FR2717195A1 - Bituminous road surface coating - Google Patents

Abstract

A bituminous coating partic. for road surfaces, comprises granulates, bitumen and mineral fibre as mineral fibre insulation and chopped mineral fibres. The insulation type mineral fibres, e.g., mineral wool have fibres less than 2 mm long, which are introduced in the form of modules. The chopped fibres are at least 3 mm long, partic. 10-25 mm in dia.. Total mineral content is 0.5-30% with ratio of insulation type to chopped fibre type of 95/5 to 5/95. Prodn. is by mixing and heating the granulate; incorporating the liq. bitumen while adding all or part of the fibrous material; and incorporating the rest of the fibrous material independent of any bitumen.

Description

BITUMINOUS COATINGS
1invention relates to bituminous mixes, especially for road surfaces, as well as their manufacturing process.

 Bituminous mixes are, in a well-known manner, mainly composed of inert materials of varied particle size of the gravel type (hereinafter collectively referred to as aggregate), the cohesion of which is ensured by coating with bitumen.

 They are suitable for making wearing courses. There are different categories, in particular according to the degree of compactness of the coatings which result therefrom, degree of compactness largely dependent on the particle size distribution chosen for the aggregate used.

Thus, if the coating has a relatively porous nature, coated materials are designated by the term "porous draining coated materials": the coating, by its permeability to water created by this porosity, allows the evacuation of rainwater avoiding any projection. Asphalt can also be "dense". Furthermore, the coating can be of variable thickness depending on its purposes.

 In all cases, the fact remains that the coatings obtained with bituminous mixes must meet certain requirements, and, in particular, must be able to withstand the rolling of vehicles in a fairly wide temperature range, avoiding cracks as well. and tearing in particular in cold weather, that deformation and softening, in particular by high heat.

 This is the reason why it has already been proposed to add, during the preparation of the mixes, polishing additives to improve the resistance of the coatings, additives which are as commonplace as ground limestone powder as are sophisticated like polymers. specific organic based on styrene and butadiene.

Furthermore, a very significant improvement in the heat behavior of coatings obtained from bituminous mixes has been obtained by incorporating the additive of fibrous nature described in the patent applications into the bitumen.
EP-A-455 553 and EP-A-509 983: this additive is in the form of calibrated nodules of short fibers obtained from mineral wool usually obtained by centrifugation processes. This type of fibrous material is also known by the term "insulation" fibers, due to its usual use for thermal or sound insulation. However, the beneficial effect of this particular additive on the quality of the coating necessarily has limits, especially in terms of mechanical performance.

 The object of the invention is therefore to optimize the quality of the coatings obtained with bituminous mixes, and more particularly to obtain an improvement in their mechanical properties combined with good temperature resistance.

 The subject of the invention is bituminous mixes, in particular intended for paving pavements, comprising aggregate, bitumen and mineral fibrous material originating from mineral fibers of the insulation type. These mixes also include mineral fibrous material from cut threads.

 In the context of the present application, the term “fibers of the insulation type” includes fibers originating from mineral wool, more particularly glass wool in the form of mattresses known for their application in insulation (mattresses obtained in particular by gaseous centrifugation and drawing of molten glass). Likewise, the term "cut yarns" includes the sections of yarns known sometimes under the name of yarns of the textile or reinforcement type and which are obtained by mechanical drawing of molten glass, then assembly, with or without twisting, of sanitary filaments.

 Surprisingly, the association of these two types of fibrous material, very different both in terms of their method of production and in terms of their structural and dimensional characteristics, has proved to be extremely beneficial: the effects of the two types of fibers are thus combined and completed in a synergistic manner.

 In fact, the use of insulation type fibers as an additive in coated materials was known from the two aforementioned patent applications to slow the softening of bitumen at high temperature by slowing the creep of the bitumen. But in fact, the primary function of these fibers is to better "fix" the bitumen, to prevent it from exuding out of the coating, which then tends to disintegrate it. The presence of insulation type fibers will therefore have a direct influence on the level of bitumen that the coating can fix. In particular, it will make it possible to significantly increase the bitumen rate in the mixes, therefore in the coatings obtained from them, which is entirely advantageous and important especially when these coatings are intended to be used in relatively small thicknesses. In fact, more bitumen, when the coating is thin, makes it possible to be sure of its waterproofness and to provide it with sufficient stability. However, a larger amount of bitumen can create rutting problems.

