RUOCCO, Alberto (Pass. Dr. Petrelluzzi 1, Sarnico, I-24067, IT)
RIVA, Mario (Via Lavoro e lndustria Traversa, 200, Rudiano, I-25030, IT)
CISANI, Sergio, Antonio (Via De Gasperi 8, Bergamo, I-24123, IT)
GIANNATTASIO, Gabriele (Via Marconi 21, Suisio, I-24040, IT)
CAMATINI, Marina (Via Balzaretti 7, Milan, I-20133, IT)
BUCHER, Paolo (Via Custoza 4, Dalmine, I-24044, IT)
RUOCCO, Alberto (Pass. Dr. Petrelluzzi 1, Sarnico, I-24067, IT)
RIVA, Mario (Via Lavoro e lndustria Traversa, 200, Rudiano, I-25030, IT)
CISANI, Sergio, Antonio (Via De Gasperi 8, Bergamo, I-24123, IT)
GIANNATTASIO, Gabriele (Via Marconi 21, Suisio, I-24040, IT)
CAMATINI, Marina (Via Balzaretti 7, Milan, I-20133, IT)
| Claims 1. Process for the preparation of a granular composition comprising the following steps: (a) mixing 100 parts by weight of granules obtained through the grinding of used pneumatic tyres, with from 15 to 30 parts by weight of an organic solvent; (b) radiating the mixture obtained in step (a) with microwaves; (c) heating the mixture obtained in step (b) to a temperature of between 120 and 160° C; (d) mixing the mixture obtained in step (c) with from 30 to 60 parts by weight of a thermoplastic polymer and with from 0 to 3 parts by weight of an anhydride ; (e) extruding and subsequently grinding the mixture obtained in step (d) . 2. Process according to claim 1, characterised in that said granules obtained through the grinding of used pneumatic tyres have an average granulometry of less than 4 mm, preferably of between 0.1 and 1.5 mm, even more preferably of between 0.2 and 1 mm. 3. Process according to claim 1, characterised in that the parts by weight of said organic solvent are from 20 to 30. 4. Process according to claim 1, characterised in that said organic solvent is an apolar aprotic organic solvent . 5. Process according to claim 1, characterised in that said organic solvent is selected from esters and aromatic and/or aliphatic hydrocarbons or mixtures thereof. 6. Process according to claim 1, characterised in that the mixing according to step (a) is carried out at a temperature of between 5 and 35°C, preferably of between 15 and 25° C. 7. Process according to claim 1, characterised in that the mixing according to step (a) is carried out for a minimum time of 2 minutes, preferably of between 2.5 and 5 minutes. 8. Process according to claim 1, characterised in that the mixing according to step (a) is carried out at a tangential peripheral speed of between 1.8 and 3.0 m/s, preferably of between 2.0 and 2.5 m/s. 9. Process according to claim 1, characterised in that the radiating according to step (b) is carried out with microwaves having a wave length of between 2.0 and 2.8 GHz. 10. Process according to claim 1, characterised in that the radiating according to step (b) is carried out for a time of between 5 and 15 minutes, preferably of between 8 and 12 minutes. 11. Process according to claim 1, characterised in that the heating according to step (c) is obtained through indirect heating with diathermic oil circulating in the jacket of the mixer, under mechanical agitation. 12. Process according to claim 1, characterised in that the heating according to step (c) is carried out at a temperature of between 130 and 150°C. 13. Process according to claim 1, characterised in that said thermoplastic polymer is selected from polyethylene (PE) , polypropylene (PP), ethylvinyla.cetate (EVA) , styrene-butadiene copolymer (SBS) , or mixtures thereof. 14. Process according to claim 1, characterised in that said anhydride has from 4 to 8 carbon atoms and it is preferably maleic anhydride. 15. Process according to claim 1, characterised in that the mixing according to step (d) is carried out at a tangential peripheral- speed of between 0.2 and 1.0 m/s, preferably of between 0.3 and 0.6 m/s. 16. Process according to claim 1, characterised in that the mixing according to step (d) is carried out at a temperature of between 10 and 140 °C, preferably at about 20°C. 17. Process according to claim 1, characterised in that the extrusion according to step (e) is carried out at a temperature of between 150 and 250° C, preferably of between 160 and 200° C. 18. Process according to claim 1, characterised in that the grinding according to step (e) is carried out until granules are obtained having an average granulometry of between 0 and 15 mm, preferably of between 2 and 8 mm. 19. Granular composition obtainable from the process according to any one of claims from 1 to 18. 20. Use of a granular composition according to claim 19, for the preparation of bituminous conglomerates and/or asphalt for paving roads. 21. Bituminous conglomerate comprising from 2 to 8% by weight of a granular composition according to claim 20, preferably from 4 to 6%. 22. Asphalt for paving roads comprising from 2 to 8% by weight of a granular composition according to claim 20, preferably from 4 to 6%. |
Process for the manufacture of bituminous conglomerates
The object of the present invention is represented by a process that allows recycled material, such as worn pneumatic tyres to be used to partially or totally replace polyethylene (PE) , polypropylene (PP) , ethylvinylacetate (EVA) , styrene-butadiene copolymer (SBS) , in the manufacture of bituminous conglomerates and/or asphalts for paving roads.
