Process and apparatus for making a coating on a surface such as a road.

The invention relates to a method for producing a surface coating comprising aggregates and bitumen, on a surface such as a floor of the type described in the preamble of claim 1.

The repair of worn or damaged roads can be done by making the surface of the carriageway surface dressing, from aggregates such as gravel and bitumen.

The current technique of producing a surface coating is sprayed on the floor is a thick layer of bituminous binder (for example a layer of 1.3 to 1.8 kg of bitumen per square meter of floor) and then to dump gravel crushed rock in an excessive amount relative to just the amount required to cover the floor, and finally to ensure the best possible adhesion of gravel on the asphalt binder layer using compactors.

It is necessary to pour on the layer of asphalt cement a larger amount of gravel that just the amount required to cover the binder layer, so that there is more free bituminous binder that would adhere to the tires of vehicles.

Non bonded by the bitumen aggregate is projected in all directions by the vehicles on the road and can cause breakage of other vehicles windshield and flaking paint and, in urban areas, breaking shop windows .

In addition, the cost of coatings thus produced is increased by the fact that waste of good quality gravel.

These losses gravel, just after the completion of the coating is called the rejection of implementation.

There is also another type of discharge that is deferred over the weeks following the completion of the coating and leading to a gradual pullout of loosely bonded gravel or glued to an insufficient portion of their surface.

Finally, we observe, in the first period of cold weather following the completion of the coating, called a rejection rejection of the first winter that is explained by the fact that aggregate bonded satisfactorily when the binder is still plastic are linked brittle manner as soon as the first frosts arrive and the bitumen becomes brittle. in vehicle traffic eliminate a few percent of grit whose connection has not withstood the first cold.

One year after the implementation of the plaster, stones that have withstood all the trials of traffic under different climatic conditions encountered during the year are now well established and generally more loose, except when they are worn and when the adhesive binder is too old.

To resist tearing, spilled gravel should have the largest possible contact surface with the adhesive binder. Because the crushed gravel do not have simple geometric shapes such as cubic shape or truncated pyramidal shape, it often occurs that a tip of a gravel is located vis-a-vis one face.

When the gravel is arranged to present a point facing upwards, the corresponding provision has advantages that the vehicle tires have good grip in wet weather. However, this results in faster tire wear set the noise created by contact with the tire edges or tips of gravel.

When poured gravel over a layer of adhesive bituminous binder, one achieves a good durable bond in the following conditions:<ul><li>the chippings shall be not dusty, unpolluted soil and dry, which is rarely the case and even the road surface must be clean and dry;</li><li>adhesive bituminous binder must be sufficiently fluid to spread out and wet gravel, which requires to achieve a sufficiently coated by hot weather. It follows that the period for completion of repair surface coatings is limited in the geographical area to which belongs to France, the five warmest months of the year, from May to September.</li></ul>

Technical coatings, in its implementation by known processes, thus poses risks because just excessive moisture, rain, a period of cold weather, the use of dirty gravel or a road surface polluted by the earth, so that the coating produced on site is of poor quality.

Pavements that must ensure the repair have mostly a defective transverse or longitudinal profile that it is not possible to rectify by known techniques for producing surface coatings. Indeed, by applying a binder layer on a buckled support and coming to attach a single layer of gravel, the profile is stored in its general form. It is the same when two superimposed layers of gravel or more to form the coating, the flatness reproducing on each of the successive layers.

These defects result in a lack of comfort in the driving of vehicles, especially the speed limits on the road network.

Next to the technique used for the coatings are also used for renovating roadways, the deposition of asphalt layers which are bound to the surface of the carriageway by means of a binder layer of very low thickness generally containing less than 10% of the total quantity of bitumen used. The coated material which comprises a mixture of bitumen and aggregates of different particle sizes is in the form of a malleable mass which is spread and compacted on the binder layer.

The resulting coating is generally very compact and smooth and the absence of steps leads to adhesion defects of this type of coating, especially in rainy weather. However, spreading and compacting a relatively homogeneous mass of malleable material on rough roads usually can compensate small pavement profile defects, when the coating is thick enough.

Known from French Patent 2,550,248, a mobile device for preparing cold and spreading on site of bituminous coated products for road paving. This machine can allow in particular the production and spreading on site of bituminous concrete consisting of a fine-grained material such as sand mixed with a bitumen emulsion.

This device can use on the road at high speed and the low speed construction site, thanks to a double transmission, presents many opportunities for the receipt or storage of solid or liquid materials for processing. This integrated device, however, has never been used so far for application of coatings of repair of a floor.

