Concrete pump

Abstract

A concrete pump comprising a pre-filling container, a delivery pipe (17) and a pump device (29) for delivering liquid concrete from the pre-filling container through the delivery pipe (17). Unlike the pre-filling containers in conventional concrete pumps, the pre-filling container is in the form of a pre-filling shaft (16) and not a pre-filling funnel.

Description

[0001] concrete pump

[0002] The invention relates to a concrete pump.

[0003] Liquid concrete, which has a higher viscosity than previously known, is used in various applications. This includes, for example, 3D printing processes with which a concrete structure is created without the shape of the concrete structure being predetermined by formwork. In 3D printing, the liquid concrete is conveyed in such a way that it emerges from the outlet end of a delivery line in the form of a strand with a predetermined cross-section. When it emerges from the delivery line, the liquid concrete has a consistency such that the cross-section of the strand is retained when the strand is placed on a surface.

[0004] It has been shown that problems arise when liquid concrete with high viscosity is pumped with a conventional concrete pump.

[0005] The invention is based on the object of presenting a concrete pump that avoids these disadvantages. This object is achieved by the features of the independent claims. Advantageous embodiments are specified in the subclaims.

[0006] A concrete pump according to the invention comprises a pre-filling tank, a delivery line, and a pumping device for conveying liquid concrete from the pre-filling tank along the delivery line. The pre-filling tank is designed as a pre-filling shaft, which distinguishes the invention from conventional concrete pumps, in which the pre-filling tank is designed as a pre-filling hopper.

[0007] In conventional concrete pumps, which are used to pump liquid concrete with a lower viscosity, the prefill tank is designed as a prefill hopper. The funnel shape allows the prefill tank to have a large volume and a large filling opening, allowing for easy filling of the liquid concrete. The inclined hopper surfaces concentrate the liquid concrete in a narrower area at the lower end of the prefill tank, allowing it to be easily drawn in by the concrete pump's pumping mechanism.

[0008] In contrast, the invention proposes designing the pre-filling container as a pre-filling shaft so that the liquid concrete can move essentially vertically downwards between the filling opening and the area of ​​the pre-filling container into which it is sucked in by the pumping device. By avoiding a strong spatial constriction between the upper and lower ends of the pre-filling container, the liquid concrete moves essentially parallel to gravity, thereby reducing the risk of the liquid concrete adhering to the wall of the pre-filling container. It is undesirable for liquid concrete to adhere to the wall of the pre-filling container because it dries quickly and then no longer has the desired consistency. If such liquid concrete were to subsequently get into the conveying line, this could result in the conveying process being disrupted and being unable to continue.Through the pre-filling shaft according to the invention, the liquid concrete is first sucked in by the pumping device, which also first poured into the pre-filling shaft (first in, first out, FIFO). This prevents partial quantities of liquid concrete from remaining in the pre-filling shaft for an excessively long time.

[0009] In conventional priming tanks, the filling cross-section is considerably larger than the suction cross-section. The filling cross-section and suction cross-section refer to the horizontal cross-section of the priming tank at two different height positions, assuming that the concrete pump is on level ground. The lower height position, where the suction cross-section is located, corresponds to the uppermost area from which liquid concrete is sucked in, which is normally the upper end of an inlet opening of the pumping device. The upper height position, where the filling cross-section is located, corresponds to the height to which the priming tank can be filled before it overflows.

[0010] The pre-filling shaft according to the invention is preferably designed such that the filling cross-section is no more than 50%, preferably no more than 30%, more preferably no more than 10% larger than the suction cross-section. This information relates to the surface area covered by the filling cross-section or the suction cross-section. Embodiments are possible in which the filling cross-section is no larger than the suction cross-section or in which the filling cross-section is smaller than the suction cross-section. Such a ratio between the filling cross-section and the suction cross-section ensures that the liquid concrete moves essentially downwards in the pre-filling shaft and that no major constriction in the horizontal direction is necessary.