A further object of the invention is represented by the bituminous conglomerates and/or asphalts for paving roads which can be obtained through the process at issue .
State of the art
The use of rubber obtained from recycling worn pneumatic tyres as a modifier for road bitumen has been an object of study for several years.
The studies carried out on the use of tyres at the end of their · life in mixtures for asphalts have demonstrated that asphalts with "rubber powder" (i.e. granules of rubber with a size of < 0.8 mm) have a greater sliding resistance, reducing the frequency of breaking and thus lengthening the life thereof (Khosla et. al., 1990. Use of ground rubber in asphalt paving mixtures. Technical Report, Department of Civil Engineering, North Carolina State University, Raleigh; Raghvan et al., 1998, Journal of Materials Science 33 (7), 1745-1752; Khatib et al., 1999, ASCE Journal of Materials in Civil Engineering 11 (3), 206-213; Fedroffet al., 1996, Transportation Research Board, Report No. .1532, Transportation Research Board, Washington, DC, pages 66-72) .
The properties of compression strength and of tensile strength are related to the dimensions, to the proportions and to the surface of the particles of rubber used (Rostami et al . , 1993. Use of recycled rubber tires in concrete. In: Dhir, R.K. (Ed.), Proceedings of the International Conference on Concrete 2000, University of Dundee, Scotland, UK, pp. 391-399; Eldin et al., 1993, ASCE Journal of Materials in Civil Engineering 5 (4), 478-496; Topcu, 1995, Cement and Concrete Research 25 (2), 304-310).
In practice it has been seen that there is a reduction of 85% in compression strength and of 50% in tensile strength, when aggregates of particles were replaced with finer particles and a reduction of 65% when the fine aggregates were replaced with fine particles.
Worn pneumatic tyres can be incorporated in bituminous mixtures by using two different methods indicated as wet process and dry process. In the wet process the rubber is added in a percentage of between 18 and 25% by mass as a bitumen modifier, due to its ability to react with it at high temperatures. The dry process foresees that the rubber is added to partially replace the fine part of the aggregate (inert fraction) in a variable percentage of between 1 and 5 % by mass of the total of the aggregates and mixed with the remaining part before the bitumen is added.
The substantially inert behaviour of the vulcanized rubber with both technological approaches, is not able, however, to give the road surface the excellent strength characteristics that are obtained, on the other hand, with thermoplastic materials (SBS, EVA, PP and virgin SBR) , that intervene modifying the chemical structure of the conglomerate and, consequently, its physical characteristics.
The technical problem tackled and solved by the present invention is thus that of implementing a process that makes it possible to use recycled material, such as , indeed , worn pneumatic tyres, for partially or totally replacing the aforementioned thermoplastic materials in the manufacture of bituminous conglomerates and/or asphalts for paving roads, and that is in any case capable of giving the road surface the characteristics typical of virgin thermoplastic modifiers and is, at the same time, compatible for technical results, high yields, stability over time and environmental compatibility.
Description of the process
The process according to the present invention makes it possible to obtain a granular composition which can, indeed, be used in the manufacture of bituminous conglomerates and/or asphalts for paving roads, from worn pneumatic tyres.
Such a process essentially comprises the following steps :
(a) mixing 100 parts by weight of granules obtained through the grinding of used pneumatic tyres, with from 15 to 30 parts by weight of an organic solvent ;
(b) radiating the mixture obtained in step (a) with microwaves;
(c) subsequent heating of the mixture obtained in step (b) at a temperature of between 120 and 160° C; (d) mixing the mixture obtained in step (c) with from 30 to 60 parts by weight of a thermoplastic polymer and with from 0 to 3 parts by weight of an anhydride;
(e) extrusion and subsequent grinding of the mixture obtained in step (d) .
According to a preferred aspect, the granules obtained through grinding used pneumatic tyres that are used in step (a) have an average granulometry which is lower than 4 mm, preferably of between 0.1 and 1.5 mm, even more preferably of between 0.2 and 1 mm.
As far as the organic solvent is concerned, it is preferably an apolar aprotic organic solvent, even more preferably selected from esters and aromatic and/or aliphatic hydrocarbons or mixtures thereof; according to one particularly preferred aspect, the aforementioned esters and/or aromatic and/or aliphatic hydrocarbons have a number of between 8 and 200 carbon atoms, preferably of between 12 and 60. According to a further aspect, the parts by weight of said organic solvent are preferably from 20 to 30.
