EP0961812A1

EP0961812A1 - Polymer stabilized bitumen granulate

Info

Publication number: EP0961812A1
Application number: EP98903960A
Authority: EP
Inventors: Zhi-Zhong Liang
Original assignee: Polyphalt Inc
Current assignee: Polyphalt Inc
Priority date: 1997-02-18
Filing date: 1998-02-18
Publication date: 1999-12-08
Also published as: AU6201798A; WO1998037146A1; IL131405A0; HUP0000539A3; CA2281590A1; KR20000071224A; BR9807421A; CN1252826A; HUP0000539A2; PL335164A1; JP2000510193A

Abstract

Granular asphalt compositions contain bitumen in an amount from about 45 % to about 80 % by wt. and crystalline and/or rigid polymer in an amount from about 15 % to about 50 % by wt., which composition has been stabilized or incorporated into the bitumen with synthetic rubber in an amount from about 3 % to about 25 % by wt. The bitumen used in the compositions may have a wide penetration range from soft to hard base and is the major component of the composition up to about 80 % by wt. The resulting compositions can be granulated and the granules stored over a considerable length of time without sticking together. The granules may be readily and rapidly dispersed in bitumen to dilute the polymer content while the polymer remains stably displaced in the bitumen. The granules are useful in varied applications, such as in paving, roofing and other construction industries, and may be transported to sites for ready use thereat.

Description

TITLE OF INVENTION POLYMER STABILIZED BITUMEN GRANULATE

FIELD OF INVENTION The present invention relates to compositions of polymer stabilized bitumen granulates and processes for their preparation, as well as commercial application thereof .

BACKGROUND TO THE INVENTION Asphalt is a black and sticky cementitious material that varies widely in consistency from springy hard to soft "solid" at normal room temperature. Polymers, such as rubbers or plastics, are added to improve the performance of the bitumen without changing traditional means for storage and transportation. Both unmodified asphalt and polymer-modified asphalts, for most applications, for example, in the preparation of bituminous compositions for paving, roofing and industrial application, have been supplied from the plant in a hot liquid form and stored hot, ready for use, in insulated tanks.

Over the years, the asphalt industry has made considerable efforts, but with limited success, to produce an asphalt granulate which can be stored at normal room temperature without losing its free flowing property.

In German Patent DE-PS 29 33 339, there is described the preparation of a pulverulant bitumen concentrate by spraying the hot liquid bitumen onto about 10% to 80 wt% of silica so that the silica is completely covered with bitumen. The asphalt coated composites, however, tend to stick together during storage, due to the static pressure forces.

In Karl-Hans Muller, U.S. Patent No. 5,382,348, there is proposed a process for making a free-flowing bitumen granulate by atomizing hot liquid base asphalt cement and, at the same time, introducing along with a stream of cooling air a filler, such as silica, which serves as a powdering and separating agent which forms a coating on the bitumen droplets. The granulate composition from this process is limited to a hard bitumen type as a hard base. Moreover, the composition is stored at elevated temperatures, bitumen migrates the surface, thereby impairing the free-flowing properties .

Although the addition of polymers (particularly rigid plastics) to asphalt cement at an incremental loading level may be expected to improve the granulating ability of the asphalt, the poor irascibility or incompatibility of the two components makes it difficult to provide a composition which can be pelletized unless the bitumen becomes a minor component and functions as an extender in the polymer based material. The granulated composition resulting from such asphalt extended polymer-based materials would also tend to stick together due to the migration of asphalt to the surface of the blend and under the static pressure during storage.

The problem, therefore, arises of preparing a polymer-stabilized bitumen granulate which can be stored over a considerable length of time without losing its free flowing property and which can be readily diluted in bitumen while retaining the performance enhancing standards of the polymer modification.

