EA040503B1 - ADDITIVE COMPOSITION FOR BITUMEN CONGLOMERATES WITH HIGH MECHANICAL PROPERTIES - Google Patents

Description

Technical field

The present invention relates to the field of technology for the production of bituminous conglomerates for pavement.

In particular, the present invention relates to an additive composition for bituminous conglomerates, which improves the mechanical properties of a bituminous conglomerate containing the specified additive, as well as to extend the life of a road surface made using such a bitumen conglomerate.

State of the art

The need to develop technologies and products that are as safe as possible for the environment is still relevant in all areas of the petrochemical industry, especially in the production of asphalt and bitumen conglomerates.

Such a need is driving the search for materials that are as compatible as possible with the natural and built environment, as well as an attempt to optimize the methods of obtaining them by reducing the total extraction of raw materials and, therefore, the carbon footprint associated with such methods.

In addition, the use of additives to improve the properties of bituminous conglomerates and asphalts in general is well known in the art, for example, such additives can be compositions including thermoplastic polymers to improve the mechanical properties of bituminous asphalt containing such additives, in particular tensile strength and stability. to the formation of cracks in the bituminous conglomerate, commonly used as a cover layer for roads.

An asphalt composition containing aggregates, granular or powdered material obtained from waste rubber compounds, such as tires, and a mixture of thermoplastic polymers and copolymers, as well as additional additives and fillers, is described in international patent application WO 2015179553.

Chinese patent application CN 106280505 relates to an asphalt additive in the form of a mixture containing polyolefins in granules and other materials, including a plasticizer, preferably dioctyl phthalate. Such an additive is also effective in reducing the formation of cracks in the asphalt obtained with its use.

Chinese patent CN 102585520 relates to an asphalt additive including polypropylene, polyethylene, PVB (polyvinyl butyral), and also containing dioctyl phthalate as a plasticizer, and in addition: a dispersing agent, a thixotropic agent, and a metal-based powder. This additive improves the performance of asphalt mixtures.

Chinese patent application CN 103509356 also relates to an asphalt mixture containing polyolefins (polyethylene, styrene-butadiene styrene copolymer, polyethylene terephthalate), polyvinyl butyral as a binder, and filler.

In any case, although such additives to improve the chemical and mechanical properties of commercially available asphalts, as well as asphalts that can be obtained using these additives, are usually made with environmental considerations in mind, for example, they may contain waste from other industrial processes or recycled materials, such as, for example, in the case of the asphalt composition described in WO 2015179553, such products in their production are still not able to combine the improvement in the mechanical properties of bituminous conglomerates with a specific reduction in the environmental impact of the raw material used, as a quality as well as at the quantitative level.

In view of the prior art described above, the problem underlying the present invention was to provide an additive composition for mixing with bituminous conglomerates for road pavement, said composition being suitable for improving the mechanical properties of the bituminous conglomerate obtained by mixing said composition with other suitable components, and at the same time was free from the disadvantages described above, thus being more environmentally sustainable.

Brief description of the invention

This problem has been solved by providing an additive composition intended to be mixed with a paving bituminous conglomerate and suitable for improving the mechanical properties of said bituminous conglomerate, containing at least one thermoplastic polymer, a polymer compound that is polyvinyl butyral (PVB), and graphene, where the specified at least one thermoplastic polymer is a polyolefin or a mixture of polyolefins.

More preferably, said at least one thermoplastic polymer is a polyolefin, preferably polyethylene or polypropylene, or any other mixture of polyethylene and polypropylene.

More preferably, said thermoplastic polymer is a mixture of polyethylene and polypropylene containing polyethylene in an amount of from 25 to 75% by weight, based on the total

- 1 040503 mass of the mixture.

Even more preferably, said thermoplastic polymer is a mixture of polyethylene and polypropylene, as indicated in the following table. 1, in which the values by weight are calculated on the total weight of the mixture of polyethylene and polypropylene.

Table 1

Polyethylene (%) Polypropylene(%) thirty 70 40 60 50 50 60 40 70 thirty

Said at least one thermoplastic polymer is preferably a recycled material.

