WO2002053646A1

WO2002053646A1 - Method of making plastic asphalt paving material and paving material and pavement made thereby

Info

Publication number: WO2002053646A1
Application number: PCT/US2001/044933
Authority: WO
Inventors: Gary M. Fishback; Dennis E. Egan; Hilary Stelmar
Original assignee: The Plasphalt Project Ltd. Co.
Priority date: 2001-01-05
Filing date: 2001-11-30
Publication date: 2002-07-11
Also published as: CA2433789C; CA2433789A1

Abstract

An asphaltic concrete or paving material (10) is produced that contains from about 5 percent or more, and up to about 20 percent, activated granular recycled plastic (22), which supplements or replaces rock aggregate (21) in the mixture. The source plastic (31) may include mixed residual classes of recyclable plastic, including thermosetting plastics and other plastics having little to no widespread utility. The paving material (10) produces roadbeds (12) of higher strength and durability, requiring less total asphalt thickness and providing greater water impermeability. The recycled plastic component (31) of the material is a mixture of any and all recyclable classes 3 through 7, or of those materials from such classes remaining after potentially more valuable recyclable materials may have been selectively removed. The paving product (10) is preferably formed by a process of shredding or mechanically granulating used and industrial waste plastic to a no.4 to 1/2 inch sieve size, and to 1/4 inch to 3/8 inch granules. The Plastic may be cooled during the granulating process. The granules are then treated with an energized activating medium, a plasma formed in preferably argon or some other plasma enhancing gas (93), to activate the surface of the granules, without burning or melting the plastic- Humidity free gas, from a dehumidifier (79) or other source, fills voids in the particle mass fed to an input hopper (82) or otherwise to the top of a vertical plasma column (81) having the argon flowing upwardly therethrough. A replaceable plastic liner (98) protects the column walls from deposits. Gas bursts prevent clogging of the particles in the column. The activated treated granules are added to the aggregate then mixed with the asphalt binder to produce the paving meterial. A slurry or sands mix of plastic and binder may also be applied over an aggregate layer, base layer or roadbed.

Description

METHOD OF MAKING PLASTIC ASPHALT PAVING MATERIAL AND PAVING MATERIAL AND PAVEMENT MADE THEREBY

This application claims priority to U.S. provisional application Serial No. 60/259,956, filed January 5, 2001, expressly incorporated herein by reference.

This application is related to U.S. patent application Serial No. 08/995,954, filed December 22, 1997, now U.S. Patent No. 6,000,877, by the inventors hereof, which is a continuation-in-part of U.S. patent application Serial No.08/555,527 filed November 9, 1995, now U.S. PatentNo.5,702,199 and which are hereby expressly incorporated by reference herein. Field of Invention:

This invention relates to pavements and paving materials and the use of recycled plastics in pavements and paving materials. More particularly, this invention relates to pavements, to paving materials for use therein, and to methods for making paving materials and pavements having unsorted, residual or other recycled or waste plastic as a component of the paving material or pavement. Background of the Invention:

Paving materials such as asphaltic concretes that are used for roadways, parking areas, walkways and other traffic surfaces have been the subject of various efforts to improve their properties. Some of these efforts have involved the addition of polymers, including plastics, in attempts to improve the flexibility, strength and life of the paving material. Such efforts have proved either ineffective or too costly.

The increasing need to dispose of, or find new uses for, previously used or recycled plastics and waste plastics has given incentives to efforts to introduce plastics from waste sources into building or paving materials, either to facilitate their disposal where it is hoped that their introduction does not degrade building or paving material and does not increase its cost, or where it is hoped that their introduction will provide a cost effective improvement in the properties of the building or paving materials . Work has been done to utilize low density plastic and films of selected and graded recycled plastic materials as an additive to the asphaltic binder component of asphaltic concrete paving material in an effort to improve the flexibility and reduce the propensity of the paving material to crack. This effort requires that the recycling task to collect suitable plastic material be selective, or that the material be specifically sorted from a general mixture of recycled plastic material. Such recycled plastic material has a cost that is significantly greater than that of the general ungraded or unsorted recycled plastic material mixture or of the residual recycled plastic material from which more useful grades have been removed. For example, it has been proposed to melt polystyrene foam with asphalt, to add sand, and to mold the material as a concrete substitute, thereby utilizing the waste plastic. Further, it has been proposed to add waste polyethylene to asphalt for road construction to increase pavement durability. Decreased deformation resistance and increased hardness and ductility have been reported by adding other plastic waste in amounts of, for example, eight percent, to paving compounds containing aggregate, where the plastic waste includes specific plastics made of specific combinations of low density polyethylene, cyclophane, cellophane, polypropylene, and polyvinyl dichloride. Fiber reinforced plastics and chopped glass have been proposed for addition to asphalt to improve wear resistance and water permeability.

Proposals to use specific waste plastics as additives to asphalt mixes have had the disadvantage of requiring specific collection of the individual material or the sorting of the desired material from the generally collected plastic waste. Therefore, such efforts calling for specific plastics are costly. Furthermore, such efforts do little to solve the problem of utilization of vast unsorted, unsortable or unclassified bulk mixtures of plastic waste.

Waste plastics are found in several forms. In one form, bulk masses of particular identified plastic materials are produced as waste in the plastics industry. In other forms, plastics are found in the form of discai'ded articles and containers. Some such plastics, particularly plastic bags and plastic bottles, are collected in recycling activities.

Recycled plastic bottles are classified according to a nationally recognized identification system known as the Plastic Container Code System (PCCS) into seven classes that are being identified by markings on the bottles. These classes are: class 1, polyethylene terephthalate (PETE); class 2, high density polyethylene (HDPE); class 3, vinyl and polyvinyl chloride or PVC (V); class 4, low density polyethylene (LDPE); class 5, polypropylene (PP); class 6, polystyrene (PS); and class 7, all other resins and layered multi-material. For convenience, these classes are used below to identify waste plastics that are also in a form other than that of bottles for which the classes were specifically established.