[0011] A conventional pre-filling hopper is essentially delimited by inclined wall surfaces through which the liquid concrete is horizontally collected on its way downwards from the large filling cross-section to the small suction cross-section. The pre-filling shaft according to the invention offers the advantage that such inclined wall surfaces can be dispensed with completely or at least largely. The pre-filling shaft according to the invention is also preferably free of horizontal surfaces and other angled portions on which the liquid concrete can deposit. The wall surfaces of the pre-filling shaft according to the invention arranged between the filling cross-section and the suction cross-section can be aligned such that the angle included with the vertical is less than 16°, preferably less than 8°, more preferably less than 4°.This can apply to at least 80%, preferably at least 90%, more preferably at least 95% of the wall surfaces between the filling cross-section and the intake cross-section. In one embodiment, this applies to the entire wall surface. It is possible for the entire wall surface of the pre-filling shaft to be oriented vertically.

[0012] In one embodiment, the concrete pump is a concrete pump suitable for 3D printing. To produce a concrete structure using 3D printing, the liquid concrete is pumped in such a way that it emerges from the outlet end of a delivery line in the form of a strand with a predetermined cross-section. Upon exiting the delivery line, the liquid concrete has a consistency such that the cross-section of the strand is maintained when the strand is placed on a surface.

[0013] A metering pump can be installed in the delivery line. The metering pump can be configured so that a steady flow of liquid concrete exits the distal end of the delivery line. Conventional concrete pumps, on the other hand, often deliver the liquid concrete intermittently along the delivery line.

[0014] An outlet end of the delivery line can be designed as a pressure head. The pressure head can be configured so that the liquid concrete emerges from the pressure head as a strand with a predetermined cross-section. The concrete pump can comprise a positioning system with which the pressure head can be moved along predetermined paths. Dosing pumps are often designed so that they cannot pump components with a large grain size. The liquid concrete fed from a liquid concrete supply can be sieved in order to filter out unacceptably large grains and foreign bodies from the liquid concrete. In one embodiment, the liquid concrete is sieved before entering the pre-filling shaft. The pre-filling shaft can have an upper edge designed so that a sieve can be placed on the edge.

[0015] The upper end edge can be designed such that the sieve placed on the end edge has an inclination of less than 16°, preferably less than 8°, more preferably less than 4° relative to the horizontal. In particular, the upper end edge can be designed so that the sieve is aligned horizontally. The upper end edge can extend uninterruptedly over the circumference of the pre-filling shaft. The upper end edge can coincide with the filling cross-section. Also included are embodiments in which the upper end edge is arranged higher than the filling cross-section.

[0016] The screen can be sized to cover the entire filling cross-section. For better screening results, the screen can be vibrated while the liquid concrete passes through the screen. The concrete pump can include a vibrating drive to drive the screen.

[0017] The pre-filling shaft can be defined by a wall made of a rigid material, meaning it does not deform when the liquid concrete is poured in. In one embodiment, the wall of the pre-filling shaft comprises a first section made of a rigid material and a second section made of an elastic material. The elastic material can be set into elastic movement under the influence of the inflowing liquid concrete, thereby reducing the likelihood of the liquid concrete sticking or of already sticky and / or hard concrete being shaken off prematurely (permissible grain size).

[0018] In one embodiment, the wall in a lower section of the pre-filling shaft consists of a rigid material and in an adjacent upper section of the pre-filling shaft of an elastic material. The elastic material can extend up to the upper end edge. The elastic material in the upper section of the pre-filling shaft can, in particular, prevent the adhesion of splashes that break away from the poured liquid concrete and hit the wall of the pre-filling shaft. Furthermore, the risk of already adhering and / or already hard concrete being shaken off prematurely can be reduced.

[0019] The risk of liquid concrete adhering to the concrete pump's structures can be further reduced by coating the wall of the pre-filling shaft and / or a switchable valve element located in the pre-filling shaft with a non-stick coating. The coating can be formed, for example, from a polyurethane-based elastomer.

