EP1324865A1

EP1324865A1 - Method for producing in a continuous installation a compacted rolled concrete composition reinforced with metal fibres, and continuous installation therefor

Info

Publication number: EP1324865A1
Application number: EP01969887A
Authority: EP
Inventors: Benoít Ficheroulle; Marc Henin
Original assignee: Chaussees Techniques Innovation
Current assignee: Chaussees Techniques Innovation
Priority date: 2000-10-10
Filing date: 2001-09-14
Publication date: 2003-07-09
Anticipated expiration: 2021-09-14
Also published as: EP1324865B1; AU2001290020A1; DE60111250D1; HUP0303660A2; CN1190302C; SK4412003A3; FR2814979B1; ATE296720T1; PL365564A1; FR2814979A1; CN1474741A; WO2002030644A1

Abstract

The invention concerns a method for producing in a continuous installation a compacted rolled concrete composition reinforced with metal fibres, which consists in feeding a vibrating metering means with pre-sized metal fibre plates to be delivered on a conveyor in a proportion ranging between 25 and 60 kg of fibres per m<3> of dry fibre-free concrete constituents, and in supplying a hydraulic binder in a proportion ranging between 180 and 400 kg/m<3> of dry fibre-free concrete constituents, the proportion of mixing water being determined such that the mixer delivers continuously a composition having a water content between 90 and 150 litres of water per m<3> of dry fibre-free concrete constituents.

Description

The present invention relates to a process for the continuous production of a reinforced compacted rolled concrete composition. of metallic fibers packaged in pre-glued plates, as well as a continuous power plant and a continuous fiber doser for the implementation of this manufacturing process. The composition of compacted rolled concrete reinforced with fibers obtained by said process allows the realization of continuous pavements or industrial areas without joints.

To produce a durable pavement in seamless poured concrete, a process is known, known as the continuous reinforced concrete (BAC) process, in which steel bars, generally 16 mm in diameter, are connected to each other continuously. along the entire length of the roadway. Once the steel bars are laid, the concrete is applied, usually using a sliding formwork machine. Continuous reinforced concrete remains a heavy technique to implement and expensive. After reinforcement with steel fibers, traditional concrete, perverted or poured, makes it possible to produce industrial pavements (often covered and therefore less subject to weathering and temperature variations than pavements) of large dimensions reaching up to 2000 m without joints. , the properties of the fibers making it possible to space the joints. On the other hand, these concretes have so far been unable to be used effectively for the production of continuous pavements without joints, despite the advantage presented by such an application. Indeed, the relatively high dosages in cement and water generate in these concretes a hydraulic shrinkage to which is added the thermal shrinkage. The mechanical stresses are such that the fibers fail to control them. As a result, the shrinkage phenomena of the concrete lead to a significantly greater cracking than in paving, with an unacceptable degree of opening usually reaching several millimeters. Thus it is necessary to practice joints in these pavements in order to localize the effects of the shrinkage and to reduce the crack openings, which makes lose the economic advantages of a continuous pavement and considerably slows down the development in pavements of perverted or poured fiber concretes.

Rolled compacted concrete compositions differ from conventional poured or perverted concrete by the fact that, for similar or better mechanical properties, they require a reduced dosage of hydraulic binder as well as a reduced water content. In the two types of conventional concrete mentioned above, it is known to insert metallic fibers. The reduction in the binder dosage and in the water content gives the advantage of compacted rolled concrete of a lower hydraulic shrinkage, with the consequence of less marked cracking: on the condition of using fibers provided with a sufficiently effective anchoring in the concrete matrix and knowing how to properly integrate these fibers at the time of concrete production, it is therefore possible to produce a continuous pavement in compacted rolled concrete reinforced with metallic fibers. The lower water content of compacted rolled concrete also makes it possible to obtain sufficient bearing capacity to use the material with road vehicles (asphalt paver paver) and then compact it using a vibrating compactor and a tire compactor, and finally put it back into circulation without delay. On the other hand, the consistency of poured concrete requires implementation with traditional techniques of sliding formwork machine or vibrating rule and allows recirculation only after a sufficient setting time which is generally at least 7 days. . The metallic fibers used in industrial paving are most often drawn fibers generally comprising wires of 1 mm in diameter. The different existing fibers differ from each other by the type of active anchoring in the concrete matrix.

To solve the problem of agglomeration of fibers into balls, some fiber manufacturers have turned to geometric shapes and surface aspects of fibers that allow direct use at the factory, without additional treatment. On the other hand, laboratory tests and experience on construction sites show that these fibers are not the most efficient on the market, at least as regards mechanical properties and control of the cracking of the composite concrete + metal fibers.

It is known from French Patent No. 2,225,392 a process for incorporating, into concrete, metallic reinforcing fillers constituted by groups held together by a bonding material capable of being attacked by a disintegrating constituent, this process consisting introducing said groups into the mixture capable of giving rise to concrete, then kneading the whole for good macroscopic distribution, then causing the disintegration of said bonding materials and prolonging the kneading of the mixture for good microscopic distribution. It is effectively an integration, in concrete, of fibers which have been pre-glued in plates beforehand. Mixing in two very distinct phases is carried out either in a mixer mounted on a vehicle called a mixer truck during its journey of 15 minutes or more, or in a mixing pass in approximately 1 minute in the mixer of the plant.

