Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR INCORPORATING WASTE RUBBER CRUMB INTO ASPHALT
EMULS I ONS
BACKGROUND OE THE INVENTION
Rubber asphalt composition for road construction
or maintenance usin~ small amounts (0.1 to 10%) o~ unvul-
canized natural or synthetic rubber have been known for over
half a eentury. Compositions of an asphalt emulsion com-
bined with a small amount of rubber latex (under 10%) are
also known. However, developments combining asphalt with
vulcanized rubber crumb, a waste product from scrap tires,
tire buffings and the like, have lagged somewhat.
A patent describing the introduction of up to 15
vulcanized waste rubber particles in~o hot asphalt for a
road surfacing eomposition was issued in the late 1930's
(Fr. 811750, U.S. 2138734) but, for several reasons was
ignored by the road constructîon industry. It was not until
the 1960's that work along similar lines was resumed through
the efforts of C.H. McDonald, reports of which first appear-
ed in the Highway Research Reeord, No: 146, published Decem-
ber 1966 by the Highway Research Board in Washington, D.C.
The proeedures developed are described in Canadian patent
1015882.
Essentially, that process involved stirring in one
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part vulcanized rubber crumb into between 2 and 3 parts
of asphalt heated between 350 - 500F (149-260C). After
the reaction between the rubber and the asphalt was com-
plete, kerosene (about 6% by volume) was added to tempora-
rily reduce the viscosity of the mixture. The binder so
produced then had to be applied to the road surface within
a relatively short period of time (0.5 to 1.5 hours) after
which the viscosity of the binder was too high for it to be
sprayed even using the special equipment designed to handle
the material.
There are a number of disadvantages of the pro-
cess just described. Firstly, temperatures of 350 - 500F
require higher energy inputs than those normally encounter-
ed in asphalt plants involved in construction Secondly,
the addition of kerosene at these temperatures, ~ell above
its flash point, presented not only a serious fire hazard,
but also an extra energy expense in the road surfacing com-
position. ~astly, the relatively short period of time during
which the rubber asphalt binder remained workable required
~0 that the manufacturing plant be situated in very close pro-
ximity of the construction site and sophisticated units de-
signed to manufacture, transport and spray this rubber as-
phalt were costly to purchase.
Recognizing some of these difficulties, the same
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inventor, C.H. McDonald, devised a method for emulsifying
the rubber asphalt paving material in water. (Canadian
Patent 1042145). This emulsion could be stirred, poured
and sprayed under ambient temperatures. Thixotropic emul-
sions thus prepared on a small scale (less than 525 grams)
were stabilized by the addition of boiled cornstarch used
as a thickener. In this process, the hazards and higher
energy inputs associated with the preparation of the rubber
asphalt prior to emulsification were not entirely elimina-
ted - temperatures of 350 - 500~F were still required and
the addition of kerosene was optional.
The object of the present invention is to provide
a new method for introducing vulcanized, unvulcanized or
reclaimed rubber crumb into asphalt in a stable emulsion
form which would avoid the hazards and energy costs of the
existing method.
~ suggestion for how this might be accomplished ap-
peared in Canadian patent 435837, where an asphalt emulsion
(prepared with bentonite) was combined with a dispersion of
~round vulcanized rubber, bentonite, oxalic acid/ wetting
a~ent and amphibole in water to produce a sealing composi-
tion for joints, seams or crevices in automobile bodies.
SUM~RY OF THE INVENTION
It has been discovered that a rubber asphalt com-
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position suitable for use as a road surfacing binder in
the form of a stable emulsion can be readily prepared by
simply combining an anionic asphalt emulsion with ground
rubber crumb whose surface has been pretreated with an
anionic emulsifier solution. This emulsion or dispersion
is stable for up to four months under ambient conditions,
during which time a small degree of reversible settling
takes place. Gentle agitation readily redisperses what
rubber had begun to settle.
In accordance with the invention there is provid-
ed a process for incorporating rubber crumb into asphalt
emulsion comprising pretreating the rubber crumb with an
anionic emulsifier solution sufficient to wet substantially
all of the surfaces of the rubber crumb, and then mixing
the pretreated rubber crumb into an anionic asphalt emulsion
in the ratio of between 1:1 and 1:19 by weight or rubber to
asphalt to form a rubber asphalt emulsion.
