slab 1, but this may be different in an alternative embodiment.

[0028] Referring to Fig. 2, the lowered region 2 has an upper surface 11 which lies at a lower level than the lower surface 5 of the upper layer 3 and at a higher level than the upper surface 7 of the lower layer 6. In this case the lowered region 2 is a continuous concrete layer, without channels, which has a thickness that is larger than a thickness of the lower layer 6, for example more than twice the thickness of the lower layer 6. At the left side of the lowered region 2 in Fig. 2 it can be seen that the upper surface 11 of the lowered region 2 abruptly transfers to the upper surface 4 of the adjacent upper layer 3, whereas upper portions of the respective channels 10 above the upper surface 11 of the lowered region 2 are open towards the lowered region 2. Lower portions of the respective channels 10 are closed by the lowered region 2. One can imagine that the sudden transition between the lowered region 2 and the ribs 9 causes an adverse resistance against a bending force and shear force on the concrete hollow-core slab 1.

[0029] The right side of the lowered region in Fig. 2 comprises a transition portion 12 between the lowered region 2 and the adjacent upper layer 3 and a portion of the ribs 9 above the upper surface 11 of the lowered region 2 at a transition between the lowered region 2 and the upper layer 3 in longitudinal direction of the concrete hollow-core slab 1. The transition portion 12 is located at a higher level than the lowered region 2 at the transition. The transition portion 12 interconnects the upper layer 3, the ribs 9 and the lowered region 2. The lowered region 2 and the transition portion 12 together close the adjacent channels 10. The upper layer 3, the lower layer 6, the transition portion 12, the lowered region 2 and the ribs 9 are made in one piece, i.e. they are integral or continuous and made of the same material. The transition portion 12 provides a relatively high structural strength of the concrete hollow-core slab 1.

[0030] In the embodiment as shown in Figs. 1 and 2 the transition portion 12 has a frontal surface 13 which borders a space above the lowered region 2. In this case the frontal surface 13 has an angle of about 235° with respect to the upper surface 4 of the upper layer 3, but this may be different in an alternative embodiment, for example between 210° and 270°. Fig. 2 shows that the transition portion 12 has a thickness which substantially equals the thickness of the upper layer 3, but this may be different in an alternative embodiment. In the embodiment as shown in Figs. 1 and 2 the upper surface 4 of the upper layer 3 transfers to the frontal surface 13 of the transition portion 12, which in turn transfers to the upper surface 11 of the lowered region 2, as seen in longitudinal direction of the concrete hollow-core slab 1.

[0031] Fig. 3 shows an alternative embodiment of the concrete hollow-core slab 1. In this case there are two transition portions 12 between the lowered region 2 and the upper layer 3, which are similar to each other. This means that all channels 10 are closed at opposite sides of the lowered region 2. The corresponding frontal surfaces 13 are directed to each other. An advantage of this embodiment with respect to the embodiment as shown in Figs. 1 and 2 is that the structural strength of the concrete hollow-core slab 1 is improved. Besides, when elements are placed in the space above the lowered region and the remaining space is filled with a liquid filler, such as a granular filler or similar material, for example concrete, gravel, sand or the like, the filler does not flow away through the channels 10. Nevertheless, it is also conceivable that the transition portions 12 are different; for example the left one in Fig. 3 may have a lower height such that the adjacent channels 10 are not entirely closed.

[0032] Fig. 6 shows an alternative embodiment, wherein the lowered region 2 is located at an end portion of the concrete hollow-core slab 1 in its longitudinal direction. Such an embodiment may be suitable for houses or apartments, for example.

[0033] Figs. 4 and 5 illustrate an embodiment of a method of creating a lowered region 2 in a non-cured concrete hollow-core slab 1 according to the invention. More specifically, these figures illustrate how the embodiment of the concrete hollow-core slab 1 as shown in Figs. 1-3 and 6 can be manufactured by showing a section of the non-cured concrete hollow-core slab 1 at one of the channels 10. First, a traditional hollow-core slab 1 is manufactured by a known technique (not shown), such as extrusion or a sliding method. Subsequently, when it is still in a non-cured state, at an intended location of a lowered region 2 a pushing element 14 is inserted into the non-cured concrete hollow-core slab 1 in a direction Y, which is in a direction from the upper layer 3 towards the lower layer 6, to a level below the lower surface 5 of the upper layer 3 and above the upper surface 7 of the lower layer 6. Consequently, the pushing element 14 locally pushes the upper layer 3 and portions of the respective ribs 9 between the channels 10 downwardly resulting in a first portion 2' of the lowered region, see Fig. 4. The first portion 2' of the intended lowered region forms a rib of concrete which projects upwardly form the lower layer 6.