It should therefore be noted that, prior to the present invention, the production of poured or extruded concrete reinforced with pre-glued fibers in platelets has always been carried out in a batch plant or in a so-called mixer truck. The fibers are introduced manually or by a specific machine, either directly in the mixer of the power plant, or in a truck known as mixer. The use of a so-called mixer truck has the disadvantage of an unsatisfactory mixing quality and the risk of heterogeneity in the distribution of the fibers. The manual introduction of fibers conditioned in a bag, on a feeder belt or directly in the mixer, has the disadvantages of the risk of dosage error and yields which remain low. The use of specific machines makes it possible to increase the rates: these are simple systems which, at best, weigh the quantities of fibers necessary for the production of each batch in the mixer of the batch plant. It should be noted that poured or extruded concrete reinforced with fibers is generally the subject of applications in fields such as industrial paving, implemented most often manually, or in civil engineering works such as piles in foundations. The production rates necessary to supply the site then remain relatively small and are suitable for batch production.

On the other hand, road works are highly mechanized and use high-efficiency machines. The supply of these sites with materials treated with hydraulic binders and road concretes (for example for continuous reinforced concrete or compacted rolled concrete sites) required the development of power stations allowing hourly outputs significantly higher than those of power stations traditional staple. A discontinuous power plant has the disadvantage of a production cycle in which the various constituents are first conveyed into the mixer as part of a first operation, then the mixer comes into action in order to mix these constituents, finally the mixer is emptied into the transport truck. This is why another type of power plant has been developed so that it can operate without requiring the mixer to be stopped at each material loading cycle. These plants are called “continuous” because the mixer is continuously supplied by a conveyor on which the required quantities of aggregates and hydraulic binder are deposited; the mixer is never stopped during the production of the concrete which it delivers in a buffer hopper used to fill transport trucks. For this reason, the production rates of continuous plants are significantly higher than those of most discontinuous plants. Continuous plants are therefore well suited to road works, especially since the manufacturers have made it possible to move them from one site to another, much more easily than discontinuous plants. We therefore speak of "mobile" or even "hypermobile" power stations (that is to say, which can in this case be transported with only two tractor trucks). French patent No. 2,633,922 discloses a process for manufacturing a compacted rolled concrete reinforced with fibers, according to which 7 to 15% of a cement or road binder is introduced continuously into a mixer of a plant. , 4 to 7% by weight of water, 0.8 to 4% by weight of metallic fibers, these being introduced by a special metering device, the rest of the composition essentially consisting of gravel from 0 to 31.3 mm . However, this patent is absolutely silent on this dispenser special and on the way the fibers are fed by the doser in the mixer.

French Patent No. 2,654,830 describes a continuous weight metering device for fibers in a construction material for engineering structures. However, the problem with this device lies in the fact that the fibers form balls or hedgehogs in the means for distributing the fibers towards the means for transporting the material to be reinforced by the fibers. According to this patent, vibrating chutes of the distribution means are associated with fiber separation means, such as toothed rotors, nozzles for injecting air under pressure or rakes with reciprocating movement, in order to dislocate these hedgehogs from fibers. However, all of these separation means are not sufficiently described or illustrated in this patent to allow their effective implementation by a practitioner. The correct introduction of metallic fibers into a continuous plant is indeed the subject of much greater difficulties than a discontinuous plant: it is necessary both to avoid the problem of agglomeration of fibers into balls, while integrating the quantity of fibers required in concrete with acceptable accuracy. The purpose of the process according to the invention is to provide a satisfactory response to these difficulties which have hitherto remained unsolved, in particular for the dosing of prepasted metal fiber wafers. The process according to the invention proposes a continuous production of a compacted rolled concrete reinforced with fibers which effectively makes it possible to avoid, or at least to limit to a very low probability, the formation of fiberballs at the manufacturing stage. compacted rolled concrete reinforced with fibers. Another object is to avoid or limit the formation of fiberballs at the other two stages of transport and implementation of the compacted rolled concrete reinforced with fibers. Finally, another goal is to completely avoid the formation of these balls. The aim of the process according to the invention is also:

- starting from metallic fibers pre-glued in platelets, to dose these fibers in compacted rolled concrete manufactured with high rates compatible with continuous central production for highly mechanized road works, - to make sure that the glue binding the fibers in platelets is dissolved so as to release the maximum of fibers for their individual action of reinforcement in bending and of control of the cracking of the compacted rolled concrete implemented on site; another object is to release into the concrete all the fibers previously conditioned in pre-glued plates; and to obtain with these fibers a dosage accuracy of between -5% and + 10% of the nominal dosage value required, on an instant sample taken at any time during the production of the fiber concrete, knowing that this objective is important to guarantee correct and homogeneous performance of the composite concrete + fibers used on site. To this end, the subject of the invention is a process for the continuous production of a compacted rolled concrete composition reinforced with fibers, comprising the following steps: a) the continuous feeding of several types of aggregates delivered on a conveyor , b) the continuous feeding of metallic fibers from a vibrating metering means on said conveyor, c) the continuous feeding in a kneader of the aggregates and of the fibers delivered by the conveyor, of a hydraulic binder and mixing water which may contain one or more concrete admixtures, characterized in that: the aforementioned step b) consists in supplying the aforementioned vibrating metering means with platelets of pre-glued metal fibers for delivering said fiber platelets and / or said fibers peeled off on the conveyor during step a) above, said fibers being fed in a proportion of between 25 and 60 kg of fibers per m ³ of constitu dry concrete of the fiber-free concrete, and that step c) consists in supplying the hydraulic binder in a proportion of between 180 and 400 kg / m of dry constituents of the fiber-free concrete, the proportion of mixing water being determined so that the mixer continuously delivers a concrete composition rolled compacted with fibers which has a water content of between 90 and 150 liters of water per m of dry constituents of fiber-free concrete. The fact of delivering fibers in the form of pre-glued plates makes it possible to eliminate or reduce the number and the size of the balls of fibers in the concrete composition. Thus, the fiber boards soaked beforehand with solvent product come off by the combined action of energetic shearing generated by the mixer and the addition of water at the level of the arms of the mixer.

