A LOW-TEMPERATURE METHOD FOR MANUFACTURING MODIFIED CRUMB RUBBER

Abstract

The invention relates to the field of road construction materials, and it is intended to improve the quality of road surfaces, roofing and insulating materials based on bitumens, which is achieved by improving the quality of bitumens with the help of using modified crumb rubber—a disposal product of used automotive and tractor tires, in particular, the invention relates to a low-temperature method for manufacturing modified crumb rubber to improve the quality of bitumens and asphalt concretes and to the technology for mixing it with bitumen, for the purpose of creating a uniform material that is not prone to destruction during long-term storage. The present invention consists in the development of a new method for manufacturing the modified crumb rubber, comprising preparing a mix from the following components: crumb rubber from used automotive and tractor tires with a particle size of up to 1 mm—50-65 wt. %, oxides and/or hydroxides of alkaline-earth metals—10-20 wt. %, petroleum oil of solvent refining with the viscosity of from 0.05 to 1.5 Pa*s at 60° C.—20-30 wt. %, an amine type antiageing agent—a heterocyclic nitrogen-containing compound—0.1-2.0 wt. %; mixing the components of the resulting mix with a shock-shear load on the material in a mixer-activator at a temperature of 80-120° C.; and further cooling the resulting mix to a room temperature.

Claims

1. A method for manufacturing modified crumb rubber, comprising preparing a mix from the following components: crumb rubber from used automotive and tractor tires with a particle size of up to 1 mm—50-65 wt. %, oxides and/or hydroxides of alkaline-earth metals—10-20 wt. %, petroleum oil of solvent refining with the viscosity of from 0.05 to 1.5 Pas at 60° C.—20-30 wt. %, an amine type antiageing agent—a heterocyclic nitrogen-containing compound—0.1-2.0 wt. %; mixing the components of the resulting mix with a shock-shear load on the material in a mixer-activator at a temperature of 80-120° C.; and further cooling the resulting mix to a room temperature.

2. The method according to claim 1, wherein the oxides and the hydroxides of the alkaline-earth metals are selected from a group of CaO, MgO, Ca(OH).sub.2.

3. The method according to claim 1, wherein an amine-type antiageing agent is selected from a group of the heterocyclic nitrogen-containing compounds, in particular, neozone D, irganox, and diafene FP.

4. The method according to claim 1, wherein the mix contains additionally a vulcanization accelerator of a guanidine class selected from a group of guanidine, diphenylguanidine in an amount of 0.2-5.0 wt. %.

5. The method according to claim 1, wherein the mix contains additionally a vulcanization activator selected from a group of stearic acid, oleic acid and the zinc and calcium salts thereof in an amount of 2.0-3.0 wt. %.

6. The method according to claim 2, wherein an amine-type antiageing agent is selected from a group of the heterocyclic nitrogen-containing compounds, in particular, neozone D, irganox, and diafene FP.

7. The method according to claim 6, wherein the mix contains additionally a vulcanization accelerator of a guanidine class selected from a group of guanidine, diphenylguanidine in an amount of 0.2-5.0 wt. %.

8. The method according to claim 7, wherein the mix contains additionally a vulcanization activator selected from a group of stearic acid, oleic acid and the zinc and calcium salts thereof in an amount of 2.0-3.0 wt. %.

9. The method according to claim 3, wherein the mix contains additionally a vulcanization accelerator of a guanidine class selected from a group of guanidine, diphenylguanidine in an amount of 0.2-5.0 wt. %.

10. The method according to claim 9, wherein the mix contains additionally a vulcanization activator selected from a group of stearic acid, oleic acid and the zinc and calcium salts thereof in an amount of 2.0-3.0 wt. %.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0055] FIG. 1 shows the reaction chemical mechanism illustrating a principle of the rubber modification.

[0056] FIG. 2 shows the photographs from a microscope, wherein the process of dissolving 10% of the modified crumb in the bitumen of BND 60/90 grade in time is shown.