Or also known (US Patent 4,011,023) a pavement rehabilitation process in which worn emobé heated, demolished, regenerated by the bituminous binder and reapplied on the pavement after spraying liquid asphalt. The machine moves slowly and inevitably restores a coating of the same thickness as the old.

The object of the invention is therefore to propose a method for producing a surface coating comprising aggregates and bitumen, on a surface such as a floor of spreading a layer of bituminous binder on the surface and at least one layer aggregates on the layer of binder and in compacting the layer of aggregates in contact with the layer of binder, spraying and compacting these operations being carried out successively by a spreader traveling in a displacement direction corresponding to the site of the advancing direction this process should allow to avoid discards gravel, whether releases of implementation or delayed discharges, reduce road noise and tire wear of vehicles traveling the roadway of increase opportunities for realization of the plaster according to climatic conditions significantly improve the qualilité the coating produced and allow reshaping of the road.

For this purpose, the invention relates to a method of the aforementioned type, characterized by the characterizing part of claim 1.

The invention also relates to a device similar in its general design of the device described in French Patent No. 2.550248 and comprising means adapted for producing a coating by the process according to the invention.

The device described in claims 7 and 8, two embodiments can be used either for the preparation of cold granulate coated, for their spreading on site, for the spreading of the binder layer and the surfacing of the coating or even for receiving and spreading of hot drawn to aggregates, the spreading of the binder and surfacing the coating.

In order to understand the invention, will now be described, by way of non-limiting examples, with reference to the accompanying drawings, several embodiments of the inventive method and the corresponding implementation mechanisms.

Figure 1 is a longitudinal sectional view of a mobile machine for the cold preparation of coated granules and producing a surface coating from these aggregates.

Figure 2 is a section along 2-2 of Figure 1.

Figure 3 is a longitudinal section view of a mobile machine for producing a surface coating from heat produced aggregates.

Figures 1 and 2, the mobile machine shown is similar in its general structure to the device subject of the French patent 2,550,248.

In Figure 1, the device is shown in its working position on the site and the tank of a tanker truck of gravel receiving hopper of this device.

The device comprises a frame 1 resting on four wheel sets 2a, 2b, 2c, 2d, the axles of the train 2c, 2d motors being via bridges connected kinematically to a thermal motor 5 associated with a gearbox 6. the motor unit ensures the movement of the machine both on road and on site. This group of motorization is described in detail in the 2,550,248 patent.

The machine moves on the floor 7 of the construction formed by the upper surface of a roadway on which is carried a coating layer 8 by the method of the invention.

The chassis 1 carries a driving cab 10 whose width is less than the frame of the half-width and occupying a position offset toward one of the lateral sides of the chassis. In an adjacent position relative to the cabin 10 and in a central poposition relative to the chassis, is placed a bucket elevator 12 interposed between the two frame members 1. The bucket elevator 12 is one of constituent elements a self-feeding of the machine which device comprises a receiving hopper 14 placed at the front of the machine and in its lower part just above the ground 7. the receiving hopper 14 is fixed on the ends of the frame members 1 and communicates with the lower end portion of the bucket elevator 12.

The bucket elevator 12 has a casing 17 and a set of buckets carried by two chains 18 whose direction is upward towards the rear of the machine and makes an angle of about 60 ° with the plane of the frame 1.

The upper frame 17 communicates through its outlet opening 19 with the upper part of a hopper 20 storing granular materials such as gravel.

It is obvious that the bucket elevator could be replaced with a lift of another kind.

As shown in Figures 1 and 2, the hopper 20 occupies the greater part of the length of the machine and a substantial part of its width, at least in its upper part. Above the hopper 20 and throughout its length, is arranged a lug régaleur distribution of gravel called device to ensure the spreading of gravel over the entire length and across the width of the storage hopper 20.

The lug 31 régaleur consists of one or two endless chains wound on pulleys or gears and end bearing transverse bars 23. The route of the régaleur bars is slightly tilted upward from front to back.

Instead of a lug régaleur, one could use a screw régaleur.

The bucket elevator 12 and the lug régaleur 31 are driven in their movement for transporting chippings 27 by hydraulic or electric motors associated with gearboxes which have not been represented.

