Process for the production of an additive for bituminous conglomerates with high mechanical performances

Abstract

The present invention refers to a process for the production of an additive composition intended to be mixed into a bituminous conglomerate for road paving. The process includes grinding a mixed waste material containing a mixture of plastic materials, which includes at least one plastic material based on a polyolefin thermoplastic material, washing the ground mixed waste material and separating a portion of low-density material which contains the plastic material based on a polyolefin thermoplastic polymer from the mixed waste material. This portion of low-density material is then ground to a particle size between 10 mm and 20 mm; and then mixed with a material based on polyvinyl butyral. The resultant mixture is further ground to produce an additive composition having a particle size between 4 mm and 6 mm.

Claims

1. A process for the production of an additive composition intended to be mixed into a bituminous conglomerate for road paving comprising: a) providing a mixed waste material containing a mixture of plastic materials, wherein the mixture of plastic materials comprises a plastic material based on a polyolefin thermoplastic polymer; b) grinding the mixed waste material until reaching a particle size between 40 mm and 80 mm; c) washing the ground mixed waste material and separating a portion of low-density material from the mixed waste material, wherein the portion of low-density material comprises the plastic material based on a polyolefin thermoplastic polymer; d) grinding the portion of low-density material until reaching a particle size between 10 mm and 20 mm; and e) mixing the ground portion of low-density material with a material based on polyvinyl butyral and further grinding the mixture in order to produce an additive composition having a particle size between 4 mm and 6 mm; wherein step c) of washing and separation is carried out by means of a technique of density separation, selecting a predetermined limit density value and separating from the mixed waste material a portion of low-density material having a density lower or equal to said limit value, the predetermined limit density value being lower than or equal to 1.2 kg/m.sup.3.

2. The process according to claim 1, wherein in the step a) of providing a mixed waste material, the mixed waste material comprises solid residues made of plastic material, which result from urban solid wastes or from industrial or handcrafted productions of items made of plastic material or any combination thereof, the solid residues being not recovered or not recoverable in the recycling chain of plastic materials.

3. The process according to claim 1, wherein in step a) of providing a mixed waste material, the mixture of plastic materials comprises plastic materials comprising a polymer selected from the group consisting of polyethylene, a polyethylene co-polymer, polypropylene, a polypropylene co-polymer, polyethylene terephthalate, polyvinyl chloride, acrylonitrile butadiene styrene, polycarbonate, polystyrene, polyurethane and any combination thereof.

4. The process according claim 1, wherein in the step a) of providing a mixed waste material, the polyolefin thermoplastic polymer is selected from the group consisting of polyethylene, a polyethylene co-polymer, polypropylene, a polypropylene co-polymer and any combination thereof.

5. The process according to claim 1, wherein the mixed waste material is previously subjected to a preliminary step of separation during which possible fractions made of polyvinyl chloride and/or fractions made of unwanted materials such as paper, cardboard, wood, fabrics, metal or glass are removed.

6. The process according to claim 1, wherein in the step b) of grinding, the ground mixed waste material is subjected to a procedure of separating a metallic fraction.

7. The process according to claim 1, wherein the predetermined limit density value is lower than or equal to 1.1 kg/m.sup.3.

8. The process according to claim 6, wherein the portion of low-density material has an average density between 0.65 kg/m.sup.3 and 0.95 kg/m.sup.3, as determined according to the DIN 55990 procedure.

9. The process according to claim 1, wherein the portion of low-density material comprises a plastic material based on a polyolefin thermoplastic polymer in a quantity higher than or equal to 75% by weight on the total weight of the portion of low-density material.

10. The process according to claim 1, wherein in the step c) of washing and separating, a second mixture of plastic materials comprising a plastic material based on a polyolefin thermoplastic material is added and mixed with the mixed waste material.

11. The process according to claim 10, wherein the second mixture comprises a quantity equal to at least 75% by weight of its total weight of the plastic material based on a polyolefin thermoplastic material.

12. The process according to claim 10, wherein the second mixture of plastic materials comprises residues made of plastic material from recoverable wastes, which are recyclable and are collected by waste sorting.

13. The process according to claim 10, wherein the second mixture of plastic materials is added to the mixed waste material in a quantity between 5-35% by weight on the weight of the mixed waste material.

14. The process according to claim 1, wherein the material based on polyvinyl butyral comprises a quantity of polyvinyl butyral higher than or equal to 80% by weight on the total weight of the material based on polyvinyl butyral, the material based on polyvinyl butyral being a recovery material based on polyvinyl butyral resulting from post-consumer waste items including automotive windscreens, double-glazed windows, panes of thermal glass, panes of safety glass and/or results from swarf from industrial manufacturing for the production of the post-consumer waste items.

15. The process according to claim 14, wherein the material based on polyvinyl butyral is added to the portion of low-density material in a quantity equal to 5-25% by weight on the weight of said portion of low-density material.