 However, the cut strands are already used to mechanically reinforce, for example, organic polymer matrices. Incorporating them in asphalt therefore makes it possible to mechanically reinforce the bitumen, to "arm" it in a way by giving it a mesh, a "framework", and in fact to combat the rutting phenomenon, which is all the more crucial as the bitumen rate is important.

 It can also be emphasized that the effects of the two types of fibrous material on the coating complement and "take turns" according to the variable temperature conditions that the coating once in place must undergo. In fact hot, that is to say when the temperature is so high, in summer for example, it is particularly the fibers of the insulation type which intervene in order to avoid creep, softening of the bitumen when it tends to have a viscous behavior. By cons, cold, that is to say when the temperatures are low, of those that can be encountered in winter, bitumen tends to have rather an elastic behavior. And it is in this scenario that the cut wires are most effective in exercising their reinforcing role, a role which is all the more increased as the proportion of bitumen is high, a proportion which moreover is strongly correlated with the quantity. of insulation type fibers introduced, as indicated above. When cold, in particular, the complementarity of the two types of fiber makes it possible to fight against cracks by better distribution of stresses, and this in a wide range of coating thickness.

 The combination of insulation type fibers and cut yarns actually allows the elastic limit temperature of the bitumen to be pushed to higher values, thus widening "upwards" the range of temperatures where the bitumen (and consequently the coating which contains it) can keep its elasticity and thus not deform permanently.

 One can thus realize that the effects of these two types of fibrous material are very linked.

 It has thus been noted that the coatings obtained from bituminous mixes comprising both fibers of the insulation type and cut wires exhibit good resistance to high temperature, but also high mechanical performance. The coatings obtained in particular have a very significant capacity to resist rutting as well as cracking. They have a high modulus of rigidity and have a high resistance to fatigue. These results could not have been achieved so satisfactorily if only one or the other type of fibrous material had been added.

 It should also be emphasized that the invention can be adapted as a function of the requirements for the surface, requirements which are not necessarily identical depending on the type of road: by "modulating" the relative proportion between the two types of fibrous material, and their overall rate as well as that of bitumen in asphalt, it is possible to focus on this or that property more particularly sought after.

 The invention is therefore very flexible in its implementation, flexibility which would be excluded if, again, only one type of fibrous material was used.

 As previously mentioned, if the combination of the two types of fibrous material is so advantageous, it is because they differ in many characteristics, and, therefore, in fact "complement each other".

 Thus, the mineral fibers of the insulation type introduced into the bituminous mixes are obtained by shredding glass wool mattresses. These are separate fibers, of small diameter. The diameter, in the case of this type of fiber is difficult to assess directly, and to average. In addition, the parameter that counts more to assess their ability to fix bitumen is what is called the specific surface, which can be estimated by measuring the micronaire, a standardized measurement (DIN 53 941 or ASTM D 1448). which is described in particular in patent application EP-A-455 553.

 In the present case, a micronaire value less than or equal to 7 under 5 grams is preferred, in particular close to 4.

 The length of these fibers is quite short, firstly because of the very process of manufacturing mineral wool, then by the operation of shredding into nodules thereof, nodules which can be "calibrated" more or less specifies the size. Here, the fibers preferably preferably have a length of less than 2 mm, preferably less than 1 mm: the nodules which contain them advantageously have, for example, at least 75% of fibers having a length of less than 0.5 mm. The fibers described in the two aforementioned patent applications are, in particular, usable in the context of the present invention.

 The cut threads come from the cutting of con tifl0S threads, often called textile or reinforcement threads which are obtained by mechanical drawing and assembly of filaments.

They are therefore, at the outset, produced in the form of continuous threads having a certain consistency; wires which can then be cut to well defined and selective lengths using cutters. The yarns which can be used in the context of the invention can be what are called basic textile yarns, in particular single yarns (that is to say having undergone a single twist, with a number of turns per meter between for example 20 and 40). it may thus be so-called plied yarns, that is to say yarns formed from two or more single yarns, twisted together in the opposite direction to the single yarns. However, in the invention, it is rather the yarns called laminates (or "roving" in English) that are preferred: these are wicks obtained either directly under the die by assembling a large number of filaments, either by assembling several threads in parallel and without twisting.

