FR2845100A1 - METHOD FOR IMPROVING THE SURFACE QUALITIES OF A TRAFFIC LANE AND DEVICE FOR IMPLEMENTING SAME - Google Patents

Abstract

The road surface is formed with a layer (21) of gravel coated in bitumen (2), and after this layer has been laid disperses (4) over it a controlled quantity of fine grains of a solid material (50) which adheres to the bitumen covering the top (22) of the surface layer. The roller (3) follows close behind, before the bitumen has time to cool, so the roller forces the surface grains into the bitumen.

Description

The invention relates to a method for improving the surface qualities of

  the wearing course of a road as well as a

  device for implementing this method.

  The roads are usually carried out by spreading, on a platform, a wearing course made up of aggregates coated in a bituminous binder which may be cold or hot, natural or synthetic, depending on the process used. The equipment used for this purpose is mounted on a tractor which carries a reserve bucket periodically filled with coated aggregates and which opens into a coating spreading member forming a layer of regular thickness and over a working width. which depends on the device used and can be 4 to 8 meters. The tractor advances continuously and a strip-like surface course of constant width is thus produced, centered on a longitudinal axis. This layer of asphalt is then compacted

  by known means in order to produce the running surface.

  However, it has been noted that, immediately after the completion of such a wearing course and for a certain time, the road thus produced does not have satisfactory adhesion. 20 Indeed, the binder which coats the aggregates forms an external film

  relatively smooth, which completely covers the upper surface of the wearing course. The passage of vehicles gradually eliminates this external film by showing the aggregates, but it is only after a certain period, of the order of six 25 months, that the running surface becomes sufficiently rough.

  To solve this problem, we can consider incorporating

  solid elements such as fine sand in the external binder film which covers the running surface in order to make it rougher, for the time necessary for the removal of this film, until the aggregates are discovered.

  However, these fine elements are only useful during

  this short period and are removed with the external binder film.

  However, such fine sand has a significant cost. To limit consumption as much as possible, it is necessary that the sand 35 used is spread only on the running surface, and in a layer thin enough to avoid rejection, outside the track, from the commissioning of this one, of a part of the fine elements spread. On the other hand, it is also necessary to avoid irregularities in thickness which would cause a variation in the effect of improving the adhesion obtained by the incorporation of fine elements in the

external binder film.

  Finally, this operation must be carried out quickly and with

  fairly simple means so as not to excessively increase the cost of making the wearing course.

  The invention makes it possible to solve such problems by means of a particularly simple method and installation, making it possible to spread the desired quantity of fine elements very homogeneously over the rolling surface, this operation being able, moreover, to be carried out by a single pass over a relatively large width, of the order of several meters, corresponding to the width covered by the asphalt spreading means for the

  installation of the wearing course.

  The subject of the invention is therefore a method of improving the surface qualities of a traffic lane produced by spreading,

  on a platform, with a layer of aggregates coated in a bituminous binder, by means of a spreading device moving at a forward speed along a longitudinal axis of the platform and transversely covering a certain working width.

  In accordance with the invention, after spreading the coating layer, a controlled quantity of fine-grained solid material is dispersed above the coating layer, which is deposited on the binder film covering the face 30. upper layer of asphalt, and we then compact it, the dispersion of the granular material being carried forward, at a speed substantially equal to the longitudinal speed of advancement of the device spreading and at a distance low enough downstream of it so that the temperature of the binder remains high enough to allow the bonding of the dispersed grains upon contact with the binder film, said grains then being embedded in said binder film by compaction carried out downstream, to form a surface of

rough rolling.

  In general, in the context of the present invention, the expression "traffic lane" applies to any platform covered with a wearing course made up of coated and compacted aggregates, the invention allowing the realization, not only roads or highways of all sizes, but also 10 parking, taxiing, take-off / landing areas

in airports, etc ...

  Particularly advantageously, the dispersion of the granular material is carried out at a fairly short distance from the spreading means, above an area of the wearing course where the temperature of the binder is still at least 1000C.

  and preferably around 120 ° C to 1400.

  According to a variant of the process of the invention, the granular material is slightly heated in order to avoid any risk of

  cooling of the binder film in contact with cold grains.

