EP1307326B1 - Hollow pre-stressed concrete slab and method for production thereof - Google Patents

Abstract

The invention relates to a method for production of hollow pre-stressed concrete slabs (1), whereby several strands (2) are tensioned in parallel, either individually or groupwise, between two fixtures arranged separate from each other and are enveloped in concrete in an extrusion process, whereby cavities (3) remain, running between the strands enveloped in concrete and parallel to said strands. According to the invention, conventional hollow pre-stressed concrete slabs and the method for production thereof may be improved such that the economic advantages of using said slabs in construction is improved and the load capacity of said slabs is increased, above all in the transverse direction, making it possible to produce wider slabs, whereby a fibre concrete is used as the concrete material.

Description

The present invention relates to a prestressed concrete hollow slab and a method for producing a prestressed concrete slab in which a plurality of strands between spaced brackets are clamped individually or in groups parallel to each other and wrapped in concrete by extrusion, wherein extending parallel to the strands extending cavities between the concrete Strands remain. The hollow concrete slabs produced by such a method consist of a top chord, a bottom chord and webs extending between the bottom chord and the top chord, each delimiting parallel extending cavities, wherein prestressed strands are arranged parallel to the voids in the concrete material, the strands being extruded during extrusion Betons are embedded in these.

A corresponding method for producing hollow concrete slabs and also the hollow concrete slabs produced therefrom are known from US Pat. No. 4,067,676. The hollow concrete slabs made therefrom are simply made by cutting to length sections of the total one piece slab.

These plates are manufactured in plants in which the holders for tensioning the strands are spaced very far from e.g. 100 or 120 m and a corresponding extruding machine, which has a bucket for receiving concrete, travels along the tensioned strands and extrudes the concrete so that the strands are thereby embedded in certain desired cross-sectional areas, in the concrete, the extrusion openings are provided with tubes or pins which define the cavity cross-sections and are moved along with the machine, the machine leaves the extruded plate cross-section and the plate finally extends substantially between the two jigs. It is understood that the concrete in this case must have a very high viscosity and a very pronounced green strength, that is, he must already have a sufficient dimensional stability when pressed out of the extrusion, so that the plate cross-section, including the flat upper and lower surfaces and the cavity cross sections remain and the plate is not deformed or at best in a precisely controllable manner subsequently. After extruding, the concrete must finally cure before the strands can be separated at the two ends of the thus prepared, approximately 100 to 120 m long cavity plate. After hardening of the concrete, the strands remain in the prestressed state due to their firm connection with the concrete material.

The high stability of the concrete in the green state, which is necessary in this process, requires that the concrete mixture used has a correspondingly high viscosity. Only in this way can corresponding plates be extruded and finished at the desired speed by which the method obtains the desired economy.

However, this manufacturing method by means of an extruding machine does not allow reinforcement of the prestressed concrete hollow plates in the transverse direction. Therefore, while the load bearing capacity and load carrying capacity of the slabs are relatively good in terms of supporting points in the longitudinal direction, the carrying capacity in the transverse direction is very limited. In particular, such plates are designed only for static loads, but not for dynamic loads. They are therefore used e.g. used only as a ceiling in residential, commercial and industrial buildings. The hollow slabs have the advantage of a considerably lower weight compared to solid slabs, on the other hand, the advantage of a lower thermal conductivity, since the cavities have an insulating effect.

Usually, the long extruded sheets are cut to lengths of a desired length for a specific construction project, usually on the order of a few meters and up to 15 m, and to form a ceiling or a floor, the panels are placed side by side on supporting walls. Foundations or carriers launched. Since the plates have a slightly trapezoidal cross-section in such a way that the top chord between 2 and 5 cm is narrower than the bottom chord, when laying the plates, only the bottom chords along the longitudinal edges of adjacent plates abut each other and the gap formed therebetween with concrete, mortar or another binder or grout filled.

The manufacture of the plates in the form of cavity plates entails considerable material and weight spatter without sacrificing the load bearing capacity of the plates.

However, as already mentioned, these plates have the disadvantage of only a low load capacity in the event of loads in the transverse direction and, in particular, they can not be loaded dynamically, ie they are not suitable for driving on vehicles with fork-lift trucks or for setting up machines which generate vibrations. Because of the low Quertragfähigkeit the plates can be produced only in maximum widths of about 1.2 m. This impairs the economics inherent in the use of such panels in the manufacture of corresponding buildings, as there are accordingly more joints to be filled between the side-by-side panels, which is relatively labor intensive.

