US3006831A

US3006831A - Radiation of asphalts

Info

Publication number: US3006831A
Application number: US683250A
Authority: US
Inventors: John C Illman
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1957-09-11
Filing date: 1957-09-11
Publication date: 1961-10-31
Anticipated expiration: 1978-10-31

Description

Oct. 31, 1961 J. c. n LMAN RADIATION oF AsPHALTs Filed Sept. 11, 1957 INVENTORI JHN c.. BY:

@S/w14 mf- ILLMAN Unite 3,006,831 Patented Oct. 31, 1961 3,006,831 RADIATIGN F ASPHALTS John C. Illman, El Cerrito, Calif., assiguor to Shell Oil Company, a corporation of Delaware Filed Sept. 11, 1957, Ser. No. 683,250 3 Claims. (Cl. 204-154) This invention relates to an improved process for the preparation of asphalt compositions. More particularly, it is concerned with a process for the improvement in viscosity-temperature relationship of asphalt compositions and improvement in their weathering characteristics. Another aspect of this invention concerns an improved process for the operation of radiation producing apparatus.

Asphalts have been divided arbitrarily with respect to their components into two general classes thereof, namely, asphaltenes and maltenes. This division is normally achieved by means of solvent fractionation. The asphaltenes constitute that portion of the asphalt which is precipitated by lower aliphatic hydrocarbons, such as gasoline or isopentane or the like. Maltenes comprise the portion fully soluble in the medium employed for asphaltene precipitation and consist `of saturates, aromatics and resins. Asphaltenes are normally regarded as high molecular weight polycyclic materials containing substantial proportions of heterocyclic rings wherein nitrogen, sulfur and oxygen are present in the ring structures.

Depending upon the source and previous history of asphalts relative to their isolation and preparation, they may vary widely in their response to thermal influences with respect to changes in viscosity. Moreover, there is a wide variation in the quality of an asphalt relative to its ability to withstand the adverse effects present during weathering, such as may occur when the material is employed Ias a shingle coating or for other types of rooting and the like.

The change of viscosity with temperature should be kept within certain desired limits depending on the use to which the asphalt is to be put. The slope of the viscosity-temperature line should for many purposes be kept as fiat as possible so as to maintain a relatively narrow range of viscosity diierence upon changes in the temperature of the asphalt composition. For example, if the asphalt is to be applied under low temperature conditions such as winter preparation of roads and the like, it is highly disadvantageous for the asphalt to stiffen to an unworkable consistency wherein it is diicult or impossible to employ the usual road building equipment or where it is as stiff as to make satisfactory coating of the aggregate employed in road compositions impossible. On the other hand, roofing asphalts, which are applied while hot, should not be too Huid at such application temperatures. Likewise, it is necessary for an asphalt to withstand the adverse effects of weathering to a substantial extent if the material is to be employed for rooting or coating purposes. For example, it should not exhibit any abnormal tendency to form cracks or pin holes in the coating if it is to be employed for these purposes.

It is an object of the present invention to improve the compatability of the several asphalt components, namely, of asphaltenes with maltenes of high saturate content or of low carbon-to-hydrogen ratio. It is a further object of the present invention to improve the viscosity-temperature relationship of asphalt compositions. It is another object of this invention to provide a process for the improvement in weathering characteristics of asphalt compositions. Other objects will become evident during the discussion of the invention.

Now, in accordance with the present invention, it has been found that these and other asphalt properties can be substantially improved by subjecting a mixture of asphaltene-containing asphalts and alkylating agents containing alkyl radicals of 5-36 (preferably 8-24) carbon atoms per molecule to the elfect of ionizing radiation for a radiation period sufficient to substantially improve the weathering characteristics of the asphalt. Again, in accordance with the present invention, an improved process has been found for the operation of radiation emitting apparatus which comprises utilizing as the moderatorcoolant therefor the mixture as described above.

One aspect of the invention comprises the discovery that treatment of asphaltenes by radiation in the presence of alkylating agents is far more effective if the asphaltenes have been isolated or concentrated prior to irradiation, the remaining components of the original asphalt (maltenes) not being present during -the radiation period. If desired, of course, the irradiated asphaltenes can thereafter be recombined with the maltenes and/ or other components for the eventual preparation of a great variety of asphalt compositions.