A further aspect of the invention consists of a
process for incorporating rubber crumb into asphalt emulsion
~0 comprising pretreating the rubber crumb with an anionic ernul-
sifier solution sufficient to wet substantially all the sur-
faces of the rubber crumb, and then mixing the pretreated rub-
ber crumb into an anionic asphalt emulsion to form a rubber
asphalt emulsion wherein the emulsifier solution includes an
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emulsifier which effects wetting of the rubber crumb and in
which the proportion of the emulsifier in the pretreatment
solution is between 0.1% and 25% by weight depending upon
the stability of the rubber asphalt emulsion required, and
in which the proportion of emulsifier solution to rubber
crumb is between 0.3 and 1.2 to 1 by weight.
With the foregoing in view, and other advantages as
will become apparent to those skilled in the art to which this
invention relates as this specification proceeds, a descrip-
tion of the preferred typical embodiment of the principles of
the present invention, is herein described.
DETAILED DESCRIPTION
In a preferred embodiment of this invention, an as-
phalt emulsion is prepared in a manner known to anyone skilled
in the art using whatever hardness of asphalt is desired for
the application and an anionic emulsifier such as tall oil,
vinsol resin or the like. The resulting emulsion contains pre-
ferably between 55% to 70~ asphalt by weight.
Suitable rubbers are those which undergo swelling
upon exposure to aromatic, naphthenic or aliphatic oils or sol-
vents and include natural rubber, isoprene rubber, butadiene
rubber, butadiene-styrene rubber, butyl rubber and ethylene
propylene rubbers which may be vulcanized, unvulcanized or re-
claimed rubbers.
Depending upon the properties desired in the rubber
asphalt emulsion or its residue, the proportions of rubber
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to asphalt in the composition may range from 1:1 to 1:19
or even lower.
The particle size of the ground rubber crumb is
preferably from about 16 mesh to about 200 mesh USS.
The crumb is treated with a sufficient amount of
anionic emulsifier solution to wet its surface. It is then
added to the asphalt emulsion and simply stirred in, yield-
ing a stable emulsion or dispersion whose pH should exceed
10 and would preferably be in the range of 11-12.5 for im-
proved storage stability.
The emulsifier used in the solution to precoatthe rubber crumb is preferably the same emulsifier as was
used in preparation of the anionic asphalt emulsion. While
it is possible to use a nonionic emulsifier, an anionic
emulsifier other than that used in the asphalt emulsion, or
no pretreatment of the rubber crumb at all, experience has
shown that in those cases pumping the resultant rubber as-
phalt emulsion leads to the formation of irreversible agglo-
merations (lumps), indicating the instability of the emul-
~0 sion which has begun to b,reak. An exception to this is the
addition of rubber crumb directly (without pretreatment) in-
to a very stable slow setting asphalt emulsion prepared with
vinsol resin.
The emulsifier solution used in rubber crumb pre-
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treatment is prepared by heating a mixture of emulsifier,sufficient sodium or potassium hydroxide to saponify the
fatty and resin acids in the emulsifier and water of such
quantity to bring the emulsifier content to the desired
content.
In all of the following examples, a slight amount
of reversible settling of rubber was detected after several
days. The settling solids were readily redispersed upon
~entle agitation. A thin, nearly clear layer of water form-
ed at the top of the rubber asphalt emulsion after several
days of standing undisturbed, demonstrates a process simi-
lar to syneresis observed in gels. Water in excess of the
emulsion's re~uirement for a stable structure is expelled.
This same phenomenon was observed when an asphalt emulsion
was diluted with an aqueous emulsifier solution and allowed
to stand for several days.
The following represents the preferred rubber as-
` phalt emulsion formulation used as a seal coat binder applied
to a road surface:
Anionic asphalt emulsion (65% asphalt).... 3100 gallons
30 mesh rubber crumb....................... 4945 pounds
5% anionic emulsifier solution............. 280 ~allons
EXAMPLE I
30 mesh vulcanized rubber crumb (162.5 grams) was
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precoate~ with a 5~ solution of basic tall oil solution (150
grams) then stirred into an anionic asphalt emulsion (250
grams, 65% asphalt) prepared with tall oil as the emulsifier.
The resulting dispersion had a viscosity which would enable
the product to be pumped and sprayed through a nozzle. After
storage overnight, the dispersion was still smooth (not
lumpy) but its viscosity had risen to a point where it would
not have sprayed evenly through a nozzle.
