This invention relates to pavements and pavmg materials and the use of recycled plastics therein, and more particularly, to pavements, to paving mateπals for use therein, and to a method of making such pavmg mateπals and pavements having residual recycled plastic components Background of the Invention:

Pavmg matenals such as asphaltic concretes that are used for roadways, parking areas, walkways and other traffic surfaces have been the sublets of vanous efforts to improve their properties Some of these efforts have involved the addition of polymers, including plastics, m attempts to improve the flexibility, strength and life ofthe paving mateπal 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 have given incentives to the efforts to introduce plastics from recycled sources into building or pavmg mateπal, either to facilitate their disposal where it is hoped that their introduction does not degrade building or pavmg material and does not increase its cost, or where it is hoped that their introduction will provide a cost effective improvement in the properties ofthe building or pavmg mateπal Work has been done to utilize low density and films of selected and graded recycled plastic mateπals as an additive to tl e asphaltic bmder component of asphaltic concrete pavmg matenal m an effort to improve the flexibility and reduce the propensity ofthe paving material to crack This effort requires that the recycling task to collect suitable plastic matenal be selective, or that the matenal be specificalh sorted from a general mixture of recycled plastic matenal Such recycled plastic matenal has a cost that is significantly greater than that ofthe general ungraded recycled plastic mateπal mixture

For example, it has been proposed to melt polystyrene foam with asphalt, to add sand and to mold the mateπal 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 bv addmg other plastic waste in amounts of, for example eight percent to pavmg compounds contammg aggregate, where the plastic waste includes specific plastics made of specific combinations of low density polyethylene, cyclophane, cellophane, polypropylene, and polwinvl dichloride Fiber remforced plastics and chopped glass have been proposed for addition to add to asphalt to improve wear resistance and water permeability Proposals to use specific waste plastics as additives to asphalt mixes have had the disadvantage ol requiring specific collection ofthe mdividual matenal or the sorting ofthe desired matenal from the generallv collected plastic waste Such efforts calling for specific plastics are therefor 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 m several forms In one form, bulk masses of particular identified plastic matenals are produced as waste in the plastics industry In other forms, plastics are found in the form of discarded articles and containers Some such plastics, particularly plastic bags and plastic bottles, are collected m recvclmg activities Recycled plastic bottles are classified accordmg to a nationally recognized identification system known as the Plastic Contamer Code System (PCCS) mto seven classes that are bemg identified bv markings on the bottles

These classes are class 1, polyethylene terephthalate (PETE), class 2 high density polyethylene (HDPE), class 3, vinyl and polyvinyl chlonde or PVC (V), class 4, low density polyethylene (LDPE), class 5, polypropylene (PP), class 6, polystyrene (PS) and class 7, all other resms and layered multi-matenal For convenience, these classes are used below to identify waste plastics that are m a form other than that of bottles for which the classes were specifically estabhshed

Recycled plastics correspondmg to classes 1 and 2, and sometimes classes 4, 5 and 6, have been sorted from the general mass of recycled matenal or separately collected, all at mcreased cost Bulk mixtures of recycled plastics from more than one of the PCCS classes, particularly mateπals from class 7 and from class 3 when mixed with mateπal from other classes, generally have been regarded as lacking utility and are accordingly routed to landfills Such mateπals have lacked an alternative use or manner of disposition

The employment of plastics in asphalt mixes has presented vaπous problems Many of the plastic additives have lacked an ability to bond to or combme with the asphalt bmders ofthe mix Chemical treatments have been proposed, but such treatments have been ineffective, add to the cost, and introduce additional noxious and toxic substances mto the process, aggravating the waste disposal problems Accordingly, there remains a need for a low cost manner of enhancing the properties of pavmg material and there remams a need for a use of residual plastic waste, particularly unclassified or unseparated matenals or materials of mixed classes Summary of the Invention:

It is an objective ofthe present mvention to improve the properties of pavements and of pavmg matenals, particularly asphaltic concrete mateπals, and most particularly, to improve the strength and useful life of the pavements made ofthe pavmg matenals

It is a particular obiecϋve of the present mvention to improve the properties of paving matenals at a minimum increase in cost or at a savings in cost from that ofthe standard asphaltic paving material