US Pat. No. 5,798,151 discloses a method and an apparatus for producing hydraulically settable mixtures, in particular concrete, and correspondingly produced articles, both continuous reinforcing strands and fibers being introduced into the material. However, this document does not disclose the manufacture of prestressed concrete and the corresponding use and arrangement of tensioned strands during extrusion, but describes other shapes, e.g. a spiral insertion of strands into the concrete. Natural fibers are given as preferred fibers, but metal fibers are also mentioned as discontinuous fibers to be incorporated. The specific examples dealing with the use of fiber concrete do not provide any more detailed specifications of the fibers introduced and describe the use of a piston extruder for introducing the mixture into a mold.

Compared to this prior art, the present invention seeks to improve the known prestressed concrete slab and the process for their production to the effect that the efficiency in the use of such plates under construction is further increased and the sustainability of the plates, especially in the transverse direction clearly is improved, so that it can be produced in larger widths.

With regard to the method, the object underlying the invention is achieved in that a fiber concrete is used as the concrete material, fibers being used as fibers with a volume fraction of at least 0.1%, which have a cross section between 0.1 and 1 mm ² and an average length between 20 and 100 mm.

Accordingly, the prestressed concrete hollow plate according to the invention is characterized in that the concrete material of this plate consists of fiber concrete, wherein the fibers are steel fibers with a cross section between 0.1 and 1 mm ² and a length between 20 and 100 mm and at least 0.1% of the volume of Make out concrete.

Steel fibers are preferably used in an amount of about 60 kg / m ^{3 of} concrete, which corresponds, for example, to a volume fraction of about 0.8%. The fibers have a cross section between 0.1 and 1 mm and an average length between 20 and 100 mm, preferably between at least 30 or 50 and 70 mm. In particular, steel fibers with a round cross-section and a diameter of about 0.5 mm and a mean length of 60 mm can be used.

Although the steel fibers have a considerable influence on the flowability of the concrete, which is much more difficult to process and extrude due to the fiber content, it has been shown that the individual parameters and the constituents of the concrete are quite so adjustable that the one corresponding amount of fibers still containing concrete to the desired plate cross section is extrudable. At the same time, the required green state stability, that is to say the dimensional stability of the concrete immediately after the extrusion, is retained to a sufficient extent. Ideally, compared with conventional prestressed concrete slabs, the minimum wall thicknesses of upper and lower flange are increased slightly to values above 40 mm, in particular to at least 45 or approximately 50 mm. Due to the slightly larger wall thicknesses of the top and bottom chords, the concrete is significantly easier to extrude, although it has a significantly higher toughness and poorer flowability than conventional concrete, which is normally used to extrude hollow slabs. has. The prestressed concrete hollow slabs produced in this way have a significantly better load capacity with bending moments in the transverse direction and, moreover, can also be loaded dynamically. The prestressed concrete hollow slabs according to the invention have already been produced in widths of up to 3 m, although, in principle, production in larger widths would also be possible, which, however, does not make sense in practice for reasons of poor transportability of such wide plates.

The advantageous properties of the panel according to the invention not only considerably extend the field of use of such prestressed concrete hollow panels, e.g. On ceilings in industrial buildings, which can even be used by forklifts, but also the installation of appropriate plates is considerably more economical, since the number of required for a ceiling plates when using 3 m wide plates compared to the conventional, a maximum of 1.2 m wide panels is reduced by a factor of 2.5 and thus also reduces the number of joints between the plates, which considerably accelerates the completion of corresponding ceilings and floors.

From the dependent claims, there are preferred embodiments of the present invention, both in terms of the manufacturing process and in terms of prestressed concrete hollow plate itself.

Thus, it is understood, for example, that as fibers not only steel fibers can be used, but optionally also natural fibers or other metal fibers, which can vary considerably in cross-section and length from the preferred steel fibers. Also, the plates need not be manufactured exclusively in widths of 3 m, but should preferably have a width of at least 1.2 m or more, the differences in the width dimensions between different plates preferably being 60 cm each. In addition to the plates in widths of 1.2 m, which can of course also be produced as required by the method according to the invention and as prestressed concrete slabs with fiber concrete, so plates in widths of 1.8 m, 2.4 m and preferably 3 m should be prepared , Of course, when using fiber concrete with the method according to the invention also plates of greater width could be produced, as far as they can be easily transported to their place of use.

