METHOD AND PLANT FOR THE PRODUCTION OF CONCRETE

Description

[0001] The present invention relates to a method and an installation for manufacturing concrete.

[0002] Concrete manufacturing methods are known comprising transferring quantities of granular materials having different particle sizes into separate storage hoppers, discharging metered quantities of at least one of said granular materials from at least one of said storage hoppers onto a transport means, transporting these metered quantities by said transport means to a conveyor belt which conveys them to the top of a mixing stage, mixing, in this mixing stage, said metered quantities, conveyed, of at least one of said granular materials with hydraulic binder, water and possible additives, to form a pasty mass of concrete, and discharging said pasty mass of concrete from the mixing stage, for its exploitation.

[0003] For the implementation of such a method, an installation is provided in a known manner which comprises storage hoppers for receiving granular materials having different particle sizes, which are provided with an upper loading opening and a lower, closable discharge orifice, a transport means onto which metered quantities of granular materials are discharged from said storage hoppers, a conveyor belt onto which said transport means brings said metered quantities of granular materials, and a mixing stage having an inlet, where said conveyor belt carries said metered quantities of granular materials, means for supplying hydraulic binder, water and possible additives and a closable outlet for discharging a pasty mass of concrete.

[0004] According to the invention, the term "mixing stage" means all the elements and devices that allow material to be mixed, and therefore not only the mixer, but also the mixer's feed systems. Typically, this mixing stage has the form of a tower, the upper level of which comprises scales for water, cement and any additives, as well as an aggregate tank for receiving the already dosed quantities of granular materials, and the lower level of which consists of the mixer itself. When the mixer is empty, the scales and the aggregate tank can be emptied simultaneously into the mixer.

[0005] Concrete manufacturing facilities are used to supply products of several types, such as Bénor concretes that comply with European standards or rich concretes known as "on composition", lean concretes, or various mixtures based on cement and aggregates such as stabilized stone, stabilized sand, screeds, specific concretes (road, cavernous, colloidal, etc.). Special admixtures are sometimes required and it is increasingly sought to be able to recycle certain materials already used in concrete.

[0006] Concrete is mixed in a mixing tank called a batching tank, and production is therefore carried out in batches which are obtained every 20 to 50 seconds, then poured into mixing vehicles, for example, mixer trucks, each mixer truck being able to contain, for example, 3 batches. This pouring can also take place in dump trucks, flatbed trucks or even simple trailers attached to cars.

[0007] These installations generally show limited performance. They do not allow for rapid increase or decrease in concrete production, depending on demand, and above all they do not allow for easy and rapid transition from the production of batches of one composition to that of batches of another composition.

[0008] In order to solve this type of problem, a method for manufacturing concrete has already been provided, comprising a transfer of quantities of granular materials having different granulometric sizes into separate storage hoppers, a discharge of metered quantities of at least one of said granular materials from at least one of said hoppers of a first series of storage hoppers onto a first conveyor belt which, as a means of transport, runs in one direction, in a first direction, a discharge of metered quantities of at least one of said granular materials from at least one of said hoppers of a second series of storage hoppers onto a second conveyor belt which, as a means of transport, runs in said direction, in a second direction opposite to the first,and transporting these metered quantities of granular materials by said conveyor belts to a conveyor belt which carries them to the top of two separate mixing towers, in each of which these granular materials are mixed with hydraulic binder, water and possible additives, to form a pasty mass of concrete, to be discharged for its exploitation, said transport step comprising selectably feeding the conveyor belt by the first conveyor belt or feeding the conveyor belt by the second conveyor belt (see FR2953423).,

[0009] This latter process makes it possible to produce several concretes of different compositions successively in a simplified manner and therefore speeds up the overall production of the installation using this process. However, it still lacks flexibility and has disadvantages that are difficult to overcome in terms of the distribution of granular materials in one or other of the mixers.

[0010] The present invention aims to solve these problems and to propose a method and a concrete manufacturing installation which make it possible to improve the performance of concrete production installations and which allow great flexibility in the manufacturing of different concretes in the same installation.

[0011] Thus, according to the invention, there is provided a method for manufacturing concrete according to claim 1.

