WO2012160555A1

WO2012160555A1 - Process for recycling asphalt mixes

Info

Publication number: WO2012160555A1
Application number: PCT/IL2012/000206
Authority: WO
Inventors: Ronen Alexander Peled; Andrey Vorobiev; Gregory Svechinsky; Ilan Ishai
Original assignee: Dsi - Dimona Silica Industries Ltd.
Priority date: 2011-05-24
Filing date: 2012-05-24
Publication date: 2012-11-29

Abstract

A process for rehabilitating used asphalt is provided. The process involves mixing the used asphalt with a novel rehabilitating agent comprising the mineral porcelanite, an activating agent and a polymer. The process restores the elastic properties of asphalt and provides a rejuvenated asphalt with superior stability relative to asphalt rejuvenated with traditional rejuvenating agents.

Description

PROCESS FOR RECYCLING ASPHALT MIXES

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to U.S. Provisional Patent Application Serial No. 61/489,338, filed May 24, 2011 and entitled PROCESS FOR RECYCLING ASPHALT MIXES, the disclosure of which is hereby incorporated by reference and priority of which is hereby claimed pursuant to 37 CFR 1.78(a)(4) and (5)(i).

FIELD OF THE INVENTION

The present invention relates to a process for recycling used asphalt mixes using a novel rehabilitant.

BACKGROUND OF THE INVENTION

The following publications are believed to represent the current state of the art:

U.S. Patent Nos. 6,769,836, 7,503,202, 7,811,372, 7,838,575; and Basic Asphalt Recycling Manual, Asphalt Recycling and Reclaming Association (Annapolis, MD, USA), 2001.

SUMMARY OF THE INVENTION

The present invention seeks to provide a process for recycling used asphalt mixes using a novel rehabilitating agent.

Accordingly, there is provided in accordance with one embodiment of the present invention a process for rehabilitating a used asphalt mix including: combining porcelanite, an activating agent and a polymer to form a rehabilitant; and mixing the rehabilitant with the used asphalt mix at a temperature of at least about 140 °C.

Preferably, the activating agent includes a quaternary ammonium compound. The quaternary ammonium compound preferably includes at least two alkyl chains of 10 - 30 carbons, more preferably 15 - 18 carbons. Most preferably, the quaternary ammonium compound is di(hydrogenated tallow)dimethylammonium chloride.

In accordance with a preferred embodiment of the present invention, the rehabilitant includes the activating agent in an amount of 3 - 20% of the porcelanite weight. More preferably, the rehabilitant includes the activating agent in an amount of 10 - 15% of the porcelanite weight.

Preferably, the polymer is a thermoplastic polymer. The thermoplastic polymer is preferably selected from polyethylene, polypropylene, EPDM rubber, styrene- butadiene-styrene copolymer and ethylene-vinyl acetate copolymer. Most preferably, the polymer is selected from styrene-butadiene-styrene copolymer and ethylene-vinyl acetate copolymer.

In accordance with a preferred embodiment of the present invention, the ratio of the weight of the polymer to the combined weight of the porcelanite and the activating agent in the rehabilitant is from about 1:10 to about 10:1. More preferably, the ratio is from about 1:3 to about 1:1, and most preferably about 1:2.

Preferably, the combining includes: blending the porcelanite with the activating agent to form an activated porcelanite, mixing the activated porcelanite with the polymer in an extruder at a temperature of about 100 °C to about 250 °C to form an extruded mixture; and granulating the extruded mixture. More preferably, the mixing the activated porcelanite with the polymer is at a temperature of about 100 °C to about 160 °C. The granulating preferably produces granules of about 3 - 5 mm. In accordance with a preferred embodiment of the present invention, the mixing the rehabilitant with the used asphalt mix is carried out on the surface where the used asphalt is laid. In accordance with an alternative embodiment of the present invention, the mixing the rehabilitant with the used asphalt mix is carried out in an asphalt plant. The mixing is preferably carried out at about 140 - 190 °C, more preferably about 150 °C.

There is provided in accordance with an additional embodiment of the present invention a composition for rehabilitating a used asphalt mix including: porcelanite, an activating agent and a polymer.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawing in which:

Fig. 1 is a simplified diagram of the structure of particles of an asphalt mix recycled according to the process of the present invention. DETAILED DESCRIPTION OF THE INVENTION

Hot recycling of used asphalt mixes is very widely used in the practice of pavement rehabilitation. Asphalt, once laid on a road surface, typically lasts for about 10-15 years, during which time it is exposed to oxygen, moisture and UV radiation from the sun. Due to oxidation and aging resulting from such exposure, the bitumen in the asphalt becomes brittle and loses its elastomeric properties that are required for asphalt pavements. It is desirable to recycle used asphalt rather than dispose of it in order to reduce costs and environmental impact.

