EP0478441B1 - Method and device for forming a road construction layer - Google Patents

Abstract

The road construction layer (8') is formed by deposition and compacting of a material (5') containing an inorganic filler such as aggregates and a binder, on a support (1'). A first liquid and preferably a supplementary quantity of binder are incorporated in a fraction of the material (5') intended to constitute a lower part (8'a) of the layer (8') deposited on the support (1'), before compacting thereof. If appropriate, a second liquid is sprayed onto the support (1') before the deposition of the material (5'). In the case of a material containing a (hydraulic) binder, a third liquid is sprayed over the material (5') during spreading over the support (1'). The binder may be incorporated at the same time as the first liquid, in the form of an emulsion or of a suspension. The method and the device according to the invention are applicable to the case of road layers consisting of materials bound either with bitumen or with (hydraulic) binders. <IMAGE>

Description

The invention relates to a method for producing a layer of a roadway by depositing and compacting a composite material consisting of a filler such as aggregates and a binder, in the compactable state, on a support which can be consisting of a lower layer of the roadway previously made.

Road pavements generally consist of a succession of superimposed layers which are produced continuously by machines moving around the site. These different successive layers have different functions which are necessary to obtain the desired characteristics of the road surface. Road pavements are very often made up of three layers of which the first, or foundation layer, is deposited on the ground, whose second, or base layer, rests on the foundation layer and whose third, or coating layer, covers the base layer.

These various layers are produced by depositing and compacting in the pasty state, a composite material consisting of a filler such as aggregates and a binder which may be in liquid form or constituted by a solid to which a liquid such as de the water.

Depending on the nature of the binder, a distinction is made in road construction, the so-called "black" techniques which use bitumen as a binder and the so-called "white" techniques which use as cement binder or, more generally, a hydraulic binder which can be substituted for cement and which can consist, for example, of fly ash, slag or pozzolan.

In the case of "black" techniques, the bitumen can be mixed with the load incorporating the aggregates in the form of an emulsion (so-called cold techniques) or in the molten state (so-called hot techniques).

Also known from FR-A-2,611,766 is a device for carrying out the spreading of a bituminous binder in the form of an emulsion constituting a bonding layer and on the bonding layer, just after its spreading, a layer hot bituminous mixes.

EP-A-0.215.139 describes a method for renovating a road surface which consists in heating and then breaking up a bituminous surface layer of the road to obtain particles which are mixed with additives and spread and compacted on the road surface.

Whatever the binder used, the superimposed layers of the roadway undergo the same types of stress, when passing vehicles; consequently, these layers undergo deterioration, in particular by fatigue, which are identical.

When a vehicle wheel in circulation on the roadway applies a certain load to it, the layers constituting the roadway flex under the effect of this load and deform.

• 1°/ Les efforts de flexion dans les différentes couches se traduisent par des contraintes de traction plus importantes dans la partie inférieure de ces couches ; en d'autres termes, la fibre supérieure de chacune des couches est comprimée et la fibre inférieure est tendue,
• 2°/ Selon que les couches ou dalles successives sont totalement assemblées entre elles et solidaires ou totalement indépendantes, les effets de traction sont entièrement différents ; on démontre mathématiquement, qu'à épaisseur égale de matériau, les contraintes de traction, donc les phénomènes de fatigue sont minimaux si toutes les couches sont totalement collées entre elles.

There follow two main consequences which result from the properties of the flexed slabs:

• 1 ° / The bending forces in the different layers result in greater tensile stresses in the lower part of these layers; in other words, the upper fiber of each of the layers is compressed and the lower fiber is stretched,
• 2 ° / Depending on whether the successive layers or slabs are completely assembled together and integral or totally independent, the traction effects are entirely different; we demonstrate mathematically, that with equal material thickness, the constraints of traction, therefore fatigue phenomena are minimal if all the layers are completely bonded together.

A perfectly bonded monolithic block therefore has a much longer lifespan than a laminated assembly whose layers are imperfectly bonded.

To ensure maximum durability of a roadway, it is therefore necessary to achieve effective bonding between the successive layers of this roadway.

On the other hand, the durability of the pavement largely depends on the fatigue strength of the lower part or bottom of each of the layers which is subjected to the greatest tensile stresses.

