WO2012081010A1

WO2012081010A1 - Warm stone-matrix asphalt mix

Info

Publication number: WO2012081010A1
Application number: PCT/IL2011/000941
Authority: WO
Inventors: Andrey Vorobiev; Ronen Alexander Peled; Gregory Svechinsky; Ilan Ishai
Original assignee: D.S.I - Dimona Silica Industries Ltd.
Priority date: 2010-12-15
Filing date: 2011-12-15
Publication date: 2012-06-21

Abstract

An asphalt mix, such as stone matrix asphalt and porous (Open Grade) asphalt, capable of being prepared at temperatures used for "warm-mix" asphalts is disclosed. The asphalt mix comprises a first additive comprising the mineral porcelanite and an activating agent and a second additive. The asphalt mix is stable and meets performance requirements according to national standards. The asphalt mix requires less bitumen than fiber-stabilized mixes, and can be mixed for less time at a lower temperature. The asphalt mix is thus more economical and environmentally friendly than existing asphalt mixes.

Description

WARM STONE-MATRIX ASPHALT MIX

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to U.S. Provisional Patent Application Serial No. 61/423,149, filed December 15, 2011 and entitled WARM STONE-MATRIX ASPHALT MIX, 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 stone matrix asphalt (SMA) mix with a reduced mixing temperature as compared to traditional SMA mixes.

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

U.S. Patent Nos. 5,217,530; 5,711,796; 5,827,568; 6,156,828; 6,562,118;

6,758,892; 7,241,337; 7,297,204; 7,767,259;

U.S. Patent Publication Nos. 2001/0047738; 2002/0108534; 2004/0101365; 2008/0060551; 2008/0168926; 2008/0224345 ; 2008/0271639; 2008/0287570; 2009/0061236; 2009/0105376; 2010/0022686;

Published PCT Application: WO 2005/100479;

Published European Applications: 1737914; 1767581; 2055744; Warm-Mix Asphalt: European Practice, Technical Report No. FHWA-PL- 08-007, U.S. Department of Transportation, 2008; and

Brian D. Prowell, Graham C. Hurley "Warm mix Asphalt: Best Practices" NAPA 53th Annual Meeting, 2008. SUMMARY OF THE INVENTION

The present invention seeks to provide an asphalt mix that can be mixed at a lower temperature than traditional asphalt mixes.

Accordingly, there is provided in accordance with one embodiment of the present invention an asphalt mix including mineral aggregates, bitumen, a first additive including porcelanite and an activating agent, and a second additive.

In accordance with a preferred embodiment of the present invention, the activating agent includes a quaternary ammonium compound. Preferably, the quaternary ammonium compound 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.

Preferably, 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 mix includes 0.2 - 0.8% of the first additive by weight, based on 100% dry aggregate weight, more preferably 0.4% of the first additive.

In accordance with a preferred embodiment of the present invention, the second additive includes at least one composition selected from the group consisting of Fisher-Tropsch waxes, Montan Wax, fatty-acid amides, synthetic and natural zeolites, wet sand, amine-based surface active agents and chemical packages for warm-mix asphalt. Preferably, the second additive includes Fisher-Tropsch wax. In accordance with a preferred embodiment of the present invention, the mix includes 0.05 - 0.5% of the second additive by weight, based on 100% dry aggregate weight, more preferably about 0.1% of the second additive.

Preferably, the bitumen is road grade bitumen. Most preferably, the road grade bitumen conforms to Israel Standard 161, Part 1. Preferably, the mix includes 4.5 - 6.5% bitumen by weight, based on 100% dry aggregate weight, more preferably 5.0 - 6.0% bitumen, most preferably 5.5% bitumen.

In accordance with a preferred embodiment of the present invention, the mix is stone matrix asphalt (SMA). In accordance with an alternative embodiment of the present invention, the mix is porous asphalt. Preferably, the drain-down of bitumen from the mix is less than 0.1%. Preferably, the retained Marshall stability after 24 hours is at least about 100%.