In Figure 1, the bucket 28 of a truck providing a supply of grit of the machine has been shown in its discharge position in the receiving hopper 14. The truck frame is connected via a fixture 29 to the machine and the rear door of the bucket is connected to a pivotable hook 30. in this way, the chippings 27 are discharged perfectly controlled manner in the receiving hopper 14 and then transported by the bucket chain 18 to the upper part of the hopper 20 where the lug régaleur 31 allows spreading the gravel load on the entire surface of the hopper 20 of large cross section.

Thus a perfectly balanced filling the hopper 20 despite its great length and great width. Using a steep bucket conveyor can raise materials to great heights despite a small footprint of the elevator in the longitudinal direction of the machine.

The machine, although it remains to road standards, can be self-powered and has a large gravel storage capacity. As stated in the patent 2,550,248, this hopper can have a capacity of 10 m³.

Under the hopper 20 is arranged a conveyor belt 34 carrying the extraction and the volumetric dosing of chippings of the hopper 20 which are driven by the conveyor 34 to above the inlet opening of the mixer 35 in which fall chippings brought by the conveyor 34. the conveyor drive rollers 34 are rotated by a hydraulic motor which is not shown.

In the opening of the mixer 35 also flows in a metered amount of powder contained in a storage hopper 36. The powder material can consist of stone powder and fine sand and poured in metered quantity in the mixer 35 together with the gravel 27.

As shown in Figure 2, the device comprises two lateral tanks 43 and 44 placed on either side of the storage hopper 20. The reservoirs 43 and 44 contain bitumen emulsions which may be different or identical.

Below the mixer 35 and to the rear of train wheels 2d is fixed on the bottom of the chassis 1, a spray boom 40 for bituminous binder consisting of emulsion contained in one of the reservoirs 43 and 44.

The emulsion contained in the second tank is used to supply the mixer 35 which performs mixing aggregates from the storage hopper 20, the powder material from the hopper 36 and the bituminous emulsion fed to the mixer 35 from one of the reservoirs 43 and 44.

The quantities of gravel, bituminous emulsion and powder material are dosed so as to prepare in the kneader 35, aggregates consisting of chippings coated with bitumen mixed with the pulverulent material in a proportion such that the coating granulate has a pasty consistency .

The proportion of bitumen with respect to the solids is less than 6% and the resulting product is in the form of separate aggregates from each other and not in the form of a pasty mass, as in the case of the manufacture of an asphalt.

Such aggregates consist of gravel covered with bitumen mixed with a powdered material may be designated later by the name of pralines aggregates to distinguish asphalt mixes perfectly forming an indistinct mass in which are blended bitumen, aggregates, a or more sand and powdered material, the aggregates being completely joined together by the asphalt, the powder material and the sand fill all the interstices between the aggregates.

Pralines aggregates are discharged on the surface 7 of the road, at the exit of the mixer 35, upstream of a spreading and distributing device 41.

A heating surfacing and vibrating table 42 is hingedly attached to the rear end 1a of the chassis 1, immediately following the répartion device 41 aggregates chocolates 45 produced cold in the mixer 35.

The table 42 of a type well known specialists roadworks carried compaction and surfacing aggregates to form the coating layer 8 at the rear of the machine, which moves in the direction and the direction of the arrow 46 (Figure 1), this direction corresponding to the progress of construction management.

The realization of the coating layer 8 is performed in the manner to be described below.

The ramp 40 supplied with bituminous emulsion from one side tanks of the mobile machine pours the entire width of the roadway or strip of pavement, a bituminous emulsion layer of constant thickness, through a set regularly spaced spray nozzles in the direction of the ramp 40 corresponding to the cross-machine direction.

It should be noted that the bituminous emulsion is poured in the back of the last set of wheels 2d, so that the realization of the coating machine never moves by rolling over the emulsion layer that has been spread on the surface 7 of the floor.

Specific numerical examples will be given later regarding the quantity of bitumen deposited on the surface of the carriageway by the ramp 40 of binder distribution. Generally, these quantities are approximately two to three times lower than the loads to the case of the embodiment of a conventional coating from dry gravel and three times higher than the discharged amount to achieve adhesion to the surface of a floor with a layer of asphalt.

Aggregates outgoing praline mixer 35 is discharged on the surface 7 of the road where they are spread initially by a screw device 41.

The vibrating and heating table 42 or finishing table makes compaction and surfacing pralines aggregates which have been dumped on the layer of bituminous binder.

The spray boom 40 of binder, the aggregates pralines discharge zone 45 and the finishing table 42 are arranged one after another at short distances to the rear part of the machine embodiment of coating that moves in a direction of the arrow 46.