In general, the fatigue strength of a composite material comprising grains and a binder increases with the number of resistant bonds between the grains provided by the binder. The endurance of the material therefore increases with the content of binder and with the number of surfaces in contact in the composite material. It therefore seems desirable to increase the amount of binder in the material and to decrease the number of holes between the grains, that is to say to increase the compactness of the binder-aggregate mixture, in the case of a material. composite for road construction.

It has actually been shown by tests, in the case of road pavement layers constituted by conventional bituminous mixes, that the durability of these layers and in particular their resistance to fatigue depended very significantly on the content of binder of coated materials and , to a lesser degree, of the compacting energy of the layers.

In order to increase the durability of road pavement layers, it has been proposed, in French patent application 89-16662 filed by the company SCREG ROUTES & TRAVAUX PUBLICS, to apply before the deposition and compaction of a pavement layer road on a support, a layer of enrichment by binding of the lower part of this layer. The enrichment layer includes aggregates and a binder dosed at more than 800 g / m².

This process which makes it possible to enrich by binding the bottom of the deposited layer ensures a significant improvement in the resistance to fatigue and the durability of the road surface. However, this process requires for its implementation the application of an additional layer on the support and does not allow perfect control of the adjustment of the binder content in the bottom of the deposited layer. In addition, this method does not make it possible to very significantly increase the compactibility of the bottom of the deposited layer, over a sufficient thickness.

There are also known methods for producing road pavements, using bituminous products, in which the bonding of the various superposed layers is effected by bonding layers which can be produced by spreading a bituminous emulsion (FR- A-2.611.766). However, these methods do not make it possible to increase the content of binder in the bottom of the deposited layer and to increase the compactibility of this bottom of the layer.

The object of the invention is therefore to propose a process for producing a layer of a road pavement, by depositing and compacting a material composed of a filler such as aggregates and a binder, in the compactable state, on a support which may consist of a lower layer of the pavement previously produced, this method making it possible to appreciably increase the durability of the pavement, while being of a simple implementation requiring no substantial modification of the process of the layers of the roadway and of the materials used for this realization.

For this purpose, a first liquid is mixed with a fraction of the composite material intended to constitute a lower part of the layer deposited on the support, before its compaction, this first liquid being capable of increasing the compactness of the binder-aggregate mixture.

Preferably, an additional quantity of binder is also mixed with the fraction of the material intended to constitute the lower part of the layer deposited on the support, before its compaction.

The invention also relates to devices making it possible to implement the method according to the invention, both during the production of road pavement layers by a technique using bituminous products and in the context of the use of 'a technique using hydraulic binders.

In order to clearly understand the invention, we will now describe, with reference to the appended figures, an example of implementation of the method according to the invention in the case of the production of a layer from asphalt bituminous and in the case of a layer produced from a composite material containing a hydraulic binder.

Figure 1 is a schematic elevational view in partial section of a device for producing a layer of a roadway from bituminous coated materials.

Figure 2 is a schematic elevational view in partial section of a device for producing a road pavement layer from a composite material containing a hydraulic binder.

In FIG. 1, we see a mobile installation making it possible to continuously produce, on a road construction site, a layer of a road pavement constituted by bituminous materials.

It is known to produce layers of road pavement from bituminous materials constituted by mineral particles such as aggregates, sand and powdery material mixed with a viscous and sticky bituminous binder.

The bituminous binder can consist of pure hot melted bitumen which ensures the coating of previously dried and heated particles. The corresponding techniques are designated as hot techniques.

The bituminous binder ensuring the coating of the particles can also consist of bitumen dissolved in a solvent or dispersed in water in the form of an emulsion. The corresponding techniques are designated as cold techniques.

The various superposed layers constituting the roadway can be bonded together by bonding layers produced by spraying a thin layer of bitumen emulsion on the support on which bituminous materials are deposited and compacted. The emulsion layer is generally spread on the support by means of a spreader independent of the asphalt spreading and compacting machine.

Bituminous materials are spread over the bonding layer in the form of a layer having a constant thickness of between 8 and 16 cm. This layer of materials is compacted by vibrating and / or pneumatic compactors.

