GB1594070A

GB1594070A - Devices for pre-heating concrete before pouring

Info

Publication number: GB1594070A
Application number: GB1093378A
Authority: GB
Original assignee: Electricite de France SA
Current assignee: Electricite de France SA
Priority date: 1977-03-24
Filing date: 1978-03-20
Publication date: 1981-07-30
Also published as: BR7801810A; FI780925A; FR2385289A1; FI62244C; FI62244B; CA1103295A; FR2385289B1; AT353465B; ATA214378A

Description

(54) IMPROVEMENTS TO DEVICES FOR PRE-HEATING CONCRETE BEFORE POURING (71) We, ELECTRICITE DE FRANCE (SERVICE NATIONAL) of 2, rue Louis Murat, 75008 Paris, France, a French Company, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention concerns the preheating of concrete and has more particularly for an object an improved device for preheating concrete just before pouring.

It is known that it is advantageous, for improving the setting of concrete, to pre-heat it before pouring into shuttering or moulds.

Generally this heating is achieved with steam.

Recently, it has been suggested to heat the concrete in a horizontal bucket on a working site, before its use, by means of metal plates forming electrodes between which is applied an electric current, the mass of the concrete between these electrodes acting as an electric resistor and so heating up by Joule effect. In this case an electric current is passed through the concrete for ten minutes or so to bring it to a temperature of about 50"C, the concrete thus pre-heated being directly poured into the usual shuttering.

The electrical pre-heating of concrete is particularly advantageous for it permits an excellent use of the electrical energy, the kilowatts used being transformed, with a yield substantially equal to unity, into heat for directly heating the concrete whose temperature may thus rapidly reach 50 , as indicated previously. Furthermore, if the concrete thus pre-heated to 50 is poured into lagged shuttering, the dismantling of the shuttering can be carried out in a very short time while avoiding heating in the mass or through the shuttering which has overall an inferior yield.

Present devices for the electric heating of concrete use horizontal buckets which it is necessary to set upright again before the pouring of the pre-heated concrete; now this setting upright requires the use of a crane which may break down and in this case the concrete sets in the bucket which becomes unusable and which must be overhauled at great cost. Moreover, known devices use parallel electrodes which do not allow homogenous current densities to be obtained throughout the mass of fresh concrete, which leads to the formation of hot points and even the risk of causing the water contained in this concrete to boil, resulting in a reduction of the water content in the final concrete, and consequently a poor quality thereof.

The present invention has an object to overcome the above-mentioned disadvantages of known devices for pre-heating concrete before pouring. According to this invention we provide a device for pre-heating concrete before pouring, comprising: at least one bucket with a vertical axis which comprises, at its upper part, a first opening for introducing concrete to be preheated and, at its lower part, a second, closable, opening for discharging the preheated concrete;; a movable horizontal plate capable of closing said first opening and a set of elongated electrodes depending vertically from the lower face of the plate around a central vertical axis means for vertically moving said plate with said electrodes between an upper position, in which it is clear of said first opening and a lower position, in which the electrodes are immersed in any concrete in the bucket and the first opening is closed by said plate and for ensuring that in the lower position said central vertical axis coincides with the vertical axis of the bucket; and means for supplying the electrodes with current and for earthing the bucket.

Preferably, the electrodes have different lengths and sections, the longest electrode having the smallest section.

In a first application, the device serves for pre-heating concrete before pouring into shuttering on a working site and in this case it comprises furthermore a horizontal platform on which there is permanently disposed at least one bucket of the above-mentioned type, the platform having a discharge hole in register with the discharge opening of the bucket, a gallows which comprises a vertical upright fixed on the platform and a horizontal arm slidable on said upright, the free end of the arm carrying said set of electrodes; in the preferred embodiment, the platform carries two buckets and, in this case, it has two discharge holes, the horizontal arm of the gallows being not only slidably but also rotatably mounted on the upright, so that the set of electrodes may plunge at will into one or the other of the two buckets.

In a second application, the device serves for pre-heating concrete in an installation for producing concrete castings and in this case it comprises, in combination with a set of vertically mobile electrodes of the abovementioned type, several buckets, also of the above-mentioned type, able to come in their turn underneath said set of electrodes, means being provided for collecting the pre-heated concrete leaving a bucket underneath a said set of electrodes and for transporting this concrete to the place for casting said parts.

