Plastomer-modified asphalt binders meeting MSCR specifications, asphalt paving materials with such asphalt binders, and methods for fabricating such asphalt binders

Abstract

Plastomer-modified asphalt binders meeting MSCR specifications, asphalt paving materials with such asphalt binders, and methods for fabricating such asphalt binders are provided. The asphalt binder contains a base asphalt and a plastomer. If the plastomer has a drop point no greater than about 139° C., the asphalt binder further contains sulfur; sulfur-containing compounds, such as hydrocarbyl polysulfides and thiuram disulfides; phenolic resins; metal oxides; or a combination thereof. The asphalt binder is substantially free of elastomer.

Claims

1. An asphalt binder comprising: a base asphalt; and a plastomer comprising; a maleated polypropylene having a drop point of from about 152° C. to about 155° C., a polypropylene homopolymer having a drop point of about 167° C., or a combination thereof; wherein the asphalt binder is substantially free of elastomer.

2. The asphalt binder of claim 1, wherein the maleated polypropylene has a drop point of about 152° C. and a saponification number of from about 75 to about 95 mg KOH/gm.

3. The asphalt binder of claim 1, wherein the maleated polypropylene has a drop point of about 155° C. and a saponification number of about 14 to about 22 mg KOH/gm.

4. The asphalt binder of claim 1, wherein the polypropylene homopolymer has saponification number of about 0 mg KOH/gm.

5. The asphalt binder of claim 1, further comprising an additive selected from the group consisting of sulfur, sulfur-containing compounds, phenolic resins, metal oxides, or a combination thereof.

6. The asphalt binder of claim 1, wherein the plastomer is present in the asphalt binder in an amount no greater than about 10 wt. % based on a total weight of the asphalt binder.

7. The asphalt binder of claim 5, wherein the additive is present in the asphalt binder in an amount no greater than about 1 wt. % based on a total weight of the asphalt binder.

8. The asphalt binder of claim 1, wherein the base asphalt is utilized for paving applications, coating applications, sealant applications, roofing material applications, or adhesive applications.

9. An asphalt paving material comprising: an asphalt binder comprising: a base asphalt; and a plastomer comprising; a maleated polypropylene having a drop point of from about 152° C. to about 155° C., a polypropylene homopolymer having a drop point of about 167° C., or a combination thereof; wherein the asphalt binder is substantially free of elastomer; and an aggregate.

10. The asphalt paving material of claim 9, wherein the maleated polypropylene has a drop point of about 152° C. and a saponification number of from about 75 to about 95 mg KOH/gm.

11. The asphalt paving material of claim 9, wherein the maleated polypropylene has a drop point of about 155° C. and a saponification number of about 14 to about 22 mg KOH/gm.

12. The asphalt paving material of claim 9, wherein the polypropylene homopolymer that has a drop point of about 167° C. and a saponification number of about 0.

13. The asphalt paving material of claim 9, further comprising an additive selected from the group consisting of sulfur, sulfur-containing compounds, phenolic resins, metal oxides, or a combination thereof.

14. The asphalt paving material of claim 13, wherein the additive is present in the asphalt binder in an amount no greater than about 1 wt. % based on a total weight of the asphalt binder.

15. The asphalt paving material of claim 9, wherein the plastomer is present in the asphalt binder in an amount no greater than about 10 wt. % based on a total weight of the asphalt binder.

16. An asphalt binder comprising: a base asphalt; and a plastomer comprising; a maleated polypropylene having a drop point of about 152° C., a maleated polypropylene having a drop point of about 155° C., a polypropylene homopolymer having a drop point of about 167° C., or combinations thereof; wherein the asphalt binder is substantially free of elastomer.

17. The asphalt binder of claim 16, wherein the maleated polypropylene has a saponification number of from about 75 to about 95 mg KOH/gm.

18. The asphalt binder of claim 16, wherein the maleated polypropylene has a saponification number of from about 14 to about 22 mg KOH/gm.

19. The asphalt binder of claim 16, wherein the polypropylene homopolymer has a saponification number of about 0 mg KOH/gm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

(2) FIG. 1 is a table illustrating the results of MSCR tests of asphalt binders containing plastomers exhibiting various drop points. The asphalt binders are formed from a PG 64-22 base asphalt from the mid-continent region of the United States. The tests are conducted at the operational environmental temperature of 64° C.; and

(3) FIG. 2 is a graph illustrating the results of FIG. 1.

