Note: Descriptions are shown in the official language in which they were submitted.
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A NOVEL ASPHALT COMPOSITION
This invention relates to a novel asphalt composition
which is suitable for use in hot mixes for road surface courses
and overlays and to a method for the production of said compo-
sition.
The upper layer of a road is directly exposed to traf-
fic loads and it distributes the immediately imposed stresses.
Temperature changes in this upper layer are large and the layer
is most prone to deformation and, during periods of cold wea-
ther, to cracking. Deformations in this relatively thin upper
layer represent approximately one half of the totai deforma-
tion of the road structure. The lack of stability in this up-
per layer leads to quick deformation and ultimately to the de-
terioration of the entire structure.
Thus, the top layer of road which carries heavy traf-
fic requires a binder which will retain high stability at the
highest road temperatures, will not become too hard and brit-
tle at low temperatures and will retain its flexibility during
repeated dynamic loadings.
It is known that much work has been done on the devel-
opment of asphalt/polymer compositions, known as binders, hav-
ing improved properties and many different types of polymers
have been evaluated.
The styrene-butadiene-styrene tri- or poly-block co-
polymers, which are linear or radial block copolymers, are
known as materials with good miscibility with asphaltic mat-
erials at elevated temperatures. These copolymers substant-
ially improve the rheological properties and some of the other
properties of asphalts. The viscosity of the asphalt/polymer
binder increases considerably at highest road temperatures
(about 60C). At the same time, the flexibility improves at
low temperatures and, overall, the elastic portion of the vis-
coelastic properties of the asphalt/polymer binder is grossly
enhanced. This results in improved stability of the asphaltic
road surface as well as decreased low temperature cracking.
From non-rheological properties, it is known that the adhesive
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properties of the binder improve, thereby enhancing the anti-
stripping resistance of the road surface. The chemical com-
position, properties and performance of styrene-butadiene-
styrene block copolymers in asphalt are described by, for ex-
ample, M. J. Folkes in "Processing, Structure and Propertiesof Block Copolymers", Elsevier Applied Science Publishers
Ltd., London, N.Y., 1985 and by G. Kraus in "Modification of
Asphalt by Block Polymers of Butadiene and Styrene", Rubber
Chemistry and Technology, Vol. 55, No. 5, Nov/Dec 1982. There
are also patents on the use of styrene-butadiene-styrene tri-
and poly-block copolymers i,n asphalt, as evidenced by U.S.
Patents Nos. 3,611,888; 3,856,732; ~,217,259; 4,368,22~i 4,
420,524; 4,430,465 and 4,612,152. According to these patents,
such copolymers have been used in various applications such
as in waterproofing membranes and for road construction in
the form of hot mixes, cutbacks and emulsions.
Deficiencies have been found in several areas for as-
phalt compositions prepared by the combination of asphalt and
styrene-butadiene-styrene block copolymers. One such defici-
ency is an increase in the viscosity of the asphalt/polymercomposition used for road construction at operating tempera-
tures. Thus, temperatures have to be increased considerably
resulting in a decrease in the productivity of mixing plants,
there is an increase in the release of fumes during road con-
struction and there are difficulties during the placement ofthe hot material during cold days.
These known asphalt/polymer compositions have a tend-
ency to separate during extended periods of hot storage into
polymer rich and asphaltene rich phases. We have found that
this separation can have two stages, namely, total separation
of the phases into two layers and the coagulation of the pol-
ymer rich phase while still dispersed in the asphaltene rich
phase~ Good rheological properties of the asphalt/polymer
compositions diminish and, in the case of total separation,
the composition cannot be used.
While several means are available for the prevention
of phase separations in such materials, the simplest way to
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prevent demixing of the asphalt/polymer composition is to ag-
itate the blend continuously during hot storage and transpor-
tation. Another method is to use selected asphalts with very
low asphaltenes content and a sufficiently high content of
aromatics and naphthenes. However, it is difficult -to trans-
port large quantities of this suitable asphalt over long dis-
tances where it is to be used for road applications.
A further method of improving the long term stability
of the asphalt/polymer compositions is by the addition of cer-
tain amounts of aromatic/naphthenic oils which change the as-
phaltene/aromatics balance in the asphaltic composition making
more aromatics available for the polymer. Yet another solu-
tion for the improvement of compatibility in the asphalt/
polymer composition lies in the addition of small amounts of
diblock butadiene-styrene copolymers (U.S. 4,490,493) or the
use of chemical bonding between the block copolymers and the
asphalt (U.S. 4,273,685 and U.S. 4,485,144).