Advantageously, the transport of the compacted rolled concrete reinforced with fibers is carried out by a dump truck, and not by a mixer truck, and the implementation of the concrete on the road is carried out by a paver, to maintain the desired characteristics for mixing the constituents of fiber-reinforced concrete.

Preferably, the method consists in continuously feeding, during the aforementioned step a), onto the conveyor, a solvent product, for example water, to dissolve the adhesive which keeps the fibers in platelets, said solvent product being delivered to the conveyor at or near the drop point of the fibers delivered by the metering means. According to a first variant, the metering means successively comprises at least one vibrating metering tank and a vibrating passage or a weighing belt. For example, the method consists in supplying solvent product to said corridor so that the fibers bathe at least partially in the corridor, the bottom of which is filled with solvent product and are delivered together with said solvent product on the conveyor from said corridor.

According to another variant, the method consists in delivering said solvent product by at least one nozzle situated just downstream from the point of fall of the fibers on the conveyor. Advantageously, the method consists in delivering the fibers onto the conveyor, after the feeding of a first type of aggregates and before the feeding of the last type of aggregates, so that the fibers are integrated into the mass of the different types of aggregates. .

According to another characteristic of the invention, the method consists in calculating the proportion of mixing water delivered in step c) above in the mixer, depending on the water content specific to each type of aggregate supplied in step a).

In a particular embodiment, the method consists in feeding in step a) a total proportion of the aggregates between 83 and 93% by weight of dry constituents of the concrete without fiber, and in step c) a cement or a binder road in a proportion of between 7 and 17% by weight of dry constituents of the fiber-free concrete, of which 0.3 to 1.8% by weight of the hydraulic binder consists of a concrete setting retarder and / or plasticizer additive in mixing water to lubricate the intergranular contacts and delay setting of the concrete.

The subject of the invention is also a continuous power station for implementing the method defined above, comprising:

a series of hoppers arranged at intervals above a motor-driven conveyor, each hopper being capable of delivering to the conveyor a type of aggregate, each hopper being associated with a means of weight or volumetric measurement of the amount of aggregate delivered by said hopper,

a vibrating metering means capable of delivering metallic fibers onto the conveyor, said metering means being associated with a means of weight measurement of the quantity of fibers delivered,

one or more silos capable of delivering each a hydraulic binder, each silo being associated with a means of weight or volumetric measurement of the quantity of binder delivered, another silo can be used to dose an additional pulverulent such as fly ash for example,

a mixing water supply means associated with a means for adjusting the mixing water flow rate, a mixer comprising a network of injection nozzles in the mixing chamber, said network being supplied with mixing water by said means for adjusting the flow rate, the hydraulic binder being delivered to the inlet of the mixer from said silo and all of the fibers and aggregates being delivered by the conveyor into the mixer, for the mixing of all the constituents of rolled compacted concrete reinforced with fibers, characterized in that it comprises a means for supplying solvent product for delivering on the conveyor, at or near the outlet of the vibrating metering means, a solvent product intended to dissolve the adhesive of the wafers and thus to release the pre-glued metal fibers delivered by said metering means. Advantageously, said means for supplying solvent product is arranged so as to deliver the solvent product downstream from the first hopper for supplying aggregates and upstream from the last hopper for supplying aggregates.

In a particular embodiment, the vibrating metering means comprises a first vibrating tank having on its internal cylindrical wall a helical ramp on which the fiber plates are able to move by vibration from the bottom of the tank towards its top, said ramp helical extending at its top by an intermediate chute opening above the center of a second vibrating tank, said second tank also having on its cylindrical internal wall a helical ramp on which the fiber plates are able to move from the bottom to the top of the second tank, the helical ramp of the second tank opening onto a vibrating corridor which delivers the fibers above the conveyor, said means for supplying solvent product comprising at least one nozzle located substantially above the end upstream of said vibrating corridor. The advantage of providing two vibrating tanks in series is to eliminate irregularities in the supply and distribution of fibers from the only first vibrating tank, the latter being supplied discontinuously with fibers by a forklift truck regularly filled with fiber boards from large bags called "big bags". Advantageously, the first vibrating tank comprises an articulated arm interposed between the top of the helical ramp and the intermediate chute, said arm being able, in a closed position, to prevent passage to the chute and to return the fibers to the center and the bottom of the first tank, and in a variable open position, to allow the passage of a controlled quantity of fibers to said intermediate chute. According to another characteristic, said intermediate chute has parallel vibrating fingers situated substantially in vertical planes, fixed at their upstream end and free at their downstream end, so as to be able to separate the agglomerations of fiber boards and obtain a more regular distribution in the supply of fiber platelets to the second tank, the longitudinal extension of the fingers being parallel to the direction of movement of said fiber platelets.