SUMMARY OF THE INVENTION In accordance with the present invention, there are provided novel bituminous compositions of high dispersed polymer concentration which are able to be pelletized or granulated and the pellets or granules so formed retain their free flowing condition. In addition, the pellets or granules may be readily diluted with bitumen to a lower polymer loading level while the dispersed polymer remains stabilized and is able to impart performance-enhancing properties to the resulting bituminous composition.

In accordance with the present invention, there is provided a bituminous composition suitable for granulating or pelletizing into stable free-flowing pellets or granules, which comprises about 10 to about 50 wt% of at least one crystalline and/or rigid polymer which has been stabilized or incorporated into the bitumen using at least one rubber in an amount of about 3 to about 25 wt%. The crystalline or rigid polymer (s) are present preferably in an amount of about 15 to about 30 wt% while the rubber (s) are present preferably in an amount of about 5 to about 15 wt%. Bitumen is the major component of the composition and may be present in an amount of from about 45% to about 85%, preferably about 50 to about 75% by wt . The bitumen composition retains the ability to improve performance as a polymer modified asphalt, resists polymer phase separation upon dilution with asphalt, and acts as a binder after the composition has been melted.

The bitumen which is used herein may have a wide penetration range, from soft to hard base. Bitumen is the major component of the composition from which the pellets or granules are formed, and may be present in an amount of up to about 85 wt% of the composition.

The bitumen compositions of the invention exhibits considerable homogeneity and storage stability upon dilution with bitumen to a lower polymer concentration and pellets formed therefrom are free-flowing and are readily and rapidly dispersible in bitumen for use. In addition to pelleting or granulating the compositions, any other shapes and forms may be provided, such as bricks, pucks and sheets of bituminous composition. GENERAL DESCRIPTION OF INVENTION The term "bitumen" used herein means a class of black or dark-colored (solid, semi-solid or viscous) cementitious substances, natural or manufactured, composed principally of high molecular weight hydrocarbons of which asphalts, tars, pitches and asphaltites are typical. The term "asphalt" used herein means a dark, brown to black, cementitious material, solid or semi-solid in consistency, in which the predominating constituents are bitumens that occur in nature, as such, or are obtained as residue in petroleum refining.

The provision of the high levels of dispersed polymer phase achieved herein can be effected using a variety of different stabilization systems for the dispersed polymer phases, as discussed in detail below. Such stabilization systems include steric stabilization, depletion stabilization and domain stabilization.

In U.S. Patents Nos . 5,280,064, 5,494,966 and 5,708,061 as well as in copending United States Patent Application No. 08/563,600 filed November 28, 1995, and corresponding WO 93/07219 in which the inventor herein is named as an inventor, there is described the steric stabilization of crystalline polyethylene and other crystalline polyolefins in bitumen by the formation of chemical bonds between functionalized polyethylene, as an anchor polymer, and functionalized polybutadiene, as stabilizing moieties, to provide stable dispersions of polyethylene in bitumen. The elastic steric stabilization described therein may be employed in providing the compositions of the present invention.

According to the disclosures of WO 94/22957, the disclosure of which is incorporated herein by reference, wherein the inventor herein is named as an inventor, one or more additional polymers may be incorporated into the steric ^■ stabilized compositions of the aforementioned patents. Such additional polymers are generally copolymers and may contain residual unsaturation. Such additional copolymers are often incompatible with bitumen and hence normally separate or coalesce rapidly when stirring of the composition is stopped. However, in accordance with the invention of WO 94/22957, when such copolymers are incorporated into the stabilized polyolefin compositions of WO 93/07219, they become stabilized and resist separation from the bitumen. Some copolymers which can be employed herein are already somewhat compatible with bitumen or can be rendered so by suitable processing. The presence of the dispersed polyolefin phase in bituminous compositions comprising such materials at worst does not destabilize such materials and frequently may improve such stability.

The manner in which the additional copolymers become stabilized in the compositions of WO 94/22957 depends on the nature of the polymer employed, and may include entanglement, physical entrapment, chemical cross-linking or combinations of two or more of such mechanisms .

