Method of preparing an asphalt paving material containing recycled plastics

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.

Description

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 3% and 5%. A typical Canadian standard for stability would be in excess of 6000 Newtons. A typical Canadian standard for flow would between 8 mm and 16 mm. U.S. Pat. No. 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 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.

SUMMARY 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 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

• • 48.2% Sand
  • 21.7% one quarter inch rock
  • 12.7% one half inch rock
  • 7.9% five-eighths inch rock
  • 3.0% Class 2 recycled plastic
  • 6.5% liquid asphalt
  • (all ingredients are shown by weight and not by volume)

Referring to THE FIGURE, 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 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—16 mm

Although the formulation described above contained Class 2 recycled plastic. It is believed from the work of Fishback 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.

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 1 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.

In 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 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.

Claims

1. A method of forming an asphalt paving material containing recycled plastics, comprising the steps of:

forming recycled plastics into plastic particles;

dry mixing and heating aggregate and sand;

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; and

adding liquid asphalt to the mixture of 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 mixture of plastic particles and aggregate being brought within a temperature range of between 280 degrees and 310 degrees fahrenheit.

5. The method as defined in claim 1, the plastic particles constituting between one percent and ten percent of by weight of the plastic particles, aggregate and liquid asphalt.

6. The method as defined in claim 5, the plastic particles constituting between one percent and four percent by weight.

7. The method as defined in claim 1, the recycled plastic being an unclassified mixture of plastics.

8. The method as defined in claim 1, the recycled plastic being from Class 2.

9. A method of forming an asphalt paving material containing recycled plastics, comprising the steps of:

forming recycled plastics into plastic particles ranging in size from a powder to one quarter inch granules;

dry mixing and heating aggregate and sand;

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 of between 280 degrees and 310 degrees Fahrenheit; and

adding liquid asphalt to the mixture of 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.

10. The method as defined in claim 9, the plastic particles having jagged edges.

11. The method as defined in claim 9, the plastic particles constituting between one percent and four percent by weight.

12. The method as defined in claim 9, the recycled plastic being an unclassified mixture of plastics.

13. The method as defined in claim 9, the recycled plastic being from Class 2.