While 1.2 m wide plates preferably have only four cavities, 1.8 m wide plates should have six cavities, 2.4 m eight cavity plates and 3 m wide plates should have ten cavities. This results in a typical pitch between the cavities in the order of 30 cm or slightly below. The ridges remaining between two adjacent cavities should have a width of well over 40 mm, typically about 60 mm, as a minimum, and the ridges on the side plate edges may be slightly wider, e.g. be at least 70 mm or 80 mm wide. The height of the cavities depends on the thickness of the plates, wherein the height of the cavities is dimensioned in the preferred embodiment so that the minimum thickness of the upper and lower belt above and below the respective cavities is 50 mm. The basic shape of the cavities is either circular, elliptical or rectangular, but in the latter case with clearly rounded corners. Preferably, the cross-sectional shape of the cavities should be designed so that the minimum radius of curvature in cross section is 50 mm, preferably 60 to 100 mm. The typical plate thicknesses are 265, 320 and 400 mm. The cavities should each have approximately the same width even with different thicknesses, but of course have different heights at different plate thicknesses, so that there is the mentioned minimum flange thickness of the upper and lower chords. The minimum web width of the webs connecting the upper and lower chords can remain the same for the different board thicknesses, since the width of the cavities and their positioning remain the same. This facilitates in particular the production by changing only the spacings of the upper and lower edges of the extrusion dies at different plate thicknesses on the extrusion dies and the tubes forming the cavities need to be replaced, but their position remains unchanged.

Often, recesses must be made in corresponding plates. While this is relatively simple in conventional prestressed concrete slabs in the not yet set concrete material, in the present case, a method has been developed by the applicant, with the inventions cavities are prepared by cutting with a high-pressure jet of dry ice. This method allows the walls of corresponding cavities to be made with sufficiently smooth surfaces. At the same time, however, in cavities extending over prestressed strands, these strands remain undamaged. Thus, after the cavities have been produced in the not yet hardened concrete by cutting with a dry ice jet, one can wait for the setting of the concrete and, if necessary, separate the strands which may be passing through the produced cavities. This gives sufficiently accurate cavities with small dimensional tolerances that would otherwise be produced only subsequently with appropriate effort in the hardened concrete. Procedures such as hollowing out the cavities by hand or sucking off a delimited area, each still in the fresh state of the concrete, are practically impractical with fiber-reinforced concrete

The cutting by means of a dry ice jet can of course be applied to other types of concrete than fiber concrete and can be applied in particular to concrete and fiber concrete, which is not used for the production of prestressed concrete hollow slabs apply.

The cutting with dry ice has the advantage that the dry ice itself, namely CO ₂ in solid form, leaves no residue and does not have to be eliminated, the process is also environmentally friendly, as the CO _{2 used is} previously deprived of air.

For cutting with dry ice, only compressed air at a relatively low pressure of the order of magnitude between 5 and 10 bar is required.

Further advantages, features and possible applications of the present invention will become apparent from the following description of preferred embodiments and the associated figures.

Figur 1

eine perspektivische Ansicht eines Abschnittes einer erfindungsgemäß hergestellten Spannbetonplatte und

Figur 2

den Querschnitt von drei Platten mit einer Breite von 3 m, jedoch mit unterschiedlichen Höhen zwischen ca. 265 und ca. 400 mm.

Show it:

FIG. 1

a perspective view of a portion of a prestressed concrete slab produced according to the invention and

FIG. 2

the cross section of three plates with a width of 3 m, but with different heights between about 265 and about 400 mm.

It can be seen in Figure 1 is a perspective view of a prestressed concrete hollow plate, which is generally designated 1 and which is traversed by parallel, tubular cavities, wherein in the example shown a total of ten cavities are provided and the plate has a width of about 3 m, from which a pitch between the cavities of slightly less than 30 cm, eg about 28 cm, results. Further details will be described in connection with the cross sections of three different prestressed concrete hollow slabs shown in FIG.

The three prestressed concrete hollow slabs 1, 1 'and 1 ", the cross-section of which is shown in Figure 2, differ only in their different thicknesses and correspondingly different heights of cavities provided therein Each of the slabs consists of a top chord 4, ie the concrete layer which extends continuously above the cavities, a lower flange 5, namely the concrete layer extending below the cavities and the webs 6 which interconnect the upper flange 4 and the lower flange 5 between the individual cavities The same width, but different heights, they have the basic shape of a rectangle with strongly rounded corners, with the radius of curvature of the corner areas of the order of 80 mm.

The webs 6 between the cavities 3 have a width of about 60 mm and the minimum thickness of the top and bottom chord is 45 mm, in some embodiments 50 or 55 mm, depending on the desired load capacity and other parameters. At the same minimum thickness of the upper and lower chords and the same minimum width of the webs between the cavities results for the plate with the largest diameter and the largest ratio of the cross-sectional area of the cavities to the cross-sectional area of the concrete or the total cross-section of the plate, while this ratio at the thinnest plate becomes minimal. Die.vorgespannten strands 2 are each in the gussets, that is arranged at the transition of the individual webs 6 to the upper flange 4 and lower flange 5. In the lower gusset, e.g. arranged in each case three parallel strands, while one can be content in the upper gusset with one or two strands, since when loads corresponding concrete ceilings, especially the lower flange must absorb tensile loads. However, the steel fibers contained in the concrete also increase the tensile strength of the concrete in the transverse direction and in particular lead to a significantly improved dynamic load capacity. As you can see also, all plates have a slightly trapezoidal, symmetrical cross-section, the lower flange in cross-section is about 50 mm wider than the upper flange. This results in a wedge-shaped, in the upper region 5 cm wide gap, which is filled after the flush juxtaposition of the plates with their lower chords with a suitable grout. Undercuts of the lateral wall sections below the upper belt and above the lower belt ensure a good grip of the grout and a good connection of adjacent plates with each other.

