Note: Descriptions are shown in the official language in which they were submitted.
~66~33~L
The present invention relates to improvements in a method of pre-
paring a bituminous binder for construction materials containing dispersed
solid materials~ such as broken stone and/or sand, and of producing the
construction materials with such a binder. The bituminous binder of this
invention is particularly useful for making rolled and mastic asphalt sur-
faces.
It has been proposed to hot mix bitumen and a polyolefin to melt
the bitumen and dissolve the polyolefin therein while stirring the hot mixture
to homogenize the blend in a hot mixing installation.
Many construction materials are kno~n which use a bituminous
binder. Such construction materials have found extended utili7ation in the
production of surfaces as well as bases for roads as well as roofings, includ-
ing such materials as mastic asphalt) rolled asphalt and bituminous gravel or
macadam. In road surfaces, the bituminous binder usually comprises less than
15%, by weight, of the gravel and/or sand component. -
Bitumen as a binder for such cons*ruction materials has advantages -~
as well as disadvantages. At elevated temperatures, for instance, caused by `
sun rays and favored by the dark color of bitumen, bituminous binders soften,
which may cause serious deformations of the road surface under heavy traffic.
2a~ On the other hand, sub-freezing temperatures ~ill cause the bitumen to become
. . .
embrittled, which also damages the road surface. The tendency of softening
and embrittlement of the bituminous binder may be considerably reduced by add-
ing a polyolefin to the bitum0n, the added polyolefin component generally
: :
improvlng~the ~igidity of constructlon materials containing a bituminous
binder.
~ccordingl~y-, various proposals have been made to add either
specially selected polyolefins to bitumen and/or to blend bitumen and poly-
.
olePms in a special manner. ~hen the properties of the resultant bi~uminous
binders and/or the construction materials containing them are ~ested, it is
found that the sotening tendency at elevated temperatures and the embrittle-
~683~
ment at low temperatures decrease proportionally to an increase in the amount
of added polyolefin, the rigidity and tensile strength of the construction
materials improving correspondingly in a desirable manner. However, at the
same time, the increased addition of polyolefin causes increased stiffness
of construction materials containing such binders at the usual working tem-
peratures, which leads to difficulties in the production of construction mate-
rials containing bituminous binders with conventional blending techniques,
for instance when it is desired to lay a road surface with a commercially ~ :
available asphalting machine. rrhis and the fact that polyolefin is more
expensive than bitumen are probably responsible for the practice tending to
blend bitumen-;and polyolefin under gentle conditions so as to maintain the -
chemical structure of the components as unchanged as possible, based on the
apparently obvious conclusion that the desired improvements in the binder's
properties under adverse temperature conditions and the increased strength of ;
the resultant construction material may be obtained with smaller amounts of
polyolefin if the chemical structure of the polyolefin remains as untouched
as possible durine the blending process. The concomitant conclusion can
. . .
readiIy be reached that a construction material contaming such a binder may
be worked the easier the lower the amount of polyolefin addition causing an
~20 ~increase in the stiffness of the material.
It~ls~an ob~ect of the mvention to improve the first-mentioned
method of preparing a bituminous binder for construction materials by prepar-
ing a b mder which can be incorporated into the construction material in a
simple~manner and enables the construction material to be worked with conven-
ional~methods and~machines, and more particularl~ to enable impro~ved bitu-
minous~road~surfacing~mateTials to be laid do~n with modern road surfacing
machines;.~lt is anotheT~ob~ect to provide~a method of this ~ype which CoUnteT-
acts~the~separ æ lon of~the~bitume~n and polyolefin components in the blend. ;~
e abovè and~other objects of the present invention are accom-
~ pllshed~in the improved method of the~indicated type by continuing the hot
~06~i~31
mixing and homogeni%ing of the bitumen and polyolefin material until the
viscosity of the resultant bituminous binder has been signiicantly reduced,
In this improved method, the bitumen and polyolein are ~horoughly homo-
genized into a unitary blend, and if the blending is continued for a suf-
ficiently long time, the viscosity of the resultant binder can be reduced
so that a construction material containing this bituminous binder may be
worked in the usual manner and without taking special measures, for instance
in laying an asphalt macadam road surface. Nevertheless, the advantages of
the polyolefin addition to the bitumen binder are maintained, including its
improved resistance to temperature changes. Furthermore, the resultant
binder sho~s no tendency to separate into its components and stable bitumen-
polyolefin blends are obtained under all practical conditions while it had
heretofore been assumed that there is a blending gap between bitumen-poly-
olefin ratios of 80:20 and 20:80, in which gap the two components tended to
separate in the blend.