[0020] For 3D printing, liquid concrete is usually used, the flowability of which improves when the liquid concrete is circulated. The concrete pump can comprise a switchable valve member which establishes a connection between the pumping device and the delivery line. The pumping device can be designed as a double-piston pump which comprises a first delivery cylinder and a second delivery cylinder which, in an alternating cycle, suck in liquid concrete from the pre-filling shaft and pump it towards the delivery line. In a first switching state, the switchable valve member can establish a connection between the first delivery cylinder and the delivery line, while the second delivery cylinder can suck in liquid concrete from the pre-filling shaft.In a second switching state, the switchable valve element can establish a connection between the second delivery cylinder and the delivery line, while the first delivery cylinder can draw liquid concrete from the pre-filling shaft. The switchable valve element can be designed as an S-pipe.

[0021] The concrete pump can be designed so that the movement of the switchable valve element displaces liquid concrete at the lower end of the pre-filling shaft. The liquid concrete can thus be kept moving in precisely the area of ​​the pre-filling shaft from which it is drawn by the delivery cylinders. The improved flowability facilitates the transfer of the liquid concrete from the pre-filling shaft into the delivery cylinders.

[0022] Conversely, there is a risk that the liquid concrete, whose flowability has been improved by the action of the switchable valve element, will repeatedly overflow into the conveying cylinders, while the liquid concrete from other areas of the pre-filling shaft moves only slowly.

[0023] The pre-filling shaft can be provided with an agitator to set liquid concrete contained in the pre-filling shaft in motion. The agitator can be arranged in a region of the pre-filling shaft where the liquid concrete is otherwise subject to less movement. In the case of a pre-filling shaft that extends between the conveyor cylinders and the conveyor line, the end of the pre-filling shaft closest to the conveyor cylinders is referred to as the proximal end and the end closest to the conveyor line is referred to as the distal end. The agitator can be arranged in the pre-filling shaft such that it is a shorter distance from the distal end than from the proximal end. The distance is measured from the shaft of the agitator and from there from the section of the shaft to which the stirring blades are connected.At the proximal end, the liquid concrete is already kept in motion by the switchable valve element, which is why additional stirring near the distal end is useful. The agitator can also help to promote the suction of the liquid concrete into the intake opening, thus avoiding air bridges, where air is sucked in instead of liquid concrete. Air can be sucked through the concrete along the hopper plates or through the formation of air bridges into the inlet opening of the pumping device.

[0024] Since the switchable valve element requires more lateral space on the proximal side than on the distal side, the pre-filling shaft can have a smaller width at the distal end than at the proximal end. The width is the dimension that is aligned perpendicular to a longitudinal center plane of the pre-filling shaft. By tapering the pre-filling shaft at the distal end, less space is made available within the pre-filling shaft within which the liquid concrete can come to a standstill.

[0025] The agitator can comprise a shaft that extends through the wall of the pre-filling shaft. A drive for the agitator can be arranged outside the pre-filling shaft. The agitator can comprise one or more agitator blades that are arranged inside the pre-filling shaft. In one embodiment, the agitator comprises two agitator blades that extend in opposite directions from the shaft. Each agitator blade can have one or more openings through which the liquid concrete can pass when the agitator is in operation. In particular, a agitator blade can be provided with a strut so that one opening is divided into two major openings. The agitator blades can be arranged close to a wall of the pre-filling shaft.

[0026] The axis of the agitator can be aligned horizontally. Within the horizontal plane, the axis of the agitator can enclose an angle of between 10° and 80°, preferably between 20° and 70°, with a vertical longitudinal center plane that coincides with the axis of rotation of the switchable valve element. The angle can be included between the distal end of the longitudinal center plane and the axis. If the axis of the agitator is not in a horizontal plane, the information refers to the projection of the axis into the horizontal plane.

[0027] The agitator can be operated in such a way that the liquid concrete is moved away from the wall of the pre-filling shaft by the agitator blades. For this purpose, the agitator blades can extend outwards away from the axis of the agitator. The blades can form an angle of between 40° and 50°, for example, with the axis of the agitator. In relation to the axis of the agitator, the agitator blades can span a distance in the radial direction which corresponds to at least 20%, preferably at least 30%, more preferably at least 50% of the distance between the proximal end and the distal end of the pre-filling shaft. The main conveying direction can coincide with the axis of the agitator. The liquid concrete can be conveyed in such a way that it moves in the direction of the longitudinal center plane.