[0012] This process allows, depending on the various orders, not only to increase or reduce very significantly and very quickly the production capacity of the installation, but also to quickly supply batches of concrete of different compositions successively or even simultaneously. Indeed, the aforementioned granular materials, also called aggregates, which include sands, gravels, and gravels of predetermined granulometric sizes, can be brought to the mixers in successive mixtures that are easily adaptable. The conveyor belt can be fed by one or more conveyor belts, each supplied from one or more storage hoppers, which substantially multiplies the number of different granular mixtures that can be conveyed to the aggregate tank of one of the mixing towers or the other.And, in each mixer, the quantity of hydraulic binder, water or admixture can be adjusted independently according to demand. Two concrete trucks can therefore collect two concretes of different qualities from the bottom of the mixers almost simultaneously.

[0013] According to one embodiment of the invention, said transfer step comprises pouring at least one of the granular materials into at least one storage hopper from a carrier vehicle. Such direct pouring into the storage hoppers allows for an enormous saving of time. As carrier vehicles, it is advantageous to envisage, for example, dump trucks.

[0014] According to another embodiment of the invention, said transfer step comprises an intermediate storage of one of said granular materials opposite each storage hopper, and a loading thereof by simple pushing of the granular material. This makes it possible to avoid the usual filling of the hoppers from a single reservoir located higher than the storage hoppers and successively supplied with each of the granular materials from a primary storage located lower down. Optionally, the method according to the invention comprises a primary storage of said granular materials, separately, at a distance from said storage hoppers, and at the same level as the intermediate storage and said transfer step comprises a step of preliminary movement of the granular material from the primary storage directly to the hoppers or to the intermediate storage, prior to loading the hoppers.

[0015] This allows for simple transfer of materials to the hoppers or to an intermediate storage area, for example, by a loading machine, without requiring the materials to be lifted to the aforementioned tank. Furthermore, the aforementioned pushing can also be carried out, for example, by these same loading machines.

[0016] According to a particular embodiment of the invention, the method comprises weighing the granular materials discharged onto the conveyor belts. Weighing each conveyor belt during each aforementioned discharge onto it of one of said granular materials allows metering of the quantities discharged from the storage hoppers.

[0017] The present invention also relates to a concrete manufacturing plant according to claim 7, which comprises storage hoppers for receiving granular materials having different particle sizes, which are provided with an upper loading opening and a lower discharge opening, a first series of storage hoppers being aligned above a first conveyor belt, as a means of transport which runs towards a lower end of a conveyor belt in a direction, in a first direction, a second series of storage hoppers being aligned above a second conveyor belt, as a means of transport which runs towards the lower end of said conveyor belt in said direction, in a second direction opposite to the first, the two conveyor belts each having a discharge end arranged above said lower end of the conveyor belt, and a mixing stage, comprising at least two mixing towers each having an upper inlet opening,each of these mixing towers being provided with means for supplying hydraulic binder, water and possible additives, a mixing device and a lower closable outlet opening for discharging a pasty mass of concrete, the conveyor belt running obliquely from said lower end to an upper end located above the upper inlet openings of the mixing towers.

[0018] In this installation according to the invention, an impact plate is arranged between the two discharge ends of the two conveyor belts so as to be able to pivot freely around an axis perpendicular to the direction of travel of the conveyor belts, the upper end of the conveyor belt opening onto an inclined, pivoting guide plate, which directs the metered quantities of granular materials into an aggregate tank of one of the mixing towers or into an aggregate tank of the other of said mixing towers,the installation further comprising control means which are arranged to produce an opening or a closing of the discharge orifice of one or more hoppers of one or both series of storage hoppers and a setting in motion of one or both of the conveyor belts simultaneously so as to allow a simultaneous supply of the granular materials to the conveyor belt from the first and second conveyor belts or a stopping of this supply from one of the two conveyor belts and to control a pivoting of the pivoting guide plate so as to direct the granular materials into the aggregate tank of one or other of the mixing towers.,

[0019] Advantageously, the control means are integrated into a remote control unit.

[0020] According to the invention, the moving conveyor belts are therefore arranged so as to move towards a lower end of the conveyor belt. They are, in a selected manner, loaded or not with one or more granular materials. The impact plate can pivot freely under the thrust of the aggregate flows discharged from the left and / or right by the conveyor belts. In this way, it directs this or these flows at all times and in a quasi-vertical manner towards the lower end of the conveyor belt. When granular materials are discharged from a single conveyor belt, this impact plate pivots to the opposite side under their thrust, which has the effect of preventing the granular materials from overflowing beyond the conveyor belt.When granular materials are discharged from both conveyor belts simultaneously, the impact plate remains static in a vertical position and has the additional effect of channeling the flows and thus preventing them from interacting with each other in an undesirable manner. The conveyor belt runs obliquely from this lower end to an upper end located above the upper inlet openings of the mixing towers, and the upper end of the conveyor belt opens onto an inclined, pivoting guide plate, which directs the metered quantities of granular materials directly into the aggregate tank of one or other of the said mixing towers. Such an arrangement makes it very simple to provide for simultaneous production, in several mixers arranged in parallel, of identical or different concretes, depending on requirements.

