CA1087805A - Rubberized asphalt paving composition and use thereof - Google Patents

Abstract

"Abstract of Disclosure"
The dissolving and/or dispersing of relatively large proportions of reclaimed rubber into molten paving asphalts is facilitated by incorporating into the asphalt a minor porportion of a highly aromatic, high-boiling, high-flash-point mineral oil.
The resulting mixtures can be held at temperatures above 300°F
for substantial periods of time without becoming too viscous for convenient handling, thereby facilitating the application thereof to roadways. The rubberized asphalt mixtures are particularly useful in the form of stress absorbing membrane interlayers between old, damaged pavement surfaces and an overlayer of new asphalt concrete, for providing chip-seal coatings over old pave-ment, as crack fillers in Portland Cement concrete or asphalt concrete pavements, and bridge deck waterproofing membranes.

Description

~L~3~'7~i/05 In recent years numerous advantages have been found for inco~porating various rubbers, or rubber-like polymers into paving asphalts. The added rubber can give the asphalt improved tensile strength, elasticity, and ductility, and can reduce its susceptibili~y to cracking and disintegration due to mechanical stress and/or extreme temperature changes. The extent to which these advantages can be realized however depends upon the pro-portion and type of rubber which is utilized, and the extent to which it is dissolved or uniformly dispersed in the asphalt.
Until very recen~ly, the art has contemplated the use of rubber-ized asphalts primarily as the cement for asphalt concretes and for this particular use economics dictated that no more than about 5 weight-percent of rubber could be used. These small pro-portions give some benefit, primariIy in the area of improved ductility (as disclosed for example in U.S. patent No, 3,779, 964), but give little improvement in other physical properties.
It was also found difficult under practical conditions to obtain a uniform solution or dispersion of rubber in the asphalt. One known procedure was the addition of a latex emulsion, but -this was found to be impractical because of the necessity of flashing the water from the asphalt mixture thus formed. In addition, asphalt viscosity is often reduced adversely by aqueous latex emulsions. ~
In U.S. patent No. 3,891,585 to McDonald, some progress ~ ;
was made toward achieving more of the potentially available bene-fits from the addition of rubber to asphalts. In this patent, relatively large proportions of ground~ reclaimed rubber, rangmg be*ween 25% and 33% by weight~ are ~tilized in the asphalt mix~
and the mixture is used in the form of relatively thin layers or membranes applied over old pavernents~ the membranes then being dressed with mineral aggregate or rock chips. The asphalt-rubb~r :

' mixture was prepared by heating the granulated rubber with the asphalt at temperatures between about 350~ and 500F, to form a "jellied" composition which provided a coating of excellent elasticity, tensile strength and durability under adverse weather conditions. However, as acknowledged by the patentee and his co-inventor Winters in their subsequent U.S. patent ~o. 3,919,1483 the use of this jellied material present2d one ~ , drawback; because of îts viscous nature, special equipment and techniques were required for its application. It must be applied ;~
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1~ rapidly before it sets up, and the chips or aggregate must be applied to the layer of material before it sets up, in order to insure retention of the chipso All of this imposes severe time limitations upon the mixing and application of the mixture to the pavement.
To overcome the a~ove noted difficulty, Winters et al in their patent No. 3,919,148, suggest adding to the jellied rubber-asphalt mixture of small proportion of a light hydrocarbcn solvent such as kerosene. This is said to bring about a tempo rary reduction in viscosity for up to about 1 hour, during which 20 time the mixture can be applied to the roadway and the applica-tion of rock chips completed. After rolling the chips into place it is said that "a reaction occurs between the kerosene and the asphalt-rubber composition that results in a rapid increase in ~ viscosity and the chips are set into place so that they are not ; dislodged by traffic." It is conceded that if the applioation of ;
chips is delayed beyond the "set'l, the chips will not sufficient-i ~, --:
ly adhere to the asphalt to withstand vehicle traffic.
7 From the foregoing, it will be apparent that even with ~ the addition of kerosene, Winters et al are still faced with a !. 30 critical and troublesome timing schedule for first forming the hot asphalt-rubber "gell', adding and homogeneously mixing the kerosene with the asphalt-rubber, applying the resulting mixture

