Method and device for producing a concrete slab made of prestressed concrete

Abstract

The invention relates to a method for producing a concrete slab made of prestressed concrete, the stressing elements of which comprise a plurality of rovings (6, 7), in particular carbon fiber rovings, extending through the concrete slab and running parallel to the slab plane, said method comprising the steps of: - producing formwork, which is delimited at the bottom by a production table (1) and through the side walls of which prestressed rovings (6, 7) extend, and - pouring concrete into the formwork and allowing the concrete to set, wherein the pouring of the concrete into the formwork comprises the dispensing of the concrete through one or a plurality of adjustable outlet openings (16) of a movable pouring container (10) while the pouring container (10) is moved over the length of the formwork, said one outlet opening extending over substantially the entire width of the formwork or said plurality of outlet openings being distributed over the width, wherein the fill level of the pouring container (10) is monitored during the dispensing and concrete is replenished from a reservoir (11), and wherein the amount of replenished concrete is controlled such that the fill level in the pouring container (10) is kept between a minimum value and a maximum value during the dispensing.

Description

[0001] Method and device for producing a concrete slab from prestressed concrete

[0002] 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 of:

[0003] Producing a formwork which is limited at the bottom by a production table and whose side walls are interspersed with pre-stressed rovings, and

[0004] Pouring concrete into the formwork and allowing the concrete to set.

[0005] Furthermore, the invention relates to a device for producing a concrete slab from prestressed concrete.

[0006] During the production of prestressed concrete, tendons such as prestressing wires or strands are force-fitted to the concrete so that relative displacement between the two materials practically does not occur. This allows a direct bond to be created between the tendons and the concrete, as is often the case during the production of precast concrete elements in precast plants, where tensioned prestressing wires or strands are embedded in the precast element. After the concrete has been poured and the concrete has hardened, the prestressing is released. The prestressing force in the precast element is applied through the bond between the concrete and the tendons and by wedging the relaxed tendons.

[0007] WO 2014 / 040653 A1 discloses a precast concrete component in which the reinforcement or tendons are formed from a large number of rovings, i.e. bundles, strands or multifilament yarns made of parallel arranged filaments or continuous fibers. The rovings can comprise or consist of carbon or glass fibers. To manufacture such fiber-reinforced concrete components, the rovings must be tensioned one on top of the other in several layers in the longitudinal and transverse directions. This process must be completed before the concrete components are manufactured, and the tensioned rovings must penetrate the formwork for the concrete component. Once the formwork has been manufactured, the area enclosed by the formwork is filled with concrete, ensuring that the height of the fresh concrete is as uniform as possible over the entire length and width of the concrete slab to be constructed.Precisely maintaining a predefined height across the entire extension of the concrete slab is particularly important in the case of concrete components reinforced with prestressed rovings, because it must be ensured that the rovings have a defined position within the concrete slab with respect to a zero stress line. Otherwise, warping of the slab would occur, particularly in the case of thin concrete slabs with high prestressing forces.

[0008] The invention therefore aims to improve the production of prestressed concrete slabs using rovings with regard to the introduction of fresh concrete into the formwork. In particular, an automated pouring process is to be implemented with which a specified fresh concrete thickness can be achieved within narrow tolerances. Furthermore, the fresh concrete is to be introduced in such a way that the fragile rovings are not damaged.To achieve this object, the invention, according to a first aspect, in a method of the type mentioned at the outset, essentially consists in that the pouring of the concrete into the formwork comprises the discharge of the concrete via an adjustable outlet opening (s) of a movable hopper extending over substantially the entire width of the formwork or via several adjustable outlet openings distributed over the width, while the hopper is moved over the length of the formwork, wherein the fill level of the hopper is monitored during discharge and concrete is topped up from a storage container and wherein the quantity of replenished concrete is regulated in such a way that the fill level in the hopper is kept between a minimum and a maximum value during discharge.