Due to the dispersion of the compaction energy in the thickness of the asphalt layer, the lower part of this layer or base which comes into contact with the support is always less well compacted than the upper part or above the layer, which is unfavorable, in order to obtain satisfactory fatigue resistance of the layer, the lower part of which undergoes the greatest tensile forces, has the lowest compactness. The thickness difference between the top and the bottom of the layer is greater the thicker the layer. In practice, we are led to limit, in these techniques of construction of a roadway, the thickness of the layers at an upper limit close to 16 cm.

In addition, the mix has a constant composition, so that the bituminous binder content of the deposited layer is constant from the top to the bottom of the layer. The weakening of the bottom of the layer due to its lower compactness is therefore not compensated for by a gradient of the binder content.

The method according to the invention which can be implemented using the device shown in Figure 1 overcomes these drawbacks.

The device represented in FIG. 1 is constituted by a mobile machine moving on a support 1, in the direction of advancement of the site symbolized by the arrow 2, by means of tracks such as 3 supporting a chassis not shown. The machine comprises at its front part a device for receiving coated materials or means for preparing cold coated materials which make it possible to continuously feed a conveyor belt 4 ensuring the transfer of bituminous coated materials 5, towards the rear of the chassis of the mobile machine.

At the outlet of the conveyor belt 4, the coated materials 5 are poured onto a lateral distribution screw 6 fixed to the rear part of the chassis. The screw 6 has a transverse arrangement relative to the machine and makes it possible to distribute the materials 5 over the entire width of the roadway.

A finisher table 7, of known type, suspended by arms at the rear of the chassis makes it possible to adjust, smooth and compact the asphalt layer 5 deposited and spread on the support 1, at the rear of the distribution screw 6.

A compactor 10 moves behind the mobile machine so as to complete the compaction of the layer 8 of coated materials deposited on the support 1.

The level of coated materials 5 at the front of the distribution screw 6 is adjusted by means of a movable deflector 11 comprising an inclined surface delimiting the external surface of the mass of coated materials 5 distributed in the transverse direction by the screw 6. L the inclination of the deflector 11 can be adjusted as a function of the angle of the slope naturally formed by the materials 5 poured onto the support.

The deflector 11 makes it possible to adjust the flow of the materials 5 in the direction of the kneading device and to avoid a segregation of the aggregates by size, by ensuring a certain retention of the aggregates of large size.

A kneading screw 12 of transverse direction linked to the chassis of the machine is disposed at the front and below the deflector 11, so that a fraction of the coated materials 5 spread at the front of the screw 6 comes in contact with the kneading screw 12. This fraction of the coated materials 5 constitutes the lower part 8a or bottom of the layer 8 coming into contact with the support 1.

A liquid spreading ramp 14 fixed transversely to the chassis at the front of the mixing screw 12 makes it possible to spray liquid bituminous binder, for example constituted by an aqueous emulsion, on the screw 12 and on the coated materials 5 intended to constitute the bottom 8a of the layer 8.

The kneading screw 12 has blades of radial direction making it possible to achieve a significant shearing of the materials coated with the layer 8a and effective kneading of these materials with the liquid bituminous binder poured out by the spreading ramp 14.

It is also possible to use, at the outlet of the conveyor belt 4, a flow separator making it possible to direct a portion of the materials to a mixer placed at the front of the screw 6 in which bituminous emulsion is incorporated into this fraction of the materials intended to constitute the bottom of layer 8a. The flow separator ensures the distribution of the materials between the front and the rear of the screw 6. The materials intended to constitute the bottom of the layer are then treated completely separately from the materials intended to constitute the rest of the layer 8.

A second liquid spreading ramp 15 is arranged between the rear part of the tracks 3 of the finisher and the kneading screw 12. The ramp 15 makes it possible to spread a layer of bituminous binder which can be constituted by an emulsion on the support 1, before depositing the coated materials 5.

The device which has just been described makes it possible to incorporate into the fraction of coated materials intended to constitute the bottom of layer 8a, a regulated quantity of liquid containing bituminous binder.

