WO1979000167A1

WO1979000167A1 - Method of moulding concrete

Info

Publication number: WO1979000167A1
Application number: PCT/SE1978/000045
Authority: WO
Inventors: S Hasselqvist; A Thoreson; P Helenelund
Original assignee: Scanovator Handel; S Hasselqvist; A Thoreson; P Helenelund
Priority date: 1977-09-30
Filing date: 1978-09-27
Publication date: 1979-04-05
Also published as: SE7710946L; DK433578A; SE7907135L; FI782972A; EP0007358A1; GB2035880B; NO783262L; GB2035880A

Abstract

A method of moulding articles from a concrete mixture. As shown in Fig 1, the water (12) is first poured into the mould (14, 14"), whereafter the dry cement mixture (2) is poured into the mould, soaking up the water. Another form of the invention is shown in Fig 2, where instead of pouring the water into the mould, the cement mixture (2) is moistened by water (1) sprayed into the dry mixture just before the mixture is poured into the mould. The invention is especially advantageous when mixtures containing fibres are used or when the articles are formed by centrifugal moulding.

Description

A Method of Moulding Concrete

Concrete is normally strengthened using reinforcing rods of steel. In this case the rods most often pass throughout the section which is loaded between supports. In order to improve bonding between the basic material and the reinforcement the latter is nowadays often manufactured with ribs or other types of roughness on the surface.

Fiber-reinforced concrete is a new material with especially short fibers dispersed in the basic material, the matrix, which normally consists of concrete with or without additives. The fibers should lie relatively closely and be distributed in those directions which a loading may be assumed to take. Primarily, the tensile-loaded concrete receives great!y improved strength qualities through reinforcement. Improvement in impact resistance is also noted as a prominent characteristic of fiber-reinforced concrete. Previously, asbestos fiber was mainly used as reinforcement in concrete. However, since asbestos cement involves a health hazard this is now heavily restricted in use.

Other fiber materials are glass and steel. Both materials are making a rapid advance, even if the production methods used in their application to concrete leave much to be desired. It is easily understandable that the use of conventional mixing methods is regarded as the cheapest way of introducing the fibers into the concrete. On the other hand, it must be realised that the fibers provide reinforcement not only in the hardened end product but also during the plastic condition of the concrete. As soon as the fibers are introduced into wet concrete they behave as reinforcement and often become difficult to handle, especially in drier consistence One way of solving the problems of production technique here is given in Swedish Patent No. 400501.

Concrete materials are easier to handle in dry powder form than in a wet concrete mix. Greater freedom in choice of handling equipment, dosing etc is permitted. Fiber materials can be added without the critical mixing. or transport characteristics of a damp concrete mix. With no addition of water the concrete will not, of course, harden and can therefore be stored as long as necessary. Considerable savings in cleaning expenses can be made and production stops due to clogging and, even worse, hardening of the concrete before reaching the mould, are avoided entirely. The sight of a concrete truck travelling at top speed with a load of fresh, wet concrete mix will serve, to exemplify this point.

This invention consists of methods of mixing concrete with water so that considerable advantages are achieved compared to previously known techniques. Either a mould is filled with the amount of water required for the moulding process, after which the concrete material is added in dry powder form, or, as in one variant, the concrete material is poured in as dry powder while water in atomized form is added to the powder stream.

German patent number 2 232 390 describes a method of mixing concrete with water whereby the material is tumbled in a suitable mould (spherical) after which the speed of rotation is increased and the ready-mixed concrete material flows out into the intended even layer in the mould by virtue of centrifugal force. This differs from the method used in our invention in that the first concrete particles due to their higher density sink towards the mould surface, passing the lighter particles of the liquid so that outstandingly good wetting is achieved even with small amounts of water.

