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Patent Searching and Data


Title:
METHOD AND APPARATUS FOR COMPACTING CONCRETE
Document Type and Number:
WIPO Patent Application WO/1993/004832
Kind Code:
A1
Abstract:
The invention relates to a method of compacting concrete. Concrete mass is fed gradually into a pipe under vacuum so that air is discharged from the concrete mass in a bursting manner when the mass is subjected to vacuum.

Inventors:
PALM CARL-OLOF (FI)
Application Number:
PCT/FI1991/000272
Publication Date:
March 18, 1993
Filing Date:
September 04, 1991
Export Citation:
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Assignee:
PARTEK CONCRETE LTD (FI)
International Classes:
B28B13/02; B28B17/02; (IPC1-7): B28B13/02; B28B17/02; B28C5/46
Foreign References:
CH125657A1928-05-01
US1931956A1933-10-24
US3477380A1969-11-11
US3485481A1969-12-23
FI901114A1991-09-06
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Claims:
Claims :
1. A method for compacting concrete by utilizing vacuum, c h a r a c t e r i z e d in that concrete mass, before casting, is fed gradually into a space under vacuum so that air is discharged in a bursting manner from a small amount of the concrete mass at a time when the concrete mass is subjected to vacuum and the volume of air bubbles contained in the concrete mass is increased, that the concrete mass under vacuum is compressed by means of a transfer plunger (6) or screw and the compressed concrete mass is pressed out by means of the same plunger or screw into a flexible transfer pipe ( ), that a straight cylindrical pipe (3) with required feed and discharge openings is provided as the path of the transfer plunger, and that the flexible transfer pipe (4) after the plunger or screw of the pipe (3) is moved to create shearing compaction within the concrete.
2. A method according to claim 1, c h a r a c ¬ t e r i z e d in that a revolving plunger with an oblique end surface is used in compressing and press¬ ing out the concrete mass, whereby shearing compaction is created in the mass.
3. An apparatus for compacting concrete, c h a r a c t e r i z e d in that it comprises a container (1) for concrete mass (2), a cylindrical pipe (3) under vacuum provided in connection with the container (1), means or a mechanism (11, 12) for feeding concrete mass (2) into the pipe (3) under vacuum gradually so that air is discharged from the concrete mass (2) in a bursting manner when the concrete mass is subjected to vacuum, and a plunger (6) or a screw moving in the pipe (3) for compressing the concrete mass under vacuum and further into a flexible transfer pipe (4).
4. An apparatus according to claim 3, c h a r ¬ a c t e r i z e d in that the container (1) and the cylindrical pipe (3) with its plunger (6) are formed as a displaceable unit.
5. An apparatus according to claim 3, c h a r ¬ a c t e r i z e d in that a nonreturn valve is provided in the lower end of the plunger pipe (3) or in the transfer pipe (4) to prevent the transfer of the concrete back under the action of vacuum, or that the screw conveyance system is so constructed that the concrete is all the time conveyed onwards to the casting point.
Description:
Method and apparatus for compacting concrete

The invention relates to a method of compacting concrete. Concrete mass is deteriorated by two excess materials which are tried to be avoided: air and water.

The concrete technology has typically utilized vibration for the removal of air, whereby air bubbles are expelled from the mass by utilizing great density differences.

In the present-day concrete technology, vacuum concreting refers mainly to an operation performed on a finished cast surface by means of a suction mat, whereby excess water can still be sucked from the concrete mass, thus improving the strength of the concrete by decreasing the water/cement ratio. At the same time, of course, air is also removed to some extent but if the concrete is not simultaneously compacted, more air pores and capillaries are formed in spaces from where water has been removed. It is also known that another gas, such as carbon dioxide, can be introduced into this air space under vacuum so as to speed up the reactions. Vacuum concreting of this type is thus performed after the casting, and the primary object is not to remove air but water.

As the removal of air has been carried out previously mainly by vibrating after the concrete has been poured into the mould, plenty of air always remains in the concrete mass. Part of this is necessary in view of frost resistance, but most of it is excessive, deteriorating the strengths and causing blisters against ' the mould surfaces. The object is to provide a new method and

apparatus for compacting concrete especially by removing more air from the concrete than with the previous methods and apparatuses.

The method according to the invention is mainly characterized in that concrete mass, before casting, is fed gradually into a space under vacuum so that air is discharged in a bursting manner from a small amount of the concrete mass at a time when the concrete mass is subjected to vacuum and the volume of air bubbles contained in the concrete mass is increased, that the concrete mass under vacuum is compressed by means of a transfer plunger or screw and the compressed concrete mass is pressed out by means of the same plunger or screw into a flexible transfer pipe, that a straight cylindrical pipe with required feed and discharge openings is provided as the path of the transfer plunger, and that the flexible transfer pipe after the plunger or screw of the pipe is moved to create shearing compaction within the concrete.

In the apparatus construction according to the invention, the unit effecting the vacuum and the transfer of concrete mass, i.e. a screw or plunger assembly, operates within the concrete mass and operates simultaneously as an advantageous unit for pumping or further transportation of concrete. Said plunger assembly is operated by hydraulic or pneumatic operating means or preferably by steam. Further, the pneumatic operating means can preferably utilize carbon dioxide as drive gas, whereby possible gas leakages merely contribute to the later hardening of the concrete mass, when the mass is pumped direct¬ ly into the casting point. The operating means may also be a screw..- In the following the invention will be

described with reference to an exemplifying embodi¬ ment shown schematically in the attached drawing.

Figure 1 shows a situation in which a transfer plunger is at the final stage of the thrust movement. Figure 2 shows a situation in which the transfer plunger is in a retracted position.

