WO2012160554A1

WO2012160554A1 - Modified hot-mix asphalt with anti-rutting properties and method of manufacturing the same

Info

Publication number: WO2012160554A1
Application number: PCT/IL2012/000205
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

An hot asphalt mix with improved resistance to rutting is disclosed. The asphalt mix comprises a stabilizer comprising the mineral porcelanite and an activating agent and optionally a polymer. The asphalt mix is stable and meets performance requirements according to national standards. The stabilizer provides an improved rutting resistance of 30 - 50% relative to traditional hot asphalt mixes, and is much less expensive than polymer stabilizers. The asphalt mix is thus more stable and economical than existing asphalt mixes.

Description

MODIFIED HOT-MIX ASPHALT WITH ANTI-RUTTING PROPERTIES AND METHOD OF MANUFACTURING THE SAME

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to U.S. Provisional Patent Application Serial No. 61/489,334, filed May 24, 2011 and entitled MODIFIED HOT-MIX ASPHALT WITH ANTI- RUTTING PROPERTIES AND METHOD OF MANUFACTURING THE SAME, 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 hot-mix asphalt (HMA) mix with a higher resistance to rutting as compared to traditional HMA mixes and to a method of manufacture thereof.

BACKGROUND OF THE INVENTION The following publications are believed to represent the current state of the art:

U.S. Patent Nos. 4,547,399, 4,835,199, 5,002,987, 5,710,196, 5,744,524 and 6,214,908; and

Usmani, A. "Polymer Modification of Asphalt: Chemistry and Technology", Polymer News, 21(8):262-267, 1996.

SUMMARY OF THE INVENTION

The present invention seeks to provide a hot asphalt mix that has a higher resistance to rutting than traditional hot asphalt mixes and a method of manufacture thereof.

Accordingly, there is provided in accordance with one embodiment of the present invention an asphalt mix including: mineral aggregates graded for hot mix asphalt (HMA), bitumen, and a stabilizer comprising porcelanite and an activating agent.

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 activating agent includes a quaternary ammonium compound in an amount of 1 - 15% of the porcelanite weight, more preferably 1 - 10% of the porcelanite weight. Preferably, the weight of the stabilizer in the mix is about 10 - 20% of the combined weight of the bitumen and the stabilizer, more preferably about 15% of the combined weight of the bitumen and the stabilizer.

Preferably, the bitumen is road grade bitumen. More preferably, the road grade bitumen conforms to Israel Standard 161, Part 1. The asphalt mix preferably includes 3 - 6% bitumen by weight, based on 100% dry aggregate weight, more preferably 4.0 - 5.0% bitumen, most preferably about 4.4% bitumen.

In accordance with a preferred embodiment of the present invention, the asphalt mix further includes a polymer. Preferably, the polymer is selected from the group consisting of polyurethane, silicones, atactic polypropylene, ethylene-vinyl acetate, styrene-butadiene and styrene-butadiene-styrene. More preferably, the polymer is styrene-butadiene-styrene. The polymer is preferably added in an amount of 1 - 10% of the bitumen by weight, more preferably about 5% of the bitumen by weight.

Preferably, the rutting resistance of the asphalt mix is greater than that of an identical mix lacking the stabilizer. More preferably, the rutting resistance of the mix is at least about 30% greater, most preferably at least about 50% greater, than that of an identical mix lacking the stabilizer.

There is also provided in accordance with an additional embodiment of the present invention a method of providing an asphalt mix, including: drying aggregate particles graded for hot mix asphalt, mixing bitumen and a stabilizer including porcelanite and an activating agent to form a stabilized bitumen, and mixing the aggregate particles with the stabilized bitumen to form a homogenous asphalt mix.

Preferably, the bitumen and the stabilizer are mixed for about 5 - 10 minutes, allowed to rest for about 30 minutes, and mixed for an additional 5 - 10 minutes. Preferably, the total mixing time of the aggregate particles and the stabilized bitumen is about 50 - 80 seconds, more preferably about 60 seconds.

In accordance with a preferred embodiment of the present invention, the mixing temperature is about 165-170 °C. In accordance with a preferred embodiment of the present invention, the process is carried out in a batch process. In accordance with an alternative preferred embodiment of the present invention, the process is carried out in a continuous process.

DETAILED DESCRIPTION OF THE INVENTION

Hot asphalt mixes are commonly used as roadway materials due to their low material cost and ease of application. Typically, bitumen, often referred to as "asphalt cement" or "asphalt binder," is mixed with a mineral aggregate to form an asphalt concrete suitable for paving. Thus, asphalt mixes usually comprise aggregates held within a continuous phase of bitumen by adherence of the bitumen to the aggregate.