A further increase in the wetting effect can be obtained by raising the mass-dependent forces. In this way it is possible to minimise water consumption to the amount necessary for hydration, thereby considerably improving the quality of the final concrete product. This procedure increases the possibilities for building up products layer by layer. It is possible, for example, to introduce different layers for tensile strength, impact resistance, heat and sound insulation, wear resistance, imperviousness, low friction surfaces etc.

The present technique of first adding a certain amount of water and then a dry mix can be applied practically to those cases where it is possible both to pour the water where required and to distribute it as necessary in order to thoroughly dampen the concrete powder and hydrate it. The two cases in which it is most suitable to use this technique are when a surface is horizontal and approximately even, so that the water is distributed satisfactorily, and in centrifugal spinning. This invention is not however limited these cases alone. Other methods may involve the use of other materials to retain moisture in a mould, for example porous material, which can supply the correct amount of water to the concrete material when this is introduced.

In centrifugal spinning a balanced mould is used. It is suitable to have a circular cross section mould or at least a mould so designed that its mass is balanced during rotation. If the axis of the mould is held horizontal and water is added during rotation, this can be retained by centrifugal force. When adding dry concrete mix with a suitable device (a preferable method is a conveyor belt moving in an axial direction along the inside of the mould) the water and concrete mix are thoroughly blended. Since the density of the dry powder is greater than that of the water the powder is pressed against the walls of the mould while the water passes through and dampens the material. By regulating the rotational speed it is possible to a certain extent to control the amount of water used so that optimal strength of the end product is obtained. Fibers may be introduced either in the dry mix where blending takes place in conjunction with transfer to the mould or on an individual basis. In this case it is often suitable to use a special sequence for introducing different materials. For example, it is possible to insert an insulation layer between supporting surfaces.

The particle aggregate in the concrete consisting of sand graded according to a special scale is distributed together with the cement so that the spaces between the coarser particles are well filled with finer particles and cement particles. Micropores are reduced and the imperriousness and density of the concrete are increased at the same time as both the compressive and tensile strengths are raised. This is of the greatest significance for efficient bonding between the basic material and the added fibers of, for example, steel. Improved interfacial bonding and minimal porosity provide especially high strength increases when fibers are used in concrete.

By first introducing water into the mould, in accordance with this invention, and then adding the dry concrete material, considerable advantages are obtained in comparison with other techniques, e.g. UK 1 273 693, where the dry concrete powder is introduced first and then water is injected. In the procedure described therein, special measures are required, such as extra compressive force in order for the aggregate particles to be kept in contact, while the accumulated spaces are filled from below by the addition of water. The invention described herein requires no evacuation since water already fills the space from the outset. Our technique thus makes it possible to supply water to all the particles in an efficient way and allows the amount of water to be reduced to the level necessary for hydrating the cement. This eliminates weakening pores where surplus water otherwise collects and later evaporates.

It is appropriate to mention at this point some especially advantageous elements of. the process. It was stated above that experience has shown that a conveyor belt is suitable for transporting both concrete materials and fiber into the rotating mould. The conveyor belt may be placed in a frame which is in turn movable in the longitudianl direction of the belt. It is not necessary to manufacture fiber in direct conjunction with the process. Using a suitable separating device the fibers can be apportioned and placed on the conveyor belt. Other means of transport can be used instead of the conveyor belt. One possible method is the worm conveyor. Generally, the elements in a well run-in process may be advantageously replaced by others. In a rational, highly mechanized plant it may well be considered appropriate to use pipe transportation for the materials.

In order to increase productivity in a centrifugal casting process it may be advantageous to keep the moulds in a magazine where the materials are placed in one mould which is then moved aside while still rotating in order to make room for a new rotating mould. Both water and dry material are added as described above.

It has proved advantageous to use disposable moulds in casting in accordance with this invention. If these are constructed of a material wich fulfills certain requirements they can be used both for transport protection and insulation. For example, when laying pipes in earth disposable moulds may be made of a material which can remain around the pipes when buried. Both sealing and insulation properties are improved by a mould of this type. There are various types of magazine having practical designs. One variant uses horizontal rotating moulds placed on belts stretched between rollers and with a device for allowing a horizontal product flow. In this case several conveyors can work simultaneously parallel to each other; water is placed in one form, dry fiber concrete mix in the next and so on.