A further objective o the present invention is to provide a use for recvcled or waste plastic mateπals particularly thermosetting and other PCCS class 7 materials, and other combinations of matenals of more than one class, particularly classes 3 through 7

A further ob|ectιve of tl e present mvention is to provide a method of pavmg mateπal, particularly asphaltic paving matenal, and of utilizing waste plastic m pavmg material manufacture

Accordmg to principles ofthe present mvention, there is provided a method of making a pavmg material that mcludes the step of providing bulk residual plastic waste matenals mcludmg matenals ofthe type corresponding to PCCS classes 3-7, and preferably matenals of more than one such class, the step of processing the plastic to a form suitable for combining with asphalt, and the step of combining the processed plastic with asphaltic bmder and with rock aggregate to form an asphaltic concrete paving mateπal Further, the step is added of forming a pavement with the mateπal In addition, a pavmg matenal and pavement are provided that are made accordmg to such process

According to the preferred embodiment of the invention, recycled plastic matςpal that is unclassified, or us in the form of bulk matenal contammg plastics corresponding to more than one ofthe PCCS classes 3 through 7 or contains thermosetting plastics and other plastics of PCCS class 7, are provided The plastic matenal is either pelletized, is shredded or otherwise mechanically granulated, or otherwise formed into particles Conventional asphaltic bmder material and graded aggregate that includes rock particles ranging in size are also provided

Typically the aggregate will mclude from five to seven sieve sizes ranging from no 40 to three-fourths inch in size, or preferably from no 200 to one inch m size The particles of plastic are preferably of a size that corresponds to one of tl e intermediate sizes ofthe rock aggregate Preferably further, the pavmg matenal is formed by mixing from five to twenty-five percent or more ofthe plastic particles, measured by volume, with the rock aggregate and the asphaltic bmder Also the amount of aggregate may be vaned from the standard ratio mixture with the bmder by reducmg the amount of mid-range aggregate by an amount not more than the amount of added plastic, and preferably by an amount that is somewhat less than the amount of added plastic Preferably, the particles of plastic are m the one- eighth to one-quarter mch 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

Further in accordance with the preferred embodiment of the present mvention, the plastic particles are further processed to activate the surfaces ofthe plastic particles to mcrease the surface tension and to cause free or active carbon atoms to be present in the molecules o the plastic matenal at the particle surface The activation of the particle surfaces is preferably performed with minimal heating, burning or melting of tlie plastic, and may achieved by exposing the surface to high energy treatment gas atoms, ions or molecules for a limited duration Such a gas may be m the form of a flame or in the form of a plasma or corona other electπcally or otherwise enhanced gas or vapor, that will cause the activation or mcreased energization at the surfaces of the plastic particles Such a treatment is achieved, m one embodiment descnbed below, with the use of a reducmg flame, exposmg the particles to the outer envelope of such flame The exposure may be earned 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 tlie flame The use of a ionized or plasma enhanced gas to activate the particle surfaces is also suitable, and may be earned out by transporting the particles on an electncally conductive conveyor Other forms of gas reactant treatment may be used to activate or etch the surface The activated surfaces ofthe plastic particles are thought to enhance tlie bonding between the asphaltic bmder and the plastic particles and do so with minimal or insignificant heating of the plastic Such plastic particles are blended with the asphaltic bmder and with rock aggregate at normal low temperatures of below 300°F

The present mvention provides a paving matenal and pavement that is thirty to fifty percent stronger than the required strength of road pavmg materials, and is up to thirty to fifty percent stronger than standard asphaltic concrete that is not modified with the addition ofthe plastic particles as described above The invention provides a use tor the low use or otherwise useless recycled plastic compositions, and disposes of unclassified or residual class plastic matenal The cost ofthe added plastic material is very low. with the untreated plastic material approaching no cost at all. compared with the cost of its disposal The invention allows the reduction in the total amount of pa ing mateπal in proportion to the mcreased strength ofthe mateπal, 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

These and other objectives and advantages ofthe present mvention will be more readily apparent from the following detailed descnption of the ofthe preferred embodiments ofthe mvention Detailed Description of the Preferred Embodiment:

One preferred embodiment of the mvention is set forth herem in the form of a descnption of a test or example of a process of making a paving matenal In accordance with this preferred embodiment of the present mvention, a standard asphaltic mix is selected 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 aggregate suitable for asphaltic concrete for use in highway construction Such a rock aggregate mixture used in this example includes particles ofthe following sizes, as set forth m Table 1