[0009] By using two containers arranged in a cascade, the filling container and the storage container, it is sufficient to keep just enough fresh concrete in the filling container for the pouring process, so that the weight load caused by the fresh concrete it contains, as well as any shock loads and the associated deformations and bending of the filling container are minimized. This makes it possible to position the outlet opening(s) of the filling container just above the tensioned rovings and thus to pour the fresh concrete onto the rovings from a low height, so that the shear force acting on the rovings and thus the risk of breakage is minimized. Preferably, the outlet opening(s) of the filling container is / are moved at a normal distance of 3-100mm, in particular 3-15mm, above the rovings.Optionally, the hopper or its outlet opening(s) can be continuously adjusted in height.

[0010] According to the invention, the concrete is refilled from the storage hopper into the hopper in such a way that the fill level in the hopper is constantly kept between a minimum and a maximum value while the concrete is being poured. This ensures, on the one hand, that only the required amount of fresh concrete is present in the hopper at any given time, and, on the other hand, limits the hydrostatic pressure exerted by the fresh concrete in the hopper on the fresh concrete already present in the formwork. In particular, this is intended to prevent the hydrostatic pressure from causing the concrete in the formwork to swell and thus to exceeding the desired concrete thickness.

[0011] To maintain the fill level between the minimum and a maximum value, a control loop is preferably provided in which the current fill level represents the controlled variable and the refilled volume flow represents the manipulated variable.

[0012] The minimum and maximum fill level values ​​are specified in such a way that control can be achieved within relatively narrow limits, thus minimizing fluctuations in hydrostatic pressure. According to a preferred embodiment of the invention, the minimum value can correspond to 60-80% of the maximum value.

[0013] The concrete is preferably refilled from the storage hopper into the hopper continuously. This facilitates maintaining a constant fill level in the hopper and avoids shock loads on the hopper that could be caused by intermittent refilling.

[0014] Because the concrete is discharged according to the invention via an adjustable outlet opening(s) of a movable hopper extending over substantially the entire width of the formwork or via a plurality of adjustable outlet openings distributed over the width, it is possible to achieve uniform filling across the entire width and length of the formwork. The hopper is preferably moved in the longitudinal direction in an automated manner, i.e. by means of an automatic drive. The drive can be designed, for example, as an electric motor or hydraulic drive. During the concrete discharge, the hopper is moved in the longitudinal direction in particular at a constant speed. The hopper is moved, for example, on wheels or in a sliding guide.

[0015] In the context of the present invention, the width and the length preferably refer to two mutually perpendicular directions of the formwork or the concrete slab to be produced, wherein the width preferably has a shorter extent than the length.

[0016] The bulk container preferably has a cross-section that narrows in a funnel shape towards the outlet opening(s) and is designed in particular as a bulk funnel.

[0017] The one or more outlet openings may have an adjustable outlet cross-section to regulate the volume flow through the outlet opening(s). This ensures that only as much concrete can flow from the outlet opening(s), in particular the funnel-shaped one, into the formwork as is required for the desired thickness of the concrete slab.

[0018] Furthermore, it has proven advantageous if the storage hopper is moved synchronously with the bulk hopper in the longitudinal direction of the formwork, while being decoupled from the bulk hopper in the vertical direction. The decoupling here means that the storage hopper has a support independent of the bulk hopper, so that no vertical forces are exerted by the storage hopper on the bulk hopper.

[0019] In order to ensure that the desired amount of concrete is available at any point along the width of the hopper at any time, the storage hopper preferably extends substantially over the entire width of the formwork, with the concrete being refilled into the hopper via a plurality of discharge openings distributed over the width of the storage hopper, with the refilling preferably taking place by means of at least one conveyor device, preferably a plurality of conveyor devices each assigned to a discharge opening. The conveyor device can, for example, be designed to achieve a uniform distribution of the fresh concrete along the entire width of the storage hopper, so that a correspondingly uniform filling of the hopper is achieved. The conveyor device can preferably comprise a spiked roller extending over the entire width of the storage hopper.Alternatively or additionally, several conveyors can be provided, distributed across the width of the storage container, which convey the fresh concrete through a respective discharge opening into the hopper located below. Such conveyors can be designed, for example, as slides or screw conveyors.