Alternatively, the thermoplastic polymer used in the additive composition of the present invention is virgin material or a blend of the recycled material described above and virgin material.

The advantage is that the additive composition according to the present invention, intended for mixing with bituminous conglomerates, can essentially consist of the above components without the use of other components such as plasticizers, sulfur compounds, salts and/or other materials.

It is equally preferred that the polymeric compound contained in the additive composition of the present invention is polyvinyl butyral (PVB).

According to a preferred embodiment, the above polymeric compound is a recycled compound, preferably recycled PVB, more preferably obtained by recovering it from a used vehicle windshield and/or double glazing used in buildings.

Alternatively, the above polymeric compound, in particular polyvinyl butyral, used in the additive composition of the present invention is a virgin material or a mixture of the above recycled material and virgin material.

According to the present invention, the term graphene means a carbon material with a two-dimensional structure of carbon monoatomic layers with a hexagonal matrix, in which each carbon atom is bonded to the other three carbon atoms through a covalent bond and is bonded to the atoms of neighboring layers through van der Waals forces, and also means any functionalized derivative of such a carbon material, such as graphene oxide, i.e. graphene partially functionalized with oxygen-containing groups.

The graphene used in the additive composition of the present invention preferably has an apparent density of 2 to 100 g/dm ³ , more preferably 10 to 70 g/dm ³ ; wherein the graphene used in the additive composition of the present invention simultaneously has a surface area of 10 to 300 m ² /g.

Said surface area is measured using the Bruner-Emmett-Teller (BET) method for inert gas (nitrogen) absorption, in particular according to the procedure described in ISO 9277:2010.

In addition, the horizontal dimensions of the graphene layers are less than 200 μm, preferably less than 100 μm, more preferably less than 50 μm.

In a preferred embodiment, the graphene used in the additive composition of the present invention is recycled graphene.

Alternatively, the graphene used in the additive composition of the present invention is virgin graphene or a mixture of recycled graphene and virgin graphene.

Accordingly, it is an absolute advantage that the additive composition to be mixed with the paving bituminous conglomerates according to the present invention can exist as a mixture of partially or completely recycled materials; therefore, the additive composition of the present invention is particularly environmentally sustainable, not only due to the apparent net savings in raw materials, but also the associated reduction in carbon dioxide emissions (which would otherwise be released into the environment during the synthesis processes of the materials in question).

The graphene included in the additive composition of the present invention is preferably present in an amount of 0.005 to 1%, more preferably 0.005 to 0.15%, even more preferably 0.01 to 0.1% by weight based on the total weight of the composition. .

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It is equally preferred that the above thermoplastic polymer in the additive composition of the present invention is contained in an amount of from to 95%, more preferably from 50 to 90% by weight based on the total weight of the composition.

It is equally preferred that the above polymeric compound in the additive composition of the present invention, preferably polyvinyl butyral, is present in an amount of 5 to 55%, more preferably 10 to 50% by weight based on the total weight of the composition.

A particularly preferred additive composition for mixing with bituminous conglomerates consists of the following components, expressed as a percentage by weight based on the total weight of the composition:

thermoplastic material 50-95 polyvinyl butyral 5-50 graphene 0.005-1

All percentages given in the text of this application should be understood as percentages by weight, unless otherwise indicated.

The additive composition according to the present invention is obtained in the form of particles, for example in the form of granules or in the form of crumbs, preferably with particles whose average diameter is from 0.5 to 10 mm, more preferably from 4 to 6 mm, or in the form of a powder, preferably with particles , the average diameter of which is from 0.08 to 3 mm, more preferably from 0.5 to 3 mm.

Accordingly, the additive composition according to the present invention can be obtained by a method comprising separately grinding the above-described thermoplastic polymer, a polymer compound, preferably polyvinyl butyral, and graphene, and then mixing them.

It is absolutely preferred that the above-described method for preparing an additive composition according to the present invention leads to the production of an additive composition according to the present invention in the form of a powder or in the form of granules with particles whose average diameter is from 0.08 to 3 mm, preferably from 0.5 up to 3 mm.

The above grinding step can preferably be carried out using a cooled mill or granulator rotor or by cryogenic grinding.