In a particular embodiment, the second vibrating tank is equipped with a level detector of fibers stored in said second tank, said detector being connected to a motor for controlling the articulated arm, in order to move said arm towards its closed position or inversely towards its open position, when the quantity of fibers stored in the second tank is greater or inversely less than a predetermined threshold value.

According to another characteristic, the second tank is equipped with a frequency modulator to vary its vibration and thus its fiber flow rate, said modulator being able to be controlled by weighing the quantity of fibers delivered at the outlet of the second tank. In fact, the second tank can be mounted on load cells, the fiber flow rate being fixed by the centralized control of the metering device in the central control cabin. The central operator can enter the desired fiber flow rate on a digital controller, then the central unit will operate automatically to control the frequency modulator. The fiber flow can also be checked by a graphic recorder and a printer edition.

Advantageously, the central unit is equipped with a centralized control unit connected to the various means of weight or volumetric measurement of the hoppers, of the silo and of the metering means, as well as to the means of adjusting the flow rate of the water supply means of mixing, to calculate and control the flow of water to be fed into the mixer according to the water content, the flow of each aggregate and / or the flow of the solvent product.

According to yet another characteristic, each hopper and each silo open onto a weighing conveyor belt driven by its own drive motor, the speed of which can be controlled by the centralized control unit, according to the measured weight, to control the flow rate of each concrete component.

The invention will be better understood and other objects, characteristics, details and advantages will appear more clearly during the detailed explanatory description which will follow of a particular currently preferred embodiment of the invention, with reference to the appended schematic drawing. .

On this drawing :

- Figure 1 is a schematic view of the assembly of the continuous power plant according to the invention;

- Figure 2 is an enlarged and partial schematic view of a hopper associated with a weighing belt;

- Figure 3 is a perspective view of a wafer of fibers that can be used in the method of the invention; - Figure 4 is a schematic view in side elevation of the vibrating metering means used in the plant of the invention;

- Figure 5 is a schematic top view of Figure 4 along the line V-V, in the open position of the articulated arm;

- Figure 6 is a partial view similar to Figure 5 showing the articulated arm in the closed position;

- Figure 7 is an enlarged and partial schematic view of the mixer visible in Figure 1;

- Figure 8 is a sectional view of Figure 7 along the line VIII-VIII; FIG. 9 represents a screen page visible on the terminal of the centralized control unit of FIG. 1.

In Figure 1, there is shown schematically the whole of an installation for a continuous plant for the production of compacted rolled concrete reinforced with fibers. This power station comprises a first hopper 1 shown in FIG. 2, intended, for example, to contain and distribute gravel, a first load cell 2, the chassis of which is articulated substantially at point 3 on the lower end of the hopper 1. The chassis of the load cell 2 carries an endless conveyor belt 4, driven by a drive motor 7 which rotates the rollers 5, by means of a chain 6, the drive shaft being fixed at one end Weighing frame 2 relative to the joint 3. The other end of the load cell 2 is connected to a strain gauge 8, suspended from the frame B of the power station, which frame also supports the first hopper 1. The gravel contained in the first hopper 1 falls , as indicated by the arrow FI, on the weighing belt 4, which is rotated anti-clockwise, according to arrow F2, so that the gravel falls at the left end of the weighing belt, as indicated by the arrow F3, on the underlying conveyor belt 9. The strain gauge is connected by an electric cable 10 to a centralized control unit U, as visible in FIG. 1. Of course, the first conveyor belt 9 is also motorized and its motor, as well as the aforementioned motor 7, can be controlled by the unit U.

A second hopper 11 is located near the first hopper 1 and also has a load cell 12 at its lower end, the chassis of which is inverted with respect to that of the first load cell 2. In fact, its motor 17 is located at the end left of the chassis, while the strain gauge 18 is fixed at its right end, the weighing belt of the second load cell 12 being driven clockwise in FIG. 1 so that the aggregate contained in the second hopper 11 falls to the right on the conveyor belt 9 and covers the first aggregate previously deposited. Of course, the conveyor belt 9 is driven counterclockwise in FIG. 1. The strain gauge 18 is also suspended from the frame B and is connected by a line 20 to the unit U. The first conveyor belt 9 pours all of the first two aggregates onto a second motorized conveyor belt 19, as visible in FIG. 1. Above this second conveyor belt 19 are located two other hoppers 21 and 31, the third hopper 21 being intended to deliver a third aggregate constituting concrete, while the fourth hopper 31 may not be operational in the example described below for carrying out the invention. Of course, the number of hoppers may vary and provision could be made, for example, for six hoppers containing different types of aggregates for different types of concrete. Like the other hoppers, each hopper 21 and 31 is associated with a load cell 22, 32, each load cell being associated with its own electric motor 27, 37 and its own strain gauge 28, 38. Each strain gauge as well as each engine can be connected by lines 30 and 40 to the U unit.

As visible in FIGS. 1 and 4, the central unit also includes a metering means D provided with a vibrating passage 41, the outlet end of which opens onto a chute 42 situated above the second conveyor belt 19, upstream of the third hopper 21.