The most common technique for renewing used asphalt is to add a maltenic petroleum fraction to the used asphalt. Maltenic fractions are aromatic extracts from the heavy distillate fraction of crude oil and are characterized by the following properties: viscosity at 100°C 7-12 cSt, density at 15°C 0.96-0.99, pour point 15°C - 21°C. The maltenic aromatic compounds in asphalt bitumen are destroyed by oxidation and aging. This causes the bitumen to become brittle and no longer suitable for road use. The added maltenic fraction restores the lost elastomeric properties of bitumen.

In a typical recycling process, the maltenic fraction or its dispersion in water and the heated oxidized asphalt are mixed and intensively agitated together. During this process, maltenic oils penetrate into the old bitumen structures and soften them. The short mixing time characteristic of asphalt production and the very high viscosity of old bitumen both retard this process.

One of the drawbacks of this method is that the maltenic oils do not penetrate the used asphalt uniformly. Bitumen structures located close to the surface of the asphalt particles are softened too much by a portion of the oils, while the residual oils remain on the surface and lubricate the particles. The resulting asphalt mix acquires the desired elasto-plastomeric properties but has low mechanical stability. Additionally, since the added fraction consists of fast-oxidizing aromatics, the recycled asphalt mix is as susceptible to oxidation and aging as was the original asphalt.

Polymer-modified asphalt mixes usually have much better mechanical stability and elasticity and also age slower than unmodified asphalt mixes. The polymer modifiers, such as styrene-butadiene-styrene (SBS) and ethylene-vinyl acetate (EVA) block copolymers, are added to bitumen and form three-dimensional networks inside the W

continuous bitumen phase. Typical concentrations of polymer in the bitumen are 3-6% by weight. Although the polymers modify the mechanical properties of bitumen and reduce the effects of bitumen aging, the bitumen is nonetheless still exposed to oxygen, moisture and UV radiation.

A composition for lowering the mixing temperature of stone matrix asphalt (SMA) and other asphalt mixes to about 165 °C is disclosed in WO 2010/116354, assigned to the assignee of the present invention and incorporated by reference herein in its entirety. It has now been found that this relatively inexpensive composition, can be used as part of an asphalt rehabilitating composition.

A first embodiment of the present invention is a process for rehabilitating used asphalt mixes comprising:

forming a composition (hereinafter "rehabilitant") comprising porcelanite, an activating agent and a polymer; and

mixing the rehabilitant with a used asphalt mix at high temperature.

Porcelanite is a mineral found, inter alia, in deposits in the Dead Sea area of Israel and is described in detail in WO 2010/116354. In one preferred embodiment, the activating agent is a quaternary ammonium compound.

The quaternary ammonium compound preferably has at least two long carbon chains. The long carbon chains preferably comprise between 10 and 30 carbon atoms, more preferably from 15 to 18 carbon atoms. An especially preferred compound is di(hydrogenated tallow)dimethylammonium chloride, available from Akzo-Nobel (Stockholm, Sweden) as Arquad 2HT-75 (hereinafter "2HT-75").

Activation of the porcelanite is preferably achieved by crushing the porcelanite to about 3 - 8 mm particle size granules, adding the activating agent, and blending the mixture until the desired particle size is achieved. Alternatively, the porcelanite can be blended for about 5 minutes, followed by addition of the activating agent and further blending for an additional 1 - 5 minutes.

The weight of the activating agent in the rehabilitant is preferably between about 3 and 20% of the porcelanite weight. More preferably, the weight of the activating agent in the rehabilitant is between about 10 and 15% of the porcelanite weight.

The polymer is preferably a thermoplastic polymer. Preferable examples of the thermoplastic polymer include polyethylene, polypropylene, EPDM rubber, styrene- W

butadiene-styrene copolymer and ethylene-vinyl acetate copolymer. The ratio of polymer to activated porcelanite in the rehabilitant is preferably about 1:10 - 10:1, more preferably about 1:3 - 1:1, and most preferably about 1:2.

The rehabilitant is preferably formed by mixing the activated porcelanite with the polymer in an extruder at a temperature above the softening point of the polymer, typically about 100 - 250 °C and more preferably about 100 - 160 °C. The extruded mixture is then granulated and cooled. The granule size is preferably about 3 - 5 mm.

