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Characterization of bakelite-modified bitumen

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Technical Note
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Abstract

This study investigated the influence of Bakelite on the physical, performance, and mechanical properties of bitumen binder. Bakelite is the trade name of phenol formaldehyde—a thermosetting type of plastic. It is a polymer amorphous in nature having three-dimensional structure. This imparts hardness, strength, and rigidity. Bakelite was blended in the bitumen in variegated percentages from 1 to 5% with an increment of 1%. The blended bitumen was characterized by penetration, softening point, and dynamic viscosity using rotational viscometer and compared with unmodified bitumen of penetration grade 60/70. The rheological parameters were investigated using Dynamic Shear Rheometer (DSR) (AASHTO Provisional Standards: AASHTO T315-08, Standard test method for determining the Rheological properties of asphalt binder using a Dynamic Shear Rheometer (DSR) Washington, 2011), and mechanical properties were investigated using Marshall stability test. The results indicated an increase in softening point, dynamic viscosity, and decrease in binder penetration up to 2% modifier content and then follow the reverse trend. The blending of bitumen with bakelite increased complex modulus, decreased phase angle, and improved rutting resistance as well. There was a significant improvement in Marshall stability, rather a marginal improvement in flow value. The best improvement in the modified binder was obtained with 2% bakelite. This project demonstrates that the properties of bitumen can be improved by adding Bakelite in it. With negligible raise in initial cost of the construction, the life and performance of pavements can be increased for a long duration.

Keywords

Bakelite Stripping Complex shear modulus Phase angle Rutting resistance Marshall stability 

Abbreviations

AASHTO

American association of state highway and transportation officials

ASTM

American society for testing and materials

DSR

Dynamic shear rheometer

HMA

Hot mix asphalt

IS

Indian standards

MORTH

Ministry of road transport and highways

Introduction

E-waste consists of all waste from electronic and electrical appliances which have reached their end-of-life period or are no longer fit for their original intended use and are destined for recovery, recycling, or disposal. It includes computer and its accessories, monitors, printers, keyboards, central processing units, typewriters, and mobile phones. The composition of e-waste is diverse and falls under ‘hazardous’ and ‘non-hazardous’ categories. Broadly, it consists of ferrous and non-ferrous metals, plastics, glass, etc. Recycling can recover reusable components in the form of Bakelite. Globally, about 20–50 MT (million tons) of e-wastes is disposed of each year. By 2020, e-waste from old computers would jump by 400% to 2007 levels in China and by 500% in India. Additionally, e-waste from discarded mobile phones would be about seven times higher than 2007 levels and, in India, 18 times higher by 2020 [2]. E-waste plastics are generated as domestic waste and are available in plenty amount. These are generally thermosetting plastic which cannot be re-melted to form a new product and are generally landfilled or incinerated, both of which lead to environmental problems [3]. However, such problems can be mitigated using e-waste in road construction.

Most of the highways are flexible pavement, and their top surfaces are formed by bituminous binder and aggregates. Normally bituminous concrete pavement gets softened at high temperature and under repetitive heavy traffic load, resulting rutting [4]. On the other hand, at low temperature, cracking occurs. Due to these phenomena, the pavement gets the premature failure, and a lot of money is wasted every year for their maintenance.

Bakelite is a type of thermosetting plastic. Thermoplastic polymers, thermosetting plastics, rubbers, and block copolymers are usually used to modify bitumen with the intent to improve the performance of binders [5]. They also reported that Marshall stability test, viscosity test, rheological tests(unaged and aged binder), etc., indicated an increasing trend with the increase in bakelite content up to certain extent and then it decreased [5]. Ahmed et al. concluded the Rutting resistance improved by 29 and 38% for class A and class B hot mix asphalt (HMA) mixtures using bakelite [6].

Cubuk et al. [9] investigated the influences of phenol formaldehyde resin on the rheological properties of bitumen. Different amounts of phenol formaldehyde were mixed with the bitumen of 50/70 penetration grade, and variations in viscosity as a function of temperature and additive concentration were determined. The effects of the phenol formaldehyde additive were examined by conventional and Superpave test methods. Adhesion and stability of bitumen-aggregate mixtures prepared using pure and modified bitumen were compared using Nicholson stripping and Marshall tests. They found that appreciable decrease in the formation of rutting, bleeding, stripping, and cracking in bitumen may be obtained through phenol formaldehyde addition.

The objective of this study is to conduct a comparative test program on binders and bitumen mixtures containing standard and bakelite-modified bitumen and assess the effects of bitumen properties on pavement performance.

