EP0716186A1 - Method for making reinforced soil with fibrous additives - Google Patents

Abstract

The procedure consists of delivering chopper fibres from a cutter (21) onto a conveyor (11), where they are covered with layers of the mineral or organic material forming the soil from hoppers (12, 13). The soil and fibres, e.g. of glass in bundles of 40 filaments each with a diameter of 5 - 25 micrometres, are fed into a continuous mixer (15), where a binding agent and water are delivered from separate containers (16, 17). From the continuous mixer the material goes into a hopper (19), from where it can be fed into trucks (20) for transport to the spreading site.

Description

The invention relates to soil preparation techniques in which sands or granular substitute materials are used, it relates in particular to the production of underlays for paths, roads or sports grounds.

When you create a road on new ground, you proceed in different stages, the first consisting in leveling the ground with devices such as bulldozers which level the overhanging parts and fill in the holes. The second phase consists in depositing on the ground thus prepared a layer of form the first function of which will be to allow the movement of the convoys and the machines on the ground while avoiding degrading it or clogging the machines. On the form layer, one or more other layers of a different nature, called the foundation layer, base layer, etc., are then deposited, the common role of which is to support the more superficial layers linked by hydraulic or bituminous binders.

Each of the underlying layers is made with well-defined quality sand which unfortunately is generally not available in the vicinity of the site. Although the price of such a material is not high its transport can be very expensive.

One of the aims of the invention is to make it possible to use, for the production of underlying layers, materials, in particular sands, coming from quarries close to the site to which fibers are added which give them the desired properties.

Another object of the invention is to improve the participation of the underlying layers in the stability of the road and in the resistance of the roadway over time.

In the field of land development to prepare them for a new destination such as creating a path, a sports field, a racetrack, where we start by leveling the ground with bulldozers, in the next step , we can bring as a new material, not only a sand of defined particle size but also suitable all-purpose materials.

It is also an object of the invention to allow a modification of the most varied general materials to allow their adaptation as constituents of an underlying layer which prepares the leveled ground for a new function such as the use as path, as a sports, maneuvering, racetrack, etc.

It is known, in particular from patent application WO 91/17311, to add to fine sand of granularity defined by the ratio d / D in which d corresponds to the particles of small diameter and D to the particles of larger diameter, this sand satisfying the relationships d = 0 and D ≦ 6 mm, synthetic fibers in an amount of between approximately 0.2 and 5 per thousand by weight, preferably between 0.5 and 1 per thousand.

Synthetic fibers have a length of 15 to 100 mm and their diameter is between 3O and 100 µm. Fibers made of various materials are cited, the examples relate to polyacrylonitrile fibers.

In the patent application PCT / FR94 / OO643 filed on O1 / O6 / 1994, a technique is described for mixing fibrous additives with pulverulent materials intended for the production of underlying road layers in which a layer of powder is deposited or of granules on a conveyor then where gravity bundles of filament bundles which have been obtained by cutting at least one wick of textile glass threads are deposited by gravity on the layer of powder or granules, then the possible recovery of the bundles of filaments by a layer of granules and finally, with the mixture of the granules and bundles of filaments.

The present invention proposes to provide other methods of incorporating fibrous additives into pulverulent materials intended to constitute the bases of roads or various terrains.

• mise en contact unilatérale des additifs fibreux avec les granulés,
• mélange des granulés et des additifs fibreux.

Dans l'une des variantes, le mélange est effectué en continu par un malaxeur et les additifs fibreux sont, soit déposés sur un transporteur sur lequel sont déposés ensuite, au-dessus, les granulés, l'ensemble étant alors introduit dans le malaxeur, soit introduits au-dessus des granulés dans le malaxeur lui-même.The invention provides a method for mixing with mineral or organic granules intended to constitute the layers of a soil, fibrous additives, in particular based on mineral fibers such as glass fibers with the following steps:

• unilateral contact of the fibrous additives with the granules,
• mixture of granules and fibrous additives.

