A METHOD OF CASTING CONCRETE OBJECTS AND A FORM HEREFOR

Description

[0001] This invention refers to a method of casting elongated, hollow, thin-walled concrete objects, such as concrete posts, in which fluid concrete is pumped into a form or mould.

[0002] The invention also relates to a form or mould for the manufacture of such cast concrete objects.

[0003] Pumping of concrete into a form or mould has recently become common practice for producing various concrete products.

[0004] However, in the conventional manufacture of concrete objects, such as concrete posts or pillars for example, wet concrete is normally poured into a form and vibrated or centrifuged.

[0005] When vibrating the concrete, excesses of air are liable to be drawn into the fluid concrete mass and to form air bubbles therein, which result in irregular surface structures when the concrete hardens.

[0006] Such air bubbles also amass around the reinforcing elements cast in the concrete object, causing the mechanical strength properties of such elements to be impaired.

[0007] In conventional concrete casting techniques, attempts are sometimes made to accelerate curing or hardening of newly cast concrete by applying heat thereto. This causes entrapped air bubbles to expand and subsequently the concrete to burst, therewith to form microcracks in the concrete mass. Consequently, it is necessary to wait until the concrete has hardened at least partially, normally after some few hours, before applying heat thereto. This slows down the production rate and lowers the overall efficiency of the expensive form equipment used.

[0008] There is known to the art-cf. DE-A-1 683 945 (Rocla Concrete Pipes)-a method in the manufacture of concrete pipes which incorporate prestressed reinforcements, in which the inner wall of the concrete pipe is subjected to the effect of a pressurised medium prior to the concrete hardening completely so as to stretch the pipe and tension the reinforcing elements. The method is particularly characterized by using a form constructed from an elastic material, so as to enable the reinforcing elements to be given the tension desired. Since the reinforcing elements can be prestressed in other, simpler ways, however, this particular known method would not be seen to be of any great practical significance.

[0009] SE-B-308 270 (Jasba-Keramikfabriken) describes a method in which hydraulic pressure is employed in the casting of ceramic moulded bodies. The primary object in this case is to force water into the absorbent form more quickly. The method described in this publication, however, cannot be applied when manufacturing, for example, thin-walled concrete posts of great lengths.

[0010] SE―B―331 646 (Construction Techniques) describes the method of casting concrete objects in a closed form while using a concrete porridge containing an excess of water. In accordance with this known method the form is filled with cement porridge and the cement then subjected to an overpressure applied to the form, so as to drive water out through a filter lining. This method cannot be applied when casting objects of the kind for which the present invention is intended.

[0011] This also applies to the method described in SE-B-355 745 (Deutsche Bauakademie) in accordance with which concrete objects are produced by compressing fresh concrete in forms with the aid of vacuum techniques.

[0012] DE-A-2 204 685 (Gismondi) describes a more or less conventional concrete casting process in which concrete is poured into a form and compressed by expanding flexible bodies within the form.

[0013] DE-C-295239 (van der Daehle & Co) describes a process in which concrete by gravity is fed from a container into a sloping form. A rotatable means accomplish stirring and an excentric wheel contributes to the feeding and forms a closable valve or damper when the form has been filled. Pressurized air acts on the concrete surface in the container.

[0014] DE-Al-3 302 469 (VEB Betonleichtbaukom- binat) describes an open rather conventional form into which concrete is poured from above. Steam is supplied via a pipe within the form core to accomplish a heat treatment of the concrete.

[0015] FR-A-619 754 (Frote) describes a process in which concrete in a vertical or sloping container with the aid of pressurized air is supplied into a form which may be conical.

[0016] FR-A-2 058 742 (Reed) describes a rather complicated movable form-arrangement into which concrete is injected by means of a piston- cylinder unit.

[0017] DE-B-1 058 908 (Max Giese Stahlbetonbau) describes another known method in which a paper-layer is wound around a metal core in a concrete form.

[0018] One object of the present invention is to provide a method of the aforesaid kind in which the disadvantages of known and conventional methods are avoided, and in which cast concrete objects of higher quality can be produced more quickly with more efficient use of the form equipment.

[0019] A further object is to provide a method for the manufacture of elongated, thin-walled hollow concrete constructions, for example posts and pillars, which exhibit advantageous mechanical strength properties and superior surface structures.