The -type of asphalt to which the present invention particularly applies is not critical other than that the asphalt should contain a suiiicient amount of asphaltene components to be substantially `altered upon irradiation in the presence of an alkylating agent, preferably an alkane. Hence, the well-known varieties of straight run, blown or cracked asphalts as well as mixtures thereof. Paving grade, coating grade, and saturant `grade asphalts may be utilized in the process under consideration or mixtures of these may be so utilized. In addition and preferably the asphaltene components of these asphalts as obtained by the usual refinery processes are concentrated or isolated from the other non-asphaltene components of the asphalt prior to exposure to radiation. Asphaltenes showing the most favorable response to the process comprise those of highly aromatic character containing few or short side chains. Economically, of course, it is preferable to employ an asphalt having at least 5% by weight of asphaltenes and preferably more than about 20% by weight of asphaltenes so as to have a minimum of disposable maltene fractions and a maximum of radiation sensitive asphaltene fractions.

One aspect of the invention comprises irradiation of maltenes or aromatic petroleum fractions having molecular weights above 400 in the presence of alkylating agents and thereafter oxidizing (air blowing) the irradiated product to convert a portion thereof to asphaltenes. Hence, the present process will be understood to apply not only to hard asphalts, i.e. those having penetrations from 0 to 10 (ASTM Method D525, 77 F., 100 gram load, 5 seconds), but also other relatively softer asphaltic residues, preferably having a maximum of about 200` penetration and such materials as residual industrial fuel oils having viscosities as low as about 45 SSF at 122 F., for example, 45-300 SSF as measured by the same test. In addition to having such penetration characteristics, the asphalts will generally have softening points between about 70 F. and 350 F. They include straight run asphalts, steam distilled asphalts, blown asphalts, solvent reiined asphalts, cracked asphalts, vacuum ashed asphalts and similar asphaltic residues as well as native asphalts and asphaltites, all of which preferably comprise at least about 5% by weight of asphaltenes.

The term asphaltenes is defined in Abraham, fifth edition, of Asphalts and Allied Substances on pages 1165-6 as being the non-mineral constituents remaining insoluble in petroleum naphtha, thus differentiating them from the maltenes (petrolenes) which dissolve in the same medium and under the same conditions. As the test is made at room temperature (65-75 F.), this latter would constitute a further limitation. A still further limitation would comprise the proportion of petroleum naphtha employed for the purpose of causing the separation. According to the standardized method, 50 volumes of petroleum naphtha are employed, the test temperature normally being ambient (room) temperature. While this standard procedure defines the term, it will be understood that the asphaltic fraction insoluble at room temperature in any-aliphatic hydrocarbon having 5-12 carbon atoms per molecule may be regarded as asphaltene for the present invention. Y Y Y The asphalts may be introduced into the aliphatic hydrocarbon precipitant (C5 12 alkanes) by lseveral alternative means, dependent upon their physical characteristics. For example, hardasphalts (especially cracked or blown), i.e. those 'having a penetration at 77 F. less than about 10 are preferably introduced by first dissolving them in a minimum amount of aromatic hydrocarbon solvent. In order to minimize the effect of the solvent upon the precipitation of the asphaltene, it is preferred that the proportion'of solvent be restricted to between about 0.5 and 2 volumes Yfor each volume of the asphaltic residue. The aromatic solvent is preferably onepredominating in aromatic hydrocarbons having less than l carbon atoms per molecule of which benzene andtoluene are suitable members. Preferably, the aromatic solvent contains at least about 70% by weight of such aromatic hydrocarbons and'more desirably contains 85% or more of such hydrocarbons. r The solution may take place at room temperature or, preferably, at reflux temperature in order to hasten the process. Softer asphalts, i.e. those having penetrations 4greater than about l0 at 77 F. may be dispersed suiciently for the present purpose by reiluxing in the presence of a Vlimited proportion of the precipitating aliphatic hydrocarbon, although the aromatic solvent may be used in addition to or in place of the aliphatic medium. The proportion again is preferably limited to'between about 0.5 and 2 volumes of the refluxing medium for each volume ofthe asphalt, 4regardless of whether or not the reuxing medium comprises entirely aliphatic hydrocarbons havingr5l2 carbon atoms per molecule or additionally contains aromatic hydrocarbons as well.

