Use of waste rubber products in oil bitumen modification processes

XV Международный конкурс научно-исследовательских и творческих работ учащихся
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Use of waste rubber products in oil bitumen modification processes

Ахмедова Н.И. 1
1Азербайджанский Государственный Университет Нефти и промышленности
Сейфиев К.Ш. 1
1Азербайджанский Государственный Университет Нефти и промышленности
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As a result of research, a new technology for obsolete tires recycling has been developed.

Modification of petroleum road bitumen based on crumb rubber obtained from obsolete tires resulted in the production of asphalt concrete with high physical and mechanical properties.

It has been demonstrated that due to the use of the new crumb rubber modified bitumen technology the service life of asphalt concrete pavement increases 3 times. Such asphalt coating reduces the noise level on the road by 2 times, prevents ice formation on the road pavement, increases the adhesion of the canvas to the car tires, and reduces the braking distance.

It is being shown that during the construction and maintenance of roads, high efficiency can be achieved by using a rubber-bitumen composition. Only in Baku roads can be paved having received high-quality asphalt mix with the use of 5-10 thousand tons of rubber powder per year.

Keywords:
bitumen, polymer waste, crumb rubber, modification, ecology,

INTRODUCTION

When researching recycling methods for obsolete tires, we have found that they have been used for various purposes. Kang(2011). İbrahimov(2016).Chen(2018),

Using obsolete rubber and polymeric materials, road bitumen has been modified.

Demand for oil bitumen is increasing day by day. However, bitumen produced in our republic is substantially different from bitumen produced abroad. Bitumen’s success used does not meet the requirements of GOST 22245. Therefore, there is a need to modify construction bitumen (CB) used in the manufacture of asphalt pavements.

Nowadays, the bitumen-polymer composition is used as a binder in asphalt road pavement construction. To this end, a very expensive thermoplastic elastomer DST-30 is used.Chen(2017), Shixaliyev(2018,2019,2021). Alizade (2022).

Usually, the plasticity range of road bitumen is not higher than 60-65 °C, which is not sufficient to cover the surface layer of asphalt. Furthermore, in bitumen with low viscosity, there’s no elasticity. Belov(2012) Amirov(2018, .Since the stability of the composite material largely depends on the elastic properties of bitumen, asphalt concrete made on its basis quickly collapses and has an err mechanical influence. Therefore, to increase the elastic properties of the bitumen binder, there is a great need for its modification with polymers. Asphalt concrete pavement, obtained only based on polymer-modified bitumen has high physical and mechanical properties. Chen(2017),Cario(2016). Shixaliyev(2018,2020).

Our research has revealed that in terms of its comprehensive capabilities, crumb rubber is the only one that improves the properties of the bitumen binder and gives it highly elastic properties. Serenko(2007), Zhao(2012) Zaikin(2014), Taking into account the fact that crumb rubber is made from obsolete tires, then we can see that this modification not only enhances the physical and mechanical properties of bitumen but at the same time acquires economic and environmental significance.

Given the above, to toe bitumen and crumb rubber which is obtained from obsolete tires we proposed, we have investigated the technology of its combining with bitumen. For this purpose, we used the bitumen brand “Baku 85/25” produced at the Heydar Alieve Oil Refinery. The main physical and mechanical properties of the bitumen brand “Baku85/25” are given in Table 1.

As Table 1 indicates, this bitumen used as a binder for preparing asphalt mixtures for road paving in terms of its physical and mechanical properties is much lower than the key indicators of road bitumen made abroad. Shixaliyev(2018,2020).

Taking all this into account we have modified the bitumen brand “Baku 85/25” with the resulting crumb rub The formula mule of crumb rubber-bitumen composition is given in Table 2. Rubber-bitumen composition has been obtained as follows: crumb rubber (particle size from 0,8 to 10 mm) is mixed with bitumen at 1800C then added sulfur and antioxidants in 10 minutes.

Table 1.

Main physical and mechanical parameters of bitumen brand “Baku 85/25”

Name of indicators

Baku 85/25”

BDN 60/90

ROB 70/00

Needle penetration depth at 250C, 0,1kmm

90

88

87

Softening temperature, 0C

44

47

46

Ductility at 25 0C, cm

>150

>140

79

Flashpoint, 0C

247

284

290

Brittleness temperature, 0C

-19

-20

-22

CST

239

420

274

Dynamic viscosity at 600C, Pas

-

-

-

Change in mass when heated, wt.% after testing by ASTMD 1754 method

0,92

0,18

0,09

Softening temperature, 0C

49

50

51

Residual penetration of the initial value, %

89

74

69

Ductility at 25 0C, cm

>38

125

135

Kinematic viscosity at 135 0C, CST

329

520

366

Dynamic viscosity at 60 °С, Pas

972

436

169

Table 2.

