FR2923242A1 - Low-density concrete e.g. hemp lime concrete, projecting method for e.g. wall, involves humidifying mixture by mist blower due to dispersion of water in gas so as to obtain concrete, and projecting concrete on surface or substrate - Google Patents

Abstract

The method involves homogenization of light granulate with a hydraulic binder e.g. cement, to obtain a mixture at atmospheric pressure by a homogenization unit (9), and transferring the mixture to a pneumatic conveying path (13) at predetermined pressure higher than the atmospheric pressure by a transferring unit (10). The mixture is pneumatically conveyed to a projection outlet (17) at the predetermined pressure. The mixture is partially humidified by a mist blower (14) due to dispersion of water in gas so as to obtain low-density concrete. The concrete is projected on a surface or support. An independent claim is also included for a device for projecting low-density concrete on a surface or support.

Description

METHOD FOR THE CONTINUOUS PROJECTION OF LOW DENSITY CONCRETE

The present invention relates to a process for continuous spraying of low density concrete. The invention also relates to a device for continuously projecting such a concrete. The invention applies mainly to the construction sector, in particular for the thermal and acoustic insulation of surfaces, such as walls, screeds, slabs or roofs, for the renovation of walls or as framework filler. By low density concrete is meant a compound comprising at least one binder, especially an air binder, and at least one lightweight plant-type granulate, in particular based on hemp, straw, flax, corn, wood. or the like or a mixture thereof, as well as optionally a solid and / or liquid additive and / or adjuvant. The interest of this type of concrete resides in a very good thermal insulation but also an acoustic correction. In order to optimize the insulation coefficient, the proportion of lightweight aggregate, of insulating nature, is then maximized relative to the other components of the low density concrete. Large thicknesses of these concretes will often be applied to ensure good insulation. Low density concrete will be envisioned in the present invention as consisting mainly of a light aggregate as defined above, consolidated, or even coated with at least one binder and not the reverse. The low-density concrete thus obtained is therefore substantially compressible when it is used before curing, unlike most concretes for which the aggregate (s) are embedded in a mass of binder (s) and which are little or no compressible. Such low density concrete will have a density of between 150 kg / m3 and 950 kg / m3 and preferably a density of between 200 kg / m3 and 500 kg / m3. Among the binders mentioned above, mention may be made of aerial binders, such as hydrated dolomite, hydrated dolomite, or hydraulic binders, such as cements, natural hydraulic lime or hydraulic binders based on lime, or a mixture of them.

By "air binder" is meant binders whose uptake results from a carbonation, in particular by the 002 of the atmosphere. The term "hydraulic binder" means binders whose uptake results from a pozzolanic reaction in the presence of water. Hydraulic binders based on lime, means any combination of a pozzolanic reagent fin (clay, ash, metakaolin ...) and lime. As light aggregate (sometimes called aggregate) of vegetable origin, mention may in particular be made of chenevot, the non-fibrous part of the hemp stalk, after mechanical defibration or any other method of transformation of the plant, and / or of other hemp components, such as fibers, fibrils, dust and hemp powder, or wood, flax.

The terms slaked lime or hydrated lime represent a compound consisting mainly of calcium hydroxide. Low density concretes, in particular hemp concretes, are well known in the field of construction, in particular for their insulating property, as described, for example, in patent EP 1 406 849. Their use is essentially carried out by bunching. . It is a question of pouring the concrete between 2 walls (banches). This process suffers from many disadvantages. First of all, this process is fundamentally discontinuous in its preparation, mixing and processing phase. This makes it slower than a continuous process, resulting in low productivity.