Thus, the invention provides a method of preparing a bi~uminous
binder for construction materials containing dispersed solid materials of a
largely inorganic nature, comprising the step of hot mixing bitumen and a
polyolefin material to melt the bitumen and di~solve the polyolefin material
while stirring the hot mixture to homogenize the bitumen and polyolefin
~aterial~ the hot mixing and homogenizing being continued until the viscosity
of the resultant bituminous binder has been reduced to 75% or less of the
viscosity of the mixture immediately after the polyolefin is dissolved in the
molten bitumen.
According to a preferred feature of this invention, the molten
bitumen and dissolved polyolefin material is hot mixed and homogenized until
the viscosity of ~he resultant binder has been reduced to one fifth to sne
tenth o~ the viscosity of the mixture immediately after the polyole~in-mate-
rial is dissolved in the molten bitumen.
It is particula~ly advantageous if at least 10%, by weightJ based
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~ ~0668~
on the weight of the bitumen, of the polyolefin material is added to the
bitumen and to homogenize at a temperature exceeding by at least 60C the
melting point o the polyolefin material until the polyolefin material has
been depolymerized, decomposed or cracked to form polyolefin ~oieties form-
ing a chemical compound with the bitumen, particularly the naphthene moietles
thereof. During such a homogenizing process, the clepolymerization o the
polyolefin material due to the heat will provide ~ree valences which react
with the bitmmen and particularly its naphthene moi.eties and it may be as-
sumed that the heat causes similar molecular decomposition of the bitumen,
which favors this reaction. The pre~erred minimum amount of polyolefin in
respect of the
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~06~83~L
bitumen has particular significance for initiating the chemical reaction
between the cracked polyolefin material and bitumen.
Various polyolefin materials may be usecL in the process of the
inven~ion. Low as well as high-pressure polyethylene has been found very use-
ful but other polyolefins, such as polypropylene, may also be used. The raw
material :Eor the polyolefin may be waste materials, even if they contain syn-
thetic resins of different compositions, since the process of preparing a
bituminous binder according to the present in~ention also proceeds without
difficulty in the presence of foreign substances, such as, for example, parti-
cles of thermosetting synthetic resins or thermoplastic synthetic resins having
a high ~elting point, as well as otherj non-olefinic thermoplastic resins, ~ -
all of which act like fillers which do not participate in the chemical ;~
reaction.
It may be assumed that the cracking of the molecules of the poly-
olefin material produced during the homogenizing process causes the low vis-
cosity of the resultant binder and9 consequently, the reduced stiffness of the
construction material containing it.
T~e temperature resistance of the binder will be increased by an
increase in the amount of polyolefin material added to the bitumen beyond the
point which reacts and forms a compound with the naphthalene moieties of the
bitumen ~hereb~ a residual amount of polyolefin remains finely dispersed in
the blended binder. It may be theorized in this respect that the polyolefin-
naphthene compound have the property in the range of the homogenizing tempera-
-:
tures to emulsify the cracked polyolefin, particularly polyethyleneJ and thus
to disperse it in ver~ finely divided form in the bitumen. The emulsified
polyolefin then probabl~ is solidified primarily in crystalline form in view
.
of its finely divided form duri~g the subsequent cooling stage, thus producing ~`
~the temperature resistance of the ~inder.
T~e~bituminous binder prepared according to the method of this
. . .
30invention has also been found to have the advantage of a~lering strongly to
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` ~661~3~
alkaline- and acid-reacting minerals. This can be explained by the formation
of salt bridges formed at the interfaces between the mineral and bitumen,
which produce an added chemical bond between mineral and binder.