[0028] The pre-filling shaft can be equipped with a first agitator and a second agitator. The second agitator can have the same features that are described in connection with the first agitator. The two agitators can be arranged on two different sides of the longitudinal center plane. The agitators can be arranged such that the longitudinal center plane is not intersected. The two agitators can have a symmetrical position within the pre-filling shaft with respect to the longitudinal center plane. The distance between the agitator blades of the first agitator and the agitator blades of the second agitator can be smaller, preferably at least 20% smaller, more preferably at least 40% smaller than the radial span spanned by the agitator blades of one agitator. This information relates to the smallest distance that the agitator blades have from one another when the agitators are in operation.

[0029] A concrete pump with an agitator, in which the agitator has one or more of the features mentioned, has independent inventive content even without the pre-filling container being designed as a pre-filling shaft.

[0030] To avoid areas within the pre-filling shaft where the liquid concrete comes to a standstill, it is advantageous if the volume of the pre-filling shaft is not too large. The pre-filling shaft can have a volume between 200 l and 700 l, preferably a volume between 300 l and 600 l. This is significantly smaller than the volume of conventional pre-filling hoppers, whose volume is often larger than 700 l.

[0031] Particularly when the pre-filling shaft has a smaller volume than a conventional pre-filling hopper, it is possible to design the pre-filling shaft as an insert that is inserted into a pre-filling hopper. This makes it possible to convert conventional concrete pumps so that they are suitable for 3D printing. The insert can be designed so that it can be detachably connected to the pre-filling hopper, so that the concrete pump can be operated either with the pre-filling shaft according to the invention or with the conventional pre-filling hopper. The invention also relates to an insert for a pre-filling hopper or a concrete pump, wherein the insert forms a pre-filling shaft with which the concrete pump can be operated instead of the pre-filling hopper. The disclosure includes developments of the insert with features that are described in connection with the concrete pump according to the invention.

[0032] The invention is described below by way of example with reference to the accompanying drawings using advantageous embodiments. They show:

[0033] Fig. 1: a concrete pump vehicle with a boom arm in the folded state;

[0034] Fig. 2: the concrete pump vehicle from Fig. 1 with the boom arm unfolded;

[0035] Fig. 3: a schematic representation of components of a concrete pump according to the invention;

[0036] Fig. 4: Elements from Fig. 3 in greater detail;

[0037] Fig. 5: a schematic longitudinal section through a pre-filling shaft of a concrete pump according to the invention;

[0038] Fig. 6, 7: horizontal sections through the pre-filling shaft from

[0039] Fig. 5;

[0040] Fig. 8-10: the view according to Figures 5-7 in an alternative embodiment of the invention;

[0041] Fig. 11: the view according to Fig. 5 in an alternative

[0042] Embodiment of the invention;

[0043] Fig. 12: a view from above into the pre-filling shaft according to

[0044] Fig. 11; Fig. 13: the view according to Fig. 7 in the embodiment according to Fig. 11;

[0045] Fig. 14, 15: Embodiments of stirring blades of concrete pumps according to the invention;

[0046] Fig. 16: a schematic representation of an alternative

[0047] Embodiment of the invention.

[0048] A truck 14 shown in Fig. 1 is equipped with a concrete pump

[0049] 15, which pumps liquid concrete from a pre-filling shaft

[0050] 16 through a delivery line 17. The delivery line 17 extends along a boom arm 18, which is rotatably mounted on a slewing ring 19. The boom arm 18 comprises three boom arm segments 20, 21, 22, which are connected to one another in an articulated manner. By pivoting the boom arm segments 20, 21, 22 relative to one another via the joints, the boom arm 18 can be moved between a folded state (Fig. 1) and an unfolded state (Fig. 2). The delivery line 17 extends beyond the distal end of the third boom arm segment 22, so that the liquid concrete can be applied in an area remote from the concrete pump 15.