Moreover, if one of the two faces of the panels can be mounted directly on the entire height of the wall or the wall to be erected, the other is mounted in levels or layers. The formwork levels thus obtained are gradually filled one after the other. At the interface of two concrete beds, the successive layers do not bind and constitute zones of weakness. Removal cracks appear. This process by peeling therefore has a reduced efficiency in terms of the insulation sought by this type of low density concrete because there are discontinuities in the implementation of aggregates between the different levels of filling. A shrinkage of the concrete, linked to an excess of water during the mixing, also occurs from one layer to another, due to a partial take of one layer before processing of the next. Finally, the composition of the concrete may vary from one level to another, resulting in a lack of homogeneity in the insulating wall. This process still presents constraints, related to the difficulty of pouring the concrete in approach of the ceilings or slopes of roofs, bracing (wood in diagonal) and in general in the presence of all the obstacles such as the electrical networks, of water, of heating ... Borage also promotes hydration of the light aggregate, incorporated in the binder. However, the added water for the preparation of low density concrete must be used to hydrate the binder or binders but it is detrimental that the water is too in contact with light aggregates, such as hemp, which can absorb up to about 400% of its weight of water. This results in excessive water consumption and a critical drying problem, the duration of which will be increased unnecessarily. All of the above considerations argue for another method of setting up low-density concretes, which would be basically continuous, with high productivity and allowing a more homogeneous application, with a single support wall, unlike benching. According to the invention, it is intended to use a method of spraying low density concretes. Several techniques of projection (or gunning) of concretes are known among which are distinguished in particular wet or wet projection methods and dry projection methods. Wet or wet projection methods are particularly dedicated to high density concrete (that is to say a concrete having a density up to 5 times higher than a low density concrete), the majority of which is granulated. is often sand (sand concrete). Their use for spraying low-density concretes, in particular hemp-lime concretes, would require an excessive dosage of lime as well as an addition of sand because of the compressibility of hemp-lime concretes which would be avoided in the - 4- frame of a wet projection. The thermal performance of coatings made in this way would then be reduced, compared to the use of hemp-lime concrete correctly dosed without sand. Moreover, a wet projection technique also promotes hydration of the light aggregate, incorporated into the binder, which is detrimental, as mentioned above. The drying time of wet cast concrete is long, because of the time required to evacuate the mixing water, which can disrupt the progress of the construction.

Dry spray methods provide that raw materials are mixed in dry form and that the mixture is hydrated only a short time before the release of the lance. Such a method often resorts to a high pressure and a high speed of the product to be used. Also this method is it suitable for concretes generally not or little compressible, in which the aggregates are embedded in a mass of binder (s) majority. With this dry method, the rebound losses on the treated wall are greater than in the case of the wet process. The dry projection techniques are therefore not suitable for the continuous preparation and projection of low density concrete comprising at least a light aggregate of the plant type, in particular based on hemp, straw, corn, flax. of wood or the like which are compressible materials. Indeed, these aggregates are very bulky (they have a very low density) and are difficult to dose and transfer from one stage to another of the projection process. The mainly fibrous and bulky nature of the light aggregates leads to frequent blockages, especially at the transfer stage, after the mixing of the constituents to dry at atmospheric pressure, to the pneumatic transport under high pressure. Obstructions at the level of the metering units and the transfer unit compromise a truly continuous operation because such blocking requires disassembly, cleaning, reassembly and a new supply of dry constituents. In addition, the dosage and above all the above-mentioned transfer step are irregular with the traditional techniques of preparation and dry concrete spraying. This is due to an irregular and time-varying filling of the equipment used in these steps, in particular of the cellular locks, notably because of the fibrous and voluminous nature of the light aggregate and the variability of the composition and the density of the mixture before transfer, as well as irregular size of light aggregates. The filling of the cells which are positioned vertically is irregular because the concrete of the hemp type has a strong propensity to remain agglomerated and difficult to descend into the cell at the time of the passage thereof, which will lead downstream irregular flow mixing which then causes an irregular projection of the concrete after wetting. To overcome this disadvantage, it is possible to use a higher amount of air to avoid clogging at the outlet of the wetting equipment. Another disadvantage that appears as a consequence of the too high proportion of air relative to the concrete of low density transported is the speed of impact too high, which causes rebound and thus lost materials or that must be collected. Furthermore, the low density and high compressibility of low density concrete comprising at least one light aggregate, makes it difficult to transport pneumatically (under pressure) to achieve the projection. It is understood that traditional projection techniques, developed for conventional concrete not or slightly compressible are poorly suited to low density concrete.

