Research on properties of bio-asphalt binders based on time and frequency sweep test

Construction and Building Materials xxx (2018) xxx–xxx

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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Research on properties of bio-asphalt binders based on time and frequency sweep test Junfeng Gao a, Hainian Wang a,⇑, Zhanping You b, Mohd Rosli Mohd Hasan c a

School of Highway, Chang’an University, South Erhuan Middle Section, Xi’an, Shaanxi 710064, China Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA c School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang, Malaysia b

h i g h l i g h t s
Bio-asphalts prepared with different dosages of bio-oil extracted from sawdust were studied.
The influence of short-term aging condition on the rheological properties of bio-asphalt was analyzed.
The rutting factor master curves of bio-asphalt based binders were developed.
Incorporations of bio-oil into the SBS modified asphalt has greatly increased the rutting factor.

a r t i c l e

i n f o

Article history: Received 3 May 2017 Received in revised form 3 January 2018 Accepted 6 January 2018 Available online xxxx Keywords: Bio-asphalt Rheological properties Time sweep Frequency sweep Master curve

a b s t r a c t Bio-asphalt is a binding agent that is made of bio-oil and petroleum asphalt, or bio-oil modified with incorporations of some other additives under certain conditions. This study was carried out to evaluate the properties of bio-asphalt binder-based in terms of the value of complex shear modulus (G⁄) and the phase angle (d) tested by dynamic shear rheometer (DSR). Four bio-oil dosages of 5, 10, 15, and 20% based on the weight of asphalt (S100) were used to alter the SBS-modified binder. Whereby, the SBS content is approximately 1% of the weight of the virgin asphalt. The complex shear modulus and frequencies of virgin and short-term aged binders were tested. The master curves of rutting factor (G⁄/sind) of different bio-asphalt were then generated to survey its rheological properties in a broad range of frequencies and temperatures. Based on the results, it was found that the addition of bio-oil extracted from sawdust has significantly increased the complex shear modulus of asphalt binder at the same frequency conditions after going through rolling thin film oven (RTFO), which is desirable for rutting prevention of asphalt mixtures. The rheological properties of bio-binders are more susceptible to the RTFO aging condition compared to the reference binder. The master curve of rutting factor of bio-binder indicated that the rutting factor of bio-asphalt increased with the increase of frequency before and after RTFO. Additionally, incorporations of bio-oil into the SBS modified asphalt, has greatly increased the rutting factor (G⁄/sind) after RTFO, regardless of the loading frequency. However, the degree of enhancement was dominated by the percentage of bio-oil and aging condition. Ó 2018 Elsevier Ltd. All rights reserved.

1. Introduction With the rapid development of road and highway networks, alongside with the pavement maintenance and rehabilitation, the demand towards asphalt materials has been continuously increased since it was first introduced. At the same time, the source of crude oil that typically used to produce petroleum asphalt is also ⇑ Corresponding author. E-mail addresses: [email protected] (J. Gao), [email protected] (H. Wang), [email protected] (Z. You), [email protected] (M.R. Mohd Hasan).

dwindling. Thus, it creates attention among researchers and engineers to seek into potential alternative to overcome the shortage of the asphalt binder or any uncertainties that could be facing by the asphalt industry [1]. Among a variety of renewable energies, biomass energy has large reserves and the characteristics of wide distribution [2–5]. It could be used to extract bio-oil through further processing. Bio-asphalt is a binder made of bio-oil and petroleum asphalt under certain conditions or bio-oil modified with some other additives. Bio-asphalt is renewable and environmentally conscious so it has become the new direction of research.

https://doi.org/10.1016/j.conbuildmat.2018.01.048 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.

Please cite this article in press as: J. Gao et al., Research on properties of bio-asphalt binders based on time and frequency sweep test, Constr. Build. Mater. (2018), https://doi.org/10.1016/j.conbuildmat.2018.01.048