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to the roadway, and then applying the chips. In most ca6es, all of these oparations mus~ still be carried out in less than about l hour, which is obviously a difficult limitation to cope with in any sizeable job. It would appear therefore that the use of kerosene merely alleviates but does not solve the basic problem acknowledged by the patentees.
In addition to the foregoing, we have found that even with the use of kerosene as dcscribed by Winters et al, other problems are encountered in using the rubber-rich mixtureO
Firstly, the adhesive qualities of the asphalt~rubber blend are not as good as most other liquid asphalts and it is therefore generally necessary to make a light application of a liquid asphalt first, as a tack coat to the pavement being treatedg to act as a "glue" to assure that the rubberized asphalt will stick.
It is also generally necessary to use clean, dry~ high quality rock chips to cover the hot asphalt-rubber membrane; wet or -dirty chips do not a~quately adhere. These factors increase the cost of any project, and at times traffic is tied up longer due to the need for a tack coat.
Moreover, the high viscosity and gel-like nature of the rubber-asphalt mixture usually means that the hot blend will not flow readily into pavement cracks when such cracks are being sealed. This means that the cracks may be sealed over by a bridging action, or it is necessary to rout out the cracks first to widen them. Sealing is then accomplished in a separate opera~
tion, which is an added inconvenience and expense. Also, in -applying membranes of the mixture by conventional spraying -~
methods, the high viscosity of the mixture makes it more diffi-cult to obtain an even, smooth spray pattern from the asphalt distributor bar. '1Roping" or "ridging" can more easily occur~
which reduces the smoothness of the pavement9 It can also be unsightly and the ridges can pose tire tracking problems for a ~ Q~ I)S
vahicle.
Finally, the use of a light hydrocarbon solvent such as kerosene in itself presents additional problems. Since kerosene generally has a flash point of about 1300-150F, a fire hazard is presented. Further, some of the lighter fractions of the k~rosene are released to the atmosphere, creating an aiT pollution problem.
We have now discove~ed a novel technique by which all of ~he foregoing problems can be avoided or at least substantially alleviated.
According to our procedure, the base asphalt stock is ~irst modiied by blending therewith at elevated tempera~ures a minor pTOportion of a heavy, high-boiling, highly aromatic, high~flash-point mineral oil solvent, there-by forming a base stock ~o which the r~bber corponent, in granulated and powdered form, is then added. The resultin~ mixture is then heated with agitation a~ about 300-450F for about 0.5-2 hours, to obtain a homogeneous dispersion or solution of rubber in the base stock. Under no~nal conditions the resulting mix~ure presents no fire hazard o~ atmospheric pollution problems, and at temperatures abo~e about 325~ retains a fluid, easily spreadable consistency for periods of at least about 12 houTs or more in most cases. The resul~ing mixture can be spread over a roadway using standard equipment and spraying techniques to form a highly adherent membrane over the roadway, which generally requires no tack coat. Due to its relative-ly non-viscous consistency when applied to the roadway, cracks are illed and sealed rather than bridged overt No difficulty is encountered in ob-taining an eYen, smooth spray pattern from the asphalt distributor bar, to lay down smooth membranes ranging in thickness between about l/16-inch and 1/4-inch.
According to one aspect of the invenbion there is pro~ided a paving composition comprising a hea~-blended, substantially homogeneous com-posite of ~1) about 50 - 89 weight peTcent of an asphaltic co~ponent selected ~xo~ the class con~istlng o paving grade asphalts, slow cuTing liquid asphalts and road oils, (2~ between about 10% and 30% by weight of a re~
claimed rubber component, about 10~60 weight~percent o said reclaImed : , ~LO~'7~ S
~Ibbe~ component belng g~ound ~ulcanized natural rubber, and about 15-70 weight-percent the~eo~ being ground devulcanized rubber, and ~3) between about 1% and 20% by ~eight of a mineral oil solvent having a flash point above about 300F, and containing more than about 50 weight-peTcent aro-matics, at least about 50% of said solvent boiling above 700F, and at least about YOqO the~eof boiling above 600F.
AccoTding to another aspect of the invention theTe is provided a method for the manu~acture of a paving composition which comprises:
(l~ blending about 50-89 weight-percent, based on the final com- :
position, of an asphaltic component selected from the class consisting of molten paving gradR asphalts, slow curing liquid asphalts and road oils, with about 1-20 weight-percent of a mineral oil solvent having a flash point above about 350F, and containîng more than about 50 weignt-percent aro~atics, at least about 50% of said solvent boiling abo~e 100F~ and at least about 90% therof boiling above 600F;
~2) adding to the blend rom step ~l) about lO-30~ by weight, based on the final composition, of a granulated reclaimed Tubber component, about 1~-60 weight-percent of said reclaimed rubber component being ground :
vulcanized natural rubber, and about 15-70 weight-percent thereof being devulcanized rubber; and j (3) heating and agitating the resulting mixture at a te~perature between abou~ 300 and 500F for a time sufficient to produce a substantially homogeneous composite.
In addition to the fo~egoîng, it has been found that the added high-boiling solvent substantially increases the life, as well as the cold tempera~ure characte~istics and durability of '..' ''' ~ , .:, ., :.~ :