[0020] In its widest aspect the method according to the present invention is mainly characterized by utilizing the generated pump pressure to maintain the concrete under pressure while the concrete hardens in the form and supplying heat to the pressurized hardening concrete mass in the form while pumping it into the form.

[0021] By holding the concrete under pressure during the hardening or curing process, the formation of cracks, which always occur when applying conventional concrete casting techniques, is practically completely avoided.

[0022] Heat is applied to the concrete mass pumped into the form, in order to accelerate the curing process. Distinct from prior art techniques in this respect, the present invention constitutes an essential step forward in the art, since in accordance with the invention heat can be applied directly when or substantially directly when pumping the concrete into the form.

[0023] The concrete mass is suitably held under a pressure of 1-2 Mpascal, i.e. from about 10-20 kp/cm², or at higher pressures in certain cases. Pronounced positive results, however, can be obtained by pumping at far lower over-pressures, for example, pressures in the region of 1-2 kp/cm² or even less. A slight overpressure as small as a few hundred pascal may in some cases be sufficient to obtain the desired result, i.e. no cracks in the surface of the cast product.

[0024] A concrete pump of conventional design used when applying the method according to the invention generates in the concrete mass a pressure of from 10-20 kp/cm². Consequently, when applying the method according to the invention the pump can be kept running subsequent to having filled the form with concrete, during the time taken for the concrete to harden.

[0025] In practice, however, subsequent to filling a form with concrete, the concrete is held under pressure by holding a valve means located in the vicinity of the form-inlet opening closed while the pump is still operating.

[0026] The valve means is preferably of simple construction, and may advantageously comprise a flat plate or disc arranged to close and open the form inlet.

[0027] When the concrete is held under pressure in the form, there is no tendency towards the formation of microcracks in the concrete. Because heat can be applied at a much earlier stage in the curing or hardening process, the concrete grows in mechanical strength much more quickly than would otherwise be the case.

[0028] This means in practice that in the event of a core being used in the casting process, the concrete has become sufficiently strong, or rigid, for the core to be removed within the space of only from 1 to 2 hours.

[0029] After a further 1-2 hours have lapsed, i.e. from 2-4 hours of commencing the casting operation, the outer form can be opened and the hardened concrete object removed from the form, therewith leaving the form free for a further casting operation. Heat is applied through the agency of a suitable fluid, such as air, and/or steam, which is distributed through a first perforated tube, extending centrally through the form core, and through a second perforated tube, located beneath the form. The fluid is preferably heated to a temperature of at least 40°C, and suitably to a temperature of from 60-90°C.

[0030] When concrete is pumped into the form and held under pressure therein, air enclosed in the form will be effectively expelled therefrom. This, in turn, affords the following advantages: the air content of the concrete will be at a minimum; resultant concrete surfaces exposed by the air will be devoid of air pores; and the concrete will seat firmly around the reinforcing elements, located in the cast concrete objects, i.e. no air cushions will form in the immediate close vicinity of the reinforcing elements.

[0031] Another important advantage is that when applying the method according to the invention it is not necessary to vibrate the form or the concrete mass therein.

[0032] The invention relates to an advantageous method of manufacturing elongated, thin-walled, concrete objects, such as concrete posts, for example. In accordance with the invention, the concrete is preferably pumped into the form through one end thereof in an axial direction, and air present in the form is permitted to leave in the vicinity of the other end of the form.

[0033] When manufacturing posts, or similar concrete objects, of conical tapering cross-section, the concrete is preferably pumped into the narrow end of the form.

[0034] When manufacturing conical objects, where the form has arranged therein a core which tapers conically towards one end thereof, the narrow end of the core is preferably given a greater conicity than the remainder of the core. The core therewith obtains a pointed tip which facilitates the flow and distribution of the pumped concrete in the form. In addition hereto, there is formed in the cured concrete object a thickened and stiffening end part which improves the mechanical strength of the object.

[0035] When manufacturing a hollow object, for example, a hollow concrete post, where the form accommodates a core supported by core support means, the core supports can be withdrawn to a location outside the form, subsequent to filling the form with concrete and leaving the pump operating, so that the core is supported in the form substantially solely by the concrete under pressure in its form.

