APPARATUS AND METHOD FOR MAKING CONCRETE CONSTRUCTION ELEMENTS

Abstract: Described is an apparatus (1) for making concrete construction elements (100) having hollow channels (104) extending in the longitudinal direction thereof. Such an apparatus (1) comprises a first concrete-pouring element (20) for making a bottom layer (110) for the construction element (100) to be made; vibrator shoes (31) for compacting the concrete of the bottom layer (110); a second concrete-pouring element (40) for pouring a second concrete layer (120) onto the bottom layer (110); a vibrator plate (51) for compacting the concrete of the second layer (120); and bars or pipes (61) extending from the vibrator shoes (31) to beyond the vibrator plate (51) for ensuring that the hollow channels (104) are made in the constuction element (100) to be made. According to the invention, this apparatus (1) is improved in that between the vibrator shoes (31) and the bars or pipes (61) there is arranged a flexible filling piece (200) having a gradually extending contour.

Description: Title: Apparatus and method for making concrete construction elements The invention relates to an apparatus for making concrete construction elements having hollow channels extending in the longitudinal direction of these construction elements. Apparatuses for making such concrete construction elements are known in practice. An example thereof is described in US-A-3,177,552. The known apparatuses are intended for making the concrete construction elements in great lengths, with the concrete construction elements lying still on a work floor and the apparatus moving over the work floor to make the concrete construction element in two cycles of operations. To that end, the apparatus has a first concrete-pouring element for applying a bottom layer of the concrete construction element, means for compacting the concrete of the bottom layer, a second concrete-pouring element for pouring a second concrete layer onto the bottom layer, means for compacting the second layer as well, and means for ensuring that the hollow channels are made in the concrete construction element. .The first compacting element is a vibrator element having vibrator shoes which, on the lower side thereof, have a contour that corresponds to the contour of the lower side of the channels to be formed. The vibration causes the thixotropic concrete mass to become fluid, so that it compacts and the lower side of the channels to be formed is formed. The elements serving to give the channels their final form consist of bars or pipes having a contour that corresponds to the contour of the channels to be formed, which pipes extend from the first vibrator elements to beyond the second concrete- pouring element and the second vibrator element. During pouring the second concrete layer onto the first layer, the pipes ensure that the concrete can only reach the channel walls between the channels, with the help of the second vibrator element which renders the concrete fluid, so that it also compacts. In this connection, the second vibrator element has a flat lower side, i.e. a lower side whose shape corresponds to the shape of the upper side of the concrete construction element to be formed. The pipes or bars move with the apparatus and can in principle be held still relative to the apparatus, thus having a uniform speed relative to the concrete mass formed, but in order to reduce friction of the pipes relative to the concrete mass, these pipes are given a vibrating motion in their longitudinal direction. This vibrating motion takes place at a frequency of, for instance, approximately 5 Hz and a travel of, for instance, approximately 6 mm, while the vibrator shoes of the first vibrator apparatus vibrate at a frequency of typically circa 3,000-9,000 Hz and an amplitude which is typically less than approximately 1 mm. Thus far, the vibrator shoes of the first vibrator element and the pipes have been arranged as separate parts, while the distance from the pipes to the vibrator shoes should be chosen in dependence on the amplitude of the pipes and the greatest cross dimension of the gravel grains present in the concrete mass to be poured. If this greatest dimension is approximately 22 mm, this distance should be at least approximately 30 mm. As a resul , the wall portions which have already been formed between the channels have no support between the first vibrator shoes and the pipes, so that the height of those wall portions that can be realized during the first cycle of operations is limited. As a result, in the second cycle of operations the concrete, should flow over a reasonably great depth between the pipes in order to form the walls of the channels, which means that the " concrete to be formed should be relatively fluid. This is achieved by using relatively moist concrete, which has negative consequences for the strength that can eventually be realized, which consequences can be compensated by using more cement in the concrete, which, however, is relatively expensive. A further consequence of the distance between the first vibrator shoes and the pipes is the fact that the cross dimension of the pipes should be less than the cross dimension of the lower side of the channel such as this is formed by the first vibrator shoe, because otherwise the front side of the pipes would scrape the formed concrete during a forward movement, resulting in uncontrolled thickness variations of the side walls, cracks in the side walls, or even the complete destruction of the side walls. However, the space between the channel walls already formed and the