Materials and methods

Bitumen

Bitumen is a common binder used for the construction of the top layer of flexible pavement. It is derived from petroleum crude by refinery process. It is a viscoelastic material having elastic properties at low temperature and form viscous liquid at high temperature. The bitumen of 60/70 penetration grade was used for this study as basic properties are shown in Table 1.
Table 1

Properties of bitumen used

Properties

Value

Penetration 0.1 mm, 100 g, 25 °C, 5 s

60/70

Softening point min °C

58

Viscosity at 135 °C (Pa s)

0.407

Bakelite

Bakelite is the trademark of phenol–formaldehyde. It is a kind of thermosetting plastic that is formed by polymerization of phenol (C6H5OH) and formaldehyde (HCHO) through the condensation process. It is a cheap and high-performance engineering material. It has high water and chemical-resistant properties and suitable for thermal resistivity as well. It has not been used in roadway construction before [3]. It was taken from R. D. Trading Co., Delhi. Bakelite in powdered form is shown in Fig. 1, and its properties are given in Table 2.
Fig. 1

Bakelite powder

Table 2

Basic properties of bakelite

Physical state

Solid and granular

Color

Black & brown

Melting point

>100 °C

Molar mass

Variable

Chemical formula

(C6H6O·CH2O) n

Density

1.3 g/cc

Blending of bakelite in bitumen

Bakelite was mixed with bitumen at sufficiently high temperature and rotation so that it may get mixed homogenously throughout the bitumen. Melted bitumen was mixed with bakelite sample of 1, 2, 3, 4, and 5% by weight of bitumen and stirred mechanically using centrally aligned motor at 2000 rpm and 130 °C for 30 min.

Test program

Empirical tests, such as penetration and softening point, were carried out as per guidelines of IS: 1203-1978 and IS: 1205-1978, respectively. Adhesion effect was observed using stripping test (as per AASHTO T 182 and ASTM D 1664). Cohesion effect was observed using viscosity test by rotational viscometer (AASHTO T 316 and ASTM D 4402). Dynamic shear rheometer (DSR) was used to find rheological properties of bitumen as per AASHTO T315 and Marshall stability test (ASTM D 1559) was used to determine mechanical characteristics of bitumen concrete mix.

Results and discussions

All the tests were performed in the laboratory in order to examine the influence of bakelite-modified bitumen. Every quest is presented along with their concernment in the following subsections.

Penetration and softening point

The penetration value initially decreases rapidly and then increases gently, whereas softening point gently increases and then decreases as shown in Fig. 2. The minimum value of penetration and the maximum value of the softening point test are found at 2% of bakelite content. Penetration value decreased by 69% and softening point value increased by 15% at the same modifier content when compared to virgin bitumen.
Fig. 2

Structure of bakelite

Source: accessed at 8th September 2015, 12:48 pm from http://www.britannica.com/science/phenol-formaldehyde-resin

Stripping test

The test is done as per ASTM D1664. This determines the effects of moisture upon the attraction of a bituminous film to the aggregate particle. The stripping value initially decreases rapidly and then increases gently as shown in Fig. 3. This follows the similar trend like penetration. Use of 2% of bakelite in bitumen reduces the stripping to a large extent, and coated area of aggregate is more than 95%. This shows that the effect of water on bakelite-modified bitumen-coated aggregate is less, and the mix is less susceptible to moisture damage.
Fig. 3

Effect of bakelite on penetration and softening point

Viscosity

The viscosity of bakelite-modified bitumen first increases and then decreases with the increase of bakelite content as shown in Fig. 4. Viscosity increases up to 2% and then decreases at a particular temperature. It is observed that maximum value of viscosity was found at 135 °C as shown in Fig. 5. The viscosity varies from 0.407 to 0.971 Pas when added 0 and 2% bakelite at 135 °C. These observed values lies within specified limit as mentioned, i.e., less than or equal to 3 Pas at 135 °C [7]. The maximum value of viscosity is found at 2% of bakelite content.
Fig. 4

Effect of bakelite on stripping

Fig. 5

Effect of bakelite on viscosity

Complex shear modulus (G*)

Complex shear modulus decreases with the increase of temperature over the range as shown in Fig. 6. At a particular temperature, G* increases with the increase of bakelite content. It attains a maximum value at 2% of bakelite content; afterward, the value of G* decreased. The maximum value of G* indicates higher stiffness; this reflects that the bituminous pavement will become stiffer.
Fig. 6

Effect of bakelite on viscosity showing peak point

Phase angle (δ)