The incorporation of a liquid such as water into the materials coated with the bottom of layer 8a ensures enrichment in liquid lubricant of these materials, which makes it possible to increase their compactibility. This effect of increasing the compactibility of the materials at the bottom of the layer 8a, the importance of which can be adjusted by adjusting the quantity of liquid poured out by the ramp 14 makes it possible to obtain a substantially constant compaction over the entire thickness of the layer. , produced by the finisher table 7 and by the compactor 10. In fact, the lower compaction forces exerted on the layer bottom 8a are offset by the better compactibility of the materials constituting this layer bottom 8a. In addition, the proportion of binder in the layer 8a is increased by the fact that the liquid spilled by the ramp 14 contains bitumen.

The additional quantity of binder introduced into the coated materials constituting the base layer 8a improves the mechanical properties and in particular the resistance to fatigue of this base layer.

The introduction of a liquid containing a certain proportion of bitumen in the coated materials intended to constitute the bottom of layer 8a therefore makes it possible both to obtain better compactness and a higher content of binder in this lower part 8a of the layer 8.

The fatigue resistance and therefore the durability of the layer 8 are therefore significantly improved compared to a layer produced according to a conventional process resulting in a constant binder content throughout the thickness of the layer and a reduced compactness in the part. lower layer.

In addition, the realization of a bonding layer by spreading a bituminous emulsion immediately in front of the spreading area of bituminous mixes makes it possible to achieve an effective bonding of the layer 8 on the support 1, which increases still the durability of the whole.

The bonding layer achieves a particularly effective bonding, in the case where the coated materials 5 are hot coated materials which are spread on the bituminous emulsion at a temperature of the order of 120 to 150 ° C. The evaporation of water from the emulsion under the layer of hot mixes, in contact with the support 1, makes it possible to improve the penetration of the bitumen of the bonding layer and the bonding of the layer 8. The following process the invention makes it possible to produce a layer of a road pavement having increased durability, whether this layer constitutes a base or seat layer of a pavement deposited and compacted on a foundation layer or a coating layer deposited and compacted on the base layer of the pavement or a foundation layer.

Conventionally, a road pavement made of bituminous materials and produced by the method of the invention may include a base layer of gravel-bitumen with a thickness of 12 cm on which is deposited a base layer of gravel-bitumen 12 cm thick glued to the foundation layer with a bituminous bonding layer. A coating layer 8 cm thick is deposited on the base layer with the interposition of a bituminous bonding layer.

The bitumen content in the foundation layer and in the base layer is around 4% and the bitumen content in the coating layer is 6%.

In the case of a layer produced by a method known from the prior art, the compactness rate decreases very substantially throughout the thickness of the layer; the compactness is likely to show a decrease of 5% between the top and the bottom of the layer.

The method according to the invention makes it possible to increase the compactibility of the bottom of the layer and to obtain, in the pavement layer, a compactness which is substantially constant over the entire thickness of the layer and close to 95%.

The method according to the invention also makes it possible to increase the bitumen content in the lower part of the road layer. This lower part can have a thickness of between 20 and 50% of the total thickness of the layer and the bitumen content of this lower part can be increased from 0.5 to 2%.

In the case of the layer 8 deposited and compacted on the support 1 shown in FIG. 1, the layer 8 can be constituted by the covering layer, by the base layer of the roadway, or by the foundation layer, the support consisting respectively of the base layer, the foundation layer or a form layer.

In Figure 2, there is shown a device for making a layer of a roadway by a technique using a composite material containing a hydraulic binder.

In such a material, the mineral particles constituted for example by aggregates and sand are linked together by a crystal lattice formed in situ by hydration of a hydraulic binder or based on pozzolan.

The binder is in the form of a finely pulverized solid (for example cement or fly ash) or in the form of small grains (in the case of blast furnace slag for example).

The mixture of binder and aggregates is produced at ordinary temperature and the bonds between the grains only appear after a certain time ("setting phenomenon").

When making, using currently known techniques, road pavement layers in gravel-cement for example, a mixture of sand, gravel and cement is mixed with a little water in order to obtain a wet mixture which must be both compactable and sufficiently resistant to compression to carry the compacting machines.

An excessively dry mixture is very load-bearing for trucks or compaction machines brought to circulate on the deposited layer but it is not sufficiently lubricated and can therefore only be densified with difficulty.

