FIBER REINFORCED POST-TENSIONED CONCRETE SLAB WITH OPENINGS

Abstract

A concrete slab, the slab containing conventional concrete and a combined reinforcement of both post-tension steel strands and fibers, said post-tension steel strandshaving a diameter ranging from 5 mm to 20 mm,having a tensile strength higher than 1700 MPa, said fibers being either steel fibers and being present in a dosage ranging from 5 kg/m.sup.3 to 90 kg/m.sup.3 or being macro-synthetic fibers and being present in a dosage ranging from 1.5 kg/m.sup.3 to 9.0 kg/m.sup.3, whereby the slab has upper as well as lower surfaces and sides, whereby further each strand or a group of strands has two ends, whereby further each strand or a group of strands is provided with end anchors on at least one of its ends, whereby the slab has at least one opening in its upper surface so that said anchor is accessible from said upper surface through said opening.

Claims

1. A concrete slab, the slab comprising conventional concrete and a combined reinforcement of both post-tension steel strands and fibers, said post-tension steel strands having a diameter ranging from 5 mm to 20 mm, having a tensile strength higher than 1700 MPa, said fibers being either steel fibers and being present in a dosage ranging from 5 kg/m.sup.3 to 90 kg/m.sup.3 or being macro-synthetic fibers and being present in a dosage ranging from 1.5 kg/m.sup.3 to 9.0 kg/m.sup.3, whereby the slab has upper as well as lower surfaces and sides, whereby further each strand or group of strands has two ends, whereby further each strand or group of strands is provided with an end anchor on at least one of its ends, whereby the slab has at least one opening in its upper surface so that said anchor is accessible from said upper surface through said opening.

2. The concrete slab according to claim 1, whereby each opening corresponds to between 0.005 to 10%, preferably 0.01 to 5%, further preferred 0.05 to 2.5%, even further preferred 0.1 to 1.5%, further preferred 0.2 to <1.5%, further preferred 0.25 to 1.25% of the volume of the slab and/or the openings allow to apply tension to the post-tension steel strand and/or release tension applied to the post-tension steel stands.

3. The concrete slab according to claim 1, wherein said conventional concrete has a characteristic compressive cube strength of 25 N/mm.sup.2 or higher, preferably 28 N/mm.sup.2 or higher, further preferred 30 N/mm.sup.2 or higher and/or wherein the slab does not contain any further reinforcement elements beside steel fibers and post-tensioning steel strands within the body of the slab, and/or wherein the slab is cast in one or multiple steps.

4. The concrete slab according to claim 1, wherein said fibers are steel fibers or wherein the fibers are glued or wherein macro-synthetic fibers may be selected from carbon fibers, glass fibers, basalt fibers or other non-steel based fibers, preferably polyolefin fibers, further preferred polypropylene fibers or polyethylene fibers.

5. The concrete slab according to claim 1, whereby the outline of an opening or of each opening may be a polygon, preferably for example a polygon comprising angles of 100 or less, especially for example a rectangle or square and/or whereby the outline of an opening or of each opening maybe an ellipse, especially for example a circle or an oval and/or whereby the outline of an or of each opening may be partially elliptic, especially semi-circular or partially oval and/or whereby the outline of an or of each opening a polygon comprising only 2 angles being 90, a polygon comprising only 2 angles being 90 and arranged as angles at or closest to the outside border of the concrete slab, a polygon comprising only 2 angles being 90 and arranged as the angles that are the farthest away from the center of the upper surface of the slab, further preferred a polygon comprising only 2 angles being 90 and at least 2 angles being >90, further preferred a polygon comprising only 2 angles being 90 and at least 4 angles being >90.

6. The concrete slab according to claim 1, whereby the depth of the opening(s) corresponds to at least 50%; preferably 55%; further preferred 60% of the thickness of the slab or the depth of the opening(s) may for example correspond to the thickness of the slab and/or whereby the opening(s) have a width/length ratio <1 and/or a length between 2 cm and 100 cm, preferably between 5 cm and 50 cm, preferably between 6 cm and 20 cm.

7. The concrete slab according to claim 1, whereby the opening can be filled with grout or concrete, especially conventional concrete.

8. The concrete slab according to claim 1, wherein the post tensioning strands are draped and/or arranged in the middle of the slab and/or in the upper third of the slab and/or in the lower third of the slab and/or whereby the ends of the strand are straight or pointing upwards or pointing downwards.

9. The concrete slab according to claim 1, wherein the fibers are substantially homogenously or homogeneously distributed in the slab.