[0057] FIG. 3 shows a graph of the viscosity change of the mix prepared by the claimed method, depending on time.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0058] FIG. 1 illustrates the principle of the rubber modification, when it is introduced into the bitumen, after which the process of its dissolution occurs.

[0059] FIG. 2 illustrates the photographs made with the help of a special Zeiss AXIO SCOPE.A1 microscope with an N-Achroplan 40×/0.65 lens at 400× magnification, which show a course of the dissolution of 10% of the modified crumb in the bitumen of BND 60/90 grade in time after 15, 60 and 90 minutes from the process start. As can be seen, practically full homogeneity of the mix is achieved already by the 90th minute, what is also illustrated by the graph shown at FIG. 3.

[0060] The dissolution of the modified crumb in the bitumen to obtain the indistinguishable particles is provided under the mild conditions, that is, at the temperatures of up to 160-170° C. Without applying a mechanical action, which reduces significantly the cost of the required equipment and reduces the costs of the technological process.

[0061] FIG. 3 shows a graph of the viscosity change of the mix depending on time. As the graph shows, the mix viscosity is much less than the bitumen viscosity with the conventional rubber, while a rapid viscosity reduction occurs at 80-90th minute, which is absolutely not typical for the conventional rubber (the conventional rubber, with this concentration, has in fact a line graph of the viscosity increase, with the formation of a site with a size of about 3 Pa.Math.s), which is an experimental evidence of a high degree of the mix homogenization. At the same time, it should be noted that mixing the bitumen with this activated crumb should be carried out mainly in a temperature range of 80-120° C. to create the conditions for the transition of the long caoutchouc molecules into the mix at a low activation of the mix.

[0062] This mixing process also afford distinguishing this material from the possible fakes, since the conventional crumb rubber is not conceptually dissolved at such temperatures with a weak activation (a low speed of mixing).

[0063] During the preliminary preparation and activation of the crumb rubber, a number of components are introduced, one of which (petroleum oil of solvent refining with the viscosity of from 0.05 to 1.5 Pa.Math.s at 60° C.) leads to effective swelling of the crumb rubber, which at a molecular level leads to a separation of the caoutchouc macromolecules from each other. This makes it possible to reduce significantly the probability of the formation of new cross-linked sulfur bonds during the dissolution process.

[0064] Another component (the amine-type antiageing agent, which can be selected from the group of different heterocyclic nitrogen-containing compounds, neozone D, irganox, and diafene FP) cleaves selectively the sulfur bonds, while this component does not in fact affect the carbon-carbon bonds.

[0065] The distinctive feature of the claimed method is the optimal selection of the components in such a way that their percentage ratio in the course of the activation of the crumb rubber would exclude a bifurcation process (this process is characteristic of the chemical reactions in the complex systems, where oppositely directed processes can occur simultaneously).

[0066] Thus, the possibility of occurring the uncontrolled processes that are opposite to the dissolution is excluded.

[0067] As a result, the claimed method provides obtaining an unidirectional, predictable, reproducible, relatively simple, low-temperature and economically more advantageous process for modifying the crumb rubber.

[0068] The creation of the mix is carried out by active mixing the components with the shock-shear load on the material in the mixer-activator at the temperatures optimally of 80-120° C. and with further cooling the resulting mix to a room temperature before packaging.

[0069] The optimal mixing temperature in the specified range is selected empirically depending on: [0070] the chemical composition of the crumb rubber; [0071] the ratio of the crumb rubber particles from tires for cars and trucks; [0072] the technology for grinding the crumb rubber; [0073] a specific surface area.

[0074] At the same time, it should be taken into account that the lower mixing temperatures (up to 80° C.) will lead to a non-full absorption of the bulk components and petroleum oil by the crumb.

[0075] A mixing temperature of more than 120° C. will lead to the beginning of a chemical reaction in the material, smoke emission, the material will be segregating, it will become unsuitable for long-term storage and transportation, in the future, it will not be mixed effectively with bitumen, it will not form a completely homogeneous mix suitable for long-term storage.