[0051] The concrete pump 15 is designed for 3D printing so that a mold can be built directly using the concrete emerging from the delivery line 17, without the need for formwork. For this purpose, the concrete pump 15 comprises, as shown in Fig. 3, a metering pump 36 with which the liquid concrete is conveyed so that it emerges from the delivery line 17 as a continuous strand. The distal end of the delivery line 17 is formed by a pressure head 37 from which the strand emerges with a predetermined cross-sectional profile. Using a positioning system (not shown), the pressure head 37 can be moved along predetermined paths. The concrete pump 15 comprises a pumping device 29 which is designed as a double-piston pump. The pumping device 29 comprises a first delivery cylinder and a second delivery cylinder which suck in liquid concrete from the pre-filling shaft 16 in an alternating cycle and convey it along the delivery line 17.The pumping device 29 is equipped with an S-pipe 30 which, in a first switching state, establishes a connection between the first delivery cylinder and an inlet of the delivery line 17, and which, in a second switching state, establishes a connection between the second delivery cylinder and the inlet of the delivery line 17. Liquid concrete delivered by the pumping device 29 through the S-pipe enters the delivery line 17 and is moved from the proximal to the distal end of the delivery line 17.

[0052] The pumping device 29 is operated in a closed control loop with the aim of maintaining the pressure of the liquid concrete at the inlet of the metering pump 36 at a constant value. A control unit (not shown) of the pumping device 29 is supplied with a measured value of the pressure of the liquid concrete at the inlet of the metering pump 36, and the pumping device 29 is controlled such that the power of the pumping device 29 is increased in order to counteract a reduction in the pressure at the metering pump 36, and vice versa.

[0053] A working cycle of the pumping device 29 comprises the steps that, in a state in which the S-pipe 30 forms a connection between the first delivery cylinder and the delivery line 17, the first delivery cylinder delivers liquid concrete from the interior of the first delivery cylinder into the S-pipe 30 with a forward movement. In parallel, the second delivery cylinder sucks liquid concrete from the pre-filling shaft 16 with a backward movement. With a drive unit 31 (Fig. 4), the S-pipe 30 is switched via a shaft 39 into a second switching state in which the S-pipe 30 forms a connection between the second delivery cylinder and the delivery line 17. After switching, the second delivery cylinder delivers liquid concrete into the S-pipe 30 with a forward movement, while the first delivery cylinder sucks liquid concrete from the pre-filling shaft 16.

[0054] The pre-filling shaft 16 has an upper end edge 34 which extends in a horizontal plane. A sieve 35 rests on the end edge 34 and can be vibrated by a drive motor 38. The liquid concrete is fed to the pre-filling shaft 16 from a supply (not shown) via a chute 33. The liquid concrete falling from the chute 33 strikes the sieve 35 and passes through the sieve 35, while larger chunks of rock are sieved out. The sieve 35 is adapted to the design of the concrete pump and is designed, for example, so that grains up to a size of 8 can pass through. The liquid concrete in the pre-filling shaft 16 is therefore less coarse-grained than conventional liquid concrete, which can, for example, contain grains up to a size of 32.

[0055] The wall of the pre-filling shaft 16 and the outer surface of the S-pipe 30 are provided with a coating formed by a polyurethane-like elastomer. The coating forms a non-stick coating, thus reducing the risk of liquid concrete adhering to the surfaces inside the pre-filling shaft 16.

[0056] The pre-filling shaft 16 extends vertically between a filling opening 40 at the upper end and a base 41. A section of the S-pipe 30 adjoining the pumping device 29 is arranged just above the base 41 of the pre-filling shaft 40. The section of the S-pipe 30 adjacent to the delivery line 17 is somewhat higher, with the base 41 rising slightly in this direction. The level of the pre-filling shaft 16 up to which the liquid concrete can flow into the pumping device 29 is referred to as the suction level 43. The suction level 43 coincides with the upper end of the inlet opening through which the liquid concrete flows into one of the delivery cylinders of the pumping device 29. The uppermost level up to which the pre-filling shaft 16 can be filled without overflowing is referred to as the filling level 42.