It is also known from U.S. 4,145,322 that bitumen ~as-
phalt)/polymer compositions have been described wherein there
is present from 80% to 98% w/w of bitumen, having a penetra-
tion value between 30 and 220, associated with 2% to 20% w/w
of a block copolymer and from 0.1% to 3% w/w of sulphur. This
type of composition suffers from the disadvantage that the
bitumen (asphalt) used as starting material is relatively hard
with a low penetration value of from 30 to 220. When it is
necessary to soften this relatively hard bitumen, it is usual
to add oils of different origin but the properties of the
final compositions are not as good as might be expected. A
further problem arises in the actual manufacture of such com-
positions because of the relative hardness of the bitumen.
We have now found, and herein lies our invention, that
it is possible to prepare novel, valuable asphalt/polymer com-
positions wherein the asphalt ingredient used as starting ma-
terial is a relatively soft asphalt having a penetration fig-
ure in the range of from 240 dmm to 400 dmm provided that a
particular polymer is used in combination with such soft as-
phalt together with very small quantities of sulphur. These
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novel asphalt/polymer compositions are easier to manufacture
and they are useful for various purposes, for example in the
production of hot mixes for road surface courses and over-
lays.
Thus, according to our invention, as claimed herein,
we provide a novel asphalt composition consisting of from
95% to 97% w/w of asphalt, said asphalt having a pene-tration
range at 25C betwen about 240 dmm and about 400 dmm, from
3~ to 5~ w/w of a styrene-butadiene-styrene block copolymer
and from 0.08% to 0.12% w/w of sulphur calculated on the com-
bined weight of asphalt and polymer.
A particularly useful asphalt to be used as starting
material is the asphalt obtained from western Canadian heavy
crude oil by straight-run distillation. The penetration of
this asphalt, determined according to ASTM Standard D5 "Pene-
tration of Bituminous Materials" ranges from 240 dmm to 400
dmm at 25C depending on the consistency required in the fi-
nal asphalt/polymer composition. Such Canadian asphalt is
generally characterized by having an asphaltene content of
from about 12% to about 17% by weight. The group composition
of this Canadian asphalt, as determined by the procedure des-
cribed in ASTM Standard D4124 "Separation of Asphalt into
Four Phases" is as follows:
saturates from 11~ to 16% w/w
asphaltenes from 12% to 17% w/w
- combined naphthene-
aromatics and
polar-aromatics from 67% to 77% w/w
As a suitable sytrene-butadiene-styrene block copoly-
mer used as the second ingredient in the composition there
may be mentioned, for example, a linear or radial block co-
polymer as in a tri- or poly-block copolymer. Such a co-
polymer may have a molecular weight in the range of from ab-
out 120,000 to about 160 r 000 . The styrene/butadiene ratio
in said block copolymer may be within the range of from ab-
out 25:75 to about 35:65. A preferred block copolymer is a
radial block copolymer particularly one having a molecular
weight of about 140,000. A particularly valuable radial
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block copolymer is one having a styrene/butadiene ratio of
about 30:70 and a molecular weight of about 140,000. One es-
pecially useful radial block copolymer is the product known
as Finaprene 416 which is a styrene-butadiene-styrene radial
block copolymer having a styrene/butadiene ratio of 30:70 and
` a molecular weight of 140,000.
As a preferred Eeature of the invention, the asphalt/
polymer compositions preferably contain from about 95.5% to
about 96.5% w/w of asphalt, from about 3.5% to about 4.5% w/w
of a styrene-butadiene-styrene block copolymer and from about
0.09% to about 0.10% w/w of sulphur calculated on the com-
bined weight of asphalt and polymer.
The relatively soft asphalt used as starting material
is such that it has a penetration range of from about 240 dmm
to about 400 dmm. A preferred asphalt has a penetration range
between 275 dmm and 325 dmm and a more preferred asphalt has
a penetration range between about 290 dmm and 310 dmm.
An asphalt/polymer composition of choice is that con-
taining from about 95% to about 97% w/w, preferably 95.5% to
96.5% w/w, of asphalt from western Canadian heavy crude oil
by straight-run distillation, said asphalt having a penetra-
tion range of 240 dmm to 400 dmm, especially a range of 275
dmm to 325 dmm and more particularly a range of 290 dmm to
310 dmm, from about 3% to about 5% w/w, preferably about 3.5%
to about 4.5% w/w, of a radial styrene-butadiene-styrene block
copolymer, especially Gne having a styrene/butadiene ratio of
about 30:70 and more particularly having a molecular weight
of 140,000, and from about 0.08% to about 0.12% w/w, especi-
ally about 0.09% to about 0.10% w/w, of sulphur, the amount
of sulphur being calculated on the combined weight of asphalt
and polymer.
A most valuable asphalt/polymer composition is one
wherein there is present about 96% w/w of asphalt, about 4%
w/w of a radial styrene-butadiene-styrene block copolymer and
about 0.10% w/w of sulphur, the asphalt having a penetration
range of from about 290 dmm to about 310 dmm, and the copoly-
mer has a styrene/butadiene ratio of about 30:70 and a molec-
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ular weight of about 140,000. A particular valuable asphalt/
polymer composition consists of about 96% w~w of asphalt hav-
ing a penetration between about 290 dmm and 310 dmm, about 4%
w/w of a radial styrene-butadiene-styrene block copolymer
identified as Finaprene 416 and about 0.10% w/w of sulphur.
