The Relevant Technology Asphalt is a commonly used material for construction purposes, such as a road pavement or roofing material. Asphalt alone, however, often does not possess all the physical characteristics desirable for many construction purposes. For instance, unmodified asphalt may exhibit a poor Performance Grade Rating (PG Rating) as a road pavement material. As used herein, PG Rating is defined as the average seven-day maximum and the single-day minimum pavement design temperature, wherein the maximum is determined 20 mm below the surface of the pavement and the minimum is determined at the surface of the pavement.

Although the PG Rating for asphalt may widely vary, asphalt generally used in road pavement applications exhibit PG Ratings of about 64-22, which indicates a 64° C average seven day maximum and a-22° C single day minimum pavement design temperature.

When used as a road pavement material, asphalt is typically subjected to temperatures in excess of 64° C twenty mm below the pavement surface and below

-22° C at the pavement surface. Temperatures outside this range lead to deterioration of the asphalt pavement. Hence, it has for some time been an objective to broaden the PG Range of asphalt used in road pavement applications.

To broaden the PG Range of the asphalt pavement, modifiers are added to the asphalt. In addition to increasing the PG Range of the asphalt, modifiers also improve other qualities of the asphalt, such as its toughness, flexibility and wear characteristics.

It is, therefore, apparent that there is a need for an asphalt modifier capable of modifying the physical characteristics of asphalt. In addition, there is a need for an asphalt modifier that is easily dispersed in asphalt, which forms an asphalt mixture suitable for road paving purposes.

SUMMARY OF THE INVENTION The present invention relates to an asphalt mixture having a polymer dispersed therein that modifies the characteristics of asphalt, so that the asphalt mixture is particularly well suited for road paving applications. More particularly, the present invention is directed to an asphalt mixture having an excellent PG Rating and that exhibits increased toughness and flexibility so that premature rutting, thermal cracking, and fatigue cracking of the asphalt are reduced.

The present invention further relates to a polymer that is compatible with asphalt so that the polymer is easily dispersed in asphalt to form a mixture having long-term storage stability and good workability. For example, polymers within the scope of the present invention preferably melt and disperse rapidly upon

addition to molten asphalt at low shear mixing conditions which is a significant improvement over conventionally used processes.

The present invention is directed to a mixture comprising asphalt and a polymer having at least one polar functional group and having a density from about 0.97 to about 1.1 g/cm3 at 25°C. The asphalt is present in an amount from about 25 weight percent to about 99.9 weight percent based on the total weight of the mixture. The polymer is a homopolymer or a copolymer and is present in an amount from about 0.1 weight percent to about 75 weight percent based on the total weight of the mixture.

The present invention is further directed to an article formed from the polymer modified asphalt mixture referred to in detail above. In a preferred embodiment of the present invention, the article formed from the polymer modified asphalt mixture is a road pavement.

Furthermore, the present invention is directed to a process for preparing a mixture for use as a road pavement, including the steps of preparing a molten asphalt material; adding the polymer modifier referred to in detail above to the molten asphalt material; and mixing the molten asphalt until the polymer modifier is dispersed into the asphalt.

These and other features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the of the invention as set forth hereinafter.

DETAILED DESCRIPTION OF THE INVENTION Use of Terms It must be noted that, as used in the specification and the appended claims, the singular forms"a,""an"and"the"include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to"a polymer having at least one polar functional group and having a density from about 0.97 to about 1.1 g/cm3 at 25° C"includes mixtures of polymers having the recited characteristics, reference to"an asphalt"includes mixtures of two or more such asphalts, and the like.

Ranges are often expressed herein as from"about"one particular value, and/or to"about"another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent"about,"it will be understood that the particular value forms another embodiment.

Definitions The term"asphalt"is a dark brown to black cementitious material which is solid or semi-solid in consistency, having bitumens as its predominant constituent.

Typically, asphalt is described as a black solid with a dull luster.