Copolymers which may be incorporated into the bituminous compositions according to the invention include elastomeric copolymer, including: - styrenic copolymers, such as styrene-butadiene rubber (SBR) , styrene-butadiene-styrene block copolymers (SBS) , styrene-ethylene-butadiene- styrene block copolymers (SEBS) and styrene- isoprene-styrene block copolymers (SIS) ; - olefinic copolymers, such as polypropylene copolymers, ethylene-vinyl acetate compolymers (EVA) , ethylene methacylate copolymers (EMA) and ethylene propylene diene copolymers (EPDM) . - other polymers, such as nitrile-butadiene rubber (NBR) , polyvinylchloride (PVC) , polyisobutene, and polybutadiene (PB) . Mixtures of two or more of such polymers may be incorporated into the bituminous compositions along with the polyolefin. The compositions of WO 94/22957 may but do not necessarily employ components, such as process oils, which render the polymers more compatible with the bitumen.

In general, the choice of the copolymer to be incorporated into the bitumen in the compositions of WO 94/22957 is influenced by the following parameters, as well as possibly others:

- the asphalt chemical composition

- the molecular weight of the asphalt

- the molecular weight of the polymer (s)

- the shear force applied during mixing of the components

- the ratio of constituents of the copolymer, such as the mole ratio of E:VA in EVA

The polymeric materials may be present in the bitumen composition in the form of particle dispersions, strand-like dispersions, solutions and combinations in which the (co) polymer (s) is stabilized against separation.

In WO 97/28220, the disclosure of which is incorporated herein by reference, wherein the inventor herein is namely as inventor, there is described the stabilization of polyolefins in bitumen by the mechanism of depletion stabilization by the utilization of a macromolecular material decreased in the bituminous phase and stabilizing the dispersed polyolefin against separation without the necessity of forming chemical bonds or physical attachments between the macromolecular material and the particulate polyolefin. The macromolecular material dissolved in the bituminous phase provides a potential energy barrier to coalescence and flocculation of the dispersed polymer phase to maintain a stable dispersion of the particulate polyolefin phase. In this case, there is no necessity for a functionalized polyolefin to impart the stability. The macromolecules used in the depletion stabilization of the dispersion of polyolefin particles in bitumen may be any desired material, including the unsaturated polymers or copolymers which are elastomeric, such as a polybutadiene, a styrene- butadiene-styrene (SBS) block copolymer, random styrene- butadiene copolymers (SBR) , or other polybutadiene based copolymer, which may be provided in the form of devulcanized or otherwise dissociated rubber vulcanate.

Other macromolecular material which may be employed includes natural rubber, polyisoprenes and nitrile- butadiene rubbers. Such macromolecules may have a molecular weight of about 5,000 to about 300,000 or higher, provided that the molecules are soluble in or can be fully digested into the bitumen.

The crystalline polyolefins used in the invention may be virgin or recycled polyethylene (PE) , polypropylene (PP) , comingled PE/PP and/or maleic anhydride functionalized polyethylene in the case of steric stabilization, which may be either high or low density and/or high or low melt flow. The percentage of the functionalized polyethylene based on the total amount of the crystalline polyolefin polymers used generally is in the range from 3 to 100% by wt, preferably from 10 to 20% by wt, based on the total amount of crystalline polymers used. The functionalized polyethylene is the anchor polymer in the steric stabilization systems, which functions as a receiving structure to combine with non-functionalized polyethylene which is blended in.

An effective dispersion temperature for the polyethylene or other polyolefin is obtained at least about 10°C above the melting or fusion temperature of the polyolefin being dispersed, depending on factors, such as polymer molecular weight, matrix viscosity and shear force of mixing.