In one of the variants, the mixing is carried out continuously by a mixer and the fibrous additives are either deposited on a conveyor on which the granules are then deposited above, the assembly then being introduced into the mixer, either introduced above the granules in the mixer itself.

In another variant, the mixing is carried out batchwise in a mixer, the fibrous additives being introduced in particular onto the granules.

According to the method of the invention, the fibrous additives preferably comprise reinforcing glass fibers in the form of bundles of at least 40 filaments each, with a unit diameter between 5 and 25 μm. Either the beams are cut on site and then we can use a beam cutting machine whose operating speed is controlled by the speed of introduction of the granules into the mixer, or else the beams are already cut before their storage on site and they are removed by an extractor-doser, the operating speed of which is preferably controlled by the speed of introduction of the granules into the mixer.

It is often advantageous that the system for supplying fibrous additives, fiber bundle cutter or stock of fibrous additives is kept at a distance from the place where the introduction of the additives is carried out, the invention provides a device which comprises in particular a sluice valve and an air blowing system which transports the fibrous additives. In a variant, the device is placed downstream of a reservoir of fibrous additives and comprises a demott eur which precedes a carding machine.

• la figure 1 représente le dispositif de l'art antérieur permettant la mise en oeuvre d'un procédé de préparation centralisée du matériau granulaire.
• la figure 2 représente un mode de mise en oeuvre du procédé de l'invention, et
• la figure 3 un autre mode de réalisation, tous deux avec découpe des fils sur le site,
• la figure 4 montre un exemple d'extracteur-doseur tel qu'on les utilise lorsque les fibres sont stockées après avoir été coupées.

The figures and the description which follow will make it possible to understand the operation of the invention:

• FIG. 1 represents the device of the prior art allowing the implementation of a centralized preparation process for the granular material.
• FIG. 2 represents an embodiment of the method of the invention, and
• FIG. 3 another embodiment, both with cutting of the wires on the site,
• Figure 4 shows an example of a dosing extractor as used when the fibers are stored after being cut.

FIG. 1 illustrates a known centralized method for producing the mixture between the granular or pulverulent material and the fibers.

When you build a land or build a road, you generally choose, in its vicinity, a site on which all the materials to be used during construction will be prepared. It is there for example that often, if it is a road, is the power plant. Trucks are constantly transporting the prepared materials from the production site to the mobile site which follows the progress of work on the ground or on the road under construction.

The devices for implementing the methods of the invention are installed on this site for preparing materials.

In the figure, we see two hoppers 1, 2 containing the pulverulent or granular materials to be used, for example on the one hand an all-purpose sand from a quarry close to the site and a corrective sand, that which, added in large quantities is - in the absence of fibers - necessary to provide the mixture with the desired lift. Below the hoppers, and leading from one to the other, a conveyor belt 3 has been installed. The hopper 1 deposits on the conveyor a certain thickness of the material, such as all-purpose sand. This sand then passes into 4 under a machine 5 for cutting the glass strands. This is supplied with strands of wire 6 from several coils such as 7 unwound from the inside. The machine 5 generally comprises several rollers 8, at least one of which is fitted with knives 9 which cut all the wicks 6 into sections of defined length 10. Each wick has a very large number of threads, in general more than 400, 1200 per example.

To carry out the cutting of the threads, the usual machines are advantageously used for cutting the textile glass threads. European patent EP-B-00 40145 proposes for example a machine intended for cutting wires into sections of a predetermined length which comprises a rotary drum whose surface is smooth and a second drum equipped with blades arranged perpendicularly to its periphery, the blades being fixed by their ends only and their bases opposite their cutting edge remaining completely free while organs ensure the compression of the wire.

The filament bundles 10 are preferably deposited over the entire width of the sand transported by the strip 3. After the fibers have been deposited, the materials pass under the hopper 2 where an amount of sand, for example a corrective sand from a distant quarry (but then, thanks to the stabilizing effect of the fibers, in minimum quantity) is deposited. This avoids immediately covering the fibers that the dispersion is disturbed. The next operation is the mixing of the whole.