EMBODIMENT EXAMPLES OF THE INVENTION

Example 1

[0076] At a preliminary stage, a mix is prepared, which includes the following components: [0077] crumb rubber from used automotive and tractor tires with a particle size of up to 1 mm—60 wt. %, [0078] building lime (CaO+MgO˜75:25%)—15 wt. %, [0079] petroleum oil of solvent refining with the viscosity of from 0.05 to 1.5 Pas at 60° C.—24.4 wt. %; [0080] neozone D—0.6 wt. %.

[0081] Then comes mixing the components of the resulting mix with the shock-shear load on the material in the mixer-activator at a temperature of 80° C.;

[0082] After obtaining a uniform homogeneous resulting mix, it is cooled to a room temperature.

Example 2

[0083] At a preliminary stage, a mix is prepared, which includes the following components: [0084] crumb rubber from used automotive and tractor tires with a particle size of up to 1 mm—50 wt. %, [0085] MgO+Ca(OH).sub.2 (˜25:75%)—20 wt. %, [0086] petroleum oil of solvent refining with the viscosity of from 0.05 to 1.5 Pas at 60° C.—28.0 wt. %; [0087] irganox—2.0 wt. %.

[0088] Then comes mixing the components of the resulting mix with the shock-shear load on the material in the mixer-activator at a temperature of 120° C.;

[0089] After obtaining a uniform homogeneous resulting mix, it is cooled to a room temperature.

Example 3

[0090] At a preliminary stage, a mix is prepared, which includes the following components: [0091] crumb rubber from used automotive and tractor tires with a particle size of up to 1 mm—65 wt. %, [0092] MgO—10 wt. %, [0093] petroleum oil of solvent refining with the viscosity of from 0.05 to 1.5 Pas at 60° C.—20.0 wt. %; [0094] diafene FP—0.1 wt. %; [0095] guanidine—4.9 wt. %.

[0096] Then comes mixing the components of the resulting mix with the shock-shear load on the material in the mixer-activator at a temperature of 90° C.;

[0097] After obtaining a uniform homogeneous resulting mix, it is cooled to a room temperature.

Example 4

[0098] At a preliminary stage, a mix is prepared, which includes the following components: [0099] crumb rubber from used automotive and tractor tires with a particle size of up to 1 mm—55 wt. %, [0100] CaO+MgO+Ca(OH).sub.2˜50:25:25%)—10 wt. %, [0101] petroleum oil of solvent refining with the viscosity of from 0.05 to 1.5 Pas at 60° C.—30.0 wt. %; [0102] irganox—0.8 wt. %. [0103] diphenylguanidine—4.2 wt. %.

[0104] Then comes mixing the components of the resulting mix with the shock-shear load on the material in the mixer-activator at a temperature of 80° C.;

[0105] After obtaining a uniform homogeneous resulting mix, it is cooled to a room temperature.

Example 5

[0106] At a preliminary stage, a mix is prepared, which includes the following components: [0107] crumb rubber from used automotive and tractor tires with a particle size of up to 1 mm—50 wt. %, [0108] Ca(OH).sub.2—20 wt. %, [0109] petroleum oil of solvent refining with the viscosity of from 0.05 to 1.5 Pas at 60° C.—20.0 wt. %; [0110] diafene FP—2.0 wt. %; [0111] guanidine—5.0 wt. %; [0112] stearic acid—3.0 wt. %.

[0113] Then comes mixing the components of the resulting mix with the shock-shear load on the material in the mixer-activator at a temperature of 100° C.;

[0114] After obtaining a uniform homogeneous resulting mix, it is cooled to a room temperature.

Example 6

[0115] At a preliminary stage, a mix is prepared, which includes the following components: [0116] crumb rubber from used automotive and tractor tires with a particle size of up to 1 mm—65 wt. %, [0117] MgO—10 wt. %, [0118] petroleum oil of solvent refining with the viscosity of from 0.05 to 1.5 Pas at 60° C.—20.0 wt. %; [0119] diafene FP—2.0 wt. %; [0120] diphenylguanidine—0.2 wt. %. [0121] stearic acid zinc salt—2.8 wt. %.