[0021] According to one embodiment of the invention, the installation comprises an intermediate storage area in front of the upper loading opening of each of the storage hoppers. These intermediate storage areas can form a buffer storage space before storage in the hoppers. They can also be used to accommodate a carrier vehicle capable of directly pouring granular material into the corresponding hopper, when the latter is empty. Dump trucks can then dump their contents directly into the hopper, thus avoiding costly handling by a loader machine which still has to push the stored material.Advantageously, the installation further comprises primary storage areas for the granular materials, located at a distance from the storage hoppers, and the primary storage areas and the intermediate storage areas are arranged at the same level which is equal to or higher than the upper inlet openings of the storage hoppers. For example, these primary storage and intermediate storage areas are arranged on a single platform on which, for example, several loading machines can circulate simultaneously and carry out a transfer of each of the granular materials to its or their intermediate storage areas, as required. These same loading machines are also capable of pushing the granular materials from their intermediate storage area into their storage hopper. To reach the platform, an access ramp for trucks, or any other common means of transport, can be envisaged.This general arrangement allows each hopper to be loaded independently of the others according to requirements and therefore allows for faster and easier feeding of the installation.

[0022] According to a particular embodiment of the invention, at least one storage hopper comprises an upper part opening onto a lower part comprising at least two separate compartments each provided with a lower discharge opening, closable independently of the discharge opening of the other compartment. This arrangement facilitates precisely regulated metering of the mixture of granular materials to be fed by the respective conveyor belt to the conveyor belt and allows an adjusted discharge speed. Depending on requirements, one or two of the lower discharge openings are opened. The openings of the above-mentioned compartments can be closed by conventional means such as, for example, flaps for gravel and extractor belts for sand.

[0023] Other details and particularities of the invention will emerge from the description of an example of an installation embodiment according to the invention, given below without limitation and with the aid of the appended figures. There figure 1 represents a schematic plan view of an installation according to the invention. The figure 2 represents a sectional view along line II-II of the figure 1 . There figure 3 represents a plan view of the aggregate transport system to the top of the mixing towers. The figure 4 represents a side view of the conveyor belts and the conveyor belt illustrated in the figure 3 .

[0024] It should be noted that these figures are schematic and are not intended to be drawn to the same scale. Identical or similar elements are designated in the different figures by the same references.

[0025] As is clear from the figure 1 , the illustrated installation comprises a platform 1, to which dump trucks containing granular materials can reach via an access ramp 2. Several primary storage areas 3 are provided on one side of the platform, in housings separated by partitions 4. In each housing it will therefore be possible to store in piles different granular materials, such as sand, gravel, gravel of various particle sizes, naturally at a rate of only one material per housing. These granular materials have particle sizes corresponding to common standards, for example 0 / 80, 0 / 63, 32 / 63, 63 / 150, 0 / 20, 0 / 6.3, 6.3 / 20 etc. which will then be used independently depending on the finished product to be produced. These standards correspond to the mesh openings of the screens and are to be expressed in mm.

[0026] In the illustrated example, on the other side of the platform there are two rows of each five storage hoppers 5 and 5' respectively, each of which is aligned above a conveyor belt 6 and 6' respectively. As is clear in particular from the figure 2 , at their upper end these hoppers 5, 5' each have an upper loading opening 7 and respectively 7', which, in the example illustrated, is located at the level of the platform 1. Intermediate storage areas 8 and respectively 8' are arranged on the platform 1 in front of each storage hopper, being separated from each other by partitions 9 and respectively 9'. These intermediate storage areas 8, 8' serve as buffers between the primary storage areas 3 and the storage hoppers 5, 5'. Several mobile machines, for example the aforementioned dump trucks, can easily reach the platform 1 and circulate simultaneously on it to supply the granular material which is suitable for it not only each storage area 3, but also each intermediate storage area 8 or 8', or they can even pour their load directly into a suitable hopper.These same machines are also capable of loading part of the pile of granular material stored on areas 8 or 8' into hoppers 5 or 5', by simply pushing through their upper opening 7 or 7'. It will be easily understood that the level of platform 1 may possibly be slightly higher than that of the upper openings 7, 7' of the hoppers.