The rehabilitant is preferably mixed with used asphalt at a temperature of at least about 140 °C. The mixing of the rehabilitant with the used asphalt can be performed in accordance with a method described in Basic Asphalt Recycling Manual, Asphalt Recycling and Reclaiming Association (Annapolis, MD, USA), 2001, hereby incorporated by reference herein in its entirety.

In accordance with one embodiment of the present invention, the rehabilitant is mixed with the used asphalt using hot in-place recycling (HIR) technology, wherein 100% recycling of the existed asphalt pavement is completed on site. In this method, the existing asphalt pavement is heated to about 140 - 190 °C, preferably about 150 °C, and softened, permitting it to be scarified or hot rotary milled to a specified depth. The scarified or loosened asphalt pavement is then mixed, placed and compacted with conventional equipment. New aggregate, new asphalt binder, recycling agents and/or new asphalt mix can be added on an as-required basis.

In an alternative embodiment, the recycling process is carried out in an asphalt plant. The used asphalt is crushed to a size suitable for use as aggregates for asphalt mixes, typically less than 5 cm. Rehabilitant is mixed with the crushed asphalt at a temperature of about 140 - 190 °C, preferably about 150 °C.

The rehabilitant is preferably added to the asphalt in an amount of about 1 - 10% of the asphalt weight, more preferably about 3 - 6% of the asphalt weight. The mixing time is preferably about 50 - 80 sec, more preferably about 60 seconds.

The rehabilitated asphalt can be prepared in a batch or continuous process. After production, the hot rehabilitated asphalt can be loaded into trucks for delivery to a worksite, or stored in a hot storage facility.

The asphalt rehabilitated according to the present invention has superior properties relative to asphalt rehabilitated according to previously known methods and even relative to original asphalt mixes. When asphalt mixes are produced, a portion of bitumen is absorbed into the aggregate particle, while the balance remains on the surface of the particles. It is this surface bitumen which oxidizes and hardens during the lifetime of the asphalt on the road.

Reference is now made to Fig. 1, which demonstrates the distribution of layers in a particle 2 of asphalt after rehabilitation. Due to the high viscosities of both the bitumen in the used asphalt mix and the rehabilitant, the rehabilitant does not penetrate through the entire thickness of the surface bitumen layer.

A layer 4 of old bitumen, absorbed by an outer layer of aggregates 6, stays unchanged. A layer 8 of oxidized bitumen located close to the stone surface 10 also stays unchanged due to its very high viscosity. Both of these layers provide high adhesion between the aggregate stones and the old oxidized bitumen.

The rehabilitant penetrates into an outer bitumen layer 12, which obtains visco- elastic properties similar to those of polymer-modified bitumen. As only a part of the bitumen is mixed with the rehabilitant, the concentration of the rehabilitant in outer bitumen layer 12 is relatively high. This effect improves the mechanical and anti-aging properties of the rehabilitated asphalt as compared to an original polymer-modified asphalt mix with a similar concentration of polymer.

Additionally, since it is difficult for the rehabilitant to penetrate into the oxidized bitumen, a layer 14 of rehabilitant forms on the outside of the aggregate particles. Layer 14 provides a rehabilitant-enriched zone with mechanical and chemical stability much better than those of even polymer-modified bitumen. Furthermore, since bitumen layer 12 is covered by layer 14, it has no direct contact with oxygen and humidity, which slows down the bitumen oxidation processes.

A further embodiment of the present invention is a composition for rehabilitating used asphalt mixes (hereinafter "rehabilitant") comprising porcelanite, an activating agent and a polymer. Preferable examples of the activating agent and polymer are described hereinabove with reference to the process for rehabilitating used asphalt mixes.

The weight of the activating agent in the rehabilitant is preferably between 3 and 20% of the porcelanite weight. More preferably, the weight of the activating agent in the rehabilitant is between 10 and 15% of the porcelanite weight. The ratio of polymer to activated porcelanite in the rehabilitant is preferably about 1:10 - 10:1, more preferably about 1:3 - 1:1, most preferably about 1:2.

The present invention provides, in addition to the rehabilitation of used asphalt, the possibility to impart to the used asphalt new properties, specific for high-grade polymer-modified asphalts. Mechanical and aging properties of the asphalt, rehabilitated by the process of the invention, are even better than those of standard polymer-modified asphalts.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as modifications thereof which would occur to a person of skill in the art upon reading the foregoing description and which are not in the prior art.

Claims

1. A process for rehabilitating a used asphalt mix comprising:

combining porcelanite, an activating agent and a polymer to form a rehabilitant; and

mixing said rehabilitant with said used asphalt mix at a temperature of at least about 140 °C.