The distance between the ramp 40 and the rear part of the finishing table 42 is such that, given the machine speed corresponding to the advancement speed of the site, it does not flow more than five seconds between spreading the bituminous binder on the surface 7 of the floor and the end of the compacting and surfacing the coating on the corresponding floor portion.

The three operations of spreading the binder, pralines spreading and compacting granulates are therefore performed in less than five seconds on any part of the roadway.

In addition, the forward speed of the site corresponding to the speed of the machine in the direction of the arrow 46 is always greater than a value approximately equal to ten meters per minute, the feed rate may be of the order of twenty to twenty-five meters per minute.

This speed is much higher than the speed of advance of a finisher, in the case of the embodiment of a coating layer consisting of bituminous mixes allows to obtain a particularly good quality surface cleaning and a very effective reprofiling the road being repaired.

This benefit is in addition of course to the benefits of increased system productivity.

Reprofiling of the road is achieved through the formation of a coating comprising a different number of superimposed layers of gravel, according to the areas of this roadway profile may include defects resulting in hollow parts with a depth more or less important.

Indeed, surfacing carried out by the finishing table provides a coating layer whose upper surface is perfectly flat, the recessed parts of the floor are filled by a number of superimposed layers of praline aggregates enough to catch the the upper surface of the coating layer. Aggregates successive layers are in direct abutment on each other, which allows to obtain a material for filling cavities incompressible.

Praline granules are coated in a thick layer that is both tacky and lubricating and set up easily on the surface of the floor or on a lower layer of aggregate, sliding favored by pralinage layer. The displacement speed higher than ten meters per minute of the finishing table allows to facilitate the movement and the establishment of the layers of granulates.

Compaction of granules ensures a bond and an effective bonding of these aggregates spread on the binder layer on the surface of the roadway.

Pralines aggregates coated in a thick, sticky layer on bitumen are immediately set upon each other at the time of compaction, so that one avoids rejecting implementation. In addition, compaction is greatly facilitated by the fact that the chippings are coated with a lubricating bituminous layer. It is therefore possible to use very quickly the roadway to traffic, after completion of the coating.

The coating obtained reduces the vehicle rolling noise, to the extent that the surface asperities of the chippings do not exist and where the cavities between the chippings absorb sound waves.

These features included with the excellent profiling of the road can significantly increase comfort for motorists.

There are over flying gravel and thereby eliminates the disadvantages.

Despite its excellent qualities of rolling, the coating obtained by the method of the invention provides good adhesion for vehicles, even in the rain, to the extent that it has asperities and surface cavities.

In Figure 3, there is shown an alternative embodiment of the device described above and shown in Figures 1 and 2.

The device shown in Figure 3, the general structure is similar to that of the mobile device described in the French patent 2,550,248 is intended to be used for producing compound according to the invention from pralines aggregates prepared by mixing hot gravel dried and heated, bitumen and pulverulent material in a separate installation of the embodiment of the coating machine.

Pralines aggregates can be produced for example in a coating drum of conventional hot then transported to the site by dump trucks which are fixed to the front of the machine for carrying out the coating, at the hopper 14 to carry out the discharge of hot chocolates in the aggregate hopper, from the bucket 28 'truck. This operation is performed in the same manner that the discharge of gravel 27 in the case of the device shown in Figure 1.

Pralines aggregates 50 poured into the hopper 14 are listed here by a lug conveyor 12 ', then poured into the central hopper 20 to the output of the conveyor 12'.

A barred chain 34 'carries hot chocolates aggregates to the back of the machine where the aggregate 50 is discharged on the surface 7 of the road.

As in the case of the device shown in Figures 1 and 2, the central hopper 20 may comprise a régaleur to webs or like living in régaleur 31 to increase the storage capacity of the hopper 20.

The machine shown in Figure 3 does not include a mixer, pralines granules being hot-drawn in a separate facility.

The powder material storage hopper 36 is replaced with a tank 51 for containing bituminous binder which can be constituted by an emulsion.

In the case of the device shown in Figure 3, both side tanks similar to tanks 43 and 44 of the device shown in Figures 1 and 2 that the cistern 51 may contain bituminous binder such as an emulsion intended to be spread over the surface 7 of the floor, by a spreading ramp 52 variable width fixed to the frame 1 of the machine, to the rear of train wheels posterior 2d. The ability of asphalt cement storage of the machine is greatly increased and more one quality emulsion is necessary to achieve the bonding layer of praline aggregates.