[0020] In the event that the storage container has a plurality of discharge openings through which the fresh concrete can be conveyed into the hopper by means of a respective conveying device, a preferred embodiment provides that the monitoring of the fill level in successive width sections of the hopper takes place separately from one another using a fill level sensor arranged in the respective width section, wherein the fill level measurements of each fill level sensor are used to control the refilling of the concrete via the discharge opening which is located in the same width section as the respective fill level sensor. In this way, the fill level in the hopper is controlled separately in each width section from other width sections, so that any level differences along the width of the hopper can be taken into account and compensated for.

[0021] In order to achieve a smooth surface of the fresh concrete mass at a defined height, it is preferably provided that a screeding device extending over the entire width of the concrete slab to be produced is pulled over the concrete poured into the formwork behind the hopper, wherein the screeding device is preferably designed as a rigid or flexible screeding support which rests on the surface of the concrete and is pulled behind the outlet opening of the hopper. The screeding device is preferably fastened to the hopper, in particular on the rear side in the direction of travel. The screeding device prevents the fresh concrete from being pushed up by the hydrostatic pressure coming from the hopper.

[0022] Preferably a liquid such as water is applied across the width of the screed pad and allowed to run onto the surface of the concrete over the rear edge of the screed pad in the direction of travel. This creates a layer of water on the fresh concrete surface, which ensures defined setting conditions for the concrete. Because the liquid is not applied directly to the concrete, but first to the screed pad, it is prevented that the applied liquid is applied unevenly and that the surface is not affected until it has finally hardened. A layer of liquid 1-2 cm thick is preferably applied.

[0023] According to a second aspect of the invention, a device for producing a concrete slab from prestressed concrete is provided, comprising a hopper for discharging concrete into a formwork, wherein the hopper has one or more adjustable outlet openings extending substantially over the entire width of the concrete slab to be produced, and is arranged to be movable in a longitudinal direction running transversely to the width, and further comprising a storage container for refilling concrete into the hopper with at least one conveying device, wherein the hopper has at least one fill level sensor for monitoring the fill level during the discharge of the concrete, the measured values ​​of which are fed to a control unit which cooperates with the at least one conveying device of the storage container in order to regulate the quantity of the refilled concrete in such a way thatthat the fill level in the hopper is kept between a minimum and a maximum value during application.

[0024] Preferably, the minimum value corresponds to 60-80% of the maximum value.

[0025] Preferably, the control unit is designed for the continuous, controlled refilling of concrete into the hopper.

[0026] Advantageously, the storage container extends substantially over the entire width of the formwork and has a plurality of discharge openings arranged distributed over the width of the storage container, wherein preferably at least one conveying device, preferably a plurality of conveying devices each assigned to a discharge opening, is or are arranged for discharging the concrete into the filling container.

[0027] To monitor the fill level in successive width sections of the hopper, a fill level sensor is preferably arranged in each width section, wherein the fill level measured values ​​of the fill level sensors are fed to the control unit, which is set up to use the fill level measured values ​​of each fill level sensor to control the refilling of the concrete via that of the discharge openings which is located in the same width section as the respective fill level sensor.

[0028] It is preferably provided that the outlet opening(s) of the bulk container is / are arranged at a normal distance of 3-100mm, in particular 3-15mm, above the rovings.

[0029] Preferably, a screeding device extending over the entire width of the concrete slab to be produced is arranged downstream of the filling container, wherein the screeding device is preferably designed as a rigid or flexible screeding support which can be pulled behind the outlet opening of the filling container while resting on the surface of the concrete.

[0030] Furthermore, fluid nozzles can be provided, directed at the screed pad, to apply the fluid across the width of the screed pad. The fluid can be used for concrete curing.

[0031] The invention is explained in more detail below with reference to exemplary embodiments shown schematically in the drawing, in which Fig. 1 shows a plan view of a production table including formwork for the production of concrete slabs and Fig. 2 shows a section through a device for introducing fresh concrete into the formwork.