Thus, a grade of polyethylene having a melting or fusion point of 130° to 135°C can be dispersed at a temperature of above about 140°C. Commonly found low density, linear low density and high density polyethylenes thus may be dispersed and stabilized by a stabilizer system in the present invention, including steric stabilization and depletion stabilization. Most polyethylenes thus may be dispersed and stabilized by a stabilizer in the present invention. Most polyethylene used in consumer products have fusion temperatures in the acceptable range and polyethylene blends, such as are obtained as pelletized, flaked or powdered of recycled material, are suitable for dispersal in bitumens and may be stabilized according to the present invention.

The synthetic rubbers which serve as co- stabilizers with the functionalized polyethylene for the dispersion of the crystalline polymers in bitumen in steric stabilization may be a diene rubber, which may have a wide range of molecular weights, as described in the above-mentioned U.S. patents, such as polybutadiene (BR) , styrene-diene rubbers (including SBS, SB and SBR) , or treated diene rubber vulcanate, such as devulcanized rubber, tire rubber produced according to the procedure of WO 94/14896, combined with a small proportion of amine-functionalized diene based polymer, such as amine functionalized poly (butadiene-co-acrylonitride) , from about 3% to about 35% by wt., preferably from about 5 to about 20% by wt . , based on the total amount of the rubber stabilizer component. Two rubbers used as co- stabilizers, namely the unfunctionalized and the functionalized rubber, are co-cross-linked and in-situ compatibilized into bitumen, which may be effected in presence of sulfur or other suitable reagent.

In WO 94/14896, the disclosure of which is incorporated herein by reference, wherein the inventor herein is as named inventor, there is disclosed a method of devulcanizing rubber and of forming bituminous compositions containing the devulcanized material. Softened and swollen rubber particles are subjected to high shear to more effectively break down the rubber vulcanate network, which is then incorporated into the bitumen.

In WO 97/30121, the disclosure of which is incorporated herein by reference, wherein the inventor named herein is the inventor, there is described the provision of a composition of an elastomeric triblock copolymer comprising at least two polystyrene segments and stabilized and compatibilized in bitumen. A dispersed particulate polymer phase consisting of polystyrene or the rigid styrene-based copolymers miscible in the molten state with polystyrene is dispersed in the bituminous phase and is normally incompatible with the bituminous phase and is stabilized against separation from the bituminous phase by the elastomeric triblock copolymer by domain stabilization.

The bitumen-soluble elastomeric copolymer containing a styrene segment serves a dual function, namely (1) effects a uniform dispersion of polystyrene- based rigid polymers normally incompatible with bitumen and (2) provides a styrene domain as a receiving unit for stabilization of the dispersed polystyrene-based rigid polymer against separation from the bitumen. The polystyrene domains, which are dispersed throughout the bitumen by reason of the stabilization or compatibilization of the elastomeric triblock copolymer in the bitumen enable the normally-incompatible rigid polystyrene macromolecules to be incorporated into the bitumen by receiving the polystyrene particulates into the domains. The domains in the rubberized bitumen continuous phase become larger once the rigid polystyrene macromolecules are blended in and increase in dimension with increasing levels of dispersed rigid polystyrene.

The domain of the elastomeric copolymer of styrene which is readily dispersed or stabilized in the bitumen is provided by an elastomeric triblock copolymer in which the butadiene rubber segments are compatible with or soluble in or are able to be compatibilized with or solubilized in bitumen. Elastomeric triblock copolymers may comprise about 20 to about 80% of terminal styrene blocks, preferably about 24 to about 45%.

Examples of block copolymers which may be employed include styrene-butadiene-styrene triblock copolymers (SBS) , styrene-ethylene/butylene-styrene triblock copolymers (SEBS) and styrene-isoprene-styrene block copolymers (SIS) . These triblock polymers may be employed for forming stable dispersions of the rigid styrenic polymers in the bitumen.

Elastomeric block copolymers which may be used in the composition of the present invention may have a molecular weight (Mn) of from about 30,000 to about 375,000, preferably about 75,000 to about 275,000.