The metering means D has an elevator 43, which comprises at its lower end rollers 43 a guided in vertical grooves 44 and at its upper end rollers 43b guided in vertical grooves 45, the upper portion of these grooves 45 being bent horizontally to allow the tilting of the lifting tank 43 in the high position, as visible in FIGS. 1 and 4. The lifting tank 43 is intended to be filled by loads in large bags (whose weight is for example 1,100 kg) platelets of pre-glued fibers P, for example of the type of platelets visible in FIG. 3. These platelets are, for example, poured into the elevator tank 43 in the low position from large bags filled with platelets, as indicated by arrow F4 in FIG. 4. In the high position of the lifting tank 43, the latter pours its contents as indicated by arrow F5 in a first cylindrical tank 46, which is provided at its upper end with a deflector 47 to prevent the fiber plates P from falling outside the tank. The first tank 46 is mounted on a base 48, which rests on an intermediate frame 50a with a set of springs 49 interposed and shock absorbers not shown, said intermediate frame 50a resting on a base frame 50b equipped at each corner with a load cell 51. The base 48 is equipped with two vibrating motors 52 arranged on either side of the base 48, to vibrate the first tank 46 by adding the combined effect of the springs and dampers. The two motors rotate at the same speed so as to generate sufficient vibrations in the cylindrical tank 46 to cause the fiber platelets to rise by vibration along a helical ramp 53 arranged on the cylindrical internal wall of the first tank 46. As best seen in FIGS. 5 and 6, the fiber platelets rise from the bottom to the top of the tank by turning counterclockwise, as indicated by arrow F6, and an articulated arm 54 is provided at the top of the tank 46 to allow the passage of the fiber plates either towards an intermediate chute 55, as indicated by the arrow F7 (see FIG. 5), or towards a plate 56 inclined towards the center of the tank 46 to allow the return of the plates towards the bottom of it, as indicated by arrow F8 (see Figure 6). As indicated by line 57, the articulation of the arm 56 is motorized and its motor can be controlled by the unit U, via the sensor 70.

The chute 55 is provided with a plurality of fingers 58, parallel to each other, oriented substantially in the direction of movement F7 of the fiber plates, so as to better distribute the plates. The chute 55 opens above the center of a second cylindrical tank 59, smaller, which also includes a base 60 on which are mounted on either side two vibrating electric motors 61 and a set of springs and dampers 49 on the aforementioned intermediate chassis 50a. The second small tank 59 also has a helical ramp 63 on its internal wall, to bring the fibers and / or the fiber platelets up from the bottom to the top by turning counterclockwise, as visible by the arrows F9 on the Figure 5. The helical ramp 63 opens at its top on a second chute 64, which extends radially outward from the tank 59 and opens above the corridor 41 which is provided with vibrating motors (not shown). Vibrating fingers can also be provided at the outlet of the trough 64. This vibrating passage 41 is mounted via springs 65 on an upright 66, at its upstream end, and suspended at its downstream end via springs 67 from the frame B. At the end upstream of the vibrating corridor 41 it is possible to provide at least one nozzle 68 for injecting water from the network, a valve 69 making it possible to adjust this flow rate, for example via the unit U. For example, the vibrating corridor 41 can be filled with about half a centimeter of water to start peeling off the fiber boards. The direction of travel of the fibers in the corridor 41 is indicated by the arrows F 10. The fibers as well as the water or the solvent product fall from the corridor 41 onto the aforementioned second conveyor belt 19. In a variant preferred shown in Figures 3 and 4, the nozzle 68 is disposed above the last chute 64, to increase the duration of humidification of the fibers before they fall on the conveyor.

As can be seen in FIG. 4, the entire metering means D rests on the ground S or on a mobile trailer, like the frame B.

Under the intermediate chute 55 is provided a support for a level detector, for example an ultrasonic sensor 70, for detecting the level of the fibers in the second tank 59 and automatically controlling the movement of the articulated arm 54, depending on whether the level in the second tank is greater than a predetermined threshold value. The fact of having two tanks in series makes it possible to avoid irregularities in the supply and distribution of the fibers leaving the metering means, these irregularities being inevitable in the case of the use of a single tank.

The position of the articulated arm 54 relative to the intermediate chute 55 is electronically controlled according to the information given by the sensor 70, so as to vary the flow of fibers which passes from the first tank 46 to the second tank 59. Of course, other systems for metering fiber platelets to the conveyor belts of the plant could be provided.

By way of example, one can choose plates P, the metallic fibers of which consist of substantially cylindrical wires comprising a substantially straight longitudinal central portion extending on each side by means of an intermediate portion of a curved end portion. whose shape is of the type which prohibits the attachment of two neighboring fibers, said threads having

- a diameter between 0.38 and 1.05 mm,

- a total length between 19 and 80 mm, - a length of the end parts between 1.5 and 4 mm,

- a transverse offset between the central part and each end part of at least 0.75 mm,

- a bending angle, defined between each intermediate portion and the central part, at least equal to 20 °, and - an obtuse angle less than or equal to 160 ° between each intermediate portion and the central part, - an obtuse angle between each intermediate portion and end portion, and,

- a minimum tensile strength of 900 N / mm ² .