The term"thermal cracks"is defined as cracks resulting from internal stresses induced by temperature change and stresses exceeding the strength of the pavement. Thermal cracks typically occur at low temperatures.

The term"rutting"is defined as a form of permanent deformation, where shearing forces, such as from an automobile wheels push the asphalt layers apart resulting in ruts. Rutting generally occurs at high temperatures.

The term"fatigue cracking"is defined as crack patterns that can lead to potholes. Fatigue cracking generally occurs over a period of time and at low to moderate pavement temperatures.

Discussion It is a feature of the present invention to provide an asphalt mixture that can be used in road pavement applications.

It is further a feature of the present invention to provide a polymer that is compatible with asphalt and which is easily dispersed in asphalt without the use of expensive mixing equipment or processes.

The present invention is directed to an asphalt mixture having a polymer dispersed therein. The mixture is composed of from about 25 weight percent to about 99.9 weight percent asphalt and from about 0.1 weight percent to about 75 weight percent polymer having at least one functional group and having a density of from about. 97 to about 1.1 g/cm3 at 25° C. All weight percents are calculated on the total weight of the mixture.

In one embodiment of the present invention that is particularly well suited for use in road pavement applications, the polymer is present in the asphalt mixture in an amount from about 0.5 weight percent to about 15 weight percent, preferably from about 1 weight percent to about 10 weight percent, more preferably from

about 2 weight percent to about 4 weight percent, and most preferably about 3 weight percent. The asphalt is present in the mixture in an amount from about 85 weight percent to about 99.5 weight percent, preferably from about 90 weight percent to about 99 weight percent, more preferably from about 96 weight percent to about 98 weight percent and most preferably about 97 weight percent.

Alternatively, the asphalt mixture can be used as a concentrate that is later combined with other road construction materials, such as additional asphalt, to form a mixture used as a road pavement. When the asphalt mixture is used as a concentrate, the polymer is present in amounts from about 15 weight percent to about 75 weight percent, preferably from about 35 weight percent to about 70 weight percent and most preferably about 45 weight percent to about 55 weight percent and the asphalt is present in an amount from about 25 weight percent to about 85 weight percent, more preferably from about 30 weight percent to about 65 weight percent and most preferably from about 45 weight percent to about 55 weight percent. The exact amount of polymer present will depend on the use of the asphalt concentrate mixture and the amount of other road construction materials to be combined with the concentrate.

The asphalt used in the present invention may be any asphalt conventionally used in road paving applications. Such asphalt may be obtained from different sources, such as naturally occurring asphalt, vacuum distillation residue, or hydrocarbon cracking residue. The use of asphalt derived as a residue from vacuum distillation is preferred. Asphalt may be further described by using its penetration value ("PEN"), asphalt cement viscosity value ("AC"), or asphalt aged

residue viscosity ("AR"). The measurement of PEN values is defined by ASTM D5. Asphalt, as used herein, preferably has a PEN value of from 40 to 300 dmm.

The measurement of AC viscosity values is defined by ASTM D2171. Asphalt, as used herein, preferably has an AC value of from 2.5 to 40 hundreds of poises. The measurement of AR values is defined by ASTM D2171. Asphalt, as used herein, preferably has an AR value of from 1,000 to 16,000 poises.

The asphalt used in the present invention may be unmodified or modified asphalt. In some applications, oxidized asphalt provides different weather resistance and stability characteristics. The asphalt can be oxidized by any means known in the art, including mixing the asphalt with air and heating to between 179°C and 260°C with or without a catalyst. When no catalyst is used, it typically takes between four to six hours to oxidize the asphalt. With a catalyst, the processing time is shortened to between about two and four hours. A preferred catalyst is ferric chloride (FeCl3).

In a preferred embodiment, the asphalt is an AC-20 type asphalt which is commercially available from Ashland (ASHLAND AC-20), Coastal, Chevron, and Exxon.