The rigid styrenic polymeric which are stably dispersed in bitumen according to the invention may be polystyrene homopolymers, such as crystal polystyrene and polystyrene foam, or may be grafted copolymers and physical blends/alloys with various rubbers, or may be polymer of styrene derivatives, such as poly(alpha- methylstyrene) , poly (p-tert-butylstyrene) and polychlorostyrene . The rigid styrenic polymers also may be comprise styrene based rigid copolymers, such as poly (styrene-co-vinylacetate) and poly (styrene-co- vinylthiophene) . The styrenic polymers may be natural or recycled polymer, including comingled blends of styrenic polymers.

The SEBS, SBS or SIS triblock copolymers also may be used to disperse and form stable dispersions of other polymers in place of polystyrene, provided that the polymer is miscible with polystyrene in the molten state and hence particulates can be received by the polystyrene domains. One such polymer is polyphenylene oxide (PPO) , which is difficult to disperse in bitumen but which is miscible with polystyrene in a molten state at any ratio and may be dispersed and incorporated into the bitumen by the domain effect.

Such styrenic polymers may have a molecular weight of from about 40,000 to about 1,400,000, preferably about 100,000 to about 300,000.

In addition to the specific stabilization systems employing steric stabilization, depletion stabilization and domain stabilization, discussed in detail above, the present invention also is applicable to other systems of stabilization of crystalline or rigid polymers in bitumen utilizing the procedures described herein.

The incorporation of the chemically-reactive blend of the above described multi-polymer components into bitumen generally is carried out in a two-step reaction procedure to prepare a polymer-stabilized asphalt composition which is capable of being granulated or otherwise processed to a desired physical form. The procedure which may be employed according to the invention involves 1) reactively blending the polymeric components in bitumen and 2) then chemically incorporating the polymers into bitumen by the incremental addition of a cross-linking agent, such as sulfur, to the mixture. According to the present invention, the crystalline and/or rigid polymers, such as polyethylene and polystyrene, in the granulate compositions are incorporated in-situ into the bitumen base matrix at an elevated temperature.

In the case of polyolefins, the polymer is heated above the crystallization temperature of the polymer used to produce a profusion of dispersed microscopic particles of molten polyolefin. The polyolefin (s) stably incorporated in the bitumen matrix do not lose the ability to crystallize once cooled below their melting temperature.

The small size of the crystalline or rigid polymer particles incorporated into the bitumen and the loading levels of the crystalline or rigid polymer in the compositions ensure that the compositions have a stiffness and cohesion high enough to be granulated or pelletized and permit their granular nature to be maintained over a considerable length of storage time at ambient temperatures.

The compositions provided according to the present invention may be granulated or pelletized by any conventional or appropriate granulation process. Alternatively, the compositions may be processed to any desired physical shape.

The ability to produce free-flowing pelletized polymer-modified bitumen, as effected herein, is significant, in that, by providing the bitumen in this form, a much broader distribution area can be served from a polymer modified asphalt manufacturing facility less expensively. The necessity for insulated tanks to maintain asphalt in a molten condition from plant to use site is avoided.

The pelletized or granulate material, which retains a free-flowing condition, may be shipped in bulk to the user in any convenient form of packaging, such as bags, boxes or bulk containers. At the site of use, the pellets can be diluted and let down with molten asphalt under low shear stirring, providing a polymer-modified asphalt in which the dispersed polymer, usually polyethylene or polystyrene, remains stable and is able to impart beneficial characteristics to the bitumen, as a result of elastic stabilization by the techniques described above.

Alternatively, the pellets or granules may be blended directly into the pug mill of an asphalt hot mix plant to produce polymer modified asphalt hot mix.

Different formulations may be prepared for different commercial end uses, for example pelletized composition for use in stone mastic asphalts (SMA) to which cellulosic fibres are added to minimize run off of the asphalt binder from the aggregate.