Advantageously, the threads constituting the fibers have a diameter between 0.65 and 0.85 mm and a total length / diameter ratio between 65 and 85. In particular, the fibers have a total length / diameter ratio of the order of 80. According to a particular feature, each curved end part is formed of a rectilinear part connected to the central part by said inclined part comprising at least two elbows. Advantageously, the fibers used in the present invention are fibers of 0.75 mm in diameter, with a total length of 60 mm and with a tensile strength of at least 1100 N / mm ² , sold for example under the brand "Dramix 80/60". This fiber also has the advantage, with an equal dosage by weight in concrete, of a number of fibers double that of the number of fibers of diameter of 1 mm traditionally used. Due to a hardening pushed further to the wire drawing, the thinner wire moreover has a higher elastic limit which makes it more efficient than a wire of 1 mm in diameter.

The plate P comprises a plurality of fibers fl, f2 ... fh, where n is any integer, for example equal to 20.

In the example described here, the metal fibers are therefore poured onto the first two layers of aggregates and before the deposition of the third layer of aggregates.

The second conveyor belt 19 pours all of the fiber aggregates onto a third conveyor belt 79, which opens into a mixer 80.

The plant comprises one, or two, or more silos 81, each of which contains a hydraulic binder, for example a standardized CPJ cement (Portland cement) or CLK (slag cement), or even a road binder, for example the product sold under the brand "LIGEX" by the company CALCIA. The lower outlet of each silo 81 leads to a pipe containing an endless screw 82 for transporting the binder to a hopper 83. This hopper 83 can receive hydraulic binders from several silos. The lower outlet of the hopper 83 leads to another transport worm 84, which delivers the hydraulic binder on a weighing belt 85 inside a casing 78, one end of which is linked to a strain gauge 86 to weigh the quantity of hydraulic binder.

Of course, the level sensor 70, the load cells 51 and the other motors of the metering means D are connected by different lines 71 to 73 to the centralized control unit U. The strain gauge 86 is also connected by a line 74 to unit U.

The weighing belt 85 delivers the hydraulic binder to the inlet of a double conveyor containing two endless conveyor screws 87 to introduce said hydraulic binder into the aforementioned mixer 80, substantially in the vicinity of the inlet of the fiber and aggregate mixture delivered by the third conveyor belt 79.

The mixer is also supplied with mixing water via the water network, as indicated by the valve 88, and with plasticizing additives contained in a tank 89. A mixing valve 90 makes it possible to mix the adjuvant coming from the tank 89 with the water from the network 88. This mixture of water and adjuvant is distributed inside the mixer 80 via a network of pipes 91 pierced with orifices to inject the mixture into the mixer above two kneading shafts 92. As can be seen in FIG. 8, the network of pipes 91 preferably comprises a simultaneous arrival of the mixture on either side of the mixer, the network comprising a U-shaped branch in parallel above the trees 92. Each shaft 92 comprises diametral blades 93 provided at their ends with pallets 94 inclined so as to constitute a discontinuous helical ramp. The blades of each shaft are offset so as to allow the mixing of all the constituents of the compacted rolled concrete reinforced with fibers, when the two shafts are rotated in opposite directions, as visible by the arrows Fi l in the figure 8.

For example, the admixture makes it possible to delay setting of the concrete for several days, with a proportion of 0.8% of the weight of the hydraulic binder. Such a plasticizer can be a plasticizer sold under the brand "CIMAXTARD" by the company Axim.

At the outlet of the mixer 80, the concrete and fiber mixture reaches a fourth conveyor belt 99, which transports the composition to a hopper 100 whose bottom is closed by a helmet consisting of two oscillating arms 101 which are able to move apart in order to unload the contents of the hopper 100 in a truck 102.

The opening of the swinging arms 101 is controlled by the manager of the plant for filling the trucks. The unit U is connected to a terminal comprising a screen 110 and a keyboard 111 for entering set values for the different component flow rates and speeds of the different conveyor belts.

In Figure 9, there is shown a page of the screen 110, during operation of an exemplary embodiment of the method of the invention.

In FIG. 9, D1 designates gravel with a diameter of between 5 and 12 mm, with a flow rate of 75.4 T / H (ton per hour), having a natural water content of approximately 1.70%, the gravel being intended to constitute 44% of the dry constituents of fiber-free concrete, D2 designates crushed sand, the diameter of which is between 0 and 4 mm, with a flow rate of 48.3 T / H and a water content of 4, 30%, to constitute 27.30% of the weight of the dry constituents of fiber-free concrete, D3 of wet rolled sand having a diameter between 0 and 4 mm, with a flow rate of 28.9 T / H and a water content of 8.40%, to constitute 15.80% of the weight of the dry constituents of fiber-free concrete, D4 to D6 can denote other types of aggregates or aggregates, but are not used in this example, PI denotes the hydraulic binder which is fed with a flow rate of 21.7 TH to constitute 12.9% by weight of the dry constituents of the fiber-free concrete, P2 possibly being another pul convoluted (for example fly ash) added to PI, XI being a first adjuvant which constitutes 0.35% of the dry weight of the hydraulic binder PI, which corresponds to a flow rate of approximately 80 kg or 80 liters per hour, X2 or X3 can designate other additives and E designates the mixing water which has a proportion of 5.20% of the weight of the dry components of the concrete with a flow rate of 3.3 T / H.

