Modified asphalt concrete mixtures containing waste polyethylene plastic

Abstract

A direct correlation is established between air voids in asphalt concrete mixes and degree of crystallinity and viscosity properties of polyethylene included in the mixes as a partial replacement for virgin asphalt binder. Accordingly, the present invention provides for recycling of waste polyethylene materials. Homogeneous polyethylene materials are grouped by common source and the degree of crystallinity and viscosity properties are identified. Plastic with low viscosity and degree of crystallinity can serve as a binding agent in partial replacement for asphalt binder in an asphalt concrete mix while still meeting volumetric air void objectives, such as the Superpave design target of about 4% air void content. Accordingly, asphalt concrete mixes can be designed as a function of plastic degree of crystallinity and viscosity properties, and plastic material can be reliably sourced according to these properties so that asphalt concrete mixes meeting the design objectives can be produced reliably.

Description

MODIFIED ASPHALT CONCRETE MIXTURES CONTAINING WASTE POLYETHYLENE PLASTICCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 63 / 559,632, filed February 29, 2024, the entire disclosure of which is hereby incorporated herein by reference.STATEMENT OF GOVERNMENT INTEREST

[0002] The invention was made with government support under Grant No. W913E521 C0020 awarded by the Engineers Research and Development Center (ERDC). The government has certain rights in the invention.FIELD OF THE INVENTION

[0003] The present invention relates generally to asphalt mixtures for use in pavement applications, and more specifically to asphalt mixtures using waste plastic (polyethylene) materials, e.g., as a binder material in substitution for conventional asphalt binder material.DISCUSSION OF RELATED ART

[0004] It is common in the roadway paving industry to use asphalt concrete material in constructing flexible pavement. Asphalt concrete material is generally formed by mixing crushed aggregate (e.g., stone) with an asphalt binder material that acts to bind / bond / hold the aggregate together. Generally, asphalt binder material is produced as part of a petroleum refining system (used to produce gasoline, diesel fuel, etc.). The asphalt binder is generally produced from residuum material that remains after distillation of petroleum to remove fuels and lubricants.

[0005] Material properties of the asphalt binder material must be carefully controlled in order to have satisfactory asphalt concrete / roadway performance. In some circumstances, small amounts of additives are sometimes blended into the asphalt binder to produce a modified binder (e.g., in a wet mixingprocess), to achieve certain performance objectives. In some cases, dry additives are first blended with aggregates followed by addition of asphalt binder (e.g., in a dry mixing process). For example, excessive asphalt binder content may result in stiffness / brittleness and resulting pavement cracking at low environmental temperatures, and / or fluidity / softness resulting in pavement rutting at high environmental temperatures.

[0006] The asphalt industry has been experimenting with the incorporation of waste plastic materials into asphalt binders, mixtures and pavement construction, which has the potential to offer a cost savings and be environmentally friendly. The inclusion of polymeric additive in the form of waste plastic has been known to impart stiffness to resultant asphalt mixtures. This behavior may be desirable for producing rut resistant mixtures, particularly in hot climates. However, imparting stiffness may be detrimental in cold climates, due to the more brittle behavior of the resultant asphalt mixture. The use of waste plastics in either asphalt binders or asphalt mixtures can be an environmentally friendly solution for use / disposal of waste plastic materials, which is desirable.

[0007] However, there are challenges to the incorporation of waste plastics into asphalt mixtures and / or asphalt binders. One significant challenge is the variability of the materials and material properties of available waste plastic materials.

[0008] For example, the existing approach of identifying suitable polyethylene waste plastic for asphalt applications is based on densities (low / high) and / or source or origin. Such identification approaches categorize numerous polyethylene plastics into a single classification that do not replicate each other during asphalt mixture design. For example, LDPE from grocery bags is not the same as LDPE from milk bottles. The melting characterization on exposure to heat, adhesive nature on melting, flowability on applying shear is expected to be different. Accordingly, these metrics are not reliable for use in designing and manufacturing asphalt binder mixes and / or PE-modified asphalt concrete mixtures meeting desired material property and / or performance characteristics, due to the variability in material properties of waste materials having a common source or common density characteristic.

[0009] In the case of identifying polyethylene plastics in terms of source (e.g., polyethylene from “grocery bags”, polyethylene from “milk cans”, polyethylenefrom “panels”, etc.), an asphalt mix designer cannot determine the reason for variation in volumetric properties with variation in sources of polyethylene. There is also no basis or standards currently available for deciding the suitability of polyethylene in asphalt mixtures, thus hindering its usage.

[0010] Due to the existence of potentially millions of sources across the globe, there is a significant variability in the plastics (polyethylenes) that are being available for use and that could be candidates for incorporation in asphalt binder materials. Such variability results in a disorganized state for selecting an appropriate plastic, or for using a mixture of plastic, for use in an asphalt binder having desired properties, and the plastics actually used will influence the asphalt binder and asphalt concrete mix properties, likely unpredictably where waste material used is heterogeneous.

[0011] What is needed is an effective and suitably informative method for identification of a suitable waste plastic product, and a method for identifying suitable waste plastic products, for inclusion in asphalt. The present invention provides a process for analysing waste plastics (i.e. , polyethylene) and determining their suitability for use (e.g., for volumetric designs, performance enhancement) in asphalt binder material and resulting asphalt concrete materials.SUMMARY

[0012] A direct correlation is established between observed air voids in asphalt concrete mix and degree of crystallinity and viscosity properties of polyethylene, such that polyethylene materials, including waste polyethylene materials, may be assessed for suitability for inclusion in asphalt mixes and / or pavement as a partial replacement for virgin asphalt binder. Accordingly, the present invention provides for recycling of polyethylene waste plastics.