pipes should be filled up in order to give the channels their desired shape, because shape variations of the channels may cause cracks. This filling up is realized in that at the second vibrator apparatus the concrete is rendered fluid again and flows to below the pipes. However, this requires that the second vibrator element has a relatively great operating depth. Further, the concrete construction elements are generally provided with metal pre-stress bars between the • channels, at least some of these bars being surrounded by the concrete poured in the first cycle of operations. Because the concrete already poured is rendered fluid again in the second cycle of operations to flow below the pipes, this concrete as it were flows along the above-mentioned pre-stress bars, which in practice proves to result in imperfections in the adhesion between the concrete and these bars. These problems have as a consequence that the manufacture of the concrete construction elements is a complex process wherein a number of variables should be controlled in order to obtain a product which meets the criteria that have been laid down. In this connection, it is important that the process remains the same over the entire length of the construction elements to be formed, which elements are made in lengths of circa 120 m and subsequently sawn to length according to specifications of the customers. Unallowable deviations lead to rejects. Thus far, the above-described ' problems have been accepted. The fact that in practice an insufficient adhesion of the concrete to the pre-stress wires was realized, was considered to be a consequence of the operating parameters not having been set properly, which, as mentioned above, should take place within narrow limits. However, the object of the invention is to provide a solution to these problems, and to provide an apparatus in which the number of parameters to be controlled is reduced and/or can be controlled more suitably, and thus the percentage of rejects of the concrete construction elements formed can be smaller. To that end, the invention is based on the insight that an insufficient adhesion of the concrete to the pre-stress wires occurs as a consequence of an after-flow of the concrete poured at the first working stroke, which after-flow is a consequence of the fact that the pipes have a smaller dimension than the channel portions already formed, which smaller dimension should be chosen obligatorily because of the fact that the first vibrator shoes and the pipes are located at a certain distance, ' which interspace had hitherto been left free. Further, the invention is based on the insight that it is possible to fill up that , space with a flexible material without the first vibrator shoes and the pipes influencing each other negatively, but which, on the contrary,, even involves an improvement being realized. Thus, according to the invention, the apparatus of the type mentioned above is characterized in that flexible filling elements are arranged between the respective vibrator shoes and the respective pipes, the contour of which filling elements, at least on the lower side and at least partially on the lateral side, constitutes a gradual transition from the contour of the vibrator shoes to the contour of the pipes. Preferably, the vibrator shoes, the filling element and the pipes have identical contours and identical dimensions at the positions mentioned. The invention further relates to a method for making concrete construction elements. The method according to the invention is distinguished by the use of an above-mentioned apparatus, so that the concrete construction elements formed have better properties. The invention will be further explained hereinafter by a description of a preferred embodiment of the apparatus according to the invention, with reference to the accompanying drawings, wherein: Figs 1A and IB show a longitudinal section and a cross section respectively of a concrete construction element; Fig. 2A shows a schematic side view of an apparatus for making the concrete construction elements; Fig. 2B shows a schematic front view of the apparatus of Fig. 2A; Figs 3A-B show cross sections of a concrete construction element in successive stages of the manufacturing process; Figs 4A-B are helpful in illustrating the drawbacks, of the prior art; Fig. 5A shows a side view of a flexible filling piece according to the invention, arranged between a vibrator shoe and a recess pipe; and Fig. 5B shows a section taken on the line B-B in Fig. 5A. Figs 1A and IB respectively show a longitudinal section and a cross section of an example of a concrete construction element 100, for instance suitable for functioning as an element in a system floor. The construction element 100 has a lower side 101, an upper side 102, and side walls 103, which may have a suitable profile. The lower side 101 and the upper side 102 are preferably flat, as shown. The construction element 100 further comprises a number of hollow channels 104, extending in the longitudinal direction of the construction element 100, with channel walls 106 in between, and, near the lower side 101 of the construction element 100, always next to a hollow channel 104, a number of metal pre-stress bars 105 for taking up tensile forces in the concrete resulting from a load exerted on the upper side 102. Such concrete construction elements 100 are known per se. Fig. 2A shows a schematic side view of an apparatus l for making the concrete construction elements 100. The apparatus l comprises a machine frame 10, capable of travelling by means of wheels 11 