16. The process according to claim 1, comprising an additional step of mixing the additive composition with a modifier compound, wherein the modifier compound is selected from graphene, an adhesion enhancer, a regenerating agent, a plasticizer, lignin or any combination thereof.

17. The process according to claim 1 comprising the following additional steps: feeding the additive composition in an extruder; heating the additive composition up to a predetermined temperature; extruding and cooling the additive composition in order to obtain an additive composition in form of extruded granules having a particle size between 1.85 mm and 4.5 mm.

18. The process according to claim 1, comprising an additional step of further grinding the additive composition in order to obtain an additive composition in form of fine granules having a particle size between 0.85 mm and 2.5 mm.

19. The process according to claim 18, comprising the following additional steps: dosing a predetermined quantity of the additive composition in form of fine granules and pressing it; coating the pressed additive composition with a plastic material film which is based on a thermoplastic polymer, thus obtaining a capsule.

20. The process according to claim 19, wherein the step of dosing comprises a step of adding to the additive composition a predetermined quantity of a liquid modifier compound, the liquid modifier compound being selected from an adhesion enhancer, a regenerating agent, a plasticizer, lignin or any combination thereof.

Description

DETAILED DESCRIPTION

(1) Outlined below is a way of performing the process according to the present invention to produce an additive composition for high performance bituminous conglomerates. An example follows, in which the mechanical properties regarding a bituminous conglomerate obtained by using an additive composition according to the present invention are evaluated.

Example 1: Obtaining an Additive Composition According to the Process of the Invention

(2) At a platform of collection of domestic waste and the like, open top containers were provided to an operator, which had been previously loaded with wastes which are not collected by waste sorting comprising a mixture of plastic materials, mainly containing solid residues derived from items made of plastic materials non-recoverable in the recycling chain of plastic materials according to the current technological standards, such as for example toys, writing material made of plastic materials, flip-flops, bins and baskets made of plastic, fruit crates, pipes, tables and chairs made of plastic, garden furniture, buckets, washbowls and basins, cases for audiocassettes, etc.

(3) As it is known, the above-mentioned items are mainly made of plastic material based on polyolefin thermoplastic polymers, specifically polyethylene and polypropylene.

(4) An operator took from the above open top containers residues made of plastic material, mainly comprising hard plastics, avoiding as much as possible to insert fractions or objects consisting of PVC (cables and laminates), as well as fractions of incidental, undesired materials such as wood, tissues and metals.

(5) The plastic material which was thus taken was accumulated in an open top container, providing a mixed waste material containing a mixture of plastic materials, the latter comprising at least a plastic material based on a polyolefin thermoplastic polymer.

(6) The mixed waste material was loaded onto a conveyor belt to be firstly deprived of further fractions consisting of PVC, as well as fractions made of incidental, undesired materials.

(7) Below, the mixed waste material was sent to a single-shaft waste grinder, for a first grinding step which reduced the material to a size of about 60 mm.

(8) Said first grinding step allows to obtain a mixed waste material which is easier to handle and has a homogeneous particle size for subsequent processing.

(9) Below, the material so ground was distributed onto a conveyor belt to a station of magnetically-operated separation.

(10) A ferrous fraction was then separated from said waste mixed material; following this procedure a weight loss of about 3% on the total weight of the material was recorded.

(11) The mixed waste material thereby iron-deprived was fed, by means of a conveyor belt, to an induced current separator capable to separate non-magnetic metals, including aluminum, stainless steel and copper.

(12) Following said step of removing non-ferrous metallic residues, a further weight loss of about 2% on the total weight of the material was recorded.

(13) By means of the conveyor belt, the metal-free material was sent to the washing and separation section.

(14) Together with the material at issue, in a tank on purpose arranged for carrying out the step of washing and density separation, the mixed waste material was fed together with a second mixture of plastic material comprising at least one plastic material based on a polyolefin thermoplastic polymer.

(15) The second mixture of plastic material was in form of scrap from processes of recovery of recyclable waste made of plastic material or composite material, disposed and recovered in the collection based on waste sorting of plastic.

(16) The weight of second mixture of plastic material corresponded to 25% by weight on the total weight of the mixed waste material depleted of the metallic fraction to which it has been added.

(17) The percentage by weight of polyolefins in the plastic material constituting the second mixture, as such and/or possibly reinforced with mineral charges mixed in the plastic material, was higher than 85% by weight on the dry weight of the latter.

(18) The mixed waste material was thus enriched with clean polyolefin materials derived from procedures of plastics recycling and mixed therewith.