  Preferably, the dispersed granular material is a fine or very fine sand having, a particle size between 100 and 500 μm, and the quantity of dispersed fine sand can range from 300 to

  500 g / m2 depending on the nature of the mix.

  According to another preferred characteristic, the granular material is dispersed, in a substantially homogeneous manner, in a space closed at least on its sides and extending downwards to a lower edge placed a short distance from the wearing course. and delimiting a rectangular orifice allowing the material dispersed in said space to be deposited regularly, as and when the wearing course is produced, over a width corresponding to the working width of the spreading device. The invention also covers an installation for producing a wearing course comprising successively, in a direction of advance along a platform, means for spreading thereon a layer of aggregates coated with a bituminous binder, a device for substantially homogeneous dispersion of a fine-grained solid material above the wearing course and compacting means, the dispersing device moving at substantially the same speed as the spreading device and being kept downstream thereof at a sufficiently low distance to avoid a significant lowering of the temperature of the binder film covering the coated materials and thus allow the bonding of the dispersed grains on the whole of the upper face of the wearing course then their inlay in

said film by compaction.

  In a particularly advantageous manner, the dispersing device comprises at least one member for projecting the granular material with a homogeneous distribution, in at least one widely open dispersion sector from at least one

  orifice supplied with granular material with a controlled flow.

  In a preferred embodiment, the sector for dispersing the material opens about 1800 towards the rear of the spreading means relative to the direction of advance, the flow of 20 grains projected per unit of time in the sector of dispersion being adjusted as a function of the speed of advance of the device

spreading of asphalt.

  In a preferred embodiment, the dispersing device comprises at least one reserve enclosure associated with supply means with a controlled flow opening into the center of at least one rotating hearth driven in rotation about a substantially vertical axis for the projection by centrifugal effect of the granular material, and the speed of rotation of which is adjusted so that, taking into account its density, the granular material is distributed homogeneously in a sector of

  dispersion covering at least part of the width of the wearing course made in one pass by the spreading device.

  Thus, each rotating sole disperses the granular material over a part of the width of the wearing course, the dispersing device comprising a sufficient number of rotating sole plates spaced apart from one another, in order to cover all the width of the wearing course made in one pass by the spreading device. Preferably, each rotary hearth is associated with means for limiting the extent of the dispersion sector inside a dihedral opening towards the rear from the axis of

  rotation of the rotating floor and on an angle of the order of 1800.

  It is not essential that the action radii of the revolving hearths overlap, since this only results in an under-dosing of sand at the limit of the two paths, that is to say in the

  area covered by the axial marking on the ground.

  It should be noted that, because of the very fine fineness of the granular material, a large part of the projected grains do not immediately fall on the wearing course, but may risk being entrained by a movement of air at the outside the area that has just been completed. This is why, according to another particularly advantageous characteristic of the invention, the dispersing device is associated with means for limiting a substantially rectangular space covering at least part of the wearing course and extending above of it on a protective height against external disturbances, so that

  the dispersed matter remains confined in this space.

  The installation comprises, in known manner, a tractor movable on the platform and carrying a reserve enclosure 25 of the coated aggregates emerging in spreading means extending transversely to the longitudinal axis over a working width. According to the invention, the device for dispersing the granular material is integral, in displacement, with the tractor in order to maintain a short distance, behind the spreading means. In particular, the dispersing device can advantageously be mounted on a support frame fixed to a rear part of the tractor and extending in a cantilevered fashion towards the rear thereof, above the wearing course which comes from be performed by the

spreading device.

  In a preferred embodiment, the support frame of the dispersing device is associated with a frame-shaped part having two lateral sides extending on either side of the dispersing device, parallel to the longitudinal axis and each carrying a light bulkhead extending vertically from the level of the wearing course on a

protective height.

  Advantageously, the dispersing device is supplied with a controlled flow rate from a buffer tank, the latter 10 being able itself to be supplied from bags which are opened in

  as needed to pour into the buffer tank.

  But the invention also covers other characteristics

  advantageous which are the subject of dependent claims and which will emerge from the following description, given by way of example, of an embodiment of the installation according to the invention and of the

  process implemented, with reference to the accompanying drawings in which FIG. 1 is a side view of the assembly of a

installation according to the invention.

  Figure 2 is a top view of the installation.