[0057] The horizontal cross-section of the pre-filling shaft 16 at the level of the filling level 42, referred to as the filling cross-section 44, is circular, see Fig. 6. The horizontal cross-section of the pre-filling shaft 16 at the level of the suction level 43, referred to as the suction cross-section 45, is also circular and has the same diameter as the filling cross-section 44, see Fig. 7. The wall 46 of the pre-filling shaft 16 has a cylindrical shape between the filling level 42 and the suction level 43. Due to the continuously vertical wall without any bends, the risk of the liquid concrete adhering to the wall 46 of the pre-filling shaft 16 is reduced. The liquid concrete introduced into the pre-filling shaft 16 moves continuously downwards, so that the liquid concrete fed in first is the first to leave the pre-filling shaft 16 (first in first out, FI FO).

[0058] Fig. 8 shows an embodiment in which the pre-filling shaft 16 has a rectangular cross-section and in which the end edge 34 is inclined. The filling plane 42 is defined by the lower end 34 of the end edge 34. The filling cross-section 44 and the suction cross-section 45 are identical, see Figs. 9, 10. Between the filling cross-section 44 and the suction cross-section 45, the cross-sectional shape of the pre-filling shaft 16 also remains constant. Fig. 10 shows the working area 47 within which the S-pipe 30 moves while it is in one of the two switching states and is switched between the switching states. The movement of the S-pipe 30 leads to a mixing of the liquid concrete in the area adjacent to the proximal end 48, while the liquid concrete at the distal end 49 of the pre-filling shaft 16 is only slightly circulated by the S-pipe 30.

[0059] In order to prevent the liquid concrete from remaining in the distal region for too long before it is sucked in by the pumping device 29, the pre-filling shaft 16 is provided with an agitator 50. The agitator comprises a motor 51 which, via a shaft 52, drives agitator blades 53 which extend outwards from the shaft 52. The shaft 52 extends at the distal end 49 through the wall 46 of the pre-filling shaft 16, so that the agitator blades 43 are arranged in the interior of the pre-filling shaft 16 and the motor 51 is arranged outside the pre-filling shaft 16. The agitator blades 53 are aligned such that the liquid concrete is forced by the agitator 50 towards the proximal end 48 of the pre-filling shaft 16. From there, the liquid concrete can quickly flow into the pumping device 29 .

[0060] In the embodiment according to Figs. 11-13, the wall 46 in the lower region of the pre-filling shaft 16 is made of a rigid material, such as steel. An upper section of the pre-filling shaft 16 is made of an elastic material 57, such as rubber sheets. The elastic material 57 can be set in motion by impacting liquid concrete. The probability of liquid concrete adhering to the elastic material 57 is lower than with conventional rigid material. Splashes thrown from the introduced liquid concrete against the elastic material 57 fall back into the pre-filling shaft 16 due to the movement of the elastic material 57.

[0061] The pre-filling shaft 16 has a cross-section which tapers towards the distal end 49 compared to the rectangular cross-section of Figs. 9 and 10. As a result, there is less space available at the distal end 49 within which the liquid concrete can settle.

[0062] The pre-filling shaft 16 comprises a first agitator 55 and a second agitator 56, which are arranged on two sides of a vertical longitudinal center plane 54 of the pre-filling shaft 16. The shafts 52 of the agitators 55, 56 extend through the wall 46 of the pre-filling shaft 16. The two shafts 52 are arranged in the same horizontal plane, which, similar to Fig. 8, lies slightly above the S-pipe 30. Within the horizontal plane, the shafts 52 each enclose an angle of significantly less than 90° with the distal end of the longitudinal center plane 54. When the two agitators 55, 56 are in operation, the liquid concrete is forced in the direction of the longitudinal center plane 54 and in the direction of the proximal end 48 of the pre-filling shaft 16.

[0063] Fig. 14 shows an exemplary embodiment of stirring blades 53 of the agitators 50, 55, 56. Starting from the shaft 52, two stirring blades 53 extend radially outward in opposite directions. With respect to a plane defined by the shaft 52 and the radial direction, the stirring blades 53 are rotated by approximately 45°. Each of the stirring blades 53 is provided with an opening 61 through which the liquid concrete can pass when the respective agitator 50, 55, 56 is in operation. In order to prevent a dead space from forming in the extension of the shaft 52, within which the liquid concrete does not move, the stirring blades have a projection 58 at the distal end, which approaches a plane that extends along the shaft 52 and is arranged centrally between the two stirring blades 53. In the alternative embodiment according to Fig.15, each stirring blade 53 has a strut 62 which reinforces the stirring blade 53 and by which the opening 61 is divided into two partial openings.