Conventional methods of producing and paving with asphalt mixes typically require mixing the bitumen and aggregates at a temperature of at least about 150 °C and paving at temperatures between about 130 and 160 °C. Asphalt paving compositions made by such methods are often referred to as "hot mix asphalt" (HMA). In terms of handling, hot mix asphalt can be paved to the technical specifications and mechanical properties required by many governmental regulating agencies.

Road surfaces paved with asphalt are subject to various faults that develop due to traffic and weather. For example, asphalt road surfaces can develop relatively narrow depressions or ruts in the direction of traffic flow caused by heavy trucks and the like. These ruts can be relatively short and localized, or often can continue for a considerable distance up to several miles along the road.

Rutting on asphaltic pavement has been a significant concern in many countries. Rutting is caused by a load passing repeatedly across the surface of pavement and results in lateral spreading of the pavement from the location of load application, thereby producing a rut or groove. This problem has increased in severity as the wheel loads and truck traffic on highways have increased. Rutting may cause roads and highways to become non-serviceable and dangerous. If excessive, rutting may produce hazardous conditions, such as increased likelihood of vehicle hydroplaning due to water accumulating in the formed rut.

In general, maintenance is required to repair these ruts in the pavement, often at significant costs. This has become a major issue in recent years due to higher traffic volumes, increased loads and higher tire pressures. Clearly, improved overall performance grades of asphalt which will lead to a reduction in maintenance costs are desirable. It is known that a variety of polymer additives, such as polyethylene and thermoplastic elastomers, can improve the level of road performance of asphalt. The addition of elastomers to asphalt has been shown to improve flow characteristics and reduce cracking of the asphalt, especially cracking due to heavy loads at low temperatures. The addition of elastomers, however, presents difficulties at higher temperatures. As the elastomers melt, the asphalt becomes more plastic and less elastic resulting in rutting in high traffic areas of the roadway. One solution to this problem is to add a graft copolymer resin comprising a rubbery polymeric substrate and a rigid polymeric substrate.

However, since asphalt is an inexpensive thermoplastic, the inclusion of costly polymer additives is economically unattractive despite the property gains observed. Therefore, polymer additives are as yet not widely used in asphalt paving despite the improvements they impart in pavement properties such as crack resistance and reduced rutting. A cost-effective additive for improving the performance of HMA is therefore needed.

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, hereinafter "stabilizer", improves the performance properties of HMA.

A first embodiment of the invention is an asphalt mix comprising mineral aggregates, bitumen, and stabilizer. The aggregate preferably conforms to a local standard for HMA. In one embodiment, the aggregate gradation is in accordance with Israel Standard 51.04, shown in Table 1.

Table 1. HMA aggregate gradation according to Israel Standard 51.04

The bitumen is preferably road grade bitumen in accordance with a national standard. Preferably, the bitumen is performance grade (PG) bitumen, such as PG 68-10 or PG 76-10, according to Israel Standard 161, Part 1. In this standard, the first number in the bitumen grade refers to the maximum pavement temperature (°C), and the second number refers to the minimum pavement temperature (°C). For example, PG 68-10 is appropriate for roads that reach a maximum temperature of 68 °C and a minimum temperature of -10 °C.

The stabilizer comprises porcelanite, a mineral found, inter alia, in deposits in the Dead Sea area of Israel and described in detail in WO 2010/116354, and an activating agent. 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 quaternary ammonium compound is preferably between 1 and 15% of the porcelanite weight. More preferably, the weight of the quaternary ammonium compound in the stabilizer is between 1 and 10% of the porcelanite weight.

Asphalt mixes of the present invention are preferably prepared as follows: aggregates are dried for about 16 hours at about 170 °C. Separately, stabilizer is added to hot bitumen at about 165-170 °C with mixing for 5 - 10 minutes. The bitumen- stabilizer mixture is maintained at about 165-170 °C for about 30 minutes and then mixed again for an additional 5 - 10 minutes. The bitumen-stabilizer mixture is mixed with the aggregates for about 50-80 sec, such as about 60 sec.

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

Preferably the asphalt mix comprises 3 - 6% of bitumen-stabilizer mixture, more preferably 4.0 - 5.0%, and most preferably about 4.4% (based on 100% dry aggregate weight). The stabilizer is added to the bitumen in an amount of about 10 - 20% of the total bitumen-stabilizer mixture by weight. Most preferably, the bitumen-stabilizer mixture comprises about 15% stabilizer by weight.