In addition, it is an advantage that the use of the additive composition of the present invention in any of its implementations preferably allows to obtain bituminous conglomerates with improved mechanical properties, as well as to extend the life of the pavement made using such bitumen conglomerates.

The above-described additive composition according to the present invention can in turn be used to produce a bituminous conglomerate suitable for the manufacture of a road surface with high mechanical properties. Such a bituminous conglomerate contains aggregates, including, for example, inert inorganic materials such as crushed stone, granulated and crushed slag, artificial aggregates obtained, for example, by high-temperature melting of certain minerals or rocks (for example, bauxites or certain clays), fillers , bitumen, as well as the additive composition described above, which is usually contained in an amount of from 0.09 to 15%, preferably from 2 to 6%, more preferably 5% by weight, based on the total weight of said bitumen.

Said bituminous conglomerate preferably contains bitumen in an amount of 3 to 7% by weight based on the total weight of the bituminous conglomerate, more preferably in an amount of 4 to 6.5% by weight based on the total weight of the bituminous conglomerate.

According to the present invention, the term bitumen usually means a material containing a solid dispersion phase at room temperature with thermoplastic properties, while said dispersion phase contains high molecular weight organic compounds, mainly hydrocarbons, the number of carbon atoms in which is more than 25. In general, in trace amounts of sulfur, nitrogen, oxygen and metal such as nickel, iron and vanadium can be dispersed in said continuous phase.

Thus, according to one of the additional aspects, the present invention relates to a method for producing a bituminous conglomerate suitable for the manufacture of a road surface with high mechanical properties, including the step of adding to these aggregates, with stirring and at a varying temperature from 130 to 200 ° C, preferably from 165 to 185° C., more preferably 170 to 180° C., of the above additive composition according to the present invention, said bituminous conglomerate also containing bitumen and filler.

The absolute advantage is that the additive composition of the present invention, when added to bituminous conglomerates for pavement, makes it possible to obtain a pavement with high mechanical properties such as high tensile strength, high stiffness and high fatigue strength, as explained in more detail with

- 3 040503 with reference to the detailed description.

Accordingly, the pavement made using the bituminous conglomerate containing the additive composition of the present invention also exhibits a weak tendency to rutting as compared to the pavement made using the bitumen conglomerate not containing the additive composition of the present invention, as will explained in more detail with reference to the detailed description.

The high mechanical properties imparted to the road surface by the additive composition mixed with the bituminous conglomerate, as well as the significant reduction in the phenomenon of rutting, lead to a significant increase in the life of the road surface, as well as its safety, compared to the traditional road surface.

It is an absolute advantage that when a bituminous conglomerate containing an additive composition according to the present invention is used in the manufacture of a road surface, the layers of the latter (base course, tie layer and surface layer) can have a thinner thickness, considering the same service life, compared to with a road surface made using a bituminous conglomerate that does not contain an additive composition according to the present invention.

Therefore, the use of a conglomerate containing such an additive composition not only results in the need to use less aggregates and bitumen, resulting in a reduction in carbon dioxide emissions that would otherwise occur during the production/mining and transportation of the above raw materials, but also results in significant energy savings (and corresponding lower environmental impact) due to less production of bituminous conglomerate, which, as shown earlier, requires processing at rather high temperatures.

In addition, the composition according to the present invention is convenient and safe to handle because it does not contain fine powders that can be inhaled by its operators.

In addition, the composition according to the present invention can be stored for long periods of time, even for many months, without the risk of caking and retains its flow properties unchanged over time, which is important when adding such a composition to a bituminous conglomerate from the point of view of ensuring accurate and reproducible dosing of said composition.

Features and advantages of the present invention will be further demonstrated using some of its implementation options, which are set forth below by way of illustration and not limitation.

Detailed description of the invention

The following are some examples of additive compositions according to the present invention, which have been prepared and studied with positive results in relation to their effect on improving mechanical properties in the production of bituminous conglomerate. In conclusion, a comparative example is given, which shows a possible additive composition that does not contain graphene and does not correspond to the present invention.