In preparation of a 5% basic tall oil solution,
first a 25~ solution was made by heating crude tall oil (500
grams, 25%) with sodium or potassium hydroxide (55 - 200 grams,
2.75 - 10~ and soft water (1445 - 1200 grams, 72.25~ - 60%)
to 165F (74C) while stirring, then diluting 1 part of this
solution with four parts soft water.
EXA~IPLE 2
30 mesh ground vulcanized rubber crumb (97.5 grams)
was precoated with a 5% basic tall oil solution (95 grams)
and then stirred into an anionic asphalt emulsion (300 grams,
65% asphalt) prepared with tall oil emulsifier. The viscosity
~0 of the emulsion, taken at 77F (25C) using the #2 spindle
o~ a Brookfield RVT viscometer, was as follows:
RP~i VISCOSITY RPM VISCOSITY
(Centipoise) (Centipoise)
0.5 12,000 10 1320
1 7,400 20 810
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2.5 3,760 50 44~
2,400 100 294
EXAMPLE 3
30 mesh rubber crumb (65 grams) was precoated
with a 5~ basic tall oil solution ~63.2 grams) then stirred
into an anionic asphalt emulsion (300 grams, 65% asphalt)
prepared with tall oil emulsifier. The rheological charac-
teristics of this dispersion were studied over a period of
65 days, as was that of the asphalt emulsion used, using a
Brookfield RVT viscometer, Spindle #2, at 77F.
R~MVISCOSITY-DAY 1VISCOSITY-DAY 4 VISCOSITY-DAY 65
(centipoise) (centipoise) (centipoise)
Rubber Asphalt Rubber ~er Asphalt
dispersion ~m~sion Dispersion Dispersion Emulsion
0.58,800 16,400 11,200 34,80027,600
15,600 12,800 6,400 19,4001~,000
2.52,800 7,520 3,040 10,400 9,760
51,640 4r600 1,760 6,480 5~640
960 2,860 1,040
570 - 630
312 - 348 - -
100 210 - 252
E~LE 4
16 mesh rubber crumb (216.7 grams) was precoated with a 5~
basic tall oil solution (150 grams) then added to an anionic asphalt
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emulsion (1000 grams, 65% asphalt). The viscosity of thedispersion and of the asphalt emulsion used was determined
at 77F and at 140F using Spindle #2 of the Brookfield
RVT viscometer.
RPM DISPERSION VISCOSITY ASPHALT EMULSION VISCOSITY
(centipoise) (centip~ise)
@ 77F @140F @ 77F @ 140F
0.5 6~00 4400 15,600 6,800
3800 2600 9, 800 4,000
2.5 1920 1360 4,800 2,000
1120 880 2,720 1,280
660 560 1,560 820
410 380 920 560
228 220 488 360
100 168 174 652 506
EXAMPLE 5
30 mesh rubber crumb (48.75) grams) was precoated
with a 5% basic tall oil solution (47~5 grams) then added to
an anionic asphalt emulsion prepared with tall oil as the
emulsifier (300 grams, 65~ asphalt). The viscosity of the
dispersion was determined, as was that of the asphalt emul-
sion, using the #2 spindle of a Brookfield RVT viscometer, at
77F.
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RPM DISPERSION VISCOSITY ASPHALT EMULSION
VISCOSITY
(centipoise) (centipoise)
0.59200 14,800
1 5800 11,200
2.52800 6,240
1600 3,720
940 2,260
570 1,420
296
100 186
EXAMPLE 6
30 mesh rubber crumb (20.6 grams) was precoated
with a 5% basic tall oil solution (20 grams) then stirred
into an anionic asphalt emulsion (300 grams, 65% asphalt).
The viscosity of a sample of the asphalt emulsion and of the
rubber asphalt dispersion was determined using the #2 spin-
dle of the Brookfield RVT viscometer at 77F.
RPMDISPERSION VISCOSITYASPHALT EMULSION
VISCOSITY
(centipoise) (centipoise)
0.512,800 14~800
1 8,000 11,200
2.53,920 6,240
5 2,200 3,720
10 1,240 2,260
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720 1,420
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EXA~IPLE 7
30 mesh rubber crumb (10.3 grams) was precoated
with a 5% basic tall oil solution (10 ~rams) then stirred
into an anionic asphalt emulsion (300 grams, 65% asphalt)
prepared with tall oil as the emulsifier. The viscosity of
the dispersion was determined over a period of 15 days and
compared with the original viscosity of the asphalt emul-
sion at 77F using Spindle #2 of the Brookfi~ld RVT visco-
meter.