In the case of a machine having a frame width of 2.50 m, a height of 4 m and a length of 11 m, the embodiment of the machine according to the invention makes available a reserve of aggregates 15 tons in the central hopper and a reserve of 12 tonnes binder in the wing tanks and tank 51 in the rear.

This gives great autonomy to the machine allowing it to function normally even in the case of irregular supply by trucks.

In the case of normal operation of the machine, a single replenishing emulsion binder tanks is necessary, during a working day on site.

As in the case of the machine shown in Figures 1 and 2, the rear part of frame 1 carries a finishing table 42 vibrating and heating. The table 42 is mounted articulated on the frame, through three points of articulation.

The binder spraying ramp 52 and the finishing table 42 are placed on the rear part of the chassis 1, so that it does not flow more than 5 seconds between the spreading of the binder on the surface 7 of the floor by the ramp 52 and the end of the compacting and surfacing made by the finishing table 42, given the speed of advance of the machine.

50 hot chocolates aggregates are discharged at a point between the ramp 52 and the spreading finisher 42 slightly in front of a distribution device worm 41.

Pralines aggregates are usually a temperature above 120 ° C and which can be close to 150 ° C at the time of spreading the bituminous binder layer discharged by the ramp 52 on the surface 7 of the floor.

As indicated above in the case of the machine shown in Figures 1 and 2, the forward speed of the machine shown in Figure 3, in the direction and sense of arrow 46 must be greater than ten meters per minute to obtain a coating layer 8 perfectly surfaced and realizing an effective reprofiling of the road.

Advantages of the process according to the invention implemented using the device shown in Figure 3 supplied with hot chocolates aggregates are at least equivalent to the advantages obtained during the implementation of the method using the machine shown in Figures 1 and 2.

The amount of bitumen contained in the binder layer spread on the floor before the spreading pralines aggregates is significantly lower than the amount of bitumen spilled on the floor to perform the bonding of dry gravel in the prior art. This amount can be two to four times lower in the case of the technique according to the invention.

Pralines aggregates are covered with a relatively thick layer and paste composed of bitumen and of pulverulent material. Incorporating the chippings of 2 to 6% of bitumen and, as a powder material, is 4 to 5% by weight of stone powder, is 10 to 20% of fine sand.

Stone powder or sand have for role to make the pasty fluid bitumen and thicken the adhesive layer so that the chippings are bonded together by a thicker layer.

This is a very important concept because the bitumen-coated gravel is surrounded only by a thin fluid film very hot bitumen and that always tends to flow.

Stone powder (or added sand) has for role to make pasty bitumen is too fluid and thicken the binder layer is too thin to ensure sustainable links between the grains.

The thickening agent added is so for two reasons:<ul><li>it is primarily a thickener in the geometric sense,</li><li>this is then a thickener as defined increase in consistency.</li></ul>

For example, we will give below the composition of a surface coating of the prior art having two layers (bi-layer coating) and the composition of a coating according to the invention.

The following prior art surface coating comprises a first layer of bitumen emulsion spread at 1.1 kg / m² that is to say 0.8 kg of pure bitumen per square meter.

A first layer of gravel to large particle size is spread on the emulsion layer. This first layer comprises 17 kg of coarse gravel square meter.

On this first layer of gravel is spread a second emulsion layer at 1.5 kg of emulsion per square meter, that is to say 1 kg of pure bitumen per square meter.

On this second emulsion layer is spread a second layer of gravel to fine particle size, in an amount of 8 kg of fine gravel per square meter.

The coating according to the prior art undergoes compaction after which a relatively high proportion of gravel is not located suff iciently bound to the surface of the carriageway by the bituminous binder so that the chippings may be ejected passing vehicles.

The coating according to the invention given by way of example is formed by plating on the surface of the roadway a bitumen emulsion layer in an amount of 0.95 kg per square meter emulsion, 0.60 kg of pure bitumen per square meter.

Is sprinkled on the emulsion layer a layer of gravel pralines to 22 kg of gravel pralines per square meter. The chippings chocolates spilled onto the layer of bituminous binder immediately after application and compacting and smoothing the gravel layer pralines are themselves made immediately after spreading the gravel pralines.

The amount of bitumen covering the gravel pralines by coating per square meter was 1.4 kg. The bitumen coating praline aggregates is thickened by mixing with 5 to 6 kg of fine sand or 1-2 kg per square meter of plaster stone powder.