[0122] Then comes mixing the components of the resulting mix with the shock-shear load on the material in the mixer-activator at a temperature of 120° C.;

[0123] After obtaining a uniform homogeneous resulting mix, it is cooled to a room temperature.

[0124] Below, there are the test results confirming the advantages of the present invention, namely, the process of manufacturing the modified crumb is low-temperature (up to 120° C.), it does not require special equipment and expensive components, and it is cost-efficient—the cost value of the modified crumb remains almost equal (comparable) with the cost of the main raw material—crumb rubber. The resulting product does not become caked, it is easy transported and suitable for long-term storage.

[0125] Table 1 shows a comparison of the characteristics of the Portuguese bitumen of 50/70 grade, improved by the addition of 14% of the crumb rubber modified by the claimed method at the mixing temperatures the bitumen of 160° C. and 180° C. From Table 1, it is obvious that at a mixing temperature of 180° C., the properties of the mix deteriorate significantly.

TABLE-US-00001 TABLE 1 Bitumen Viscosity Softening Additive (%) Additive (mPa .Math. s) temperature ≥ Penetration Elasticity type 50/70 (%) 175° C. 55 (0.1 mm) (%) Remarks Modified 86 14 625 60 42 29 2 hours of crumb mixing at a rubber temperature of 160° C. Modified 86 14 548 57 32 17 2 hours of crumb mixing at a rubber temperature of 180° C. Initial 100 0 160 55 55 8 Initial bitumen bitumen

[0126] The dissolution of the modified crumb rubber in the bitumen to obtain the indistinguishable particles is provided under the mild conditions, that is, at a temperature of 160-170° C. without applying an abrasive mechanical action, which reduces significantly the cost of the required equipment and reduces the cost of the technological process; the modified rubber easily penetrates into the bitumen, and after an hour and a half, it is actually completely dissolved, forming a uniform solution of bitumen with caoutchoucs, which, although delaminated without mixing, but does not degrade, and it is absolutely suitable for long-term storage, in no way inferior in quality to the SBS-modified bitumen, which is a unique property of this mix.

[0127] The dissolution of the modified crumb rubber to obtaining the indistinguishable particles prevents rapid sedimentation and makes possible long-term storage of the resulting bitumen-rubber compositions for their further use; the possibility of storing the bitumen-rubber composition at a temperature of 160° C. is of particular interest, so, for example, when storing the mix with 10% and 14% of the modified crumb rubber during 120 hours, there is no deterioration of the indicators of the binder.

[0128] Due to the fact that the bitumen improved with the help of the crumb rubber modified by the claimed method, unlike the bitumens modified with the help of SBS or the crumb rubber, is not prone to degradation (the degradation of the bitumen mixes with the conventional crumb rubber occurs already during 4 hours) during storage (delamination due to the difference in the specific densities of the constituent materials, when stored without mixing, is possible, the similar delamination like, when storing some paints), which is similar to the bitumen behaviour with the caoutchouc additives, in this case, after such storage, it is sufficient to mix the bitumen improved by this way by a conventional paddle stirrer during 10-15 minutes at a temperature of 150-160° C. Table 2 shows the data on the comparison of the parameters of the mix containing 10% of the modified crumb rubber (MC) immediately after the manufacture of this mix and after five days of storage.

[0129] The comparison of the characteristics of the bitumen of BND 60-90 grade, improved by adding 10% of the crumb rubber modified by the claimed method immediately after the manufacture and after 5 days of storage in a heat chamber at 160° C. and at mixing by the paddle stirrer with a speed of 350 rpm during 10 minutes every 24 hours. As can be seen from the data, the viscosity of the mix is not increasing, and the penetration becomes even slightly greater (or it is decreasing by not more than 8 units), which indicates of a uniform mix that is not prone to degradation and coking, which is ready for the use in road construction.