The polymer used in the present invention is a homopolymer or a copolymer having at least one polar functional group and having a density from about. 97 to about 1.1 g/cm3 at 25°C. The polymer is preferably selected from oxidized polyolefins, maleated polyolefins and acrylic acid grafted polyolefins.

More preferably, the polymer is selected from maleated polyethylene, maleated polypropylene, oxidized polyethylene, acrylic acid grafted polyethylene, acrylic

acid grafted polypropylene and mixtures and derivatives thereof. Most preferably, the polymer is an oxidized polyethylene.

The polymer preferably has an acid number from about 0.1 to 50, a needle penetration hardness less than about 50 dmm at 25°C and a viscosity from about 1 to about 100,000 cP at 135°C.

In a preferred embodiment, the polymer is an oxidized polyethylene homopolymer having a density from about. 97 to about 1.1 g/cm3, a hardness less than about. 5 dmm at 25°C, an acid number from about 5 to about 41, and a viscosity from about 2500 to about 85,000 cP at 135°C. Suitable polymers are commercially available from AlliedSignal under the trademark A-C Polyethylenes, specifically A-C 307,307A, 316,316A, 325, 330,392,395, and 395A; Hoechst under the trademark Hoechst-Wachs PED 121, Hoechst-Wachs PED 191, Hoechst- Wachs PED 153, Hoechst-Wachs PED 261, Hoechst-Wachs PED 522; and BASF under the trademark Luwax OA 2, OA 3, and OA 5. The polymer is preferably A- C 325 polyethylenes from AlliedSignal.

The polymer modified asphalt mixtures can be used to form any suitable articles. More particularly, the polymer modified asphalt mixtures are used to form road pavement surfaces. To form a road pavement, the polymer modified asphalt mixture is applied to a surface, such as earth that has preferably been leveled, using any method, including any method commonly used in the road paving industry.

While the polymer modified asphalt mixture provides excellent physical characteristics for road paving applications, these mixtures may also be used for other construction purposes, such as roofing applications.

The polymer modified asphalt mixture according to the present invention is prepared by providing asphalt in its molten phase; adding a polymer referred to in detail above to the molten asphalt and mixing the asphalt and the polymer until the polymer is dispersed in the asphalt to form a polymer modified asphalt mixture.

Polymers within the scope of the present invention are dispersible in asphalt. In a preferred embodiment, polymers melt and rapidly disperse in molten asphalt. For example, oxidized polyethylene having a density from about. 97 to about 1.1 g/cm3 melts and disperses in molten asphalt quite rapidly. The oxidized polyethylene and the molten asphalt mixture is preferably mixed to ensure dispersion of the polymer in the molten asphalt. Any type mixing equipment and process can be used that mixes the polymer and the asphalt, including low shear mixing equipment and high shear mixing equipment.

Another advantage of the use of polymers within the scope of the present invention is that when the polymers are added to asphalt, the viscosity of the mixture is only slightly increased over the viscosity of asphalt alone. By increasing the viscosity only slightly, the mixture exhibits good hot-mix workability and no observable separation.

Furthermore, polymers within the scope of the present invention exhibit dispersibility with a large number of asphalts, resulting in an mixtures that are storage stable, with no polymer phase separation.

The present invention will be more readily understood by reference to the following examples. There are, of course, many other forms of the invention which will become obvious to one skilled in the art, once the invention has been fully

disclosed, and it will accordingly be recognized that these examples are given for the purpose of illustration only and are not to be construed as limiting the scope of the invention in any way.

EXAMPLES The following test procedures were used in evaluating the analytical properties of the mixtures herein and in evaluating the physical properties of the mixtures of the examples.

Ring and Ball Softening Point (RBSP); ASTM D36 Penetration Hardness; ASTM D5 Compatibility; ASTM D5976 Rotational Viscometer (RV); ASTM D4402 Dynamic Shear Rheometer (DSR); AASHTO TP5 Rolling This Film Oven (RTFO); AASHTO T240 Pressure Aging Vessel (PAV); AASHTO PP1 Bending Beam Rheometer (BBR); AASHTO TP1 Example 1 Samples of polymer modified asphalt cement (ASHLAND AC-20 asphalt cement) were prepared and their physical characteristics were tested against a standard of unmodified asphalt cement (ASHLAND AC-20 asphalt cement).