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1~ ~7 ~(15 pavement constructions made from the resulting asphalt-rubber compositions.
It was found however that when the ground rubber stock employed was composed exclusively of devulcanized and/or synthe-tic rubber, the cooled membranes were somewhat lacking in tough-ness and resiliency. But it was found further that this defici-ency could be remedied by including in the rubber stock employed a substantial proportion o vulcanized, ground reclaimed n~tural rubber. Road testing conducted to date indicates that such suitably compounded and applied membranes retain their toughness and resiliency over extended periods of time, in a manner similar to ~he membranes described in the McDonald and Winters et al patents.
Detailed Description Asphalts which may be utilized herein include any of the well known bituminous materials used heretofore in the paving art such as natural asphalts or those derived from petroleum refining, for example by vacuum distillation, solvent refining, steam refining with or without air blowing, and the like.
Paving grade asphalts are variously characterized t~roughout the United States, but for purposes of this invention the asphalt specifications adopted January l, 1974 by the Paciflc Coast Division of the Asphalt Institute will be utilized. According to these specifications, five basic grades of paving asphalt are designated, and characterized principally on theba~s of viscosity of their "aged residue" (AR), i.e., their viscosity after a standard aging procedure designed to correlate with the hardening which occurs during pug--mill mixing of asphalt and aggregate. The specifications for these asphalts are as follows:

?';t~ 5 _____ , UNIFORM PACIFIC COAST ASPHALT SPECIFICATIONS
PAVING ASPHALT VISCOSITY GRADED AT 140 DEG.F(60C)ON ~FC RESIDUE
_ _ _ _ Specification Viscosity Grade Designation AR-1000 AR-2000 AR-40b~ -8000 AR-16000 ~, ......................... _ Tests on Kesldue ~rom RTFC Procedure-Calif.
Method 346E
Absolute Viscosl~
at 140~F (60C) 750- 1,500~ 3,000- 6,000-12,000-poise 1,250 2~500 5,000 10,00020,000 Klnematlc Vlscoslty at 275F (135C) cs,min.140 200 275 400550 _ _ _~
Penetration at 7~F
(25C) 100 g/5 sec.~n.65 40 25 20 20 ~. . . ~ __ , .
Percent o~ orlglnal penstration at 77F
(25C), min~ -- 40 45 50 52 Duc~rlity at 77F
(25C) cm,min. 100 100 75 75 75 _ TEST ON ORIGINAL ASPHALT
Flash point, Pensky-- Martens, F. min. 400 425 440 450 460 ~-,~ - . ~ . , _ __ _ __ ~olublllty ln Tr1-chlorethylene percent, min. 99 99 99 99 99 Any of the foregoing asphalts may be utilized herein, as well as others having suitable characteristics for use in pav-ing mixtures. Other suitable paving asphalts are penetration grade asphalts per A.S.T.M. specification D 946-69a and AASHTO
designation M-226 and similar specifications issued separately by several states. Slow curing (sc~ liquid asphalts or road oils-produ~ed either by reducing petroleum crude oil directly to grade by distillation, or by fluxing a paving asphalt with a light Qi are also suitable for such asphalt-rubber blends.
Those skilled in the art will readily understand that the selection of a suitable grade of asphalt depends primarily upon climatic conditions to which the paving will be subjected, softer grades being used in cold climates and harder grades for . ~ .