TABLE-US-00002 TABLE 2 Mix after BND 10% 5 days of Indicator name 60/90 of MC storage Depth of needle penetration, 89 61 69 0.1 mm, at 25° C. Ring-and-ball softening 47 55 56 temperature, ° C. Tension load 0.927 3.408 2.116 Elasticity, % at 25° C. 8 60 61 Dynamic viscosity at 135° 0.24 1.03 1.12 C., Pa*s Dynamic viscosity at 160° 0.158 0.43 0.54 C., Pa*s

[0130] Table 3 shows a comparison of the characteristics of the Portuguese bitumen of 50/70 grade, improved by the addition of 14% of the crumb rubber modified (MC in the Table) according to the claimed technology immediately after the manufacture and after 1, 3, 6 days of storage in the heat chamber at 160° C. and at mixing with the paddle stirrer with a speed of 350 rpm during 10 minutes every 24 hours (when stored during 6 days; however, it was not mixed at days 4.sup.th and 5.sup.th).

[0131] At the same time, after the first day of storage, the upper and lower layers of the bitumen mix were checked separately for delamination, and the test showed a positive result complying with the European and Russian standards. Moreover, the viscosity is increasing slightly, but at the same time, it remains within the standards.

[0132] As can be seen from the data, the quality of the bitumen is even slightly improved during storage: the softening temperature is slightly but increasing, while the penetration is becoming slightly greater. The checks by a RTOF test comply with the international and Russian standards, which indicates of a uniform mix that is not prone to degradation and coking, which is ready for the use in road construction.

TABLE-US-00003 TABLE 3 Softening St Penetration Bitumen Viscosity temperature St after increase (0.1 mm) Additive (%) Additive (mPa .Math. s) (St) Penetration Elasticity RTOF after RTOF after type 50/70 (%) 175° C. (° C.) ≥ 55 (0.1 mm) (%) (° C.) (° C.) ≤ 8 RTOF(%) Remarks MC 86 14 625 60 42 29 65 5 28 Mixing during 2 hours MC 86 14 275 54 35 Mixing during 2 hours (the upper sample - during 24 hours) MC 86 14 838 62 39 Mixing during 2 hours (the lower sample - during 24 hours in an oven at 160° C.) MC 86 14 763 59 35 33 67 8 29 Mixing during 2 hours + 3 days in an oven at 160° C. (mixing during 15 minutes per day) MC 86 14 1150 63 33 35 69 6 29 Mixing during 2 hours + 6 days in an oven at 160° C. (mixing during 15 minutes per day, except for days 4.sup.th and 5 .sup.th) Initial 100 0 160 55 55 8 60 5 38 Initial bitumen bitumen Viscosity at 160° C. (mPa .Math. s) Additive Bitumen Time (minutes) (%) (%) 5 15 30 45 60 90 120 Remarks 14.00 86.0 625 600 625 650 663 675 700 Mixing during 2 hours 14.00 86.0 838 738 700 688 688 675 675 Mixing during 2 hours (the lower sample - during 24 hours in an oven at 160° C.) 14.00 86.0 275 250 238 238 238 238 238 Mixing during 2 hours (the upper sample - during 24 hours in an oven at 160° C.) 14.0 86.0 763 788 813 825 863 875 888 Mixing during 2 hours + 3 days of storing in an oven at 160° C. (mixing during 15 minutes per day) 14.0 86.0 1150 1112 1137 1200 1250 1325 1362 Mixing during 2 hours + 6 days of storing in an oven at 160° C. (mixing during 15 minutes per day, except for days 4.sup.th and 5 .sup.th)

[0133] The sharp unpleasant smell of rubber that occurs in the current technologies during the process of dissolving the crumb rubber in the bitumen and in the asphalt concrete mix made on its basis is eliminated; in the asphalt concrete mixes, the modified crumb rubber can be applied both by “dry” (an additive to the asphalt concrete mix during its manufacture) and “wet” (an additive directly to the bitumen) methods, in both cases, the asphalt concrete does not have the unpleasant smell.