 The laminates, in the form of balls or reels, indeed have a very compact shape, are easy to handle, and are very easily unwound. We can then make the cut either separately or at the time of manufacture of the asphalt. Their wicking structure is favorable to good reinforcement of the bitumen, by more or less extensive filamentization.

 All these wires, to be able to fulfill this reinforcement function, are preferably cut to fairly great lengths, in particular lengths of at least 3 mm.

Thus, an adequate length range is between 3 and 50 mm, for example 25 mm.

 The diameter of the unitary filaments which constitute the threads, and more particularly the laminates, is preferably between 10 and 24 and in particular between 10 and 15 micrometers, ie a diameter significantly larger than that of fibers of the insulation type in general.

 More generally, and in a known manner, the size and compactness of the chopped strands are evaluated by measuring the titer expressed in Tex of the continuous strands from which they originate (Tex corresponds to a thread of one gram per kilometer). Here, it is preferable to choose a title of at least 300 Tex, in particular between 300 and 4800 Tex.

 The overall proportion by weight relative to the bitumen of all of the fibrous material, ie the insulation type fibers and the cut yarns, is adjustable. Preferably, a proportion of between 0.5 and 30% is chosen.

 One can also play on the relative proportion of the two types of fibers for reasons of performance levels or for economic and practical reasons. The weight ratio of the fibrous material from fibers of the insulation type to the fibrous material from cut yarns is advantageously between 95/5 and 5/95, in particular between 25/75 and 75/25.

 Furthermore, the fibers and / or yarns can, before their introduction into the coated materials, be treated with a non-ionic finish, which will promote their compatibility with the bitumen, and therefore help their good dispersion in this latest. This primer can in particular be that described in patent application EP-A-455,553.

It advantageously comprises a tertiary amine oxide such as a fatty acid amine oxide.

 The invention applies to all types of bituminous mixes, in particular either those of the porous-draining type, or those having a more or less marked dense character (which is a function, in particular, of the particle size ranges selected for the constituent aggregate mixes).

The improvement in mechanical performance is indeed significant for all road surfaces from these different mixes. It can however be noted that this improvement is particularly advantageous for coatings derived from porous draining mixes which, because of their porosity, are in fact a little more "fragile" intrinsically.

 The invention also relates to the process for the preparation by mixing of bituminous mixes.

 It is preferable to take care to introduce the fibrous material into the mixes in the least "destruc jack" possible: the fibers or threads, if they were too deteriorated, weakened, fragmented and / or if they broke during their introduction in asphalt, would be much less effective. It is thus, in particular, that the chopped strands, in order to provide satisfactory reinforcement, must keep, once dispersed in the mixes, a sufficient length. It is, of course, necessary that the mixture is also sufficient for all of the fibrous material to be distributed and dispersed as homogeneously as possible in the mixes, and in particular in the bitumen.

 Several preparation methods are envisaged, without limitation. Thus a possible method provides for the following stages - mixing and heating of the aggregates, - incorporation of the liquefied bitumen into which all or part of the fibrous material will have been introduced, - optionally incorporation of the rest of the fibrous material in the mixture independently of the bitumen.

 A prior incorporation in the bitumen of fibers of the insulation type is thus described in patent application EP-509,983.

 Another possible method provides for - mixing and heating the aggregates, - incorporating the liquefied bitumen therein, - incorporating the fibrous material therein, either by separate introduction of fibers of the insulation type and of cut yarns of the textile or reinforcement type, either by joint introduction. The two types of fibrous material can then be premixed beforehand.

 The preparation process can also provide for an operation for cutting continuous son into cut son, an operation which can be carried out "in situ", that is to say just before the latter are incorporated into the aggregates and / or bitumen.

 Other characteristics and advantages of the present invention will appear more clearly in the following nonlimiting detailed description, with the aid of FIGS. 1 to 4 showing schematic views of different variants of devices for preparing bituminous mixes.