The mixing step according to step (a) is normally carried out at a temperature of between 5 and 35 °C, preferably of between 15 and 25° C. Such mixing is preferably carried out for a minimum time of 2 minutes, even more ' preferably for between 2.5 and 5 minutes; the tangential peripheral mixing speed is preferably of between 1.8 and 3.0 m/s, even more preferably of between 2.0 and 2.5 m/s.
The radiating step according to step (b) is advantageously carried out with microwaves having a wave length of between 2.0 and 2.8 GHz, preferably equal to about 2.45 GHz. On average, the radiating time is of between 5 and 15 minutes, preferably between 8 and 12 minutes.
According to a preferred aspect of the invention, the heating according to step (c) is obtained through indirect heating with diathermic oil circulating in the jacket of the mixer, under mechanical agitation; according to a further aspect, it is carried out at a temperature of between 130 and 150°C.
According to further aspects of the invention, the thermoplastic polymer is selected from polyethylene (PE), polypropylene (PP) , ethylvinylacetate (EVA), styrene-butadiene copolymer (SBS) , or mixtures thereof whereas the anhydride has from 4 to 8 carbon atoms and it is, preferably, maleic anhydride. Moreover, the parts by weight of thermoplastic polymer are preferably from 40 to 50 whereas those of anhydride are preferably from 0 to 2.
As far as the mixing according to step (d) is concerned, it is preferably carried out at a tangential peripheral speed of between 0.2 and 1.0 m/s, even more preferably between 0.3 and 0.6 m/s; such mixing is easily carried out at room temperature, i.e. at a temperature of between 10 and 140°C, preferably at about 20°C. —
The extrusion step is normally carried out at a temperature of between 150 and 250° C, preferably at a temperature of between 160 and 200° C. The product thus obtained is then cooled, ground until granules are obtained having an average granulometry preferably of between 0 and 15 mm, even more preferably of between 2 and 8 mm. The following examples are purely for illustrative purposes and are not intended to limit the invention.
Examples
Example A
A.l 100 kg of granules of recycled rubber from pneumatic tyres having a granulometry of between 0 and 0.8 mm were mixed with 20 kg of organic solvent with the trade name Iteroil 70, normally used as an additive for improving the flow of asphalts.
A.2 The mixing step was carried out at a temperature of 20°C, and it lasted 2.5 minutes; the tangential peripheral mixing speed was equal to 2.3 m/s.
A.3 The radiating of the obtained mixture with microwaves was carried out on about 5 kg of material at a time. The radiating step was carried out with microwaves having a wave length equal to 2.45 GHz. On average, the radiating time of each batch of 5 kg was equal to 10 minutes, at the end of which the material had an average temperature of around 95÷100°C.
A.4 The radiated material was discharged inside an agitated mixer and heated through the circulation in its jacket of diathermic oil at a temperature equal to 140°C; the average sitting time of the mixture in the mixer is equal to about 2.5 hours.
A.5 The mixture obtained in the previous step was mixed at room temperature with 50 kg of polyethylene, whereas, maleic anhydride was not added.
A.6 Subsequently, the mixture obtained in the previous point underwent extrusion and subsequent grinding. The extrusion step was carried out at a temperature of 210° C. The product thus obtained, once cooled, was ground in a mill having a control grid with holes with a diameter of 10 mm, thus obtaining a product with a granulometry of < 10 mm.
Example B
B.l 100 kg of granules of recycled rubber from pneumatic tyres with a granulometry of between 0 and 0.8 mm were mixed with 25 kg of organic solvent with the trade name Iteroil 70, normally used as an additive for improving the flow of asphalts.
B.2 The mixing step was carried out at a temperature of 20°C, and it lasted 2.5 minutes; the tangential peripheral mixing speed was equal to 2.3 m/s.
B.3 The radiating of the obtained mixture with microwaves was carried out on about 5 kg of material at a time. The radiating step was carried out with microwaves having a wave length equal to 2.45 GHz. On average, the radiating time of each batch of 5 kg was equal to 10 minutes, at the end of which the material had an average temperature of around ' 95÷100°C.
B.4 The radiated material was discharged inside an agitated mixer and heated through the circulation in its jacket of diathermic oil at a temperature equal to 140 °C; the average sitting time of the mixture in the mixer is equal to about 2.5 hours.
B.5 The mixture obtained in the previous step was mixed at room temperature with 50 kg of styrene-butadiene copolymer, whereas, maleic anhydride was not added.
B.6 Subsequently, the mixture obtained in the previous point underwent an extrusion and subsequent grinding. The extrusion step was carried out at a temperature of 210° C. The product thus obtained, once cooled, was ground in a mill having a control grid with holes having a diameter of 10 mm, thus obtaining a product with a granulometry < 10 mm.
The aforementioned mixtures were used to make the bituminous conglomerates with fixed dosage of bitumen at 6% by weight of the aggregates, and with 6% of the aforementioned mixtures by weight of the bitumen.
As can be seen from the table, increased values are obtained for the parameters of Marshall stability, tensile strength and compression strength.