PROCESS FOR PREPARING FOAMED POLYMER-MODIFIED BITUMEN COMPOSITIONS

Abstract

The invention relates to a process for preparing foamed polymer-modified bitumen compositions and to the use thereof for the production of asphalt. The invention also relates to foamed polymer-modified bitumen compositions obtainable by this process. Furthermore, the invention relates to a process for producing an asphalt composition and to the use thereof in road applications. The process for the preparation of the foamed polymer-modified bitumen composition comprises the following steps: i) Heating and pressurizing a bitumen to obtain a hot flowing bitumen stream, ii) Injecting under pressure an aqueous polymer dispersion into the hot flowing bitumen stream obtained in step i), to obtain a pressurized flowing mixed stream of the bitumen and the aqueous polymer dispersion; iii) Expanding the flowing mixed stream, in particular to atmospheric pressure, such that the water contained in the aqueous polymer dispersion vaporizes and foams the mixed stream to obtain a foamed polymer-modified bitumen.

Claims

1.-17. (canceled)

18. A process for the preparation of a foamed polymer-modified bitumen composition comprising the steps: i) heating and pressurizing a bitumen to obtain a hot flowing bitumen stream; ii) injecting under pressure an aqueous polymer dispersion into the hot flowing bitumen stream obtained in step i), to obtain a pressurized hot flowing mixed stream of the bitumen and the aqueous polymer dispersion; iii) expanding the flowing mixed stream, in particular to atmospheric pressure, such that at least a majority of the water contained in the aqueous polymer dispersion vaporizes and foams the mixed stream to obtain a foamed polymer-modified bitumen.

19. The process according to claim 18, where the amount of aqueous polymer dispersion, which is injected into the flowing bitumen stream, is such that the amount of water in the pressurized flowing mixed stream is in the range from 0.5 to 8.0% by weight, based on the total weight of the bitumen.

20. The process according to claim 18, where the amount of aqueous polymer dispersion injected into the flowing bitumen is such that the resulting amount of polymer of the polymer dispersion in the flowing mixed stream is in the range from 0.5 to 7.0% by weight, based on the total weight of the bitumen, results.

21. The process according to claim 18, wherein the aqueous polymer dispersion is an aqueous dispersion of butadiene-styrene copolymer.

22. The process according to claim 21, wherein the butadiene-styrene copolymer, the weight ratio of styrene to butadiene is in the range from 20:80 to 80:20.

23. The process according to claim 18, wherein a vulcanizing agent is injected into the flowing bitumen stream concomitantly with the aqueous polymer dispersion.

24. The process according to claim 18, wherein the water, which is introduced into the flowing bitumen stream by injecting the aqueous polymer dispersion contributes at least 20% to the total amount of water contained in the flowing mixed bitumen stream prior to the expansion of step iii).

25. The process according to claim 18, where in step i) the bitumen is heated to a temperature of at least 105° C.

26. The process according to claim 18, where in step i) the bitumen is pressurized to a pressure of at least 1 bar above the atmospheric pressure.

27. The process according to claim 18, wherein the polymer dispersion is injected into the flowing bitumen in a mixing chamber to obtain the pressurized flowing mixed stream, which is discharged from the mixing chamber through an orifice and thereby expanded.

28. The process according to claim 18, wherein the step ii) is performed without dynamic mixing.

29. The process according to claim 18, wherein the aqueous polymer dispersion is injected into the flowing bitumen stream at an angle of >90°, with respect to the flow direction of the flowing bitumen stream.

30. A foamed polymer-modified bitumen composition obtained by the process as defined in claim 18.

31. The process for producing an asphalt composition, which comprises providing a foamed polymer-modified bitumen composition by a process according to claim 18, and mixing the foamed bitumen composition with aggregates.

32. Use of the foamed polymer modified bitumen composition as defined in claim 30 for the production of asphalt, in particular asphalt for road construction.

33. An asphalt composition, which is obtained by the process as defined in claim 31.

34. The asphalt composition of claim 33, which contains at least 3% by weight, based on the total weight of the asphalt composition, of the foamed polymer modified bitumen composition.

35. The process according to claim 18, where the amount of aqueous polymer dispersion, which is injected into the flowing bitumen stream, is such that the amount of water in the pressurized flowing mixed stream is in the range from 1.0 to 5.0% by weight, based on the total weight of the bitumen.

36. The process according to claim 18, where the amount of aqueous polymer dispersion injected into the flowing bitumen is such that the resulting amount of polymer of the polymer dispersion in the flowing mixed stream is in the range from 1.0 to 5.0% by weight, based on the total weight of the bitumen, results.

37. The process according to claim 18, where in step i) the bitumen is heated to a temperature in the range from above 110 to 230° C.

Description

[0115] The invention is described in more detail in the following examples and figures.

[0116] FIG. 1: Schematic drawing of the foam bitumen device

[0117] FIG. 1 schematically depicts the foam bitumen device used for the examples described below. (1) displays the mixing chamber which is equipped with elements (13) of a static mixer and a gas inlet (11 & 17). The mixing chamber is connected with a bitumen line (2), a fluid line for the aqueous polymer dispersion (5) and a fluid line for further liquid additives or water (7) via a dosing nozzle, respectively (3, 6, 8). Each feeding line consists of a reservoir containing the respective feeding agent (14, 18, 9), a pump (12) and a flowmeter (10). The bitumen mixture in the chamber (1) can be readily discharged into the asphalt mixer (16) via a nozzle (15). By discharging it via the nozzle, the water contained in the pressurized mixture of bitumen, polymer dispersion and optional further additives, spontaneously expands and forms a foamed polymer modified bitumen.