Formulation of rubber-bitumen composition

Components

Composition of the components, wt. %

Sample 1

Sample 2

Sample 3

Sample 4

Sample 5

Bitumen brand “Baku85/25”

100

100

100

100

100

Crumb rubber (particle size) 1,0 mm

-

2

4

6

8

Sulfur

-

0,04

0,08

0,12

0,16

Neozone D

-

0,04

0,08

0,12

0,16

2. Method

The production technology of rubber-bitumen composition is as follows: crumb rubber with a particle size of 1.0 mm is loaded into a rubber mixer and Neozon-D is added to it and mixed for 12 minutes at 25 ° C. Then the mixing process is transferred to a paddle mixer, where bitumen heated to a temperature of 140-160 ° С is pumped simultaneously with a pump. The mixing process is carried out at a temperature of 150-169 °C for 60 minutes.

During this time, bitumen interacting with crumb rubber forms a homogeneous system. Sulfur is added to the resulting rubber-bitumen composition and mixed again for 3-5 minutes. The resulting composition is tested using standard methods. The results obtained are provided in Table 3.

Table 3.

Physical and mechanical indicators of crumb rubber-bitumen composition

Name of indicators

Indicator values

According to the requirements of OST 218·010-98

1

2

3

4

5

Needle penetration depth, 0,1 mm

at 250C

at 00C

60

32

108

54

104

52

98

48

93

45

90

44

Ring-and-ball softening point, 00C

54

67

75

83

90

58

Brittleness temperature, 00C

-20

-25

-27

-31

-30

-25

Elasticity, %

at 250C

at 00C

80,0

70,0

87,0

80,0

88

81

91

84

95

86

89

82

Adhesion (to concrete), MPa

0,11

0,13

0,15

0,17

0,18

0,13

As Table 3 indicates physical and mechanical properties of the rubber-bitumen composition obtained by modification are significantly higher.

As a result of using a cross-linking agent (sulfur) in the composition, it changes the low-temperature characteristic of bitumen and gives it high elastic properties. The resulting bitumen is softer, more elastic, and easily deformable, at low temperatures easily recovers to its original state when the force is applied. At the same time, even at high temperatures, bitumen does not soften, has good deformation resistance, and easily recovers its original state after deformation. Kerem(2019), Khazanov(2018).

Taking this into account, the resulting rubber-bitumen composition was used for the manufacture of the surface layer of asphalt pavements. The test results of the resulting asphalt mixture are shown in Table 4. The results obtained have shown that when using modified bitumen in the manufacture of the surface layer of the pavement, the physical and mechanical properties of asphalt concrete are significantly increased.

Only in Baku, city rubber-concrete composition obtained with the use of 5,000-10,000 tons of obsolete tires can be used in road construction and repair per year. This amount of crumb rubber is enough to cover more than 8 million square meters of road.

The results have shown that using rubber-bitumen composition in road construction, two main problems can be solved:

1) To increase the service life of asphalt concrete pavements, save on raw materials, reduce repair costs and achieve great economic benefits.

2) Large-scale recycling of obsolete tires that pose a threat to the environment can be achieved.

Table 4.

Physical and mechanical properties of asphalt-concrete composition covering surface layer of the pavement

Name of indicators

Indicator values

Norm according to GOST 31015-2002

1

2

3

4

5

Density (weight),g/cm3

Not normalized

2,38

2,39

2,395

2,406

2,410

Compression resistance, MPa

at 200C

at 500C

No less than 2,5

No less than 0,7

3,51

0,72

4,08

0,78

4,26

0,85

4,59

0,89

4,72

0,92

Crack resistance, MPa

at 00C

No less than 0,20

0,20

0,32

0,55

0,59

0,63

Water absorption capacity, volume %

1,5-4,0

3,07

2,68

2,52

2,33

2,05

Coefficient of water resistance

Not normalized

0,85

0,89

0,90

0,92

0,94

Coefficient of water resistance with prolonged water saturation (15 days)

Should not exceed 0,70

0,83

0,84

0,87

0,89

0,91

Internal friction coefficient

Should not exceed 0,94

-

-

-

-

-

Binder melt flow index, 10/min

Should not exceed 0,20

0,20

0,19

0,15

0,13

0,12

Residual porosity, %

2,0-4,0

3,64

3,57

3,13

2,46

1,83

3. Results and discussion

Properties and characteristics of polymer modified bitumen structures

At present 90% of bitumen produced globally is used in road construction. Bitumen is one of the cheapest and most versatile materials used in road pavement.

After one year of operation of asphalt-concrete coatings made using bitumen produced in our republic, the process of their destruction begins. Therefore, it is necessary to increase the key indicators of bitumen used in road construction.