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warmer climates~ Also, for use a-t high elevations, above about ~500 feet, softer grades, conforming approximately to the AR-1000 or AR-2000 specifications 7 are preferred.
The rubber component employed herein may be either natural reclaimed rubber or synthetic reclaimed rubber. The synthetic rubbers are preferably polymer~ of open-chain conju-gated dienes having from 4 to 8 carbon atoms per molecule, for example 1,3 butadiene, 2,3-dimethyl-1~3-butadiene, and the like.
Examples of such polymers are polybutadiene, polyisoprene, poly-chlorQprene, butadiene-styrene copolymers and the like. Copoly-mers of mixtures of such conjugated dienes can also be used, as well as copolymers of monomer systems having a major amount of conjugated diene with a minor amount of copolymerizable monomer containing a vinylidene group.
As previously indicated, it is much preferred to util-ize a mixture comprising ground reclaimed, vulcanîzed natural rubber, and ground devulcanized natural and/or synthetic re-claimed rubber. The devulcanized reclaimed rubber component contributes to improved ductility, while the vulcanized reclaimed natural rubber (or partially devulcanized reclaimed natural rubber) contributes greatly to adhesion, toughness and resiliency. Vulcanized synthetic rubbers vary considerably in their rheological properties and solubilities in asphalt, but -they generally contribute somewhat to toughness and resiliency.
To obtain optimum combinations of their desirable physical characteristics, the relative proportions of the basic types of ground rubbers should fall within the following ranges~
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Weieh~ Percent ~ro~ ~a~
Devulcanized Reclaimed Natural or Synthetic Rubber 15 - 70 20 - 50 Vulcanized Scrap Natural Rubber 10 - 60 25 - 45 Vulcanized Scrap Synthetic Rubber 0 - 50 20 - 40 .~
Since the vulcanized rubber components are more diffi- ~
cult to blend in the solvent-asphalt mixture, it is preferred ~ ~`
that they be ground to pass at least 95% thereof through a No. -30 sieve ~AASTO designation M 92 sieve size). The devulcanized rubber component can be considerably more coarsely ground, such that 100% thereof will pass the No~ 10 sieve. ;
The mineral oil solvents employed herein are heavy -aromatic fracti~ns of petroleum, coal tar, tar sand oils, shale ~-~
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oils and the like, boiling generally in the range of about 700-1100F, and having a gravity ranging be~ween about 3 and 12~
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API. Th~ aromatic content of these oils generally ranges be~
20tween about 50 and 100 percent, preferably between about 60 percent and 95 percent by weight (clay-gel method). The content of saturated hydrocarbons should be lass than about 20 weight percent, preferably less than 12 weight percent. Polar compounds, such as heterocyclic nitrogen and sulfur compounds, may range between about 5 and 25 weight percent. The flash point, c.o.c. ';
of the oil should be above about 300F, preferably above 350F. ~ ~;
Oils of this character are generally derived from the solvent extraction of distillate or residual lubricating oil stocks, ~ usin~ solvents such as phenols, cresols, furfural and the like.
They may or may not contain asphaltenes, depending upon whether a distillate or residual feedstock is extracted. Heavy recycle --~
- oils derived from catalytic cracking operations, sometimes -8- ` ~

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called "slurry" oils, can also be utilized.
Examples of suitable solven~ oils are -those marketed by Shell Chemical Company under the trade ~ "Dutrex", those marketed by Sun Oil Company under ~he trade ~a~e "Sundex", and those marketed by Witco Chemical Company under the trade "Petroflux" and "Califlux". Particularly suitable oils are the following:

Dutrex Dutrex Dutrex Dutrex 419 739_ gl6 957 Gravity, API 8.8 5 Q 6 9.4 5.6 Flash Point, F 365 425 430 510 Distillation, F

50% 736 818 917 930 90% 840 884 Crk. Crk.