 The devices of Figures 1 to 3 relate to types of mixer operating continuously, while the device of Figure 4 comprises a mixer operating discontinuously. For more details on their mode of operation, reference may usefully be made to patent application EP-A-509 893.

 Whatever the mode of preparation envisaged, mineral fibers of the insulation type are advantageously used in the form of nodules, in particular according to the nodule preparation technique described in European patent application EP-0 455 553. It allows the transformation a layer of mineral fibers sized into nodules ready to be incorporated into the bitumen. These nodules are made of mineral fibers having a micronaire before any chemical or mechanical treatment measured according to DIN 53941 or ASTM.D standards. 1448 which is at most equal to 7 under 5 grams, in particular approximately 4. The fibers are ground and cut by the blades of the device so that 75% have a length less than 500 microns and then they are transformed into nodules which will facilitate the introduction and dispersion of the fibers in the bitumen.

 As for the cut threads, this is, for example, a standard assembled stand, cut to a length of about 25 mm and of a titer greater than 300 Tex, the diameter of the filaments being chosen from about 10 to 14 micrometers.

 The proportion by weight between the two types of fibrous material is extremely flexible. It is advantageous to choose, for example, a ratio of 2/3 of insulation fibers to 1/3 of cut son.

 The overall proportion of the fibrous material relative to the bitumen is also adjustable, it can in particular be between 0.5 and 30%, for example around 10 to 15%.

 It is preferable to recommend the introduction of fibrous materials originating from fibers of the insulation type as described in application EP-O 509 893, that is to say an introduction of the fibers into the bitumen before it is added to the aggregate. However, it is not essential.

 The fibrous material originating from cut threads of the textile or reinforcement type can be introduced in the same manner as that originating from the insulation fibers, or independently of any prior incorporation into the bitumen.

 This point will be clarified using the figures.

 The device according to a first variant of mixer shown in FIG. 1 comprises a coating dryer drum comprising a part 2 into which the aggregates are introduced by a conveyor belt 6. This rotating drum 2 makes it possible to dry the inert materials 5 and to heat them by making circulate, perpendicular to their direction of movement when they fall after being driven towards the upper part of the cylinder by vanes 24, a hot gas stream supplied by a burner 3. The hot gases charged with dust are evacuated by a hood 23 at through a filter to collect the dust before gas evacuation by a fan to a chimney. The burner 3 is located in the axial zone of part 2 of the coating dryer drum. Downstream of the flame zone of the burner 3 is a curtain 20 of inertia. In the coating zone 22 there opens a tube 4 terminated by holes 40 for supplying the hot liquid bitumen supplied by a reservoir 41 by means of a pump 13.

 The device is generally provided with a recycling ring 21 for the introduction of recovery mixes through a funnel 210. This ring 21 is located downstream of the burner and upstream of the bitumen feed nozzle 40. The bitumen supply nozzle 40 allows it to flow through the holes 40 in currents which allow a homogeneous distribution of the bitumen on the inert materials which come into contact with the currents 42 and move towards the outlet hopper 7 and then , after final mixing, be elevated by a bucket chain not shown to a storage silo while waiting for the passage of the trucks that come to take their samples.

 Near the bitumen distribution area also opens a nozzle 11 for feeding fibrous material. This nozzle 11 ends with an end allowing the fibers to diffuse in the form of a jet 110 which intersects the currents 42 of bitumen so that the bitumen-fibers association takes place before any contact with the inert materials 5. The transfer pipe 111 is of relatively large section, which allows good "dilution" of the fibers in the air stream and prevents any agglomeration during their entrainment through the supply tube towards the spray nozzle. The transfer pipe 111 comes from a device 12 for decompacting and pneumatically transporting the fibrous materials in an air stream such as, for example, that represented by the device of French patent FR-2,557,817 allowing, thanks to a blower to convey the fibrous material in the pipe 111. This pipe can be equipped with a non-return device not shown. When the introduction of the fibers stops, it prevents dust, the "fines", contained in the installation from being forced back towards the device 12.

 The pneumatic decompaction and transport device 12 is fed by a hopper with the fibrous material.