The aforementioned drawbacks are all the more acute as the content of light aggregate in the low density concrete is high and therefore the binder content is low to maximize its insulation coefficient. In addition, for the hydration of concrete, the traditional techniques of dry projection, provide wetting at the end of pneumatic transport by simply adding water. This technique is likely to cause a non-uniform distribution of water during the placement of concrete and especially to moisturize substantially the light aggregate, which is highly detrimental, as mentioned above Finally, the Traditional projection techniques favor an acceleration of the mass to be sprayed at the end-piece of the projection unit, which causes compacting, in order to favor the resistance, the sealing, the reduction of the shrinkage and to improve the adhesion of the concrete layer to the receiving wall. This acceleration is detrimental to low density concrete, which must be deposited on the wall without being compressed, in order to maximize its insulation coefficient. Such acceleration also produces a lot of material rebound on the wall so a lot of loss because these material rebounds are not often recovered. In general, several layers are required for walls covered with high density concrete with traditional techniques, in order to obtain the desired thickness, unlike low density concrete with light aggregates, which is used in a thickness up to a few tens of centimeters, typically 20 to 30 cm, ideally at one time. It is also useful for the support wall to be covered to be openwork, of the small mesh type, in order to produce breathable walls made up of an interior wall made of hemp concrete, an air space and an air space. exterior wall made of bricks or stones. Conventional projection techniques, because of the high pressure, do not make it possible to work in support on perforated walls of lattice type because the shotcrete passes through, which excludes the application in certain countries. The use of small mesh meshes also reduces the time of intervention on site.

Machines for flocking, for example cellulose, are also known; these are able to transport light aggregates, but not to obtain a mechanical strength of the projected coating. Low density concrete is a heterogeneous material that will intervene in the mechanics of the wall and not just insulate it. It is therefore necessary to obtain mechanical strength during the projection. Indeed, the density of a low density concrete is about 5 to 6 times higher than the density of flocking. It is therefore necessary to avoid the creep of said concrete, despite the aforementioned thickness of its implementation. The present invention aims to overcome at least in part the aforementioned drawbacks of the state of the art by providing a method of spraying a low density concrete comprising: a homogenization of a lightweight granulate of vegetable origin with a binder for obtaining a dry mixture, at atmospheric pressure, a transfer of said dry mixture at atmospheric pressure to a pneumatic conveying path in which a predetermined pressure prevails, greater than said atmospheric pressure, said transfer being carried out in a sealed and continuous manner, a pneumatic transport of said dry mixing at said predetermined pressure to a projection outlet, wetting with a water dispersion in a gas of said dry mixture during said pneumatic transport, and a projection of said concrete thus obtained on a surface. The projection method according to the invention makes it possible to overcome the main disadvantages of the known method of the bunching, namely that the bunch is slow, basically discontinuous, requires two full support walls, has withdrawals and ruptures detrimental to isolation at the level of the layer transitions and favors harmful hydration of the light granulate as well as the inhomogeneity of the filling. Indeed, the method according to the invention requires a support surface of only one side, which support can even be perforated, of tight mesh type mesh; the light aggregate sticks itself, and entangles continuously over the entire surface to be covered, without risk of removal or breakage of the aggregate layer. According to the invention, the method has a sealed and continuous transfer step which makes it possible to bring the constituents of the low density concrete at atmospheric pressure to a pneumatic transport where the homogeneously mixed constituents are transported towards the projection outlet. in a stream of air from a blower. The production of dust is limited. In addition, during pneumatic transport, the homogeneous mixture of constituents is wetted by a dispersion of water in a gas. As a result, the humidification step makes it possible to incorporate water to preferentially hydrate the binder without excessively wetting the granulate, which is in this case a material capable of strongly absorbing water. In summary, according to the invention, the discharge rate of the low density concrete is constant even for a concrete containing little binder and therefore compressible because the waterproof and continuous transfer also reduces the risk of blockage. In addition, the regularity of the outlet flow is also due to a controlled humidification which also avoids obstructions and undesirable agglomerations. In addition, the humidification according to the invention avoids the creep of the applied layer while promoting drying. These qualities increase the insulation coefficient of the coating produced by the process according to the invention, which coating is otherwise homogeneous and regular in its composition over the entire surface to be coated. In order to ensure the continuous nature of the process according to the invention, despite the presence of light aggregates often majority of said low density concretes, the dosage of said aggregates is adapted to their light nature, especially fibrous.

