Patent Application
20110180966
The present invention relates to concrete elements and, in particular, to methods and devices for making hollow concrete elements.
Hollow concrete elements are used in various constructions, often as buried pipes, but also as constructional elements in buildings, bridges, towers, etc.
Elongated reinforced concrete structures are used in a variety of fields. Examples of elongated reinforced concrete structures include masts and towers, pylons, chimneys, architectural structures, straight and curved beams, etc.
Traditionally, such elongated structures are cast in moulds onsite, either in one single moulding or in a sequence of moulding steps wherein reinforcement elements moulded in a preceding moulding are integrated in the subsequent moulding to achieve a continuous or overlapping longitudinal reinforcement structure throughout the structure. However, onsite moulding is time- and labour-consuming, as well as requiring the transportation of moulding equipment to the site. Moreover it is difficult onsite to completely control all the parameters of the moulding process which means that the material properties of the finished structure are likely to be suboptimal. As a direct consequence of high risk that the final structure will suffer from suboptimal material properties, to ensure an adequate safety margin, the structures must be overdimensioned.
An alternative to onsite moulding is the prefabrication of elongated concrete segments that can be assembled onsite. As the prefabrication of segments can be performed under well-controlled conditions and the whole segment can be moulded in one integral moulding, many of the above disadvantages are avoided.
One method for making elongated concrete structures, such as pipes, known as the “Hume” method and described, for example, in U.S. Pat. No. 3,577,505 involves rotating a drum mould which has end flanges which extend towards the longitudinal axis of the mould by a placing it on a drive roller and a driven roller. In modern devices the driving force of a motor is transmitted to the drive roller to rotate said drum mould such that an acceleration of centrifugal force of normally 3 to 5 g or even up to 15 g is obtained at an inner periphery of the mould.
In this condition, concrete is cast or poured into the drum mould by means of a movable conveyor as the conveyor is inserted longitudinally into the mould through an opening formed in one of the edge flanges. The deposited concrete is intended to form a concrete layer of uniform thickness in the inner surface of the drum mould and is prevented from leaving the drum mould by the edge flanges. The motor output is raised to increase the rotation of the drum mould to such an extent that acceleration of the centrifugal force in the proximity of the inner surface of the drum mould is raised to a range of 20 to 50 g. As a result, water is squeezed out of the concrete layer to tighten or physically harden said concrete layer. The time required for this step depends on the thickness of the finished pipe, the consistency of concrete and the magnitude of the centrifugal force. In general, however, about 15 minutes are needed for the pipe of 500 m/m in diameter while 40 to 60 minutes are needed for that of 3 meters in diameter. These devices rely on centrifugal force to distribute the concrete, remove excess water from it and compact it. This leads to long process times. This is a wet casting system and the concrete, even if some water is lost during the process, is still very wet when it is being cured. This means that the concrete is liable to suffer from shrinkage cracks during curing and due to the high centrifugal force applied during the curing the concrete also will become heterogeneous. Hence, this method is only really suitable for underground pipes which are subjected to low stress.
Another relatively successful method of manufacturing open-ended hollow concrete elements in the form of concrete pipe sections is the roller suspension method—known as the “Rocla” method. This method involves suspending a pipe mould which has end flanges which extend towards the central longitudinal axis of the mould, on a rotatable compaction roller which is aligned parallel to the pipe axis. As the compaction roller rotates, the mould, which is arranged about and suspended by its end flanges on the compaction roller, rotates about the compaction roller. Earth dry concrete is fed into the interior of the mould as the mould rotates and, since the mould is suspended on the compaction roller, the concrete is compacted in the nip between the inner surface of the mould and the outer surface of the compaction roller resulting in a well-compacted concrete and a relatively smooth pipe of uniform thickness. This roller suspension method of pipe formation is well-known and therefore is not described herein in any greater detail. See for example publication WO9836886 A1 and GB1391763. However this method suffers from the disadvantage that compaction of the concrete by compression in the nip between the compaction roller and the interior of the mould only takes place once the thickness of the concrete in the mould is sufficiently deep such that it comes into contact with the compaction roller. This leads to long process and compaction times. Additionally the contact pressure between the compaction roller and the concrete can never be higher than the weight of the mould plus concrete distributed on the contact area. The contact pressure depends on the geometry of the pipe and the amount of concrete actually present in the pipe, and producing consistent products is dependent on the skill of the operator of the machine.