[0134] A comparison of the chemical formulation of the samples of the atmospheric air with the emissions, when the bitumen is improved with the help of the modified crumb rubber prepared by the claimed method, and when the bitumen is improved with the help of the crumb rubber prepared by the standard technology is shown in Table 4.

[0135] The results of the chemical analysis of the indoor air. Sample No. 1—taken during the process of improving the bitumen with the help of the modified crumb rubber. Sample No. 2—taken during the process of improving the bitumen with the help of the crumb rubber prepared by the standard technology.

TABLE-US-00004 TABLE 4 (Hygienic Regulatory Standard) HRS 2.1.6.3492-17 (Maximum Measurement Permissible results, Concentration) MPC The components mg/m.sup.3 in the atmospheric air (Regulatory to be Sample Sample of populated areas, Document) RD Sr. no determined No. 1 No. 2 mg/m.sup.3. for test methods 1. Polycyclic aromatic 0.0117 0.0443 phenanthrene-0.01** (Guideline hydrocarbons: Document) GD 1.1. fluorene anthracene-0.01** 52.04.186-89 1.2. anthracene <0.0001 <0.0001 1.3. pyrene 0.0027 0.0016 1.4. phenanthrene 0.0036 0.0303 1.5. fluoranthene 0.0054 0.0070 <0.0001 0.0054 2. Phenol 0.0022 0.0034 0.01 GD 52.04.799-2014 (Hydroxybenzene) 3. Formaldehyde 0.0084 0.0079 0.05 GD 52.04.186-89 (Methodological Instructions) MI 4.1.619-96 4. Dimethylbenzene (Xylene), 0.0229 0.0118 0.2 GD 52.04.186-89 isomer mix 5. Methylbenzene (Toluene) 0.0684 0.0534 0.6 MI 4.1.637-96 6. Benzene 0.0047 0.0054 0.3 GD 52.04.186-89 7. (1-Methylethyl)benzene 0.0124 0.0057 0.014 GD 52.04.186-89 (Cumene) 8. Hydroxymethylbenzene 0.0040 0.0042 0.005 GD 52.04.186-89 (Cresol), isomer mix 9. Carboxylic ethers 0.0691 0.0551 0.1 MI 4.1.625-96 (by ethyl acetate) 10. SO.sub.X 0.009 0.010 0.5 GD 52.04.794-2014 11. NO.sub.X 0.002 0.002 0.2 GD 52.04.792-2014 12. Ethenylbenzene (Styrene) 0.0146 0.0140 0.04 MI 4.1.662-96 13. Ethyl benzene <0.0001 0.0016 0.02 GD 52.04.186-89 14. Vinyl chloride (Chlorethene) 0.0068 0.0078 0.01 GD 52.04.186-89 15. Diphosphorus pentoxide <0.002 <0.002 0.05 GD 52.04.186-89 (P.sub.2O.sub.5) 16. Mineral acids (by 0.0091 1.2842 0.2 GD 52.04.186-89 hydrochloride) 17. Hydrogen sulfide 0.0064 0.0040 0.008 GD 52.04.186-89 (dihydrosulfide) + mercaptans

[0136] As a result of the quantitative chemical assay of the air, it was found: [0137] The concentration of the mineral acids (by hydrochloride) in Sample No. 2 (with the standard crumb rubber) exceeds Maximum Permissible One-Time Concentration (MPC.sub.OT) by 6.421 times according to HRS 2.1.6.3492-17 and it is by 141.12 times higher than in Sample No. 1 (with the modified crumb rubber); [0138] The total concentration of the PAHs (polycyclic aromatic hydrocarbons) in Sample No. 2 (with the standard crumb rubber) is by 3.786 times higher than in Sample No. 1 (with the modified crumb rubber).

[0139] The quality indicators of the bitumen improved with the help of the crumb rubber modified by the claimed method are increasing significantly, in particular, the temperature range of the bitumen performance is expanding significantly, elasticity is increasing, and the bitumen adhesion to the mineral fillers of the asphalt concrete is increasing. Some quantitative characteristics of improving the quality indicators of the improved bitumen are shown in Tables 5-6.