(19) The mixed waste material thus enriched with polyolefin materials of interest (polyethylene and polypropylene, in particular) was separated by means of a technique of density separation from the component with the highest molecular weight, specifically from residues of plastic material, and not only, having density higher than 1.1 kg/m.sup.3, using an aqueous solution having a value of density higher than the plastic materials of particular interest, i.e. high density polyethylene, low-density polyethylene and polypropylene, but lower than plastic materials comprised in said mixed waste material and having a density value higher than the density of the plastic materials of interest.

(20) Together with the above listed materials, the portion of low-density material thereby obtained comprised also polystyrene and expanded polystyrene.

(21) The non-plastic inert materials and the plastic material with density higher than 1.1 kg/m.sup.3, such as nylon ropes or polyvinyl chloride and/or polyethylene terephthalate residues, were allowed to decant, precipitating onto the bottom of the tank.

(22) The weight of the portion of material of highest density so separated corresponded to about 21% by weight on the total weight of the mixed waste material introduced into the washing and separation tank.

(23) In the upper part of the tank, thanks to the movement of a comb-type rostrum placed slightly off the water, the residues of low-density material were easily separated from residues of higher density material, possibly stuck with them. The comb-type rostrum also moved the floating material to a zone of the tank in correspondence with a drained screw, placed at the water outlet.

(24) By means of the screw, the portion of low-density material was then sent to the step of further grinding, while the size of the material was reduced to about 13 mm by means of a wet granulator. The material so ground was collected in containers.

(25) The portion of low-density material so ground and collected was then sent to a horizontal centrifuge for drying the material; specifically, the material was introduced in a hopper and then it was delivered into a perforated basket, inside which a blade rotor was let rotate at a very high speed, so as to transmit a strong acceleration to the material, the residual humidity being expelled from the holes of the perforated basket.

(26) The material thereby deprived of a part of humidity was then further dried by means of a fan.

(27) The portion of low-density material thereby dried had the composition and physical characteristics showed in the following Table 1:

(28) TABLE-US-00001 TABLE 1 Content of polyolefins as such Higher than 90% by weight on the and/or reinforced with mineral total dry weight charges Content of other plastics, Lower than 10% by weight on the composite materials also total dry weight comprising Al foils with thickness ≤ 50 μm and other materials Volumetric mass on the dry Higher than 100 Kg/m.sup.3 Particle size 13 mm Physical form Chips and granules of different forms Humidity Less than 10% by weight

(29) The portion of low-density material so obtained had thus the characteristics requested by the UNI standard 10667-16, therefore it was potentially usable as ground material for extrusion processes and/or for injection molding.

(30) In addition, the portion of low-density material thereby dried had the physical and rheological characteristics showed in the following Table 2:

(31) TABLE-US-00002 TABLE 2 Density 0.8 g/cm.sup.3 (determined according to the DIN 55990 procedure) Melt flow index (MFI) 2.5 g/10 min (calculated with procedure ISO 1133 with T = 190° C. and load equal to 2.16 kg)

(32) The dry material was sent by means of pneumatic transport in a mixing silo of 20 cubic meter capacity in which it was homogenized and mixed with a recycled material provided as post-consumer recovery material based on polyvinyl butyral, in particular the recycled material comprising a quantity equal to 90% by weight of polyvinyl butyral on its total weight.

(33) The weight of the recycle material added corresponded to 10% by weight on the total weight of the portion of low-density material thereby dried.

(34) During homogenizing and mixing, the materials were subjected to grinding at room temperature by means of knife mills until reaching a particle size of about 5 mm.

(35) Finally, the material so obtained was sent to a subsequent step of pulverization and then fed to a disk grinding chamber, where it was ground and in which granules sizes are determined by the distance between the discs. Such distance is adjustable from the outside of the grinding chamber.

(36) The additive mixture so obtained had the composition and physical characteristics showed in the following Table 3:

(37) TABLE-US-00003 TABLE 3 Content of plastic matter (and, 98.6% by weight on the possibly, rubber); of which: total dry weight polyolefins as such and/or 82.7% by weight on the reinforced with mineral charges; total dry weight polyvinyl butyral; 8.2% by weight on the other plastics total dry weight 7.7% by weight on the total dry weight Content of other materials (paper, 1.4% by weight on the cardboard, wood, glass, metal, total dry weight stones, etc). Apparent volumetric mass 0.25 g/cm.sup.3 (calculated with UNI EN ISO 61 procedure) Particle size 1.2 mm Physical form Fine granules Humidity Lower than 10% by weight

(38) The portion of low-density material so obtained had thus the characteristics provided by the UNI standard 10667-14, therefore it was usable as mixture of recycle polymeric materials and of other materials, such as aggregates in cement mortars, in bitumen and in asphalt.

(39) Finally, the additive mixture was sent to a silo provided with a pneumatic recirculation for a potential mixing with further modifying compounds capable of conferring specific properties to the resulting additive mixture comprising the present additive composition and the further modifying compound. The resulting additive mixture may be advantageously employed as modifying agent for road bituminous conglomerates.