When the composite material is too wet, it compacts easily but no longer has a sufficient bearing capacity for the construction machinery to circulate on the layer of materials. In the case of plastic concrete, the material is self-compacting but no longer has any lift.

The choice of the water content of a serious cement at the time of its implementation is therefore very important and the material must be neither too dry nor too wet. The water content of the material is generally adjusted at the time of its implementation to a value called "water content of the modified Proctor optimum", this optimum content being designated by W _opm . This optimal value is determined from a laboratory test. In a conventional material based on gravel, the water content W _opm is of the order of 6%. When it contains 4 to 5% of water, the mixture is the site of very high friction forces during its compaction; it does not compact well. On the other hand, it provides very good lift vis-à-vis the compactors which leave little trace on the deposited layer.

When it contains around 10% water, the mixture has only the consistency of a fluid concrete which compacts very easily and which is no longer capable of supporting machines, the concrete having the consistency of a mud.

The water content W _opm represents a compromise between the lift of the mixture and its state of lubrication.

When it contains a water excess of 1 to 2% compared to the optimal value, the mixture based on gravels is deformed in a continuous way with the passage of the compactors, the granular friction having practically disappeared because the water fills practically all the voids between the particles of the grave (phenomenon called quilting). It is no longer possible to obtain a road layer of constant thickness and in the case where a new road layer is superimposed on a base layer of non-constant thickness, the new layer also has a thickness which cannot be constant. The durability of the roadway is then variable depending on where you are.

• le support ne subit pas de préparation spéciale,
• on déverse sur le support le matériau composite humide constitué par les particules minérales, un liant hydraulique et de l'eau puis on étale le matériau avec une niveleuse de manière à régler l'épaisseur appliquée,
• on compacte le matériau qui renferme une teneur en eau voisine de la valeur optimale W_opm, de manière à obtenir la densité maximale que l'on peut atteindre ; en fait, on n'obtient une densité optimale que dans la partie supérieure de la couche qui reçoit la plus grande partie de l'énergie de compactage ; la densification décroît très vite en fonction de l'épaisseur vers le bas de la couche, cette épaisseur pouvant être comprise entre 18 et 28 cm ; il y a donc un fort gradient de densité et le bas de la couche qui subit les plus fortes contraintes, lorsque la couche de chaussée est mise en flexion, est également la partie de la couche qui est la moins dense et qui présente donc la plus faible tenue à la fatigue ; on compense généralement cette faiblesse du fond de la couche de chaussée en augmentant l'épaisseur de la couche, ce qui accroît le coût de construction de la chaussée,
• on effectue ensuite un finissage de la couche qui a été précédemment compactée, en utilisant une niveleuse pour découper la partie supérieure de la couche compactée sur une épaisseur de 2 à 3 cm, de façon à supprimer tous les petits défauts de surface de la couche compactée et à obtenir une surface parfaitement plane ; la couche peut être recompactée une dernière fois en utilisant un compacteur à pneus pour redonner une cohésion satisfaisante à la surface fraîchement découpée ; la surface définitive parfaitement plane permet en particulier de réaliser une couche superposée à la première couche, d'épaisseur parfaitement constante.

The processes currently known for the construction of pavements from mineral particles such as gravel and sand mixed with a hydraulic binder are carried out as follows:

• the support does not undergo any special preparation,
• the wet composite material consisting of mineral particles, a hydraulic binder and water is poured onto the support, then the material is spread with a grader so as to adjust the thickness applied,
• the material which contains a water content close to the optimum value W _{opm is compacted} , so as to obtain the maximum density which can be reached; in fact, an optimal density is obtained only in the upper part of the layer which receives the greater part of the compaction energy; the densification decreases very quickly as a function of the thickness towards the bottom of the layer, this thickness possibly being between 18 and 28 cm; there is therefore a strong density gradient and the bottom of the layer which undergoes the greatest stresses, when the pavement layer is flexed, is also the part of the layer which is the least dense and therefore has the most poor resistance to fatigue; we generally compensate for this weakness at the bottom of the road layer by increasing the thickness of the layer, which increases the cost of construction of the pavement,
• the layer which has been previously compacted is then finished, using a grader to cut the upper part of the compacted layer to a thickness of 2 to 3 cm, so as to remove all the small surface defects of the compacted layer and to obtain a perfectly flat surface; the layer can be recompacted one last time using a tire compactor to restore satisfactory cohesion to the freshly cut surface; the perfectly flat final surface makes it possible in particular to produce a layer superimposed on the first layer, of perfectly constant thickness.