Viscosity-Gravity Constant 0.986 10004 ~-- 0.980 Molecular Analysis . (Clay-Gel, W%) Asphaltenes 0 0 3.9 n : Polar Compounds 15.4 18.0 22.1 26.8 : Aromatics 76.0 76.0 57.6 66.2 S~turates 8.6 6.0 16.4 7.0 The technique employed for compounding the three com-ponents is not particularly critical, the general requirements being to provide suitable means for agitating and heating the mixture at temperatures between about 300 and 500F, preferably about 350-450F. Agitation may be provided by suitable mechani- ;
cal means such as propellors, paddles, high-speed augers or the ` like, or by air injection through the body of liquid. All three components may be æimultaneously admixed and brought up to the desir~d temperature, but a much preferred procedure is to first . blend the solvent oil with the asphalt and bring the homogeneous mixture up to the desired blending temperature, and then mix in the ground, reclaimed rubber component. Preferably, the ground --: natural reclaimed rubber component is added first, and after - ':

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thorough mixing the devulcanized rubber is added. The time required to achieve homogeneity following addition of the natural rubber component generally ranges between about 0.5 and 2 hours, assuming that there is good agitation. Suitable pro-portions of *he three components in the final mixture fall with-in the following ranges:

Wei ht-Percent Broad Ran~e Preferr d R_nge A~phalt 50 - 89 65 - 86 Rubber (Total~ 10 - 30 12 - 20 Solvent Oil 1 - 20 2 - 15 .
The selection of specific optimum proportions of the ;
three components will depend upon several interrelated consid- ;
erations. Firstly~ ~or use in conjunction with the relatively soft grades of asphalt, in the AR-1000 to AR-4000 range, pro~ ` ~
portions of solvent oil in the lower ranges wiIl be utilized, ~-while higher proportions will be utilized in conjunction with the harder grades of asphalt. Also, it will generally be desir-20 able to utilize relatively large proportions of solvent oil ~ ~
when the overall rubber content of the composition is in the ~ ~-high range of e.g., 20-30 percent, especially when a large pro~
portion of the total rubber is ground, vulcanized natural rubber.
For use in chip seal overlays, where adhesivenes~ is an impor-tant consideration, rubber proportions of about Z0 percent should generally be used. If the final composition is to be utilized as a stress absorbing membrane interlayer or stress ;; ~
relieving interface, where the primary consideration is toughness A ~ ';,~-'', and elasticity, preferred rubber proportions should range between about 15-30 weight-percent~ By judicious experimentation under these precepts~ those skilled in the art will have little ~ -~~ difficulty in arriving at an optimum proportion of the three -10~

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components for any specific use.
Several important uses for th~ compositlons of this invention have been developed. On old roadways which have not been too badly damaged by weathering andtor stress cracking, a chip seal membrane overlayer is very effective. For this appli- ;
cation the pavement is first thoroughly bruomed~ and the hot asphalt-rubber mixture i5 then applied in conventional manner from a tank spray truck. Generally from about 0.5 - 1 gallon per square yard is sprayed on the pavement to provide a me~rane ranging in thickness between about 1/6-inch and 3/16-inch. The application is carried out at about 325~450F, usually about 375-425F~ After spreading, rock chips are applied to the surface in conventional manner, and immediately rolled into the membrane. Such chip seal membranes provide an effective ~later-proof sealant with good resiliency and wearing qualities.
Another important use, generally involving more heav-ily damaged roadways, lies in the area of stress absorbing membrane interlayers or stress relieving interface applied ahead of a conventional asphalt concrete overIay. For this purpose, 20 the ~ubber-asphalt membrane is applied substantially as des- ;
cribed above, and then given a light coating of rock chips or sand to enable temporary traffic and construction equipment to run on the membrane without damage. Then the hot asphalt con~
crete mixture is applied in conventional manner in varying thickness. The membrane interlayer seals -the concrete overlay from ground moisture and retards the appearance of reflection cracking in the overlay from the cracks in the old pavement Due to its elasticity, the interlayer membrane also substantially retards the appearance of new stress cracking in the overlay.
Membrane interlayers of this type are particulàrly desirable in cases where the asphalt concrete overlayer is limited ~n thick-ness to about 005-4 inches~ for it is in thin constructions of '; ~