There is also provided in accordance with another embodiment of the present invention a method of providing an asphalt mix, including drying aggregate particles; mixing bitumen into the aggregate particles; adding activated porcelanite and a second additive to the aggregate and bitumen; and mixing to form a homogenous asphalt mix.

Preferably, the total mixing time is about 50 - 80 seconds, more preferably about 60 seconds. Preferably, the mixing temperature is about 105-140 °C, more preferably about 140 °C.

In accordance with a preferred embodiment of the present invention, the method is carried out in a batch process. In accordance with an alternative preferred embodiment of the present invention, the method is carried out in a continuous process.

DETAILED DESCRIPTION OF THE INVENTION

Stone Matrix Asphalt (SMA), also referred to as Stone Mastic Asphalt, is widely used for paving road surfaces. SMA provides maximum resistance to studded tire wear, high resistance to plastic deformation under heavy traffic loads with high tire pressures, good low temperature properties, good friction properties, increased durability, improved aging properties, reduced traffic noise and reduction or prevention of runoff of storm water on pavement surfaces.

SMA, which comprises a high proportion of large aggregate particles, leading to interlocking and direct stone-to-stone contact is described in detail in NCAT Report 93-05, "Evaluation of laboratory properties of SMA mixtures", National Center of Asphalt Technology, Auburn University, 1993, incorporated by reference herein in its entirety. Another popular asphalt mix for paving is porous (Open Grade) asphalt mix (also called "silent asphalt" or "drainage asphalt"), which comprises large and small aggregate particles with no medium size particles.

Advanced asphalt mixes, especially porous asphalt and SMA, suffer from drain-down of bitumen from the asphalt mix after production and during transport and storage. This phenomenon makes it impossible to use these mixes without stabilization. The usual method of stabilization is the addition of filaments, usually cellulose or mineral fibers to the mix. Polymer fibers can also be used for this purpose. The usual content of fibers in asphalt mixes is between 0.3-0.5 percent based on 100% dry aggregate weight.

While fiber stabilization reduces drain-down of bitumen to a suitable level (less than 0.1%), it also causes a decline in the mixing properties. The required mixing time for fiber-stabilized mixes is about 2 minutes, as opposed to the 1 minute mixing time required for traditional hot-mix asphalt. Additionally, a higher mixing temperature (180 - 190 °C) relative to traditional asphalt mixes is required because of the increase in compaction resistance of the filament-filled asphalt mix. Finally, the bitumen content must be increased from about 5% in traditional hot-mix asphalt to about 7 - 10% in order to provide proper coating of the fibers as well as the aggregate particles.

It is desirable to lower the mixing time and temperature of SMA mixes in order to reduce the cost and environmental burden of asphalt mix production and to improve the workability of the mixes. Warm-mix asphalt (WMA) mixes are produced by adding modifiers, such as Fischer-Tropsch waxes, to reduce bitumen viscosity and allow for mixing at less than about 140 °C. However, these mixes are not compatible with SMA and porous asphalt due to the need to add stabilizers as mentioned above.

A composition for lowering the mixing temperature of 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. However, it is desirable to further lower the mixing temperature of SMA to the level of warm-mix asphalt (i.e. less than about 140 °C).

A first embodiment of the invention is an asphalt mix comprising mineral aggregates, bitumen, and two functional additives. The aggregate preferably conforms to a local standard for SMA, porous asphalt or gap-graded asphalt. In one embodiment, the aggregate gradation is in accordance with Israel Standard 1865, part 2, shown in Table 1. In an alternative embodiment, the aggregate gradation conforms to the European Standard EN 13108 - 5, also shown in Table 1.

Table 1. Aggregate gradation, % passing sieve

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 first functional additive 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 composition is between 1 and 10% of the porcelanite weight.

The second functional additive is preferably an organic additive selected from Fisher-Tropsch waxes, such as Sasobit^®, available from Sasol Wax GmbH (Hamburg, Germany), Montan Wax, available from Romonta GmbH (Amsdorf, Germany), fatty-acid amides (such as Ν,Ν-diethanol bistearin amides), and mixtures thereof. The second functional additive may also be selected from foaming agents such as synthetic or natural zeolites (e.g. alumosilicate of alkali metals containing about 20% water such as aspha-min^® (Hanau, Germany)), wet sand, and amine-based surface active agents such as Wetfix^® N (Akzo-Nobel, Stockholm, Sweden).