Example 1

Mixture of polyethylene and polypropylene (70:30) 49 995%

Polyvinyl butyral 49 995%

Graphene primary production 0 01%

Example 2

Blend of polyethylene and polypropylene (50:50) 49.95%

Polyvinyl butyral 49.95%

Graphene virgin 0.1%

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Example 3

Blend of polyethylene and polypropylene (60:40)

Polyvinyl butyral

recycled graphene

Example 4

Blend of polyethylene and polypropylene (30:70)

Polyvinyl butyral

Primary Graphene

Example 5

A mixture of polyethylene and polypropylene (50:50)

Polyvinyl butyral

Primary Graphene

Example 6

Blend of polyethylene and polypropylene (70:30)

Polyvinyl butyral

Primary Graphene

Example 7

Blend of polyethylene and polypropylene (40:60)

Polyvinyl butyral

Primary Graphene

Example 8

Blend of polyethylene and polypropylene (70:30)

Polyvinyl butyral

Primary Graphene

Example 9

49.95%

49.95%

0.1%

74.995%

24.995%

0.01%

74.95%

24.95%

0.1%

79.995%

19.995%

0.01%

79.95%

19.95%

0.1%

89.995%

9.995%

0.01%

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Blend of polyethylene and polypropylene (70:30)

Polyvinyl butyral

Primary Graphene

Example 10

Blend of polyethylene and polypropylene (60:40)

Polyvinyl butyral

Primary Graphene

Example 11

Blend of polyethylene and polypropylene (70:30)

Polyvinyl butyral

Primary Graphene

89.95%

9.95%

0.1%

89.5%

9.5%

1%

89.990%

9.995%

0.005%

Example 12 (comparative example not according to the present invention)

Mixture of polyethylene and polypropylene (70:30) gg gg%

Polyvinyl butyral jg θθ%

Compositions according to examples 1-11 were prepared by separately grinding a mixture of polyethylene and polypropylene, polyvinyl butyral and graphene and then mixing the crushed components inside the mixer to obtain a homogeneous mixture with particles whose average diameter was 2 mm.

The composition according to example 12 was prepared in the same way on the basis of only a mixture of polyethylene and polypropylene and polyvinyl butyral.

Example 13

Using the composition according to example 8, eighteen briquettes of bituminous conglomerate with a diameter of 100 mm and a thickness of about 25 mm were prepared in the laboratory, containing the specified composition in accordance with the proportions of the ingredients indicated in the following table. 2 (conglomerate A). In addition, eighteen bituminous conglomerate briquettes were prepared with the same composition, but containing the additive composition according to example 12 (conglomerate B), and eighteen bitumen conglomerate briquettes containing neither the additive composition according to example 8, nor the additive composition according to example 12 (conglomerate C) , as well as nine panels of bituminous conglomerate, three panels for each type of conglomerate A, B and C.

table 2

Bituminous conglomerate A containing the composition according to example 8 Bituminous conglomerate B containing the composition according to example 12 Bituminous conglomerate C, without any additive materials Share by weight Share by weight Share by weight Gravel as inert materials 12/20 25 25 25 Gravel as inert materials 6/12 35 35 35 Gravel as inert materials 3/6 10 10 10 Sand 0/4 25 25 25 Filler (CaCO3) 5 5 5 Bitumen 70/100 4.5 4.5 4.5 Additive composition 0.27 0.27 0 Total 104.77 104.77 104.5

Bituminous conglomerate was prepared in the laboratory using the procedure described below using devices that functionally mimic the larger scale equipment commonly used in asphalt conglomerate plants:

- 6 040503 metric composition depending on the road surface, which is supposed to be made using a bituminous conglomerate, which is currently in the process of preparation; the choice of aggregates in accordance with the indicated particle size distribution curve, in this case aggregates in accordance with Table. 2, and bringing the aggregates to a temperature of 170 to 180°C inside the mixer; adding a suitable amount of the additive composition, in this case the additive composition according to example 8, in the amount indicated in table. 2 followed by stirring for 40 to 60 seconds to obtain a mixture; adding to the mixture a suitable amount of bitumen, in this case the amount indicated in table. 2, followed by stirring for at least 20 to 30 seconds; adding to the mixture a suitable amount of filler, in this case the amount indicated in table. 2, followed by mixing for at least 5 minutes (in accordance with the normative law EN 12697-35) to obtain a homogeneous mixture of bituminous conglomerate.