[0036] This results in a fully homogeneous concrete object exhibiting totally smooth and uniform surfaces. The resultant concrete object compares very closely to a cast steel object.

[0037] The concrete used in accordance with the invention is suitably a high-quality class concrete, K 80 MPa-K 120 MPa. The concrete shall have a pumpable consistency and a setting or slump value of little more than 25 cm. The reinforcement may comprise pretensioned rod, a box reinforcement or shear reinforcement being optionally arranged in the close proximity of the ends of the object.

[0038] The invention also relates to a form for use when applying the method according to the invention, the main characterizing feature of the form being set forth in the following claims.

[0039] An embodiment of the invention will now be described in more detail with reference to the accompanying schematic drawings.

Fig. 1 is a side view of a two-part form for manufacturing hollow, conical concrete posts having lengths, for example, of 30 meters, and an associated concrete pump.

Fig. 2 is a sectional view, in larger scale, of the forward and rearward end of the form illustrated in Figure 1, in a state ready to receive concrete from the pump.

Fig. 3 is a corresponding sectional view of the form illustrated in Figure 1, subsequent to concrete having been pumped into the form and the concrete has begun to harden and removal of the core from the form has commenced.

[0040] The concrete pump illustrated in Figure 1 may have a working pressure of 1-3 MPa. The pump co-acts with a concrete-mass collecting cone 2 and is connected, via a distribution line 3, and a connecting flange 4, with a form 5, described in more detail hereinafter.

[0041] When seen horizontally the form 5 narrows conically towards the connecting flange 4, and may have a length, for example of 30 meters. The form is divided into two parts longitudinally and is constructed to enable it to absorb the axial forces to which the reinforcements are subjected when tensioning the same. The form is also able to absorb radially acting forces generated through the concrete pump 1 and as a result of expansion of the concrete as it hardens. The narrow end of the form 5 merges with a conduit 6, having at one end thereof a connecting flange 7 which lies against the flange 4 of the distribution line 3.

[0042] The conduit 6 is also arranged to co-act with a closable and openable valve plate 8, and is provided with a holding-on device 9 for co-operation with the prestressing steel. The reinforcing lines 10 are tensioned by means of tensioning devices 11, having an active dolly-plate 12, at the other end thereof. Located beneath the form is a longitudinally extending perforated tube or pipe 13, through which steam is dispensed for heating the concrete.

[0043] The form accommodates a core 20, the major part of which has a conicity corresponding to that of the form. The conicity of the narrower end 20a of the core is greater than that of the major part of the core, therewith to form a pointed tip 20b. In this way, the core will facilitate distribution of the pumped concrete in the form.

[0044] Located centrally along the core is a perforated pipe or tube 21, through which hot air is distributed to the surrounding concrete, through the outer surface of the core.

[0045] The core is reinforced and held together by lines 22, extending therewithin, these lines being anchored in the vicinity where the core exhibits its greatest conicity, and at the thick end 23 of the core. The lines are tensioned to the extent desired by means of a tensioning device 24, located at the thick end of the core.

[0046] As concrete is pumped into the form 5, the core 20 is held in position in the outer form 5, by means of radially movable core supports 25, which support the core radially, and by means of bolts 26, having nuts 27, which secure the position of the core in the axial direction.

[0047] When a post is to be cast in the form 5, both the outer form 5 and the core 20 are first treated with a suitable form oil. Reinforcements in the form of lines 10 are then positioned in the form 5 together with the core 20, which is held in position by core supports 25 and nuts 30, respectively. The outer form is then closed and the reinforcement elements tensioned with the aid of the tensioning devices 11, on the periphery of the form 5. The concrete pump is then connected to the form, by connecting the flange 4 to the flange 7 of the conduit 6. The concrete can now be pumped in between the form 5 and the core 20, at the same time as air enclosed in the form is forced/evacu- ated therefrom through holes 38. Subsequent to filling the form with concrete, and with the pump still working, cf. Figure 3, the holes 38 are plugged by threaded plugs 39 and the core supports 25 are withdrawn radially from the form, and the valve plate 8 is moved to its conduit closing position. The entire form is then covered (not shown) to reduce heat losses during the concrete hardening or curing process..