The step of transferring homogenized constituents at atmospheric pressure to pneumatic transport under high pressure is critical in order to avoid frequent blockages. The transfer step must therefore both satisfy sealing and regularity constraints as well as preventing any blockage.

According to the invention, advantageously, the transfer step is provided by sealed equipment, with wear and anti-lock recovery system and a regular filling system. In addition, the step of dosing the light aggregate is also carried out by equipment preventing the blockage.

According to a particular embodiment of the invention, the humidification by dispersion of water in a gas is obtained by nebulization or spraying, ensuring, by a control and a distribution of the spray, to preferentially humidify the binder (s) and as little as possible the light granulate (s), whose wetting is detrimental as indicated above. Advantageously, the step of homogenizing the raw materials is a moderate stirring, or even a coating of the granulate (s) by the binder (s). This homogenization step may take place in the device according to the invention or outside thereof, beforehand, for example, by introducing a ready-to-use mixture into said device. Advantageously, the step of spraying the low density concrete is directional, ensuring the convergence of the concrete during its application. Advantageously, the method according to the invention comprises, prior to said homogenization, storage, dosing and transport of said light granulate and said binder. In a preferred embodiment, the method according to the invention comprises a recycling of said low density concrete projected onto said surface and having undergone a rebound. According to the invention, the low-density concrete is sprayed pneumatically, it is projected on a surface with a predetermined flow rate and a predetermined speed which must be sufficient to prevent clogging and to ensure an exit of the appropriate material, while allowing an application of a layer of relatively large thickness without or reduced creep. For this purpose, it is difficult to completely avoid this rebound phenomenon, but to minimize losses it is advantageous to recycle the bounced material. This is what the invention provides. Advantageously according to the invention, the recycled low density concrete is further stored, metered and then introduced and kneaded with said mixture of light aggregate and binder. Since the low density concrete is recycled after homogenization, it is incorporated by post-mixing into the fresh mixture and is thus diluted in fresh material. According to the invention, the binder is chosen from an aerial binder, a hydraulic binder or a mixture thereof. Preferably, the binder comprises an air binder, such as slaked lime. It can also be envisaged that the binder is a cement, a whitewash, a natural hydraulic lime or a lime-based hydraulic binder or a mixture thereof. According to the invention, the light aggregate of vegetable origin is based on hemp, preferably hemp hemp, or base straw, corn, wood or flax or the like. The invention also relates to a device for spraying a low density concrete to at least partially overcome the disadvantages of known projection devices, in that the device is a continuous device that does not lock and allows avoid double bunching and / or creep. To solve this problem, there is provided according to the invention a device comprising: a homogenization means connected to a feed in a light granulate and to a binder feed, to form a homogenized dry mixture at atmospheric pressure, a pathway pneumatic conveying said homogenized mixture in which a predetermined pressure prevails, greater than said atmospheric pressure and which has a projection output of said low density concrete, a sealed and continuous transfer unit, arranged to connect said homogenizing means to the atmospheric pressure at said pneumatic conveying path where said predetermined pressure prevails, and humidifying means comprising means for dispersing water in a gas, disposed in said pneumatic transport path, before said projection outlet. As mentioned above, said sealed and continuous transfer unit prevents jamming, which allows a regularity of mixed flow within the pneumatic transport path. In addition, the sealing of the transfer unit is of considerable importance because of the pressure differences upstream and downstream of said transfer unit. The constituents (light aggregate and binder) will therefore be homogeneously transported and will be able to pass through said humidification means disposed in said transport path, which will allow regular humidification. In addition, this incorporation of water is controlled and partially humidifies the mixture in order to hydrate the binder optimally by moistening the granulate as little as possible.