The concrete pre-heating device of the invention enables perfect homogeneity of heating of the concrete to be achieved since the arrangement provided for the electrodes affords an excellent distribution of the equipotential lines in the mass of the concrete, the electric field and so the current density being uniform in the mass of the concrete.

The invention will, in any case, be well understood from the detailed description which follows considered in combination with the accompanying drawings, which are, of course, given especially by way of illustration.

Fig. 1 shows, in perspective, an embodiment of a device according to the invention for pre-heating concrete before pouring on a working site.

Fig. 2 is a section, along Il-Il of Fig. 1, showing the arrangement of the electrodes.

Fig. 3 illustrates, similarly to Fig. 2, a variation of the shape of the electrodes.

Fig. 4 shows the distribution of the equipotential lines in the neighbourhood of an electrode of the type illustrated in Figs. 1 and 2.

Fig. 5 shows, in side eievation, a device according to the invention for pre-heating concrete in an installation for producing concrete castings in a workshop manufacturing such parts.

Fig. 6 shows, schematically and in elevation, another modification of the electrodes.

Fig. 7 shows, in section the arrangement of the electrodes of figure 6.

With reference to Figs. 1 to 4, there will first of all be described an embodiment of the invention for the electric pre-heating of concrete before pouring on a working site.

The device properly speaking is mounted on a horizontal plate or platform 1. This platform may carry one or more vertical buckets, particularly two buckets, as illustrated in Fig.

1, in which one of the buckets (bucket 2) is shown in continuous line and the other (bucket 3) schematically with a broken line. Netting 4 surrounds the device for safety's sake, netting 4 enclosing two chambers or boxes 5 and 6 in each of which is placed a bucket, respectively 2 and 3. On the input face is provided a sliding door 7 which may close either chamber 5 or chamber 6. In practice one of buckets 2 or 3 is in operation and the other in preparation, sliding door 7 being normally in front of the bucket in operation so as to ensure the safety of the workmen.

Platform l is provided therethrough with holes 8, 9, i.e. a hole opposite each bucket 2, 3. Around each hole 8, 9 there is disposed a support 10 for supporting a bucket such as 2 or 3.

A bucket such as 2 or 3 comprises essentially an upper cylindrical part lla and a lower conical part 1 lib, part 11b finishing in an aperture 12 which may be closed by means of a hood 13 operable by means of a wheel 13a. A hook 15 allows bucket 2 to be moved about axis 13v.

The concrete pre-heating device comprises also, in addition to bucket 2 or 3, a set of electrodes 14 with three electrodes 15a, 15b and 15c, made for example from stainless steel, whose arrangement can be seen in Fig. 2; these electrodes, in the form of glove fingers (i.e. closed at their lower end), are sectionally in the form of hollow circular sectors, with an angle at the apex a equal to 1200 in the case where there are three electrodes, as in the illustrated embodiment. These electrodes are carried by an upper circular shaped plate 16, which is pierced at right angles to the electrodes for the fixing of these latter.

Assembly 14 is supported by a gallows 17 comprising a vertical upright 18 fixed on platform 1 and a horizontal arm 19 vertically slidable on upright 18 for lifting or lowering assembly 14 out of bucket 2 or into bucket 3.

Furthermore, in the case where two (or more) buckets such as 2 and 3 are provided, mounted on platform 1, the same gallows 17 may serve for both buckets, the assembly of electrodes 14 being common to both buckets. In this case arm 19 may not only slide vertically along upright 18 but may also rotate about this upright, so that assembly 14 may cooperate with one or other of the two buckets.

From the electrical point of view, electrodes 15a, 15b and 15c are supplied with electric current, for example 500 amps at 380 volts, by a cable 20, whereas bucket 2 is connected to the electrical neutral which is connected to earth for ensuring the safety of the workmen.

The unit illustrated in Fig. 1 is for continuous operation, one of the buckets 2 being in operation while the other bucket 3 is being prepared for later operation. In one of the buckets (bucket 2) is fed the cement to be pre-heated, the opening 21 of this bucket being disengaged by removing assembly 14 from the bucket. Then once the bucket 2 is filled assembly 14 is lowered and electrodes 15a, 15b and 15c are supplied with current for five to ten minutes, for example to bring the cement to about 50"C. When the operation is finished, wheel 13a is actuated to move hood 13 and free opening 12 at the bottom of bucket 2. The cement flows through hole 8 and is collected by means such as a tip-wagon or truck for transporting it to the desired place or preferably is fed directly into a shuttering.