The chemical reaction between the polyolefin and bitumen during
the hot mixing and homogenizing thereof in the hot mixing installation pro-
ceeds at a rate directly proportional to the elevation of the temperature
during the process. Preferably, blending is effected at a tem~erature between
260C and 310C, the most advantageous temperature being about -290C. At the
latter temperature and at a mixing ratio of polyethylene to bitumen of 30:70,
the reaction begins within about twenty minutes. If the ratio is changed to
50:50, the reaction has been observed to be initiated within about 40 minutes.~
The chemical reaction and the control of the viscosity has been found to pro- ~ -
ceed under particularly favorable conditions if the polyolefin material is
added to the bitumen in an amount between 30% and 100%, by weight, based on
the weight of the bitumen.
If the temperature is kept relatively low, homogeni~ing is con-
tinued or séveral ~ours to obtain an impro~ed bituminous binder for road
surfacing asphalt materials.
.
; During the blending process, the binder ~ixture passes through
~20 seYeral phases~ At first, the viscosity is rat~er low, corresponding practi-,~
cally to the viscosity of the bitumen~at the beginning of the mixing since,
at that stage, the polyolefin material has not yet been molten but is dispers-
ed in t~e bitumen in the form of small particles. Slowly, the polyolefin par-
ticles begin to melt, and, correspondingly, the viscosity of the mixture in- ~ -
creases as~ the polyolefin becomes dissolved in ~he molten bitumen. After
.
~ t~is phase~ ~he viscosity decreases noticeably, which is explained by the
:~ ~
molecular~crack mg or decomposltion of the polyolefin material. This reduced
~ ~ VlSCOSity remains relatively constant for a substantial period of time or even
; increases very slightly hy~the formation of ~he polyolefin-bitumen compounds.
30 ~ ~ In the preparation of binders for road surfacing asphalts, for
_ 5 _
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~C36~3~
instance, it is advantageous to measure the melt index repeatedly during the
hot mixing and homogenizing to determine the reduction of the viscosity of the
mixture.
Since, as mentioned, binders o~` practically any bit~en-polyole-
fin ratio may be prepared by the method of the invention, a homogenized binder
blend with a high proportion of polyolefin material may first be prepared in
the interest of simplicity and economy of procedure, and the final desired
ratio between the two components for any par~icular usage may then be adjus-
ted simply by adding to the blend an additional amount of bitumen. In this
manner, the ratio between the two components may be selected solely on the
basis of preferred reaction conditions during ~he blending process and without
regard to the ratio desired for ~he ultimate use of the binder. This is poss-
ible because the binder blend may be readily stored and, after prolonged
storage, may simply be heated to add additional bitumen to obtain a desired
component ratio at a later date. Tt has been found that such a later addition
of bitumen to the previously prepared blend to adjust the ratio~between bitumen
and polyolefin in the binder does not reduce the stability of the binder
against separation of the components. A particularly homogenous binder is
obtained when the additional bitumen is added to the previously prepared blend
2a and this mixture is then mixed with broken stone or sand. But it is also
possible to add the homogenized binder blend and the additional bitumen separ-
ately into a mixer which contains the hot broken stone or sand material, which
is particularly advantageous in making use of many existing bitumen instal-
lations which are provided with a so-called "Trinidad vessel". In this case,
. . .
; the entire heat treatment of the polyolefin material and bitumen may be effec-
ted in the "Trinidad vessel" and the mass produced therein can be introduced,
for instance sprayed, in~o the mixer in which the broken stone and/or sand is
blended with the bitumen. In this way, the process of the present lnvention
may be readily practiced in existing installations and~ in vie~ of the lo~
viscosity of the resultant binder, road surfacing materials containing the
;~ - 6
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~C166~33:~
same may be laid down with conventional machinery.
The invention also concerns a method of producing a construc~ion
material containing a solid mineral material, i.e. broken stone and/or sand,
dispersed in a bit~linous binder prepared according to the method hereinabove
described, the solid mineral material being heated to an elevated temperature
below the decomposition temperature of the bituminous binder, and the binder
and the heated solid mineral material being hot mixed. The resultant construc-
tion materials have excellent properties.