[0013] Homogeneous (e.g., waste) polyethylene materials are grouped by common source and the degree of crystallinity and viscosity properties are identified. Plastic with relatively low viscosity and degree of crystallinity can serve as a binding agent in partial replacement for asphalt binder in an asphalt concrete mix while still meeting volumetric air void objectives, such as the Superpave design target of about 4% air void content. Accordingly, asphalt concrete mixes (e.g., for pavements) can be reliably designed as a function of the degree of crystallinity and viscosity properties of polyethylene, and waste polyethylene material can be reliably sourcedaccording to these properties so that asphalt concrete mixes / pavements meeting the design objectives can be produced reliably.BRIEF DESCRIPTION OF THE FIGURES

[0014] An understanding of the following description will be facilitated by reference to the attached drawings, in which:

[0015] Fig. 1a is a graph of the influence of degree of crystallinity (Xc) on plastic modified volumetries, showing a change in air voids with polyethylene source for mixing condition at 151 °C and compaction at 140°C;

[0016] Fig. 1 b is a graph of the influence of Xc on plastic modified volumetries, showing a change in air voids with polyethylene source for mixing condition at 165°C and compaction at 156°C;

[0017] Fig. 2a is a graph of the influence of viscosity (q) on plastic modified mixture volumetries, showing the role of Xc value of PE on air void content at for a mixing condition at 151 °C and compaction at 140°C;

[0018] Fig. 2b is a graph of the influence of viscosity (q) on plastic modified mixture volumetries, showing the role of Xc value of PE on air void content at for a mixing condition at 165°C and compaction at 156°C;

[0019] Fig. 3a is a graph of the role of q value of PE on air void content at a mixing condition at 151 °C and compaction at 140°C; and

[0020] Fig. 3b is a graph of the role of q value of PE on air void content at a mixing condition at 165°C and compaction at 156°C.DETAILED DESCRIPTION

[0021] The present invention provides a framework to identify suitable (for use in asphalt concrete mixtures) polyethylene (e.g., waste) plastic products and to analyse the appropriate (waste) products from thousands of products (e.g., different / varied waste polyethylene plastic products) for asphalt mixture design. While conventional approaches have identified polyethylene in terms of source, the present invention provides a method by which the suitability of polyethylene for asphalt mixtures is assessed in terms of its material property characteristics, namely, degree of crystallization - Xc and viscosity - q. Using known Xc and q values for particular waste plastics, suitable asphalt mixes meeting desired design objectivescan be prepared by dry mixing particles of the particular waste plastic having the known Xc and q values in a suitable proportion with aggregate, which mix can then be combined with asphalt binder, to form a suitable asphalt mix in which the dry mixed waste polyethylene acts as a replacement to asphalt binder material, to reduce the quantity of typical asphalt binder material that would otherwise been needed for the suitable asphalt binder and / or asphalt mix.

[0022] More particularly, in accordance with the present invention, particular (homogeneous) polyethylene waste plastics (e.g., recycled batches of waste Coca-Cola brand cola beverage bottles, roof panels, flower pots, postal carts, packaging waste materials, etc.) are assessed for possible suitability for use in asphalt mixtures by testing / analyzing and / or classifying them in terms of specific material properties, namely their degree of crystallinity (Xc) and viscosity (q) properties. For example, batches of recycled plastics from plastic recyclers may be collected and tested to determine their classification (e.g., as a polyethylene, polystyrene, polyethylene terephthalate etc.), e.g. according to their melting characteristics. By way of example, conventional methods and conventional equipment (such as a Differential Scanning Calorimeter (DSC) and a Dynamic Hybrid Rheometer (DHR)) may be used to test plastic materials to determine their respective degree of crystallinity (Xc) and viscosity (q) properties, as will be appreciated by those skilled in the art.

[0023] Polyethylene waste may be determined to be potentially suitable for use, although individual items may have different material properties according to their different sources (e.g., a batch of recycled roof panels vs. a batch of recycled flowerpots, etc.). More particularly, the present invention involves use of Xcand q of a polyethylene (or other material) as the determinative factor in determining volumetric requirements for waste polyethylene material in asphalt mixtures. Therefore, characterizing polyethylene in terms of Xc and q, rather than source, is used for asphalt mixture modification.

[0024] Accordingly, the present invention allows for the recycling of a wide range of plastics (for this purpose) that satisfy certain Xc and q values, without having to understand the source of plastics. Accordingly, the present invention can reduce the amount of virgin asphalt binder in new flexible pavement construction, and can reduce greenhouse gas emissions due to the reduction in use of asphalt binder, due to the inclusion of the waste polyethylene material in the asphalt binder.

[0025] Although waste plastics from different sources may be polyethylenes, their respective material properties, and particularly their respective degree of crystallinity and viscosity properties, may vary according to the particular plastic makeup, etc. For example, in five exemplary batches of recycled polyethylenes from different sources (different source materials), the Xc values of the polyethylenes varied from 55% to 92% and q varied from 1091 Pa. sec to 7738 Pa. sec at 165°C.

[0026] The polyethylenes are then evaluated as a replacement to asphalt binder during asphalt concrete mixture design. At mixing temperature of 151 °C, PE with crystallinity (Xc) value less than 55% acted as a binding material up to 9% replacement along with asphalt binder. With an increase in mixing temperature to 165°C, PE with even 65% Xc could serve as binding agent up to 6% replacement. Thereafter, the Xc and q properties are known for that waste plastic (from a particular source / for a particular source material), and asphalt concrete mixes can be designed to use such waste plastic as a function of the known Xc and q material properties, to achieve desired volumetric / air void and / or performance objectives. Accordingly, this nullifies the concern of variability in source of the waste plastic by addressing the plastics and their properties for asphalt applications. In this way designers can ignore the source and assess the core properties of polyethylene, determining suitability for recycling in asphalt concrete mixtures.

[0027] The present invention thereby provides a solution for identifying appropriate polyethylene plastics that can act as a partial asphalt binder replacement (e.g., at 3%, 6%, 9% etc. dosage levels in replacement for asphalt binder) in asphalt concrete mixtures. The use of waste plastics (polyethylene) as a binder material can reduce the overall cost of asphalt binder in the asphalt concrete mixture. More particularly, polyethylene is not mixed into an asphalt concrete mixture material, but rather asphalt is partially substituted by polyethylene during asphalt concrete mixture preparation. In general, the incorporation of plastic in asphalt concrete mixes is carried out by blending plastics with aggregates followed by mixing with asphalt binders to produce a polyethylene-modified asphalt concrete mixture. Waste polyethylene materials are used as a replacement to asphalt binder content in a dry mixing process, due to the melting behavior of the waste polyethylene material. In accordance with the present invention, plastic (polyethylene) is assessed in terms of asphalt binder replacement in outlook of economic and environmental benefits.