DETAILED DESCRIPTION

(4) The following detailed description is merely exemplary in nature and is not intended to limit the various embodiments or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

(5) The various embodiments contemplated herein relate to asphalt binders that include a base asphalt and a plastomer. When the plastomer has a drop point no greater than 139° C., the asphalt binder also may also contain (a) sulfur; (b) sulfur-containing compounds, such as hydrocarbyl polysulfides and thiuram disulfides, particularly tetramethyl thiuram disulfide (TMTD), tetraethyl thiuram disulfide (TETD) and tetrabutyl thiuram disulfide (TBUT); (c) phenolic resins, particularly phenol-aldehyde resin; (d) metal oxides, such as zinc oxides; or (e) a combination thereof. The asphalt binders contemplated herein can meet both the MSCR non-recoverable creep compliance, J.sub.nr specification and also the MSCR stress sensitivity J.sub.nr,diff specification without the presence of elastomers. In this regard, they can be used to fabricate asphalt paving materials at lower temperatures than if elastomers were present and result in lower temperature road paving while also effectively facilitating reduced road rutting.

(6) Methods for measuring an asphalt binder's performance have changed over time, exposing shortcomings of conventional asphalt binders. The Performance Graded (PG) System is a method of measuring asphalt binder performance that was originally developed during the Strategic Highway Research Project Program in the United States in the early 1990's. The Superpave™ performance grading (PG) specification classifies asphalt binders into performance grades that change at 6° C. intervals according to service climate. For example, a Superpave Performance Grade PG 64-22 meets high temperature physical properties up to 64° C. and low temperature physical properties down to −22° C. While this system works well for conventional-speed, moderate-traffic volume pavements, research indicates that it needs some refinement for pavements that have slow-speed loading and high traffic volume. Rather than change criteria and/or test conditions to reflect a change in loading time and traffic volume, in the PG System traffic speed and volume are adjusted for by “grade-bumping” or testing at higher temperatures than indicated by the climate. For example, for a standard traffic asphalt pavement, a PG 64-22 asphalt binder might be used but a high-volume highway pavement might require a PG 76-22 asphalt binder—even though the pavement temperature would likely never get above 64° C.

(7) More recent research has resulted in the Multiple Stress Creep Recovery (MSCR) test, with the methodology described in AASHTO T350-14 and the specification in AASHTO M332-14. The MSCR test provides the user with a new high temperature binder specification that is intended to more accurately indicate the rutting performance of the asphalt binder. The MSCR test uses the well-established creep and recovery test concept to evaluate the binder's potential for permanent deformation. Using the Dynamic Shear Rheometer (DSR), the same piece of equipment used in the existing PG specification, a one-second creep load is applied to the asphalt binder sample, which has been short-term aged using the Rolling Thin Film Oven (RTFO). After the 1-second load is removed, the sample is allowed to recover for 9 seconds. The test begins with the application of a low stress (0.1 kPa) for 10 creep/recovery cycles, then the stress is increased to 3.2 kPa and repeated for an additional 10 cycles. The average of the non-recoverable strain divided by the applied stress (for both 0.1 and 3.2 kPa) at ten loading cycles are the non-recoverable creep compliance, J.sub.nr.

(8) A major difference between the MSCR specification and the PG System is how grade bumping is done. With the MSCR specification, the binder testing is done at the high environmental temperature that the pavement is expected to experience. If the climate grade is a PG64 or PG58, all high temperature testing is conducted at 64° C. or 58° C. If heavy traffic is expected the specification requirement is changed, i.e., a lower J.sub.nr value is required to reflect the increased stress the pavement will actually experience, but testing is still done at, for example, 64° C. for a PG 64 climate. For example the MSCR specification J.sub.nr for standard fast moving traffic is a maximum of 4.5 kPa.sup.−1 and for slow moving or higher traffic the required J.sub.nr value would be a maximum of 2.0, 1.0 or 0.5 to require a more rut-resistant material instead of testing at a higher temperature. High temperature testing for each S, H, V or E grades (as explained below) would be done at the same pavement climate temperature of, for example, 58° C. or 64° C. This allows for accurate evaluation of the binder at the expected operating temperature. A section of the AASHTO specification is shown in Table 1 below, where grade bumping is done by changing the required specification value of standard, heavy, very heavy, or extreme traffic, not by changing temperature.