EXAMPLES

[0118] The following starting materials were used:

[0119] Bitumen 1: Bitumen type 50/70 available from the refinery MiRo in Karlsruhe, Germany

[0120] Bitumen 2: Bitumen Type 25/50-55: SBS modified bitumen: Olexobit 45 of Puma Energy

[0121] Aqueous polymer dispersion 1: An aqueous XSB polymer dispersion having a solid content of 53% by weight, a glass transition temperature of −27° C., a viscosity of 220 mPas (100 s.sup.−1, T=23° C.) and a pH of 6.8, which had been modified by addition of colloidal sulfur in an amount of 4% by weight, based on the polymer in the XSB polymer dispersion.

[0122] Aqueous polymer dispersion 2: An aqueous SB polymer dispersion having a solid content of 71% by weight, a glass transition temperature of −53° C., a viscosity of 1500 mPas (Brookfield RV, Spindle #3, at 20 rpm, 23° C.) and a pH of 10.

Production of Asphalt:

[0123] For the technical evaluation of the addition of polymer dispersions using a foam bitumen module, asphalt samples of type AC 11 DS with a bitumen content of 6 mass % were prepared. The production was carried out in an asphalt mixing plant equipped with a foam bitumen module according to FIG. 1. The basic function of the foam bitumen module used is described with respect to FIG. 19.

[0124] Besides the foam bitumen module, the asphalt mixing plant comprises containers for bitumen, containers for adding aqueous additives, both being connected with the foam bitumen module and mixing equipments for the foamed bitumen and the aggregates.

Examples 1 to 3 According to the Invention

[0125] In the examples 1 to 3 according to the invention, a hot bitumen stream, which was heated to a temperature of about 170° C. was introduced at a pressure of 5 bar into the foam bitumen module and the polymer dispersion 1 was injected with a pressure of 10 bar into the pressurized hot pressurized bitumen stream present in the foam bitumen module. In the foam bitumen module, a temperature of 135° C. and a pressure of 6 bar was maintained before the sample was expanded to a foam. Foams with a polymer content of 2.5% b.w., 3.0% b.w., and 3.5% b.w. (solid dispersion on mass of bitumen) were produced accordingly. The foamed bitumen was then mixed with the preheated aggregates in an amount of approximately 6% by weight of foamed bitumen based on the amount of aggregates to obtain an asphalt of type AC 11 DS. Mixing was carried out in a twin-shaft compulsory mixer at temperatures of about 175° C. for about 30 s.

Example 4 According to the Invention

[0126] Example 4 was prepared according to the general procedure of example 2 but with the exception that the aqueous polymer dispersion 2 was used instead of the aqueous polymer dispersion 1. Foams with a polymer content of 3.0% b.w. (solid dispersion on mass of bitumen) were produced accordingly.

Comparative Examples

[0127] In comparative examples 1 and 2, asphalt samples of type AC 11 DS with a bitumen content of 6 mass % were produced using bitumen 1 and bitumen 2, respectively, each of which was heated to 180° C. The heated respective bitumen types were mixed for 30 s in a twin-shaft compulsory mixer with the aggregates preheated to 220° C.

[0128] In comparative examples 3 and 4, asphalt samples of type AC 11 DS were produced by analogy to examples 1 to 3 but using bitumen 1 and 2, respectively and replacing the polymer dispersion by the 3% by weight of water.

The Asphalt Samples

Wheel-Tracking-Test:

[0129] The form stability of the asphalt was determined by means of the tracking test carried out in accordance with TP Asphalt-StB Part 22. 10000 load cycles were carried out at 60° C., and the track depth in mm was then determined (WTS Air).

Cooling Test and Tensile Test:

[0130] The low temperature stability of the asphalt was measured by the cooling test according to TP Asphalt-StB Part 22 46 A. Furthermore, the bitumen produced conventionally on the basis of bitumen 1 and bitumen 2, respectively as well as the example 2 (3% dispersion) were characterized by means of a uniaxial tensile test at −10° C.

[0131] The experimental data are summarized in table 1.

TABLE-US-00001 TABLE 1 tracking formation sample body [%] tracking for- tensile test degree of groove groove mation rate cooling test elonga- Exam- density compression depth depth WTS air Temp. tension strength tion ple bitumen composition [g/cm.sup.3] [%] [mm] [%] [mm] [° C.] [N/mm.sup.2] [MPa] [%∘] 1 Bitumen 1 + 2.355 100.1 2.2 5.4 0.08 −21.7 4.526 2.5% b.w. of polymer of dispersion 1 (F) 2 Bitumen 1 + 2.347 100.6 2.4 5.9 0.10 −21.5 4.341 4.931 0.458 3.0% b.w. of polymer of dispersion 1 (F) 3 Bitumen 1 + 2.330 100.3 1.6 3.9 0.04 −22.8 4.620 3.5% b.w. of polymer of dispersion 1 (F) 4 Bitumen 1 + 2.322 100.4 1.6 3.8 0.03 −23.1 4.078 3.0% b.w. of polymer of dispersion 2 (F) Comp 1 Bitumen 1 2.625 99.6 >10 >20 >1 −27.6 3.674 4.533 0.728 Comp 2 Bitumen 2 2.332 100.4 2.6 6.2 0.10 −21.7 3.886 4.601 0.411 Comp 3 Bitumen 1 (F) 2.351 100.2 6.4 15.6 0.32 −23.9 4.026 Comp 2 Bitumen 2 (F) 2.343 99.9 3.8 9.3 0.21 −21.2 4.006 F = foamed bitumen