The mould is retained by belts on tension rollers which are placed somewhat higher than the axis of the mould and are thus separated by an arc greater than 180º. The tension rollers thereby retain the mould in position so that it cannot be accidentally dislodged.

Another variant is based on a construction with moulds arranged in revolving magazine. All axes are horizontal in this case. Materials can be placed in one or several moulds.

In a process plant for, for example, centrifugal spinning of fiberreinforced concrete control of the process can be considerably rationalized. It is thus suitable to use the methods described above for automatic metering and introduction of constituents incorporation indicators for fiber distribution - preferably using inductive sensors for ferromagnetic fiber. The production cycle can be program-controlled and the process would require a minimum of personnel for supervision and service.

In manufacturing slabs, floors and roads a horizontal mould is used which encloses the water while the concrete powder and where applicable, the fiber, is added. Checks on the individual phases of the process permit a very high quality in the end products, at the same time as achieving a simple process which obviates the need for subsequent cleaning of the equipment.

Fig. 1 shows dry mix which is placed in a mould containing a suitable amount of water. Fig. 2 shows dry mix transported from hopper to mould and mixed with atomized water . Fig. 3 shows schematically an arragement for centrifugal spinning of, for example, fiber-reinforced concrete pipes using a mould hung on belts and which is rotated while an axially movable conveyor places materials along the entire inner mantle of the mould. Fig. 4 shows the same process as Fig. 2 except that fibers 19 are also loaded directly on the conveyor 11. Fig. 5a shows how a dry mass 2 is added to a mould to provide a covering layer nearest the mould surface 3. Fig. 5b shows how concrete powder 2 and fibers 19 are added separately to the mould with space for repeated loading. Fig. 6 shows the same situation as Fig. 3 except that short fibers 19 are added directly via the conveyor 11 to the dry concrete mix 2 to produce a dry mix 20 containing fibers.

Fig. 1 shows a mould surface which is supported within a type of frame 14 which permits water 1 to be added first, after which concrete mix 2 in dry powder form is poured in.

Fig. 2 shows a hopper 13 with dry mix 2 which falls onto a conveyor belt 11 and in falling onto the horizontal surfase is sprayed with atomized water 1 for suitable dampening. Fiber may be added to the dry mix before it is poured into the hopper. Fiber may also be added directly on the conveyor belt, which may either be loaded with dry concrete mix or be empty, depending on the required speed of the process or the layer in which the fiber is required.

Fig. 3 shows a cylindrical mould 4 of either disposable or reusable type supported between rollers 6' and 6" using belts 5' and 5", of which only one need be driven.. Furthermore, roller 7, for example, is a driving roller provided with suitable transmission, here a pulley 16, from the motor. Conveyor belt 11 moves longitudinally so that it can supply the whole of the inside of the mould with concrete mix. This figure also shows that water 12 has first been poured into mould 4 so that this example involves filling the above mould with dry concrete mix 2.

The technique used in the present invention may be varied considerably in detail without, altering the basic idea. Materials can be introduced by injecting them through channels or by pumping wet concrete mix, followed by direct addition of fiber in the mould.

Claims

Patent ClaimsWhat we claim is

1. A method of manufacturing a concrete product in which the mould or a part of the mould is previously filled with the amount of water (12) or hardener required for casting, after which the concrete material (2) in dry powder form is distributed in the mould in the place where it is finally to remain.

2. A method of manufacturing a concrete product in which water in atomised form (1) is added to a mechanically transported stream of dry powder (2) and thereby made to dampen the concrete material while it is transported to the casting location.