[0028] Further, determination of the degree of crystallinity and viscosity (Xc% and q, respectively) for particular waste plastics (polyethylene) in accordance with the present invention can further be used to identify the suitability of polyethylene as a partial replacement for asphalt binder in an asphalt concrete mixture, e.g., to increase the stiffness of asphalt mixture, enhancing rutting resistance. It is expected that use of waste plastic in an asphalt mix has the potential to reduce 3% to 9% of asphalt binder for flexible pavement construction, i.e. replacing 3% to 9% by weight of optimum asphalt binder content with polyethylene. Accordingly, the waste plastic material is dry mixed with aggregates, without mixing it into asphalt binder. Accordingly, both asphalt binder and the waste polyethylene plastic act as binding substances without any pre-blending of plastic with asphalt binder.

[0029] The present invention enables the recycling of a wide range of polyethylene plastics that satisfy certain Xc and q values. Waste polyethylene plastics with crystallinity <65% and viscosity <4019 Pa. sec determined at a temperature of 165°C and frequency of 10 rad / sec have been found to be suitable for dry mixed asphalt concrete mix preparations as described herein, without having to understand the source of plastics (polyethylene) in order to design an asphalt concrete mixture having certain overall material property and / or performance characteristics. The present invention can thereby reduce the amount of virgin asphalt binder in new flexible pavement construction, and can subsequently reduce the greenhouse gas emissions due to reduction in use of asphalt binder material.

[0030] The replacement of asphalt binder with appropriate polyethylene reduces the quantity of asphalt binder material needed, which is the most expensive part of asphalt concrete mixture mix. By incorporating plastics into asphalt concrete mixture mixes, a new path for their recycling is also established. This recycling channel reduces the amount of landfill, contributing to sustainability and economy. In general, the present invention will help asphalt plants to reduce their costs and help plastic producers to find an environmentally-friendly, cost-effective method for recycling plastics.

[0031] Accordingly, the present invention removes the barrier of source variability for polyethylene waste to be used in flexible pavements. More particularly, the present invention provides improved selection criteria for use of polyethylenewaste (waste plastic) as asphalt binder replacement in Superior Performing Asphalt Pavement (“Superpave”) asphalt mixture design.

[0032] The present invention addresses the concern of plastic (polyethylene) source variabilities and their use in asphalt mixture designs by providing for determination of the suitability of polyethylene waste in asphalt mixtures as a replacement to asphalt binder. The present invention identifies the critical properties that are necessary for polyethylene to act as a replacement to asphalt binder regardless of the waste source stream. In accordance with the present invention, polyethylene plastics are categorized based on the degree of crystallinity and viscosity (Xc% and q, respectively), which is a new and innovative approach in asphalt applications. This approach makes the use of plastic (polyethylene) source independent and also serves as a catalyst to significant increase in use of plastic modified mixtures. Characterizing polyethylene plastics for use in asphalt mixtures in terms of their Xcand q properties therefore nullifies the variability in source. In this way, asphalt designers can ignore the sources of waste plastics and instead assess these material properties of polyethylene to determine their suitability for use in asphalt mixtures.

[0033] Overall, the present invention provides that Xc and r / values of a polyethylene are useful as parameters in ensuring that the polyethylene-modified asphalt mixtures meet Superpave mix design volumetric / air void requirements, and / or other performance objectives.

[0034] In accordance with the present invention, it has been determined that polyethylene with crystallinity <65% and viscosity <4019 Pa.sec (determined at a temperature of 165°C and frequency of 10 rad / sec), is suitable for use for asphalt binder replacement up to 9% in certain applications. This is because the cumulative viscosity of binding agents including polyethylene and asphalt would be least influenced by such polyethylenes. Eventually, the Superpave design / target of air voids of approximately 4 (e.g., 4.0% + / - 0.5%) can be achieved successfully with such polyethylenes.

[0035] Accordingly, suitability of waste polyethylene is determined according to its consensus properties including degree of crystallinity (Xc %) and viscosity (q) rather than by the source of the waste plastic. Identifying polyethylene in terms of such properties eliminates the concern of source variability, as it represents their melting characteristics for asphalt modification purposes. Polyethylene with alower Xc value (e.g., less than about 65 %) subsequently results in low viscosities (e.g., less than 4019 Pa. sec at 165 °C). Such low viscous nature is desirable when polyethylene is used as an asphalt binder replacement as it does not reduce the workability and compactability of the resulting asphalt mixtures. Therefore, the resultant polyethylene-modified asphalt mixtures satisfy the Superpave asphalt mixture volumetric requirement (e.g., approximately 4% air voids at design gyrations).

[0036] The present invention (i.e., grouping the polyethylene plastics based on core thermal properties of polyethylene (Xcand q)) can eliminate the density and source concern. Nomenclating polyethylene plastics in terms of Xcand q would enable the predictability of polyethylene to act as a binding agent along with asphalt binder. This invention eliminates the uncertainty of polyethylene suitability in asphalt applications. It also allows for a broad range of polyethylene plastics to undergo recycling through asphalt pavements.

[0037] The present invention is about identification of direct correlation between plastic properties (Xcand q) and observed air voids when polyethylene is used as a partial replacement to asphalt binder. Based on this observation, it was identified that nomenclating polyethylene plastics based on their thermal properties can help asphalt engineers decide its suitability for asphalt applications. Plastic with low viscosity and degree of crystallinity can serve as a binding agent along with asphalt binder. Plastics with higher viscosities and degrees of crystallinity tend to have increased in rigidness and flow resistance, and PE-modified asphalt mixtures including such plastics tend to result in higher air void levels, including higher air void levels that would tend to exceed the Superpave design targets, e.g., about 4% air void content.