The maltene solution and the precipitated particles are separated by any suitable means including filtration, centrifuging, sedimentation, decanting or similar treatment. Following separation of the asphaltene particles they are then suspended in the alkylating agent which should be fluid at the handling temperatures and subjected to radiation. As stated hereinbefore, of course, it is possible to irradiate full asphalts without previous fractionation to concentrate or isolate the asphaltene proportion thereof. However, the effectiveness of radiation is greatly increased by removing or substantially decreasing the maltenes or, conversely, concentrating or isolating the asphaltenes and subjecting the latter to irradiation in the substantial absence of the maltene fraction.

The kinds o f radiation suitable for usc in the present invention include high energy electrons and photons. Electron beams are suitably produced by electron accelerators such as the Van de Graa and linear accelerators or conceivably by a suitable arrangement of certain isotopes, e.g. strontium 90. High energy photons suitable for use are, for example, X-rays produced by conventional X-ray tubes and electron accelerators and gamma rays which may be produced by decay of radioactive materials such .as cobalt 60, cesium 137 and iission products.

Although somewhat different eifects may be observed in irradiation by heavy particles, the present invention contemplates particularly the use of high energy protons, alpha particles or neutrons. Proton beams are produced, for example, by accelerators such as Van de Graaff, linear accelerators and cyclotrons. Alpha particles may be produced in the same type of accelerators such as protons or can be produced by decay of radioactive materials, e.g. radium, polonium, uranium and plutonium. Fast neutrons may be obtained within a nuclear reactor or may be obtained as a beam out of a nuclear reactor. Fast neutrons act on hydrocarbons mainly by transferring their energy to protons, which, being charged, induce ionization and excitation as they pass through the asphaltene and alkylating agent mixture.

The devices suitable for producing beams of electrons, protons, alpha particles, X-rays, fast neutrons and slow neutrons are Well known in the art and need not be described herein detail. The preferred process comprises passage of an asphaltene-alkylating agent mixture through a nuclear reactor which may at the same time be ernployed for power producing purposes or may be utilized exclusively for the treatment described and claimed herewith, AMethods and apparatus for irradiating materials by means of radiation resulting from decay of radioactive substances are also` well known. Y Sources such as rods containing a highconcentration of .cobalt 60 are used in various arrangements for the irradiation of materials as described, for example, in the pertinent paper by Burton etal. ANucleonics 1,3(No. 10), 74 (1955) and references cited therein,

transparent to the beam so that itis irradiated in a flow system. In either case, provision is made to remove a small amount. of gas,. generally mainly hydrogen and/ or 'Y methane, which may be formed during the irradiation.

Table I- illustratesV suitable windows and cell construction materials to be used with Various types of radiations. The Whole cell or conduit withinthe eld of radiation may be made of the transparent material.

TABLE 1 Radiat-i011 oen Material Window` X olf Gamma 1/4 @LDI/10" S.S. (or any other none needed.

me a

fast neutrons Aluminum (or metals of low Do.

p Y capture cross section). electrons Any Thin aluminum foil. Y

VIn a-special modification of the present invention the reaction mixture is exposed to radiation in a nuclear reactor. A suitable reactor is described in substantial detail in Ythe'l-"ermi et al.V patent, UgS. 2,708,656.

'One ofthe preferred means of exposure, due particularly tothe relatively low cost of the treatment, comprises suspension of spentY nuclear fuel elements (removed from nuclear reactors) in a tank containing the asphalts and alkylating agents. An ordinary storage tank, properly shielded may be used, and theV mixture of asphalts and alkylating agents Vshould be circulated, so as to eiect unif orm exposure to the spent fuel elements. Y

,e In effecting irradiation of the typev herein contemplated,

the feed mixtures may be introduced into the interior'of areaetor as,'for example, in a'well designed for` that purpose or through a coolingl tube or tubes.

' The `mixtures to be treated may be introduced into the Y reactor or into the path o'f the fast or high energy beam in a continuous liow through a conduit, or Vmay be placed inV a receptacle'in the reactor or in the path of the beam and subjected to irradiation while they are substantially static. Y VIt is particularly contemplamed to modify a reactor such as described in theabovefidentied Fernii et alfpatent andl reactor, Yconversion of theV asphaltene-containing 'material (Whether it constitutes a whole asphalt or the asphaltene fraction thereof) and, secondarily, the production of heat which is absorbed by the reaction mixture just described and can be transmitted by any direct heat transfer and thereafter utilized in well known heat utilization processes.