During the operation for heating the concrete in bucket 2, the other bucket (bucket 3) is charged with concrete. At the end of the operation for heating bucket 2, assembly 14 is raised by vertical movement of arm 19, then this arm is rotated so that assembly 14 is brought opposite the other bucket (bucket 3) then lowered and electrodes 15a, 15b and 15c are again supplied with current for preheating the concrete in bucket 3. Meanwhile, the cement is discharged from bucket 2, then this latter is again charged with concrete.

It can then be seen that continuous operation is effectively achieved by emptying, then loading one bucket whilst, in the other, the heating of the concrete is carried out.

In Fig. 3 are illustrated electrodes 35a, 35b and 35c having a hollow elliptical shape, also in the form of glove fingers closed at the lower part, which may be provided instead of electrodes 15a, 15b and 15c of Figs. 1 and 2.

In Fig. 4 are shown the equipotential lines E in a third of the drawing around electrode 15a and around centre 0. The equipotential lines in the whole drawing may be readily deduced therefrom. These curves show that the heating of the concrete is very homogenous.

There will now be described with reference to Fig. 5 an embodiment of the device according to the invention for the electric pre-heating of concrete in a workshop producing concrete castings.

In such a shop beams, flagstones, frontage blocks, shaped sections and similar pieces may be prefabricated from concrete. In this embodiment also there are provided several buckets, e.g. three buckets A, B and C, two only of which (buckets C and A respectively in positions 22 and 23) can be seen in Fig. 3 and a single set of electrodes 24. Buckets A, B and C are of the type shown at 2 in Fig. 1, whereas the set of electrodes 24 may be of the type shown at 14 in Fig. 1 and comprises three electrodes 25a, 25b and 25c having, in section, the shape shown in Fig. 2 (electrodes 15a, 15b and 15c of this Fig. 2) or the shape shown in Fig. 3 (electrodes 35a, 35b, 35c of this Fig. 3).

The unit shown in Fig. 5 comprises also an overhead crane 26 provided with a hopper 27 which goes and fetches aggregates and cement from storage hoppers not shown. The preparation of the concrete takes place in a mixer 28, of known type, which receives the cement and the aggregates from hopper 27 when this latter is brought by overhead crane 26 above mixer 28. Instead of overhead crane 26, a belt may be provided for bringing the aggregates and the cement to mixer 28.

Once the concrete is mixed in mixer 28, the lower opening 29 of this latter is disengaged and the freshly mixed concrete is collected in bucket A at position 23.

The three buckets (only two of which at 22 and 23 are shown) may move in a closed circuit, for example by means of a rail 30.

Bucket A in position 23 once filled with mixed concrete moves in the direction of arrow f to assume position 22 which was occupied by bucket C in Fig. 3, whereas bucket C moves to take up a third position in which it cannot be seen and bucket B comes to 23. Once bucket A is in place in position 22, the set of electrodes 24 is lowered into this bucket in position 22 by means of a hoist 31. Then, for the desired time, electric current is applied to the electrodes, bucket A at 22 being earthed. The pre-heating of the concrete in the bucket at 22 finished, the lower opening thereof is opened so as to let the pre-heated concrete, e.g. at 50"C, flow into a distributing vehicle 32. This vehicle, once filled, is brought to the casting moulds or shuttering, such as mould 33, into which it discharges a part of its charge through an endless screw distribution system 34.

It will be noted that in Fig. 5, for simplification thereof, the distributing vehicle 32 feeds rnould 33, whereas it is underneath the bucket at 22, but in general vehicle 32 moves from the position illustrated in Fig. 5 to the position for casting in mould 33, as previously indicated.

After closing the lower hole of bucket A at present at 22, this latter is moved to take up the third position not shown in which it may, for example, be cleaned by means of a shower type device. Meanwhile a new bucket (bucket B) which has been charged in the position illustrated at 23 is brought into the position illustrated at 22. When the concrete, in this new bucket B at position 22, has been pre-heated by electrodes 25a, 25b and 25c, then discharged into a distributing device 32, this bucket B is brought under the "shower" whereas bucket A which was originally at 23 and which was under the shower comes back to this position; finally bucket C comes back to position 22 illustrated in Fig. 5.