RPM ASPHALT EMULSION RUBBER ASPHALT DISPERSION
VISCOSITY VISCOSITY (cps)
(cps) DAY 1 DAY 4 DAY 15
0.514,800 15,20016,400 17,~00
1 11,200 9,60010,600 11,600
2.5 6,240 4,960 5,520 6,320
3,720 2,840 3,160 3,760
2,260 1,620 1,820 2,220
1,420 950 1,090 1,340
- 512 600 744
100 - 348
EXAMPLE 8
30 mesh rubber crumb (16.24 Kg) was precoated
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with 5% basic tall oil solution (10.83 Kg) then stirxed
into an anionic asphalt emulsion (68.1 Kg., 67.2% asphalt)
prepared with tall oil as the emulsifier and the viscosity
determined at 77F using the #2 spindle of a Brookfield RVT
viscometer.
RPMVISCOSITY (cps)
0.5 8,000
1 4,400
2.5 2,080
1,240
760
480
296
100 234
EXA~LE 9
30 mesh rubber crumb (4945 lb., 2245 Kg) was pre-
coated with a 5% basic tall oil solution (260 gallons, 1180.4
Kg) then stirred into an anionic asphalt emulsion (3100 gal-
lons, 14,074 Kg, 65% asphalt) prepared with tall oil as the
emulsifier. The viscosity of this emulsion, taken at 77F
with a #2 spindle of the Brookfield RVT viscometer at 0.5
rpm was 24,400 cps. This product was readily sprayed onto
a road surface as a seal coat binder using a conventional
emulsion distributor.
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EXAMPLE 10
30 mesh rubber crumb (4945 lb., 2245 Kg) was pre-
coated with a 5% basic tall oil sol~tion (280 gallons,
127~.2 Kg) then stirred into an anionic asphalt emulsion
prepared with tall oil as the emulsifier (3100 gallons,
14,074 Kg., 65% asphalt). The viscosity of this emulsion,
taken at 77F with a #2 spindle of the Brookfield RVT vis-
cometer at 0.5 rpm was 11,200 cps. This product was readily
sprayed onto a road surface as a seal coat binder using a con-
ventional asphalt emulsion distributor.
EXAMPLE 11
30 mesh rubber crumb (183 grams) was added direct-
ly to a sample of slow setting emulsion prepared with vinsol
resin (1000 grams, 55% asphalt). The emulsion was pumped
continuously for 6 minutes at zero pressure and then for 4
minutes at 30 pounds pressure. Passing the dispersion
through a screen of 18 x 12 mesh showed it to be free of
irreversible agglomerations or lumps.
~0 EXAMPLE 12
30 mesh rubber crumb (184 grams) was precoated
with a 10% solution of nonionic emulsifier Igepal C0-990 (200
grams) then stirred into an anionic asphalt emulsion pre-
pared with tall oil as the emulsifier (1000 grams, 60% as-
phalt). The dispersion was pumped continuously for 6 minutes
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at 30 pounds pressure then passed through a 12 x 18 mesh
screen to collect agglomerated solids. The weight of the
precipitate after it had been washed and dried was 105.6
grams.
EXAMPLE 13
30 mesh rubber crumb (184 grams) was precoated
with a 20~ basic solution of vinsol resin (lOa grams) then
added to an anionic asphalt emulsion prepared with tall oil
as the emulsifier (1000 grams, 60% asphalt). The disper-
sion was pumped continuously for 6 minutes at 30 pounds
pressure then passed through 18 x 12 mesh screen to collect
agglomerated solids. After washing and drying, the weight
of the precipitate collected was 201.8 grams.
EXAMPLE 14
30 m~sh rubber crumb (65 grams) was precoated
with a 25% basic solution of tall oil (63.05 grams) then
mixed into an asphalt emulsion prepared with tall oil as
the emulsifier (300 grams, 65~ asphalt). A Brook~ield RVT
~2 spindle was used to det:ermine the viscosity of the as-
phalt emulsion used and that of the resulting rubber dis-
persion at 77F.