[0048] The concrete mass 5 enclosed under pressure in the form is heated immediately upon completion of the pumping action. Heating of the concrete mass 5 is effected via the core 20 by passing hot air through the perforated pipe 21, and via the outer form by passing steam through the perforated pipe 13. In order to avoid microcracks forming in the concrete mass 32, and simultaneously obtaining a rapid growth in mechanical strength, a rapid temperature increase up to about 60°C is effected. After 1-2 hours, the concrete is sufficiently strong to enable the core to be withdrawn without damaging the concrete.

[0049] As a result of locking the pretensioned lines 22, within the core 20, against the form 5, through various holding-on devices 35, and eliminating the hydraulic pressure on the tensioning device 24 in the core, the pretensioning forces in the lines loosen and withdraw the core from the surrounding concrete. When the core has loosened in the concrete, it is withdrawn from the concrete and the outer form with the aid of a winch (not shown).

[0050] Depending upon the requirements placed on the detensioning strength of the concrete, the finished concrete post can be lifted from the form 5, from two to four hours from the time at which the form was filled with concrete.

[0051] As will be understood the valve-plate 8 may be replaced with other means for ensuring that the concrete is held under pressure in the form 5. Alternatively, the valve means may be dispensed with altogether and the pump allowed to run until the concrete has hardened sufficiently. Another alternative is one of providing suitable means for this purpose.

[0052] When the pump is shut off and the valve or other means brought into place the overpressure in the concrete mass is normally somewhat reduced for instance from 1.5 Mpascal to about 0.8 Mpascal or the like.

Claims

1. A method of casting elongate, hollow, thin-walled concrete objects such as concrete posts, in a form or mould intended therefor, comprising pumping the concrete into the form, characterized by utilizing the generated pump pressure to maintain the concrete under pressure while the concrete hardens in the form, and supplying heat to the pressurized hardening concrete mass in the form while pumping it into the form.

2. A method according to Claim 1, characterized by maintaining the concrete under pressure in the form by holding a valve means located in the vicinity of the form inlet opening closed subsequent to filling the form with concrete and with the pump still working.

3. A method according to Claims 1 or 2, characterized in that the heat is supplied through the agency of a hot fluid distributed through a perforated pipe arranged centrally in the mould core, and through a perforated pipe located beneath the form.

4. A method according to any one of Claims 1-3 for manufacturing elongated, for example post-like objects of conically tapering cross-section in which the form accommodates a core, which tapers conically towards one end thereof, characterized by giving the narrow end of the core a conicity greater than the remainder of said core, therewith to form a pointed tip, effective to facilitate the flow and distribution of the concrete pumped into the form, so that there is formed a relatively thick and rigidifying end part in the hardened concrete object.

5. A method according to Claim 4, characterized by permitting air entrapped in the form to depart therefrom through holes located in the vicinity of the widened end of the form, and plugging the holes with bolts subsequent to filling the form with concrete.

6. A form for casting elongated hollow, thin-walled, concrete objects, such as concrete posts according to the method of any of the preceding claims, said form having an inlet opening (61) for connection to the outlet or supply line (3) of a concrete pump, characterized in that the inlet opening (6a) is provided with or adapted to co-act with means, for example valve means (8), effective to hold the concrete pumped into the form under pressure during the hardening process of the concrete and in that the form is provided with means (13; 21) for supplying heat to the concrete mass in the form while pumping it into the form.

7. A form according to Claim 6, having arranged therein a core (20) supported by core supports (25) for the manufacture of hollow objects, characterized in that the core supports (25) can be withdrawn to a position externally of the form (5) wherewith subsequent to filling the form with concrete and with the pump still working, the core supports (25) are arranged to be withdrawn so that the core is supported substantially by the concrete under pressure in the form.

8. A form according to Claims 6 or 7, and accommodating a conically tapering core (20), characterized in that the narrow end (20a) of the core has a conicity that is greater than the remainder of the core, to form a pointed tip, facilitating the flow and distribution of the concrete pumped into the form and contributing to provide a thickened and rigidifying end part of the cast concrete object.

9. A form according to any of Claims 6-8, characterized in that in the end opposite to the inlet end of the form there are provided holes (38) permitting air entrapped in the form to depart therefrom when the concrete is pumped into the form, said holes being plugged by threaded plugs (39) when the form is filled.