In one embodiment, the asphalt mix further comprises a polymer. The polymer is preferably selected from typical polymers used to modify bitumen, such as polyurethane, silicones, atactic polypropylene (APP), ethylene-vinyl acetate (EVA), styrene-butadiene (SB) and styrene-butadiene-styrene (SBS). The polymer is added to bitumen in an amount of 1 - 10% of the bitumen weight, preferably about 5%.

An additional embodiment of the invention is a method of providing a hot asphalt mix comprising mixing bitumen and stabilizer, and then mixing the bitumen- stabilizer mixture with aggregates. The aggregates, bitumen and stabilizer are preferably as described hereinabove. The asphalt mix comprises 3 - 6% bitumen- stabilizer mixture, more preferably 4.0 - 5.0%, and most preferably about 4.4% (based on 100% dry aggregate weight). The bitumen-stabilizer mixture comprises about 10 - 20% stabilizer, most preferably 15% stabilizer.

EXAMPLES

Stabilizer was prepared as follows: 100 g of crushed porcelanite with a particle size between 3 and 8 mm was mixed with 5 g of 2HT-75 in a laboratory blender at 20,000 RPM for 5 minutes. The particle size distribution was measured by Malvern Mastersizer 2000. Maximum particle size was 40 μπι.

Asphalt mixes were prepared as follows: bitumen (grade PG 68-10) was used plain or mixed with stabilizer at 165 °C for 5 minutes. Plain or modified bitumen was added to aggregates and mixed for 1 minute at 165 °C. The gradation of the aggregate conforms to Israel Standard 51.04 and is given in Table 2.

Table 2. HMA aggregate gradation

Example 1

Two types of asphalt mixes were prepared, one with plain bitumen, and the other with bitumen comprising 15% stabilizer. The optimal bitumen content of each of the mixes was determined by the Marshall Method, described in Manual MS-2 "Mix Design Methods" of the Asphalt Institute (Lexington, KY, USA), incorporated herein by reference in its entirety, and in Standard ASTM D 1559. The Marshall Method is a quantitative engineering tool for designing hot asphalt mixes by determining the optimal bitumen content in the mix, for a given type of aggregate and gradation and bitumen type, under specified road and traffic characteristics. The results are shown in Table 3. As can be seen, the optimal bitumen content for both plain and stabilized HMA was 4.4%, based on 100% aggregate weight.

Table 3. Optimal bitumen content

Example 2

The stabilized asphalt mix with 4.4% bitumen-stabilizer prepared in Example 1 was evaluated according to the aforementioned Manual MS-2 and Standard ASTM D 1558. The results are shown in Table 4. It can be seen that the stabilized asphalt mix conforms to all of the standard requirements. Table 4: Properties of Stabilized HMA

Example 3

Three samples were prepared and subjected to stability and rutting tests. Sample 1 comprised 4.4% bitumen. Sample 2 comprised 4.4% bitumen with 10% stabilizer. Sample 3 comprised 4.4% bitumen with 15% stabilizer. The samples were tested according to the Marshall Method of Design and Testing of Asphalt Mixes, described in Manual MS-2 and in Standard ASTM D 1559.

Compacted cylindrical specimens of asphalt mixes were produced following the mixing. The compaction procedure was performed by the Marshall Hammer Compaction Method (Reynolds model). The compacting procedure was conducted as follows: 1200 g of hot asphalt mix was weighed and poured into a metal mold cylinder with inner diameter 102 mm, the mold cylinder was installed on the base of a Marshall Hammer and compacted with 50 blows of a 4.5 kg hammer from both sides of the specimens. Compaction temperature was 145 °C.

The compacted specimens were immersed in a thermostatic water bath at 60 °C for a period of 48 hours. For each measurement point three specimens were prepared. The Marshall Stability, the maximal force the specimen can sustain, was measured before and after the hot water treatment using a Marshall Testing Machine. The results are shown in Table 5. The resistance to rutting was measured by a wheel tracking test in accordance with Spanish standard NLT 173/00. Briefly, a wheel is applied to the asphalt at 50 °C, and the number of cycles of applying the wheel until a 1 mm rut develops is measured. These results are also shown in Table 5. As can be seen in Table 5, the HMA mix with 15% stabilizer in the bitumen has a Marshall stability comparable to that of unmodified HMA and has a 32% increased resistance to rutting.