FIG. 2 represents a first embodiment of the method of the invention. We can see in the figure the different devices of a power station located near a construction site, road for example. 11 shows a conveyor belt similar to the carpet 3 in FIG . 1 . The dosing hoppers 12 serve to bring and pour on the belt the granular materials 13. A conveyor 14 feeds a continuous mixer 15 with the products coming from the conveyor belt 11. In the continuous mixer 15 are also possibly introduced the usual additives, such as '' a binder from silo 16 and water from tank 17.

At the outlet of the continuous mixer 15, a conveyor 18 loads the silo 19, the hopper of which loads the trucks 20 which transport the materials to the nearby site.

The process of the invention is implemented at the start of the cycle: before any other material, the cut fibers are placed on the conveyor belt, these are covered on one side only by the granular materials with which they are thus find themselves in unilateral contact.

In FIG. 2, the cutting is done on site using a cutting machine (21) similar to the machine 5 in FIG . 1 . It is important that the speed of this machine is a linear function of the material flow transported by the elevator 18. This guarantees, all other things being equal, that the proportion of fibrous additives in the mixture remains constant.

In place of the cutting machine 21, it is also possible, within the framework of the method of the invention, to install a tank of cut fibers equipped with an extractor-doser. At the bottom of the fiber tank is an extractor device. Such a device must fulfill two functions, extract the fibers while preventing them from jamming at the bottom of the tank and measure the flow of fibers. Several devices make it possible to fulfill these two functions, one of them comprises a vibrating grid located at the bottom of the tank which overcomes a series of parallel Archimedes screws, with horizontal axes whose speed of rotation defines the flow rate.

To facilitate the separation and the dosing of the fiber bundles, another device represented in FIG . 4 was also used. It is a pneumatic decompression and transport device which is supplied by a hopper 120 with the fibers. The device such as that described in French patent 2,557,817 shown in FIG. 4 essentially comprises a feeder 127 preceding a carding machine 121 which feeds a valve sluice 122 and it comprises a turbine with controlled flow rate not shown which supplies the orifice 125 the air necessary for the transfer of fibers. The fibrous materials can be introduced in bulk, for example using a silo located above the device.

In the two previous techniques using fibers cut in advance, the dosing systems have advantageously, as we have seen, their speed controlled by that of the introduction of granular materials so as to guarantee a defined proportion of fibrous additives.

The device of FIG. 4 possibly devoid of the unstuffer 127 and the carding machine 121 is also advantageously used for transferring the fibrous additives at a considerable distance from the place where they have been dosed whether they have been cut on the site or that they were simply stored there and possibly unpacked before their transfer. In particular, it is often advantageous to carry out the handling and dosing of fibers under cover in a protected room, away from the handling of granular materials which are carried out by more rustic machines.

In all the tests in which bundles of reinforcing glass fibers were cut and stored in bulk, it was found to be much easier to use if the cutting of the wires had been carried out in the glass factory, under die immediately after the gathering of the filaments to constitute a thread. In comparison, the bundles of fibers cut from "rovings" tended to constitute bundles of fibers, which the extractor devices located at the outlet of the fiber tanks have difficulty in separating.

The arrangement of the cutter (or of the reservoirs with their metering device) of FIG. 2 is chosen when space is lacking along the conveyor belt, in fact, at the end of the carpet, it is possible to have cutter and coils of roving in the optimal conditions to avoid incidents due to blockage of the wires, wear of the wire guides, etc.

FIG. 3 essentially comprises the same elements as FIG. 2 , the essential difference is that here, the fibrous additives are introduced above the granular materials in the mixer 15, they are thus in unilateral contact with them. In the figure, we can see the coils of roving 25, the rovings 22 assembled in a wick 23, the cutter 24 similar to the cutter 21 of FIG. 2 which delivers bundles of cut fibers 26 directly into the mixer 15. In the figure, these beams are visible, however it is preferred that they be channeled in a closed pipe. One of the advantages of direct introduction into the blender is that it prevents the fibers from flying off. Another advantage is the introduction of fibers at the last moment which limits handling, risks of breakage, segregation, etc.