According to one preferred feature of this method, an acidic
component, such as broken quartz or quartz sand, is added to the mixture.
The solid mineral material is preferably first heated to a temper- -
ature between 200C and 280C but at least 10C below the decomposition tem-
perature of the polyolefin material.
Road surfacing material produced according to this invention has
excellent mechanical properties and is largely stable against deformation by
traffic passing thereover at elevated temperatures. This has been confirmed
by subjecting bituminous road surfacing ma~erials to the conventional Marshall
Test, as has been done with a series of samples of road surfacing materials
prepared according to the invention.
The invention will be further elucidated in connection with the
following examples and~measured values.
ample 1
Irregularly shaped, transparent pieces of film of a polyethylene
waste material having approximate sizes of about 1 to 10 square millimeter were
mixed with a conventional road surfacing bitumen B 80 at temperatures of 180C
to 200C in a Kotthoff mixer, and the mixture was homogenized. Respective
mixtures con~ained 3, 10 and 20%, by weight, of polyolefin, the mixing times
for the homogenization being 10 minutes for the 3% mixture, 15 minutes for
t~e 10% mixture and 30 minutes for the 20% mixture. The resultant polyolefm-
30` bitumen blends attained a gel-like character, becoming more v;scous with in-
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creasing contents of polyolefln. The softening point, ring and ball, of these
blends was measured according to DIN (Deutsche Industrienormen) 1995 and their
penetration was measured according to DIN 19~5. The results compared to the
values measured for bitumen B 80 are shown in the following Table.
Table 1 ;
Mixture Composition Softening P. Penetration DIN 1995
Bitumen PolYethylene DIN 1995 at 2C at 25C
No. %wt. %wt. C l/10mm 1/10mm
_ _ _ .... . ~ . . _ _ ,,
1 100 0 48.2 5 79
2 97 3 50.1 5 79 ~ -
3 90 10 73.8 7 ~2 -
4 80 20 110.0 2 12 -
... . ...
Example 2
The bituminous binders of Example 1 were used to produce asphalt
. ,... - .. . .
mixtures according to prevailing standards for bituminous road surfacing~ the
mixtures containing 6.7%, by weight, of the binder and, by weight, 10% of
limestone dust, 13% natural sand 0/2, 25% broken basalt sand 0/2, 26% broken
basalt rock 2/5 and 26% broken basalt rock 5/8. As expected from the gel-like
consistency of the polyethylene-containing binder, the resultant asphalt
mixtures containing 10% to 20% of the polyethylene were relati~ely stiff,
~hich made it impossible to work them by the usual techniques~ partîcularly
by auto~atically, to lay down a road surface.
The resultant asphalt ~ixtures were formed into Marshall test
bodies with 2 x 50, 2 x 35 and 2 x 75 impacts, and the test bodies were then
tested in the usual manner, the results being indicated in the following
Table.
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Example 3
The viscosities of polyethylene, polypropylene, polyethylene-
bitumen blends and polypropylene-bitumen blends were investigated by means .
of a Brabender plastograph at constant temperatures ~290C and 270C) over
an ex~ended period of time, the stirrer of the plastograph being rotated at
60 rpm and the required torque being measured in meter/gram.
Seven tests were run, comminuted polyethylene waste material be-
ing examined at 290C in Test 1, the same material at 270C in Test 2, a mix-
ture of 50:50 polyethylene waste material and road surfacing ~itumen B 80 at . ~ .