Recycled plastics of types corresponding to PCCS classes 1 and 2, and sometimes classes 4, 5 and 6, whether in the form of used containers or other forms made of the materials, have been sorted from the general mass of recycled material or separately collected, all at increased cost. Bulk mixtures of recycled plastics from more than one of the PCCS classes, particularly materials from class 7 and from class 3 when mixed with material from other classes, generally have been regarded as lacking utility and are accordingly routed to landfills. Such materials have lacked an alternative use or manner of disposition.

The employment of plastics in asphalt mixes has presented various problems . Many of the plastic additives have lacked an ability to bond to or combine with the asphalt binders of the mix. Chemical treatments have been proposed, but such treatments have been ineffective, add to the cost, and introduce additional noxious and toxic substances into the process, aggravating the waste disposal problems.

Accordingly, there remains a need for a low cost manner of enhancing the properties of paving material and there remains a need for a use of residual plastic waste, particularly unclassified or unseparated materials or materials of mixed classes.

Summary of the Invention:

An objective of the present invention is to improve the properties of pavements and of paving materials, particularly asphaltic concrete materials, and most particularly, to improve the strength and useful life of the pavements made of the paving materials. A particular objective of the present invention is to improve the properties of paving materials at a minimum increase in cost or at a savings in cost from that of the standard asphaltic paving material.

A further objective of the present invention is to provide a use for recycled or waste plastic materials, particularly thermosetting and other PCCS class 7 materials, and other combinations of materials of more than one class, particularly classes 3 through 7 and of those waste and recycled materials in these groups that have few uses in relation to their abundance.

A further objective of the present invention is to provide a method of making a paving material, particularly an asphaltic paving material, and of utilizing waste plastic in paving material manufacture.

A particular objective of the present invention is to improve the efficiency of the method and of the apparatus for making plastic asphalt material and to improve the properties of the plastic asphalt product, especially of the method, apparatus and product described in the related U.S. patents 6,000,877 and 5,702,199.

According to principles of the present invention, there is provided a method of making a paving material that includes the step of providing bulk residual plastic waste materials, the step of processing the plastic to a form suitable for combining with asphalt, and the step of combining the processed plastic with asphaltic binder. The processed plastic may serve as an aggregate in the paving material, and may replace at least some of, or combines with, the rock aggregate to form an asphaltic concrete paving material. Further, the process of the invention may include the step of forming a pavement with the paving material. In addition, a paving material and pavement are provided that are made according to such process.

According to one described embodiment of the embodiment of the invention, recycled plastic material that is either unclassified, or is in the form of bulk material containing plastics corresponding to more than one of the PCCS classes 3 through 7, or contains thermosetting plastics and other plastics of PCCS class 7, or otherwise has few uses for all that is available, are provided. By one method of the invention, the plastic material is either pelletized, shredded or otherwise mechanically granulated, or is otherwise formed into particles. The particles are then processes to activate their surfaces so that asphaltic binder adheres to them. Conventional asphaltic binder material and graded aggregate that includes rock particles ranging in size are mixed with the treated plastic panicles. The binder and plastic material are, in the most common application of the invention, premixed as an aggregate component with binder and rock aggregate and applied as a pavement. In alternative applications, the processed plastic is mixed with the binder, then applied as a slurry, for example, over an existing pavement or over a base or a pre-laid layer that may contain a rock aggregate, with which it combines to form a pavement. In one suitable mixture, the aggregate includes from five to seven sieve sizes ranging from no.40 to three-fourths inch in size, and may be from no. 200 to one inch in size. The particles of plastic are of a size that corresponds to one of the intermediate sizes of the rock aggregate. Further, the paving material is formed by mixing from five to twenty-five percent or more of the plastic particles, measured by volume, with the rock aggregate and the asphaltic binder. In one form, an amount of rock aggregate is used which may be varied from the standard ratio mixture of rock aggregate and binder, and may reduce the amount of mid-range or correspondingly sized rock aggregate by an amount not more than the amount of added plastic, and by an amount that is somewhat less than the amount of added plastic. The particles of plastic are in the one-eighth to one-quarter inch sieve range, and may be three-eighths inch or larger. The particles of plastic will be generally flatter and more elongated in shape than the shapes of the particles of the rock aggregate component of the mixture. The formation of the granules of the plastic may be carried out in a number of ways. One method that can be employed at high efficiency is to first shred the plastic so that all particles are roughly two inches or less in diameter or smaller, then to feed this shredded plastic to a granulator that further reduces the size of the particles to, for example, one-quarter inch in diameter or less. Cooling the granules as they are transported to and processed in the granulator, for example by injecting cold gas, for example, carbon dioxide gas, into the particle mass, produces more fractured surfaces on the granules for better adhesion in the asphalt mixture, reduces the energy needed by the granulator by making the particles more brittle, and reduces the frequency of necessary cleaning of the granulator by generally maintaining the plastic at lower temperatures at which adhesion of the plastic to the granulator surfaces is less likely. Further in accordance with the described embodiment of the present invention, the plastic particles are processed to activate the surfaces of the plastic particles to increase the surface tension and to cause free or active carbon atoms to be present in the molecules of the plastic material at the particle surface. The activation of the particle surfaces may perform with minimal heating, burning or melting of die plastic, and may be achieved by exposing the surface to high energy treatment-gas atoms, ions or molecules for a limited duration. Such a gas may be in the form of a high thermal energy gas, and may include a plasma or corona, or other electrically or otherwise enhanced gas or vapor, that will cause the activation or increased energization at the surfaces of the plastic particles.

Treatment of the plastic is achieved, in one embodiment described below, by exposing the surfaces of granulated plastic particles to a reducing flame, for example, by exposing the particles to the outer envelope of such flame. The exposure may be carried out by passing the particles on a conveyor through the flame, dropping the particles through a flame treatment tower or otherwise contacting the particles briefly with a flame.