[0038] Figs. 1 A and 1 B represent the change in air void content with change in plastic source and dosage. The plots included the information of Xcvalue and q value of respective polyethylene plastics at mixing temperatures. Fig. 1A, which represents binder mixing and compaction temperatures at 151 °C and 140°C respectively, shows a trend of an increased air void content with increased use of PE waste plastic instead of or as part of the asphalt binder. Except for the case of PE-1 with Xcvalue of 55.01 % and q value of 1342 Pa.s, none of the plastic replacements would satisfactorily satisfy the Superpave target air void content of 4±0.5 %. With an increase in the Xcvalue of polyethylene, i.e. with the increased rigidity of polymer,the tendency of melted polyethylene to act as a binding agent was observed to decrease substantially. The observation was no different at elevated mixing and compaction temperatures of 165°C and 156°C, respectively. This is because the increase in asphalt replaced portion with PEs resulted in increased air void levels. However, increasing the mixing temperature to 165°C allowed PE-1 , PE-2, PE-3 to meet the design air void content of 4%, as shown in Fig. 1 B.

[0039] Figs. 2A and 2B are graphs representing the role of Xcvalue of PE on air void content at two mixing conditions, namely, (a) Mixing at 151 °C and compaction at 140°C, (b) Mixing at 165°C and compaction at 156°C. Figs. 2A and 2B are plotted between degree of crystallinity (Xc) of plastics and air void variation in plastic modified mixtures at both mixing conditions. At a mixing temperature of 151 °C as seen in Fig. 2A, replacing asphalt with 9% of PE that has an Xcvalue of 55% resulted in air void range within 4±0.5%. With an increase of mixing temperature to 165°C as in Fig. 2B, binder consisting of PE with Xcvalues up to 65% could satisfy as a binding agent. This can be related to weakening of polymer structure with increase in temperature which enhances the mobility of polymer chains. Such a state would result in plastic acting as an adhesive fluid along with asphalt binder rather than acting as a filler. An increase in Xcvalue of PE reduced the binding tendency of plastic. Such high rigidness of plastic behavior eventually increased the air void content in the resultant mixture.

[0040] A linear correlation was observed between air voids and Xc. The value of the slope of the regression lines gradually increased with PE replacement content from 3% to 9%, From the two mixing temperatures, it can also be interpreted that the dependency of Xcis reduced with increase in temperature. Since the resulting air voids at constant gyration also depends on the viscosity of the binding constituents, the viscosity of polyethylene and its workability during compaction was assessed further.

[0041] Similar to observation with Xcversus air voids, the influence of the melted PE viscosity on air voids of mixtures was assessed as shown in Figs. 3A and 3B. As shown in Fig. 3A, polyethylenes with viscosity values less than 1800 Pa. sec at the compaction temperature are favorable for achieving the target air voids. However, considering the high range of air voids within viscosities from 800 to 1800 Pa. sec from both Fig. 3A and 3B, it can also be inferred that there are chances for higher air voids when using PE with lower q values. Eventually, PEs with higher qvalues (>3800 Pa. sec) reduced the workability of asphalt mixture, as shown in Fig. 3A. Using such PEs failed to meet the design air void content during the compaction process. With an increase in mixing temperature to 165°C, PE with q values up to 5700 Pa.sec could satisfy the design air void content, as shown in Fig. 3B.Accordingly, the increased temperature favored reducing the viscosity of the plasticasphalt blend.

[0042] While the above observations were perceived in view of polyethylene source rather than the material characterization, they may not represent polyethylene plastics from other sources. However, identifying the polyethylene in terms of either Xcvalue or q value would assist to predict the behavior of plastic in the asphalt concrete mixture design, and thus support asphalt concrete mix design activities.

[0043] Previous methods of identifying suitability of polyethylene plastics for use in asphalt mixes results in air void variability during mixture design. In contrast to previous methods, the present invention enables designers to filter the appropriate polyethylene that can fulfill the asphalt mixture volumetric design. More particularly, the present invention provides for nomenclating polyethylene plastics based on crystallinity and viscosity, for use in asphalt applications, in contrast to previous methods in which polyethylene was either called out based on source, density or melting point. Identifying plastics based on consensus properties such as degree of crystallinity and viscosity better enables prediction of their influence in asphalt mixture design and ultimately their suitability, allowing for suitable asphalt binder and asphalt mix design.

[0044] Accordingly, the present invention addresses the concern of variabilities that could occur from using plastic (polyethylene) from various disparate sources. The present invention identifies the key properties that are necessary for polyethylene to act as a suitable asphalt replacement without regarding to the source. Accordingly, the present invention can be used as an assessment tool in determining the suitability of a given plastic in an asphalt mixture design.

[0045] In accordance with one aspect of the present invention, polyethylene (plastic) materials, including waste polyethylene materials, may be prepared for use to prepare an asphalt concrete mixture. Bay way of example, this may be performed by a plastics recycler, a plastics supplier / distributor, etc.

[0046] For example, an exemplary method in accordance with the present invention may involve gathering homogeneous polyethylene material having a common source (e.g., waste Coca-Cola beverage bottles).

[0047] Next, the exemplary method involves determining a degree of crystallinity and a viscosity for a sample of the homogeneous polyethylene material having a common source. This may involve recycling the waste polyethylene material to form a homogenous batch of recycled polyethylene material, and obtaining a sample from the batch for the purpose of waste plastic characterization. Further, this method involves determining the degree of crystallinity Xc and viscosity q values for the plastic sample. Such determining of such characteristics may be performed using conventional materials and methods, as will be appreciated by those skilled in the art.

[0048] Next, the method may include assigning the Xc and q values as characteristic of the particular homogeneous plastics, such that such values may be accepted as accurate for all similar waste plastics from a similar source, e.g., without a need for further testing unless a formulation of the waste plastics changes. In this manner, the material has been assessed and classified in a meaningful way, in terms of degree of crystallinity Xc and viscosity q, that will support design of asphalt concrete mixes as a function of (e.g., waste) plastic degree of crystallinity and viscosity properties, and thus waste plastic material can be reliably sourced according to these properties so that asphalt concrete mixes meeting the design objectives can be produced reliably, without unexpected variations due to unknown variations in the material properties as would be the case if non-homogenous plastic materials having differing degrees of crystallinity Xc and viscosities were to be used in the asphalt concrete mixture.