Figure 7 shows the trend of phase angle which represents that with the increase of temperature, phase angle increases. It is also observed that with the increase of modifier content phase angle decreased generally over the range of the temperature. Phase angle varied from lower to higher temperature indicates a transition from elastic behavior to viscous behavior. The phase angle value lies from 80° to 90°; it means viscous in nature. The combined effect of phase angle and complex modulus may give its actual effect on pavement performance.
Fig. 7

Effect of bakelite on complex shear modulus (G*)

Rutting resistance (G*/Sin δ)

The complex shear modulus elastic portion G*/Sin δ should be large when rutting is of greatest concern. A minimum value for the elastic component of the complex shear modulus is specified for short-term failure of roads [8]. The results obtained in the present study satisfy the specified limit, i.e., greater than or equal to 2.2 kPa [7]. Figure 8 shows the variation of rutting resistance parameter with the increase of bakelite content at different temperature points. Rutting resistance parameter initially increased and then decreased; this trend indicates an optimum value [9]. The optimum value of rutting resistance parameter is found at 2% of bakelite content. There is a drastic change in rutting resistance when temperature increased from 46 to 52 °C and further slowly decreased with the increase of temperature. Therefore, bitumen with the higher value of rutting resistance parameter at 46 °C may perform better than that with lesser value of G*/Sin δ.
Fig. 8

Effect of bakelite on phase angle

Marshal stability

Marshall stability test was performed on the bituminous concrete mix as per Ministry Of Road Transport and Highways (MORTH) specification. Optimum bitumen content is 5.475% obtained for 2% of bakelite content. Marshall stability value rose by almost 60%, whereas flow value reduced slightly and density showed a small increase in its value. Voids and voids filled with the binder in the mix are almost unchanged. All the observed values are in limiting range as specified shown in Table 3 (Figs. 9, 10).
Table 3

Result of Marshall stability test

Specification

Unmodified bitumen

Bitumen modified by 2% bakelite

As per MORTH specification

Stability (kg)

1600

2570

>900 kg

Flow (mm)

3.2

2.8

2–4 mm

Density (g/cc)

2.437

2.450

–

V v

4.5

4.7

3–6%

VFB

74.5

74

65–75%

Fig. 9

Effect of bakelite on G*/Sin δ

Fig. 10

DSR test data at optimum bitumen content of 2%

Conclusions

  • The lowest value of penetration at 2% of bakelite may indicate better improvement in shear resistance at high temperatures. Antipode, the highest value of the softening point at 2% of bakelite may indicate better improvement in resistance to deformation. Hence, this modified bitumen binder can be considered suitable to be used in the places where the climate remains hot.

  • The stripping test result indicates that the effect of water on 2% bakelite-modified bitumen is less, and the mix is less susceptible to moisture damage.

  • The viscosity of bakelite-modified bitumen increases with the increase of modifier content up to 2% of bakelite while temperature kept constant. This shows increment in cohesive force, which results in resistance to flow. To make it flowable, more energy will be required.

  • An acquired value of complex modulus extent is about 2.56–615 kPa at 2% bakelite additive, whereas the phase angle extent is about 80°–90° over the temperature range for unaged modified bitumen. This higher value of phase angle suggests about the more viscous material. Complex modulus and phase angle are used as predictors of hot bituminous mix performance.

  • Rutting resistance parameter enhanced from 2.54 to 633 kPa at 2% addition of bakelite, when temperature decreased from 88 to 46 °C. Rutting resistance parameter found at 52 and 46 °C is greater than 100 kPa. Hence, this can pertinent to resistance to rutting.

Based upon rutting parameter (G*/Sin δ) obtained from DSR test, 2% bakelite was observed to be optimum. At this optimum content, Marshal stability was compared with that of the bituminous concrete sample of pure bitumen. The addition of 2% bakelite increases the stability by 60% but flow value decreased by 12.5%, whereas, no significant change in other factors. This may manifest resistance against permanent deformations such as rutting, corrugation, and local settlement.

Based on the research work done so far on bakelite additive in bitumen, it may be recommended that this can be used in the places where rutting is of greater concern [10]. Bakelite addition also improves the strength of pavement and reduces deflection. It may also be beneficial in areas where heavy rain is a major problem causing stripping. Since the cost of bakelite powder is not much, so its use may cause a negligible increase in the cost of construction. If waste material is used by crushing in plants, it may not only eliminate the cost but also helps in cleaning the environment from such non-disposable pollutants.

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Copyright information

© Springer International Publishing Switzerland 2017

Authors and Affiliations

  1. 1.Department of Civil EngineeringNIT PatnaPatnaIndia

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