10. The concrete slab according to claim 1, wherein the post-tension steel strands are in a banded-banded steel strands configuration or in a banded-distributed steel strands configuration or distributed-distributed steel strands configuration or in a configuration resulting from any combination thereof, and/or wherein the post-tension steel strand are used for bonded or unbonded post-tensioning.

11. The concrete slab according to claim 1, whereby fibers are steel fibers and are present in a dosage ranging from 5 kg/m.sup.3 to 90 kg/m.sup.3, preferably whereby steel fibers are present in the slab in a dosage ranging from 7 kg/m.sup.3 to 75 kg/m.sup.3, preferably from 7 kg/m.sup.3 to <65 kg/m.sup.3, preferably from 10 kg/m.sup.3 to 60 kg/m.sup.3, preferably 15 kg/m.sup.3 to 50 kg/m.sup.3, further preferred 20 kg/m.sup.3 to 45 kg/m.sup.3 or alternatively >45 kg/m.sup.3 to 60 or <65 kg/m.sup.3, further preferred from 15 kg/m.sup.3 to 40 kg/m.sup.3, further preferred from >20 kg/m.sup.3 to <40 kg/m.sup.3, preferably from 15 kg/m.sup.3 to 35 kg/m.sup.3, preferably from 20 kg/m.sup.3 to 30 kg/m.sup.3 or from 10 kg/m.sup.3 to <30 kg/m.sup.3 or further preferred from 10 kg/m.sup.3 to 27 kg/m.sup.3. In an embodiment, the amount of steel fibers used according to the present invention may be for example preferably below or equal to 1.2 times, preferably 1.0 time, further preferred between >0 and 1.1 times, the amount or level of steel recommended and used for the steel bars or rebars to be replaced and/or the amount or level of steel fibers may be below or equal 1.2 times, preferably 1 time, further preferred between >0 and 1.1 times, the amount or level recommend as rebar or steel bar replacement.

12. A method of making a concrete slab according to claim 1, said method comprising the following steps: positioning post-tensioning steel strands including end anchors at their ends positioning opening formers to allow the formation of at least one opening in the upper surface of the slab, so as to permit access to the strands and/or the end anchors from the upper surface of the slab pouring concrete to form a concrete slab according to claim 1.

13. The method of making a concrete slab according to claim 12, said method comprising filling the openings with grout or concrete, especially conventional concrete.

Description

[0070] FIG. 1 shows a schematic top down view of a slab (1) according to the invention with openings having a semi-circular outlines (2) next to a wall (8) to allow access to post-tensioning strands (9).

[0071] FIG. 2 illustrates a preferable embodiment of a steel fiber (3). The steel fiber (3) has a straight middle portion (4). At one end of the middle portion (4), there are three bent sections (5), (6) and (7). At the other end of the middle portion (4) there are also three bent sections (5), (6) and (7). Bent sections (5), (5) make an angle (a) with respect to a line forming an extension to the middle portion (4). Bent sections (6), (6) make an angle (b) with respect to a line forming an extension to bent sections (5), (5). Bent sections (7), (7) make an angle (c) with respect to bent sections (6), (6).

[0072] The length of the steel fiber (3) may range between 50 mm and 75 mm and is typically 60 mm.

[0073] The diameter of the steel fiber may range between 0.80 mm and 1.20 mm.

[0074] Typical values are 0.90 mm or 1.05 mm.

[0075] The length of the bent sections (5), (5), (6), (6), (7) and (7) may range between 2.0 mm and 5.0 mm. Typical values are 3.2 mm, 3.4 mm or 3.7 mm.

[0076] The angles (a), (b) and (c) may range between 20 and 50, e.g. between 24 and 47.

[0077] The steel fibers may or may not be provided with a corrosion resistant coating such as zinc or a zinc aluminium alloy.

[0078] In a particular preferable embodiment of the invention, there may be three or four bent sections at each end of the middle portion.

[0079] FIG. 3 show a schematic top down view of a slab (1) according to the invention having a openings (2) with a square and a semi-circular outlines, whereby cracks (10) may appear especially in the corners of the opening with a square outline and a rebar (11) may thus be foreseen at or near such corners to contribute to counter crack formation.

Other Reinforcing Fibers

[0080] Examples of other reinforcing fibers may be selected from carbon fibers, glass fibers, basalt fibers or other non-steel based fibers, such as fibers based upon polyolefins like polypropylene or polyethylene or based upon other thermoplastics.