METHOD AND APPARATUS FOR THE MANUFACTURE OF A PRECAST BUILDING ELEMENT OF CONCRETE

Abstract: Method and apparatus for the manufacture of a concrete hollow slab by means of slide-casting. According to the method, the cavities are formed around tubes (13) of flexible material into which a pressurized medium, particularly water (15), is fed. The apparatus comprises a stationary base (1 to 4) and a casting device (7 to 11) arranged to travel in the longitudinal direction of the base (1 to 4). A number of parallel shaping pipes (10) forming part of the travelling casting device (7 to 11) and having a cross-section corresponding to the desired cross-section of the cavities to be formed are open at both ends. The flexible tubes (13), which are fastened at their rear ends to a pressurized liquid source (14), pass during the casting process from reels (12) in the casting device through the pipes (10) so as to give the cavities their final form.

Description: Method and apparatus for the manufacture of a precast building element of concrete The present invention concerns a method in accordance with the preamble of claim 1 for the manufacture of a precast building element of concrete. The invention also concerns an apparatus for carrying out the method. Precast building elements of concrete frequently consist of the following functional parts: a straight, plane top or bottom face, or simultaneously both of them, and of a supporting material connecting these faces, which material may be continuous or, as is frequently the case, made of longitudinal beams and of reinforcements that carry tensile strains. In practice, such a precast element serves as a floor, ceiling, wall, or equivalent, the highest strains applied to such components being, besides their own weight, other strains directed downwards, mostly caused by the force of gravity. •In such a situation, the upper face of this precast concrete element must withstand compression forces, and the bottom face tensile strains. Out of these reasons, a portion of relatively low strength is required to bind the top face and the bottom face; in construction technology, an I-beam is known. When such I-beams are connected to each other, in the building technology, on the other hand, the notion ■ of hollow slab has been adopted. The problem in the manufacture of such a hollow slab or corresponding element is the formation of a cavity of desired shape continuously and without restric¬ tion in respect of the properties of the concrete mix used. The shape of the cavities is in each case determined by many individual factors. In the prior art methods for the manufacture of hollow slabs that are used today, many compromises must be made between these factors and the properties of the concrete mix. In such prior art methods in which the hollow slab is shaped continuously while taking advantage of the vaulting properties of fresh, substantially viscous concrete mix, at the stage of formation of the slab, a strong, rapidly varying force is required, which is, in concrete technology, called vibration. In such a method, when attempts are made to form hollow cavities of desired width in thick slabs, the intensive vibration causes difficult noise problems at the working sites as well as problems of strength of the machine elements to be used. In order to avoid these drawbacks, attempts have been made to manufacture such hollow slabs or corresponding structural elements so that the cavity is shaped ' out of some inexpensive material while the concrete mix of substantially low viscosity is being cast around this material forming the hollow cavity. Typically, such a material forming the cavity is sand or gravel or any other rock material / which can be removed on hardening of the building element of concrete in accordance with prior art technique (Finnish Patent No. 47,295), e.g., by pouring, and which material can be used again as filler material for subsequent hollow slab elements to the extent that it did not adhere to the preceding element. In such a method a drawback consists of complicated machinery and equipment, recirculation of a large quantity of rock material with resulting losses of energy, and further the uneven faces of the cavities formed, which are harmful in the cases of certain application of use. In an attempt to minimize the capital cost of such hollow slab factories, heating of the hollow slab elements has been introduced so as to make the 5 necessary setting time of the concrete mix shorter. This heating is mostly carried out so that the casting base of the concrete element cast is heated, the heat being conducted from the base further into the structural element itself. 10 Such a method always results in highly uneven heating of the cast object, with detrimental strains resulting therefrom./ the strains being derived from different local temperatures and from resulting different degrees of setting of the concrete. 15 Now, after having studied how to form such a hollow slab most advantageously, it has surprisingly been discovered that there is a- method. inrwhich all the desired: aspects can be accomplished at the same time In this method, the desired cavities are pro- 20 duced by means of a liquid filler agent, said agent being isolated from the fresh concrete mix by a tight tubular wall made of a resilient material. More specifically, the method in accordance - . with the present invention is characterized in what is "25 stated in the characterizing portion of claim 1. On the other hand, the apparatus in accordance with the invention is characterized by. what is stated in the characterizing portion of claim 2. In such a method, it is possible, by means 30 of the liquid filler of the cavities, both to support and to heat the cast formed piece of concrete, and in the method, no restrictions are imposed on the con¬ sistency of the concrete mix. Nevertheless, the casting apparatus required becomes simpler when a concrete mix 35 of a relatively low viscosity is used in connection with this method. The invention will be examined below in more detail by means of the exempliying embodiment in accordance with the attached drawing. Figure 1 is a sectional side view of one apparatus in accordance with the invention. Figures 2 and 3 show sections along lines A - A and B - B, respectively, in Fig. 1 on an enlarged scale. Figures 4 and 5 are sectional front and side views, respectively, of a flexible tube. in practice, the element is cast on a base 2 which is sufficiently robust and provided with hinges 4 ,side boards 3 ,and frame members 1. Onto this base 2, the concrete quantity 19 forming the bottom face of the desired element is cast, and air-tight tubes 13 with resilient walls, described in more detail below, are placed onto the bottom concrete, whereby the tubes 13 may be discharged/ e.g., from reels 12 provided in the travelling casting device. During the glide casting operation, the casting device consisting of a frame 7, a storage 8, a funnel 9, the tubular shaping pipes 10, a rear forming board 11, and the reels 12 moves in the direction of the arrow C in relation to the base 2. At the same time, these tubes 13 are filled, starting from the initial point of casting, with a liquid at constant pressure, which liquid has been heated to the desired temperature. Further, at the same time or slightly after the above, the casting process follows, wherein the space 21 between the filled tubes 13 and the top layer 20 covering the tubes and the spaces between them are filled with the concrete mix used. The rear end of each tube 13 is connected to a tank 14 from which the liquid, e.g., water 15, enters the tubes 13 through openings 16 so as to create a pressure within the tubes 13. By means of a partition wall 17 forming an overflow member for the extra water 18 in the tank 14, the pressure can be kept constant. When such a precast element is being formed, it is almost as a rule desirable to place structural components carrying tensile strains near the bottom face, these components being usually continuous iron bars or wires placed between the cavities formed into the element, these bars or wires being prestressed in certain embodiments. These reinforcement strands 5,which carry tensile strains,may be placed inside the hollow slab element to be manufactured either after the casting of the separate bottom 19 of the element or by already placing them on the base before the casting of any concrete layer and by raising them during the casting process mechanically so that a desired quantity of fresh concrete mix remains underneath them. Reference numeral 6 denotes the stretching blocks for the strands 5. In this method, when the latter concrete mix is being cast, which forms the space 21 between the hollow cavities and the top layer 20, it is possible to make the flexible tube.13 forming the cavities, now filled with liquid, to pass through the rigid shaping pipe 10, which, when travelling with the casting device, gives the tubes 13 filled with liquid the desired shape. This shape can be readily made permanent by vibrating a sufficiently tixotropic concrete mix at the time when the shaping pipes 10 described above are still closely surrounding the tubes 13 with resilient walls. A sufficiently tixotropic nature of the concrete mix, which permits the permanence of the obtained shape on removal of the vibration, is best obtained by means of such a concrete mix as has been liquefied by using appropriate quantities of sulphonated organic polyelectrolytes and, correspondingly, essentially little quantities of water. It should be mentioned that the degree of con¬ sistency of the concrete mix used is, e.g., VB°-0-10, and the temperature of the water used preferably 20 to 85°C. Suitable organic polyelectrolytes are, e.g., naphtalen≥ sulphonate condensation products, sulphonated melamine resins, as well as lignos lphonate-products. It is preferable to bring the concrete mix to be cast substantially to the same temperature as the liquid in the tubes. After the concrete mix has set sufficiently, the heating liquid is drained out of the tubes forming the cavities, whereupon the flexible tubes with resi¬ lient walls can be pulled out of the completed con¬ crete product. It is also preferable to cast the concrete product on a substantially heat-insulating base and to cover the product with a heat insulation. As seen in Figures 4 and 5, the tube 13 is provided with stiffening members 22 on the upper and lower inner side thereof. The members 22 are arranged in parallel relationship in the transversal direction of the tube 13 such that the slanting edges 23 of adjacent members 22 form grooves 24 reaching the inner side of the tube 13. Due to this arrangement, the tube 13 under pressure assumes a cross-section with " two opposite sides in parallel relationship and, at the same time,- allows an easy winding of the tube in deflated state on the reel 12. The members 22 are preferably made of a plastic material. Within the scope of the invention, the tubes 13 can also be pressurized by means of pressurized gas, e