Other processes of chemically or mechanically acti ating the surfaces of the particles will improve adhesion of the particles to the asphalt. Processes that can be used for increasing surface adhesion include those which combine chemical and wave energy as described in U.S. Patent Nos. 5,922,161 and 5,879,757, for example, both hereby expressly incoiporated herein by reference. These patents describe methods of modifying or tailoring the surface of polymers, polymer matrix composite material or polymer based materials by oxidizing the surf ace of tire polymer or polymer matrix material and then treating the oxidized surface with an organofunctional coupling agent or chelating agent or both, simultaneously with a static and/or a high frequency alternating physical field. The field may be an ultrasonic field, a microwave field or a radio frequency field, for example. The surface of the polymer or polymer matrix material is oxidized by corona discharge, flame treatment, plasma treatment, chemical oxidation or ultraviolet radiation. The oxidized surface may be treated with a low concentration of an aqueous or non-aqueous solution of the organofunctional coupling agent and/or chelating agent. The agent may be, for example, an organofunctional silane, organo-zirconate, organo-titanate, organo-tin or organo-aluminate. Such agent may have the general structure X_αS-,Y_b, where X is an organoreactive alkyl group, Y is an hydrolyzable group, a is an integer from 1 to 3, and b is 4-a. The agent may be an aminofunctional coupling agent. The energy fields may be, for example, an ultrasonic field having a frequency in the range of approximately 1 to 500 kHz, particularly in the range of approximately 10 to 50 kHz, a microwave field having a frequency in the range of approximately 1 GHz to 300 GHz, or a radio frequency field having a frequency in the range of approximately 10 kHz to 1 GHz. Other variations of treating the oxidized surface may include treatment with a multifunctional amine-containing organic compound to bind said compound to the oxidized polymer surface wherein the multifunctional amine-containing organic compound consists of the elements carbon, hydrogen and nitrogen and optionally comprises one or more elements selected from the group consisting of oxygen, sulphur, halogen and phosphorous and comprises at least one amine functional group which is not a nitiOgen heterocyclic group and at least one further functional group which may be an amine or other functional group. The multifunctional amine-containing organic compound may be applied to the oxidized polymer surface in admixture with an acidic group containing compound and at a ratio of amine to acidic group of greater than 1. Such methods when used in the paving material of the present invention and in the method of making such material are expected to produce treated material with a greater shelf-life and with improved strength, durability and other physical properties.

The use of ionized gas atoms or a plasma enhanced gas to activate the particle surfaces is particularly suitable, and may be carried out by transporting the particles on an electrically conductive conveyor. Other forms of gas reactant treatment may be used to activate or etch the surface. In one process, granulated plastic particles are fed into the top of a vertical plasma treatment column with the gas that occupies the space between the particles being ionized by arrays of electrodes along the height of the column. The ionized gas in the column plasma treats the surfaces of the particles as the particles pass through the column from top to bottom, so that the particles are discharged from the bottom of the column with highly stable activated surfaces.

The activated surfaces of the plastic particles are thought to enhance the bonding between the asphaltic binder and the plastic particles and do so with minimal or insignificant heating of the plastic. Such plastic particles are blended with the asphaltic binder and with rock aggregate at normal low temperatures, such as at temperatures below 300°F. The treated plastic may be used to form a paving material by combining it with a binder before the activated state of the surfaces of the particles decays. Typically, this time ranges from days to months, depending on the treatment process used, the extent of the treatment and other various treatment parameters such as the energy level of the treatment gas and the time duration of the particles in the gas during treatment.

The present invention provides a paving material and pavement that is believed to be up to fifty percent or more stronger than the required strength of road paving materials or than standard asphaltic concrete that is not modified with the addition of the plastic particles as described above. The invention provides a use for the low utility or otherwise useless recycled and waste plastic compositions, and provides a use for unclassified or residual class plastic material. The cost of the added plastic material is very low, with some untreated plastic material approaching no added cost at all, considering the cost of its disposal as waste. The invention allows the reduction in the total amount of paving material used for making a pavement in proportion to the increased strength of the material, thereby providing a cost savings in the reduced amount of asphaltic concrete required, which may more than offset the cost of providing, treating and blending the plastic.

One embodiment of the present invention provides for the flowing of ionizable gas through the granulated plastic material during plasma treatment thereof. The gas is flowed, for example, from a plurality of ports and sources, counter to the flow of the material through an ionizing chamber. In the described embodiment, granulated plastic material is caused to move downward through a vertical column while ionizable gas flows upward through the column. The gas may be air, but according to one described embodiment of the invention, the gas is a plasma enhancing gas, that is, is a gas that sustains a plasma more easily or more efficiently than does air. Such a gas should be a gas of low humidity and low oxygen content to minimize arcing and combustion of the plastic material. Such a gas may be an inert gas, such as argon which enhances plasma and reduces the likelihood of arcing and combustion. The gas may alternatively be helium, neon, krypton, or xenon. Argon gas is particularly suitable due to its low cost. Other gases that are effective in enhancing plasma, given the plastic material and the process conditions, may be used. Gas compounds, including, for example, carbon dioxide, as well as gas mixtures, for example, of argon and carbon dioxide, as well as other plasma enhancing gases or gas mixtures may be used. Such other gases may be selected from among those plasma enhancing gases used in certain types of arc welding such as TIG (tungsten inert gas) and

MIG (metal inert gas) welding, for example. In addition, prior to being fed into the column, the granulated plastic material may be pre-mixed with the plasma enhancing gas, or at least mixed with dehumidified air or an inert gas or other gas having a low humidity content or gases at low temperature so as to pre-cool the plastic. Carbon dioxide, for example, from a liquified or compressed gas source, may be used as a plasma enhancing gas as well as a cooling gas. Cooled air can also be supplied using cooling devices such as vortex tubes, examples of which are those manufactured under the mark EXAIR by Tech Sales Co. of Toronto, Canada. The particles may also be subjected to magnetic fields before plasma treatment to remove certain metals.

In one embodiment, the particles are caused to move downwardly through a column through which argon or other ionizable gas flows upwardly. The particles are caused to circulate in the column, and the gas may be injected into the column in such a way as to facilitate the circulation and prevent the particles from binding. Pulsed or jetted air can be used to free the particles and prevent their jamming in the column. The plasma is produced by high voltage DC potential on electrodes embedded in opposite side walls of the column, although RF energy may be used. The column walls, or at least portions thereof, are not electrically conductive. Energy is coupled from the electtodes through the electrically non-conductive wall to produce a field inside of the column that energizes a plasma in the gas in the column. A removable plastic liner covers the inner wall of the column. The liner protects the more permanent walls from damage from the plasma or sticking of the plastic. The liner can be replaced, thereby making cleaning of the inside of the column easier and reducing the down-time of the equipment.