[0049] Next, in this exemplary embodiment, the method includes, for the homogeneous polyethylene material, correlating the degree of crystallinity and viscosity with air void volume for a waste polyethylene material particle size and a set of asphalt concrete mix parameters. Accordingly, these results in data that can be expressed in graphical form in a manner similar to that shown in Fig. 1 A. After the data shown in Fig. 1A has been generated, this data may be referenced for asphalt concrete mix design purposes, e.g., to determine which plastic material / plastic source (e.g., that of PE-1 in Fig. 1A, which is capable of meeting avolumetric design objective of approx. 4% air voids for associated concrete mix parameters).

[0050] It should be noted that each correlation, such as that shown in Fig. 1 A, relies upon a number of associated concrete mix parameters, such as asphalt binder material properties, mixing temperature, compaction temperature, etc. Accordingly, for asphalt concrete mix design purposes, it is useful to incorporate those same general mix parameters (identically or with modification) into the design of an asphalt concrete mix, so that the data is accurately representative of what is to be expected in the designed asphalt concrete mix. A number of different correlations may be developed for different materials, different concrete mix parameters, etc., as will be appreciated by those skilled in the art.

[0051] Further, it should be noted that there may be a polyethylene particle size parameter associated with the data in the correlation, e.g., the correlation in Fig. 1A. Accordingly, it may be similarly desirable to identify the particle size associated with the data in the correlation, and to include the same or a similar particle size in the design for an asphalt concrete mix, so that the data is accurately representative of what is to be expected in the designed asphalt concrete mix.

[0052] Notwithstanding the foregoing, a waste polyethylene material particle size within a range of approximately 1 .0 to approximately 3.0 mm in its largest transverse dimension, and more particularly 2.36mm or approximately 2.36 mm in its largest transverse dimension (or having a volume approximately equal to a sphere having a diameter of 2.36 mm), has been found to be particularly suitable in many applications, as polyethylene particle sizes according to these dimensions appear to allow for a desirable level of melting and aggregate coating in support of formation of an asphalt concrete mix meeting common volumetric design objectives (e.g., 4.0% + / - 0.5% air voids). By way of example, such particle sizes may be obtained by shredding / chopping waste polyethylene materials, and waste polyethylene materials may be prepared by a plastics supplier and be made commercially available in such form for use in the asphalt industry.

[0053] Next, the exemplary method may involve, as part of the correlation, determining asphalt mix volumetries with control (only asphalt binder) and with suitable waste plastic material as a replacement to asphalt binder at desired dosages, e.g., at 3% / 6% / 9% by weight of asphalt binder material. The polyethyleneneed not be melted to dry mixing, but may be shredded, e.g., to a particle size of about 3.0 mm or below, for an enhanced waste plastic distribution within an asphalt concrete mixture. See Fig. 1 B.

[0054] Next, the exemplary method involves identifying asphalt mix volumetric / air void and / or performance objectives, e.g., characteristics consistent with Superpave or other volumetric requirements.

[0055] In one example, the exemplary method involves determining whether the Xc and q values of one or more particular waste polyethylene materials fall outside a suitability threshold or range (e.g., suitable below a threshold, e.g., an Xcvalue less than about 65 % and / or a viscosity less than about 4019 Pa. sec at 165 °C with frequency of 10 rad / sec), for a given mixing temperature. If so, the method may involve determining the particular waste plastic to be unsuitable for use in an asphalt mix due to mild viscous behaviour with ease of flow ability. For example, waste polyethylene with higher values, e.g., Xc > 70%, q > 8000 Pa. s at 150 °C with a frequency of 10 rad / sec may be determined to be unsuitable as the waste polyethylene tends to remain rigid, with its viscous quality leading to inadequate coating and flowing in the mixture, which makes it undesirable for its binding role at asphalt working temperatures (e.g., <175°C).

[0056] If, however, the Xc and q values are within the suitability range, e.g., less than the threshold, then the method involves determining that particular waste plastic to be suitable for use in an asphalt concrete mix.

[0057] Accordingly, for example, Xc and q values may be determined just once for each plastic source. Subsequently, the volumetric asphalt mix design may be performed for each source of plastic, since the design can be sensitive to change in asphalt binder, aggregate size, aggregate source, mixing and compaction temperatures. This information can then be used for later asphalt mix designs.

[0058] In accordance with another aspect of the present invention, a method for designing an asphalt mix comprising waste polyethylene material is provided. By way of example, this may be performed by an asphalt concrete mix designer and / or manufacturer / contractor. Accordingly, an asphalt concrete mix may be designed as a function of Xc and q of a particular waste plastic, to include a design combination of the particular waste plastic from the particular source in combination with aggregate and asphalt binder material and in accordance with certain asphalt concrete mix parameters, to achieve volumetric / air void and / orperformance objectives, the design combination comprising at least a combination of mixing temperature, compaction temperature, asphalt material property, and % dosage of the particular polyethylene by weight of asphalt binder.

[0059] More particularly, an exemplary method for designing an asphalt mix comprising waste polyethylene material comprises determining a volumetric property objective for an asphalt concrete mixture. By way of example, an exemplary volumetric property objective for an asphalt concrete mixture is volumetric air voids of 4.0% + / - 0.5%, which is consistent with industry-standard Superpave design criteria, as is well known in the art.

[0060] Next, the exemplary method involves referencing at least one correlation of degree of crystallinity and viscosity with air void volume for a waste polyethylene material particle size and a set of asphalt concrete mix parameters for at least one homogeneous waste polyethylene material. For example, this may involve reference data similar to that show in the representative graphs of Figs. 1 A- 3B, which shown data correlations.

[0061] Next, the exemplary method involves identifying, as a function of degree of crystallinity and viscosity, a selected waste polyethylene material capable of inclusion in the asphalt mix to meet the volumetric property objective, for an intended waste polyethylene material particle size and set of asphalt concrete mix parameters. For example, in the context of Fig. 1A, this may involve identifying PE-1 as the selected waste polyethylene material, because it is capable of achieve air voids of 4% + / - 0.5% as shown in Fig. 1A, under certain asphalt concrete mix parameters (in the example of Fig. 1A, mixing temperature of 151°C, compaction temperature of 140°C, and a dosage of 3%-9% by weight substitution for asphalt binder material in the asphalt concrete mix.