Claims: Patent Claims: 1. Method for the manufacture of a precast hollow slab element of concrete (19, 20, 21) by means of slide-casting, wherein each cavity is formed around a tube (13) of flexible material into which a pressurized medium, such as water or air. is fed, and the tube (13) is fed into position synchronously with the progress of the slide-casting at the same time as the medium is fed as replenishment, preferably at a constant pressure, from the rear end (16) of the tube (13), c h a r a c t e r i z e d in that the tube (13) is allowed to pass through a rigid shaping pipe (10) open at both ends and having the cross- sectional shape of the corresponding cavity to be formed in the hollow slab and travelling forwards synchronously with the progress of the casting. 2. Slide-cast apparatus for carrying out the method as claimed in Claim 1 , comprising a stationary casting base (1 to 4), - a casting device (7 to 11) arranged to travel in the longitudinal direction of the casting base (1 to 4), and - at least one rigid shaping pipe (10), which, forming part of the casting device (7 to 11), is arranged to travel synchronously with the progress of the casting and whose cross-section shape at least approximately corresponds to the cross-sectional shape of the cavity to be formed, at least one tube (13) made of flexible materia which tube is, at its rear end (16), fixed and, the front end (12) of which is arranged to be fed with the shaping pipe (10) synchronously . with the progress of the casting, the cross-section of the tube (13) at least approximately corresponding to the cross- section of the shaping pipe (10), and - a liquid supply device (14 to 18) for the supply of pressurized liquid into the pipe (13) through its rear end (16), c h a r a c t e r i z e d in that - each shaping pipe (10) is open at both ends, and - the casting device (7 to 11) is provided with cube storage means (12) for the flexible bube (13) and from which the tube (13) can be fed through the shaping pipe (10) synchronously with the progres of the casting. 3. Apparatus as claimed in Claim 1, c h a r a c t i z e d in that the tube storage comprises at least one reel (12) from which the flexible tube (13) can be fed to the front end of the shaping pipe (10).

Inventors: VIRTANEN PENTTI, VIRTANEN, PENTTI
Applicants: KAUTAR OY
Application year: 1983
Main classification: B28B7
IPC codes: B28B1, B28B7