[0034] Then, the pushing element 14 is moved with respect to the non-cured concrete hollow-core slab 1 in longitudinal direction thereof, i.e. in a pushing direction X, over a predetermined distance, which is shown by an arrow to the right in Fig. 5. The height level of the pushing element 14 with respect to the non-cured concrete hollow-core slab 1 is selected such that the latter step causes the material of the upper layer 3 and the ribs 9 at a right side of the pushing element 14 in Fig. 5 to move both downwardly and to the right such that concrete accumulates below and at the right side of the pushing element 14. The downward movement of concrete may be caused by crumbling of the non-cured or fresh concrete of the upper layer 3 and at least a portion of the ribs 9, which fresh concrete is still in a deformable condition, when the pushing element 14 moves in the pushing direction X.

[0035] The above-described process is further optimized by vibrating the pushing element 14 up and down in the direction Y during moving the pushing element 14 in the pushing direction X. This serves to compact the fresh concrete below the pushing element 14 and appears to create a proper transition portion 12, which results in a continuous material characteristic between the lowered region 2, the transition portion 12, the ribs 9 and the upper layer 3. In this way the concrete hollow-core slab 1 can be made in one piece. The compacted lowered region 2 due to the vibrating motion contributes to a relatively high structural strength of the concrete hollow-core slab 1. After making the lowered region 2 the concrete hollow-core slab 1 can be cured and transported to a building site. Vibrating non-cured concrete makes the material more liquid, displaceable and compact. It is noted that the vibrating action may be in three orthogonal directions.

[0036] The pushing element 14 may be an elongated beam which extends in transverse direction of the longitudinal direction of the non-cured concrete hollow-core slab 1. In the embodiment as shown in Figs. 4 and 5 the pushing element 14 has a flat lower side 15, a vertical back side 16 and an inclined front side 17, but this may be different if a different shape of the lowered region 2 is desired. For example, the embodiment of the concrete hollow-core slab 1 as shown in Fig. 3 can be made by using a pushing element 14 which has also an inclined back side 16 and is moved in opposite direction with respect to the pushing direction X. The latter embodiment of the method may also be used if a relatively wide lowered region in longitudinal direction of the concrete hollow-core slab 1 is required. If such a wide lowered region would be made by moving the pushing element in a single horizontal direction too much concrete would be pushed along to form an appropriate transition portion. In other words, the distance of pushing in the pushing direction X may be limited.

[0037] Fig. 7 shows an alternative embodiment wherein the lowered region 2 is similar to the lowered region 2 as shown in Fig. 3, but in this case the concrete hollow-core slab 1 is also provided with an elongate slot 18 which extends in longitudinal direction of the concrete hollow-core slab 1. The elongate slot 18 ends at the space above the lowered region 2 such that a T-shaped element (not shown) can be received in the space above the lowered region 2 and the elongate slot 18. The bottom of the elongate slot 18 may be flush with the upper surface 11 of the lowered region 2. The elongate slot 18 may be manufactured by pushing the upper layer 3 and a portion of the adjacent ribs 9 at the intended location of the elongate slot 18 in the non-cured concrete hollow-core slab 1 downwardly, possible assisted by a vibrational movement. This results in a compacted layer below the elongate slot 18 which is integral with the lowered region 2.

[0038] Fig. 8 shows a cross-section of the elongate slot 18 on a larger scale. The slot 18 is temporarily closed with a cover 19, for example a panel, in order to provide a safe walking area for workers on the floor. Opposite side edges of the cover 19 are received in recesses 20 at opposite sides of the slot 18 such that an upper surface of the cover 19 is substantially flush with the upper surface 4 of the upper layer 3 adjacent to the cover 19. It is also possible to place a cover at the lowered region 2 so as to close the space above the lowered region 2 in a similar way.

[0039] The invention is not limited to the embodiments shown in the drawings and described hereinbefore, which may be varied in different manners within the scope of the claims and their technical equivalents.

