METHOD OF PREPARING AN ASPHALT PAVING MATERIAL CONTAINING RECYCLED PLASTICS

METHODE DE PREPARATION DE MATERIAU DE REVETEMENT ROUTIER A L'ASPHALTE CONTENANT DES MATIERES PLASTIQUES RECYCLEES

English Abstract

A method of forming an asphalt paving material containing recycled plastics. A first step involves forming recycled plastics into plastic particles. A second step involves dry mixing and heating aggregate and sand. A third step involves dry mixing untreated plastic particles with the aggregate and sand, while continuing heating until the mixture of plastic particles, aggregate and sand reaches a temperature range provided in accepted road building specifications for heating aggregate. A fourth step involves adding liquid asphalt to the mixture of plastic particles, aggregate and sand.

French Abstract

La présente description porte sur une méthode de préparation de matériau de revêtement routier à l'asphalte contenant des matières plastiques recyclées. Une première étape suppose la transformation de matières plastiques recyclées en particules de plastique. Une seconde étape implique le mélange à sec et le chauffage des agrégats et du sable. Une troisième étape consiste à mélanger à sec les particules de plastique non traitées avec les agrégats et le sable, tout en continuant le processus de chauffage jusqu'à ce que le mélange de particules de plastique, d'agrégats et de sable atteigne une plage de températures mentionnée dans les spécifications de construction des routes validées relatives au chauffage des agrégats. Une quatrième étape suppose l'ajout d'asphalte liquide au mélange de particules de plastique, d'agrégats et de sable.

Claims

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THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of forming an asphalt paving material containing
recycled plastics, comprising the steps of:
forming recycled plastics into untreated plastic
particles;
dry mixing and heating aggregate and sand;
dry mixing the untreated plastic particles with the
aggregate and sand, while continuing heating until the mixture
of the untreated plastic particles, aggregate and sand reaches
a temperature range of between 280 degrees and 310 degrees
fahrenheit; and
adding liquid asphalt to the mixture of the plastic
particles, aggregate and sand.
2. The method as defined in Claim 1, the plastic particles
ranging in size from a powder to one quarter inch granules.
3. The method as defined in Claim 1, the plastic particles
having jagged edges.
4. The method as defined in Claim 1, the plastic particles
constituting between one percent and ten percent by weight
of the plastic particles, aggregate and liquid asphalt.
5. The method as defined in Claim 4, the plastic particles
constituting between one percent and four percent by weight.
6. The method as defined in Claim 1, the recycled plastic
being an unclassified mixture of plastics.
7. The method as defined in Claim 1, the recycled plastic
being from Class 2.
8. A method of forming an asphalt paving material containing
recycled plastics, comprising the steps of:

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forming recycled plastics into untreated plastic
particles ranging in size from a powder to one quarter inch
granules;
dry mixing and heating aggregate and sand;
dry mixing the untreated plastic particles with the
aggregate and sand, while continuing heating until the mixture
of the plastic particles, aggregate and sand reaches a
temperature range of between 280 degrees and 310 degrees
Fahrenheit; and
adding liquid asphalt to the mixture of the plastic
particles, aggregate and sand until the there is between 6
percent and 8 percent liquid asphalt by weight, between 1
percent and 10 percent plastic particles by weight, aggregate
and sand.
9. The method as defined in Claim 8, the plastic particles
having jagged edges.
10. The method as defined in Claim 8, the plastic particles
constituting between one percent and four percent by weight.
11. The method as defined in Claim 8, the recycled plastic
being an unclassified mixture of plastics.
12. The method as defined in Claim 8, the recycled plastic
being from Class 2.

Description

CA 02444307 2003-10-24
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TITLE OF THE INVENTION:
Method Of Preparing An Asphalt Paving Material Containing
Recycled Plastics
FIELD OF THE INVENTION
The present invention relates to a method of preparing an
asphalt paving material containing recycled plastics.
BACKGROUND OF THE INVENTION
Placing recycled plastics into asphalt paving materials
is an attractive alternative, from an environmental point of
view, to other methods of disposing of plastic waste. If
disposed of at a landfill site, plastic waste takes hundreds
of years to break down. If disposed of through incineration,
there are polluting agent in the gas emissions during
incineration.
A lot of research effort has gone into developing an
asphalt material with suitable Marshall properties in terms of
percentage of air voids, stability (mechanical strength) and
flow (plastic resistance). The Marshall properties required
for asphalt roads varies from jurisdiction to jurisdiction. A
typical Canadian standard for air void would be between 3o and
5%. A typical Canadian standard for stability would be in
excess of 6000 Newtons. A typical Canadian standard for flow
would between 8mm and 16 mm. United States Patent 5,702,199
(Fishback 1999), describes an asphalt material containing
recycled plastics that is able to meet the corresponding
United States standards. According to the teachings of the
Fishback reference, in order to meet those standards one must
form the plastic material into particles. Preferably, most of
the Class 1 and Class 2 plastic is removed, leaving Classes 3
through 7. Fishback also suggests that it would be
undesirable to have too large a proportion from Class 4 and
Class 6. Preferably, the plastic particles are in the one
eighth of an inch to one quarter of an inch size. One must
then further process the plastic particles to activate the