Of course, since the aggregates D1 to D3 are not dry but contain water, the water flow rate to be supplied will not be equal to 5.5% of the total machine flow rate.

We will calculate below the actual water flow to be supplied. For this purpose, we start from the total machine flow, namely the wet concrete flow without fiber supplied by the machine, which corresponds to 177.6 T / H, namely the sum of the flow rates of the components Dl to D3, PI and E.

To obtain the dry flow delivered by the plant, excluding fiber, divide the wet flow by 1 + 5.2% = 1.052, which gives a total dry flow equal to 168.8 T / H.

The theoretical water flow is then equal to this total dry flow 168.8 T / H x 5.2% = 8.78 T / H.

The quantity of water coming from the aggregate Dl is equal to 0.44 x 168.8 x 0.017 = 1.26 T / H of water. Similarly, the amount of water provided by the D2 aggregate is 0.273 x 168.8 x 0.043 = 1.98 T / H of water. For D3, the quantity of water supplied is equal to 0.158 x 168.8 x 0.084 = 2.24 T / H, i.e. in total, for all of the aggregates Dl to D3, a water flow rate equal to 5.48 T / H which must be deducted from the theoretical water flow of 8.78 T / H, or 3.3 T / H of water actually to be supplied in the mixer.

The power plant is used with a flow rate of 177.6 T / H which corresponds to only 60% of its nominal capacity of the order of 400 T / H here limited to 300 T / H by the capacity of the hydraulic binder dispenser used. The aggregates used may contain from 70 to 100% of crushed material, having sharp angles and a shape close to the square, and a particle size between 0 and 14 mm so as to avoid the phenomena of segregation, that is to say separation of large elements. The concrete composition also preferably comprises a plasticizing aid which facilitates compaction by intergranular lubrication and makes it possible to obtain a density close to 2400 kg / m ³ of wet concrete without fibers with favorable consequences, such as higher strength and the possibility of reducing the dosage by hydraulic binder The optimal water content is determined by the Proctor test

Modified and varies between 4 and 6% of the dry constituents of concrete.

Advantageously, the composition comprises a content of hydraulic binder close to 250 to 300 kg per cubic meter of dry concrete without fiber, a water content of 4 to 6% of the weight of the dry constituents of concrete without fiber, that is to say about 100 to 150 liters of per cubic meter of concrete, a dosage of metal fibers between 30 and 40 kg per cubic meter of dry concrete without fiber. For example, the composition includes 280 kg of hydraulic binder and 110 liters of water per cubic meter of dry concrete without fiber.

Advantageously, the composition also comprises a content of retarder plasticizer varying between 0.3 and 1.8% of the weight of the hydraulic binder.

Furthermore, the instantaneous fiber metering precision obtained with the plant according to the invention is between - 5% and + 10%, which cannot be obtained with a truck mixer. The production rates in the continuous plant of the type of the invention are between 200 and 1,000 tonnes / hour of concrete, while batch plants can generally only reach half of these rates.

Although the invention has been described in conjunction with a particular embodiment, it is obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these are within the scope of the invention.

Claims

1. A method of continuously manufacturing a compacted rolled concrete composition reinforced with metal fibers, comprising the following steps: a) continuous feeding of several types of aggregates

(Dl, D2, D3, D4) delivered on a conveyor (9, 19, 79), b) the continuous feeding of metallic fibers (fl, f2 ... fh) from a vibrating dosing means ( D) on said conveyor, c) continuous supply to a kneader (80) of the aggregates and fibers delivered by the conveyor, of a hydraulic binder (PI) and of mixing water (E) which may contain one or more several concrete admixtures characterized in that: the aforementioned step b) consists in supplying the aforementioned vibrating metering means with plates of pre-glued metal fibers (P) to deliver said fiber plates and / or said fibers peeled off on the conveyor during the aforementioned step a), said fibers being fed in a proportion of between 25 and 60 kg of fibers per m ³ of dry constituents of the concrete without fiber, and that step c) consists in feeding the hydraulic binder in a proportion between 180 and 400 kg / m ³ of dry constituents of concrete without f ibre, the proportion of mixing water being determined so that the mixer continuously delivers a rolled concrete composition compacted with fibers which has a water content of between 90 and 150 liters of water per m ³ of dry concrete constituents fiber free.

2. Method according to claim 1, characterized in that it consists in feeding continuously, during step a) above, on the conveyor (9, 19, 79), a solvent product, for example l water, to dissolve the adhesive which keeps the fibers in platelets, said solvent product being delivered to the conveyor at or near the point of fall of the fibers (P, fl, f2 .. fh) delivered by the metering means ( D).

3. Method according to claim 1 or 2, characterized in that the metering means (D) successively comprises at least one tank (46, 59) vibrating metering and a vibrating passage (41) or a weighing belt.

4. Method according to claims 2 and 3 taken in combination, characterized in that it consists in supplying solvent to said corridor so that the fibers (P, fl, £ 2 .. fia) bathe at least partially in the corridor whose bottom is filled with solvent product and are delivered together with said solvent product on the conveyor (9, 19, 79) from said corridor.

5. Method according to claim 2, characterized in that it consists in delivering said solvent product by at least one nozzle located just downstream of the point of fall of the fibers (P, fl, £ 2 .. fh) on the conveyor (9, 19, 79).