290C in Test 3, the same mixture of polyethylene waste materi.al vith road .
surfacing bitumen B 120 at the same temperature in Test 4, the same components
in a ratio of 30:70 at the same temperature in Test 5, comminuted polypropy~
lene waste material at the same temperature in Test 6, and a mixture of 30:70
comminuted polypropylene waste material and bi~umen B 70 at the same tempera-
ture in Test 7. The test results are giv~en in the following Table
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The preceding Table clearly shows by the indicated measured values
that, during the homogenizing heat treatment, the polyolefin material mole-
cules are cracked, decomposed or depolymerized, which expresses itself physi-
cally in a reduction of viscosity. This, combined with the chemical reaction
of the resultant polyolefin moieties with bitumen moieties, produces a marked
viscosity reduction in the polyolefin-bitumen blend during the homogenizing
treatment, which lowered viscosity then remains substantially stable for an
extended period of time. The initial increase in the viscosity during the
tests is based on the fact that, at the start, the polyolefin is not yet dis-
solved in the bitumen so that the test measuring instrument essentially mea-
sures the viscosity of the bitumen at ~his stage, the viscosi~y of the blend
appearing only after a certain period of time when the polyolefin becomes
dissolved.
As the tests of Example 3 show~ the blends produced according to
the invention have a substantially lower viscosity after the homogenizing
treatment, which makes it possible to use them with the usual mineral sub-
stances in asphalt co=positions in conventional asphalt working apparatus.
Example 4
A hot mixing installation normally used for working Trinidad
asphalt was utilized to homogenize a mixture of polyethylene flakes and a con~
ventional road surfacing bitumen B 120 at a temperature reaching above 240C
for about three hours. The mixture consisting of 50% polyolefin and 50% ~-
bitumen, this ratio being subsequently changed by the addition of hot bitumen
to a polyolein content o 15%, 18%, 20% and 25%. These binders were sprayed
into a convsntional mixer filled with mineral aggregate heated to a tempera-
tare Df 23nc to produce asphalt compositions. Strips of road surfacing of
abou~ 600 meter leng~h and 5 metsr width for a road carrying average traffic
.:
were produced from ths asphalt containing respective bitwnen bindsrs blended
with 15%9~18% and 25% polyethylene, as well as a comparative asphalt with a
bitumen binder rse of polyethylens. These road surface strips were laid down
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6E~3~
with a conventional asphalt laying machine and the asphalt layer was then
compressed with a train of rubber rolls. It was found that even the bitumen
blend containing 25% polyethylene permitted laying down of the asphalt strip
by machine without any difficulty, i.e. the asphalt had a stiffness low enough
to make automatic working possible, with conventional means. Yet, subsequent
tests on test bodies, some of which were made from the mixture and some of
which were removed from the finished road surface in the form of so-called
boring samples, showed the improvements obtained by the polyolefin addition
leading to a cracking of the polyolefin molecules, and parameters were also
measured which showed the improvement compared with a simple polyolefin addi-
tion withoutcracking the polyolefin molecules.
It may be pointed out in this connection that the measurement of
the notch tensile strength of Marshall-bodies taken at 20C showed that the
break in bodies whose binders are free of polyolefin occurs in the region of
the binder between the aggregate particles while the break occurs }n a plane
and across the aggregate particles and the binder in Marshall-bodies made of
mixtures K IIl and K IU, i.e. bodies made of asphalt containing binders pro-
duced according to the invention. This proves the e~traordinary adhesion of
~ the bituminous binder of this invetnion to the aggregate particles, which may
be explained by the foxmation of salt bridges formed between the polyolefin-
naphthene compounds and the surfaces of the aggregate particles.
Furthe~more, measurements of the gliding value tested with an RRL-
pendulum instrum~nt according to British Standard 812:1967 and SNV 640 555 on
the road surface showed that the road strips with the binders according to the
invention had somewhat better traction ~average value obtained from a large
number of measurements SRT 63) than those with bitumen P 120 binders without
polyolefin content Caverage value obtained from a large number of measurements
SRT 61), the binder contents being 7%.
The following Tables 4 and 5 show the test values obtained with
Marshall-bodies and boring samples. Measuring values obtained from M~rshall-
~ 13
~LID6~1~3~
bodies from polyolefin-free bitumen ar~ listed under AB 0/]2 wh:ile those
listed under AB 0/12K are those measured on Marshall-bodies made from asphalt
containing the same mineral aggregate but a binder of a polyethylene-bitumen
blend containing 20% polyethylene. In both cases, the binder content was 7%.