In particular, the resulting mixture was maintained at a temperature of from 170 to 180°C during all stages of its processing.

In the case of bituminous conglomerate B, instead of the composition obtained in example 8 according to the present invention, the composition obtained in example 12, which does not correspond to the present invention (containing no graphene), was added. In the case of bituminous conglomerate C, the step of heating the aggregates was followed directly by the step of adding bitumen to them.

The bituminous conglomerate mixture thus obtained was then discharged from the mixer, dosed into containers in an amount of about 1210 g, and further conditioned in an oven at 150° C. for about 3 hours (to simulate transport conditions).

Then, after a conditioning step in an oven, the bituminous conglomerate thus obtained was placed inside the matrix. Next, to achieve a relative void volume of approximately 2.5%, sealing was performed using a rotary compactor (as an alternative to a rotary compactor, any other type of compactor suitable for this purpose, such as a Marshall compactor, can be used):

Load pressure: 600 kPa;

Gyration angle: 1.25°;

Limiting density: 2400 kg/m ³ .

18 briquettes were made for each type of bituminous conglomerate for mechanical testing, at the same time three panels were obtained with a size of 50 cmx70 cm, one for each type of bitumen conglomerate.

Eighteen briquettes of conglomerate A, eighteen briquettes of conglomerate B and eighteen briquettes of conglomerate C, as well as panels made of conglomerate A, panels made of conglomerate B, and panels made of conglomerate C, were finally placed in climatic chambers for appropriate conditioning for carrying out mechanical tests.

Example 14 Determination of Tensile Strength

For the tensile strength test, six conglomerate A briquettes, six conglomerate B briquettes, and six conglomerate C briquettes were used.

Each briquette was respectively placed in a mechanical press of a special test basket, then a tensile strength test was carried out in accordance with the method of UNI EN 12697-23.

The study of mechanical properties was carried out with the determination of the indirect tensile strength (ITS). ITS simulates the maximum stress generated by traffic that pavement can withstand.

The results of individual tests are shown below in table. 3.

Table 3

Mixture ITS (MPa) Conglomerate A 1.71 Conglomerate B 1.57 Conglomerate C 1.07 Blend (comparison) Percent change (%) A compared to B + 8.9 And compared to C + 59.8 B versus C + 46.7

Based on the data presented in table. 3, it can be noted that the composition of the additive according to the present invention allows to increase the indirect tensile strength by about 60% in a bitumen conglomerate made using the specified composition (agglomerate A), compared with a traditional bituminous conglomerate containing bitumen as such (agglomerate C) , and by 9% compared to a bituminous conglomerate containing an additive composition that is essentially identical in terms of the content of polyethylene / propylene and PVB, but does not contain graphene (cong

- 7 040503 lomerate B). Thus, an increase in indirect tensile strength implies a higher strength of the bituminous conglomerate when subjected to stress, and hence the additive composition of the present invention results in a bituminous conglomerate that produces a pavement having a longer service life. The significant increase in indirect tensile strength achieved with the composition of the present invention, compared to a composition that is identical except for the absence of graphene in an amount of only 0.01% by weight, should be considered completely unexpected.

Example 15. Determination of the modulus of deformation

Six briquettes of conglomerate A, six briquettes of conglomerate B, and six briquettes of conglomerate C were used for testing to determine the modulus of deformation, which refers to the ability of bituminous conglomerates to distribute in the surface part of the roadway the load created in the road surface by the rutting surfaces of vehicle tires.

Each briquette was respectively placed on a special stand of a servo-pneumatic system for dynamic testing, which in turn was located in a climatic chamber for temperature control; then a test was carried out to determine the modulus of deformation in accordance with the method of UNI EN 12697-26.

The test conditions used to determine the modulus of deformation were as follows: Temperature: variable;

Applied horizontal strain: 5 µm;

Peak time: 124ms (frequency 2Hz);

Poisson's ratio: 0.35.

The results of individual tests are shown below in table. 4.