It appears in the description above, that the road pavement layers produced according to the methods known from the prior art have a lower part or bottom of the layer whose mechanical characteristics and in particular the fatigue resistance are less than the characteristics mechanical of their upper part, due to the less effective compaction of the bottom layer. As a result, the optimal properties of the road layers are not obtained, since the most stressed part of the road layers has the poorest characteristics and in particular the lowest fatigue resistance. In addition, the bonding of the successive layers of the roadway is obtained neither satisfactorily nor automatically.

The device shown in FIG. 2 allowing the production of road pavement layers from a mixture containing a hydraulic binder is substantially identical to the device shown in Figure 1 used for the production of pavement layers from bituminous mixes.

The corresponding elements in FIGS. 1 and 2 bear the same references, with however the exponent ' as regards the references of the elements in FIG. 2.

The device shown in FIG. 2 is constituted by a mobile machine moving on the support 1 ', in the direction of the arrow 2', thanks to tracks 3 '.

The chassis of the mobile machine carries a conveyor belt 4 ′ ensuring the transfer towards the rear of the machine, of the material 5 ′ containing the hydraulic binder, intended to constitute the road layer 8 ′. The material spilled at the rear of the chassis of the mobile machine by the conveyor 4 'is distributed transversely by a screw 6' then adjusted, smoothed and compacted by a finisher table 7 'suspended at the rear of the chassis. A vibrating compactor 10 'moving behind the finisher table completes the compaction.

An adjustable deflector 11 'makes it possible to adjust the angle of discharge of the material 5' at the front of the distribution screw 6 '. The material 5 'reaching the lower part of the layer in progress and intended to constitute the bottom of layer 8'a is kneaded by a screw 12' so as to be intimately mixed with an aqueous liquid brought in by a ramp spray 14 'having a transverse arrangement relative to the chassis of the machine.

The aqueous liquid, the spraying of which is ensured by the ramp 14 ′, contains a workability additive such as a fluidizer, a plasticizer or a superplasticizer commonly used in the technique of manufacturing concretes.

The liquid also contains binder in suspension, this binder can be constituted by cement, fly ash, silica smoke or any other product which can play the role of a hydraulic binder.

The liquid is poured out by the ramp 14 'in a proportion adjusted on the one hand according to the quantity of materials intended to constitute the bottom of the layer 8'a, this bottom of the layer being able to have a thickness of between 20 and 50% of the 'total thickness of the road layer 8', on the other hand as a function of the speed of advance of the machine.

The addition of a liquid and in particular of a liquid containing a workability additive to the material intended to constitute the base layer makes it possible to improve the compactibility of this material and the compaction of the base layer 8'a, under l 'action of the finishing table 7' and the compactor 10 '.

It is thus possible to obtain a substantially homogeneous compaction of the pavement layer over its entire thickness, by compensating for the reduction in compaction forces on the bottom of the layer, by better compactibility of the material used to constitute this bottom of the layer.

In addition, the addition of a binder in a regulated quantity to the material intended to constitute the base layer makes it possible to increase the mechanical characteristics and in particular the fatigue resistance of this base layer which is the part of the road layer which undergoes the strongest stresses, during the bending in service of the pavement layer.

It is obvious that, in a similar manner to the device described above in the case of a layer of material bonded by bitumen, the device used for producing a layer of material containing a hydraulic binder may include a separator of the material flow at the outlet of the conveyor 4 ', into a flow intended to constitute the bottom of the layer and supplying a mixer at the front of the screw 6', in which water is added to the material and a flow, the spreading of which is carried out directly, at the rear of the screw 6 '.

A ramp 15 'arranged transversely to the chassis of the mobile machine, below the ramp 14' and at the front of the kneading screw 12 'makes it possible to spread a liquid on the support 1' just before deposition of material 5 'intended to constitute the layer 8'.