(9) TABLE-US-00001 TABLE 1 The MSCR gradings reflect the current grade bumping limits. Standard S grade traffic <3 million ESAL's Heavy H grade traffic >3 million ESAL's Very Heavy V grade traffic >10 million ESAL's Extreme E grade traffic >30 million ESAL's where “ESAL's” is “equivalent single axle loads.”

(10) The stress sensitivity parameter J.sub.nr,diff, is calculated using the equation J.sub.nr,diff=(J.sub.nr, 3.2kPa−J.sub.nr,0.1kPa)/J.sub.nr,0.1kPa. The J.sub.nr,diff is required under the MSCR specification to be below 75% to insure that the binder will not be overly stress sensitive to unexpected heavy loads or unusually high temperatures.

(11) As noted above, the asphalt binder as contemplated herein includes a base asphalt. All types of asphalt, naturally occurring and synthetically manufactured, may be used in accordance with the asphalt binders contemplated herein. For example, industrial asphalts used for pavings, coatings, sealants, roofing materials, adhesives, and other applications may be used. Asphalt is defined by the ASTM as a dark brown to black cementitious material in which the predominant constituents are bitumens that occur in nature or are obtained in petroleum processing. Asphalts characteristically contain saturates, aromatics, resins and asphaltenes. Naturally occurring asphalt is inclusive of native rock asphalt, lake asphalt, and the like. Synthetically manufactured asphalt is often a byproduct of petroleum refining or post refining operations and includes air-blown asphalt, blended asphalt, cracked or residual asphalt, petroleum asphalt, propane asphalt, straight-run asphalt, thermal asphalt, and the like.

(12) The asphalt binder also includes a plastomer. As used herein, the term “plastomer” generally refers to polymers possessing moderate to high degrees of crystallinity that enhance the stiffness of an asphalt binder but provides little, if any, elasticity. In one exemplary embodiment, the plastomer contemplated herein has a drop point greater than 139° C. The drop point is defined by ASTM D3954. The drop or dropping point is a characteristic property of a material and is the temperature at which the first drop of the material falls from a cup under defined test conditions. Examples of plastomers suitable for use in the asphalt binders contemplated herein include maleated polypropylenes, such as, for example, Honeywell Titan™ 7278, which has a drop point of about 152° C. and a saponification number of from about 75 to about 95 mg KOH/gm, Honeywell Titan™ 7933, which has a drop point of about 155° C. and a saponification number of about 14 to about 22 mg KOH/gm; oxidized high density polyethylenes (defined as polyethylenes with a density of about 0.94 to about 1.0 gm/cm.sup.3), such as, for example, Honeywell Titan™ 7817, which has a drop point of approximately 140° C. and an acid number of 7 mg KOH/gm; and polypropylenes, such as, for example Honeywell Titan™ 7457, which has a drop point of 167° C. and an acid number or a saponification number of about 0. All Honeywell Titan™ products are available from Honeywell International, Inc. of Morristown, N.J. In an embodiment, the plastomer or a mixture of plastomers is present in the asphalt binder in an amount no greater than 10 weight percent (wt. %) based on the total weight of the asphalt binder. These values represent the concentration for the final in-use asphalt binder. Higher concentrations can be used to make concentrates that are subsequently “let down” to the final in-use concentration.

(13) In another embodiment, the asphalt binder is substantially free from elastomer. To the extent that the asphalt binder contains elastomer, it contains an amount that does not modify or amend the physical, mechanical or chemical properties of the asphalt binder. In one embodiment, the asphalt binder contains no more than 1 wt. % elastomer based on the total weight of the asphalt binder. As used herein, the term “elastomer” refers to a polymer that can enhance the stiffness of an asphalt binder and also impart elasticity.

