METHOD FOR PRODUCING A CONCRETE SLABS FROM PRESTRESSED CONCRETE

Description

[0001] The invention relates to a method for producing a concrete slab made of prestressed concrete, the tendons of which comprise a plurality of rovings, in particular carbon fiber rovings, which penetrate the concrete slab and run parallel to the plane of the slab, comprising the steps: Construction of a formwork which is limited at the bottom by a production table and whose side walls are interspersed with pre-stressed rovings, pouring concrete into the formwork and allowing the concrete to set, and cutting off laterally protruding areas of the rovings.

[0002] During the production of prestressed concrete, tendons, such as prestressing wires or strands, are bonded to the concrete in a force-locking manner, so that relative displacement between the two materials is virtually non-existent. This allows a direct bond to be created between the tendons and the concrete, as is often the case in the manufacture of precast concrete elements in precast concrete plants, where prestressed prestressing wires or strands are embedded in the precast element. After the concrete has been poured and hardened, the prestressing is released. The bond between the concrete and the tendons, as well as the wedging of the relaxed tendons, applies the prestressing force to the precast element.

[0003] From WO 2014 / 040653 A1 a precast concrete component has become known in which the reinforcement or tendons are formed by a large number of rovings, d.h. of bundles, strands, or multifilament yarns made of parallel filaments or continuous fibers. The rovings can comprise carbon or glass fibers.

[0004] To manufacture such fiber-reinforced concrete components, the rovings must be tensioned in several layers, both longitudinally and transversely, one above the other. This process must be completed before the concrete component is manufactured, and the tensioned rovings must penetrate the formwork for the concrete component. The rovings must be removed from the formwork or reconstructed. Conventional formwork systems prove disadvantageous here. The large number of openings for the rovings to be tensioned makes the use of prefabricated formwork components difficult. Furthermore, the formwork must be designed to ensure a liquid-tight passage of the rovings to prevent the leakage of fresh concrete or other liquids.

[0005] To make matters worse, carbon fiber rovings in particular are extremely fragile and can easily be damaged during the construction or assembly of the formwork.

[0006] WO 2018 / 230855 A1 discloses a method for producing a cementitious structure made of prestressed concrete, the tendons of which comprise a plurality of rovings penetrating the cementitious structure and running parallel to the plane of the slab, comprising the steps: Construction of a formwork which is limited at the bottom by a production table and whose side walls are interspersed with pre-stressed rovings, pouring concrete into the formwork and allowing the concrete to set, and cutting off laterally protruding areas of the rovings.

[0007] The invention therefore aims to improve the formwork for the production of prestressed concrete slabs using rovings. In particular, the aim is to create a formwork that can be constructed using simple means and in a short time, allowing the rovings to be sealed in a fluid-tight manner without damaging them. Furthermore, the formwork should not generate unnecessary waste material that would require costly disposal.

[0008] To achieve this object, the invention essentially consists in a method of the type mentioned at the outset in that the side walls of the formwork are produced by pouring a powdery building material which hardens by adding liquid onto the production table and moistening the fill.

[0009] By pouring a powdered building material, the rovings are subjected to hardly any mechanical stress, thus preventing damage. Due to the powdery state, the building material can trickle into the spaces between adjacent rovings, ensuring that the rovings are fully embedded in the resulting fill. If necessary, this process can be supported by a vibrating movement, e.g. shaking the production table. Embedding the rovings in the fill ensures that, once the fill has stabilized or hardened, the rovings pass tightly through the fill or the resulting edge formwork. The fill is formed into dimensionally stable edge formwork by consisting of a building material that hardens when liquid is added and which is moistened after pouring.

[0010] Preferably, the building material contains or consists of a hydraulic binder, in particular cement. This has the positive effect that the edge formwork does not represent a foreign material to the concrete and, after the concrete slab has hardened, can be easily removed from the edge of the slab, for example, by breaking it off or sawing it off. The edge formwork can then be crushed and, depending on the composition of the hydraulic binder, reused for the production of new concrete and / or recycled products.

[0011] The cement used may be a Portland cement-based cement, such as those defined in EN 197-1, including Portland cement CEM I, Portland composite cements CEM II, blast furnace cement CEM III, pozzolanic cement CEM IV and composite cement CEM V. To ensure a short setting time, a setting accelerator may be added to the cement.

[0012] The hydraulic binder is particularly preferably a rapid-setting cement, such as a calcium aluminate cement.

[0013] Mortar can be used as a cement-containing building material.

[0014] The building material is preferably poured onto the prestressed rovings, whereby the fill may have a substantially trapezoidal cross-section.

[0015] To achieve automated production of the fill, a preferred embodiment of the method according to the invention provides for the fill to be produced by discharging the building material from a movable discharge head of a building material supply or storage device. The discharge head can be moved along the edge of the formwork to be formed, while the powdered building material is discharged onto the production table, creating a linear fill. The linear fill surrounds the area into which the concrete will subsequently be poured to form the concrete slab, allowing the formation of a peripheral edge formwork.

[0016] Moistening the fill preferably involves applying, in particular spraying, a liquid, especially water, to the fill. The liquid is applied to the surface of the fill so that the surface area of ​​the fill sets. Setting the entire fill cross-section is not absolutely necessary, as it is sufficient for the dimensional stability of the edge formwork if a stable skin forms. This is particularly important because the fill absorbs further liquid from the concrete after the fresh concrete has been poured, which promotes the further setting and hardening process of the fill.

[0017] The powdered building material can be applied in a single pass using the movable application head. Alternatively, multiple layers of the building material can be applied one above the other and / or side by side. Moistening of the fill is preferably carried out after the last layer of building material has been applied. Alternatively, moistening can be carried out after each layer of building material.