[0062] Next, the exemplary method involves designing an asphalt concrete mix meeting the volumetric property objective to include the selected waste polyethylene material as a function of the intended waste polyethylene material particle size and the set of asphalt concrete mix parameters, the asphalt concrete mix comprising a combination of a first quantity of the selected waste polyethylene material, a second quantity of aggregate, and a third quantity of asphalt binder material. For example, this may involve designing an asphalt concrete mix to have a waste polyethylene incorporated as an additive to an asphalt concrete mixture, or to incorporated as a dosage in substitution for asphalt binder material.

[0063] By way of example, this may involve designing the asphalt concrete mix by specifying a particle size for the designed asphalt concrete mix that is identical to the particle size associated with the correlation of degree of crystallinity and viscosity for the selected waste polyethylene material that is used to select the waste polyethylene material (e.g., for selection of the PE-1 material of Fig. 1 A, use of the particle size associated with the correlation data in Fig. 1A).

[0064] By way of further example, this may involve designing the asphalt concrete mix by specifying asphalt concrete mix parameters for the designed asphalt concrete mix that are identical to the asphalt concrete mix parameters associated with the correlation of degree of crystallinity and viscosity for the selected waste polyethylene material that is used to select the waste polyethylene material (e.g., for selection of the PE-1 material of Fig. 1A, use of the same mixing temperature (151 °C) and compaction temperature (140°C) associated with the correlation data in Fig. 1A).

[0065] By way of further example, this may involve designing the asphalt concrete mix by specifying a particle size for the designed asphalt concrete mix that is a function of (e.g., a modified version of), but not identical to, the particle size associated with the correlation of degree of crystallinity and viscosity for the selected waste polyethylene material that is used to select the waste polyethylene material (e.g., for selection of the PE-1 material of Fig. 1 A, use of a particle size that is a modified version of the particle size associated with the correlation data in Fig. 1 A).

[0066] By way of still further example, this may involve designing the asphalt concrete mix by specifying asphalt concrete mix parameters for the designed asphalt concrete mix that are a function of, but not identical to, the asphalt concrete mix parameters associated with the correlation of degree of crystallinity and viscosity for the selected waste polyethylene material that is used to select the waste polyethylene material (e.g., for selection of the PE-1 material of Fig. 1A, use of a mixing temperature and compaction temperature that re modified version of the mixing temperature and compaction temperature associated with the correlation data in Fig. 1A).

[0067] Accordingly, it should be appreciated that the correlation data may be used to establish asphalt concrete mix parameters, either by using the identical parameters, or my modifying them slightly to meet the volumetric objective. As will be appreciated by those skilled in the art, plastics with higher viscosities and degreesof crystallinity tend to have increased in rigidness and flow resistance, and PE- modified asphalt mixtures including such plastics tend to result in higher air void levels, including higher air void levels that would tend to exceed the Superpave design targets, e.g., about 4% air void content, and vice versa. However, these tendencies may be counteracted to meeting volumetric objectives by modifying various concrete mix parameters. For example, with an increase in the crystallinity (Xc) of PE, the mixing temperature and dosage can be altered to achieve the design Polyethylene modified asphalt mixture. In this way Xc and q can guide asphalt design decisions and mix design procedures for polyethylene modified mixtures using different binders and aggregates.

[0068] For instance, for PG 58-28 binder and 9.5 mm NMAS aggregate, if Xc < 55%, and q <1342 Pa.s at 150 °C, then PE can act as a binder replacement with 2-7% dosage rate with SP (Superpave) volumetric fulfilment, as will be appreciated from Fig. 1A. However, if Xc = (55-60) %, and q =1342-1847 Pa.s at 150 °C, then PE can act as a binder replacement with 2-7% dosage rate with SP volumetric fulfilment; provided that the mixing and compaction temperatures are increased by at least 10°C, as will be appreciated from Fig. 1 B. Further, if Xc = (GOSS) %, and q =1847-5594 Pa.s at 150 °C, then PE can act as a binder replacement with 2-4% dosage rate with SP volumetric fulfilment; provided mixing and compaction temperatures are increased by at least 10°C, as will be appreciated from Fig. 1 B. Further still, if Xc = (65-70) %, and q = 5594-8000 Pa.s at 150 °C, then PE can act as a binder replacement with 1-3% dosage rate while meeting the SP volumetric design target provided that the design provides for an increase in mixing and compaction temperature by at least 10°C, as will be appreciated from Fig. 1 B. Other ranges may be suitable under other asphalt concrete mix conditions, as will be appreciated by those skilled in the art. Accordingly, various concrete mix parameters may be varied in combination in accordance with the present invention to meet the target volumetric design objective in accordance with the present invention.

[0069] In certain embodiments, the asphalt concrete mix may be designed to have a waste polyethylene dosage of approximately 3% to approximately 9% in substitution for asphalt binder material.

[0070] In certain embodiments, the asphalt concrete mix may be designed to include waste polyethylene material having a degree of crystallinity in the range of about 55% to about 65%.

[0071] In certain embodiments, the asphalt concrete mix may be designed to include waste polyethylene material having a degree of crystallinity <65% and viscosity <4019 Pa.sec at temperature of 165°C and frequency of 10 rad / sec.

[0072] It should be appreciated that any suitable combination of asphalt concrete mix / design parameters may be used in accordance with the present invention, but that in accordance with the present invention, degree of crystallinity and viscosity of the polyethylene material are used to guide asphalt concrete mix design.

[0073] In accordance with another aspect of the present invention, a method for manufacturing an asphalt concrete mix comprising waste polyethylene material is provided. By way of example, this may be performed by an asphalt concrete manufacturer / contractor. Accordingly, an asphalt concrete mix may be manufactured as a function of Xcand q of a particular waste plastic, to include a combination of the particular waste plastic from the particular source in combination with aggregate and asphalt binder material and in accordance with certain asphalt concrete mix parameters, to achieve volumetric / air void and / or performance objectives, the asphalt concrete mix parameter combination comprising at least a combination of mixing temperature, compaction temperature, asphalt material property, and % dosage of the particular polyethylene by weight of asphalt binder.