 In the context of the invention where two types of fibers are involved, all the fibrous material, insulation fibers and cut yarns, can be introduced in bulk at the same time, for example by means of a silo above the device 12 It should be noted that mixing and transporting the two types of fibrous materials together is all the easier when the diameters of the fiber nodules of the insulation type and the lengths of the wires of the reinforcement or textile type are relatively similar. This removes any dry mixing between fibrous materials and aggregate or inert. The introduction being "very downstream", at the end of the kneading operation, the risks of deterioration of the fibrous material are limited.

 One can however choose to introduce by the device 12 only fibers of the insulation type, and prefer to introduce the cut threads differently: either by the recycling ring 21, or by a thread distribution device (shown in dotted lines in the figure 1) independent, which can lead close or not to the bitumen and insulation fiber feeds. It is thus not excluded to introduce the wires cut with the inert materials, provided that the temperature prevailing in the flame zone near the burner 3 is not excessive.

 It is advantageous to cut continuous threads, here rovings, into cut threads "in situ" before they are introduced into the mixer. It is thus possible to envisage placing cutters above the conveyor belt 6, the cut threads "falling" thus continuously and in modular quantity on the conveyor belt 6 supplying the mixer with inert material. It goes without saying that the cutting operation can also make it possible to feed continuously cut son to the kneader by the recycling ring 21 or any other means for introducing cut son.

 A second variant of a mixer, which still relates to the continuous technique, is shown in FIG. 2 in which the same elements have the same references. The device comprises a single pipe 411 for transporting a liquid bitumen-fibers premix made in an independent mixer-heater 14 receiving on one side the bitumen coming from the pump 13 and on the other side of the fibrous materials coming from the pipe 11 of the pneumatic decompression and transport device 12.

 As before, it is possible to choose to introduce all of the fibrous materials into the device 12 or to introduce therein only fibers of the insulation type for example, the cut threads being introduced in particular by the recycling ring 21, or by an independent device indicated in dotted lines, or even for a device which would bring the cut wires through a pipe to the mixer-heater 14 (case not shown).

 According to another variant, the fibrous materials are supplied separately at the end of the bitumen-inert mixture, just before the last mixing before the output of the rotating drum. This other variant of the method is implemented by an installation shown in FIG. 3, the elements identical to the installation in FIG. 1 bear the same references and the only difference of which is that the bitumen distribution nozzle 4 is located upstream of the nozzle 11 for projecting fibrous materials. The nozzle 11 for projecting the fibrous materials is oriented so that the projection occurs in a radial direction relative to the axis of rotation of the installation, while the bitumen distribution nozzle is oriented so that the distribution is produce upstream.

 Again, either only one type of fibrous material is introduced into the device 12, or all of the fibrous material.

 In the case where the fibers of the insulation type alone are introduced into the device 12, the cut wires can always be introduced through the ring 12 or through an independent device represented by dotted lines.

 An alternative embodiment of a batch production facility for bituminous mix is shown in FIG. 4 in which a drying drum 25 is rotated along an inclined axis and includes a burner 3 in its upstream part through which the inert materials are introduced. to be dried and heated and then deposited on a conveyor 62 which takes them to a buffer hopper 60 which feeds a weighing hopper 61 located above the mixer 8. The mixer 8 comprises mixing arms with horizontal axes 82 and an inlet 80 located at its upper part for inert materials 5. An outlet 87 is located at the lower part of the mixer for delivering the mix, the upper level of which is represented by the dotted line 89. The bitumen is introduced above the two mixing arms 82 by two ramps 83. One or more distributors 84 located at the same level and between the two ramps 83 allow the distribution of materials fibrous res according to jets 86.

 I1 may only be provided a distributor 84 as shown in Figure 4. In this case, it is supplied with both the insulation fibers and the cut son, possibly already premixed in bags, in relative proportion adequate.

 At least two distributors can also be provided, each one being supplied respectively only with insulation fibers or with cut wires.

 The device thus described operates according to the following process. Once the desired amount of inert material has been introduced, dry mixing is started and three operating variants are possible. According to a first variant, the liquid bitumen is introduced simultaneously by the ramps 83 to emit jets 85 of bitumen and at the same time the distributor (s) 84 emit (jets) the jets 86 of fibers and threads. Under these conditions, the bitumen comes into contact with the fibrous materials before contact with the inert materials.