[0064] In the embodiment according to Fig. 16, the concrete pump has a pre-filling container which is designed as a conventional pre-filling hopper 59. The pre-filling hopper 59 has a volume of, for example, 900 l, which is larger than is required for 3D printing applications in most cases. The pre-filling shaft 16 according to the invention is designed as an insert 60 which can be inserted into the pre-filling hopper 59 if the concrete pump is to be used for 3D printing. The pre-filling shaft 16 of the insert 16 has a volume of 450 l. If the concrete pump is to be used conventionally again after 3D printing has been completed, the insert 60 can be removed from the pre-filling hopper 59.

Claims

Patent claims 1. Concrete pump, comprising a pre-filling container, a delivery line (17) and a pumping device (29) for conveying liquid concrete from the pre-filling container along the delivery line (17), wherein the pre-filling container is designed as a pre-filling shaft (16).

2. Concrete pump according to claim 1, wherein the concrete pump is designed to produce concrete structures by 3D printing, wherein a metering pump is arranged in the delivery line, and wherein an outlet end of the delivery line (17) is designed as a print head (37).

3. Concrete pump according to claim 1 or 2, wherein a filling cross-section (44) of the pre-filling shaft (16) is not more than 50%, preferably not more than 30%, more preferably not more than 10% larger than a suction cross-section (45) of the pre-filling shaft (16).

4. Concrete pump according to one of claims 1 to 3, wherein a wall (46) of the pre-filling shaft (16) arranged between the filling cross-section (44) and the suction cross-section (45) is aligned such that the angle included with the vertical is less than 16°, preferably less than 8°, more preferably less than 4°.

5. Concrete pump according to one of claims 1 to 4, comprising a sieve (35) with which the liquid concrete is sieved before entering the pre-filling shaft (16).

6. Concrete pump according to claim 5, wherein the pre-filling shaft (16) has an upper end edge (34) on which the sieve (35) rests.

7. Concrete pump according to one of claims 1 to 6, wherein the wall (46) of the pre-filling shaft (16) consists of a rigid material in a lower section of the pre-filling shaft (16) and of an elastic material (57) in an upper section of the pre-filling shaft (16).

8. Concrete pump according to one of claims 1 to 7, comprising an agitator (50, 55, 56) for setting liquid concrete contained in the pre-filling shaft (16) in motion.

9. Concrete pump according to claim 8, wherein the agitator (50, 55, 56) has a smaller distance to a distal end (49) of the pre-filling shaft (16) than to a proximal end (48) of the pre-filling shaft.

10. Concrete pump according to claim 8 or 9, wherein the agitator (50, 55, 56) has a stirring blade (53) and wherein the stirring blade (53) is provided with an opening (61).

11. Concrete pump according to one of claims 78 to 10, comprising a first agitator (55) and a second agitator (56), wherein the agitators (55, 56) are arranged on two sides of a longitudinal center plane (54) of the pre-filling shaft (16).

12. Concrete pump according to one of claims 8 to 11, wherein the distance between the stirring blades (53) of the first agitator (55) and the stirring blades (56) of the second agitator (56) is smaller, preferably at least 20% smaller, more preferably at least 40% smaller than the radial span spanned by the stirring blades (53) of an agitator (55, 56).

13. Concrete pump according to one of claims 1 to 12, wherein the pre-filling shaft (16) has a smaller width at the distal end (49) of the pre-filling shaft (16) than at the proximal end (48) of the pre-filling shaft (16).

14. Concrete pump according to one of claims 1 to 13, wherein the pre-filling shaft (16) has a volume between 200 l and 700 l, preferably a volume between 300 l and 600 l.

15. Concrete pump according to one of claims 1 to 14, wherein the pre-filling shaft (16) is designed as an insert (60) which is designed to be inserted into a pre-filling hopper (59) of a concrete pump.

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