The dilution of the pellets with asphalt may be effected to any desired level of polymer modification of the final composition consistent with the end use contemplated, so that the bitumen granulate compositions provided herein are versatile in end use while the polymer remains stably dispersed in the final composition.

The provision of the free-flowing polymer-modified bitumen pellets or granules herein results in an improved production capacity from a polymer modified aspahlt manufacturing facility, since the production of materials in the pelletized form may be effected during what normally may be an off season for the plant. Since the pellets are free flowing at ambient temperature, no special tankage or heating is required to be associated with storage or use of the pellets. The free-flowing polymer-modified bitumen pellets may be stored at ambient temperature in any suitable packaging, resulting in a reduced energy consumption resulting from the elimination of heated tanks. Bituminous compositions produced herein from the pellets or other physical form of the concentration may be used as a paving material for all types of paving as well as finding applications in roofing membranes, shingles, waterproofing membranes, sealants, caulks, potting resins and protective finishes. Paving materials generally include aggregate, such as crushed stone, pebbles, sand etc., along with the bitumen composition. Similarly, other additives to the bitumen composition are employed, depending on the end use to which the invention is put. For example, a roofing material may be obtained by the addition of suitable filler, such as asbestos, carbonates, silicas, cellulosic fibers, mica, sulfates, clays, pigments and/or fire retardants, such as chlorinated waxes. For crack-filler application, an oxide may advantageously be added.

EXAMPLES The Examples which follow illustrate the incorporation of a chemically-reactive blend of multi- polymer components into bitumen compositions which are capable of being granulated. The compositions, in each case, were prepared by a two-step procedure, in which at least three polymeric components were reactively blended in bitumen and then the polymers were chemically incorporated into bitumen with the incremental addition of a cross-linking agent to the mixture .

The compositions prepared according to the Examples had a viscosity range from 100 poise to 10 poise at temperature around 200°C. The resultant compositions were pelletized in solid form at room temperature with conventional granulators. The resulting pellets were stored at normal ambient temperature over a considerable length of time without losing their free-flowing property. The storage stability of the pellets was tested when blended with asphalt to about 2% polymer loading level and during hot storage at 320°F for 48 hours, using the ASTM 5892- 96 test method. In accordance with this method, stability is considered satisfactory if the difference in softening temperature between top and bottom of the sample after hot storage is no greater than 4°F. Example 1:

In a 1 litre mixing vessel, 391 g of asphalt (Petro-Canada Bow River, 150/200 penetration grade) , were heated to 180°C. 139g of polyethylene (recycled low density, 1 melt index, RLDPE) , 22g of maleic anhydride grafted polyethylene (Fusabond 101; linear low density, 12 melt density, anhydride content: 0.7%), 35 g styrene-butadiene rubber (SB copolymer; Firestone Steron 210, a solid form with about 70,000 molecular weight) and 14g of amine functionalized poly (butadiene-co-acrylonitride) copolymer (Hycar; ABTN; acrylonitride content 10%, amine equiv. at 1200) were added into the asphalt, blended reactively under high shear with a Brinkman Polytron Mixer for 1.5 hours at about 180°C to 200°C. To this mixture, while still mixing, were added 2g of total amount of sulfur added incrementally with 3 divided portions: lg, 0.5g and 0.5g at half hour intervals. Following sulfur incremental loading, the mixing and reaction were continued for 1.5 hours at about 180°C to 240°C to form a polymer-stabilized bitumen composition having a viscosity of around 70 poises at 200°C. The stability of the composition was tested for polymer separation by diluting with bitumen to about 2% polymer loading level. The difference in softening point between the top and bottom was 1°F, showing acceptable stability.