These and other objectives and advantages of the present invention will be more readily apparent from the following detailed description of the of the described embodiments of the invention. Brief Description of the Drawings:

Fig. 1 is a flowchart of one embodiment of a method according to the present invention;

Fig. 2 is a diagram of a granulating system suitable for use with the method of Fig. 1.

Fig. 2A is a diagram of a two step version of the plastic granulating system of Fig. 2.

Fig. 3 is a diagram of a flame treatment tower suitable for use with embodiments of the method of Fig. 1. Fig.4 is a diagram of an alternative form of flame treatment apparatus suitable for use with embodiments of the method of Fig. 1.

Fig.5 is a diagram of one form of a plasma treatment apparatus suitable for use with embodiments of the method of Fig. 1.

Fig. 6 is a cross-sectional diagram of a roadway according to certain embodiments of the present invention. Fig. 7 is an enlarged view of a portion of Fig. 6.

Fig.8 is a diagram, similar to Fig.5, of an alternative form of a plasma treatment apparatus suitable for use with embodiments of the method of Fig. 1.

Fig. 9 is a more detailed diagram of the apparatus of Fig. 8. Figs.9A-9C are cross-sectional views along lines 9A-9A, 9B-9B and 9C-9C of the column of the apparatus of Fig. 9.

Fig. 9D is a cross-sectional view of an alternative configuration of the column of the apparatus of Fig. 9 taken along line 9B-9B. Detailed Description of the Drawings

One embodiment of the invention is set forth herein in the form of a description of a test or example of a process (Fig. 1) of making a paving material. In accordance with this embodiment of a metliod of the present invention, a standard asphaltic mix is selected (70). One such suitable mix is, for example, New Mexico State Highway and Transportation Department (NMSHTD) type I A asphaltic mix. Further, a mixture of local rock aggi-egate suitable for asphaltic concrete for use in highway construction is selected (71). Such a rock aggregate mixture used in this example includes particles of the following sizes, as set forth in Table 1:

TAE SLE 1

Sieve Size Percent Passins

1 inch 100

3/4 inch 86 ^l/ι inch 67

3/8 inch 57

No. 4 42

No. 10 34

No. 40 21

No. 200 5.1

Where aggregate is used as a component of the paving material, as in the illustrated example, this step (71) may be performed at any time prior to the blending step (75) discussed below. In other applications, the aggi-egate providing step (71) is omitted from the paving material blended in step (75), but may be in a previously applied layer of pavement to which the blended plastic and binder are to be applied.

In the example, a volume of bulk recycled plastic material is selected (72). The bulk plastic material may be ungraded or unsorted and thereby predominantly contain plastics of types corresponding to PCCS classes 1 through 7. A suitable plastic is a residual ungraded bulk of recycled plastic from which most of the items of class 1 (polyethylene terephthalate) and class 2 (high density polyethylene) have been removed. It is also contemplated that some of the class 4 plastic (low density polyethylene) and low density foam plastic from class 6 (polystyrene) may have been removed, as well as other grades or classes for which other uses have been found. The bulk material may contain plastic bottles and other waste plastic articles, layered, thermosetting or miscellaneous plastic articles from class 7, PVCs from class 3 , or masses of waste plastic from plastic production and molding industries, for example. In the example, a representative average sample including primarily an assortment of plastic waste corresponding to the plastics of classes 3 through 7 was selected. The plastic waste may include used containers but may contain, in addition or in the alternative, other plastic waste having compositions corresponding to the PCCS classes.

Then, the plastic material is granulated (73). The granulation process typically involves the shredding of the plastic material 31 in a granulating system 30 that employs a shredder or granulator having, for example, plurality of knife blades 32 to reduce the mass of plastic to a uniform blend of particles 33, as illustrated in Fig. 2. The particles include a large percentage of generally flat flake or plate-like pieces that are generally more elongated than the particles of the rock aggi-egate referred to above. In the example, the sizes of the granulated plastic particles included 18 percent that passed sieve no. 10, with all of the particles passing sieve no.4. It is contemplated, however, that, for use with the rock aggregate described above, most of the plastic particles will be in the 1/4 inch to 3/8 inch range, and perhaps larger. They will nonetheless be smaller than, and may be less than half the size of, the largest rock aggregate particles for applications in which the plastic particles are to be blended with the aggregate before paving to form an asphalt mix.

Fig. 2A illustrates an alternative or more detailed granulating sub-system 30a that may be used for the granulating system 30 of Fig. 2. As illustrated in Fig. 2A, the granulating sub-system 30a may include a shredder 34 into which the raw plastic waste 31 is fed and which reduces the size of the components of the plastic waste 31 to uniform medium size particles 33a of about two inches in diameter or less. The rough sized particles 33a are then conveyed in an auger conveyor 35 into a second-stage shredder or granulator 36 in which the particles 33a are further reduced in size by a bank of knives 37, which are driven by a motor 37a, until they pass through a screen 38 in the bottom of the granulator 36 having openings of about 1/4 inch in size, thereby producing the granulated particles 33. A supply 39 of cold carbon dioxide gas is injected at various points into the conveyor 35 and at various points into the granulator 36 to cool the particles 33a as they are being transported and ground to size. This cooling makes the particles 33a more brittle, which causes them to fracture more readily in the granulator 36 and prevents sticking of the plastic to the knives 37 and the wall of the granulator 36, thereby reducing the need to clean the drum and knives of die granulator 36 and lowering the energy requirement of motor 37a. The cooled granules 33a develop more fractured surfaces in the granulator 36, which produces plastic particles 33 that bond better to the binder in the asphalt mix.

The granulated plastic particles are then treated (74) to activate the particle surfaces. The manner of activating the surfaces of the plastic particles is, according to one embodiment of the invention, by exposing the surfaces of the particles to a flame treatment. With the flame treatment, It is helpful to expose the plastic particles to the flame intermittently, if increased exposure is desired, than to maintain the flame constantly, which could unnecessarily heat the plastic, or could burn or melt the plastic. The flame in this embodiment may be a reducing flame.