[0027] Each storage hopper comprises, in the example illustrated, an upper part, which, in the example illustrated, comprises two opposite vertical walls 11, 12, and respectively 11', 12', which are arranged perpendicular to their conveyor belt 6, 6', and two walls inclined towards each other 13, 14 and respectively 13', 14'. This upper part opens into two separate compartments 15, 16 and respectively 15', 16' which each have the shape of an inverted pyramid and which each have a discharge orifice 17 and respectively 17', which is closable. In the hopper illustrated in the figure 2 , which is intended to contain a coarse granular material, the discharge opening is closed by a valve 18. This valve closes the corresponding compartment of the hopper if the latter is not to see the granular material it contains discharged or it opens it otherwise. The passage of the valve 18 from an open position to a closed position or vice versa is carried out using any usual means known to those skilled in the art. In the example illustrated it is opened using two jacks 28 controlled remotely from a control unit 19. When the hopper contains a fine granular material, such as sand, it may be advantageous to regulate its discharge, not by a valve, but by an extractor belt known per se for this purpose, which can also be set in motion by the control unit 19.

[0028] In the example illustrated, the conveyor belts 6 and 6' are arranged so as to travel horizontally towards each other in the same horizontal direction, but in opposite directions F1, F2, towards a lower end 21 of the conveyor belt 20. In the example illustrated, the two conveyor belts 6 and 6' simultaneously discharge aggregates over the lower end of the conveyor belt 20. The aggregates, arriving at a certain speed, are stopped in their course by an impact plate 30 which pivots freely. On the figure 4 the impact plate is in a vertical position, because it is subjected to the thrust of the material flows which come simultaneously from the conveyor belt 6 and the conveyor belt 6'. In the example illustrated, as the pivoting impact plate is located between the two ends of the two conveyor belts 6, 6', it has the effect of causing an almost vertical fall of the aggregates from each of the conveyor belts towards the conveyor belt 20. When a single conveyor belt discharges aggregates onto the conveyor belt, the impact plate 30 can, under the thrust of the material, pivot along one of the arrows F3 or F4, thus preventing the aggregates from overflowing beyond the conveyor belt.

[0029] This runs obliquely, in the direction of arrow F5, from its lower end 21 to an upper end 22 located above the upper inlet openings 23 and 23' respectively of the mixing towers 24 and 24' respectively. There, using a switching system consisting of an inclined guide plate 29 which can be oriented using a pivot towards one or the other mixing tower 24, 24', the conveyor belt 20 discharges the granular material which it transports into an aggregate tank 31, 31' shown schematically in the figure 3 . In turn, this reservoir, open at the bottom, immediately pours its contents into a conventional mixing device. Advantageously, the invention thus makes it possible to avoid the passage of the different materials through an intermediate hollow distribution body. It should be noted that it is also possible to envisage the conveyor belts 6, 6' also being inclined and / or being arranged in different directions from each other.

[0030] Each mixer is provided in a known manner with various supply means, such as scales, for hydraulic binder 25, 25', water 26, 26' and possible additives 27, 27', such as plasticizers. These mixers are of course also provided with a lower closable outlet opening for discharging a pasty mass of concrete, for example, into mixer trucks brought under the mixers.

[0031] The operation of one or other of the conveyor belts 6 and 6', of the conveyor belt 20, of one or other of the mixers of the mixing towers 24, 24' or of both can advantageously be controlled or monitored remotely from a single control unit 19. This can advantageously also control the opening or closing of each compartment of the hoppers 5, 5', of the aggregate tank 31, 31', of the mixer feed scales and the pivoting of the collector 29.