(14) In another exemplary embodiment, the asphalt binder includes an additive chosen from sulfur; sulfur-containing compounds, such as hydrocarbyl polysulfides and thiuram disulfides, particularly tetramethyl thiuram disulfide (TMTD), tetraethyl thiuram disulfide (TETD) and tetrabutyl thiuram disulfide (TBUT); phenolic resins, particularly phenol-aldehyde resin; metal oxides, such as zinc oxides; or a combination thereof. One or more of these additives can facilitate lowering of both non-recoverable creep compliance, J.sub.nr, and also the stress sensitivity parameter J.sub.nr,diff, of the asphalt binder such that when used in combination with a plastomer, the plastomer no longer needs a drop point greater than 139° C., although more plastomer may be required to make the same MSCR grade. In one embodiment, the sulfur is added to the asphalt binder as elemental sulfur. In an exemplary embodiment, the additive is present in the asphalt binder in an amount greater than zero and no greater than about 1 wt. % based on a total weight of the asphalt binder.

(15) In one embodiment, an asphalt paving material contains the asphalt binder contemplated herein. In addition to the asphalt binder described above, the asphalt paving material includes an aggregate. “Aggregate” is a collective term for mineral materials, such as, for example, sand, gravel, or crushed stone that are combined with the asphalt binder to form the asphalt paving material. The aggregate may comprise natural aggregate, manufactured aggregate, or a combination thereof. Natural aggregate is typically extracted rock from an open excavation (e.g. a quarry) that is reduced to usable sizes by mechanical crushing. Manufactured aggregate is typically a byproduct of other manufacturing processes such as slag from metallurgical processing (e.g. steel, tin, and copper production). Manufactured aggregate also includes specialty materials that are produced to have a particular physical characteristic not found in natural rock, such as, for example, low density. The gradation of the aggregates is carefully controlled in a hot mix design to optimize its performance. Hot mix designs can be categorized in “dense graded,” Stone Matrix Asphalt (SMA), Open Graded Friction Course (OGFC) and the like based on the relative proportions of the aggregate sized. In an exemplary embodiment, about 3 to about 8 wt. % of the asphalt binder is mixed with about 92 to about 97 wt. % aggregate to form an asphalt paving material. Other well-known additives also can be added to the hot mix, including anti-stripping materials, warm mix additives, fibers and the like.

(16) In an exemplary embodiment, a method for preparing an asphalt binder as contemplated herein is provided. The method includes heating the base asphalt to a sufficiently liquid state such that the plastomer and any other modifier can be more easily incorporated. In one embodiment, the base asphalt is heated to a temperature of about 75 to about 200° C. For faster incorporation, the temperature can be above the melting point of the plastomer. The asphalt can be neat or can contain other additives at this point, such as, for example, ground tire rubber (GTR), reclaimed asphalt pavement (RAP), reclaimed asphalt shingle (RAS), phosphoric acid, polyphosphoric acid, ethylene/vinyl acetate copolymer, and the like, or various combinations of these modifiers. The asphalt and a plastomer as contemplated herein are combined using, for example, a low shear mixer at a sufficient mixing speed to homogeneously incorporate the plastomer into the asphalt within a reasonable time frame. In a lab, for example, the low shear mixer can operate with a mixing speed of from about 5 to about 800 revolutions per minute (RPM). If the asphalt does not yet contain sulfur; sulfur-containing compounds, such as hydrocarbyl polysulfides and thiuram disulfides; phenolic resins; metal oxides; or a combination thereof, one or more of these additives can be added to the asphalt binder at this time. The mixing continues for a time sufficient to make a homogeneous blend, such as about 30 minutes to about four hours.

(17) Table 1 illustrates the results of tests of stress sensitivity J.sub.nr,diff of asphalt binders containing plastomers exhibiting two different drop points. The asphalt binders are formed from two different base asphalts, PG 64-22A and PG 64-22B, both from the mid-continent region of the United States. The asphalt binders contained 97.55 wt. % base asphalt and 2.45 wt. % plastomer. The tests are conducted at the operational environmental temperatures of 64° C. and 76° C.

