Anti-deformation performance of asphalt modified by carbon black extracted from waste cooking oil pyrolysis waste tires rubber

2.1.1. Asphalt, CTR, WCO and Carbon Black N330

The A-70 asphalt selected in this research was produced by Maoming Donghai Asphalt Co., LTD (Maoming, China). The basic properties of asphalt were presented in Table 1. The crumb tire rubber (CTR) was 40-mesh, and its component is presented in Table 2. The fundamental characteristics and major contents of WCO are listed in Table 3. In this study, N330 was produced by Hejin Jinlong Technical Co., LTD (Hejin, China), and the characteristics of the carbon black N330 was shown in Table 4.

2.1.2. Separate carbon black from CTR

Based on the research of Song [5], Zhao [3], etc., who used oil phase medium to crack rubber at a low temperature of 140-260 °C, the mass ratio of CTR and waste cooking oil was selected as 1:1. CTR and waste cooking oil contained in steel cups were pyrolyzed at 180 °C for 2 h using a double-layer spiral fan-blade mixer with a mixing speed of 250-300 rpm, and timing was started when the temperature was stabilized at 180±10 °C. Finally, a mixture of CTR and waste cooking oil named waste rubber/oil (WRO) was obtained [3].

The waste rubber/oil (WRO) was wrapped in filter paper and extracted with toluene in a Soxhlet extractor for 48 h to remove low molecular weight solutes and other additives, and the residue was dried in a vacuum oven at 70 °C for 4 h to a constant weight. Finally, the dried residue was ground into powder using a mortar and pestle to obtain rubber-cracked carbon black (RCCB).

2.1.3. Preparation of CB Modified Asphalt

Weighing 150 g of matrix asphalt in a steel cup with an inner diameter of 9 cm, the matrix asphalt was heated to 135 °C. RCCB and industrial carbon black N330 were added at 5 % of the asphalt respectively. The carbon black modified asphalt mixtures were stirred using a three-bladed mixer with a fan blade diameter of 3cm at 300-400 rpm for 1h after the temperature had reached 180±10 ℃. To investigate the state of carbon black in WRO, modified asphalt externally blended with 5 % WRO was prepared by the same process.

2.2.1. Basic properties

Due to the limited amount of RCCB-modified asphalt, the softening point using less asphalt content was selected to characterize the basic properties.

2.2.2. Rheological properties

The rheological properties of asphalt binder can be estimated by the dynamic shear rheological test (DSR). According to AASHTO M320, the complex modulus ($G^{*}$) and phase angle ($\delta$) of the asphalt were determined by dynamic shear oscillatory test performed on TA dynamic shear rheometer AR 1500 ex. In this paper, the temperature scanning test of asphalt was performed under the controlled strain of 12 % mode. The scanning temperature ranged from 46-76 °C in increments of 6 °C/min, and the scanning frequency was 10 rad/s. The plate employed was 25 mm in diameter, and the gap between parallel plates was 1 mm.

2.2.3. Multiple stress creep recovery (MSCR) test

The MSCR test can be employed to investigate the rutting resistance of asphalt and was performed at 64 ℃ on matrix asphalt, RCCB and industrial carbon black N330 modified asphalt according to the AASHTO TP-70. The stress levels of the experiments were 0.1 kPa and 3.2 kPa, respectively. MSCR cycle consisted of constant 1s creep and 9 s recovery period, and the test was repeated 10 times for 100 s at each stress level, 20 creep and recovery cycles were performed at creeping stress of 0.1 kPa while 10 creep and recovery cycles were performed at creeping stress of 3.2 kPa, lasting for a total time of 300 s. The data were analyzed from cycles 11 to 20 at 0.1 kPa and from cycles 21 to 30 at 3.2 kPa. The cumulative strain curves at the two strain levels and the non-recoverable creep compliance measured at 3.2 kPa (Jnr3.2) were applied to evaluate the durability of asphalt to permanent deformation under repeated loading conditions [9].

3.2.1. Analysis of rheological properties

The complex shear modulus ($G^{*}$) can represent the deformation resistance of asphalt under repeated pulse shear stress to some extent. As shown in Fig. 2(a), the complex shear modulus of the two types of carbon black modified asphalt decreases with increasing temperature. The complex shear modulus of matrix asphalt was improved by adding 5 % carbon black N330, while the RCCB reduced it.

Phase angle ($\delta$) is related to the proportion of viscous components to elastic components in asphalt, the larger value indicates a larger proportion of viscous components in asphalt, which means more prone to plastic deformation under external forces. It can be seen from Fig. 2(b), that as temperature increases, the phase angle becomes larger indicating that the proportion of viscosity in asphalt increases and the deformation-recovering ability decreases. Besides, it is interesting that at the initial temperature of 46 ℃, the phase angle of RCCB-modified asphalt is greater than that of N330 and 70# asphalt. At 52 ℃, the three asphalts are very close, and RCCB-modified asphalt is still the largest among them. But after 58 ℃, the order becomes N330>70#>RCCB, which indicates that during the 46-52 ℃, the relative proportion of viscous components that are prone to plastic deformation in RCCB-modified asphalt is relatively small. However, when the temperature further increases to above 58℃, the viscous components of RCCB-modified asphalt increase and its growth rate is faster than N330 and matrix asphalt, resulting in the phase angle of RCCB-modified asphalt being the smallest among them.

The rutting factor ($G^{*}/\mathrm{s}\mathrm{i}\mathrm{n}\delta$) can be applied to evaluate the deformation resistance of asphalt. Fig. 2(c) shows the rutting factor of all types of asphalt decreases with increasing temperature. The rutting factor of carbon black N330 modified asphalt is greater than that of matrix asphalt, while the rutting factor of RCCB-modified asphalt is the smallest. The rutting factor of RCCB-modified asphalt is lower than 1.0 kPa after 64 ℃, while carbon black N330 modified asphalt and matrix asphalt are about 68 ℃. These data indicate that N330 improves the deformation resistance of asphalt at high temperatures, while RCCB deteriorates its deformation resistance. The organic shell insoluble in toluene in RCCB may soften the asphalt system with increasing temperature, thereby reducing the deformation resistance of the asphalt.

Fig. 2Results of performance grading test: a) complex shear modulus, b) phase angle, c) rutting factor

a)

b)

c)

3.2.2. Analysis of the MSCR Test

Fig. 3(a), (b) displays the cumulative strain curves of asphalt at the stress level of 0.1 and 3.2 kPa at 64 ℃. At the 0.1 kPa stress level, the cumulative strain of RCCB-modified asphalt is higher than matrix asphalt, indicating that the creep deformation of RCCB-modified asphalt is relatively large. When the stress level cone to 3.2 kPa, the cumulative strain of the three asphalt significantly increases, and the cumulative strain curve of RCCB modified asphalt becomes close but slightly higher than matrix asphalt, indicating that under heavy traffic load, the elastic recovery performance of RCCB modified asphalt is similar with matrix asphalt. However, the cumulative strain of N330 is the lowest at both stress levels, indicating that N330 improves the high-temperature deformation resistance of matrix asphalt. The asphalt with lower Jnr3.2 values is more resistant to deformation. According to Fig. 3(c), N330 modified asphalt has the best resistance to deformation and RCCB has the worst, which is consistent with the results of the rutting factor.

Fig. 3Results of MSCR test: a) 0.1 kPa stress level; b) 3.2 kPa stress level; c) Jnr3.2

a)

b)

c)