A reducing flame may be produced by natural gas, propane, or other fuel. In the example, an oxyacetylene reducing flame is used and the plastic particles were spread on a screen and brushed repeatedly with the flame from above and below, using a torch maintained at a distance of about twelve inches from the flame, with agitating and turning of the plastic particles. The duration or dwell of the flame on any of the particles may be kept sufficiently short to avoid any significant melting or burning of the particles or causing a visually perceivable change in the appearance of the plastic particles . A small percentage of the plastic that might be of the lower density, lower melting point types or include exceptionally thin sheet shreds or narrow fibers may, in such a process, melt or char without adversely affecting the process or paving material to be produced.

In one embodiment of the invention, it is contemplated that the activating gas treatment of the granulated plastic particles 33 be carried out in a flame treatment tower 40, as illustrated in Fig. 3. Such a tower may be a vertically elongated cylindrical column 41 having a plurality of inwardly directed, and possibly upwardly inclined, gas jets 42 spaced around the column and at vertical intervals. The fuel to oxygen mixture of the flame is set to create a slightly oxygen poor or reducing flame throughout the center of the column through which the granulated particles are dropped. Depending on the height of the column used, the particles 33 may be repeatedly dropped through the flame. Use of a flame treatment tower 40 in which the particles are dropped through the flame, rather than the use of a conveyor or other structure to support the particles for treatment with the flame, avoids possible sticking to the support caused by a softening or melting of a small percentage of the plastic material in the flame. Such a tower should have a cool air region 43 at the bottom of the tower to facilitate a rehardening of any softened plastic, and the collection of treated particles 45 at the bottom of the tower should include a fluidized air bed 44 or agitating mechanism to avoid a sticking together of the treated particles.

In an alternative embodiment of the invention, flame treatment is performed in an inclined drum tumbler 50, as illustrated in Fig. 4. The tumbler 50 is in the form of an elongated cylindrical barrel 51, inclined at less than 20 or 25 degrees to the horizontal, for example, at about 10 to 15 degrees to the horizontal. The barrel has a plurality of longitudinal vanes 52 running generally parallel or slightly spiraled relative to the axis of the barrel. The reducing flame 53 is made to flow upwardly through the center of the barrel around the axis thereof as the barrel is rotated. The granulated plastic particles 33 are fed into the top of the barrel and proceed to be tumbled through the flame several times as they proceed toward an outlet at the bottom end of die inclined cylinder 51. The constant rotary motion of the barrel, which is kept relatively cool, prevents the sticking to the barrel of any particles 45 that might have been softened.

It is further contemplated that the particles may, for some uses, be pelletized following shredding or granulation and prior to the activating treatment. To pelletize the particles of plastic, the particles may be fed, for example, from a hopper into a pelletizing extruder in which a mild heating element would heat the particles to soften some of the plastic components and promote sticking of the particles. An auger then compresses the warmed particles and extrude them through an extrusion die to be cut into pellets of more or less uniform size. Such pellets may then be treated as described above.

In other embodiments, a plasma, corona or ionized gas may replace or be combined with the flame. For example, as illustrated in Fig. 5, treatment is carried out by exposing the particles to ionized gas, plasma, corona discharge 60 or other electrically energized treatment medium. Such a treatment may be carried out by presenting the plastic particles 33 upon a conveyor 61, which may be effective to maintain charge on the plastic particles, while exposing the particles to the treatment medium 60.

An alternative apparatus 80 for plasma treatment of the particles is illustrated in Fig. 8, in which a vertical plasma treatment tower or column 81 is employed. The column 81 is equipped at its top with a hopper-fed infeed auger or other loading device 82 which is capable of loading a continuous stream of granulated waste plastic particles into the column 81 from its top. The particles may be allowed to fill the column and form a loosely stacked bulk mass of the particles 83 in the hollow interior of the column 81.

Opposite sidewalls of the column 81 are provided with electrodes 84 in the form of arrays of pins, electrically insulated from any metal such as a housing (not shown) spaced from and surrounding the column 81 , which may be formed of a metal and grounded. The electrodes 84 connected to a high voltage power supply which energizes the electrodes 84 sufficiently to produce an electrical discharge in the gas that occupies the spaces between the particles in the column 81. The discharge results, for example, in a purplish-blue glow resulting from the ionization of gas within the column 81. The electrodes 84 may be located on opposite sides of the column 81 in the upper half of the column and on the front and back of the column 81 on the bottom half of the column 81 (see Figs.9A, 9B and 9C) to better insure uniform treatment of the particles as they descend vertically down the column. Other electrode arrangements may be used for this purpose.

At the bottom of the column 81 is provided an outfeed auger 85, which removes treated particles of bulk plastic material from the bottom of the column 81. After the column 81 is filled, the plasma electrodes 84 are energized, and after the plasma treatment has been applied to the particles in the filled column 81 for a sufficient period of time to activate the surfaces of the particles, the outfeed auger 85 and the infeed auger 82 are operated at the same bulk transfer rate so as to cause a constant volume flow of panicles into the column at the top, downwardly through the column 81 and the plasma, and out of the outfeed 85 at the bottom of the column 81. An initial quantity of about one thousand pounds of treated plastic material should be run out of the apparatus 80 when it is first started. Thereafter, fully treated plastic is consistently produced. The initial quantity may be collected and re-fed into a hopper to the infeed auger 82 and retreated.

The column 81 may be provided with air jets to free the bulk plastic material should it become compacted in the column. In the event that the downwardly flowing particles become clogged in the column 81 or are otherwise unable to flow downwardly under the influence of gravity, air from compressor 90 or argon from tanks 93 may be injected through nozzles 94,95 in bursts or pulses to free any clogged particles.

In the plasma treatment of the plastic particles, the surfaces of the particles are treated to a desired surface tension, for example, which produces an ASTM wettability measurement of 50-55 dynes/cm or more, for example, of about 68-70 dynes/cm or even higher. For a nominal treatment rate of approximately 500-550 cubic feet per hour of plastic, which, for example, may have a bulk density of about 27 pounds per cubic foot. The column 81 that is illustrated between 10 to 14 feet tall with an approximately 13 inch square internal cross-section. Its electrodes 84 are energized to a high voltage determined by the geometry of the column 81 and electrodes 84 to ionize the gas within the chamber. The high voltage is supplied from a rectified output of rectifier 88 connected to a center- tapped secondary winding of a high voltage transformer 87. In one embodiment, the transformer 87 is connected to an input 86 of about 440-480 volts AC, 60 Hz, drawing about 30 input amps. The output of the secondary winding of the transformer for an apparatus of this configuration and capacity is about 5kVA. This power is adequate for producing paving material in these quantities. For larger scale paving projects, one skilled in the art can appreciate that larger scale equipment is desired and providing such would be within such person's skill.