[0032] Fig. 1 shows a production or formwork table 1, on the edges of which holding elements 2, 3, 4 and 5 are arranged, wherein a plurality of carbon rovings 6, 7 are stretched between opposite holding elements 2 and 4 or 3 and 5, respectively, wherein one group of carbon rovings 6 crosses another group of carbon rovings 7 and 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.

[0033] The formwork table 1 forms the base of a formwork into which fresh concrete is poured to produce a prestressed concrete slab. After the edge formwork 8 has been formed, liquid concrete is poured into the area 9 defined by the edge formwork and allowed to set. After the concrete has hardened, the edge formwork is removed, leaving a prestressed concrete slab.

[0034] Fig. 2 shows how the fresh concrete is introduced into the formwork. Immediately above the area 9, a hopper 10, here a hopper, extending across the entire width of the formwork is moved lengthwise over the formwork in the direction of arrow 12, while fresh concrete is poured from the hopper 10 onto the production table 1. Since the hopper 10 only holds a relatively small volume of concrete, a storage container 11 is moved synchronously with the hopper 10 above the hopper 10, and concrete is added to the hopper 10 from this storage container. The storage container 11 itself is in turn filled with concrete by pouring in fresh concrete as indicated by 13.

[0035] The storage container 11 has a plurality of discharge openings 15 distributed across its width, through which concrete is conveyed into the hopper 10 by means of a respective slide or screw conveyor 14. The hopper 10 in turn has a funnel-shaped outlet opening 16 which extends over the entire width of the hopper 10 and through which the concrete 17 runs onto the production table 1. On the side of the hopper 10 trailing in the direction of travel 12 there is attached a leveling pad 18 which is pulled over the fresh concrete and smooths the concrete surface to a defined height. Optionally a film 19 can be arranged on the leveling pad 18 which projects over the edge of the leveling pad 18 on the rear side and is also pulled over the concrete surface.A liquid is also applied to the screed pad 18 by means of the nozzles 20 , distributed over the width, which liquid is allowed to run onto the surface of the concrete via the rear edge of the screed pad 18 in the direction of travel 12 , or of the film 19 if present.

[0036] To control the fill level in the hopper 10, a fill level sensor 23 is provided, the measured values ​​of which are fed to a control unit 22, wherein the control unit generates control signals for the slide or screw conveyor 14 in order to keep the fill level in the hopper 10 within predetermined limits.

Claims

Patent claims:

1. A method for producing a concrete slab from prestressed concrete, the tendons of which comprise a plurality of rovings (6, 7) penetrating the concrete slab and running parallel to the plane of the slab, in particular carbon fibre rovings, comprising the steps: Producing a formwork which is limited at the bottom by a production table (1) and whose side walls are penetrated by pre-stressed rovings (6,7), and Pouring concrete into the formwork and allowing the concrete to set, characterized in that the pouring of the concrete into the formwork comprises the discharge of the concrete via an adjustable outlet opening (16) of a movable hopper (10) extending over substantially the entire width of the formwork or via a plurality of adjustable outlet openings (16) arranged distributed over the width, while the hopper (10) is moved over the length of the formwork, wherein the fill level of the hopper (10) is monitored during the discharge and concrete is refilled from a storage container (11) and wherein the quantity of the refilled concrete is regulated in such a way that the fill level in the hopper (10) is kept between a minimum and a maximum value during the discharge.

2. Method according to claim 1, characterized in that the minimum value corresponds to 60-80% of the maximum value.

3. Method according to claim 1 or 2, characterized in that the storage container (11) is synchronously with the filling container (10) in the longitudinal direction of the formwork is moved while it is decoupled from the hopper (10) in the vertical direction.

4. Method according to claim 1, 2 or 3, characterized in that the refilling of the concrete into the filling container (10) takes place continuously.

5. Method according to one of claims 1 to 4, characterized in that the storage container (11) extends substantially over the entire width of the formwork and the concrete is refilled into the filling container (10) via a plurality of discharge openings (15) distributed over the width of the storage container (11), wherein the refilling is preferably carried out by means of at least one conveyor device (14), preferably a plurality of conveyor devices (14) each assigned to a discharge opening (15).