The second functional additive can also be a chemical package for warm-mix asphalt such as Evotherm^® (Evotherm GmbH, Moosdorf, Austria), Cecabase^® RT (CECA, Colombes, France) and Rediset^® WMX (Azko-Nobel, Stockholm, Sweden). Preferably, the second functional additive is a Fischer-Tropsch wax.

Preferably the asphalt mix comprises 4.5 - 6.5% bitumen, more preferably 5.0 - 6.0%, most preferably about 5.5% (based on 100% dry aggregate weight). The asphalt mix also contains about 0.2 - 0.8% of the activated porcelanite, preferably 0.4 - 0.6%, most preferably 0.4%. The asphalt mix preferably contains 0.05 - 0.5 % of the second functional additive, most preferably about 0.1%. Asphalt mixes of the present invention are preferably prepared as follows: aggregates are dried for about 16 hours at 170 °C. Then, hot bitumen is added at about 105-140 °C with mixing for several seconds. Lastly, the functional additives are added followed by an additional mixing period of about 50-80 sec. Alternatively, the functional additives may be mixed with the aggregate for about 10 seconds followed by addition of bitumen and one minute of mixing. The functional additives may also be mixed together before being added to the aggregate.

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.

An additional embodiment of the invention is a method of providing an asphalt mix, such as SMA, porous asphalt or gap-graded asphalt, comprising mixing aggregates, bitumen and two functional additives. The aggregates, bitumen and functional additives are preferably as described hereinabove. The asphalt mix comprises 4.5 - 6.5% bitumen, more preferably 5.0 - 6.0%, most preferably about 5.5% (based on 100% dry aggregate weight). The asphalt mix also contains about 0.2 - 0.8% of the activated porcelanite, preferably 0.4 - 0.6%, most preferably 0.4%. The asphalt mix preferably contains 0.05 - 0.5% of the second functional additive, most preferably about 0.1%.

EXAMPLES

Example 1

An asphalt mix was prepared and tested in the Asphalt Laboratory of the Standards Institution of Israel (Jerusalem, Israel) according to the Marshall Method of Design and Testing of Asphalt Mixes, described in Manual MS-2 "Mix Design Methods" of the Asphalt Institute (Lexington, KY, USA), incorporated herein by reference in its entirety.

An SMA aggregate mix that conforms to Israel Standard 1865, part 2, described in Table 1 above, was collected from an asphalt plant. Bitumen was graded as PG 68-10, according Israel Standard 161, Part 1. The second functional additive was Fischer-Tropsch wax (Sasobit^®). Activated porcelanite 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 μιη.

The aggregate mix was heated and dried for 16 hours in a drying oven at 170

°C. Bitumen was added to a content of 5.5% based on 100% of dry aggregate weight in a lab mixer, mixing at 140 °C for a few seconds. Activated porcelanite (0.4% of dry aggregate weight) and wax (0.1% of dry aggregate weight) were added and the entire mixture was mixed at 140 °C for one minute, resulting in a homogeneous mix.

The preparation of samples and measuring of their properties were conducted according to the "Marshall Method" described in the aforementioned Manual MS-2 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.

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 120 °C.

The compacted specimens were immersed, in a thermostatic water bath at 60 °C for periods of 24 and 168 hours. For each measurement point three specimens were prepared. The Marshall Stability, the maximal force the specimen can sustain, was measured using a Marshall Testing Machine.

Stability of specimens measured after hot water immersion is given as percentage of retained stability relative to original stability, as described in Nesichi, S. & Ishai, I. "A Modified Method for Predicting Reduced Asphaltic Pavement Life from Moisture Damage" Asphalt Paving Technology, Vol. 55, 1986, pp. 149-174, and Ishai, I. & Nesichi, S. "Laboratory Evaluation of Moisture Damage of Bituminous Paving Mixtures by Long-Term Hot Immersion." Transportation Research Record No. 1171, 1988, pp. 12-17, both incorporated herein by reference. The results are presented in Table 2.