The resulting composition was poured out of the vessel to cool down at room temperature to form a solidified mass. A conventional granulator was used to pelletize the solid to small free flowing pellets sized about to inch. The pellets were packaged in a plastic bottle container and were stored at room temperature for 30 months without loosing their free- flowing property. Example 2 :

The method of Example 1 was repeated with a recycled low density polyethylene having a high melt flow index (MI: 100). The viscosity of the resulting composition was 25 poise at 200°C, which was significantly lower than that of the composition in Example 1. Pellets made from the composition have retained their free flowing property over the same 30 months storage time and conditions as in the samples from Example 1. Example 3 :

The method of Example 1 was again repeated using the same polyethylene as used in Example 2 except for using llOg of polyethylene instead of 139g to make a final granulate asphalt composition containing 30% of stabilized polymers, rather than 35% of the polymers as in Examples 1 and 2. The viscosity of this composition was about 18 poises at 200°C. The granulates obtained from this formulation also exhibited a good free flowing property after 30 month storage under the same condition as those set forth in Example 1. Example :

The procedure of Example 1 was repeated again using the polyethylene of Example 1 and further incorporating a composition prepared according to WO 94/14896, comprising a 40/20/40 blend of devulcanized crumb rubber, oil and bitumen, rather than the styrene- butadiene rubber. The viscosity of the resulting composition was about 75 poises at 200°C. Pellets made from the composition have retained their free-flowing property over 30 months storage time and conditions as set forth in Example 1. Example 5 : The procedure of Example 1 was repeated using the polyethylene of Example 1 but employing a harder bitumen, namely AC-20. The stability of the composition prior to pelletizing was tested by diluting the composition to a 2% polymer load level. The difference in softening point between top and bottom was 2°F, showing acceptable stability. Pellets were made from the composition and have retained their free-flowing property over 3 months storage time and conditions as set forth in Example 1. The following Table summarizes the compositions used in the Examples:

Pellet Compositions

co

SUMMARY OF THE DISCLOSURE

In summary of this disclosure, the present invention provides a novel bitumen granulate in which crystalline or rigid polymer is stably dispersed and which retains a free-flowing homogeneous condition over many months of storage and yet is able to be readily dispersed in hot bitumen and retain stable dispersion of the polymer modifier, so that the beneficial properties of the polymer modifier are retained. Modifications are possible within the scope of the invention.

Claims

1. A bituminous composition comprising: about 45 to about 85 wt% of bitumen, about 10 to about 50 wt% of particulate crystalline or rigid polymer, about 3 to about 25 wt% of a rubber compatible with said bitumen and incorporating and stabilizing the particulate polymer in the bitumen, and which is stable against separation of the particulate polymer upon dilution of the composition with bitumen to an end use composition.

2. The composition of claim 1 wherein said polymer is present in an amount of about 15 to 30 wt%, said bitumen is present in an amount of 65 to about 75 wt% and said rubber is present in an amount of about 5 to about 15 wt%.

3. The composition of claim 2 wherein said polymer is a crystalline polyolefin.

4. The composition of claim 3 wherein said polyolefin is polyethylene.

5. The composition of claim 4 wherein said polyethylene is maintained stable against separation by steric stabilization.

6. The composition of claim 4 wherein said polyethylene is maintained stable against separation by depletion stabilization.

7. The composition of claim 2 wherein said polymer is a rigid styrene-based polymer.

8. The composition of claim 2 wherein said styrene- based polymer is a rigid polystyrene.

9. The composition of claim 8 wherein said rigid polystyrene is maintained stable against separation by domain stabilization.

10. The composition of claim 7 which has been pelletized or granulated to pellets or granules which are free-flowing at ambient temperatures.

11. The composition of claim 1 which has been proceeded to the form of blocks, pucks or sheets.

12. A method of forming a bituminous composition as claimed in claim 1 which comprises:

(1) reactively blending the polymeric components into bitumen, and

(2) chemically incorporating the polymeric components into the bitumen by the incremental addition of a cross-linking agent.

13. The method of claim 12 wherein said cross-linking agent is sulfur.

14. The method of claim 12 including granulating or pelletizing the composition to granules or pellets which are free-flowing at ambient temperature.