Claims (17)

1. Method for the production of hollow pre-stressed concrete slabs (1), in which several strands (2) are tensioned individually or in groups parallel to each other between two mounts arranged spaced apart from each other and are enveloped in concrete in an extrusion process, wherein cavities (3) extending parallel to the strands remain between the concrete-enveloped strands, characterized in that a fibre concrete is used as concrete material, wherein steel fibres with a proportion by volume of at least 0.1 % are used which have a cross-section between 0.1 and 1 mm², and an average length between 20 and 100 mm.
2. Method according to claim 1, characterized in that the fibre concrete is produced with a proportion by volume of at least 1 to 3 dm³ of fibres per cubic metre of concrete, preferably at least 5-10 dm³ per cubic metre of concrete.
3. Method according to claim 1 or 2, characterized in that fibres are added to the concrete in an amount of at least 30 kg/m³, preferably between 40 and 80 kg/m³ of fibre concrete.
4. Method according to one of claims 1 to 3, characterized in that the fibres have an average length of between 30 and 70 mm.
5. Method according to one of claims 1 to 4, characterized in that the slabs are produced in a width of at least 1.2 m or more, preferably in widths of 1.8 m, 2.4 m and 3 m.
6. Method according to one of claims 1 to 5, characterized in that the slabs are produced independently of the slab thickness with cavities that are separated by a characteristic spacing averaging between 20 and 40 cm, preferably 25 to 35 cm and in particular 28 to 30 cm.
7. Method according to one of claims 1 to 6, characterized in that the cavities of the slabs are produced with a substantially rectangular cross-section with rounded corners.
8. Method according to claim 7, characterized in that the radius of curvature of the comers is at least 50 mm, preferably between 60 and 100 mm.
9. Method according to one of claims 1 to 8, characterized in that the upper chord and lower chord of the hollow slabs, as well as the sections which extend between upper chord and lower chord and separate the cavities from one another, are extruded with wall thicknesses of more than 40 mm, preferably more than 45 mm and in particular approximately 50 mm.
10. Hollow pre-stressed concrete slab (1) consisting of a upper chord (4), a lower chord (5) and sections (6) extending between lower and upper chord, which each delimit parallel-extending cavities (3), pre-tensioned strands (2) being arranged in the concrete material parallel to the cavities and the slabs being produced by extrusion of concrete along the pre-tensioned strands (2), characterized in that the concrete material contains at least 0.1 % by volume steel fibres which have a cross-section of between 0.1 and 1 mm² and an average length of between 20 and 100 mm.
11. Hollow pre-stressed concrete slab according to claim 10, characterized in that the fibres are steel fibres which are contained in the fibre concrete in an amount of at least 30 kg/m³, preferably in an amount of between 40 and 80 kg/m³.
12. Hollow pre-stressed concrete slab according to claim 10 or 11, characterized in that upper chords, lower chords and the sections extending between same have wall thicknesses of at least more than 40 mm, preferably more than 45 mm and in particular approximately 50 mm.
13. Hollow pre-stressed concrete slab according to one of claims 10 to 12, characterized in that the cavities (3) have a round or elliptical or rectangular cross-section with rounded corner regions.
14. Hollow pre-stressed concrete slab according to claim 13, characterized in that the minimum radius of curvature of the cavity cross-section is at least 50 mm, preferably between 60 and 100 mm.
15. Hollow pre-stressed concrete slab according to one of claims 10 to 14, characterized in that the slab has a width of at least 1.2 m or more, preferably a width of between 1.8 and 3 m, in particular measuring 1.8, 2.4 or 3 m wide.
16. Hollow pre-stressed concrete slab according to one of claims 10 to 15, characterized in that the characteristic spacing for the cavities (3) is independent of the width and the thickness of the slabs and is approximately 26 to 30 cm, in particular approximately 28 cm.
17. Hollow pre-stressed concrete slab according to one of claims 10 to 16, characterized in that the slab cross-section is substantially trapezoidal, the upper chord (4) having a width approximately 5 cm less than that of the lower chord (5).

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