The reaction may be carried out at atmospheric temperatures or at lower temperatures down to 20 C. or less and at higher temperatures up to 300 C. or more (but below decomposition temperatures) provided the reactions are maintained in a condensed (liquid) phase. 'Ihe pressure also does not significantly affect the results, so long as the reactants are under suicient pressure to retain them in liquid form within the irradiation equipment.

The time of exposure of the asphaltene and alkylating agent mixture to radiation is a function of the intensity of radiation employed, the geometry of the reaction zone, and the desired degree of conversion.

When utilizing an ionizing radiation source such as waste fission products from a nuclear reactor and temperatures between about 10 C. and about 50 C., the time of exposure to such ionizing radiation as is normally produced therein is preferably between about 50 hours and about 500 hours in order to substantially alter and improve the blending characteristics of the asphaltenes and thereafter the viscosity-temperature characteristics of the asphalts with which they are combined and at the same time .to improve the weatherability of the material so treated. The extent of exposure should be 10'I to 1.5 X 109 rads, a rad being defined as 100 ergs. of ionizing energy per gram of the irradiated mixture.

Alkylating agents include especially alkyl halides, alkenes and preferably alkanes, all of which should contain alkyl radicals having from 5-36 carbon atoms per molecule and preferably between about 8 and 24 carbon atoms per molecule. Maximum beneficial effects are obtained -by radiation of a mixture comprising asphaltenes and alkylating agents producing a preponderance of alkyl radicals having from l to 18 carbon atoms per molecule. Wax-containing asphalts may be irradiated, the waxes in this case constituting the alkylation agent. It is preferred practice to mix 0.1- volumes of alkylating agent with 1 volume of asphalt or asphaltene.

Following exposure of the asphaltenes to the influence of radiation in the presence of alkylating agents such as those described hereinbefore the product is thereafter separated into irradiated asphaltene-,containing material and unreacted low molecular weight alkylating agents. These agents may comprise alkanes (normal or branched) such as octane, nonane, decane, `dodecane, tetradecane, hexadecane, octadecane, etc. as well as the alkyl halides and especially the alkyl chlorides bearing the same radicals. The corresponding olefins may be utilized as well. Dependent upon whether or not the whole asphalt was subjected to irradiation, one subsequent step in the utilization of the radiated asphaltenes comprises combination with other materials for use for such pur-poses as roofing compounds, saturants for roofing felts, coating compounds or paving grade asphalts. The materials utillized for this purpose in each of the several end uses are well known in the art and do not constitute a part of the present invention. In accordance with one aspect of the invention wherein asphaltenes were irradiated in the substantial absence of non-asphaltene components of as phalts, the irradiated product after separation from the alkylating agents may be combined with maltenes either natural or synthetic in such proportions as to reconstitute a commercial grade asphalt. Of course, maltenes can be added to an irradiated product irrespective of whether or not the product was an asphalt or just the asphaltene portion thereof. It will be understood that the radiation not only causes alkylation of the asphaltenes by radicals from the alkylating agent but also effects an indeterminant amount of polymerization of the product either in the asphaltene aromatic nuclei or within or between alkyl radicals which become attached to the asphaltene nuclei.

One of the striking and beneficial effects of the present invention comprises the reduced temperature susceptibility caused by the radiation effects occurring in the presence of the alkylating agent. This improvement in the viscosity-temperature slope is `an important technical advance highly desirable for many purposes. For example, in paving grade asphalt, it is to be desired that the temperature susceptibility of the composition be as low as possible so as to minimize differences in consistency of a road during both hot and cold weather.

An additional advantage of substantial economic importance comprises the improvement in weatherability of asphalt compositions wherein the asphaltenes have been subjected to irradiation in the presence of alkylating agents such as described hereinbefore. The working examples given hereinafter demonstrate this beneficial feature. The implications of this improvement are that asphalts so treated will withstand the adverse effects of exposure to weather as experienced in commercial end uses such as roofing or paving grade asphalts and the like to a much greater degree than if the asphaltenes have not been conver-ted, alkylated, polymerized or otherwise altered by irradiation in the presence of the alkylating agents.

