Note: Descriptions are shown in the official language in which they were submitted.
~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 ;~
, . . .
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
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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
: ,
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~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
TABLE 1
_____ ,
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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TABLE 2
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 ~-~
., . ~ .
oils and the like, boiling generally in the range of about 700-
1100F, and having a gravity ranging be~ween about 3 and 12~
~. ~
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
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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:
TABLE 3
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
IBP 622 740 700 775
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:
TABLE 4
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
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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
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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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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.
. - .
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
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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.
-16~
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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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