Table 4

Mixture Stiffness of samples at different temperatures (MPa) Т=5°С Т=20°С Т=40°С Conglomerate A 21124 7809 3003 Conglomerate B 20866 6685 2691 Conglomerate C 10169 5711 1096 Blend (comparison) Percent change (%) A compared to B + 1.2% + 16.8% + 11.6% And compared to C +107.7% + 36.7% +174.0% B versus C +105.2% + 17.1% + 145.5%

It is obvious that the additive composition according to the present invention (example 8) when used to obtain a bitumen conglomerate leads in the latter to a significant increase in the modulus of deformation compared to both the traditional conglomerate (conglomerate C) and the conglomerate containing the additive composition according to example 12, which does not contain graphene (conglomerate B). In this sense, conglomerate A is particularly effective at moderately high temperatures (T=20°C; T=40°C). The increase in modulus of deformation found for conglomerate A, compared to conglomerate B, is even higher than the already significant increase in tensile strength found in the previous example, and therefore even more surprising.

Example 16 Determination of Fatigue Strength

Six briquettes of Conglomerate A, six briquettes of Conglomerate B, and six briquettes of Conglomerate C were used for the fatigue test. Fatigue failure of the pavement occurs due to the repetition over time of deformation states induced by tensile stresses, which are caused by both vehicle traffic and seasonal cycles and temperature changes.

Each briquette was respectively placed on a special stand of a servo-pneumatic system for dynamic testing, which in turn was located in a climatic chamber for temperature control; then a fatigue test was carried out in accordance with the UNI EN 12697-24 method.

The test conditions for determining fatigue strength were:

Temperature: 20°C;

Applied horizontal strain: 300 kPa;

Peak time: 248ms;

Rest time: 252ms;

Frequency: 2Hz;

Poisson's ratio: 0.35;

Failure condition: 10% of the original complex module.

The results of individual tests are shown below in table. 5.

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Table 5

Mixture Number of fatigue cycles Conglomerate A 1056933 Conglomerate B 473167 Conglomerate C 157639 Blend (comparison) Percent Change(%) A compared to B + 123.4% And compared to C + 570.5% B versus C +200.2%

Based on the data presented in table. 5, it can be seen that the number of fatigue cycles of the conglomerate A containing the additive composition according to the present invention (Example 8) increased by 123% compared to the bitumen conglomerate B containing the comparative additive composition according to Example 12, which did not contain graphene, and increased up to 570% compared to traditional bituminous conglomerate (conglomerate C). This is additional impressive evidence of an unexpected improvement in the mechanical properties of the conglomerate, this improvement being achieved by the presence of graphene, despite being added in an extremely low amount (0.01% of the total weight of the additive composition added to the bituminous conglomerate).

Example 17. Monitoring of the phenomenon of rutting

Three Aggregate A panels, three Aggregate B panels, and three Aggregate C panels were used to conduct a rutting monitoring test, which refers to the phenomenon of longitudinal deformation caused by thickening under a loaded axle, followed by lateral movement of the bitumen mixture during the passage of the wheel. Each panel was respectively placed on a special bench in a rutting machine (wheel load tester), which in turn was placed in a climate chamber for temperature control; then a fatigue test was carried out in accordance with the UNI EN 12697-22 method.

A laboratory test to simulate this phenomenon provided the following results:

Depth: This parameter physically indicates how deep the track is (greater depth means less resistance);

PRD (proportional rut depth): this parameter indicates the percentage of the rut formed during the test for a given number of cycles; with a decrease in the specified parameter, the deformation decreases and, consequently, the service life of the pavement increases;

WTS (rutting curve slope): this parameter indicates the rate at which the bituminous conglomerate deforms; as this parameter decreases, the deformation resistance increases and the deformation decreases over time, which increases the service life of the pavement.

The specified test condition for determining the rutting resistance was a temperature of 60°C.

The results of individual tests are shown below in table. 6.