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this type that reflection cracking from the old pavement is most troublesome.
Chip-seal membrane overlayers of the type described above are also very useful as bridge declc coatings, due primar-ily to their durable, wa~er sealing characteristics. In cold climates de-icing chemicals are often applied to the bridge decks, and such chemicals are highly corrosive to the metallic substructure of the bridge By providing a durable water~
proof seal, corrosion is greatly reduced. Also, such asphalt~
rubber membranes are capable of reduaing or eliminating surface cracking caused by bridga deck movement. `;
Stress absorbing membrane underlayers are useful in the case of new roadway construction. These underlayers are applied directly to the graded roadway in a manner similar to ~ `
that of membrane interlayers. The principal utility in this case lies in providing a water-proof seal against ground mois- `
ture and it keeps surface moisture from penetrating into and ~ ~
softening the roadway base. In the case of relatively thin ~ ;
asphalt concrete constructions~ stress and reflective cracking ., ~ .., 20 is also retarded. ` ~;
In addition to the foregoing, the compositions of this invention can also be utilized in conventional manner as crack ;
fillers in Portland Cement concrete or asphalt concrete pavement.
In this particular case, the qualities of resiliency, ductility and adhesiveness are~particularly beneficial in providing durable patching and sealing.
The following examples are cited to illustrate the invention, but are no~ to be construed as limiting in scope.
The rubber and soIvent components utilized in these examples are ide~tified as follows~
"Dutrex 739" - a distillate lubricating oil furfural extract, further characterized in Table 3 above.
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"Flo-Mix" - a screen size No~ 10-30 ground devulcanized reclaimed rubber (mostly synthetic) obtained from U. S. Rubber Reclaiming Company, Vicksburg, Mi&sissippi.
"G-248" - a screen size minus No. 30 mesh ground rubber scrap containing 53.7% natural vulcanized rubber, most of the remainder being vulcanized synthetic rubbcr~ This was also obtained from U. S, Rubber Reclaiming Company.
Example 1 A base asphalt stock was prepared by blending 87 parts by weight of an AR-8000 grade asphalt with 13 parts by weight of Dutrex 739, and the mixture was brought ~o a temperature of about 350F. About 20 parts by weight of Flo-Mix rubber was then blended into the base stock and the mixture was agitated for about 1 hour to provide a homogeneous blend. The mixture was held at about 350F for 2-3 hours in the mixing tank before being pumped through approximately 65 feet of pipeline to an adjacent pug-mill where it was blended with mineral aggregate to provide a hot mix asphalt concrete. The hot-mix was loaded ;
on trucks and transported to an experimental paving job where it was utilized to pave a one-half mile stretch of highway in Phoenix, Arizona. No difficulty was encountered in handling and pumping the rubberized asphalt mixture during this operation, whereas a similar mixture prepared in accordance with the Winters et al patent, utilizing a kerosene solvent~ became so viscous that it could not be pumped through the pipeline leading to the pug-mill.
Example 2 About 68 tons of a rubberized asphalt composit;on of this invention was prepared and applied as a chip-seal coating on approximately two miles of Highway 68 near Kingman, Arizona.
The rubberized asphalt was prepared in a portable production tank by blending 85 parts by weight of AR-8000grade asphalt . . .