The following polymers were used to prepare the modified asphalt cement samples: ALLIED AC-325 (HDPE), and HOECHST PED-153 (HDPE). ALLIED

AC-325 has a RBSP of 137°C, a density of. 99, and an acid number of 25.

HOECHST PED-153 has a RBSP of 115-120°C, a density of. 98, and an acid number of 23-28. Two polymer modified asphalt mixtures were prepared for each polymer; one mixture containing 3% by weight polymer and the other mixture containing 5% by weight polymer, wherein the weight percentages were based on the total weight of the mixture. Standard Strategis Highway Research Program (SHRP) SUPERPAVETM testing along with RBSP and penetration hardness tests were performed to determine the performance properties of the mixtures.

Table I X25242-651 3 4 5 6 Sample ID/Formulation Ashland 3% 5% 3% 5% AC-20 ALLIED 325 ALLIED 325 PED 153 PED 153 1. Original Binder Ring & Ball Softening Point, °C 47. 0 72. 5 99. 8 55. 6 98. 1 Penetration Hardness, 1/10 mm at 25 °C 59 34 35 31 40 at 4 °C 35 19 23 27 22 Viscosity at 135 °C cPs 425 437 482 427 442 DSR G*/sin delta, Min. 1.0 kPa 1.2698 1.1078 1.4993 1.1151 2.0582 Test Temperature at 10 rad/s °C ass/Fail Temperature, °C 66. 1 88+ 81.8 91.7 88+ Compatibility, 5 days at 163 °C RBSP-Top, °C 47. 2 67. 5 89. 5 57. 0 98. 2 RBSP-Bottom,°C 47. 2 70. 2 94. 0 553 98.2 Viscosity at 135°C cPs-Top 455 480 460 412 440 Viscosity at 13°C, cPs-Bottom 442 472 460 412 432 II.RTFO Residue DSR G*/sin delta, Min. 2.20 kPa 2.9828 3.4529 2.5818 2.4476 3.8217 Test Temperature at 10 rad/s, °C 64 70 76 70 70 Pass/Fail Temperature, °C 66. 7 74. 3 77.8 70.9 75.9 Ill. PAV Aging DSR G*sin (delta), Max. 5000 kPa 3269 4094 3530 4058 4259 Test Temperature at 10 rad/s, °C 25 25 28 25 25 Pass/FailTemperature, °C 22. 0 23. 4 25. 1 233 23. 7 Creep Stiffness, BBR S, Max. 300 MPa-Stiffness, 175 204 228 190 230 m-Value, Min. 0.300-Slope. 358. 354. 325. 339. 316 Test Temperature @ 60s, °C-12-12-12-12-12 Pass/FailTemperature, °C-15. 2-14. 5-13. 8-14. 8-14. 4 IV. Performance Grade 64-22 70-22 76-22 70-22 70-22

As shown in Table 1. the mixtures exhibited improved performance properties for use in road paving applications when compared to unmodified asphalt.

Example 2 ASHLAND AC-20 asphalt was introduced into a vessel. The asphalt was heated to approximately 150°C until the asphalt was in a molten state. ALLIED AC-325 (HDPE) oxidized polyetheylene was conveyed into the top of the stirred vessel containing the molten asphalt. The oxidized polyethylene was quickly dispersed into the molten asphalt. The mixture was stirred to thoroughly disperse the oxidized polyethylene in the molten asphalt. Stirring was continued for about one and a half to about two hours resulting in a mixture.

The rate of dispersion of the oxidized polyethylene in asphalt is measured by the change in ring and ball softening point over time. The oxidized polyethylene will exhibit a high RBSP within 15 minutes and substantially maintain the high RBSP throughout the process.