Therefore, the sealed and continuous transfer unit makes it possible to impose a regular flow rate of the dry mixture in said pneumatic conveying path and, in conjunction with the partial humidification by a dispersion of water in a gas, maintains this flow rate regularity. output of the low density concrete thus formed; the device according to the invention therefore allows to project a considerable thickness of concrete on a surface and thus avoid the bunching and / or creep. The homogenizing means may also be present in the device according to the invention or, in a similar alternative, be separated from the projection device, for example, be part of a separate homogenization installation whose output is connected to the device according to the invention. the invention. Preferably, said binder feed comprises a storage means, a metering means and a transport means which are, for example, an extended feed hopper of a tubular in which said binder can flow, and between the two find an Archimedean screw or a valve to quantify the amount of binder introduced. Advantageously, said supply of light granules comprises a scraper feeder connected to a feed hopper which allows, thanks to the presence of squeegees, to transport the light and fibrous aggregate without obstruction or blockage of the transport, in particular between the web and the chassis of the raclette feeder. Preferably, said scoop dispenser comprises an ascending part and a descending part between which there is an equalizer. This allows a transport of a reproducible amount in a space between the squeegees and thus promotes the regular flow. In addition, lightweight aggregates whose size would be too large and would interfere with the continuous operation of the device according to the invention are rejected from it. Advantageously, said sealed and continuous transfer unit comprises a rotary alveolar lock. Preferably said sealed and continuous transfer unit comprises a recovery means and / or a wear indicator and more preferably, said sealed and continuous transfer unit comprises an anti-lock system, in particular a squeegee and a release opening. In this way, the flow rate of the mixture of light aggregate and binder is as regular as possible to promote the continuous operation of the device according to the invention. The sealed rotary cellular sluice according to the invention, furthermore comprising the wear indicator and / or a recovery means as well as an antiblocking means consisting in particular of a scraper, makes it possible to fulfill the triple condition which is particularly important for a sealing continuity of operation to maintain the pressure difference, regularity of dosage and prevention of any obstruction.

Other features, details and advantages of the invention will become apparent from the description given below, without limitation and with reference to the accompanying drawings. Figure 1 is a schematic view of the device according to the invention. Fig. 2 is a sectional view of said light granulate feed of the device according to the invention. Figure 3 is a sectional view of said sealed and continuous transfer unit of the device according to the invention. Figure 4 is a sectional view of the pneumatic conveying path in which the humidifying means according to the invention is disposed. FIG. 5 illustrates the projection lance of the projection device according to the invention. Figure 6 is a sectional view of a homogenization means according to the invention. In the figures, identical or similar elements bear the same references. As can be seen in Figure 1, the device according to the invention comprises a binder feed 1 selected from an aerial binder or a hydraulic binder or a mixture thereof, and preferably contains slaked lime . As mentioned above, the feed may comprise a feed hopper 2 and a pipe 3 in which the binder contained in the hopper can flow. In addition, between the hopper 2 and the tubing 3, one can find an Archimedean screw 4 for dosing the amount of binder. The device also comprises a light aggregate feed 5, which is further illustrated in FIG. 2. The feed also comprises a feed hopper 6 and a scraper feeder 7 which dose and transports the light granulate into the tubing 8 which ends in a homogenizing means 9 at atmospheric pressure, comprising for example a worm for advancing the mixture to said transfer unit 10. The transfer unit 10 is explained in more detail in FIG. it can be seen a rotary cellular sluice 11 provided with seals 12 which makes it possible to bring the mixture at atmospheric pressure coming from the homogenization unit 9 to the pneumatic conveying path 13 at a transport speed of 30 to 50 meters / minute. . Indeed, as can be seen, the transport path 13 is powered by a fan 29. Of course, the blower 29, for example air, may be replaced by any other similar equipment to impose a flow of air or other gas for driving a powdery material in a conduit. In the transport path 13, the dry mixture is driven by the air stream created by said blower 29 or alternatively by a blower performing a similar function. In said transport path, the mixture will be partially moistened by the humidifying means 14 which comprises a tubular nebulization ring and a plurality of nebulizing nozzles 16. In addition, the tubular nebulization ring comprises a plug 15 allowing access it if necessary. The humidification means is explained in more detail in FIG. 4.

Once the mixture is partially moistened, i.e. the binder is moistened and the light aggregate is as little as possible, the low density concrete is formed and can exit through the projection lance outlet. 17 is illustrated in greater detail in FIG. 5. The transport path 13 may consist of one or more parts, flexible or otherwise, to be connected together.