. ., ., , . . .~ , , 7~1)5 with 15 parts by weight of Dutrex 739 at 375F, and then blend-ing in 12 parts by weight of G-248 and 10 parts by weight of Flo-Mix. The mixture was agitated ~ t 390F for about 2 hours until homogeneous, and then loaded on conventional asphalt distributor trucks ~or application. Because of delays in the project, approximately 3000 gallons of the rubberized asphalt blend was held overnight in a distributor truck~ By th2 next morning, the temperature of the blend had d~opped ~o approxi-mately 250F. This portion was then reheated in the truck and sprayed on the pavement at 375F with no particular difficul-ty.
The application rate was 0.6 gallons per square yard. This test proved conclusively that the rubber asphalt compositions of this invention present no gelling problems for at least about 12 hours. The coating on this particular job was covered with ~ ~;
.; , mineral chips and rolled in conventional manner and has sur-; vived one winter of use without apparent damage.
Example 3 - ~ ~
` About 46 tons of our rubberized asphalt blend was ~ -applied as a stress absorbing membrane interlayer over a damaged stretch of State Highway 180 near Flagstaff, Arizona. In this instance the blend was composed of 90 weight parts of AR-8Q00 grade asphalt, 10 weight parts of Dutrex 739, 12 weight parts ;
G-248 and 10 parts of Flo-Mix, and was prepared substantially in the manner described in Example 2. The blend was loaded into tank trucks, transported to the job site and sprayed onto the ~ ;~
pavement at about 400F, at a rate of 0.65 to 0.7 gallons per ~ -s~uare yard. In this project a delay was again encountered and it was once again proven that the blend could be held for over . .
1 hour and sprayed without difficulty. The membrane was then coated with volcanic cinder chips and rolled in conventional fashion to enable construction equipment to run on the me~brane wi~hout damage.

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i~8 Subsequently, the above chip membrane of thi8 invent~
was overlai~ with about 1.5 inches of regular asphalt concrete.
It was intended that an additional l-inch layer be added later, but despite the fact that this additional layer was not placed, this section of roadway is still in excellent condition after one winter of Flagstaff weather, which entails snow and some below zero degree temperatures.
~xample 4 A different mixture was prepared by blending 97 parte by weight of AR-2000 grade asphalt, 3 weight parts of Dutrex 739, 17 weight parts of G-248 and 6 weight parts of Flo-Mix. The blend was prepared in a distributor truck substantially as des-cribed i~ Example 2. A portion of the mixture was then applied at 400F and at a rate of 0.55 - 0.6 gallons per square yard, over a one block stretch of Highway 66 in the city of Flagstaff, Arizona. Mineral chips were then applied in conventional fashion.
To the remainder of the asphalt-rubber blend in the distributor truck was added an additional 10 gallons of Dutrex 739, which brough~ its total content to about 4.5 wcight percent of the composition. This altered blend was then applied at 0.58 gallons per square yard at 400F to a badly damaged section of rural highway located outside the city of Flagstaff, Arizona. ~ , Both of these applications provided an effective seal coat and ~ ~ `
continued to do so after one winter of Flagstaff weather.
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No liquid asphalt tack coat was used in either of the above applicatiOnS.
Example 5 .
Another chip seal membrane application of this invention ~ ~
30 was tested in the city of Phoenix, Arizona on Buckeye Road west ~' of 35th Avenue. This section of the roadway carries very heavy Interstate Highway 10 traffic and was fairly badly ravelled from l~t~5 a previous chip seal done with the McDonald-Winters patente~
system. For this test we prepared about 4 tons of a blend com-prising 94.5 weight parts of AR-400 asphalt~ 5.S wei~ht parts of Dutrex 739, 15 weight parts of G-248 and 7 weight parts of Flo-Mix. Mixing was accomplished with air agitation in a distri-butor truck under conditions essentially as described in ;
Example 2. The mixture was applied at 400F, and 0.6~0.65 g~ll~8 per square yard over ~he raw pavement, i~e., there was no tack coat. The membrane was then covered with aggregate chips that were the sweepings from previous seal coat work, and hence were very dirty. Ordinarily, suoh chips would not adhere well to asphalt or asphalt-rubber membranes, bu~ it was found that our ~;
membrane held them very well, and was also strongly adherent to the old pavement, despite the lack of a tack coat. -~
Exam~le 6 , .
About 6.8 tons of another asphalt rubber blend of this ~ `~
invention was applied to a heavily travelled, badly cracked pave-ment on Dysart Road~ Maricopa County~ near Phoenix, Ari~onar The application was made without a tack coat at about 425F, and at a rate of about 0.5 - 0.65 gallons per square yard. The rock chips applied thereto were clean and of good quality1 but through error had been drenched with water and were very wet. Normally, such chips will not stick to hot asphalt, and it was concluded ^
that the traffic would immediately whip off most of the chips, but surprisingly a large percentage of them stuck, and there was good adherency of the membrane to the underlying pavement surface.
The blend used in this test was composed of 94 weight parts of AR-4000 asphalt, 6 weight parts of Dutrex 739, 8 weight parts o~
a vulcanized scrap rubber casings made principally ~rom truck tires and containing an average of 31.8 weight-percent natura}
rubber. Blending of the components and the application technique was substantially as described in Example 2.
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The following claims and their obvious equivalents are intended ~o define the true ~cope of the invention.
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Claims (11)

1. THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
   OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
   l. A paving composition comprising a heat-blended, substantially homogeneous composite of (1) about 50 - 89 weight percent of an asphaltic component selected from the class con-sisting of paving grade asphalts, slow curing liquid asphalts and road oils, (2) between about 10% and 30% by weight of a reclaimed rubber component, about 10-60 weight-percent of said reclaimed rubber component being ground vulcanized natural rubber, and about 15-70 weight-percent thereof being ground devulcanized rubber, and (3) between about 1% and 20% by weight of a mineral oil solvent having a flash point above about 300°F, and containing more than about 50 weight-percent aromatics, at least about 50% of said solvent boiling above 700°F, and at least about 90% thereof boiling above 600°F.
2. 2. A composition as defined in claim 1 wherein said mineral oil solvent contains at least about 60 weight-percent aromatics.
3. 3. A composition as defined in claim 1 wherein said mineral oil solvent has a flash point above about 350°F.
4. 4. A composition as defined in claim 1 wherein said mineral oil solvent contains at least about 60 weight-percent aromatics and less than about 20 weight-percent saturated hydrocarbons.
5. 5. A composition as defined in claim 4 wherein said mineral oil solvent has a flash point above about 350°F.
6. 6. A method for the manufacture of a paving compo-sition which comprises:
   (1) blending about 50-89 weight-percent, based on the final composition, of an aspahltic component selected from the class consisting of molten paving grade asphalts, slow curing liquid asphalts and road oils, with about 1-20 weight-percent of a mineral oil solvent having a flash point above about 350°F, and containing more than about 50 weight-percent aromatics, at least about 50% of said solvent boiling above 700°F, and at least about 90% thereof boiling above 600°F;
   (2) adding to the blend from step (1) about 10-30%
   by weight, based on the final composition, of a granulated reclaimed rubber component, about 10-60 weight-percent of said reclaimed rubber component being ground vulcanized natural rubber, and about 15-70 weight-percent thereof being devulcan-ized rubber; and (3) heating and agitating the resulting mixture at a temperature between about 300° and 500°F for a time sufficient to produce a substantially homogeneous composite.
7. 7. A method as defined in claim 6 wherein said heat-ing in step (3) is carried out at about 350-450°F.
8. 8. A method as defined in claim 6 or 7wherein said mineral oil solvent contains at least about 60 weight-percent aromatics and less than about 20 weight-percent saturated hydrocarbons.
9. 9. A method for applying a rubberized asphalt membrane to a roadway which comprises preparing a paving composition by the method of claim 6, and thereafter spraying the resulting composition onto the untreated prepared roadway at a temperature between about 325° and 450°F, to provide an adherent membrane of about 1/16" - 3/16" in thickness.
10. 10. A method as defined in claim 9 wherein said spraying is carried out at least about 2 hours after the formation of said substantially homogeneous composite.
11. 11. A method as defined in claim 9 wherein rock chips or other mineral cover materials are subsequently applied to the surface of said membrane.