over a work floor 12, for instance over a rails arranged on the work floor 12, in a direction designated in Fig. l by the arrow FI. As the front view of Fig. 2B shows, wheels 11 are provided on the lateral sides of the machine frame 10, and between these, on the work floor 12, two moulds 13 are located having a contour that defines the contour of the side walls 103 of the construction element 100 to be made. Near the front side of the machine frame 10 and attached thereto is a first concrete-pouring element 20 for appying to the work floor 12 a bottom layer 110 for the construction element 100 to be made (see Fig. 3A) . The concrete-pouring element 20 comprises a storage vessel 21 for the concrete 22 to be poured, and a flow-out nozzle 23 for delivering the concrete 22. The flow-out nozzle 23 can have a width that corresponds to that of the construction element 100 to be made, but several narrower flow-out nozzles can also be provided side by side. Near the flow-out nozzle 23, first compacting means 30 are attached to the machine frame 10 for compacting the concrete of .the bottom layer 110. In the embodiment shown, the compacting means 30 comprise a vibrator shoe 31 for each hollow channel 104 to be made, and a motor 32 coupled to the vibrator shoe 31 for giving the vibrator shoe 31 a vibrating motion. For each vibrator shoe 31 a separate motor can be provided, but the motor 32 is preferably coupled to several vibrator shoes 31. The vibration of the vibrator shoe 31, at a vibration frequency of typically approximately 3,000-9,000 Hz and an amplitude of typically less than approximately 1 mm, causes the thixotropic concrete mass to become fluid so that it compacts and beds to the contour of the vibrator shoes 31. During making the construction element 100, the apparatus 1 moves continuously forwards (in the direction FI) , so that at a given moment the vibrator shoes 31 have left the bottom layer 110, which can be regarded as the termination of a first cycle of operations, wherein, of the construction element: 100 to be made, the lower side 101 and the lower portion 111 of the channel walls 104 have been made. Further, near the rear side of the machine frame 10, a second concrete-pouring element 40 is attached thereto for pouring a second concrete layer 120 on to the bottom layer 110. The concrete-pouring element 40 comprises a storage vessel 41 for the concrete 42 to be poured, and a flow-out nozzle 43 for delivering the concrete 42, which preferably has a composition identical to that of the concrete 22 of the bottom layer 110. If so desired, the storage vessels 21 and 41 are coupled to a common storage vessel or a common supply line, or, instead of two separate storage vessels 21 and 41, a common storage vessel is present. The flow-out nozzle 43 can have a width that corresponds to that of the construction element 100 to be made, but several narrower flow-out nozzles can also be provided side by side. Near the flow-out nozzle 43, second compacting means 50 are attached to the machine frame 10 for compacting the concrete of the second layer 120. In the embodiment shown, the compacting means 50 comprise a vibrator plate 51 having a lower side whose contour corresponds to the desired contour of the upper side 102 of the construction element 100 to be made, and can comprise, for instance, as shown, a single flat vibrator plate 51 having a width that corresponds to that of the construction element 100 to be made. Further, the compacting means 50 comprise a motor 52, coupled to the vibrator plate 51, for giving the vibrator plate 51 a vibrating motion. For instance, the motor 52 can cause the vibrator plate 51 to vibrate at the same vibration frequency and amplitude as the vibrator shoes 31. Further, recess elements 60 are attached to the machine frame 10 which extend from the vicinity of the vibrator shoes 31 to beyond the vibrator plate 51, for ensuring that the hollow channels 104 are made in the construction element 100 to be made, which recess elements 60 comprise per channel a bar or, preferably, a hollow pipe 61 with a contour that corresponds to the definitive contour desired for the channels 104. In practice, and as shown in Fig. 3B, the pipes 61 often have an oval shape. The vibration of the vibrator plate 51 causes the thixotropic concrete mass to become fluid, so that it compacts and flows between the pipes 61 and, on the upper side, beds to the contour of the vibrator plate 51 (see Fig. 3B) . hen the second concrete-pouring element 40, the compacting means 50 and the pipes 61 have been passed, the concrete 22, 42 is left in the final shape of the construction element 100 to be made (see Fig. IB) . The concrete 22, 42 is, although, of course, not yet set, strong enough to maintain this shape during setting. Coupled to the pipes 61 is a motor 62 for causing the pipes 61 to carry out a vibrating motion in their longitudinal . direction, as indicated by the arrow F2 in Fig. 2A, so as to reduce the friction between the pipes 61 and the concrete 22, 42. This vibrating motion has, for instance, a frequency of approximately 5 Hz and an amplitude of approximately 6 mm ' . In the apparatus known in practice, there is a space 70 between the vibrator shoes 31 and the pipes 61, to prevent the respective vibrating motions of the vibrator shoes 31 and the pipes 61 from influencing each other. The length of that space, measured in the longitudinal direction of the pipes 61, should be at least equal to the amplitude of the vibrating motion F2 of the pipes 61, increased by the greatest cross dimension of the gravel grains present in the