The analysis of bitumen that we modified and bitumen produced in Russia and Azerbaijan showed that by all indications value of needle penetration depth at 250C of bitumen brand “Baku 85/25”, which we obtained as a result of the modification, is much better. The results obtained are given in Table 5.

These various types of road bitumen are used to aver different ductility values at 250C. When studying these bitumen’s using ASTMD 1754 method their physical and mechanical properties change dramatically. The obtained results show that the bitumen brand “Baku 85/25” has the lowest indicators. Bitumen brand “Baku 85/25” is the most active in the chemical processes involving oxygen at high temperatures Table 5.

The main physical and mechanical indicators of bitumen are obtained from various oil residues

Name of indicators

Bitumen brands

ROB 70/100 TC

38·/D/1356-91

ROB 66/90

GST 22245-90

Baku85/25”

Modified bitumen “Baku 85/25”

1

2

3

4

5

Needle penetration depth at 200C, 0,1 mkn

90

89

95

75

Softening temperature, 0C

47

47

44

55

Ductility at 25 0C, cm

>150

>150

>79

<160

Flashpoint, 0C

284

290

247

310

Brittleness temperature, 0C

-20

-19

-16

-25

Kinematic viscosity at 600CCSTt

420

239

274

430

Dynamic viscosity at 600C, Pas

209

87

375

85

Change in mass when heated, wt.% after testing by ASTMD 1754 method

0,09

0,18

0,90

0,08

Residual penetration according to the initial value, %

74

69

64

48

Ductility at 25 0C, cm

>150

125

38

36

Kinematic viscosity at 1350C, cost

520

320

366

540

Dynamic viscosity at 600C, Pas

436

169

972

158

. This is evidenced by the loss in sample mass when tested by ASTMD 1754 method. It is known that when bitumen is mixed with mineral material it is transferred into a film state. I ton of bitumen is distributed over a surface of 10.000 m2. Certainly, in an asphalt mixer, all conditions are created for the oxidation of bitumen. As the temperature increases, the oxidation of the compound increases. This can be seen more clearly in Figure 1. The aging index of modified bitumen brand “Baku85/25” is 2-3 times greater than other bitumen

From the economic point of view, the modifier must be cheap and have a large raw material base. This modifier is a crumb rubber obtained from obsolete tires that have been exploited as a result of our research.

Presently, SBS-type polymer and sulfur are used for the modification of oil bitumen in foreign countries. Moreover, mastics produced from SBS-type polymer are used to carry out various road repairs.

The modifying effect of polymer addition in bitumen depends on the technology process for preparing the men-polymer composition. Preparation of bitumen modified with polymers should be carried out by intensive mixing of the components at a temperature range of 150 to 2000C. The decomposition temperature of most polymers (polyethylene, polypropylene, ethylene-propylene rubbers, thermoplastic elastomers, etc.) significantly exceeds bitumen mixing temperature. That is, thermal and mechanic-destructive processes in the polymer mass do not occur, but if they occur, they occur to a small extent.

Bitumen softens when heated and thermoplastic polymers pass into a viscous-fluid state. Thus, a mixture of polymer and bitumen at elevated temperatures is a mixture of two liquids that differ in viscosity. Therefore, the process of mixing them should mainly be reduced to liquid-liquid dispersion. The degree of dispersion of such systems depends on the viscosity of the components and mutual solubility. (Figure1)

 

Aging index, ηcb

1 2 3 4 5 6

ъ

 

0

Aging, month

Figure. 1. Change in the aging index of bitumen during its mixing with mineral material in the manufacture of hot asphalt mixtures.

The mixture made based on crumb rubber and bitumen at an elevated temperature is an emulsion (Figure. 2).

When a load is applied to such systems, deformation occurs.

Figure. 2. Microstructure of bitumen composition with 5 wt. % of crumb-rubber.

The structure of bitumen modified by crumb rubber differs from bitumen’s structure modified by aliphatic polymers.

Thus, the mixing process at a high temperature of bitumen with crumb rubber proceeds in two stages: emulsification of crumb rubber in liquid bitumen and subsequent swelling. The depth of dispersion of crumb rubber into bitumen depends on the particle size of the crumb rubber.

The degree of dispersion of the polymer-bitumen composition largely depends on the method of mixing the components. The best results are achieved with colloidal mills. During the preparation process of polymer modified bitumen, the stage of feeding components to the process takes quite a while. The mixing process should take at least 5 hours. This also has neutrality of the final product.At high temperatures, the bitumen that is left over is oxidized, which leads to a very rough composition.

Bitumen-polymer mixture is a micro- or macro-inhomogeneous system. Their properties are determined by the phase structure of the mixture.