6. Method according to one of claims 1 to 5, characterized in that it consists in delivering the fibers (P, fl, £ 2 .. fh) on the conveyor (9, 19, 79), after the feeding a first type of aggregates (Dl) and before feeding the last type of aggregates (D2, D3 or D4), so that the fibers are integrated into the mass of the different types of aggregates.

7. Method according to one of claims 1 to 6, characterized in that it consists in calculating the proportion of mixing water (E) delivered in step c) above in the mixer (80), depending the water content specific to each type of aggregate (D1-D3) supplied in step a).

8. Method according to one of claims 1 to 7, characterized in that it consists in feeding in step a) a total proportion of the aggregates between 83 and 93% by weight of dry constituents of the concrete without fiber, and in step c) a cement (PI) or a road binder in a proportion of between 7 and 17% by weight of dry constituents of the fiber-free concrete, of which 0.3 to 1.8% by weight of the hydraulic binder is formed an adjuvant (XI) for setting concrete and / or plasticizer introduced into the mixing water to lubricate the intergranular contacts and delay setting of the concrete.

9. Continuous unit for implementing the method according to one of claims 1 to 8, comprising:

- A series of hoppers (1, 11, 21, 31) arranged at intervals above a conveyor (9, 19, 79) driven by motor, each hopper being able to deliver on the conveyor a type of aggregate (Dl , D2, D3, D4), each hopper being associated with a means for volumetric or weight measurement (2, 12, 22, 32) of the quantity of aggregate delivered by said hopper,

- a vibrating metering means (D) capable of delivering metallic fibers (fl, f2..fh) onto the conveyor, said metering means being associated with a means of weight measurement (51) of the quantity of fibers delivered,

- one or more silos (81) each capable of delivering a hydraulic binder (PI), each silo being associated with a means of weight or volumetric measurement (86) of the quantity of binder delivered, another silo can be used to dose a additional powder like fly ash for example,

- a means of supply (88) of mixing water associated with a means of adjustment (90) of the flow of mixing water, - a mixer (80) comprising a network (91) of injection nozzles in the chamber mixing system, said network being supplied with mixing water by said flow adjustment means

(90), the hydraulic binder being delivered to the inlet of the mixer from said silo and all of the fibers and aggregates being delivered by the conveyor into the mixer, for mixing all the constituents of the compacted rolled concrete reinforced with fibers, characterized in that it comprises a means (69) for supplying solvent product for delivering onto the conveyor (9, 19, 79), at or near the outlet of the vibrating metering means ( D), a solvent product intended to dissolve the adhesive of the plates (P) and thus to release the pre-glued metal fibers from the plates (P) delivered by said metering means.

10. Plant according to claim 9, characterized in that said means for supplying (69) solvent product is arranged so as to deliver the solvent product downstream of the first hopper (1) for supplying aggregates and upstream of the last aggregate feed hopper (21).

11. Plant according to claim 9, characterized in that the vibrating metering means (D) comprises a first vibrating tank (46) having on its internal cylindrical wall a ramp helical (53) on which the fiber plates (P) are able to move by vibration from the bottom of the tank towards its top, said helical ramp extending at its top by an intermediate chute (55) opening above the center a second vibrating tank (59), said second tank also having on its cylindrical internal wall a helical ramp (63) on which the fiber plates are able to move from the bottom to the top of the second tank, the helical ramp of the second tank opening onto a vibrating passage (41) which delivers the fibers above the conveyor (9, 19, 79), said means for supplying solvent product comprising at least one nozzle (68) located substantially at above the upstream end of said vibrating corridor.

12. A unit according to claim 11, characterized in that said intermediate chute (55) comprises parallel vibrating fingers (58) located substantially in vertical planes, fixed at their upstream end and free at their downstream end, so as to be able separating the agglomerations of fiber boards and obtaining a more regular distribution in the supply of fiber boards (P) of the second tank, the longitudinal extension of the fingers being parallel to the direction of movement (F7) of said fiber boards.

13. Plant according to claim 11 or 12, characterized in that the first vibrating tank (46) comprises an articulated arm (54) interposed between the top of the helical ramp (53) and the intermediate chute (55), said arm being able, in a closed position, to prevent passage to the chute and to return the fibers to the center and the bottom of the first tank, and in a variable open position, to allow passage of a controlled amount of fibers to said intermediate chute.

14. Plant according to claim 13, characterized in that ^" the second vibrating tank (59) is equipped with a detector" (70) of the level of fibers stored in said second tank, said detector being connected to a control motor of the articulated arm (54), in order to move said arm towards its closed position, or vice versa towards its open position, when the quantity of fibers stored in the second tank is greater, or inversely less, than a predetermined threshold value.

15. Plant according to claim 14, characterized in that the last tank (59) is equipped with a frequency modulator to vary its vibration and thus its fiber flow rate, said modulator being able to be controlled by weighing the quantity of fibers delivered at the outlet of the second tank.

16. Plant according to one of claims 9 to 15, characterized in that the plant is equipped with a centralized control unit (U) connected to the various means of volumetric or weight measurement of the hoppers (1, 11, 21, 31), the silo (81) and the metering means (D), as well as the flow adjustment means (90) of the mixing water supply means, for calculating and controlling the water flow (E ) to be fed into the mixer (80) according to the water content, the flow rate of each aggregate (Dl to D3) and / or the flow rate of the solvent product.