While the irradiation of the whole asphalt is satisfactory, it has been found that the presence of non-asphaltene fractions tends to mask the beneficial alterations of the asphaltenes by irradiation in the presence of the alkylating agents. The reason for this is that the maltenes are also being alkylated by the alkylating agent to a limited degree and at the same time act as a radiation absorbent, thus preventing a maximum amount of irradiation from reaching the asphaltenes which are Amost subject to alteration by irradiation in the presence `of alkylating agents.

While irradiation may be conducted with the reaction mixtures in stationary forms such as in pans, trays, films and the like it is prefer-red and more economical procedure to treat the reaction mixture while it is under dynamic flow conditions such as in pipes or moving films. The pipe arrangements can be such that the reaction mixture is introduced into a nuclear reactor (or other irradi- .ation source), circulated for a time sufficient to cause the predetermined degree of alteration desired and thereafter passed to a refinery separator for the splitting of the asphaltene containing irradiated material from the unaltered alkylating agent. Recycling processes are contemplated and combination of the irradiated asphaltenes with maltenes from which they were separated prior to irradiation or with maltenes from entirely different sources dependent upon the properties desired in the finally constituted product.

The figure appended to this specification shows several typical processes which might be used in carrying out the present invention. In the figure, an alkylating agent such as an alkane from source 1 is combined with an asphalt from a storage tank 2, the mixture being passed by means of line 3 to a radiation source such as a nuclear power plant 4. 'Ihe irradiated mixture is passed through a heat exchanger for removal of heat adsorbed in the nuclear power plant, and the cooled irradiated mixture is sent to a distillation column 6. In this column the unconverted alkylating agent is distilled overhead, the bottoms constituting the irradiated asphalt which is sent to storage tank 7.

A second type of process which permits maximum radiation of the asphaltenes can be performed in a similar line of apparatus, the asphalt from source 2 being combined with a precipitating agent such as isopentane from tank 8, the mixture being sent to a separator 9 so that the precipitated asphaltenes may be separated and passed through line 10 and thereafter line 3 in combination with an alkylating agent such a decane or isooctane` for irradiation heat exchanging and separation of the products, the separated irradiated products being finally sent tostorage tank 12. The solution of maltenes from separator 9 is sent to a storage area 11 and thereafter blended with the improved irradiated asphaltenes yfrom source 12 in blender 13 to obtain an asphalt composition having 'improved viscosity-temperature relationship and improved Weatherability characteristics. Still a third process comprises utilization of maltenes which have been obtained by separation from asphaltenes which haveV originated from an entirely different source and type of asphalt.

The following examples illustrate the benefits to be obtained by the use of the present invention.

Example I The asphalt employed for this test was the residue from the distillation of a California San Joaquin Valley crude and had the following properties:

Penetration at 77 F., 100 g., A5 sec., `dmm., 35 Softening point (Ring and Ball) F., 124

Atomic Pen SP, Atomic Percent C/H Mol. Wt. Asphalt at C/H Asphal- Ratio of of As- 77 F. Ratio tenes Asphalphaltene tene Original 35 124 0 70 14 0. 91 2,000 Irradiated 1 104 l lll 0. 67 12 0.83 3, 700 Air Blown Original 1 205 41. 5 0. 89 2, 700 Air Blown I rradiated 4 201 40` 0 0. 83 5, 500

1 May contain a trace of unreacted cetane.

The asphaltenes precipitated from the original asphalt and also from the irradiated asphalt were mixed with squalane .to determine the compatibility therewith. It was found that the origin-al asphaltenes were compatible at room temperature with 22% by weight of a squalane while the asphaltenes from the irradiated asphalt were much more compatible with squalane, forming aV homogeneous mixture with 33% by weight of squalane.

Compositions were prepared by blending approximately equal quantities of the asphaltenes from'the blown original asphalt or from the blown irradiated asphalt with an industrial lubricating oil rainate. The compositions so obtained had approximately the same penetration and softening point andwere spreadV on panels and subjected to Weatherometer testing. TheA composition containing the blown original asphalt failed after one cycle while the blown irradiated asphalt composition did not fail until 22 cycles in the Weatherometer test machine.

Example Il The product obtained in Example I above was tested for viscosity over a temperature range and compared with the viscosity of the original non-irradiated asphalt.