\ Figure 1 shows a flow scheme of how the asphalt/polymer
compositions of this invention may be readily and conveniently
prepared. In Figure 1, the reactor (1) is connected to a high
shear pump (2) which is connected to a storage tank (3).
Asphalt having a suitable penetration figure is heated
to a temperature between about 180C and about 190C and is
delivered to the jacketed reactor (1) equipped with a low
shear (paddle) mixer. The total amount of polymer, in crumb
form, is then added to the asphalt and the mixture is circu-
lated through a high shear pump (2~ until it becomes homogen-
eous. This operation may take approximately from about 15
minutes to about 30 minutes. The amount of polymer used may
be such that a masterbatch is prepared containing up to about
30% w/w of polymer and said masterbatch can then be diluted
at the subsequent stage of the process.
After the masterbatch becomes homogeneous, it is trans-
ferred to a tank (3) equipped with a low shear (paddle) mixer
and a heater. A sufficient amount of asphalt is added to the
masterbatch to bring the final polymer concentration in the
mixture to between 3% and 5% w/w depending on the properties
required for the final asphalt/polymer composition. The mix-
ture of masterbatch and asphalt is homogenized using the pad-
dle mixer in about 15 minutes to 30 minutes at a tank temper-
ature maintained between about 180C to 190C. The total
calculated amount of sulphur is then added, either in a pul-
verized form, such as flowers of sulphur, or it may be melted
and diluted with a small amount of asphalt before addition.
While maintaining the appropriate temperature, the composi-
tion is stirred using the paddle mixer for at least one hour.
Preferably, the mixture is stirred for from two hours to four
hours to obtain a good mix and crosslinking. The composition
is then ready for transport to the site where it is intended
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to be used.
Thus, according to a further feature of the invention,
we provide a method for the production of a novel asphalt com-
position, as hereinbefore defined, which comprises dispersing
the appropriate amount of styrene-butadiene-styrene block co-
polymer in the appropriate amount of asphalt at a suitable
elevated temperature to provide a uniform dispersion contain-
ing asphalt and polymer within the specified ranges and there-
after adding thereto the requisite amount of sulphur and con-
tinuing mixing and heating to provide the desired asphalt/polymer composition.
The method of production may be conveniently carried
out by mixing a portion of the asphalt with the total amount
of s-tyrene-butadiene-styrene block copolymer under high shear
mixing conditions at an elevated temperature, such as from
about 180C to about 190C, until a homogeneous masterbatch
is obtained, adding the remaining asphalt to provide the de-
sired ratio of asphalt to polymer and mixing under low shear
mixing conditions until a uniform dispersion is obtained and
thereafter adding the total amount of sulphur with mixing to
provide the desired asphalt/polymer composition.
It is preferable that all mixing operations be carried
out at a temperature of from about 180C to about 190C. The
initial masterbatch may be prepared by passing the mixture of
asphalt and polymer through a high shear pump for a period of
from about 15 minutes to about 30 minutes and such a master-
batch may conveniently contain up to about 30% w/w of polymer.
The low shear mixing operation, following addition of
the remaining asphalt, is preferably maintained for a period
of from about 15 minutes to about 30 minutes at a temperature
of from about 180C to about 190C. The sulphur may be added
as such, in the form of powdered sulphur or flowers of sul-
phur, or it may be melted and diluted with a small amount of
asphalt before addition to the asphalt/polymer mixture. The
sulphur is preferably added at a temperature of from about
180C to 190C and low shear stirring or mixing may be con-
tinued for at least about 1 hour and, preferably, for a per-
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iod of from about 2 hours to about 4 hours.
Thus, according to a further feature of the invention,
a method of choice comprises mixing a portion of the asphalt
with the total amount of styrene-butadiene-styrene block co-
polymer under high shear mixing conditions for a period offrom 15 minutes to 30 minutes until a homogeneous masterbatch
is obtained, adding the remaining asphalt to provide the de-
sired ratio of asphalt to polymer and continuing the mixing
under low shear conditions for a period of 15 minutes to 30
minutes until a uniform dispersion is obtained and thereafter
adding the total amount of sulphur and continuing mixing un-
der low shear mixing conditions for a period of at least 1
hour, the temperature throughout the process being maintained
at from about 180C to about 190C.