[0032] A series of different feeds to the conveyor belt 20 of the illustrated installation will be described below. Cas n°1 : production of 2 consecutive identical batches using exclusively aggregates available in hoppers of a single series of hoppers. Extracted aggregates: Buir sand 0 / 4 (setpoint at 3268 kg), crushed limestone 2 / 6.3 (setpoint at 993 kg), crushed limestone 8 / 20 (setpoint at 2773 kg). Sequence: From hopper 5 side: extraction of 0 / 4, then 2 / 6.3, then 8 / 20, start of oblique conveyor belt 20, then start of horizontal conveyor belt 6, stop of the horizontal belt, start of the following extractions,... and so on. Hopper 5' side: no activity. Cas n°2 : Production of a single batch using only aggregates available on the hopper 5 side. Extracted aggregates: Buir sand 0 / 4 (setpoint at 2738 kg), crushed limestone 2 / 6.3 (setpoint at 853 kg), crushed limestone 8 / 20 (setpoint at 2272 kg). Sequence: From the hopper 5 side: extraction of 0 / 4, then 2 / 6.3, then 8 / 20, start of the oblique conveyor belt, then start of the horizontal conveyor belt, stop of the horizontal belt, stop of the oblique belt. Hopper 5' side: no activity. Cas n°3 : production of 1 batch (mixer 24) using aggregates available on both sides (hoppers 5 and hoppers 5'), followed by 1 batch (mixer 24') using aggregates available on both sides. Extracted aggregates: Batch 1: crushed limestone 2 / 6.3 (setpoint at 2354 kg), crushed limestone 6 / 20 (setpoint at 4547 kg) Batch 2: Buir sand 0 / 4 (setpoint at 2914 kg), crushed limestone 2 / 6.3 (setpoint at 880 kg), crushed limestone 8 / 14 (setpoint at 2426 kg) Sequence: Batch 1: extraction of 2 / 6.3 from the hoppers 5 side simultaneously with the extraction of 6 / 20 from the hoppers 5' side, start of the oblique conveyor belt, then simultaneous start of the two horizontal conveyor belts, stop of the horizontal belts, stop of the oblique belt. Batch 2: extraction of 0 / 4 from the hoppers 5 side simultaneously with the extraction of 8 / 14 from the hoppers 5' side, then extraction of 2 / 6.3 on the hopper side 5, start of the oblique belt, then simultaneous start of the two horizontal belts, stop of the horizontal belts, stop of the oblique belt. Cas n°4 : production of 1 batch (mixer 24) using aggregates available on both sides (hoppers 5 and hoppers 5'), followed by 1 identical batch (mixer 24') using aggregates available on both sides, followed by 1 identical batch (mixer 24) using aggregates available on both sides. Extracted aggregates: Buir sand 0 / 4 (setpoint at 3288kg), crushed limestone 2 / 6.3 (setpoint at 993kg), crushed limestone 8 / 14 (setpoint at 2737 kg). Sequence: In parallel: extraction of the 2 / 6.3 from the hoppers 5 side simultaneously with the extraction of the 8 / 14 from the hoppers 5' side, then extraction of the 2 / 6.3 from the hoppers 5 side, start of the oblique belt, then simultaneous start of the two horizontal belts, stop of the horizontal belts, stop of the oblique belt. Followed by a 2nd and a 3rd identical sequence. Cas n°5 : production of 1 batch (mixer 24') using exclusively aggregates available on the hoppers 5 side, followed by 1 identical batch (mixer 24') using exclusively aggregates available on the hoppers 5 side followed with a delay and in parallel by 1 batch (mixer 24) using exclusively aggregates available on the hoppers 5' side. Extracted aggregates: Batches 1 and 2: Buir sand 0 / 4 (setpoint at 3268kg), crushed limestone 2 / 6.3 (setpoint at 993kg), crushed limestone 8 / 20 (setpoint at 2773kg) Batch 3: limestone sand 0 / 2 (setpoint at 1545kg) Sequence 1: Hopper side 5: extraction of 0 / 4, then 2 / 6.3, then 8 / 20, start of the oblique belt, then start of the horizontal belt, stop of the horizontal belts, stop of the oblique belt. Hopper side 5': no ​​activity. Sequence 2: Same as sequence 1 Sequence 3 (occurs during sequence 2) Hopper side 5': extraction of 0 / 2, waiting for release of the oblique belt.

[0033] It should be understood that the present invention is in no way limited to the foregoing description and that many modifications could be made thereto without departing from the scope of the following claims.