Viscosity, cs. Viscosity, Asphalt Tempera- Y ture 39.2 F. 77 F. 140 F. Slope 1 Original 3. 9X10 4. 98)(10E 2. 93 l05 -4. 18 Irradiated 2. GX10 7. 50)(10E 6. 315x105 `3. 82

1 Log log vis11log log visno Example IV Y An asphalt containing 5%V by weight of hydrocarbon waxes per molecule having 20-60 carbon atoms is irradiated to 1 108 rads in a storage tank at ambient temperature by exposure to spent uranium reactor fuel elements. The product exhibited improved lowV temperature properties -and adhesion to mineral aggregate than if the Yirradiation treatment is omitted.

Y Y Example V A nuclear energy power yplant of the water boiler reactor .type is operated with uranium fuel elements, the moderator and coolant being a mixture of equal volumes of octadecanes and `an asphalt having an original penetration at 77 F. of 60. The moderator-coolant is circulated throughout the reactor for a time sumcient to receive an exposure ofA about 1.8 108 rads and then is sent to a Yrecovery system to remove unaltered octadecanes romtheirradiated mixture.

I claim as my invention:

1. In the process for the preparation of asphalt compositions having improved Weatherability, the steps comprising admixing substantial proportionsl of asphalt containing at least 5% by weight of asphaltenesand an alkane having 5-36 carbon atoms per molecule, exposing the mixture so yformed to high energy ionizing radiation for a dosage of 10FI to 1.5 X 109 rads and recovering the irradiated asphalt product, the exposure being suicient to substantially improve the weatherability of the asphalt.

2. A process for the preparation of an asphalt composition having improved weatherability which comprises solvent fractionating an asphalt whereby an asphaltenerich fraction is separated from a maltene-rich fraction, yadmixing the asphaltene-fraction with a substantial proportion of a C844 saturated aliphatic hydrocarbon, exposing the mixture so formed to high energy ionizing radiation for 50-500 hours at 20", C. to 300' C. to obtain -a dosageof 10l to 109 rads, said dosage being sufficient to substantially -alter the chemical compositionof ,the mixture, and recovering the irradiated product, Awhereby an asphalt having improved weatherabili-ty is obtained.

3. A process for the preparation of an asphalt composition having improved compatibility which comprises introducing into an electron radiation zone a mixture of an asphalt containing at least 5% by weight ofasphaltenes and 0.1-5 parts-by weight, based onthe asphalt, of asubst-antiaily straight chain alkane having between 10 and 20 carbon atoms-per molecule, whereby the'mixture is subjected to bombardment by high Yenergy electrons, maintaining the mixture for 50 to'500 hours at a temperature between about 20 C. and about- 300 C. to a dosage between 10r1 and 1.5 109, wherebyV asphaltenes are alkylated by said alkane removing the irradiated product from the radiation zone and recovering irradiated asphaltene product from-the mbture, whereby an asphalt composition is obtained.

AReferences Cited'in the file of thisfpatent i UNITED STATES PATENTS 1,868,879 Boadhead et al. July 26, 1932 y1,988,715 Bray et a1. Ian."22, 1935 2,247,375 Hersberger July 1,.'194'1Y 2,383,769 Caplan Aug. 28,*19'45 (Other references onfollowingY page) 9 FOREIGN PATENTS Great Britain May 12, 1954 Great Britain Nov. 2, 1955 Great Britain Nov. 23, 1955 France June 24, 1957 OTHER REFERENCES COO-198 Utilization of Gross Fission Product, Prog-

Claims

1. IN THE PROCESS FOR THE PREPARATION OF ASPHALT COMPOSITIONS HAVING IMPROVED WEATHERABILITY, THE STEPS COMPRISING ADMIXING SUBSTANTIAL PROPORTIONS OF ASPHALT CONTAINING AT LEAST 5% BY WEIGHT OF ASPHALTENES AND AN ALKANE HAVING 5-36 CARBON ATOMS PER MOLECULE, EXPOSING THE MIXTURE SO FORMED TO HIGH ENERGY IONIZIND RADIATION FOR A DOSAGE OF 107 TO 1.5X109 RADS AND RECOVERING THE IRRADIATED ASPHALT PRODUCT, THE EXPOSURE BEING SUFFICIENT TO SUBSTANTIALLY IMPROVE THE WEATHERABILITY OF THE ASPHALT.