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RPMRUBBER DISPERSION ASPHALT EMULSION
VISCOSITY VISCOSITY
(centipoise)(centipoise)
0.520,400 15,200
114,400 9,760
2.58,800 5,040
5 5,960 2,880
10 3,700 1,660
- g80
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100 ~ 34
Further examples are as follows:
In cases wherethe rubber crumb requires pretreat-
ment with an emulsifier solution to form a stable disper-
sion, the proportions of solution for 30-200 mesh rubber
crumb may range between 0.5:1 and 1.2:1, and preferably bet-
ween 0.6:1 and 1:1. For 16 mesh rubber crumb, the propor-
tions may be lowered to 0.3:1.
The percentage oE emulsifier in the pretreatment
solution may range between 0.1% and 25%, depending upon the
~0 stability required.
EX~MPLE 15
30 mesh rubber crumb (65 grams~ was precoated with
a 25% basic tall oil solution (63.05 grams, pH 9.8) then
stirr~d into an asphalt emulsion prepared with tall oil as
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the emulsifier (300 grams, 65% asphalt, pH 10.8) to yield
a dispersion of pH 10.3. The dispersion was allowed to
stand at room temperature for a day, aged in a 140F oven
for 22 hours, then allowed to stand at room temperature for
another 3 days. Evaporation was prevented by a polyethylene
film stretched tightly across the top of the beaker. Vis-
cosity measurements were made on the dispersion as well as
on the asphalt emulsion used in its manufacture (and treated
in the same manner) using a Brookfield RVT viscometer, Spin-
dle ~2, at 77F.
DISPERSION VISCOSITY, CPS ASPHALT E~SION VISCOSITY, CPS
RPM INITIAL A~R A F~L INITIAL AEqER A FIN~L
~y ~y
0.5 20,400 21,60046,000 15,200 14,800 20,80~
1 14,400 15,20029,800 9,800 9,600 14,000
2~.5 8,800 9,400 - 5,0~0 5,040 7,840
5 5,960 6,000 - 2,~80 2,920 4,760
10 3,700 3,640 - 1,660 1,680 2,840
EXAMPLE 16
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30 mesh rubber crum~ (65 grams) was precoated with a
25% basic tall oil solution (39 grams, pH 13.2) then stirred
into an asphalt emulsion prepared with tall oil (300 grams,
65~ asphalt, pH 10.8) to give a dispersion of pH 12.4. The
dispersion was aged overnight in a 140F oven then allowed
to stand at room temperature for three days, at which point
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the viscosity was determined using a Brookfield RVT visco-
meter, spindle #2 at 77F.
RPMVISCOSITY, CPS
INITIAL FINAL
0.5 7,600 26,400
1 4,200 23,400
2.5 2,960 15,840
2,880 off scale
EXAMPLE 17
30 mesh rubber crumb (65 grams) was precoated
with a 0.1% basic (alkaline) tall oil solution (63.05 grams,
pH 9.8) then stirred into an asphalt emulsion prepared with
tall oil as the emulsifier (300 grams, 65~ asphalt, pH 10.8)
to give a dispersion of pH 10.5. The initial viscosity of
the dispersion was determined. After aging the dispersion
in a 140F oven for 22 hours, allowing it to cool to room
temperature and stirring it, the dispersion was shown to
have been broken - irreversible agglomerations of rubber and
asphalt had begun to formp producing a lumpy consistency in
the dispersion.
RPM DISPERSION VISCOSITY, CPS
AT 77F, RVT #2
0 5 3200
1 2200
2.5 1120
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680
460
290
172
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EXAMPLE 18
30 mesh rubber crumb (65 grams) was precoated
with 0.5% alkaline tall oil solution (39 grams, pH 11.4)
then stirred into an asphalt emulsion prepared with tall
oil (300 grams, 65% asphalt, p~ 10.8~ to give a dispersion
of pH 10.75. The dispersion was heated overnight in a 140F
oven then allowed to cool. Upon being stirred, the disper-
sion was broken.
RPM VISCOSITY PRIOR TO AGING (CPS)
Brookfield RVT #2, 77~F
0.5 6000
1 3600
2.5 18~0
1120
Since various modifications can be made in our in-
vention as hereinabove described, and many apparently widely
different embodiments of same made within the spirit and
scope of the claims without departing from such spirit and
scope, it is intended that all matter contained in the accom-
panying specification shall be interpreted as illustrative
only and not in a limiting sense.
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