The cutter shown in the figure is similar to that of Figure 2 described above, it may however be advantageous to replace it with one or especially with several spray guns of cut fibers of the type of those used by manufacturers of reinforced plastics. These accessories can allow faster mixing since they allow better dispersion from the start of the operation.

Also in FIG. 3 , it is possible to replace the cutter 24 with its coils of roving 25, a reservoir of fibers cut with an extractor-doser described above.

On certain low-flow installations, the mixing of granular materials intended to produce the underlying layers of roads or various terrains is carried out in discontinuous mixers where the mixing of the products is only started after filling a load. of the different constituents. The method of the invention provides for the introduction of fibrous additives, in particular on other materials either through the use of a cutter, spray guns, the two types of apparatus being supplied with roving, or by supplying the mixer made of fibers cut beforehand and extracted from their storage tank by an extractor-metering device of the type described above. Here also as for the system of FIG. 3 , the fact of introducing the fibrous additives at the last moment prevents them from various attacks, in particular, mechanical. It is however possible to alternate supply of granular materials and fibrous additives in particular to accelerate the homogeneous mixture.

The invention also proposes a method which replaces the technique known in FIG . 1 . In place of the carpet of bundles of cut fibers deposited on the bed of granular materials transported by the conveyor belt 3, a glass mat is deposited, made of cut fibers associated and bonded, in particular by a binder which loses its effectiveness at humidity, conditioned in rolls with a width which is that of the conveyor belt. The mat when it enters the mixer is dissociated there and the dosing of the beams in the granular materials, by the very fact of the regular advancement of the mat, is very precise.

The preceding techniques which can be used for mixing fibrous additives with granular materials have been described essentially with reinforcing glass fibers associated in bundles but they are suitable for many other fibrous additives, for example based on plastic fibers. The methods of the invention have also been used to mix not reinforcing glass fibers, but insulating glass fibers. These were fibers from shredded glass wool mattresses and reconstituted into nodules in accordance with the process of patent EP-B-0 455 553. After shredding a mattress, it involves passing the flakes through a " nodular ”where the fibers are forced to pass through the knives through a plate fitted with holes from 6 to 15 mm in diameter. The nodules, like the cut reinforcing fibers, are easily dispersed within the granules. The same method used with reinforcing glass fiber waste or by-products has also given excellent results.

Claims (12)

Process for mixing with mineral or organic granules intended to constitute the layers of a soil, fibrous additives, in particular based on mineral fibers such as glass fibers, characterized by the following steps: - unilateral contact of the fibrous additives with the granules, - mixture of granules and fibrous additives. Method according to claim 1, characterized in that the mixing is carried out continuously by a mixer. Method according to claim 2, characterized in that the fibrous additives are deposited on a conveyor on which the granules are then deposited above, the assembly then being introduced into the mixer. Method according to claim 2, characterized in that the fibrous additives are introduced above the granules in the mixer itself. Method according to claim 1, characterized in that the mixing is carried out batchwise in a mixer, the fibrous additives being introduced in particular onto the granules. Method according to one of the preceding claims, characterized in that the fibrous additives comprise reinforcing glass fibers in the form of bundles of at least 40 filaments each, with a unit diameter between 5 and 25 µm. Method according to claim 6, characterized in that the beams are cut on the site. Method according to claim 7 and one of claims 2 to 4, characterized in that it uses a beam cutting machine whose operating speed is controlled by the speed of introduction of the granules into the mixer. Method according to claim 6, characterized in that the beams are already cut before their storage on the site and in that they are removed by an extractor-doser. Method according to claim 9 and one of claims 2 to 4, characterized in that the operating speed of the metering extractor is controlled by the speed of introduction of the granules into the mixer. Device for implementing the method according to claim 1, characterized in that it comprises in particular a sluice valve (122) and an air blowing system which transports the fibrous additives. Device according to claim 11, characterized in that it is placed downstream of a reservoir of fibrous additives and comprises a feeder (127) which precedes a carding machine (121).

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