[0074] More particularly, an exemplary method for manufacturing an asphalt mix comprising waste polyethylene material comprises referencing at least one correlation of degree of crystallinity and viscosity homogeneous waste polyethylene material. Next, the method involves identifying a selected waste polyethylene material capable of inclusion in an asphalt mix to meet a desired volumetric property objective for an asphalt concrete mixture. In the example of Fig. 1A, this may be material PE-1.

[0075] Next, the exemplary method involves identifying a waste polyethylene material particle size and a set of asphalt concrete mix parameters associated with the selected waste polyethylene material. In the example of Fig. 1A, this may be particle size of 2.36mm, mixing temperature of 151 °C, compaction temperature of 140°C, and plastic dosage of about 3% to about 9% for a given asphalt binder material and associated set of material properties.

[0076] Next, the exemplary method involves obtaining a first quantity of the selected waste polyethylene material having the waste polyethylene materialparticle size. For example, this quantity may be in the range of about 3% to about 9% of asphalt binder material requirements for a particular asphalt concrete mix.

[0077] Next, the exemplary method involves mixing the first quantity of the selected waste polyethylene material with a second quantity of aggregate, and a third quantity of asphalt binder material in accordance with the set of asphalt concrete mix parameters to obtain a concrete asphalt mix meeting the volumetric property objective. Determination of appropriate quantities of aggregate and asphalt binder material for a particular asphalt concrete mix are well known the art, and beyond the scope of the present invention, and thus are not discussed in detail herein.

[0078] In accordance with another aspect of the present invention, a polyethylene-modified asphalt concrete mix is provided. More particularly, in accordance with the present invention, the asphalt concrete mix comprises: a first quantity of a selected waste polyethylene material having a common source and a consistent degree of crystallinity and viscosity; a second quantity of aggregate; and a third quantity of asphalt binder material; the first quantity of the selected waste polyethylene material, the second quantity of aggregate and the third quantity of asphalt binder material having been mixed and compacted to provide the asphalt concrete mix with volumetric air voids of 4.0% + / - 0.5%.

[0079] In such an asphalt concrete mix, the first quantity of the selected waste polyethylene material may have been dry mixed with the second quantity of aggregate and the third quantity of asphalt binder material in a form of particles having a particle size of less than approximately 3.0 mm, or more particularly, approximate 2.36 mm, in its largest transverse dimension.

[0080] In accordance with another aspect of the present invention, an polyethylene-modified asphalt concrete mix is made by a process comprising: providing a first quantity of a waste polyethylene material having a common source, the waste polyethylene material have a solid form and particle size of less than approximately 3.0 mm in its largest transverse dimension, degree of crystallinity less than about 65%, and a viscosity less than about 4019 Pa. sec at a temperature of 165°C and frequency of 10 rad / sec; mixing the first quantity of waste polyethylene material with a second quantity of aggregate and a third quantity of asphalt binder material in a dry mixing process to produce an asphalt concrete mix; and compactingthe asphalt concrete mix to provide a compacted asphalt concrete mix having volumetric air voids of 4.0% + / - 0.5%.

[0081] In such an asphalt concrete mix, the first quantity of the selected waste polyethylene material may have been dry mixed with the second quantity of aggregate and the third quantity of asphalt binder material in a form of particles having a particle size of less than approximately 3.0 mm, or more particularly, approximate 2.36 mm, in its largest transverse dimension.

[0082] Accordingly, a direct correlation is established between observed air voids in asphalt concrete mix and degree of crystallinity and viscosity properties of (e.g., waste) polyethylene included in asphalt mixes / pavements as a partial replacement for virgin asphalt binder. Accordingly, the present invention provides for recycling of polyethylene waste plastics. Homogeneous waste polyethylene materials are grouped by common source and the degree of crystallinity and viscosity properties are identified. Polyethylene with low viscosity and degree of crystallinity can serve as a binding agent in partial replacement for asphalt binder in an asphalt concrete mix / pavement while still meeting volumetric air void objectives, such as the Superpave design target of about 4% air void content. Accordingly, asphalt concrete mixes (e.g., for use as pavements) can be designed as a function of plastic degree of crystallinity and viscosity properties, and thus waste plastic material can be reliably sourced according to these properties so that asphalt concrete mixes meeting the design objectives can be produced reliably.

[0083] While there have been described herein the principles of the invention, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation to the scope of the invention. Accordingly, it is intended by the appended claims, to cover all modifications of the invention which fall within the true spirit and scope of the invention.

Claims

What is claimed is:1 . A method for preparing waste polyethylene materials for use to prepare an asphalt concrete mix comprising waste polyethylene material, the method comprising: determining a degree of crystallinity and a viscosity for homogeneous waste polyethylene material having a common source; and for the homogeneous waste polyethylene material, correlating degree of crystallinity and viscosity with air void volume for a waste polyethylene material particle size and a set of asphalt concrete mix parameters.

2. The method of claim 1 , wherein the waste polyethylene material particle size is within a range of approximately 1 .0 to approximately 3.0 mm in its largest transverse dimension.

3. The method of claim 1 , wherein the waste polyethylene material particle size is approximately 2.36 mm in its largest transverse dimension.

4. The method of claim 1 , further comprising: shredding homogeneous waste polyethylene material to have a consistent particle size of less than approximately 3.0 mm in its largest transverse dimension.

5. The method of claim 1 , further comprising: shredding homogeneous waste polyethylene material to have a consistent particle size of approximately 2.36 mm in its largest transverse dimension.

6. The method of claim 1 , wherein the set of asphalt concrete mix parameters comprises at least one of an asphalt material property, a mixing temperature, and a compaction temperature.

7. The method of claim 1 , further comprising: gathering homogeneous waste polyethylene material having a common source.

8. The method of claim 1 , wherein the correlating degree of crystallinity and viscosity with air void volume for a waste polyethylene material particle size and a set of asphalt concrete mix parameters comprises correlating for at least one of a plurality of mixing temperatures, a plurality of compaction temperatures, a plurality of asphalt binder material properties.