The drawing shows a longitudinal section of the apparatus, in this case as an embodiment which can be displaced e.g. by means of a crane upon the casting point or close to it. The transfer plunger shown in the drawing can be replaced with a conveyor screw.

The reference numeral 1 designates a container which preferably tapers downwards, and the reference numeral 2 designates concrete mass contained in the container. A pipe 3 is attached to the side of the container 1, in which pipe a plunger or screw moves and from the lower end of which a concrete mass transfer pipe 4 extends. A plunger assembly 5, 6 is attached to the pipe 3, and a connecting rod 7 common to the plunger assembly moves through a fixed partition wall 8. A block 9 designates hydraulic or pneumatic operating means for the plunger assembly, the plunger being moved backwards and forwards by the operating means. A block 10 represents a vacuum pump which can preferably also be a corresponding plunger assembly operated by the same operating means as the plunger assembly 5, 6, or the vacuum creating device may be a conventional vacuum pump. The lower plunger 6 is so long that it transfers a sufficiently great amount of concrete onwards, at the same time preventing the lowest plunger of the hydraulic system or the hydraulic oil from reaching a concrete feeding valve 12 and a suction opening 13 of the vacuum system. To facilitate the transfer of the mass from the

hopper-shaped or other intermediate container to the pumping apparatus, it is preferable to use a vibrator 11 shown schematically or a feed screw positioned within the container 1 and not shown in the drawing. When the plunger 6 operates as a pump, it creates a high pressure in the concrete mass and thereby the amounts of air possibly remaining in it are dissolved completely in the concrete mix water. At a later stage, when the pressure decreases, air bubbles may be formed again, but they are now evenly distributed and extremely small.

At the pressure stage of the pump, it is preferable to introduce ' carbon dioxide into the concrete mass to replace the removed air, whereby the stiffening of the mass advantageously takes place very rapidly in cases where a wall, cavity slab or other similar concrete object is made by slip cast¬ ing, wherein it is preferable to avoid great hydraulic pressures exerted on the mould surfaces. The concrete mass transfer pipes may comprise non-return valves possibly required, depending on the consistence of the mass.

One and the same apparatus arrangement may comprise several described pump-air removal units in parallel, whereby the units are driven by the same common operating means.

A typical plunger diameter is e.g. 100 to 125 mm, the stroke length preferably about 1,000 mm, and the production rate 3 to 10 litres/second. Concrete mass is thus fed before casting into a space under vacuum gradually so that air is discharged in a bursting manner from a small amount of concrete mass at a time when the mass is subjected to vacuum and the volume of air bubbles contained in the concrete mass is increased, and that the concrete

mass under vacuum is thereafter compressed. In con¬ nection with the compression, it is possible to util¬ ize previously known auxiliary techniques, such as pressure, vibration or shearing compaction, which, for instance, can be effected in such a way that the end of the plunger is oblique and revolves while it moves. Shearing compaction also occurs in screw con¬ veyance.

Concrete mass can be fed into the space under vacuum in a batch-wise manner or continuously.

By feeding the concrete mass into the space under vacuum gradually in relatively small amounts, air bubbles contained in the concrete mass can be released and removed from the concrete effectively as if by exploding. From a greater batch, the way out is too long for an entrapped air bubble.

In the present invention, the space under vacuum is preferably a cylindrical pipe, whereby it is self-cleaning without any problematic projections or unnecessary spaces where concrete stones may get wedged or concrete may harden.

The transfer or discharge pipe 4 may be flexible and it need not be positioned vertically, whereby the casting preferably takes place by a so- called contractor method, that is, the feed opening of the pipe is all the time within concrete already cast, thus preventing the entrapping of air in the concrete at the casting step. The invention can also be utilized in extrusion, whereby the concrete mass is first pre-compacted by means of the apparatus.

The pump can be positioned at the lower end of the container in a known manner, and it can feed concrete directly into the shaft space 3, 4, the volume of which is many times greater than the volume of concrete mass introduced into it at a time. It is

to be recommended that the volume of the shaft space is at least about 0.05 m^ and that the shaft space is evacuated to a vacuum pressure of at least about 5 kPa. Alternatively, it is possible to feed concrete mass by means of a pump, for instance, into a closure pocket (not shown in the. drawing) from which concrete mass is drawn by the action of the vacuum into an "explosion space" in the lower portion of the pipe 3, through a valve 12, which may be arranged to open and close once a second, for instance. This alternative may " be more reliable in view of the maintenance of vacuum.

In place of the plunger 6, it is possible to use e.g. a conveyor screw rotated e.g. by a hydraulic motor, the upper end of the conveyor screw being sealed with respect to the pipe 3. The end of the plunger 6 making contact with the concrete may be oblique to achieve shearing compaction, similarly as with a screw, whereby the plunger 6 is arranged to revolve while it moves.

The compaction of concrete mass can preferably be further improved when the mass moves in the flexible pipe 4, in many different ways e.g. in such a manner that the concrete is exposed to shearing movements by moving the pipe portions from the out¬ side. The pipe may be wrung, twisted, bent, mangled, throttled at different angles, pumped, etc., by small twisting or backward-and-forward movements so that particles in the concrete are brought closer to each other into a package as compact as possible within the pipe when a so-called shearing compaction effect is created by internal deformations caused in the concrete mass moving within the pipe. The invention is not restricted to the embodi-

ment shown in the drawings and the dimensional values given above. It is easy for one skilled in the art to modify the apparatus construction in many different ways. An independent application of the shearing compaction effect described in the preceding para¬ graph also falls within the scope of the invention.