Table 6

Track depth after 5000 cycles (mm) Track depth after 10000 cycles (mm) PRD after 10000 cycles(%) WTS (mm/1000 cycles) Conglomerate A 0.43 0.48 0.8 0.009 Conglomerate B 0.88 0.98 1.6 0.022 Conglomerate C 1.39 1.55 2.5 0.025 Blend (comparison) Percent change (%) A compared to B -51.1% -51.0% - 50.0% -59.1% And compared to C -69.1% - 69.0% - 68.0% - 64.0% B compared to S. - 36.7% - 36.8% - 36.0% - 12.0%

The tests carried out make it possible to highlight the high performance properties of conglomerate A containing the additive composition according to the present invention, characterized by a significant reduction in rutting (-51%) compared to bituminous conglomerate B with an additional increase as a result of the service life of the road surface and road safety compared to traditional road coating (conglomerate C).

In this case, it can also be noted that the graphene contained in the additive composition according to

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Claims (15)

of the present invention, despite the fact that the specified graphene is present in a really small amount (0.01% by weight in the composition according to example 8), leads to a significant and unexpected increase in rutting resistance. Ultimately, all experimental data show that the additive composition according to the present invention allows to obtain bituminous conglomerates with improved performance in terms of mechanical properties, which consequently leads to an extension of the overall life of the pavement made using these conglomerates. This results not only in savings (less pavement maintenance and maintenance costs), but also in a significant reduction in environmental impact (the ability to make a thinner layer of conglomerate compared to conglomerate without the additive composition according to the present invention, given the same service life , with a resulting reduction in carbon dioxide emissions due to the production of the conglomerate itself), as well as an increase in overall safety in the application of the road surface in question. CLAIM 1. An additive composition intended to be mixed with a paving bituminous conglomerate and suitable for improving the mechanical properties of said bituminous conglomerate, comprising at least one thermoplastic polymer, a polymer compound that is polyvinyl butyral (PVB), and graphene, wherein said at least at least one thermoplastic polymer is a polyolefin or blends of polyolefins. 2. Additive composition according to claim 1, characterized in that said at least one thermoplastic polymer is selected from the group consisting of polyethylene, polypropylene and mixtures thereof. 3. An additive composition according to claim 2, wherein said at least one thermoplastic polymer is a mixture of polyethylene and polypropylene containing polyethylene in an amount of 25 to 75% by weight, based on the total weight of the mixture. 4. An additive composition according to any one of the preceding claims, characterized in that said thermoplastic polymer is a recycled material. 5. An additive composition according to any one of the preceding claims, characterized in that said polymeric compound is a recycled polymeric compound. 6. An additive composition according to any one of the preceding claims, characterized in that said graphene is recycled graphene. 7. An additive composition according to any one of the preceding claims, characterized in that said graphene is contained in said additive composition in an amount of 0.005 to 1% by weight based on the total weight of the composition. 8. An additive composition according to any one of the preceding claims, characterized in that said thermoplastic polymer is contained in said additive composition in an amount of 45 to 95% by weight based on the total weight of the composition. 9. An additive composition according to any one of the preceding claims, characterized in that said polymeric compound is contained in said additive composition in an amount of 5 to 55% by weight based on the total weight of the composition. 10. An additive composition according to claim 9, wherein said polymeric compound is present in said additive composition in an amount of 10 to 50% by weight, based on the total weight of the composition. 11. An additive composition according to any one of the preceding claims, characterized in that it is in granular or crumb form with particles having an average diameter of 0.5 to 10 mm or in powder form with particles having an average diameter of between 0.08 to 3 mm. 12. The use of an additive composition according to any one of the preceding claims for the production of bituminous conglomerates. 13. A bituminous conglomerate suitable for obtaining a road surface with improved mechanical properties, containing aggregates, filler, bitumen and an additive composition according to any one of claims 1 to 11, while said additive composition is contained in said bitumen conglomerate in an amount of from 0.09 to 15% by weight based on the total weight of said bitumen. 14. The bituminous conglomerate according to claim 13, wherein said additive composition is contained in said bituminous conglomerate in an amount of 2 to 6% by weight, based on the total weight of said bitumen. 15. A method for producing a bituminous conglomerate suitable for obtaining a road surface with high mechanical characteristics, including the step of adding to said aggregates, with stirring and at a temperature of from 130 to 200°C, said additive composition according to any one of claims 1 to 11, bitumen and filler . Eurasian Patent Organization, EAPO Russia, 109012, Moscow, Maly Cherkassky per., 2