3. A method in accordance with Claim 1 in which a balanced mould is made to rotate at a speed which is sufficient for material applied to the wall of the mould by centrifugal force to remain there, the mould being prefilled with the amount of water required for casting and the dry material thereafter being placed in the rotating mould.

4. A method in accordance with Claim 3 in which the mould is cylindrical (4).

5. A method in accordance with Claim 3 in which the mould is conical.

6. A method in accordance with Claim 2 in which a balanced mould is made to rotate at a speed which is sufficient for the material applied to the wall of the mould by centrifugal force to remain there, water being added in atomised form to a stream of dry concrete powder and thereby dampening the concrete material while it is introduced into the mould.

7. A method in accordance with Claim 6 in which the mould is cylindrical (4).

8. A method in accordance with Claim 6 in which the mould is conical.

9. A method in accordance with one of Claims 1 - 8 in which the concrete material consists of a dry concrete powder (2) and fibres (19) which are placed in the mould either ready-mixed or separately and possibly in successive batches.

10. A method in accordance with one of Claims 1 - 9 in which macroreinforcement is cast into the product.

11. A method in accordance with Claim 10 in which the macro-reinforcement consists of conventional reinforcing rods or mats.

12. A method in accordance with. Claim 10 in which the macro-reinforcement is pre-stressed.

13. A method in accordance with one of Claims 1 -12 in which the product is built up in layers.

14. A method in accordance with Claim 13 in which the layers are provided with different significant properties, certain layers consisting of material other than concrete.

15. A method in accordance with one of Claims 13 - 14 in which one or more layers are provided with better tensile strength than the other layers.

16. A method in accordance with Claim 15 in which one layer is provided by a particular process with increased tensile strength in a particular direction.

17. A method in accordance with Claim 16 in which the directional dependence of the tensile strength is controlled by orientation the fiber reinforcement in a particular direction.

18. A method in accordance with one of Claims 13-14 in which one or more layers are provided with better impact resistance than the other layers.

19. A method in accordance with one of Claims 13 - 14 in which one or more layers are provided with better heat insulating properties than the other layers.

20. A method in accordance with one of Calims 13 - 14 in which one or more layers are provided with better sound insulating properties than the other layers.

21. A method in accordance with one of Claims 13 - 14 in which one or more layers are rendered more impervious to liquids and gases than the other layers.

22. A method in accordance with one of Claims 13 - 14 in which a spacing layer is provided which separates the surrounding layers.

23. A method in accordance with one of Claims 13 - 14 in wihch the cast product is wholly or partly given a surface which is resistant to wear.

24. A method in accordance with one of Claims 13 - 14 in which the cast product is wholly or partly given a surface with low friction.

25. A method in accordance with one of Claims 1 - 14 in which the mould used in casting is left in place even after the concrete has hardened.

26. A method in accordance with Claim 25 in which the mould is manufactured principally of organic material.

27. A method in accordance with Claim 25 in which the mould consists of a steel strip cylindrically formed with a spiral lap.

28. A method in accordance with one of Claims 3 - 27 in which the rotating mould is suspended in belts (5') and (5") carried by rollers (6') and (6") on each side of the mould, the belts enclosing the mould with an arc of contact greater than 180º.

29. A method in accordance with one of Claims 3 - 27 in which the rotating mould is supported by at least one pair of rollers with axles parallel to the mould, the axles being driven by rollers or belts around the mould.

30. A method in accordance with one of Claims 3 - 29 in which a conveyor belt (11 ) is placed so that it can apply the dry material along the entire inside surface of the mould.

31. A method in accordance with one of Claims 3 - 29 in which a screw conveyor is placed so that it can apply the dry material along the entire inside surface of the mould.

32. A method in accordance with one of Claims 3 - 31 in which several parallel rotating moulds are placed so that they can be loaded by the handling equipment for the dry material and kept in rotation for the necessary length of time.

33. A product which is manufactured in accordance with one or more of the foregiving Claims.