As can be seen in FIG. 2, the light granulate feed 5 comprises a scraper dispenser 7 which allows the dosing of the light aggregate, and this, in order to ensure the continuous operation of the device according to the invention, in spite of the presence of light aggregates often the majority of said low density concretes. Indeed, the dosing means of said light aggregates, especially fibrous, must avoid any blockage or obstruction. This scraper dispenser 7 is connected to a feed hopper light aggregate, advantageously secured to the frame of the metering device, and preferably comprises an equalizer 18 of the light aggregate, located between the upward portion 7a and 7b down the band of the metering device. In a particular embodiment of this scraper dispenser, the rise of the scrapers 19 and therefore the aggregate is done at the bottom of the strip and not at the upper part thereof, as shown by the orientation of the scrapers 19 and the forward arrows in FIG. 2. As can be seen in FIG. 3, the transfer unit of the homogenized constituent elements coming from the homogenization means 9 at atmospheric pressure, towards the pneumatic conveying path 13, under high pressure is preferably carried out by means of a specific rotary alveolar lock 11, in order to avoid frequent blockages therein. Indeed, no commercially available equipment can fulfill the triple condition of sealing, regularity, dosage and prevention of any obstruction. Such a rotary alveolar transfer lock 11 according to the invention (see FIG. 3) preferably comprises a large number of cells 20 in order to allow a regular transfer of the homogenized material. The rotary lock 11 typically comprises at least 4 cells 20, advantageously at least 6 cells, preferably at least 8 or 10 cells 20. Advantageously, the speed of rotation of the rotor about the axis of rotation 26 of the Alveolar lock 11 is elevated, typically at least 10 rpm, preferably at least 15 and even at least 20 rpm, so as to provide as regular a feed as possible for the homogenized material from the medium. homogenization 9 to the pneumatic transport path 13.

The transfer unit of the device according to the invention further comprises a sealing system, preferably with recovery and wear indicator; in the case of the rotary alveolar lock 11 mentioned above, this system consists of two continuous lateral seals 21, preferably in the form of discs, mounted on a support plate 22, itself on pressure springs 23.

Typically, the seal provided by the continuous side seals 21 is completed by a continuous peripheral seal 12 per cell wall 20. Furthermore, the transfer unit according to the invention comprises an anti-lock system, typically produced in the form of a squeegee 24 and a release opening 25, in the case of the rotary cellular lock 11 of FIG. 3.

Advantageously, the rotary honeycomb lock will be oversized to prevent the cells are completely filled with dry mixture. This over-sizing makes it possible to add a contribution of regularity to the device according to the invention and contributes to avoiding blockages of the device.

According to a preferred embodiment of the invention illustrated in FIG. 4, the humidification means 14 of the device is a nebulizer, preferably moistening the binder (s) and, to the least extent, the light aggregate (s), whose mooring is detrimental as mentioned above. Advantageously, the nebulizer 14 comprises a nebulizing ring, which comprises a plurality of nebulizing nozzles 16, typically 3 or 4, oriented in the direction of flow of the homogenized material and disposed at a distance of 2 to 6 m, preferably 3 to 5 m upstream of the spout of the lance 17. The nebulizing nozzles 16 are a priori supplied with water dispersed in a high-pressure gas by an equipressure annular water distribution channel 28, providing an adjustable flow rate typically between 0.4 and 4 liters / minute / nebulization nozzle 16 and a pressure of 10 to 15 bar, conditions necessary to obtain the fineness of water drops dispersed in said gas in order to effect preferential moistening of the binder. This adjustable flow rate makes it possible to control the humidification and serves as a means of controlling the humidification.