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surface of the particles to increase the surface tension and
to cause free or active carbon atoms to be present in the
molecules of the plastic material at the particle surface.
Preferably, this is done by exposing the plastic particles to
a flame treatment. Preferably, the plastic particles are used
within a day or so of treatment, and are kept out of contact
with free flowing air or sunlight until used. The plastic
particle are then blended with rock aggregate and an asphaltic
mix binder.
SUNDRY OF THE INVENTION
What is required is an alternative method of preparing an
asphalt paving material containing recycled plastics.
According to the present invention there is provided A
method of forming an asphalt paving material containing
recycled plastics. A first step involves forming recycled
plastics into plastic particles. A second step involves dry
mixing and heating aggregate and sand. A third step involves
dry mixing untreated plastic particles with the aggregate and
sand, while continuing heating until the mixture of plastic
particles, aggregate and sand reaches a temperature range
provided in accepted road building specifications for heating
aggregate. A fourth step involves adding liquid asphalt to
the mixture of plastic particles, aggregate and sand.
The advantage of the above described method is that it
does not constitute a marked departure from asphalt mixing
methods prescribed by existing road building procedures. As
will hereinafter be further described, the results obtained by
the method are well above industry specifications.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention will become
more apparent from the following description in which

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reference is made to the appended drawings, the drawings are
for the purpose of illustration only and are not intended to
in any way limit the scope of the invention to the particular
embodiment or embodiments shown, wherein:
THE FIGURE is a flow diagram setting for the sequence of
steps of the method of preparing an asphalt paving material
containing recycled plastics:
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred method of preparing an asphalt paving
material containing recycled plastics will now be described
with reference to The FIGURE.
In order to demonstrate the utility of the present
invention as compared to the Fishback reference, the example
below used recycled plastic taken solely from Class 2, which
is one of the classes that the Fishback reference recommended
be removed.
Test Road
48.20 Sand
21.70 one quarter inch rock
12.70 one half inch rock
7.9% five-eighths inch rock
3.Oo Class 2 recycled plastic
6.5% liquid asphalt
(all ingredients are shown by weight and not by volume)
Referring to THE FIGUREr the recycled plastics 20 were
ground into plastic particles 22 ranging in size from a
powder to one quarter inch granules. The plastic particles
were left with jagged edges, as this was believed to be
beneficial to the bonding process.
A mixing plant 24 was used to dry mix aggregate and sand
to a temperature of 300 degrees Fahrenheit. This temperature
was the temperature specified in the road building standard

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that was being followed.
The plastic particles were then dry mixed in with the
aggregate and sand. The plastic particles were untreated, ie.
they were not subjected to any chemical or heat treatment
prior to use. The temperature of the dry mixture of plastic
particles, aggregate and sand initially dropped. Heating was
continued until the mixture of plastic particles, aggregate
and sand reached 300 degrees. Although 300 degrees was the
temperature range specified, with road building standards the
temperature usually is within a range of between 280 degrees
and 310 degrees Fahrenheit. The dry mixture was then
transported to the site of the road.
Liquid asphalt was then added to the mixture of plastic
particles, aggregate and sand, in a wet mixing process
identified by reference numeral 26. At the time of adding the
liquid asphalt, the temperature of the dry mixture was 252
degrees Fahrenheit. The wet mix, after the liquid asphalt had
been added, had a temperature of 184 degrees Fahrenheit. The
asphalt was laid onto the road at 136 degrees Fahrenheit.
Core samples taken revealed the following critical data:
Air voids - 3.34
Stability - a problem was experienced in testing
stability. The test had to be stopped at 18,318 Newtons as
the testing equipment had reached its upper limit: How much
greater than 18,000 Newtons the stability reading may be is
not know at this time. However, 18,000 Newtons is three times
the typical Canadian standard.
Flow - l6mm
Although the formulation described above contained Class
2 recycled plastic. It is believed from the work of Fishback

CA 02444307 2003-10-24
that comparable results may be obtained through the use of
Class 3 through 7 plastics. It is also believed that
comparable results may be obtained through the use of an
unclassified mixture of recycled plastics.
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Although the formulation described above contained 3%
plastic particles by weight, it is believed that comparable
results may be obtained through the use of between l percent
and 10 percent plastic particles by weight of the mixture of
plastic particles, liquid asphalt, aggregate and sand.
Cautionary Warnings:
When preparing test patches prior to construction of
the test road, there were times when softness in the
material resulted in problems being experienced in the
laying the asphalt, One problem experienced was a wave
motion during the rolling of the asphalt, which did not
allow compaction of the asphalt as well as it should.
Another problem was experienced during the screeding
process, as a back and forth motion of a bar is used to
spread the material. Should this occur, the problem can be
addressed by reducing the plastic particle content of the
mixture. For this reason a narrower range of between one
percent and our percent by weight is preferred, as no
problems in laying of the asphalt are likely to be
encountered within this narrower range. It is, of course,
recommended that some test patches be laid to ensure that
the asphalt is spreading properly before a commitment is
made to complete an entire road.
Tn this patent document, the word "comprising" is used in
its non-limiting sense to mean that items following the word
are included, but items not specifically mentioned are not
excluded. A reference to an element by the indefinite article
"a" does not exclude the possibility that more than one of the

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element is present, unless the context clearly requires that
there be one and only one of the elements.
It will be apparent to one skilled in the art that
modifications may be made to the illustrated embodiment
without departing from the spirit and scope of the invention
as hereinafter defined in the Claims.

Representative Drawing