The liquid spilled by the spray boom 15 ′ is generally constituted by water which can contain a special additive promoting the bonding of the layer of material deposited on the support.

In fact, a liquid such as pure water makes it easier to bond the material 5 'to the support 1 by ensuring the presence of a continuous liquid medium between the support 1 and the material 5' deposited on this support. This continuous liquid medium makes it possible to promote the transport of the active binder which can be constituted for example by cement between the layer 8 ′ and the support 1 ′.

An additional ramp 18 is placed at the rear of the chassis so as to spray or mist a liquid such as water on the upper surface of the material 5 'being distributed on the support 1' by the screw 6 '. This addition of water sprayed onto the material being spread makes it possible to compensate for the loss of water by evaporation of the material 5 ', in particular in hot weather.

• 1°- La couche de chaussée est collée sur le support grâce au répandage d'un liquide aqueux sur le support avant le dépôt du matériau de la couche,
• 2°- La partie inférieure de la couche venant en contact avec le support est lubrifiée par le liquide tel que l'eau renfermant éventuellement des additifs de maniabilité, de sorte que le compactage du fond de couche est réalisé de manière efficace malgré la diminution des efforts de compactage en fond de couche,
• 3°- L'addition d'une quantité supplémentaire de liant à la fraction du matériau destinée à constituer le fond de couche permet d'améliorer sensiblement les caractéristiques et en particulier la tenue à la fatigue de ce fond de couche qui subit les contraintes les plus importantes en service,
• 4°- L'aspersion ou brumisation d'eau sur le matériau en cours d'étalement permet d'éviter une déperdition d'humidité de ce matériau, en particulier par temps chaud.

The device shown in Figure 2 implementing the method according to the invention allows therefore to bring four appreciable improvements to the process known from the prior art:

• 1 ° - The pavement layer is glued to the support by spreading an aqueous liquid on the support before the deposition of the layer material,
• 2 ° - The lower part of the layer coming into contact with the support is lubricated by the liquid such as water possibly containing handling additives, so that the compaction of the bottom of the layer is carried out effectively despite the reduction in compaction efforts at the bottom of the layer,
• 3 ° - The addition of an additional quantity of binder to the fraction of the material intended to constitute the base layer makes it possible to significantly improve the characteristics and in particular the resistance to fatigue of this base layer which is subjected to the stresses most important in service,
• 4 ° - The sprinkling or misting of water on the material being spread makes it possible to avoid a loss of moisture of this material, in particular in hot weather.

The method and the devices according to the invention therefore make it possible to significantly improve the characteristics and in particular the durability of superimposed road layers and of the whole of the road surface produced by superposition of these layers.

The invention is not limited to the embodiments which have been described.

The devices for producing the road layers can be different from those which have been described and include in particular elements allowing the incorporation of liquid and binder in the material intended to constitute the bottom of the layer, of a type different from those which have been described.

In the case of materials containing a hydraulic binder, this binder can be added directly in solid form to the material intended to constitute the base of the layer instead of being suspended in the lubrication liquid and improving the compactibility of the base. layer.

The various liquids used for watering the support, improving the compactibility of the base layer and spraying the mass of materials being spread on the support may contain additives of various compositions intended to improve their effect. .

The method according to the invention can be used in particular for the manufacture of pavement layers from a new material containing a filler constituted by bituminous materials recovered from a used pavement during demolition or repair, bound by a hydraulic binder.

To obtain such a material, mills of recovered bituminous material are used which are crushed so as to obtain particles of desired particle size and mixed with a hydraulic binder and with water.

The concrete obtained has a very low modulus (10,000 MPa) and a very low tendency to crack due to exceptional deformability at break. The elongation at break of this material is three times that of conventional concrete.

Finally, the method and the devices according to the invention can be used for producing pavement layers of any kind made up of a material containing a mineral filler and a binder, whether this binder is a bituminous binder or a hydraulic binder .