Ansprüche

1. Verfahren zum Gießen langgestreckter, hohler, dünnwandiger Betongegenstände wie Betonpfosten in einer dafür vorgesehenen Form, bei dem der Beton in die Form gepumpt wird, gekennzeichnet durch Ausnutzung des erzeugten Pumpdrucks zum Halten des Betons unter Druck, während der Beton in der Form härtet, und Zufuhr von Wärme zur unter Druck gesetzten, härtenden Betonmasse in der Form während ihres Einpumpens in die Form.

2. Verfahren nach Anspruch 1, gekennzeichnet durch Halten des Betons unter Druck in der Form durch Geschlossenhalten einer Ventileinrichtung, die sich im Bereich der Formeinlaßöffnung befindet, in Anschluß an das Füllen der Form mit Beton bei noch arbeitender Pumpe.

3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Wärme vermittels eines heißen Fluids zugeführt wird, des durch ein mittig im Formkern angeordnetes perforiertes Rohr und durch ein unterhalb der Form sitzendes perforiertes Rohr verteilt wird.

4. Verfahren nach einem der Ansprüche 1-3 zur Herstellung langgestreckter, beispielsweise pfostenartiger Gegenstände mit konisch zulaufendem Querschnitt, bei dem die Form einen Kern aufnimmt, der sich konisch zu seinem einen Ende hin verjüngt, gekennzeichnet durch das Vorsehen einer größeren Konizität am engen Ende des Kerns als am Rest des Kerns, derart, daß eine zulaufende Spitze gebildet wird, die zum Erleichtern des Flusses und der Verteilung des in die Form eingepumpten Betons wirkt, so daß ein relativ dicker und versteifender Endteil im gehärteten Betongegenstand gebildet wird.

5. Verfahren nach Anspruch 4, gekennzeichnet durch das Entweichenlassen von in der Form eingeschlossener Luft durch Löcher, die sich im Bereich des erweiterten Endes der Form befinden, und Verstöpseln der Löcher mit Schrauben in Anschluß an das Füllen der Form mit Beton.

6. Form zum Gießen langgestreckter, hohler dünnwandiger Betongegenstände wie Betonpfosten nach dem Verfahren nach einem der vorangegangenen Ansprüche, wobei die Form eine Einlaßöffnung (61) zur Verbindung mit dem Auslaß oder der Zufuhrleitung (3) einer Betonpumpe hat, dadurch gekennzeichnet, daß die Einlaßöffnung (6a) mit Mitteln versehen oder zum Zusammenwirken damit eingerichtet ist, beispielsweise einer Ventileinrichtung (8), die so wirken, daß der in die Form eingepumpte Beton während des Härtungsvorgangs des Betons unter Druck gehalten wird, und daß die Form mit Mitteln (13; 21) zur Zufuhr von Wärme zur Betonmasse in der Form während ihres Einpumpens in die Form versehen ist.

7. Form nach Anspruch 6, die einen in sich angeordneten, von Kernträgern (25) getragenen Kern (20) für die Herstellung von hohlen Gegenständen hat, dadurch gekennzeichnet, daß die Kernträger (25) in eine Position außerhalb der Form (5) zurückgezogen werden können, wobei in Anschluß an das Füllen der Form mit Beton bei noch arbeitender Pumpe die Kernträger (25) zum Zurückziehen angeordnet sind, so daß der Kern im wesentlichen durch den Beton unter Druck in der Form getragen ist.

8. Form nach Anspruch 6 oder 7, in der ein konisch zulaufender Kern (20) aufgenommen ist, dadurch gekennzeichnet, daß das enge Ende (20a) des Kerns eine Konizität hat, die größer als der Rest des Kerns zur Bildung einer zulaufenden Spitze ist, die den Fluß und die Verteilung des in die Form eingepumpten Betons erleichtert und zur Schaffung eines verdickten und versteifenden Endteils des gegossenen Betongegenstandes beiträgt.

9. Form nach einem der Ansprüche 6-8, dadurch gekennzeichnet, daß in dem dem Einlaßende der Form gegenüberliegenden Ende Löcher (38) vorgesehen sind, die ein Entweichen von in der Form eingeschlossener Luft ermöglichen, wenn der Beton in die Form eingepumpt wird, wobei die Löcher durch Gewindestöpsel (39) verstöpselt werden, wenn die Form gefüllt ist.