It has been found that the best balance between the
rheological and mechanical properties and the compatibility
of the asphalt/polymer composition is achieved by using a
straight-run asphalt from western Canadian heavy crude oil
and a relatively low molecular weight radial styrene-butadi- -
ene-styrene block copolymer, for example a molecular weight
of approximately 140,000. The mechanical and rheological
properties of the asphalt/polymer composition containing as-
phalts of low consistency are enhanced by the partial in situ
crosslinking of the polymer with the asphalt using a very
small amount of sulphur.
In comparative tests using the same styrene-butadiene-
styrene block copolymer and straight-run asphalts from wes-
tern Canadian heavy crude oils three compositions having the
same consistency were evaluated~ Composition A contains as-
phalt with penetration at 25C , 220 dmm and 4% Finaprene 416.
No crosslinking by sulphur or any other crosslinking agent was
made. The ultimate consistency of -the composition measured
by penetration at 25C was 140 dmm. Composition B contains
asphalt with penetration at 25C, 90 dmm, 5% of aromatic oil
and 4% Finaprene 416, crosslinked with 0.1% of sulphur. The
ultimate consistency of this composition, measured by pene-
tration at 25C was also 140 dmm. Composition C contains as-
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phalt with penetration at 25C, 300 dmm and 4% Finaprene 416,
crosslinked with 0.1% of sulphur. The ultimate consistency
of this composition measured by penetration at 25C is also
140 dmm. The mechanical properties of composition C are sup-
5 erior to the mechanical properties of both compositions A andB, mainly in the low temperature range.
The invention is illustrated by, but not limited by,
the Examples identified as Examples I to XI in Table 1 on page
11. Two comparative examples were also prepared from asphalt
having a penetration grade 85/100 Pen and 150/200 Pen in order
to obtain a comparison of their properties to the asphalt/
polymer compositions of this invention. The properties of the
two comparative examples of conventional asphalts 150/200 Pen
and 85/100 Pen, together with Examples I to XI, are shown in
Table 2 on page 12. It will be observed that, compared with
conventional asphalts, the asphalt/polymer compositions I to
XI of this invention show a large improvement in the consis-
tency/temperature susceptibility for the novel inventive com-
positions. From stiffness measurements and dynamical testing
the enhancement of the elastic behaviour is also apparent for
the compositions of this invention.
It is particularly noticeable that the viscosities of
the asphalt/polymer compositions at 60C (i.e. the highest
road temperatures) are approximately one order of magnitude
higher than those of conventional asphalts. Moreover, the
stiffness moduli at -30C for the asphalt/polymer compositions
are considerably lower than those of conventional asphalts.
These results guarantee a substantial decrease in plastic de-
formation and road surface cracking for the asphalt/polymer
compositions when compared with conventional asphalts.
Even though the ~inematic viscosities of the asphalt/
polymer compositions at technological temperatures are higher
than those of conventional asphalts, laboratory tests and
field experience have proved that no change in the operating
temperature of the mixing plant is required. The same temp-
eratures may be used with these asphalt/polymer compositions
as with conventional asphalts. "Shear thinning" of the mat-
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erial during mixing and compaction is thought to occur.
Table 3 on page 13 shows a comparison of Marshall sta-
bilities for a conventional asphalt 150/200 Pen against the
asphalt/polymer compositions of this invention identified as
Examples I, III, V, VI, VII and VIII. Table 4 on page 14
shows the sieve analysis of mineral aggregates used for said
Marshall test.
The considerable increases in the Marshall stabilities
of mixes using the novel inventive asphalt~polymer composi-
tions over those using conventional asphalts is outstandingas shown in Table 3. Moreover, the Marshall quotient, which
is the indicator of the susceptibility of mixes to rutting,
improves strongly in favour of the asphalt/polymer composi-
tions of this invention.
It has been found that the mixes using asphalt/polymer
compositions can be placed in layers as thin as 15 mm and
still create elastic and durable surfaces on heavily traf-
ficked roads. The savings in materials and maintenance, and
the improvement in driving comfort on such roads, are sub-
stantial.
The asphalt/polymer compositions of this invention are
designed for use in hot mixes for road surface courses and
overlays on heavily used roads. It is preferable to use the
finer gradations of mineral aggregates when providing an as-
phaltic layer thickness between 15 mm and 60 mm as a roadsurface or overlay.
The asphalt/polymer composition may be delivered to
the asphalt hot mix plant and may be used in the same manner
as conventional asphalt. The use of the asphalt/polymer com-
position according to this in~ention in appropriate mixes re-
sults in a top road layer having increased stability, increased
resistance to abrasion, improved dynamic characteristics and
decreased hardness and brittleness at low temperatures. The
bond between the asphalt/polymer composition and the mineral
aggregate is strengthened and consequently the antistripping
resistance of the pavement is enhanced.
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Table 4:
Sieve Ana~sis of Mineral Aggregates
Used fo~arshall Test
__ __
Sieve Size Percent
~mmJ Pass7ne
_____
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4.75 _ ~1.8
2.3B 68.5
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