concrete 22, 42, and can in practice be approximately 30 mm. Over that length, the channel wall portions 111, formed in the first cycle of operations, have no support. In this connection, one should bear in mind that the channel wall portions 111, self- supporting in the space 70, near the vibrator shoes 31 are still affected by the vibrating motion of the vibrator shoes 31, i.e., these channel wall portions 111 are shaking without support and the material 22 at that position is still relatively fluid. To prevent these channel wall portions ill from "collapsing", the height thereof should remain relatively small. Further, the dimensions of the pipes 61 are smaller than the corresponding dimensions of the vibrator shoes 31, as shown in more detail in Fig. 4A, to prevent the pipes 61 from scraping along the poured concrete 22 of the bottom layer 110 during a forward movement (see Fig. 4B) . This results in the complications mentioned hereinabove. Fig. 4C illustrates that for applying the second concrete layer 120, the concrete 42 should flow deep between the pipes 61, and that the slit 121 between the pipes 61 and the bottom layer 110 should be filled up, for which purpose the concrete 22, 42 should be relatively fluid. The apparatus according to the invention does not have these drawbacks, because, as is illustrated in Fig. 5A, the space 70 between the vibrator shoes 31 and the pipes 61 is filled up with a flexible filling piece 200. Fig. 5A clearly shows that the flexible filling piece 200 does not need to be as high as the vibrator shoes 31 and the pipes 61. At- least over the height at which the vibrator shoes 31, the flexible filling piece 200 and the pipes 61 contact the poured concrete- 22, the flexible filling piece 200 has a contour that forms a . gradual transition from the contour of the vibrator shoes 31 to the contour of the pipes 61. Preferably, and as indicated in Figs 5A-B, the vibrator shoes 31, the flexible filling piece 200 and the pipes 61 have identical contours and identical dimensions at the positions mentioned. When the improved apparatus according to the invention is used in making a concrete construction element 100, in the first cycle of operations the wall portions can be formed to a greater height, a concrete can be used wh ~h is less fluid, and a better adhesion of the concrete to the pre-stress bars is realized, while the number of parameters to be controlled is smaller, the values of these parameters to be set are less critical, and the percentage of rejects has decreased. Figs 5A-B illustrate a preferred embodiment of the flexible filling piece 200 which can readily be mounted between a vibrator shoe 31 and a pipe 61. This can be useful in practice, because the flexible filling piece 200, which may for instance be made of a flexible material like rubber, can be subject to wear resulting from the grinding action of the concrete brushing against it and thus needs to be quickly replacable. On the ends of the flexible filling piece 200, that can have a length of approximately 12 cm, which length proved to be suitable, flanges 201 and 202 are mounted, for instance by gluing, corresponding to flanges 35 and 65 mounted on the vibrator shoe 31 and the pipe 61. The flexible filling piece 200 with the flanges 201 and 202 can readily be slid from below over the flanges 35 and 65 of the vibrator shoe 31 and the pipe 61, until the flanges 201 and 202 abut against respectively the mounting strips 36 and 66 mounted on the vibrator shoe 31 and the pipe 61. Accordingly, the flanges 201, 202 can be mounted on the respective mounting strips 36 and 66, for instance and as shown by means of mounting screws 37 and 67.

Claims: _ ___τ__2. 1. An apparatus (1) for making concrete construction elements (100) having hollow channels (104) extending in the longitudinal direction of said concrete construction elements (100) , comprising: a first concrete-pouring element (20) for applying on the work floor (12) a bottom layer (110) for the construction element (100) to be made; . first compacting means (30) for compacting the concrete of the bottom layer (110) ; a second concrete-pouring element (40) for pouring a second concrete layer (120) on to the bottom layer (110) ; second compacting means (50) for compacting the concrete of the second layer (120) ; and recess elements (60) for ensuring that the hollow channels (104) are made in the construction element (100) to be made; characterized in that flexible filling elements (200) are provided between the first compacting means (30) and the recess elements (60) , whose contour, at least on the lower side and at least partially on the lateral side, forms a gradual transition from the contour of the first compacting means (30) to the contour of the recess elements (60) . 2. An apparatus according to claim l, characterized in that at said positions, the first compacting means (30) , the flexible filling elements (200) and the recess elements (60) have identical contours and identical dimensions. 3. A method for making concrete construction elements (100) having hollow channels (104) extending in the longitudinal direction thereof, characterized in that an apparatus (l) according to claim 1 or 2 is used. 4. A concrete construction element (100) having hollow channels (104) extending in the longitudinal direction thereof, characterized in that it is made by means of an apparatus (1) according to claim 1 or 2.

Inventors: TEUNISSEN LAMBERT, TEUNISSEN, LAMBERT
Applicants: VBI ONTWIKKELING BV, VBI ONTWIKKELING B.V.
Application year: 1993
Main classification: B28B1
IPC codes: B28B1, B28B13