Sieve Size

1 mch 100

3/4 mch 86

'/. mch 67

3/8 mch 57

No 4 42

No 10 34

No 40 21

No 200 5 1

TABLE 1

Next, in the example, a volume of bulk recycled plastic matenal is selected The bulk plastic matenal mav be ungraded or unsorted and thereby contam plastics correspondmg to PCCS classes 1 through 7, but preferably is a residual ungraded bulk of recycled plastic from which most ofthe 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 density polyethylene) and low density foam plastic from class 6 (polystyrene) may have been removed The bulk matenal may contam bottles and other waste plastic articles, layered, thermosetting and miscellaneous plastic articles trom class 7, PVCs from class 3, and masses of waste plastic from plastic production and molding industries In tlie example, a representative average sample including an assortment of plastic waste correspondmg to the plastics of classes 3 through 7 was selected

Then, the plastic matenal is granulated The granulation process typically involves the shredding of he plastic matenal in a shredder that employs a plurality of knife blades to reduce the mass of plastic to a uniform blend of particles The particles mclude a large percentage of generally flat flake or plate-like pieces that are generally more elongated than the particles ofthe rock aggregate referred to above In the example, the sizes of the granulated plastic particles mcluded 18 percent that passed sieve no 10, with all ofthe particles passing sieve no 4 It is contemplated, however, that, for use with the rock aggregate descπbed above, most ofthe plastic particles will be in the 1/4 inch to 3/8 mch range, and perhaps larger They will nonetheless be smaller than, and preferably less than half the size of. the largest rock aggregate particles

The granulated plastic particles are then treated to activate the particle surfaces The manner ot activating the surfaces ofthe plastic particles is preferably by exposing the particles briefly to a flame treatment It is preferable

to expose the plastic particles to the flame mtermittently if increased exposure is desired than to maintain constant . which could unnecessaπly heat the plastic The flame in the descnbed embodiment is preferably a reducing flame In other embodiments, a plasma, corona or ionized gas may replace or be combmed with the flame A reducmg flame may be produced by natural gas, propane, or other fuel In the example, an oxyacetylene reducmg 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 mches from the flame, with agitatmg and turning if the plastic particles The duration or dwell ofthe flame on any of the particles is preferably kept sufficiently short to avoid any significant melting or burning the particles or causing a visually perceivable change m the appearance of the plastic particles A small percentage of the plastic that might be of the lower density lower melting pomt types or include exceptionally thin sheet shreds or narrow fibers may, m such a process, melt or char without adversely aft ectmg the process or paving material to be produced

In one form of the preferred embodiment of the mvention, it is contemplated that the activating gas treatment of the granulated plastic particles be carried out in a flame treatment tower Such a tower mav be a vertically elongated cylmdπcal column havmg a plurality of inwardly directed, and possibly upwardly mclmed gas tets 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 reducmg flame throughout the center of the column through which the granulated particles are dropped Dependmg on the height of the column used, the particles may be repeatedly dropped through the flame Use of a flame treatment tower m which the particles are dropped through the flame, rather than the use ot a conveyor or other structure to support the particles for treatment with the flame, avoids possible stickmg to the support caused by a softening or melting of a small percentage of the plastic matenal m the flame Such a tower should have a cool air region at the bottom of the tower to facilitate a rehardening of any softened plastic and the collection of treated particles at the bottom of the tower should mclude a fluidized air bed or agitating mechanism to avoid a sticking together of the treated particles

In an alternative form of the preferred embodiment of the mvention, flame treatment is performed m an inclined drum tumbler The tumbler is in the form of an elongated cylindrical barrel, inclined at less than 20 or 25 degrees to the honzontal. and preferablv at about 10 to 15 degrees to the honzontal The barrel has a plurality of longitudinal vanes runmng generally parallel or slightly spiraled relative to the axis of the barrel The reducing flame ι.s made to flow upwardly through the center of the barrel around the axis thereof as the barrel is rotated The granulated plastic particles are fed mto 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 ofthe mclmed cylinder The constant rotary motion of the barrel, which is kept relatively cool, prevents the sticking to the barrel of any particles that might have been softened