  FIG. 3 is a schematic view, in elevation, of the

dispersing device.

  In FIGS. 1 and 2 are shown schematically, respectively in side view and in plan view, the assembly 25 of an installation for producing a wearing course A on a platform B, comprising a spreading machine 1 of the conventional type, preferably mounted on a self-propelled tractor 10 which can move along a longitudinal axis x'x of the platform B. The tractor 10 can be provided, as usual, with a hopper II receiving a mass 2 of coated aggregates

  of a bituminous binder and it is provided, at its rear, with means 12 for spreading, on the platform B, coated aggregates 2, so as to form a wearing course 21 centered on the longitudinal axis x'x and whose width and thickness are regulated by a finishing table 13 carried by the rear part of the tractor 10.

  Such spreading means are well known and can be of different types making it possible, in general, to produce on the platform B a wearing course of desired thickness which is then compacted, for example by means of a vibrating roller. As indicated above, the bituminous binder which

  completely coats each element of the aggregate forms, after the spreading of the wearing course 21, a substantially continuous film which completely covers the upper face 22 of said layer 21, constituting the running surface.

  This external and smooth film of binder is gradually eliminated by the rolling of vehicles but decreases, however,

  grip at the start of commissioning.

  To avoid this drawback, a granular material such as fine sand is spread over the upper face 15 22 of the wearing course, which is incorporated into the external binder film and is then removed with it, but increases, however, the grip

  for the time necessary for this elimination.

  To obtain a good result, this fine sand must, however, be dispersed very homogeneously and avoiding not only the excess thicknesses, but also the loss of sand outside.

of the running surface.

  To this end, according to a first characteristic of the invention,

  fine sand is dispersed as soon as the wearing course is completed and over its entire width, before any compaction.

  As a result, the external binder film is at a temperature high enough to determine an immediate bonding of the dispersed sand as soon as it comes into contact with the upper face 22 of the asphalt layer 21 and the compaction then carried out. causes the grain of sand to become embedded in the film

thus glued on this one.

  For this purpose, a dispersing device is used which is placed as close as possible to the spreading machine and moves at substantially the same speed as the latter. In this way, the external binder film 35 covering the coated layer 21 does not have time to cool substantially before the deposition of the sandy material. For this, the dispersing device is preferably mounted directly on the rear part of the spreading machine 5 and carries out the dispersion of the sand over the entire working width (L) thereof. Thus, the dispersed sand immediately sticks to the entire upper face 22 of the wearing course 21

  as and when it takes place.

  On the other hand, the compaction carrying out the incrustation of the sand 10 can be carried out at a certain distance from the spreading machine and, possibly, by successive bands because, in the event of wind, for example, the fine dispersed sand remains stuck on the surface 22 until the moment of compaction allowing its

incorporation into the binder.

  In the preferred embodiment shown in the figures, the dispersing device 4 is mounted on a support frame 5 carried by a bracket 52 fixed directly to the part

rear of tractor 11.

  As schematically shown in FIG. 3, the dispersing device 4 advantageously comprises a reserve enclosure such as a small silo 41 having a hopper-shaped bottom 42 which opens, by a conduit 43, onto a rotating floor 44 made up of '' a plate provided with blades and driven in rotation at a sufficient speed around a vertical axis 40 by a motor 45 25 preferably located below the rotating tang 44 and connected to the

  silo 41 by means of support not shown.

  The silo 41 is filled with fine sand and, preferably, permanently supplied from a buffer tank 51 placed on the

  tractor 1 above silo 41 which is powered by gravity.

  Sand can also be transported to silo 41

by means of a conveyor screw.

  Alternatively, the sand can also be fed under

  in the form of bags which are open above the buffer tank 5, the outlet of which is provided with a grid preventing the accidental passage 35 of paper.

  The sand thus introduced into the silo 41 is poured through the conduit 43 onto the rotary hearth 44 driven in rotation at high speed and is therefore dispersed by centrifugal effect above the

  upper face 22 of the wearing course 21.

  The feed channel 43 is provided with an adjustable shutter 46 with timed electronic control 47 making it possible to adjust the flow of sand falling on the sole 44 as a function of the speed

advancement of the machine 1.