In particular, each spray nozzle 16 of the nebulizing ring is oriented at an angle α (alpha) of between 15 ° and 35 °, preferably 20 °, with respect to the axis of the lance, as shown in FIG. According to another particular embodiment of the invention, each spray nozzle 16 of the nebulizing ring produces a solid cone with an opening angle R (beta) of between 10 ° and 45 °, preferably between 15 ° and 30 °. As can be seen in FIG. 5, the projection output of the low-density concrete of the device according to the invention is a lance, the upstream end of which is situated at the level of the humidification means 14 and the downstream end ends with a spout 17, consisting of a tube of a few tens of centimeters, typically 35cm in length. Preferably, the lance is substantially rigid and includes the humidifying means. This lance may be a separate part to be fixed to the pneumatic transport path 13 or an integral part thereof with or without a change of material depending on whether the pneumatic transport path 13 is rigid or not. In particular, the spout 17 comprises one or more, in particular three grooves or projections 27, which will induce a rotary movement with respectively reentrant or protruding spirals, typically at a rotation angle of between 90 and 270 degrees and a length between 150 and 350 mm and print a concentration of the jet during application. According to another particular embodiment of the invention, the spout is flat or oblong profile, preferably constant section along its length. A particular embodiment of the homogenizing unit 9 and post-mixing is also shown in FIG. 6. As can be seen, it is composed of an outer body 30 and blades of particular profiles and -17- differentiated 31 according to the action (homogenization, coating or post-mixing) mounted on a shaft 32. The orientation of the blades and the speed of rotation of the shaft are calculated to give the final mixture a constant and regular output flow rate.

In a preferred embodiment of the device according to the invention, the dosers of raw materials, of recycled product and the homogenization unit 9 are arranged as in FIG. 6. The aggregate is dosed first (part A) followed immediately. binder (part B). A homogenization zone and / or coating (part C) allows the binder to coat the particles of the aggregate, without there remaining loose binder not adhering to the aggregates. The dosing of the recycled material (part D) is then carried out and a post-mixing zone (part E) makes it possible to incorporate the latter in a perfectly distributed manner, without forming a zone that is preferentially rich in recycled material. The homogenized mixture leaves in F. It is understood that the present invention is in no way limited to the embodiments described above and that many modifications can be made without departing from the scope of the appended claims.

For example, the unit for homogenizing the raw materials is an equipment ensuring a moderate stirring, or even a coating of the granulate (s) by the binder (s). According to a preferred embodiment of the invention, the device further comprises a specific metering device for the recycling of rebound discharges of low density concrete. This recycling avoids the loss of this rebound material. Preferably, this metering device operates in a similar manner to the transfer lock of FIG. 3 but without a sealing device, which is useless here. On the contrary, the clearance between the rotor and the stator, commonly of the order of 1 to 2 mm in the case of a commercial lock, will typically be 5 to 7 mm, or even 10 mm, to prevent the recycled material do not stick to the lock. In addition, the recycled material needs to be introduced after the stirring of the raw materials (binder (s) and granulate (s)) and to be incorporated in a mixer extending the homogenization unit 9. Advantageously, the device provides for the addition of liquid adjuvant by addition to nebulization water or concomitantly with it, or solid adjuvant at the level of the binder (s). In order to increase the autonomy and the continuous nature of the device, it can be designed to be fed by raw materials in bulk, for example contained in silos. According to a particularly preferred embodiment of the invention, the device or guniteuse according to the invention has dimensions overall allowing a transport of said device on a removable platform vehiculable, on which the constituent elements are all arranged and ready to be used, while having a nominal capacity up to about 4 m3 / h of low density concrete. The installation is mobile, autonomous and operational in less than an hour after arrival on site. By movable removable platform means that the device is transportable as such (base frame) for example, by lifting with 4 slings hung at the four corners, transportable on a trailer frame (boat chassis type) to remove the gunning module of the trailer frame and drop it to the lowest on site, while adjusting the horizontality, or even, without limitation, transportable on a container frame (not shown).

Claims (26)