The total amount relative to the solid materials bitumen is therefore approximately 5%, which represents approximately the upper limit of the proportion of bitumen spread onto grit to form pralines aggregates according to the invention.

Is plotted in the table given below, the various quantities of materials used for producing the coating according to the prior art and the coating according to the invention. <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="3" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center">Coated according to the prior art (bilayer)</entry><entry namest="col3" nameend="col3" align="center">Coating according to the invention</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">total amount of bitumen</entry><entry namest="col2" nameend="col2" align="right">1.8 kg / m²</entry><entry namest="col3" nameend="col3" align="right">2.00 kg / m²</entry></row><row><entry namest="col1" nameend="col1" align="left">Quantity of bitumen spread on the floor</entry><entry namest="col2" nameend="col2" align="right">1.8 kg / m²</entry><entry namest="col3" nameend="col3" align="right">0.60 kg / m²</entry></row><row><entry namest="col1" nameend="col1" align="left">used bitumen amount to praliner aggregates</entry><entry namest="col2" nameend="col2" align="right">0</entry><entry namest="col3" nameend="col3" align="right">1.4 kg / m²</entry></row><row><entry namest="col1" nameend="col1" align="left">Total thickness of the coating</entry><entry namest="col2" nameend="col2" align="right">15 mm at any point</entry><entry namest="col3" nameend="col3" align="right">10 to 40 mm according to the defects of the old support</entry></row><row><entry namest="col1" nameend="col1" align="left">Total quantity of gravel employees (per m²)</entry><entry namest="col2" nameend="col2" align="right">17 kg of coarse gravel + 8 kg of fine gravel = 25 kg</entry><entry namest="col3" nameend="col3" align="right">22 kg of medium-sized gravel</entry></row><row><entry namest="col1" nameend="col1" align="left">other additives</entry><entry namest="col2" nameend="col2" align="right">possibly adhesion agent in gravel-binding interface</entry><entry namest="col3" nameend="col3" align="right">mandatory 5 to 6 kg of fine sand or 1-2 kg of stone powder to thicken the bitumen</entry></row><row><entry namest="col1" nameend="col1" align="left">Total quantity of solid mineral origin</entry><entry namest="col2" nameend="col2" align="right">25 kg</entry><entry namest="col3" nameend="col3" align="right">23-28 kg</entry></row></tbody></tgroup></table></tables>

It is obvious that these values ​​are only indicative and that the invention can be implemented using amounts of material or relative proportions of these different materials from those that have been indicated in the example given above .

The amount of asphalt binder used for the preparation of chocolates aggregates from gravel can be fairly well below the amount above which substantially corresponds to the upper limit for the implementation of the invention. However, the quantity of bitumen used for pelleting the aggregates must be sufficient to prevent rejection and any ejection gravel after completion of the coating.

The quantity of bitumen used for pelleting chippings must represent at least 11% of the total amount of bituminous binder used per square meter of the finished coating.

In other words, the bitumen contained in the bituminous binder spread on the surface of the floor before the spreading pralines aggregate can represent up to 89% of the total quantity of bitumen.

On the other hand, to achieve a good bond with the roadway, the amount of bitumen contained in the binder must not be less than 11% of the total quantity of bitumen used per square meter of coating. So aggregates can contain up to 89% of the total quantity of bitumen used.

Commonly, the amount of bitumen contained in the binder is greater than 20% of the total quantity of bitumen used. Preferably, this amount of bitumen in the binder is close to 30% of the total quantity of bitumen used.

By weight solids, that is to say the weight of chippings and the pulverulent material, the proportion of bitumen is generally between 2 and 6%.

It is obvious that the method according to the invention can be implemented using a different bituminous binder emulsion and for example using bitumen incorporated in a solvent or hot liquid bitumen.

The process of the invention can be implemented regardless of the size of the grit used to form the coating, within the limits of particle sizes typically used for producing coatings according to the prior art.

Replacing the crushed rock gravel, can be advantageously used crushed products from the demolition of old layers of asphalt pavements, these recycled products are generally called RAP. In this case, in addition to the advantage of using a product which normally have to provide storage or disposal is carried out both a material saving as regards the chippings that the bitumen used in the process according to 'invention. Indeed, the solid bitumen layer remaining attached to the RAP participates in the constitution of the pasty coating of aggregates.

The process of the invention can be implemented using slightly different from those which have been described machines. The fully integrated design of these machines realization and installation of plaster, however, allows to implement the invention in the best conditions, avoiding error setting parameters necessary to achieve a satisfactory coating.