  The material thus projected disperses, by centrifugal effect, 10 in a circular sector 61 centered on the vertical axis of the hearth

rotating 44.

  To bring the dispersion axis as close as possible to the finishing table 13, it is preferable that the dispersion sector

  61 opens only towards the rear, at an angle of about 180.

  To this end, as shown in Figure 3, the device

  dispersion 4 is advantageously provided with a deflector 48 placed at the level of the rotating sole 44 and comprising two arms provided with orientable blades whose opening can be adjusted as a function of the speed and of the dosage, in order to limit the projection of the sand onto a sector 61 of variable opening, of the order of 1800.

  The sand thus dispersed in a circular sector which moves longitudinally, is deposited on the surface 22 by forming a strip parallel to the axis x'x and the width of which depends on the centrifugal effect of the rotating hearth and can be, for example. example, 4 25 meters, which corresponds to a normal working width of one

spreading machine.

  Thanks to this arrangement, it is possible to regularly spread on the surface 22 of the coated layer 21, a

  quantity of fine sand of the order of 250 to 300 g / m2.

  If you use a machine that achieves more

  large width, for example 8 m, it is possible to place on the frame 5 two dispersing devices spaced from one another, and each having an action sector of width I of the order of 4 m.

  As shown in FIG. 2, the action sectors may overlap slightly, but this is not essential since the central zone placed between the two action sectors can be under-dosed, insofar as it corresponds to a marking

axial, at the limit of two lanes.

  It is also possible to limit the width I of the sector covered by a hearth 44 and increase the number of dispersing devices so as to cover at the same time the entire working width (L) of the spreading device 13 of the wearing course 21. Each rotating sole 44 must imperatively be designed to adapt to the relatively low mass of the material

  very fine granular which must be projected.

  In this regard, it has been observed that due to the very fine fineness of the material projected, a large proportion of it does not deposit immediately on the surface 22 but remains for a certain time in suspension and can therefore be entrained by a

air movement.

  To avoid loss of material, according to another

  a particularly advantageous characteristic of the invention, the dispersing means are placed in an enclosed space, sheltered from external disturbances.

  Thus, in the preferred embodiment shown in FIG. 1, the chassis 5 for supporting the dispersion means 4 comprises a platform 51 fixed to the bracket 52 and on which are mounted, on the one hand, the dispersion devices 4 and, 25 on the other hand, a rectangular frame 54 extending horizontally towards the rear and carrying a light partition such as a tarpaulin 53 which extends vertically over a protective height h, substantially up to the upper face 22 of the layer of

bearing 21.

  In addition, the rectangular frame 54 can be covered with a

tarpaulin or horizontal partition 55.

  There is thus delimited, around the dispersing members 4, a closed space 50 which entirely covers a rectangular area of the upper face 22 of the wearing course extending over the entire width (L) produced in one pass by the device il 12, 13 and over a length L 'corresponding to the maximum distance of projection of the sand grains, taking into account

  their density and the centrifugal effect of the rotating floor 44.

  The sprayed grains therefore remain confined within this closed space 50 which moves at the same speed as the spreading means 50.

  Part of the sprayed grains is immediately deposited on the rolling surface 22 and another part can strike the longitudinal or transverse sides of the vertical wall 53 and is randomly returned towards the interior of the space 50, being distributed from substantially homogeneously. The dispersed material thus forms, inside the space 50, a cloud of grains in suspension which advances with the tractor 10 at the speed of spreading of the wearing course and whose lower part 15 is denser. and tends to stick to the upper face 22 covered with a binder film which has not had time to cool and is still at a temperature between 1200 and

1400C.

  The grains of fine sand thus bonded to the film covering the wearing course 21, then become encrusted in this film at the

passage of the compactor 3.

  This produces, on the upper face 22 of the wearing course 21, immediately after the production thereof, a

  rough surface which considerably improves grip.

  Another advantage of the invention lies in the fact that this thin layer of fine sand embedded in the binder film covering the wearing course reduces the gloss of the latter.

  and thus the risk of dazzling motorists.

  Subsequently, the binder film, with the grains of sand incorporated therein, is gradually eliminated by the movement of vehicles, but making the upper surface appear,

  irregular, aggregates of the wearing course.