Example 2: Formulation of a Bituminous Conglomerate Mixture with the Additive Composition Obtainable by the Present Process

(40) Using the additive composition according to Example 1, an appropriate number of briquettes of bituminous conglomerate with a diameter of 100 mm and a thickness of about 25 mm, containing the composition according to the proportions of the ingredients indicated in the following Table 4, were prepared in the laboratory.

(41) TABLE-US-00004 TABLE 4 Materials Parts by weight Inerts grit 12/20 25 Inerts grit 6/12 35 Inerts grit 3/6 10 Sand 0/4 25 Filler (CaCO.sub.3) 5 Bitumen 70/100 4.5 Additive composition 0.27 Total 104.77

(42) The bituminous conglomerate comprising all the components according to the recipe provided in Table 4 was prepared in laboratory by means of the procedure that follows, using devices which simulate, in function, machinery on higher scale, usually used in plants for the production of bituminous conglomerate: selecting a granulometric curve, depending on the road paving which is desired to be made with the bituminous conglomerate currently under preparation; selecting aggregates according to the above-mentioned granulometric curve, in the present case the aggregates according to Table 4, and heating the aggregates up to a temperature of 170-180° C. inside a mixer; adding an appropriate quantity of additive composition, then mixing for 40-60 seconds so as to obtain a blend; adding to the blend an appropriate quantity of bitumen, in the present case the quantity expressed in Table 4, then mixing for at least 20-30 seconds; adding to the blend an appropriate quantity of filler, in the present case the quantity expressed in Table 4, then mixing for at least 5 minutes (as provided by the regulation EN 12697-35), obtaining a homogeneous blend of bituminous conglomerate.

(43) Specifically, the blend was maintained at a temperature between 170 and 180° C. during all the steps of processing thereof.

(44) The blend of bituminous conglomerate so obtained appeared as a single bitumen-based dispersing phase, having a viscous appearance, in which the aggregates were homogeneously dispersed.

(45) The blend of bituminous conglomerate so obtained was then discharged from the mixer, dosed in a quantity equal to about 1210 g in containers and subsequently it was conditioned in oven at a temperature of 150° C. for about 3 hours (the conditioning was performed only to simulate the transportation conditions).

(46) The bituminous conglomerate so obtained, after the step of oven conditioning, was then inserted inside a template. Then, in order to obtain a voids percentage of about 2.5%, a compaction by means of gyratory compactor was performed (alternatively to the gyratory compactor it is possible to use any other type of compactor suitable for the purpose, for example a Marshall compactor): Load pressure: 600 kPa; Gyratory angle: 1.25°; Limit density: 2400 kg/m.sup.3.

(47) An appropriate number of briquettes were made for performing the mechanical tests; finally, said briquettes were placed in climatic chambers for the appropriate conditioning for performing the mechanical tests.

Example 3: Performing the Mechanical Tests

(48) An appropriate number of briquettes to obtain a reproducible result were respectively housed in a mechanical press of the designated test basket, then a tensile strength test was performed according to the methodology UNI EN 12697-23.

(49) The mechanical characterization occurred with the Indirect Tensile Strength (ITS). The ITS simulates the maximum stress generated by vehicle passage which can be tolerated by the road pavement. The Indirect Tensile Strength was evaluated through the relative parameter ITS.

(50) The mean of the results of the individual tests showed an ITS (MPa) in connection with the conglomerate obtainable by using the additive composition according to the present invention which was completely satisfying, equal or higher if compared to bituminous conglomerates obtainable by using conventional additives.

(51) After that, a test was performed for determining the stiffness modulus, meant as capability of bituminous conglomerates to propagate in the superstructure the load exerted in the road surface from the track areas of the vehicle tires.

(52) An appropriate number of briquettes to obtain a reproducible result were placed on a designated housing of a servo-pneumatic system for dynamic tests, which was in turn contained in a climatic cell for temperature control; subsequently, a test for the determination of the stiffness modulus was performed according to the methodology UNI EN 12697-26.

(53) The test conditions used for the determination of the stiffness modulus were: Temperature: variable; Imposed horizontal strain: 5 μm; Peak time: 124 ms (frequency 2 Hz); Poisson Coefficient: 0.35.

(54) The mean of the results of the individual tests showed a stiffness (MPa) of the samples at different temperatures (T=5° C., T=20° C. and T=40° C.) in connection with the conglomerate obtainable by using the additive composition according to the present invention which was completely satisfying, equal or higher if compared to bituminous conglomerates obtainable by using conventional additives.

(55) The above-mentioned tests thus showed the absolute efficacy of the additive composition obtainable by the process according to the present invention to obtain a bituminous conglomerate mixture with high mechanical performances; the so-obtained bituminous conglomerate can be used to provide a resistant and performing road paving.