So that the arrival of each of the three buckets A, B and C in the three successive positions: filling position (illustrated at 23), pre-heating and emptying position (illus trated at 22) and cleaning position (not shown), may take place in the best conditions possible it is advantageous for the three buckets travelling in a closed circuit on rail 30 to be rigidly interlocked so that the automatic positioning at the three working stations is very accurate (one being in position, the other two being automatically so), whereas if the three buckets were independent it would be necessary to position each of the buckets at each of the stations.

The assembly of Fig. 5 enables the operation of mixing, pre-heating and pre-heated concrete casting to be automated whilst only heating the concrete at the last moment.

The starting of the heating, i.e. the switching on of electrodes 25a, 25b and 25c, may be controlled directly from vehicle 32; when the driver of this latter sees that his charge of pre-heated concrete, ready to be cast, will soon be exhausted, he controls the preheating of the concrete in the bucket which is at position 22; as the time for heating is of the order of five minutes, there is no storage of hot concrete and so no loss.Moreover, the driver may control, for example also from vehicle 7, the raising of unit 24 and the movement of the buckets from one position to the next position, after he has emptied the contents of the bucket at position 22; he will then control the lowering of unit 24 into the bucket which has just arrived at position 22 and the emptying into the bucket which has just arrived at position 23 of concrete coming from mixer 28; it is also the driver who may control the actuation of the "shower" which cleans the third bucket (not shown), which is the cleaning position.

It can then be seen that the device of the invention is particularly appropriate for heating concrete, whether it is to be used on a work site, in shuttering or in a shop manufacturing concrete parts.

As is evident and as it follows moreover already from what has gone before, the invention is in no wise limited to those of its embodiments and modes of application which have been more especially considered; it embraces, on the contrary, all variations thereof.

For example it is possible to have the electrode arrangement of Figs. 6 and 7 with three electrodes 45a, 45b, 45c, two of which (45a, 45b) are shorter but of larger diameter than the third electrode (45c). These three electrodes are located around a vertical axis of trace 0 on Fig. 7 and they are pending from plate 16. In this embodiment of Figs. 6 and 7, bucket 2a has an assymetrical shape, the opening 12 being eccentric.

With such an arrangement of the electrodes, a better distribution of the electric currents and an improved heating is obtained in the lower portion of the bucket.

WHAT WE CLAIM IS: 1. A device for pre-heating concrete before pouring, comprising: at least one bucket with a vertical axis which comprises, at its upper part, a first opening for introducing concrete to be preheated and, at its lower part, a second closable, opening for discharging the preheated concrete; a movable horizontal plate capable of closing said first opening and a set of elongated electrodes depending vertically from the lower face of said plate around a central vertical axis; means for vertically moving said plate with said electrodes between an upper position, in which it is clear of said first opening and a lower position, in which the electrodes are immersed in any concrete in the bucket and the first opening is closed by said plate, and for ensuring that in the lower position said central vertical axis coincides with the vertical axis of the bucket;; and means for supplying the electrodes with current and for earthing the bucket.

2. A device according to claim 1, characterised by the fact that said set comprises three electrodes in the shape of glove fingers closed at the lower end and having, in section, the shape of hollow circular sectors.

3. A device according to claim 1, characterised by the fact that said set comprises three electrodes in the form of glove fingers closed at the lower part and having, in section, the shape of hollow ellipses.

4. A device according to any one of the preceeding claims, characterised by the fact that said electrodes have different lengths and sections, the longest electrode having the smallest section.

5. An assembly of devices according to any one of the preceding claims, characterised by the fact that it comprises several buckets according to claim 1 and a single set of electrodes according to any one of the preceding claims, the set of electrodes or the buckets being movable so as to be able to cause the set of electrodes to cooperate with each of the buckets.

6. A device according to any one of the preceding claims for the pre-heating of concrete before pouring into shuttering on a work site, characterised by the fact that it comprises furthermore a horizontal platform on which is disposed at least one bucket the platform having a discharge hole in register with the second, discharge, opening of the bucket, a gallows which comprises a vertical upright fixed on the platform and a horizontal arm being slidably mounted on said upright, the free end of the arm carrying said set of electrodes.