Table 2: Asphalt mix properties measured according to the Marshall Method

It is clearly seen from Table 2, that the sample had full Retained Marshall Stability after 24 hours. The inventive asphalt mix shows high stability against water damage and far exceeds national standard requirements for stability.

The level of drain-down in the sample was measured in accordance the "Schellenberg method" described in Standard BS EN 12697 - 18. The maximum drain- down requirement for Israel is 0.1%, for U.S.A. 0.3%, and for Europe 0.6%. The drain- down for the sample, tested at 150 °C, was 0.03%.

As has been shown above, the asphalt mix according to the present invention meets and even exceeds national requirements for asphalt mix stability and drain-down. Accordingly, this asphalt mix, which can be prepared and stored under "warm-mix" conditions, is suitable to replace the traditional "hot-mix" asphalts, thus decreasing energy requirements and C0₂ emissions, and improving the working conditions for the asphalt, which can be paved and compacted at lower temperatures and can be transported over longer distances.

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,

bitumen,

a first additive comprising porcelanite and an activating agent, and

a second additive, which when added to said asphalt mix allows said asphalt mix to be mixed at a temperature of not greater than about 140 °C.

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 claim 4, wherein said quaternary ammonium compound is di(hydrogenated tallow)dimethylammonium chloride.

6. The asphalt mix according to any one of claims 1 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 said mix comprises 0.2 - 0.8% of said first additive by weight, based on 100% dry aggregate weight.

9. The asphalt mix according to claim 8, wherein said mix comprises 0.4% of said first additive.

10. The asphalt mix according to any one of claims 1 to 9, wherein said second additive comprises at least one composition selected from the group consisting of Fisher-Tropsch waxes, Montan Wax, fatty-acid amides, synthetic and natural zeolites, wet sand, amine-based surface active agents and chemical packages for warm- mix asphalt.

11. The asphalt mix according to claim 10, wherein said second additive comprises Fisher-Tropsch wax.

12. The asphalt mix according to any one of claims 1 to 11, wherein said mix comprises 0.05 - 0.5% of said second additive by weight, based on 100% dry aggregate weight.

13. The asphalt mix according to claim 12, wherein said mix comprises about 0.1% of said second additive.

14. The asphalt mix according to any one of claims 1 to 13, wherein said bitumen is road grade bitumen.

15. The asphalt mix according to claim 14, wherein said road grade bitumen conforms to Israel Standard 161, Part 1.

16. The asphalt mix according to any one of claims 1 to 15, wherein said mix comprises 4.5 - 6.5% bitumen by weight, based on 100% dry aggregate weight.

17. The asphalt mix according to claim 16, wherein said mix comprises 5.0 - 6.0% bitumen.

18. The asphalt mix according to claim 16, wherein said mix comprises about 5.5% bitumen.

19. The asphalt mix according to any one of claims 1 to 18, wherein said mix is stone matrix asphalt (SMA).

20. The asphalt mix according to any one of claims 1 to 18, wherein said mix is porous asphalt.

21. The asphalt mix according to any one of claims 1 to 20, wherein the drain-down of bitumen from said mix is less than 0.1%.

22. The asphalt mix according to any one of claims 1 to 21, wherein the retained Marshall stability after 24 hours is at least about 100%.

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

drying aggregate particles;

mixing bitumen into said aggregate particles;

adding activated porcelanite and a second additive to said aggregate and bitumen; and

mixing to form a homogenous asphalt mix.

24. The method according to claim 23, wherein the total mixing time is about 50 - 80 seconds.

25. The method according to claim 24, wherein the total mixing time is about 60 seconds.

26. The method according to any one of claims 23 to 25, wherein the mixing temperature is about 105-140 °C.

27. The method according to claim 26, wherein the mixing temperature is about 140 °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.