Claims

1. Method for producing concrete, comprising - transferring quantities of granular materials having different particle sizes into separate storage hoppers, - pouring dosed quantities of at least one of said granular materials from at least one of said hoppers of a first set of storage hoppers onto a first transport belt which, as a means of transport, runs along a direction, in a first direction, - pouring dosed quantities of at least one of said granular materials from at least one of said hoppers of a second set of storage hoppers onto a second transport belt which, as a means of transport, runs along said direction, in a second direction opposite to the first, and - transporting these dosed quantities of granular materials by means of said transport belts to a conveyor belt which conveys them to the top of two separate mixing towers, in each of which these granular materials are mixed with hydraulic binder, water and possibly adjuvants, to form a pasty mass of concrete, to be discharged for use thereof, - said transporting step comprising, in a selectable manner, supplying the conveyor belt with granular materials by means of the first transport belt or supplying the conveyor belt by means of the second transport belt, said transporting step further comprising, in a selectable manner, supplying the conveyor belt simultaneously by means of the first transport belt and by means of the second transport belt, the method being characterised by the use of an impact plate (30) arranged between the two discharge ends of the two transport belts (6, 6') to be freely pivotable about an axis perpendicular to the running direction of the transport belts, and in that said dosed quantities of granular materials are conveyed to the top of each of the mixing towers by the conveyor belt in a selectable manner through pivoting of an inclined guide plate (29), which directs the dosed quantities of materials into an aggregate tank of one mixing tower or into an aggregate tank of the other mixing tower.

2. Method according to Claim 1, characterised in that the aforementioned granular materials comprise sand, grit and gravel of predetermined particle sizes.

3. Method according to one of Claims 1 and 2, characterised in that said transferring step comprises pouring at least one of the granular materials into at least one storage hopper from a carrier vehicle.

4. Method according to one of Claims 1 and 2, characterised in that said transferring step comprises preliminary storage of one of said granular materials in front of each storage hopper, so as to be able to be loaded thereinto by simple pushing.

5. Method according to Claim 4, characterised in that it comprises primary storage of said granular materials, at a distance from said storage hoppers, and in that primary storage and intermediate storage take place at the same level.

6. Method according to one of Claims 1 to 5, characterised in that it comprises weighing the granular materials poured onto each transport belt.

7. Concrete production facility, comprising - storage hoppers (5, 5') for receiving granular materials having different particle sizes, which are provided with an upper loading opening (7, 7') and a lower discharge opening (17, 17'), - a first set of storage hoppers (5) which is aligned above a first transport belt (6), as a means of transport that runs to a bottom end (21) of a conveyor belt (20) along a direction, in a first direction, - a second set of storage hoppers (5') which is aligned above a second transport belt (6'), as a means of transport that runs to the bottom end (21) of said conveyor belt (20) along said direction, in a second direction opposite to the first, - the two transport belts each having a discharge end arranged above said bottom end of the conveyor belt, and - a mixing stage, comprising at least two mixing towers (24, 24') each having an upper inlet opening, each of these mixing towers being provided with means for supplying hydraulic binder (25), water (26) and optional adjuvants (27), a mixing device and a sealable lower outlet opening for discharging a pasty mass of concrete, - the conveyor belt (20) running slantwise from said bottom end (21) to a top end (22) located above the upper inlet openings of the mixing towers (24, 24'), - control means (19) which are arranged to open or close the discharge opening (17, 17') of one or more hoppers (5, 5') of one or both sets of storage hoppers and to set in motion one of the transport belts (6, 6') or both of them simultaneously so as to allow the granular materials to be simultaneously delivered to the conveyor belt (20) from the first and second transport belts (6, 6') or to stop this delivery from one of the two transport belts, characterised in that an impact plate (30) is arranged between the two discharge ends of the two transport belts (6, 6') so as to be able to pivot freely about an axis perpendicular to the running direction of the transport belts, in that the top end (22) of the conveyor belt opens onto an inclined, pivoting guide plate (29), which directs the dosed quantities of granular materials into an aggregate tank (31) of one of the mixing towers or into an aggregate tank (31') of the other of said mixing towers, and in that the control means (19) are arranged to control a pivoting of the pivoting guide plate (29) so as to direct the granular materials into the aggregate tank (31, 31') of either of the mixing towers (24, 24').

8. Facility according to Claim 7, characterised in that it comprises an intermediate storage area (8, 8') in front of the upper loading opening of each of the storage hoppers (5, 5').

9. Facility according to Claim 8, characterised in that it further comprises primary storage areas (3) for storing the granular materials, located at a distance from the storage hoppers (5, 5'), and in that the primary storage areas and the intermediate storage areas (8, 8') are arranged at the same level which is equal to or higher than the upper inlet openings (7, 7') of the storage hoppers.

10. Facility according to one of Claims 7 to 9, characterised in that at least one storage hopper comprises an upper part opening into a lower part comprising at least two separate compartments (15, 16; 15', 16') each provided with a lower discharge opening (17, 17'), which can be sealed independently of the discharge opening of the other compartment.