Electrodes 84 may take many configurations and forms . For example, the arrays of electrodes may be arranged in a 1/4 inch grid pattern on polyethylene sheets 91. Connection of the electrodes 84 to the output rectifier 88 can be made with the use of a conductive oil layer 92 sealed in a thin volume that communicates with the outer ends of the electrodes 84. Plasma treatment equipment and the technology for designing and producing such equipment is known in the commercial industrial plasma treatment industry.

The plasma treatment can be satisfactorily performed where the gas in the column 81 is air, which may be supplied from the compressor 90. Much higher rates of productivity can be achieved when an inert gas such as argon is used, which may be supplied from the tanks 93 widiout the compressor 90 being activated. The argon tends to support the plasma better and is less likely to result in a burning of the plastic. Other inert or semi-inert gases and gases such as nitrogen or carbon dioxide can be used with varying degrees of plasma enhancing efficiency.

When the plastic has been treated, it is better that it be used as soon as possible. Plastic treated by flame should be mixed with asphalt within a day or days of treatment and treated plastic should be kept out of contact with freely flowing air or sunlight until used. With plasma treatment, however, a longer lasting activated particle surface results. Where a plasma enhancing gas, such as argon for example, is used as the processing gas of which the plasma is formed, the activation of the plastic remains even longer. As such, plasma treated particles can be stored in bulk for from several weeks to several months without substantial degradation of the activated state of the particle surfaces. Nonetheless, use of the treated particles of plastic material should be used as soon after treatment as practical to realize the maximum benefit of their activated surfaces.

Plasma treatment of the particles is believed to roughen the surfaces of the particles and increase the energy of the atoms near the surface, increasing the frequency of chemical bonding between the particle surfaces and the binder and increasing the strength of the particle-binder bond. Use of the plastic to produce an asphaltic pavement layer may involve the step of blending (75) the plastic particles with rock aggregate and with asphaltic mix binder in a manner that is conventional for the formulation of asphaltic paving material for road surfaces (Fig. 1), with the plastic particles being added as an alternative or supplement to the rock aggregate in the overall mix. The plastic particles function more as the rock aggregate component of the asphaltic concrete than as the asphaltic binder. Only a minor or incidental portion of the plastic, particularly that which has a lower density and a lower melting point, that might remain in the plastic material bulk, would soften and tend to blend with the asphaltic component. Instead, in the described embodiments of the invention, the plastic particles supplement the mid-size rock aggregate components. The percentage of the mid-size particles of the rock aggregate may be reduced in the mix, although that is usually not necessary.

Rather than blending a mixture of the treated plastic, binder and- rock aggregate, the present invention also provides its advantages when used as a mixture of plastic with asphaltic or oil based binder on road bases, or by applying such a mix over a rock aggi-egate base layer, where the binder and plastic mix flow down into the base

An example of the road surface produced is illustrated in Fig.6 and includes an asphaltic layer 10 overlying the base gravel layer 11 to form a roadway 12. The asphaltic layer 10 may or may not be the top layer of the roadway 12, but the roadway 12 may also include a surface layer 13 overlying the asphaltic layer 10. The asphaltic layer 10, as illustrated in Fig.7, is formed of an asphalt binder 20 and a rock aggregate 21 having mixed therewith at least five percent by volume of plastic particles 22, most of which are no. 10 sieve size or larger. The plastic particles 22 have treated activated surfaces. A major portion, or substantially all, of the plastic particles 22 are of a plastic material composition corresponding to PCCS classes 3 through 7. Most of the particles 22 of plastic are typically of a size at least 1/8 inch large, and may be of a size less than 3/8 inch large, although smaller and larger size particles may be used. The plastic material will typically include at least thirty percent recycled plastic from the group consisting of thermoset plastics, PVC, and high density polypropylene and polystyrene.

The particles of plastic are believed to strengthen the paving material by adding a slightly flexible interlocking aggregate component that bonds with the asphaltic binder with a partially chemical molecular bond, developing an increased shear resistance of the paving material. The paving material is also more highly impermeable to water, preventing such water from propagating into the gravel bed or subgrade.

Improved properties of the paving material made in accordance with the method of the present invention are illustrated by the example described above. In that example, the treated plastic particles were tested by blending them into the asphaltic mix (using asphaltic concrete 4.4% Navajo 60/70 asphalt cement) that was first heated to a temperature of 265 ^°F then mixed with the plastic at room temperature. The mixing temperature is usually that which produces an asphalt cement viscosity of 170 +/- 20 centistokes kinematic. The plastic was added to the asphaltic mix at a ratio of ten percent by volume, determined from the loose unit weights of the plastic and asphaltic mix. The material was tested by placing it in molds and compacting it to seventy-five blows per side at approximately 250°F. For comparison, other samples were similarly prepared, one sample using d e standard asphaltic concrete mix without plastic, and two samples using untreated plastic of the same composition, one added at five percent by volume to the asphaltic mix and one added at ten percent by volume to the mix. The loose unit densities of the components of the mix for the tests were 1.45 grams per cubic centimeter (90.5 pounds per cubic foot) for the asphaltic concrete mix and 0.36 grams per cubic centimeter (22.2 pounds per cubic foot) for the treated and untreated plastic. The five percent by volume of plastic mixes included 1135.88 grams (2.5 pounds) of asphaltic concrete mix and 14.67 grams (0.032 pounds) of plastic, and the ten percent by volume of plastic mixes included 1076.10 grams (2.370 pounds) of asphaltic concrete mix and 39.69 grams (0.065 pounds) of plastic. The tests performed as set forth below and the component analysis as set forth above employed the standards set forth in Table 2:

TABLE 2

Extraction ASTM D-2172

Sieve Analysis ASTM C-136

Bulk Unit Weight ASTM D-2726

Rice Unit Weight ASTM D-2041

Marshall Flow/Stability ASTM D-1559 The results of the test were as follows, as set forth in Table 3:

The above results can be compared with the NMSHTD stability requirements of 1640 pounds for non-interstate highways and 1800 pounds for interstate highways . It is found from the tests set forth above that, starting with 2821 pound asphaltic concrete (per the test), die strength increased with the addition of untreated plastic to where it had increased by almost ten percent with the addition of 5% untreated plastic particles. However, the strength decreased as the percentage of untreated plastic particles in the mix increased. With the treated plastic, the strength increased with the addition of the plastic, being about 21% higher than the original asphaltic concrete with the addition of ten percent plastic. It is believed that the strength will exceed that of the original asphaltic concrete mix with treated plastic at up to about 25% with optimally treated and optimally sized plastic particles. Other properties such as flexibility, water impermeability, crack resistance and durability are also expected to be improved over this range. Improved efficiency of the above method and apparatus can be attained with the system illustrated in Fig.9, in which a counter flow of processing gas is produced in the upward direction in the column 81 by injecting the processing gas through inlets 101 in the opposite sides of the column 81. As seen in the cross-sectional views of Figs. 9A, 9B and 9C, electrodes 84 of opposite DC potential are supported on opposite longitudinal sides of the column 81, which is of a 1 to l'/i foot square cross-section. As seen in Fig. 9, inlets 94 are carried by the other respective opposite transverse sides of the column 81 at four different levels spaced throughout the height of the column 81. These inlets 94 are off center and staggered so that a swirling action is produced by gas entering the column 81 through the inlets 94. At the bottom of the column, three inlets 95 are provided per side so that sufficient gas is injected through the inlets 95 to fill the spaces between the particles in the column 81 and to displace air from these spaces. The inlets 95 are alternately connected to different sources of gas, illustrated as pressurized tanks 93 of argon gas, each connected through a control valve 96 to opposing sets of the inlets 94 and 95. The inlets 94 are sized so that gas is supplied throughout the column 81 to fill the spaces between the more loosely packed particles toward the top of the column 81 and to insure that the air is displaced and more uniform plasma is produced throughout the column 81.

Fig. 9D illustrates an alterative cross-section of a column 81a. The wall of the column 81a is made of clear plastic, which permits viewing of the progress of the particles 83 of the granulated plastic as they flow through the column 81a, as well as viewing of the glowing plasma in the gas, which is for example argon. The cross-section illustrated is taken at the section 9B-9B of Fig. 9 as an alternative thereto. The column 8 la is rectangular in shape, approximately 24 inches by 13 inches, with the plastic panels 92 welded across to the opposing sides of the column 81a, about 5 inches from the ends, to define a vertical space of about 13x13 inches containing the plastic 83. Fluid tight chambers 97 are formed between the panels 92 and the short sides of the column 81a to contain circulating cooling oil. The electrodes 84 are embedded in the plastic panels 92 and are in communication with the oil in chambers 97 but not in communication with the argon gas or the plastic within the column 81a. The electrodes 84 may be electrically connected to the leads from the rectifier 88 or through conductive oil in the chambers 97 or by wires or a metal plate 99 within the chamber 97, in which case the oil in the chambers 97 may be non-conductive.

Because of the varied and unpredictable composition of the plastic waste material, some components can melt, react or decompose in the treatment column 81,81a and stick to or form deposits on the column walls . These deposits eventually impede the smooth flow of plastic downward through the column or interfere with the electrodes. Such deposits must periodically be removed. When such deposits form on the permanent walls of the column 81 or 81a, the apparatus 80 must be shut down and cleaned. To minimize the equipment down-time and to simplify the periodic cleaning process, a removable liner 98 may provided to line the inside walls of the column 81 or 81a, as illustrate in Fig. 9D. The liner may be formed of a heat resistant low adhesion plastic material, for example, HDPE, in the form of a rectangular or square tube that covers the inside walls of the space containing the plastic particles being treated. The liner 98 may be in the form of a smooth solid tube of film, for example, of 3/32 inch rigid plastic, through which the static electric field from the electtodes propagates with sufficient strength to sustain a plasma when the gas in which the plastic particles 83 are mixed is argon. The liner 98 resists sticking of plastic material thereto, but when such materials do stick to the liner, the liner 98 can be removed and replaced, thereby avoiding buildup of matenal on the pei manent walls of the column 81 and avoiding the need to shut down the apparatus for an extended time foi cleaning

A dehumidifiei 79 supplies dehumidified an to the augei 82 to insuie that the particles of plastic ainve in the column 81 m a controlled diy state moie suitable foi processing The poits 94 and 95 can also be alternatively connected to a compiessoi 90 through a valve 78 to supply buists of compiessed an to the column 81, if and when necessaiy, to cleai the column 81 oi to unclogjams of plastic m the event a budge oi dam of the plastic particles is foimed, which can occui it failures in opeiation occui, particularly wheie the flow of plastic is stopped and restarted with pai tides in the column 81 foi any reason

At the top of the column an exhaust plenum 77ιs pi ovided, which has a plui ahty of exhaust ports communicating with the top of the mteiioi of the column 81 The plenum 77 is connected to an exhaust fan 76 which has an outlet communicating through a roof vent to the extenoi of the building housing the unit 80 The fan 76 and the valves 96 are controlled by a contiollei 69 so that most oi all of the processing gas flows through the column 81 and out the exhaust, with little oi none of the an that aπives with the particles from the augei 82 flowing downwaid with the pat tides through the column, butiathei is exhausted through thereof vent The contiollei 69 also controls the powei to the electrodes 84, the valve 78 fiom the anti-clog compiessoi 90, the motois to the augers 82 and 85 and the dehumidifiei 79, which supplies dehumidified an supply to the augei 82

Those skilled m the ait will appreciate that the applications of the present invention aie many, and that the invention is described m exemplaiy embodiments Accoidmgly, additions and modifications can be made without departing from the piinciples of the invention Accoidmgly, the following is claimed

Claims

1. A method of making an asphaltic paving material comprising the steps of: providing bulk waste or recycled plastic material; mechanically granulating the plastic material to form particles thereof; feeding the granulated plastic material into and downwardly through a plasma processing column having a smooth wall, at least a portion of which is formed of electrically non-conducive material; counter flowing a plasma enhancing processing gas upwardly through the material while the material is being fed through the column; coupling electrical energy through electrically non-conductive material and into the column to energize a plasma in the plasma enhancing processing gas; plasma treating the particles in the plasma and thereby activating the surfaces of the particles; and while the surfaces are activated, blending an asphalt binder with an aggregate that includes at least about five percent of the treated particles of the plastic material.