It is further contemplated that the particles may, for some uses, be pelletized pnor to tlie activating treatment To pelletize the particles of plastic, the particles would be fed from a hopper into a pelletizing extruder in which a mild heatmg element would heat the particles to soften some of the plastic components and promote stickmg ofthe particles An auger would then compress the warmed particles and extrude them through an extrusion die to be cut mto pellets of more or less uniform size Such pellets would then be treated as described above

Treatment by exposing the particles to ionized gas, plasma, corona discharge or other electncally energized treatment medium may be carried out by presenting the plastic particles upon a conveyor, which may be effective to maintain charge on the plastic particles, while exposmg the particles to the treatment medium

When the plastic has been treated, it is preferred that it be used as soon as possibje, preferably within a dav or days of treatment, or that the treated plastic be kept out of contact with freely flowing air or sunlight until used Use ofthe plastic mvolves a blending of the plastic particles with the rock aggregate and with the asphaltic mix in a manner that is conventional for the formulation of asphaltic pavmg mateπal for road surfaces The plastic particles function more as does the rock aggregate component ofthe asphaltic concrete than as does the asphaltic bmder Onlv a minor or mcidental portion ofthe plastic, that which is lower density and lower meltmg pomt, would soften and blend with the asphaltic component Instead, the plastic particles supplement the mid-size rock aggregate components The percentage ofthe mid-size particles ofthe rock aggregate may be reduced m the mix, although that is usually not necessary The particles of plastic are believed to strengthen the pavmg matenal by addmg a slightly flexible interlocking aggregate component that bonds with the asphaltic bmder with a partially chemical molecular bond, developmg an mcreased shear resistance of the pavmg mateπal The paving matenal is also more highly impermeable to water, preventing such water from propagating mto the gravel bed or subgrade

Improved properties ofthe pavmg matenal made m accordance with the method ofthe present invention are illustrated by the example descnbed above In that example, the treated plastic particles were tested by blending them mto the asphaltic mix (usmg asphaltic concrete 4 4% Navaio 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 preferably that which produces an asphalt cement viscosity of 170 +/- 20 centistokes kinematic The plastic was added to the asphaltic mix at a ratio often percent by volume, determmed from the loose umt weights of the plastic and asphaltic mix The matenal was tested by placmg it in molds and compacting it to seventy-five blows per side at approximately 250°F For compaπson, other samples were similarly prepared, one sample using the standard asphaltic concrete mix without plastic, and two samples usmg untreated plastic ofthe 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 centιmeter(22 2 pounds per cubic foot) for the treated and untreated plastic The five percent by volume of plastic mixes mcluded 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 mcluded 1076 10 grams (2 370 pounds) of asphaltic concrete mix and 39 69 grams (0065 pounds) of plastic The tests performed as set forth below and the component analyses as set forth above employed the standards set forth in Table 2

Extraction ASTM D-2172

Sieve Analysis ASTM C-l 36

Bulk Unit Weight ASTM D-2726 Rice Unit Weight ASTM D-2041

Marshall Flow/Stability ASTM D-1559

TABLE 2

The results of the test were as follows, as set forth in Table 3

- 1 -

Marshall Properties of Asphaltic Concrete No plastic 5% untreated 10% untreated 20% treated

Bulk Unit Wt 2 366 2 339 2 261 2 272 gms/cm'tpcf) (147 4) (145 T) (140 9) (141 5)

Rice Wt 2 419 2 396 2 369 2 370 gms/cm^t cf) (150 7) (149 3) (147 6) (147 7)

Air Voids (%) 2 2 2 4 4 6 4 1

Stability (pounds) 2821 3078 2432 3404

Flow (1/100 m) 1 1 12 1 1 1 1

TABLE 3

The above results can be compared with the NMSFITD stability requirements of 1640 pounds for non- interstate highways and 1800 pounds for mterstate highways It is found from the tests set forth above that, startmg with 2821 pound asphaltic concrete (per the test), the strength mcreased 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 m the mix mcreased, bemg about 14% With the treated plastic, the strength increased with the addition of the plastic, bemg about 21% higher than the ongmal 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 tins range

Those skilled in the art will appreciate that the application ofthe present invention is herem are vaned, and that the invention is descnbed in preferred embodiments Accordmgly, additions and modifications can be made without departing from the principles ofthe mvention Accordmgly, the following is claimed