7. A device according to claim 6, characterised by the fact that the platform carries two buckets and that it has two discharge holes, the horizontal arm of the gallows being

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. trated at 22) and cleaning position (not shown), may take place in the best conditions possible it is advantageous for the three buckets travelling in a closed circuit on rail 30 to be rigidly interlocked so that the automatic positioning at the three working stations is very accurate (one being in position, the other two being automatically so), whereas if the three buckets were independent it would be necessary to position each of the buckets at each of the stations. The assembly of Fig. 5 enables the operation of mixing, pre-heating and pre-heated concrete casting to be automated whilst only heating the concrete at the last moment. The starting of the heating, i.e. the switching on of electrodes 25a, 25b and 25c, may be controlled directly from vehicle 32; when the driver of this latter sees that his charge of pre-heated concrete, ready to be cast, will soon be exhausted, he controls the preheating of the concrete in the bucket which is at position 22; as the time for heating is of the order of five minutes, there is no storage of hot concrete and so no loss.Moreover, the driver may control, for example also from vehicle 7, the raising of unit 24 and the movement of the buckets from one position to the next position, after he has emptied the contents of the bucket at position 22; he will then control the lowering of unit 24 into the bucket which has just arrived at position 22 and the emptying into the bucket which has just arrived at position 23 of concrete coming from mixer 28; it is also the driver who may control the actuation of the "shower" which cleans the third bucket (not shown), which is the cleaning position. It can then be seen that the device of the invention is particularly appropriate for heating concrete, whether it is to be used on a work site, in shuttering or in a shop manufacturing concrete parts. As is evident and as it follows moreover already from what has gone before, the invention is in no wise limited to those of its embodiments and modes of application which have been more especially considered; it embraces, on the contrary, all variations thereof. For example it is possible to have the electrode arrangement of Figs. 6 and 7 with three electrodes 45a, 45b, 45c, two of which (45a, 45b) are shorter but of larger diameter than the third electrode (45c). These three electrodes are located around a vertical axis of trace 0 on Fig. 7 and they are pending from plate 16. In this embodiment of Figs. 6 and 7, bucket 2a has an assymetrical shape, the opening 12 being eccentric. With such an arrangement of the electrodes, a better distribution of the electric currents and an improved heating is obtained in the lower portion of the bucket. WHAT WE CLAIM IS:

1. A device for pre-heating concrete before pouring, comprising: at least one bucket with a vertical axis which comprises, at its upper part, a first opening for introducing concrete to be preheated and, at its lower part, a second closable, opening for discharging the preheated concrete; a movable horizontal plate capable of closing said first opening and a set of elongated electrodes depending vertically from the lower face of said plate around a central vertical axis; means for vertically moving said plate with said electrodes between an upper position, in which it is clear of said first opening and a lower position, in which the electrodes are immersed in any concrete in the bucket and the first opening is closed by said plate, and for ensuring that in the lower position said central vertical axis coincides with the vertical axis of the bucket;; and means for supplying the electrodes with current and for earthing the bucket.

not only slidably but also rotatably mounted on the upright, so that the set of electrodes may plunge into either of the two buckets.

8. A device according to any one of claims 1 to 5, for pre-heating concrete in an installation producing concrete castings, characterised by the fact that it comprises several buckets, which can be moved in turn beneath said set of electrodes, means being provided for collecting the pre-heated concrete discharging from the bucket under said set of electrodes and for transporting this concrete to the place for casting said parts.

9. A device according to claim 8, characterised by the fact that it comprises three buckets able to travel on a rail or similar means in a closed circuit, the buckets being preferably rigidly interconnected.

10. A device according to claim 8 or 9, characterised by the fact that it comprises three operational positions for the buckets, viz. a position for filling these buckets from a mixer, a pre-heating and emptying position and a cleaning position, the set of electrodes being vertically mobile above the preheating position of the bucket.

11. A device according to claim 8, 9 or 10, characterised by the fact that it cooperates with a distributing vehicle capable of receiving the concrete from a bucket in the pre-heating position and of distributing the pre-heated concrete into moulds, this vehicle comprising means for controlling the preheating of the bucket which is at that moment in the pre-heating position.