  The invention therefore makes it possible to confer on the coating, from its

  production and circulation, very clearly improved adhesion properties, in particular at moderate speed.

  Of course, the invention is not limited to the details of the embodiment which has just been described by way of simple example, the arrangements used being able to be modified while remaining in the

  protective framework defined by the claims.

  For example, the spreading device 5 could bear directly, by wheels, on the asphalt layer 21 and be coupled to the rear of the tractor 11 or else constitute an independent self-propelled vehicle following the tractor 11 and placed a little behind the finisher 13, but at a distance small enough that the binder film covering the wearing course did not have the

time to cool down significantly.

  On the other hand, we could use for the dispersion of sand any means allowing to deposit light particles on a

  fairly large and homogeneously.

  For example, the device for dispersing fine sand could consist of a hopper fixed to the rear of the tractor 10 and extending transversely over the entire width (L) of the asphalt layer produced by the spreading means. 12, 13, the bottom of this hopper being equipped with a screw making it possible to regularly distribute the fine sand poured into the hopper, above an elongated slot allowing a flow of sand adjusted in

  depending on the forward speed of the tractor 10.

  The nature of the wearing course on which the very fine granular material is applied has no influence on the implementation of the method of the invention. So bituminous mixes

  can be obtained either hot or cold.

  The proportion of fine dispersed sand must be adapted to the

  nature of the mix and can range, for example, from 300 +/- 50g / m2 for a draining mix up to 500 +/- 50g / m2 for a non-draining mix.

ib r 2845100

Claims (22)