Claims (15)

1. Process for producing a layer (8, 8') of a road carriageway, by depositing and compacting a material (5, 5') consisting of a load such as granulated material and a binder, in a compactable state, on a substrate (1, 1') which may consist of an under-layer produced earlier, characterised in that a first liquid is mixed with the fraction of material (5,5') intended to form the lower part (8a, 8'a) of the layer (8, 8') deposited on the substrate, before compacting, this first liquid being capable of increasing the compactness of the mixture of binder and granulated material.
2. Process according to claim 1, characterised in that an additional quantity of binder is also mixed with the fraction of material (5, 5') intended to form the lower part (8a, 8'a) of the layer (8, 8') deposited on the substrate, before it is compacted.
3. Process according to claim 1 or 2 characterised in that a second liquid is spread over the substrate (1,1') before the material (5, 5') intended to form the carriageway layer (8, 8') is deposited on the substrate (1, 1').
4. Process according to any of claims 1 to 3, characterised in that the lower part (8a, 8'a) of the layer (8, 8') has a thickness of between 20 and 50% of the total thickness of the layer (8, 8').
5. Process according to claim 2, characterised in that the material (5) intended to form the carriageway layer (8) is a material bound with bitumen and in that the first liquid and the additional quantity of binder are incorporated in the material bound with bitumen (5) which is intended to form the lower part (8a) of the layer (8), in the form of a bituminous emulsion.
6. Process according to claim 2, characterised in that the material (5) intended to form the carriageway layer (8) is a material bound with bitumen and in that the first liquid and the additional quantity of binder are incorporated in the material (5) bound with bitunem in the form of bitumen dissolved in a solvent.
7. Process according to claim 3, characterised is that the material (5') intended to form the carriageway layer (8') is a mixture containing a hydraulic binder and in that a third liquid is sprayed on to the material (5') as it is spread to form the layer (8') in order to maintain its moisture content.
8. Process according to claim 2, characterised in that the material (5') intended to form the carriageway layer (8') is a mixture containing a hydraulic binder and in that the first liquid and the additional quantity of binder are incorporated in the fraction of material (5') intended to form the lower part (8'a) of the layer (8), in the form of a suspension of solid binder in water.
9. Process according to claims 7 or 8, characterised in that the first liquid contains a workability additive.
10. Process according to claim 7, characterised in that the second and third liquids consist of water which may contain suitable additives.
11. Process according to one of claims 7 to 10, characterised in that the mixture (5') contains recovered particles of bituminous material obtained from an old roadway.
12. Apparatus for producing a layer of road carriageway, by depositing and compacting a material (5, 5') consisting of a load such as granulated materials and a binder, in a compactable state, on a substrate (1, 1'), said apparatus consisting of a vehicle which is movable on the substrate (1, 1') in a direction of advance (2, 2'), comprising means (4, 4') for transporting material (5, 5') towards the rear of the mobile vehicle, a device (6, 6') for transverse distribution of the material (5, 5') deposited by the transporting means (4, 4') at the rear of the movable vehicle, on the substrate (1, 1'), and means (7, 7', 10, 10') for compacting the layer (8, 8') of material (5, 5') deposited on the substrate (1, 1'), said means being located at the rear of the device (6, 6') for transverse distribution of the material (5, 5'), characterised in that it further comprises means (14, 14') for incorporating a first liquid in the fraction of material (5, 5') intended to constitute the lower part of the layer (8, 8'), said means (14, 14') being located at the front of said device (6, 6') for transverse distribution of the material (5, 5'), this first liquid being capable of increasing the compactness of the mixture of binder and granulated materials, and means for mixing (12, 12') the first liquid and the fraction of the material (5, 5') intended to form the lower part (8a, 8'a) of the layer (8, 8'), said mixing means (12, 12') being arranged between said means (14, 14') for incorporating a first liquid and said compacting means (7, 7', 10, 10').
13. Apparatus according to claim 12, characterised in that it further comprises means (15, 15') for spreading a second liquid on the substrate (1, 1'), arranged in front of the mixing means (12, 12').
14. Apparatus according to one of claims 12 and 13, characterised in that it further comprises a deflector (11, 11') for guiding and regulating the flow of the material (5, 5') in the direction of the mixing device (12, 12'), without separation of the granulated materials.
15. Apparatus according to any of claims 12 to 14, where the material (5') intended to form the layer (8') of the carriageway is a material containing a hydraulic binder, characterised in that it comprises means (18) for sprinkling a liquid such as water on to the material (5') as it is being spread over the substrate (1, 1').

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