Patent documents FR2872843, EP1645701 and DE2939472 describe segmented elongated concrete structures in the form of towers for wind turbines, but they fail to describe efficient ways of producing such elements. PCTSE2007/050306 discloses a segmented tower structure and a method for producing such elements and a method for producing such towers.
Some of the problems with existing solutions and methods are that they are inefficient and require high cement and chemical content ratios or produce a lot of waste during casting or have long curing times and/or suffer from shrinkage and the subsequent formation of cracks.
The object of the invention is to provide new methods and devices for making hollow concrete elements which overcome at least some of the drawbacks of the prior art. This is achieved by the method and device as defined in the independent claims. Further improvements are achieved by methods and devices having the features of the dependent claims.
The disclosed method of making an open-ended hollow concrete element comprising the steps of:
There is further provided a new device for making such open-ended hollow concrete elements, said device comprising a tubular mould wall defining the outer peripheral shape of the concrete element, said mould wall having a first and a second end flange each with an inner periphery smaller than the inner periphery of the mould wall at each respective end, said end flanges being provided for defining the end surfaces of the concrete element. The device further comprises a compaction roller positionable inside said mould wall, the roller having a profile which defines the interior shape of the concrete element and being supported by height adjusting means so that the distance of the compaction roller from the interior surface of the mould wall can be adjusted so that the compressive contact force between the concrete being fed into the mould and the surface of the compaction roller can be maintained at a desired level or levels of compressive force.
None of the mentioned prior art documents describe such a method or device.
The method and device for making open-ended hollow concrete elements has the following advantages over the prior art:
Other embodiments of the invention are defined in the dependent claims.
First and second narrow end portions 21, 23 of compaction roller 19 are each rotatably supported in height adjustable supporting means. As an example these can be arranged as follows. Each narrow end portion is supported in a respective bearing block 27, 29. Each bearing block is supported on a respective spring 31, 33 which is mounted on a respective hydraulic ram 35, 37. The hydraulic rams are each connected to a control system (not shown) which length of each ram to be independently adjusted. Adjustment of the length of each ram 35, 37 enables the end portions the compaction roller to be raised and lowered, thereby varying the distance between the surface of the central portion of compaction roller and the interior surface of the drum mould. This enables the force exerted by the compaction roller on concrete present in the mould to be varied. Moving the compaction roller closer to the interior surface of the drum mould, as shown schematically in
It conceivable that the inner diameter of the mould wall, that is its profile, varies along its length. The inner diameter of the mould wall defines the exterior shape, this is its profile, of the concrete element formed within it and thus said exterior shape that is its profile varies correspondingly along the direction of the rotational axis of the mould e.g. is curved, tapered or locally projects inwardly or outwardly. In this case the compaction roller can also have an exterior shape, i.e. its profile, which varies along its rotational axis, thus making the interior surface of the concrete element vary correspondingly. It is not necessary that the exterior shape of the compaction roller and the interior shape of the drum mould are complementary—non-complementary shapes allow for local thickening or thinning of the concrete element and the formation of grooves or steps in its wall thickness.
In each embodiment of the present invention it is preferable that the ends of the compaction roller can be moved independently. This allows the distance of each end of the compaction roller from the inner surface of the drum mould to be independently adjusted which means that if one end of the compaction roller is at a different distance from the inner surface than the other it is possible to vary the thickness of the walls of the concrete element along its length.
While the invention has been described with reference to specific exemplary embodiments, the description is in general only intended to illustrate the inventive concept and should not be taken as limiting the scope of the invention.
It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departure from the scope thereof, which is defined by the appended claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2008/051153 | 10/8/2008 | WO | 00 | 4/5/2011 |