The elastic properties of bitumen can only be achieved by modifying it with polymer. The polymer forming a dispersed phase in the mass of bitumen forms a composite material with high physical and mechanical properties. The quality of bitumen does not affect its modification by the polymer. This is related to the nature of the polymer involved in the modification process. However, the physical and chemical properties of bitumen have a significant impact on its adaptation to the polymer. Increasing the rate of oxidation of bitumen complicates its combination with the polymer, due to the fact thabecausen the oxidation of bitumen the number of high molecular weight resins increases, while the number of low molecular weight resins decreases. Therefore, the swelling of polymer in bitumen decreases. The initial bitumen used for the preparation of the polymer-bitumen composition should be enriched in aromatic compounds to allow the adaptation of the components. This result is similar to that shown in the physical chemistry of polymers.

The introduction of polymer (crumb rubber) in bitumen leads to a sharp decrease in the values of ductility of bitumen at 25 °C. When stretching polymer-modified bitumen, to increase tensile strength it is necessary to use bitumen with the ductility of 100 cm at a temperature of 250C. For this purpose, we used mineral filler. Bitumen modified with a polymer (crumb rubber) is a dispersion system (heterogeneous), therefore it is not thermodynamically stable and hence decomposes. The more bitumen resembles the polymer, the greater the stability of the composite material.

We have determined softening temperature of bitumen modified with crumb rubber and heat resistance to other bitumen’s. The results obtained are given in Table 6. Table 6.

Properties of modified bitumen’s with different chemical nature

Name of indicators

Modified bitumen’s

Baku 85/25” with crumb rubber (10 wt.%)

Polystyrene (5 wt.%)

ROB 70/100

Needle penetration depth at 250C, 10-1 mm

45,7

58

Ductility at 250C 3 minutes after breaking, cm

77

60

Needle penetration depth at 00C, 10-1 mm

24

29

Ductility at 0 0C, cm

28

48

Softening temperature, 0C

92

82

Ductility at 25 0C, cm

60

94

Elasticity, %

94

80

Kinematic viscosity at 1350C, cost

1588

1710

Homogeneity

Homogeneous

Homogeneous

Brittleness temperature, 0C

-27

-27

Flashpoint, 0C

264

286

Marble grip

Doesn’t stick

Doesn’t stick

Softening temperature stability, 0C

29

15

Table 6


the softening temperature of bitumen modified with rubber crumb, and heat resistance to other bitumen.

After ASTM D 2672 test method

Residual penetration of the initial value, %

72

83

Ductility at 250C 3 minutes after breaking, cm Elasticity at 250C, %

52

51

84

67

Elasticity at 250C, %

84

77

Bitumen modified with crumb rubber, as a result of the elasticity inherent in rubber, increases its elasticity several times. This property is more evident in increasing the viscosity of polymer-bitumen composition.

To obtain high-quality polymer-bitumen composition, the main parameters of the components used in the composition must be closely monitored, and the technical regulations must be properly followed. Mineral oils should be used to ensure better swelling of crumb rubber (polymer) in the bitumen. However, it is important to remember that bitumen, like colloidal systems, is not resistant to aging over time. When mineral oil is added, this leads to the destruction of a relatively stable bitumen structure. Depending on the chemical structure of the mineral oil used, mineral oil either dissolves bitumen well or poorly. It is not so easy to mix bitumen with oil. Thus, the mixing mechanism of both components is similar to the fluid mixing mechanism. Thereby, the technology of mixing bitumen with mineral oil is a very complex technological problem.

The receipt of composite material has been developed to obtain a polymer-bitumen composition in laboratory conditions. Based on the optimum variant, the polymer-bitumen composition was obtained and the physical and mechanical properties of the composition obtained using the most modern methods of analysis were determined.

Table 7.

Physical and mechanical parameters of bitumen-concrete mix

Name of parameter

Samples

1

2

3

4

Compressive strength, MPa

at 200C

at 500C

2,2

0,9

2,3

0,91

2,0

0,88

2,3

0,90

Coefficient of water resistance

0,9

0,9

0,89

0,95

Water stability

0,85

0,9

0,91

0,94

Water-swelling, by volume, %

0,80

0,9

0,8

0,5

Residual porosity, by volume, %

2,1

2,4

1,9

2,0

CONCLUSIONS

The conducted research has led to the following conclusions:

From a biological point of view, non-degradable obsolete tires cause great environmental damage. Thus, the recycling of obsolete tires has both environmental and economic importance.

The problem of efficient obsolete tire recycling has not been fully resolved in any country. Tires that turn into waste in our country every year are a valuable source of raw materials. Since this valuable resource is not used, it poses an environmental threat instead of economic benefits. Therefore, the bitumen parental safety of obsolete tires is an urgent problem.

It follows from the foregoing that by using a rubber-bitumen composition in road construction, two important tasks can be solved:

- extending the service life of asphalt concrete pavement, in addition to saving on repairs, it is possible to improve the quality of the pavement;

- by recycling obsolete tires, along with solving environmental problems, very valuable raw materials can be obtained.

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