  1. Method for improving the surface qualities of a traffic lane (A) produced by spreading, on a platform (B), a layer (21) of aggregates coated (2) in a bituminous binder, at means of a spreading device (12, 13) moving at a forward speed (v) along a longitudinal axis of the platform (B) and transversely covering a working width (L), said layer (21) having an upper face (22) covered with a binder film, process in which, after spreading the asphalt layer (21), a controlled quantity of fine-grained solid material is dispersed thereon (2) distributed in a substantially homogeneous manner, which is deposited on the binder film covering the upper face (22) of the asphalt layer (21), and then the compaction thereof is carried out, the dispersion granular material (2) being produced during advancement, at a speed substantially equal to the longitudinal speed (v ) of advancement of the spreading device (12, 13) and at a sufficiently small distance downstream of it so that the temperature of the binder remains sufficiently high to allow the bonding of the dispersed grains from the contact with the film of binder, said grains then being embedded in said binder film by the compaction carried out downstream, for the formation of a surface of rough bearing (22).   2. Method according to claim 1, characterized in that the granular material (2) is dispersed over an area of the wearing course where the temperature of the binder is at least   minus 1000C and preferably around 1400C.   3. Method according to one of claims 1 and 2, characterized   by the fact that the dispersed granular material (6) is a fine or very fine sand.   4. Method according to one of claims 1, 2, 3, characterized   by the fact that the granular material (6) has a   particle size between 100 and 500 ptm.   5. Method according to one of the preceding claims, characterized in that, before the dispersion, the material   granular is heated so as to avoid any cooling, to   its contact, of the binder film on which it is spread.   6. Method according to one of the preceding claims,   characterized in that the granular material is dispersed in a substantially homogeneous manner in a closed space at least on its sides and extending downwards to a lower edge placed at a small distance from the wearing course and delimiting a rectangular orifice allowing the material dispersed in said space to deposit regularly, as and when the surface layer (21) is produced, over a width corresponding to the working width (L) produced in one pass by   the device (12, 13) for spreading the coated aggregates.   7. Method according to any one of the claims   above, characterized in that the granular material (6) 15 is projected above the rolling surface (22) by centrifugal effect, so as to be distributed evenly in at least one circular sector.   8. Installation for producing on a platform (B) the wearing course (21) of a traffic lane (A) movable continuously along a longitudinal axis characterized in that it comprises successively, in a direction of travel, a device (12, 13) for spreading on the platform (B), aggregates (2) coated with a bituminous binder, continuously movable, at a speed of travel (v), the along the longitudinal axis of the platform (B), for the formation of a wearing course (21) having an upper face (22) covered with a binder film, a device (4) for substantially homogeneous dispersion of a fine-grained solid material (6) above the wearing course (21), and means (3) of compacting, and that the dispersing device 30 (4) moves at substantially the same speed as the spreading device (12, 13) and is kept downstream of it, at a distance small enough to avoid a significant lowering of the tem temperature of the binder film covering the coated materials, so that the fine grains (6) thus dispersed stick to the whole of the upper face (22) of the wearing course (21) then   become embedded in said film by compaction.   9. Installation according to claim 8, characterized in that the dispersion device (4) comprises at least one member 5 (44) for projecting the granular material with a homogeneous distribution, in at least one dispersion zone (61) extending horizontally in all directions over at least one angular sector widely open from at least one supplied orifice   granular material with controlled flow.   10. Installation according to claim 9, characterized in that the area (61) for dispersing the material (6) extends towards the rear of the spreading means (41, 13) relative to the direction of advance , with a homogeneous distribution of the material (6)   in an angular sector of the order of 1800.   11. Installation according to one of claims 9 and 10,   characterized by the fact that the projection member (44) is associated with means (46, 47) for adjusting, as a function of the speed of advance of the installation, the flow of grains projected per unit   of time in the dispersion zone (61).   12. Installation according to one of claims 8 to 11, for the   production of a wearing course (21) extending over a working width (L) on either side of a longitudinal axis (x'x), characterized in that the dispersing device (4) comprises at least one reserve enclosure (41) associated with means (43, 25 45) for supplying with a controlled flow opening into the center of at least one rotary hearth (44) driven in rotation about an axis (40 ) substantially vertical for the projection by centrifugal effect of the granular material (6), and the speed of rotation of which is adjusted so that, taking into account its density, the granular material is distributed homogeneously in a dispersion zone ( 61) covering at least part (1) of the width (L) of the wearing course (21) produced in one pass   by the spreading device (12, 13).   13. Installation according to claim 12, characterized in that each rotary hearth (44) disperses the granular material over a width (1) and that the dispersing device (4) comprises at least two rotary hearths (44 , 44 ') whose axes of rotation are spaced from one another in order to cover the entire width (L) of the wearing course (21) produced in one pass by the spreading device (12, 13) .   14. Installation according to one of claims 12 and 13,   characterized by the fact that each rotating sole (44) is associated with means (48) for limiting the extent of the dispersion zone (61) inside a dihedral opening towards the rear at 10 from the axis of rotation (40) of the rotary hearth (44) and on a angle of around 1800.   15. Installation according to one of claims 8 to 14,   characterized in that the dispersion device (4) is associated with means (53) for limiting a dispersion space 15 (50) covering at least part of the wearing course (21) and extending to the above it on a protective height   against external disturbances.   16. Installation according to one of claims 8 to 15,   characterized in that the dispersing device (4) comprises at least one silo (41) supplied from a buffer tank (51).   17. Installation according to claim 16, characterized in that the buffer tank (51) is supplied from bags of granular material which are opened as required for   pour into the buffer tank (51).   18. Installation according to one of claims 8 to 17,   characterized by the fact that it comprises a tractor (10) displaceable on a platform (B) along a longitudinal axis (x'x) and carrying an enclosure (11) for reserving the coated aggregates (2) opening into means of spreading (12, 13) of the aggregate 30 extending transversely to the longitudinal axis for the formation of a wearing course (21) over a working width (L) and that the device (4) for dispersing the material grainy is connected to the tractor (10) so as to be kept at a short distance in   rear of the spreading means (12, 13).   19. Installation according to claim 8, characterized in that the dispersing device (4) is mounted on a support frame (5) fixed on a rear part of the tractor (10) and extending towards the rear of that here, above the wearing course (21) produced. 20. Installation according to claim 19, characterized in that the chassis (5) for supporting the dispersing device (4) is associated with a frame-shaped part (54) having two lateral sides extending from side to side. other of the dispersing device 10 (4), parallel to the longitudinal axis and each carrying a light partition (53) extending vertically from the level of the layer   bearing (21) on a protective height (h).   21. Installation according to claim 20, characterized by the   causes the chassis (5) and the frame (54) to overhang 15 towards the rear of the tractor (10).   22. Installation according to claim 20, characterized in that the chassis (5) bears on the wearing course (21) by a rolling member and is connected by a trailer to the tractor (10).