2. The process according to claim 1, wherein said activating agent comprises a quaternary ammonium compound.

3. The process according to claim 2, wherein said quaternary ammonium compound comprises at least two alkyl chains of 10 - 30 carbons.

4. The process according to claim 3, wherein said at least two alkyl chains have 15— 18 carbons.

5. The process according to any one of claims 2 to 4, wherein said quaternary ammonium compound is di(hydrogenated tallow)dimethylammonium chloride.

6. The process according to any one of claims 1 to 5, wherein said rehabilitant comprises said activating agent in an amount of 3 - 20% of the porcelanite weight.

7. The process according to claim 6, wherein said rehabilitant comprises said activating agent in an amount of 10 - 15% of the porcelanite weight.

8. The process according to any one of claims 1 to 7, wherein said polymer is a thermoplastic polymer.

9. The process according to claim 8, wherein said thermoplastic polymer is selected from polyethylene, polypropylene, EPDM rubber, styrene-butadiene-styrene copolymer and ethylene-vinyl acetate copolymer.

10. The process according to claim 9, wherein said polymer is selected from styrene-butadiene-styrene copolymer and ethylene-vinyl acetate copolymer.

11. The process according to any one of claims 1 to 10, wherein the ratio of the weight of said polymer to the combined weight of said porcelanite and said activating agent in said rehabilitant is from about 1:10 to about 10:1.

12. The process according to claim 11, wherein the ratio of the weight of said polymer to the combined weight of said porcelanite and said activating agent in said rehabilitant is from about 1:3 to about 1:1.

13. The process according to claim 12, wherein the ratio of the weight of said polymer to the combined weight of said porcelanite and said activating agent in said rehabilitant is about 1:2.

14. The process according to any one of claims 1 to 13, wherein said combining comprises:

blending said porcelanite with said activating agent to form an activated porcelanite,

mixing said activated porcelanite with said polymer in an extruder at a temperature of about 100 °C to about 250 °C to form an extruded mixture; and

granulating said extruded mixture.

15. The process according to claim 14, wherein said mixing said activated porcelanite with said polymer is at a temperature of about 100 °C to about 160 °C.

16. The process according to claim 14 or 15, wherein said granulating produces granules of about 3 - 5 mm.

17. The process according to any one of claims 1 to 16, wherein said mixing said rehabilitant with said used asphalt mix is carried out on the surface where the used asphalt is laid.

18. The process according to any one of claims 1 to 16, wherein said mixing said rehabilitant with said used asphalt mix is carried out in an asphalt plant.

19. The process according to any one of claims 1 to 18, wherein said mixing said rehabilitant with said used asphalt mix is carried out at about 140 - 190 °C.

20. The process according to claim 19, wherein said mixing said rehabilitant with said used asphalt mix is carried out at about 150 °C.

21. A composition for rehabilitating a used asphalt mix comprising:

porcelanite;

an activating agent; and

a polymer.

22. The composition according to claim 21, wherein said activating agent comprises a quaternary ammonium compound.

23. The composition according to claim 22, wherein said quaternary ammonium compound comprises at least two alkyl chains of 10 - 30 carbons.

24. The composition according to claim 23, wherein said at least two alkyl chains have 15 - 18 carbons.

25. The composition according to any one of claims 22 to 24, wherein said quaternary ammonium compound is di(hydrogenated tallow)dimethylammonium chloride.

26. The composition according to any one of claims 21 to 25, wherein said rehabilitant comprises said activating agent in an amount of 3 - 20% of the porcelanite weight.

27. The composition according to claim 26, wherein said rehabilitant comprises said activating agent in an amount of 10 - 15% of the porcelanite weight.

28. The composition according to any one of claims 21 to 27, wherein said polymer is a thermoplastic polymer.

29. The composition according to claim 28, wherein said thermoplastic polymer is selected from polyethylene, polypropylene, EPDM rubber, styrene- butadiene-styrene copolymer and ethylene-vinyl acetate copolymer.

30. The composition according to claim 29, wherein said polymer is selected from styrene-butadiene-styrene copolymer and ethylene-vinyl acetate copolymer.

31. The composition according to any one of claims 21 to 30, wherein the ratio of the weight of said polymer to the combined weight of said porcelanite and said activating agent in said rehabilitant is from about 1:10 to about 10:1.

32. The composition according to claim 31, wherein the ratio of the weight of said polymer to the combined weight of said porcelanite and said activating agent in said rehabilitant is from about 1:3 to about 1:1.

33. The composition according to claim 32, wherein the ratio of the weight of said polymer to the combined weight of said porcelanite and said activating agent in said rehabilitant is about 1:2.