[0018] The liquid can be applied to the fill immediately after the building material has been poured, in particular with the aid of a liquid application device, such as a spray nozzle, which moves synchronously with the movable application head. In this context, a preferred embodiment provides that the application takes place by means of at least one liquid application device, in particular a spray nozzle, arranged on the application head. The position of the liquid application device(s) on the application head is fundamentally arbitrary. For example, the spray nozzle can be arranged behind a discharge opening of the application head in the direction of travel of the application head and directed at the fill discharged from the preceding discharge opening. The application head preferably comprises a plurality of spray nozzles which have different nozzle axes.In this way, the liquid can be directed, for example, onto the two sloping flanks of the bed and onto the upper surface.

[0019] The discharge head may further comprise a stripping element arranged downstream of the discharge opening in the direction of travel, which strips off material exceeding a defined height in order to thereby produce a substantially flat, horizontal upper surface.

[0020] Preferably, it can further be provided that the area of ​​the production table to be covered by the fill is moistened before the fill is applied. This promotes setting of the fill at the lower boundary surface of the fill, which facilitates the subsequent separation of the hardened fill from the production table after the concrete slab has been produced. The moistening of the production table is preferably carried out using a spray nozzle arranged on the application head.

[0021] After the concrete slab has set and at least partially hardened, the side walls of the formwork can be removed, e.g., by sawing them off the concrete slab. The sawing can be done as a trimming cut, which gives the concrete slab the desired dimensions.

[0022] The invention is explained in more detail below with reference to exemplary embodiments shown schematically in the drawing, in which Fig. 1 a top view of a production table for the production of concrete slabs and Fig. 2 a section along the line II-II of the Fig. 1 .

[0023] In Fig. 1 a production or formwork table 1 is shown, on the edges of which holding elements 2, 3, 4 and 5 are arranged, wherein between opposite holding elements 2 and 4 or 3 and 5 a plurality of carbon rovings 6, 7 are stretched, wherein a group of carbon rovings 6 crosses another group of carbon rovings 7 and, as in Fig, 2 As can be seen, at least two layers of carbon rovings are arranged one above the other. The carbon rovings thus span the production table 1 in two mutually perpendicular directions.

[0024] The formwork table 1 forms the base of a formwork into which fresh concrete is poured to produce a prestressed concrete slab. The side walls of the formwork are formed by a circumferential fill 8 made of a powdered building material that hardens upon the addition of liquid, in particular dry cement or cement mortar. The building material is applied by means of a movable application head 9 of a building material supply or storage device. The application head 9 is movable in the direction of the double arrows 10 and 11 and is moved by a drive according to the desired course of the edge formwork. The fill 8 is sprayed with liquid via spray nozzles (not shown) so that the fill 8 sets at least superficially and, after setting, forms a dimensionally stable edge formwork.

[0025] After the edge formwork has been formed, liquid concrete is poured into the area 12 defined by the edge formwork and allowed to set. After the concrete has hardened, the edge formwork is removed, leaving a concrete slab made of prestressed concrete. The concrete slab produced in this way can be trimmed along its edges and / or divided into smaller slab pieces using a suitable cutting device, such as a concrete saw. Concrete components of any shape can also be milled from the concrete slab using a concrete milling machine.

[0026] In the sectional view according to Fig. 2It can be seen that the holding elements 3 and 5 are each arranged on a receiving device 13 and 14, respectively. Furthermore, it can be seen that the fill 8 has a substantially trapezoidal cross-section caused by the pouring process. The carbon rovings 8 penetrate the fill 8 and are embedded in it, thus forming a tight seal for the area 12 delimited by the fill 8 for the liquid concrete.

[0027] The application head 9 comprises an application opening 16 and is further equipped with schematically indicated spray nozzles 15 for applying liquid onto the bed 8.

Claims

1. A method for producing a concrete slab made of prestressed concrete, whose tensioning members comprise a plurality of rovings (6, 7), particularly carbon fiber rovings, extending through the concrete slab parallel to the slab plane, comprising the steps: - producing a formwork that is bounded at the bottom by a manufacturing table (1) and whose side walls are penetrated by prestressed rovings (6, 7), - pouring concrete into the formwork and allowing the concrete to set, and - cutting off laterally protruding areas of the rovings (6, 7), whereby the side walls of the formwork are produced by piling a powdery construction material that hardens through liquid addition onto the manufacturing table (1) and moistening the pile (8).

2. Method according to claim 1, characterized in that the construction material contains or consists of a hydraulic binder, particularly cement.

3. Method according to claim 2, characterized in that the hydraulic binder is a rapid-hardening cement.

4. Method according to claim 1, 2 or 3, characterized in that the construction material is piled onto the prestressed rovings (6, 7).

5. Method according to any one of claims 1 to 4, characterized in that the pile (8) has a substantially trapezoidal cross-section.

6. Method according to any one of claims 1 to 5, characterized in that the pile is produced by discharging the construction material from a movable discharge head (9) of a construction material supply or storage device.

7. Method according to any one of claims 1 to 6, characterized in that the moistening of the pile (8) comprises applying, particularly spraying, a liquid, particularly water, onto the pile (8).

8. Method according to claim 7, characterized in that the application is carried out by means of at least one liquid discharge device, particularly a spray nozzle (15), arranged on the discharge head (9).

9. Method according to any one of claims 1 to 8, characterized in that the area of the manufacturing table (1) to be covered by the pile (8) is moistened before the pile (8) is applied.

10. Method according to claim 9, characterized in that the moistening of the manufacturing table is carried out by means of a spray nozzle arranged on the discharge head.