(18) TABLE-US-00002 TABLE 1 drop point Jnr-diff @ 64° C. polymer (° C.) 64-22A 64-22B Honeywell Titan ™ 7686 136 42.20% 68.26% Honeywell Titan ™ 7278 152 26.80% 35.51% drop point Jnr-diff @ 76° C. Polymer (° C.) 64-22A 64-22B Honeywell Titan ™ 7686 136 125.05% 133.74% Honeywell Titan ™ 7278 152 30.18% 47.65%
As Table 1 shows, the asphalt binders with a plastomer having a drop point below 139° C. had higher J.sub.nr,diff values than the plastomer with the drop point above 139° C. and failed the MSCR specification at 76° C., that is, the J.sub.nr,diff is above 75%, while the asphalt binders with a plastomer having a drop point above 139° C. passed the MSCR specification, that is, the J.sub.nr,diff is significantly below 75% at both testing temperatures.

(19) FIG. 1 illustrates the results of tests of stress sensitivity J.sub.nr,diff performed on asphalt binders containing seven different plastomers. Three of the asphalt binders contained plastomers exhibiting different drop points below 139° C., that is, 136° C., 126.5° C., and 126° C. As shown in FIG. 1, these three different asphalt binders failed the MSCR specification with J.sub.nr,diff above 75%. The asphalt binders with plastomers having drop points above 139° C. all passed the MSCR specification. FIG. 2 is a graphic illustration of FIG. 1 with the plastomer drop points on the x-axis 10 and J.sub.nr,diff on the y-axis 20. From FIG. 2 it appears that as the drop point of the plastomer added to the asphalt binder increased, J.sub.nr,diff of the asphalt binder decreased.

(20) Table 2 illustrates the effects of sulfur on asphalt binders contemplated herein. Results of non-recoverable creep compliance, J.sub.nr, and stress sensitivity J.sub.nr,diff tests performed on a neat asphalt binder and the asphalt binder with plastomers having two different drop points are shown. The asphalt binder 64-22 E was from the mid-continent region of the United States. Honeywell Titan™ 7205 is a mid-density (a density of about 0.925 to about 0.94 gm/cm.sup.3) polyethylene homopolymer with a drop point of 115° C. and Honeywell Titan™ 7278 has a drop point of 152° C.

(21) TABLE-US-00003 TABLE 2 Composition PG 64-22 E 100.00% 99.90% 97.00% 96.9% 97.3% 97.5% 97.4% Honeywell Titan ™ 7205 3.0% 3.0% 2.5% Honeywell Titan ™ 7278 2.5% 2.5% Sulfur 0.1% 0.1% 0.2% 0.1% Total 1.00 1.00 1.00 1.00 1.00 1.00 1.00 MSCR Temp Specification (° C.) J.sub.nr, 3.2 kPa(kPa.sup.−1) 64 2.570 2.120 1.047 0.865 0.975 1.170 0.873 J.sub.nr diff <= 75% 64 8.88% 10.35% 102.78% 71.83% 53.79% 29.52% 26.35% MSCR grade 64S 64S failed 64V 64V 64H 64V
As shown in Table 2, for the neat asphalt binder, the addition of sulfur caused the non-recoverable creep compliance, J.sub.nr, to drop slightly, although the MSCR grade remained the same at “S.” The asphalt binder with the 3 wt. % plastomer having a drop point no greater than 139° C. failed the stress sensitivity parameter J.sub.nr,diff specification. However, the addition of 0.1% sulfur caused the asphalt binder to exhibit an “V” grade in addition to passing the stress sensitivity parameter J.sub.nr,diff specification. The addition of 0.2% sulfur to the binder containing 2.5 wt. % plastomer caused the asphalt binder to make a PG 64V grade and exhibit an even lower J.sub.nr,diff value at 53.79%. Adding 2.5 wt. % plastomer with a drop point greater than 139° C. (Honeywell Titan™ 7278) to the neat asphalt binder dropped the J.sub.nr value and raised the MSCR grade from an “S” to a “H.” However, the addition of 0.1% sulfur served to drop the J.sub.nr value even further, raising the MSCR grade from an “H” to a “V” while also dropping the J.sub.nr,diff value. Thus, use of the plastomer with a drop point greater than 139° C. enabled less plastomer to meet the PG 64H-22 grade and less plastomer and less sulfur to meet the PG 64V-22 grade.

(22) While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.