6. Method according to claim 5, characterized in that the monitoring of the fill level in successive width sections of the bulk container (10) is carried out separately from one another using a fill level sensor (23) arranged in the respective width section, the fill level measurement values ​​of each fill level sensor (23) being used to control the refilling of the concrete via that of the discharge openings (15) which is located in the same width section as the respective fill level sensor (23).

7. Method according to one of claims 1 to 6, characterized in that the outlet opening(s) (16) of the bulk container (10) are arranged at a normal distance of 3-100mm, especially 3-15mm, above which the rovings are processed.

8. Method according to one of claims 1 to 7, characterized in that a screeding device (18) extending over the entire width of the concrete slab to be produced is pulled over the concrete poured into the formwork following the filling container (10), wherein the screeding device (18) is preferably designed as a rigid or flexible screeding support which is pulled behind the outlet opening (16) of the filling container (10) while resting on the surface of the concrete.

9. Method according to claim 8, characterized in that a liquid is applied to the screeding support (18) distributed over the width, which liquid is allowed to run over the rear edge of the screeding support (18) in the direction of travel onto the surface of the concrete.

10. Device for producing a concrete slab from prestressed concrete, in particular for carrying out the method according to one of claims 1 to 9, comprising a hopper (10) for discharging concrete into a formwork, wherein the hopper (10) has one or more adjustable outlet openings (16) extending substantially over the entire width of the concrete slab to be produced, and is arranged to be movable in a longitudinal direction running transversely to the width, and further comprising a storage container (11) for refilling concrete into the hopper (10) with at least one conveying device (14), wherein the hopper (10) has at least one fill level sensor (23) for monitoring the Fill level during the discharge of the concrete, the measured values ​​of which are fed to a control unit (22) which cooperates with the at least one conveying device (14) of the storage container (11) in order to regulate the quantity of refilled concrete in such a way that the fill level in the hopper (10) is kept between a minimum and a maximum value during the discharge.

11. Device according to claim 10, characterized in that the minimum value corresponds to 60-80% of the maximum value.

12. Device according to claim 10 or 11, characterized in that the storage container (11) is moved synchronously with the filling container (10) in the longitudinal direction of the formwork, while it is decoupled from the filling container (10) in the vertical direction.

13. Device according to claim 10, 11 or 12, characterized in that the control unit (22) is arranged for the continuous, controlled refilling of the concrete into the hopper (10).

14. Device according to one of claims 10 to 13, characterized in that the storage container (11) extends substantially over the entire width of the formwork and has a plurality of discharge openings (15) distributed over the width of the storage container (11), wherein preferably at least one conveying device (14), preferably a plurality of conveying devices (14) each assigned to a discharge opening (15), is or are arranged for discharging the concrete into the filling container (10).

15. Device according to claim 14, characterized in that for monitoring the fill level in successive width sections of the hopper (10) a fill level sensor (23) is arranged in each width section, wherein the fill level measured values ​​of the fill level sensors (23) are fed to the control unit (22) which is set up to use the fill level measured values ​​of each fill level sensor (23) to control the refilling of the concrete via that one of the discharge openings (15) which is located in the same width section as the respective fill level sensor (23).

16. Device according to one of claims 10 to 15, characterized in that the outlet opening(s) (16) of the bulk container (10) is / are arranged at a normal distance of 3-100mm, in particular 3-15mm, above the rovings.

17. Device according to one of claims 10 to 16, characterized in that a screeding device (18) extending over the entire width of the concrete slab to be produced is arranged downstream of the filling container (10), wherein the screeding device (18) is preferably designed as a rigid or flexible screeding support which can be pulled behind the outlet opening (16) of the filling container (10) while resting on the surface of the concrete.

18. Device according to claim 17, characterized in that liquid nozzles (20) are provided which are directed onto the peeling support (18) in order to apply the liquid to the peeling support (18) distributed over the width.

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