9. A method for designing an asphalt concrete mix comprising waste polyethylene material, the method comprising: determining a volumetric property objective for an asphalt mixture; referencing at least one correlation of degree of crystallinity and viscosity with air void volume for a waste polyethylene material particle size and a set of asphalt concrete mix parameters for at least one homogeneous waste polyethylene material; identifying, as a function of degree of crystallinity and viscosity, a selected waste polyethylene material capable of inclusion in the asphalt mix to meet the volumetric property objective, for an intended waste polyethylene material particle size and set of asphalt concrete mix parameters; and designing an asphalt concrete mix meeting the volumetric property objective to include the selected waste polyethylene material as a function of the intended waste polyethylene material particle size and the set of asphalt concrete mix parameters, the asphalt concrete mix comprising a combination of a first quantity of the selected waste polyethylene material, a second quantity of aggregate, and a third quantity of asphalt binder material.

10. The method of claim 7, wherein designing the asphalt concrete mix comprises designing the asphalt concrete mix to have a waste polyethylene dosage of approximately 3% to approximately 9% in substitution for asphalt binder material.11 . The method of claim 7, wherein designing the asphalt concrete mix comprises designing the asphalt concrete mix to have a waste polyethylene dosage in substitution for asphalt binder material.

12. The method of claim 7, wherein designing the asphalt concrete mix comprises designing the asphalt concrete mix to include waste polyethylene material having a degree of crystallinity in the range of about 55% to about 65%.

13. The method of claim 7, wherein designing the asphalt concrete mix comprises designing the asphalt concrete mix to include waste polyethylene material having a degree of crystallinity <65% and viscosity <4019 Pa. sec at temperature of 165°C and frequency of 10 rad / sec.

14. The method of claim 7, wherein designing the asphalt concrete mix meeting the volumetric property objective to include the selected waste polyethylene material as a function of the intended waste polyethylene material particle size and the set of asphalt concrete mix parameters comprises specifying a particle size for the waste polyethylene material in the asphalt concrete mix that is identical to the particle size associated with the correlation of degree of crystallinity and viscosity for the selected waste polyethylene material.

15. The method of claim 7, wherein designing the asphalt concrete mix meeting the volumetric property objective to include the selected waste polyethylene material as a function of the intended waste polyethylene material particle size and the set of asphalt concrete mix parameters comprises specifying a particle size for the waste polyethylene material in the asphalt concrete mix that is not identical to the particle size associated with the correlation of degree of crystallinity and viscosity for the selected waste polyethylene material but is modified to ensure that the asphalt concrete mix meets the volumetric property objective.

16. The method of claim 7, wherein designing the asphalt concrete mix meeting the volumetric property objective to include the selected waste polyethylene material as a function of the intended waste polyethylene material particle size and the set of asphalt concrete mix parameters comprises specifying asphalt concrete mix parameters that are identical to the set of asphalt concrete mix parameters associated with the correlation of degree of crystallinity and viscosity for the selected waste polyethylene material.

17. The method of claim 7, wherein designing the asphalt concrete mix meeting the volumetric property objective to include the selected waste polyethylene material as a function of the intended waste polyethylene material particle size and the set of asphalt concrete mix parameters comprises specifying asphalt concretemix parameters that are not identical to the particle size associated with the correlation of degree of crystallinity and viscosity for the selected waste polyethylene material but includes at least one of an asphalt material property, a mixing temperature, and a compaction temperature that is modified to ensure that the asphalt concrete mix meets the volumetric property objective.

18. The method of claim 7, wherein determining the volumetric property objective for the asphalt mixture comprises identifying the volumetric property objective in terms of a target for volumetric air voids.

19. The method of claim 7, wherein determining the volumetric property objective for the asphalt mixture comprises identifying the volumetric property objective as volumetric air voids of 4.0% + / - 0.5%.

20. A method for manufacturing an asphalt concrete mix comprising waste polyethylene material, the method comprising: referencing at least one correlation of degree of crystallinity and viscosity homogeneous waste polyethylene material; identifying a selected waste polyethylene material capable of inclusion in an asphalt mix to meet a desired volumetric property objective for an asphalt concrete mixture; identifying a waste polyethylene material particle size and a set of asphalt concrete mix parameters associated with the selected waste polyethylene material; obtaining a first quantity of the selected waste polyethylene material having the waste polyethylene material particle size; and mixing the first quantity of the selected waste polyethylene material with a second quantity of aggregate, and a third quantity of asphalt binder material in accordance with the set of asphalt concrete mix parameters to obtain a concrete asphalt mix meeting the volumetric property objective.21 . An asphalt concrete mix comprising: a first quantity of a selected waste polyethylene material having a common source and a consistent degree of crystallinity and viscosity; a second quantity of aggregate; a third quantity of asphalt binder material;the first quantity of the selected waste polyethylene material, the second quantity of aggregate and the third quantity of asphalt binder material having been mixed and compacted to provide the asphalt concrete mix with volumetric air voids of 4.0% + / - 0.5%.

22. The asphalt concrete mix of claim 21 , wherein the first quantity of the selected waste polyethylene material having been dry mixed with the second quantity of aggregate and the third quantity of asphalt binder material in a form of particles having a particle size of less than approximately 3.0 mm in its largest transverse dimension.

23. The asphalt concrete mix of claim 21 , wherein the first quantity of the selected waste polyethylene material having been dry mixed with the second quantity of aggregate and the third quantity of asphalt binder material in a form of particles having a particle size of approximately 2.36 mm in its largest transverse dimension.

24. An asphalt concrete mix made by a process comprising: providing a first quantity of a waste polyethylene material having a common source, the waste polyethylene material having a solid form and particle size of less than approximately 3.0 mm in its largest transverse dimension, degree of crystallinity less than about 65%, and a viscosity less than about 4019 Pa. sec at a temperature of 165°C and frequency of 10 rad / sec; mixing the first quantity of waste polyethylene material with a second quantity of aggregate and a third quantity of asphalt binder material in a dry mixing process to produce an asphalt concrete mix; and compacting the asphalt concrete mix to provide a compacted asphalt concrete mix having volumetric air voids of 4.0% + / - 0.5%.

25. The asphalt concrete mix of claim 25, wherein the particle size of the first quantity of the waste polyethylene material is approximately 2.36 mm in its largest transverse dimension.

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