Under K l~ K III and K V, Table 5 lists measuring values obtained
from Marshall bodies and boring samples, the Marshall-bodies being made
respectively of the road surfacings of the three test road strips, the mineral
aggregate contents of the three respective road surfacing materials being the
same, K I listing the values with a bitumen binder free of polyethylene,
K III those with a bitumen binder containing 25% polyethylene, and K V those
with a bi~umen binder containing 15% polyethylene. The binder content in all
cases was 6.5%. In these tests, tool the Marshall-bodies and boring samples
made of asphalts containing the binders of the invention show their great
superiority under the simulated extreme weather conditions over polyethylene-
free bituminous asphalt binders.
~ Thus, the three respective Marshall-bodies were subjected to a
variety of quality tests. In the first test, the test bodies were subJected ~-
to the following cycle repeated five times:
- (a) Submersion in a saturated salt solution at a temperature from 20C to
22C for a period of 15 hours.
(b) Exposure to air at a temperature from 20C to 22C for a period of 9 ~
hours. ~i -
(c) Exposure to cold air at a temperature of -20C ~in an air cond~ d~ room)
for a period of 15 hours.
.
~(d) Exposure to air at a temperature from 20~C to 22C for a periad of 9
hours.
Immedlately after the final cold air exposure, the compression
strength was measured with a steel ram of 50 sq.cm cross section and a broken
edge, moving at a speed of 25 mm/minute. The following values were measured:
. .
3~1
MaterialCompression 2trengthCompression strength
50 cm
~ Iabove 10,000 kg above 200 kg/cmZ
K IIIabove 10l000 kg above 200 kg/cm2
K Vabove 10~000 kg above 200 kg/cm2
In a further test, a seven-hour storage alt room temperature was ~:
used subsequent to the above cycle and the compression strength was then
determined, with the following results~
MaterialCompression strengthCompression strength
50 cm
K I 4,000 kg about 80 kg/cm2
K III 6,150 kg " 123 kg/cm2
K V 6,350 kg " 127 kg/cm2
In still further tests, the Marshall-bodies were subjected five :
times to a cycle consisting of storage in cold air at a temperature of -20C
for 15 hours and a subsequen~ exposure to air at a temperature of 20C to
22C for 33 hours. Subsequen~ to ~he fmal cold air storage, the Marshall- ~
bodies were stored at a ~emperature of 20C to 22C3 whereupon the compres- ~ :
slon strength was measured, with ~he following results~
Ma~erial Compression 2trength Compression strength
50 cm
K I 3S800 kg about 76 kg/cm2
K III 6,350 kg " 127 kg/cm~
K V ~6,400 kg " 128 kg/cm2
Finally, boring samples having a diameter o~ 15 cm and à heigh~ -
:
o:5 cm were subjected 12 times to a cycle consisting of storage ~or 12 hours
at 60C and subsequent storage for 6 hours a~ -20C. The compression strength
~was then measured a~ 1,250 kg when the sample with a bitumen binder contain-
ing 15% polyethylene was subje~t~d:to:the load of a ram of 50 cm2 cross sec-
tionJ; while this rose to l,500 ~g;when the binder contained 25% polyethylene.
:Eoring samp1es with a conventional bitumen binder broke under their own
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~ .
~ - '.
-16-
. ' : . '
~L~66~33~
Table 5
Tests with Marshall-bodies and boring samples
Material K I K III K V
.~
Marshall-bodies of 3
average volumetric 2.405 2.298 2.350 g/cm
density
Boring samples of 3
average volumetric 2.437 2.303 2.364 g/CM
density
Average gross density2 . 5042 . 461 2 . 490 g/cm
Porosity Marshall4.0 6.6 5.6 vol%
3 10 Porosity boring sample2.7 6.4 5.0 vol%
Degree of compression 101 lOQ lOl %
Carrying value Marshall840 1,830 1,750 lS~
Flow value Marshall 21 16 17 1/10 mm
Notch tensile strength830 1,780 1,520 k~
at 20C
Flow value of notch 29 22 22 1/10 mm
tensile s~rength
Axial pressure test,6,730 9,850 ~ 10,600
20C, 50 mm/min -
.
.
.
.
'"'~ '
-17-
':