Revendications

1. Procédé de coulée d'objets en béton creux de forme allongée, à paroi mince, tels que des poteaux en béton, dans un moule ou une forme prévus pour cette coulée, consistant à refouler le béton dans le moule, caractérisé en ce qu'on utilise la pression de refoulement ainsi engendrée pour maintenir le béton sous pression pendant que le béton durcit dans le moule, et on apporte de la chaleur à la masse de béton mise sous pression en cours de durcissement, qui est contenue dans le moule pendant qu'on refoule le béton dans le moule.

2. Procédé selon la revendication 1, caractérisé en ce qu'on maintient le béton sous pression dans le moule en maintenant fermés des moyens du type vanne placés dans le voisinage de l'ouverture d'entrée du moule, après qu'on ait rempli le moule de béton et alors que la pompe est encore en action.

3. Procédé selon la revendication 1 ou 2, caractérisé en ce que la chaleur est apportée par l'intermédiaire d'un fluide chaud qui est distribué au moyen d'un tube perforé placé en position centrale dans le noyau du moule et au moyen d'un tube perforé placé au-dessous du moule.

4. Procédé selon l'une quelconque des revendications 1 à 3, pour fabriquer des objets de forme allongée, par exemple du type porteaux, possédant une section qui decroît en cône, dans lequel le moule renferme un noyau qui possède une section qui décroît en cône vers une de ses extrémités, caractérisé en ce qu'on donne à la petite extrémité du noyau une conicité plus forte que celle du reste du noyau pour former ainsi une pointe effilée, qui a pour effet de faciliter l'ecoule- ment et la repartition du béton refoulé dans le moule, de sorte qu'il se forme une partie d'extrémité relativement épaisse et raidisseuse dans l'objet en béton durci.

5. Procédé selon la revendication 4, caractérisé en ce qu'on laisse l'air emprisonné dans le moule s'en échapper à travers des trous ménagés dans le voisinage de l'extrémité élargie du moule, et on bouche les trous à l'aide de vis après que le moule a été remplie de béton.

6. Moule ou forme pour couler des objets en béton creux de forme allongée, à paroi mince, tels que des poteaux en béton, conformément au procédé selon l'une quelconque des revendications précédentes, ledit moule présentant une ouverture d'entrée (61) destinée à être raccordée à la conduite de sortie ou d'alimentation (3) d'une pompe à béton, caractérisé en ce que l'ouverture d'entrée (6a) est prévue ou adaptée pour coopérer avec des moyens, par exemple des moyens du type vanne (8), qui ont pour effet de maintenir sous pression le béton refoulé dans le moule pendant le processus de durcissement du béton, et en ce que le moule est équipé de moyens (13; 21) pour apporter de la chaleur à la masse de beton contenue dans le moule pendant qu'on refoule le beton dans le moule.

7. Moule selon la revendication 6, renfermant un noyau (20) agence dans ce moule et supporté par des supports de noyau (25), pour la fabrication d'objets creux, caractérisé en ce que les supports de noyau (25) peuvent être retractés à une position située à l'exterieur du moule (5) alors que le moule a été rempli de béton et que la pompe est encore en action et les supports de noyau (25) sont agencés pour pouvoir être retractes de telle manière que le noyau soit supporté pratiquement par le béton sous pression contenu dans le moule.

8. Moule selon la revendication 6 ou 7, et contenant un noyau dont la section se rétrécit en cône (20), caractérisé en ce que la petite extrémité (20a) du noyau possédé une conicité plus forte que celle du reste du noyau, pour former une pointe effilée, en facilitant ainsi l'écoulement et la répartition du béton refoulé dans le moule et en contribuant ainsi à former une partie d'extrémité épaissie et raidisseuse dans l'objet en béton coulé.

9. Moule selon une quelconque des revendications 6 à 8, caractérisé en ce que, dans l'extrémité qui est à l'opposé de l'extrémité d'entrée du moule, sont ménagés des trous (38) qui laissent l'air emprisonné dans le moule s'échapper de ce moule lorsque le béton est refoulé dans le moule, lesdits trous étant bouchés par des bouchons visses (39) lorsque le moule est rempli.

Drawing