1. A method of projecting a concrete comprising: homogenizing a light aggregate of vegetable origin with a binder to obtain a dry mixture, at atmospheric pressure, - a transfer of said dry mixture at atmospheric pressure to a pneumatic transport path (13) in which there is a predetermined pressure, greater than said atmospheric pressure, said transfer being effected in a sealed and continuous manner, a pneumatic transport of said dry mixture at said predetermined pressure to a projection outlet (17), a wetting with a dispersion water in a gas of said dry mixture during said pneumatic transport, and a projection of said concrete thus obtained on a surface. 2. The projection method according to claim 1, wherein said humidification is obtained by nebulization or water spraying. 3. The method of claim 1 or claim 2, wherein said projection is a convergent directional projection. 4. Method according to one of the preceding claims comprising, prior to said homogenization, storage, dosing and transport of said light aggregate and said air binder. 5. Method according to one of the preceding claims 25 comprising a recycling of said low density concrete projected onto said surface and having bounced on the latter. The method of claim 5 wherein the recycled low density concrete is further stored, metered and then fed and kneaded with said blend. The method of any one of the preceding claims wherein said binder is one selected from an overhead binder, a hydraulic binder, or a mixture thereof. 8. Apparatus for projecting a concrete comprising: a homogenization means (9) connected to a feed (5) in a light granulate and to a feed (1) by binder, to form a homogenized dry mixture at atmospheric pressure, a pneumatic conveying path (13) of said homogenized mixture in which a predetermined pressure prevails, greater than said atmospheric pressure and which has a projection outlet (17) of said low density concrete, a watertight and continuous transfer unit (10), arranged to connect said homogenizing means (9) at atmospheric pressure to said pneumatic transport path (13) where said predetermined pressure prevails, and, a humidifying means (14) including means for dispersing water in a gas, disposed in said pneumatic transport path (13), before said projection outlet (17). Apparatus according to claim 8 wherein said binder feed (1) comprises storage means (2), dosing means and conveying means (4). 10. Device according to claim 8 or claim 9 wherein said feed (5) light aggregate comprises a scraper feeder (7) connected to a feed hopper (6). 25 11. Device according to claim 10 wherein said scraper feeder (7) comprises an upward portion (7a) and a descending portion (7b) between which there is an equalizer (18). Apparatus according to any one of claims 8 to 11, wherein said sealed and continuous transfer unit (10) comprises a rotary honeycomb lock (11). 13. Device according to any one of claims 8 to 12, wherein said watertight and continuous transfer unit (10) comprises a recovery means and / or a wear indicator. Apparatus according to any one of claims 8 to 12, wherein said sealed and continuous transfer unit (10) comprises an anti-lock system, in particular a squeegee (24) and a release opening (25). 15. Device according to any one of claims 8 to 14, wherein said projection outlet (17) is a lance whose upstream end is connected to said transport path (13), at the level of the humidifying means ( 14) and whose downstream end comprises a projection nozzle (17). 16. Device according to claim 15, wherein said projection nozzle (17) comprises a plurality of grooves (27) or projections (27) each spiral, reentrant or outgoing. 17. Device according to one of claims 8 to 16, wherein said humidifying means (14) is a fogger, in particular a nebulizing ring connected to a plurality of nebulizing nozzles (16). The device of claim 17, wherein the nebulizing nozzles (16) of said plurality of nebulizing nozzles (16) are oriented in the direction of flow. 19. Apparatus according to claim 17 or claim 18, wherein the nebulizing nozzles (16) of said plurality of nebulizing nozzles (16) are disposed at a distance of 2 to 6m and preferably 3 to 5m upstream of said beak of the lance (17). 20. Device according to one of claims 17 to 19, wherein said nebulizing ring comprises an equipressure annular water distribution channel (28) having an adjustable flow rate preferably in the range from 0.4 to 4 liters / minute / nebulizing nozzle (16) and a pressure of 10 to 15 bar. 21. Device according to one of claims 17 to 20, wherein said nebulizing nozzles (16) oriented in the direction of flow are inclined at an angle with respect to a longitudinal axis of said pneumatic transport path ( 13). 22. The device of claim 21, wherein said angle a is in the range of 15 ° to 35 ° and is more preferably 20 °. 23. Device according to one of claims 17 to 20, wherein said nebulizing nozzles (16) form a solid cone having an opening angle / 3. 24. The device of claim 23, wherein the angle $ is in a range of 10 ° to 45 ° and preferably 15 ° to 30 °. 25. Device according to any one of claims 8 to 24, comprising a dosing means arranged to recycle low density concrete having bounced, said metering means being connected to a kneader disposed downstream of said homogenizing means. 26. Device according to one of claims 12 to 24, wherein the rotary alveolar lock (11) comprises at least 4 cells (20), preferably at least 6 cells (20), more preferably at least 8 cells (20) and most preferably 10 cells (20), and wherein the rotary honeycomb (11) has a rotational speed of at least 10 rpm, preferably at least 15 rpm, and more preferentially at least 20 rpm.25