Claims

1. A concrete hollow-core slab (1), comprising an upper layer (3) which has an upper surface (4) and a lower surface (5), a lower layer (6) which has an upper surface (7) and a lower surface (8) and at least two ribs (9) which interconnect the upper layer (3) and the lower layer (6), hence forming an elongate channel (10) between the ribs (9), the upper surface (7) of the lower layer (6) and the lower surface (5) of the upper layer (3), wherein the concrete hollow-core slab (1) has a lowered region (2) which has an upper surface (11) at a lower level than the lower surface (5) of the upper layer (3), characterized in that a transition portion (12) located at a higher level than the lowered region (2) at a transition between the lowered region (2) and the upper layer (3) in longitudinal direction of the channel (10) interconnects the lowered region (2) and at least a portion of the ribs (9) adjacent to the transition portion (12), wherein the transition portion (12), the ribs (9), the lowered region (2), the upper layer (3) and the lower layer (6) are made in one piece.

2. A concrete hollow-core slab (1) according to claim 1, wherein the transition portion (12) interconnects the lowered region (2) and the ribs (9) such that it closes the channel (10) .

3. A concrete hollow-core slab (1) according to claim 1 or 2, wherein the transition portion (12) interconnects the lowered region (2) and the upper layer (3).

4. A concrete hollow-core slab (1) according to any one of the preceding claims, wherein the lowered region (2) is elongated and extends in transverse direction of the longitudinal direction of the channel (10).

5. A concrete hollow-core slab (1) according to claim 4, wherein the lowered region (2) extends over the entire width of the concrete hollow-core slab (1).

6. A concrete hollow-core slab (1) according to any one of the preceding claims, wherein the transition portion (12) has an inclined frontal surface (13) which borders a space above the lowered region (2), which inclined frontal surface (13) preferably has an angle between 210° and 270° with respect to the upper surface (11) of the upper layer (3).

7. A concrete hollow-core slab (1) according to any one of the preceding claims, wherein the lowered region (2) is located at a distance from opposite ends of the concrete hollow-core slab (1) in longitudinal direction of the channel (10).

8. A concrete hollow-core slab (1) according to claim 7, wherein the transition portion (12) is a first transition portion and the concrete hollow-core slab (1) comprises a second transition portion at another transition between the lowered region (2) and the upper layer (3) which is located opposite to the first transition portion and preferably similar to the first transition portion.

9. A concrete hollow-core slab (1) according to any one of the preceding claims, wherein the upper surface (11) of the lowered region (2) lies at a higher level than the upper surface (7) of the lower layer (6), for example more than 100%, 200% or 250% higher than the upper surface (7) of the lower layer (6) as measured from the lower surface (8) of the lower layer (6).

10. A concrete hollow-core slab (1) according to any one of the preceding claims and claim 6, wherein the transition portion (12) has a thickness which substantially equals the distance between the upper surface (4) and the lower surface (5) of the upper layer (3).

11. A concrete hollow-core slab (1) according to any one of the preceding claims, wherein thicknesses of the upper layer (3) and the lower layer (6) are substantially the same.

12. A concrete hollow-core slab (1) according to any one of the preceding claims, wherein an upper side of the concrete hollow-core slab (1) is provided with an elongate slot (18) which extends in longitudinal direction of the channel (10) and ends in a space above the lowered region (2).

13. A method of creating a lowered region (2) in a non-cured concrete hollow-core slab (1) including an upper layer (3) which has an upper surface (4) and a lower surface (5), a lower layer (6) which has an upper surface (7) and a lower surface (8) and at least two ribs (9) which interconnect the upper layer (3) and the lower layer (6), hence forming a channel (10) between the ribs (9), the upper surface (7) of the lower layer (6) and the lower surface (5) of the upper layer (3), wherein at an intended location of a lowered region (2) a pushing element (14) is inserted into the non-cured concrete hollow-core slab (1) in a direction from the upper layer (3) towards the lower layer (6) to a level between the lower surface (5) of the upper layer (3) and the upper surface (7) of the lower layer (6) and subsequently moved with respect to the non-cured concrete hollow-core slab (1) in a pushing direction (X), which is in longitudinal direction of the channel (10), over a predetermined distance such that concrete of the upper layer (3) and at least a portion of the ribs (9) adjacent to the pushing element (14) is moved towards the lower layer (6) and in the pushing direction (X).

14. A method according to claim 13, wherein the pushing element (14) is vibrated at least up and down when being moved in the pushing direction (X).

15. A method according to claim 13 or 14, wherein the pushing element (14) is elongated and its longitudinal direction is transverse with respect to the longitudinal direction of the channel (10).

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