 According to a second operating mode, the bitumen alone is first introduced by the ramps 83, the bitumen is mixed with the inert materials 5 and the process is terminated by bringing the fibrous materials into contact with the bitumen.

 In a third variant of the discontinuous coating process, a device such as that described in FIG. 2, reference 14 can be used to effect a bitumen-fibrous material premix. In the latter case, only the ramps 83 of FIG. 4 are used to introduce the binder, the devices 84 becoming useless. It is also possible to prepare bags already dosed of fibrous materials, which are introduced via the additive flap 88, the bags being either bags containing respectively 100% of fibers of the insulation type and 100% of cut yarns, or bags comprising the two types of fibrous material in a determined weight proportion.

 In conclusion, the bituminous mixes obtained according to the invention both by continuous mixing and by batch mixing allow, by the two types of fibrous materials which they contain, to manufacture coatings with advantageous mechanical properties. Their manufacture also poses no major problem of realization, and on the contrary allows a lot of flexibility depending on the equipment available.

Claims (16)

 1. Bituminous mixes, in particular intended for wearing courses, comprising aggregates, bitumen and mineral fibrous material coming from mineral fibers of the insulation type, characterized in that said coated materials also comprise mineral fibrous material coming from cut wires.  2. Bituminous mixes according to claim 1, characterized in that the mineral fibers of the insulation type have a micronaire less than or equal to 7 to 5 grams, in particular about 4.  3. Bituminous mixes according to claim 1 or claim 2, characterized in that the mineral fibers of the insulation type have a length of less than 2 mm, preferably less than 1 mm.  4. Bituminous mixtures according to one of the preceding claims, characterized in that the mineral fibers of the insulation type are introduced into the mixes in the form of nodules, preferably having at least 75% of fibers having a length of less than 0.5 mm. .  5. Bituminous mixtures according to one of the preceding claims, characterized in that the cut wires are either based on cut base wires, or based on cut rovings.  6. Bituminous mixtures according to one of the preceding claims, characterized in that the cut wires have a length greater than 3 mm, preferably between 3 and 50 mm and in particular approximately 25 mm.  7. bituminous mixtures according to one of the preceding claims, characterized in that the diameter of the individual filaments constituting the cut son is between 10 and 24 and preferably between 10 and 15 micrometers.  8. Bituminous mixtures according to one of the preceding claims, characterized in that the title of the cut wires is at least 300 Tex, in particular between 300 and 4800 Tex.  9. bituminous mixtures according to one of the preceding claims, characterized in that the weight proportion of all of the mineral fibrous material relative to the bitumen is between 0.5 and 30%.  10. bituminous mixtures according to one of the preceding claims, characterized in that the weight ratio of the fibrous material coming from fibers of the insulation type to the fibrous material coming from cut son is between 95/5 and 5/95, preferably between 25/75 and 75/25.  11. Bituminous mixtures according to one of the preceding claims, characterized in that the fibers of the insulation type and / or cut son are previously treated with a non-ionic finish, comprising in particular a tertiary amine oxide such as 'a fatty acid amine oxide.  12. Bituminous mixtures according to one of the preceding claims, characterized in that, in particular as a function of the particle size ranges of the aggregate used, they are either porous of the draining coated type, or dense.  13. Process for the preparation by mixing of bituminous mixes according to one of the preceding claims, characterized in that it provides - for mixing and heating the aggregates, - for incorporating the liquefied bitumen into which all or part of the fibrous material. - optionally incorporating the rest of the fibrous material into the mixture independently of the bitumen.  14. Process for the preparation by mixing of bituminous mixes in accordance with one of claims 1 to 12, characterized in that it provides for - mixing and heating the aggregates, - incorporating the liquefied bitumen, - incorporating the fibrous material, either by separate introduction of the fibers of the insulation type and of the cut yarns, or by joint introduction, in particular by carrying out a pre-mixing of the fibers of the insulation type and the cut yarns before introduction.  15. Process for the preparation by mixing of bituminous mixes according to one of claims 13 or 14, characterized in that it provides for an operation of cutting continuous son into cut son.  16. Application of bituminous mixes according to one of claims 1 to 12 to the manufacture of wearing courses.