Table 5: properties of plain and stabilized HMA

Example 4

Two samples were prepared, wherein 5% of styrene-butadiene-styrene (SBS) polymer (Kraton DllOl, supplied by Kraton Polymers, Houston, TX, USA) by weight was added to the bitumen. Sample 1 comprised 4.4% SBS-modified bitumen. Sample 2 comprised 4.4% SBS-modified bitumen containing 15% stabilizer. The samples were tested as in Example 3 hereinabove. The results are shown in Table 6. As is seen in Table 6, the polymer modified asphalt mix comprising stabilizer has a slightly improved Marshall stability and 50% greater resistance to rutting.

Table 6: Properties of plain and stabilized polymer modified HMA

As has been shown above, the stabilized asphalt mix according to the present invention is superior to similar unstabilized mixes in resistance to rutting. The stabilizer, made from an inexpensive natural mineral, is more cost-effective than polymer modifiers, whose cost has prevented their widespread use. Accordingly, this asphalt mix is suitable to replace traditional hot-mix asphalts to provide longer lasting and safer road surfaces.

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. An asphalt mix comprising:

mineral aggregates graded for hot mix asphalt (HMA),

bitumen, and

a stabilizer comprising porcelanite and an activating agent.

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

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

4. The asphalt mix according to claim 3, wherein said at least two alkyl chains have 15 - 18 carbons.

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

6. The asphalt mix according to any one of claims 2 to 5, wherein said activating agent comprises a quaternary ammonium compound in an amount of 1 - 15% of the porcelanite weight.

7. The asphalt mix according to claim 6, wherein said quaternary ammonium compound is in an amount of 1 - 10% of the porcelanite weight.

8. The asphalt mix according to any one of claims 1 to 7, wherein the weight of said stabilizer is about 10 - 20% of the combined weight of said bitumen and said stabilizer.

9. The asphalt mix according to claim 8, wherein the weight of said stabilizer is about 15% of the combined weight of said bitumen and said stabilizer.

10. The asphalt mix according to any one of claims 1 to 9, wherein said bitumen is road grade bitumen.

11. The asphalt mix according to claim 10, wherein said road grade bitumen conforms to Israel Standard 161, Part 1.

12. The asphalt mix according to any one of claims 1 to 11, wherein said mix comprises 3 - 6% bitumen by weight, based on 100% dry aggregate weight.

13. The asphalt mix according to claim 12, wherein said mix comprises 4.0 - 5.0% bitumen by weight.

14. The asphalt mix according to claim 13, wherein said mix comprises about 4.4% bitumen by weight.

15. The asphalt mix according to any one of claims 1 to 14, further comprising a polymer.

16. The asphalt mix according to claim 15, wherein said polymer is selected from the group consisting of polyurethane, silicones, atactic polypropylene, ethylene- vinyl acetate, styrene-butadiene and styrene-butadiene-styrene.

17. The asphalt mix according to claim 16, wherein said polymer is styrene- butadiene-styrene .

18. The asphalt mix according to any one of claims 15 to 17, wherein said polymer is added in an amount of 1 - 10% of said bitumen by weight.

19. The asphalt mix according to claim 18, wherein said polymer is added in an amount of about 5% of said bitumen by weight.

20. The asphalt mix according to any one of claims 1 to 19, wherein the rutting resistance of said mix is greater than that of an identical mix lacking said stabilizer.

21. The asphalt mix according to claim 20, wherein the rutting resistance of said mix is at least about 30% greater than that of an identical mix lacking said stabilizer.

22. The asphalt mix according to claim 21, wherein the rutting resistance of said mix is at least about 50% greater than that of an identical mix lacking said stabilizer.

23. A method of providing an asphalt mix, comprising:

drying aggregate particles graded for hot mix asphalt (HMA);

mixing bitumen and a stabilizer comprising porcelanite and an activating agent to form a stabilized bitumen; and

mixing said aggregate particles with said stabilized bitumen to form a homogenous asphalt mix.

24. The method according to claim 23, wherein said bitumen and said stabilizer are mixed for about 5 - 10 minutes, allowed to rest for about 30 minutes, and mixed for an additional 5 - 10 minutes.

25. The method according to claim 23 or 24, wherein the total mixing time of said aggregate particles and said stabilized bitumen is about 50 - 80 seconds.

26. The method according to claim 25, wherein the total mixing time is about 60 seconds.

27. The method according to any one of claims 23 to 26, wherein the mixing temperature is about 165-170 °C.

28. The method according to any one of claims 23 to 27, which is carried out in a batch process.

29. The method according to any one of claims 23 to 27, which is carried out in a continuous process.