[0140] Table 5 shows a comparison of the characteristics of the conventional bitumen of BND 60-90 grade and the same bitumen, but improved by means of the crumb rubber modified by the claimed method at the different concentrations (10% and 15%) of the additive of the modified crumb rubber (MC).

TABLE-US-00005 TABLE 5 BND 10% 15% Indicator name 60/90 of MC of MC Depth of needle penetration, 89 61 56 0.1 mm, at 25° C. Ring-and-ball softening 47 55 59 temperature, ° C. Tension load 0.927 3.408 4.27 Elasticity, % at 25° C. 8 60 65 Dynamic viscosity at 135° 0.24 1.03 1.9 C., Pa*s Dynamic viscosity at 160° 0.158 0.43 0.69 C., Pa*s

[0141] Table 6 shows the comparative results of the Marshall tests of the asphalt concrete mixes prepared based on the conventional bitumen of BND 60-90 grade with the use of 0.4% of cellulose and the mixes based on the bitumen of the same grade, but improved by means of the use of 12% and 14% of the modified crumb rubber.

EXAMPLE

[0142]

TABLE-US-00006 TABLE 6 Bitumen and bituminous mixes (binder) Compressive strength, MPa Bitumen of BND 60/90 grade + 0.63 0.4% of cellulose Bitumen of BND 60/90 grade + 0.76 12% of the modified crumb Bitumen of BND 60/90 grade + 0.87 14% of the modified crumb

[0143] The positive changes in the properties of the improved bitumens lead to the situation that the asphalt concrete mixes prepared on their basis acquire increased resistance to rutting and cracking compared to the mixes based on the conventional bitumen.

[0144] Table 7 shows a comparison of the rutting characteristics for the asphalt concrete mix prepared based on the conventional bitumen of BND 60-90 grade using 0.4% of cellulose and the similar mix prepared based on the same, but SBS-modified bitumen, using cellulose as a stabilizer with the similar characteristics of the mixes based on the bitumen of the same grade, but improved by means of using 12% and 14% of the modified crumb rubber.

TABLE-US-00007 TABLE 7 Average rut depth after 20 thousand of wheel Bitumen and bituminous mixes (binder) running, mm Bitumen of BND 60/90 grade + 3.8 0.4% of cellulose Bitumen of BND 60/90 grade SBS- 2.9 modified + 0.4% of cellulose Bitumen of BND 60/90 grade + 2.5 12% of the modified crumb Bitumen of BND 60/90 grade + 2.2 14% of the modified crumb

[0145] In SMA and other asphalt concrete mixes, where the use of the stabilizing additives is required, the modified crumb rubber not only improves the bitumen properties, but also serves as a stabilizer, which leads to a reduction of the price for asphalt concrete. The results of the experiments for a comparison of the properties of different mixes in terms of the level of their draindown in the SMA are shown in Table 8.

[0146] Table 8 shows a comparison of the characteristics of the draindown of the binder in SMA using the bitumen of BND 60-90 grade using 0.4% of cellulose and the similar mix prepared based on the same, but SBS-modified bitumen, using cellulose as a stabilizer with the similar characteristics of the mixes based on the bitumen of the same grade, but improved by means of using 12% and 14% of the modified crumb rubber.

TABLE-US-00008 TABLE 8 Experi- Experi- ment ment Mean Bitumen and bituminous mixes (binder) No. 1 No. 2 value Bitumen of BND 60/90 grade 0.87 0.79 0.83 Bitumen of BND 60/90 grade 0.63 0.32 0.475 SBS-modified Bitumen of BND 60/90 grade + 0.07 0.089 0.0795 0.4% of cellulose Bitumen of BND 60/90 grade + 0.16 0.09 0.125 12% of the modified crumb Bitumen of BND 60/90 grade + 0.042 0.03 0.036 14% of the modified crumb