2. The method of claim 1 further comprising paving a roadway with the blended asphalt binder and aggregate that includes the treated particles of plastic material.

3. The method of claim 1 wherein the processing gas is argon.

4. The method of claim 1 wherein the processing gas is carbon dioxide.

5. The method of claim 1 further comprising: circulating the processing gas as it flows upwardly through the column to stir the plastic material that is flowing downwardly.

6. The method of claim 1 further comprising: flowing the processing gas to the particles of the plastic material through a plurality of inlet ports.

7. The method of claim 1 further comprising: dehumidifying air and injecting the dehumidified air into the granules of plastic material prior to feeding the material into the processing column.

8. The method of claim 1 further comprising: injecting cold gas into granules of plastic material prior to feeding the material into the processing column.

9. The method of claim 1 further comprising: magnetically removing metal from the granules of plastic material prior to feeding the material into the processing column.

10. The method of claim 1 further comprising: lining the inside of the wall of the column with a removable plastic tube and feeding the granulated plastic material therethrough; removing and replacing the tube in the column following the processing of plastic material in the column.

11. The method of claim 1 wherein: the providing step includes the step of providing plastic material that includes a majority of plastic materials of a composition corresponding to one or more of PCCS classes 3 through 7.

12. The method of claim 1 wherein: ' the granulating step includes the step of granulating the plastic material to form particles thereof that are predominantly between no. 10 sieve size and Vi inch in size.

13. The method of claim 1 wherein: the blending step includes the step of blending the binder with an aggregate that includes from seventy to ninety- five percent rock particles of a mixture of sizes including a substantial portion smaller and a substantial portion larger than most of the particles of the plastic material to form the paving material.

14. The method of claim 1 wherein: the granulating step includes the step of granulating the plastic material to form particles thereof predominantly larger than 1/8 inch in size.

15. The method of claim 1 wherein: the granulating step includes the step of granulating the plastic material to form particles thereof predominantly smaller than 3/8 inch in size.

16. A method making an asphalt pavement comprising the steps of the method of claim 1 and further comprising the step of: forming an asphalt layer of the pavement with the paving material.

17. A pavement made according to the method of claim 16.

18. A paving material made according to the method of claim 1.

19. A processing system configured to perform the method of claim 1.

20. The method of claim 1 further comprising injecting bursts of compressed gas to free the particles in the column.

21. An asphaltic paving material made according to the method of claim 1 and comprising a mixture of: an asphalt binder; and an aggregate including at least five percent by volume of mechanically reduced particles of waste or recycled plastic having activated surfaces, which particles, prior to mixing with the binder, have been mechanically reduced in size and thereafter treated on the surfaces thereof with the plasma to activate their surfaces to enhance bonding with the binder without substantially melting or burning the particles.

22. The paving material of claim 21 wherein: most of the particles of the plastic are of at least no. 10 sieve size.

23. The paving material of claim 21 wherein: the aggregate includes between approximately seventy and ninety-five percent by volume natural rock at least half of which includes substantial portions ranging in size from no. 40 sieve to no. 3/4 inch sieve.

24. The paving material of claim 21 wherein: most of the particles of plastic are of a size at least 1/8 inch large.

25. The paving material of claim 22 wherein: most of the particles of plastic are of a size less than 3/8 inch large.

26. The paving material of claim 21 wherein: the particles of plastic aggregate have a major portion thereof of a composition corresponding to one or more of PCCS classes 3 through 7.

27. The paving material of claim 21 wherein: the particles of plastic are substantially all from the group consisting of plastic material corresponding to PCCS classes 3 through 7.

28. The paving material of claim 21 wherein: the plastic material includes a composition of a plurality of different plastic materials corresponding to at least two different ones of PCCS classes 3 through 7.

29. The paving material of claim 21 wherein: the plastic material includes at least thirty percent recycled plastic from the group consisting of thermoset plastics, PVC, and high density polypropylene and polystyrene.

30. The method of claim 1 further comprising: providing a vertical column having electrically non-conductive vertical side-walls, a removable plastic liner inside of the column adjacent the side-walls, an inlet conveyor at the top thereof and an outlet conveyor at the bottom thereof; flowing dehumidified gas into granules of plastic material in the inlet conveyor; providing a pair of arrays of electrodes behind the inner surfaces of an oppositely facing pair of the side-walls; connecting a source of argon gas through a circularly directed set of inlet ports below the top of the column; connecting opposite terminals of a source of high-voltage DC potential across the electrodes, one terminal to each of the arrays of the pair, and coupling electrical energy therefrom through the side-walls and into the column;

31. The method of claim 30 further comprising: providing a magnet at the inlet conveyor.

32. The method of claim 30 further comprising: lining the inside of the wall of the column with a removable plastic tube and feeding the granulated plastic material therethrough; removing and replacing the tube in the column following the processing of plastic material in the column.

33. The metliod of claim 30 further comprising: providing the column with means for injecting bursts of compressed gas to free the particles in the column.

34. The method of claim 1 wherein the treating step includes: oxidizing at least part of the surface of the polymer; and treating the oxidized surface with at least one multifunctional amine-containing organic compound to bind said compound to the oxidised polymer surface wherein the multifunctional amine-containing organic compound consists of the elements carbon, hydrogen and nitrogen and optionally comprises one or more elements selected from the group consisting of oxygen, sulphur, halogen and phosphorous and comprises at least one amine functional group which is not a nitrogen heterocyclic group and at least one further functional group which may be an amine or other functional group.

35. The method of claim 1 wherein the treating step includes: oxidizing at least part of the surface of the polymer or polymer matrix material; and subsequently treating the oxidized surface with an organofunctional coupling agent and/or organofunctional chelating agent, simultaneously with a static physical field and/or a high frequency alternating physical field selected from the group consisting of an ultrasonic field, a microwave field and a radio frequency field.