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In recent years, a number of researches have been done on materials regarding bio-oil among experts. Onochie et al. studied the high-temperature viscosity and rheological behavior of composite modified bio-asphalt prepared with nano-clay and nanosilica [6]. Several studies were carried out to assess the shortterm aging properties of bio-bitumen prepared from pig manure as raw material [7–9]. Other studies tested the high temperature performance of bio-asphalt binder prepared from oak sawdust, cedar wood chips and other raw materials [10,11]. Tang et al. incorporated 3%, 6%, and 9% bio-oil to modify the base binder, and the high temperature level of bio-binder was tested before and after RTFO aging protocol [12]. Huang et al. evaluated rheological properties of asphalt binders containing waste engine oil and investigated the fatigue properties of reclaimed asphalt pavement (RAP) blending with virgin binder and waste oil [13,14]. Meanwhile, Wang et al. studied the complex shear modulus, phase angle, rutting factor, and viscosity of bio-asphalt, and evaluated comprehensive performance of bioasphalt mixtures [15,16]. He et al. conducted a series of test to evaluate the performance of modified bio-asphalt in terms of penetration, softening point, ductility, and other conventional properties [17]. Despite the significant research efforts on bio-asphalt had been made in recent years, most of the existing literatures focus on the basic performance of the bio-asphalt, the influence of each factor at a broad range of temperatures and loading frequencies are not properly studied. Motivated by the current research status, this paper aims at investigating the rheological properties of bio-asphalt based on time and frequency sweep test using the dynamic shear rheometer (DSR). The effect of bio-oil content and aging on the shear modulus (G⁄), phase angle (d), and rutting factor (G⁄/sind) of the bio-binders were investigated. The master curve of the rutting factor (G⁄/sind) of bio-binders was constructed to investigate the influence of biobinders over a broad range of temperatures and loading rates. This study can lay a foundation for the further study of high temperature performance evaluation of bio-asphalt. 2. Objective and scope The objective of this study is to evaluate the rheological performance of bio-asphalt binder by the values of the complex shear

modulus (G⁄) and the phase angle (d) based on time and frequency sweep test using the dynamic shear rheometer (DSR). The bioasphalt binder was made with conventional asphalt and the biooil extracted from biomass. The bio-asphalt binder was subjected to the rolling thin film oven (RTFO) to study the influence of short-term aging condition on its rheological performances. The effect of bio-oil content and aging on the G⁄, d and G⁄/sind of the bio-binders were also investigated. The master curve of rutting factor G⁄/sind was constructed to investigate the influence of biobinders. The bio-binders were produced in the laboratory using a bio-oil source at four bio-oil percentages (5%, 10%, 15%, and 20% based on the weight of asphalt binder) with the control and SBS-modified binders, respectively. A dynamic shear rheometer was employed to test the rheological properties of the bio-asphalt binder at different temperatures. The detailed experimental procedures are illustrated in Fig. 1.

3. Materials and test program 3.1. Asphalt binders A 50 penetration grade virgin asphalt binder (denoted by 50#) that was obtained from a construction site in Maoming, China was used in this study. The asphalt binder was graded in accordance with the standard test methods. The basic properties of the 50# base binder are shown in Table 1.

3.2. Bio-oil In this study, the bio-oil was supplied by Toroyal New Energy Company located at Shandong province of China. It was extracted through the decomposition of biomass, via a pyrolysis method and has good compatibility with the base asphalt. Bio-oil used in this study was extracted from sawdust, which is dark brown in color and exhibits plasticity state at room temperature, as shown in Fig. 2. Elemental compositions and characteristics of bio-oil are shown in Table 2.

50# Asphalt binder

Virgin asphalt

SBS modified

1%SBS Unaged

RTFOT

DSR @76,70,64,58, 52,46,40

DSR @76,70,64,58, 52,46,40

5% bio-oil

10% bio-oil

15% bio-oil

20% bio-oil

Same testing procedures as virgin asphalt

Same testing procedures as virgin asphalt

Same testing procedures as virgin asphalt

Same testing procedures as virgin asphalt

Fig. 1. Experimental design of assessments on the bio-asphalt binders.

Please cite this article in press as: J. Gao et al., Research on properties of bio-asphalt binders based on time and frequency sweep test, Constr. Build. Mater. (2018), https://doi.org/10.1016/j.conbuildmat.2018.01.048

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J. Gao et al. / Construction and Building Materials xxx (2018) xxx–xxx Table 1 The properties of base asphalt 50#. Test index

50#

Technical requirements

Standard test methods

Penetration (25 °C)/(0.1 mm) Softening point/°C Ductility (10 °C)/cm RTFO (163 °C, 85 min)

53 49.5 19.5 0.286 68.4 6.3

40–60 49 15 ±0.8 63 4

ASTM D5 ASTM D36 ASTM D113 AASHTO T240-06 ASTM D5 ASTM D113

Mass loss/% Residual penetration (25 °C)/% Residual ductility (10 °C)/cm

film oven (RTFO) aging protocol based on AASHTO T240-06 (AASHTO 2006a) [18]. The virgin binders and short-term aged bio-asphalt binders were then tested using DSR based on AASHTO T315-06 (AASHTO 2006b) [19]. The test frequencies were 0.01, 0.05, 0.1, 0.5, 1, 5, 10, and 25 Hz, and the test temperatures ranging from 40 °C to 76 °C with an increment of 6 °C. During the test, the controlled strain loading mode was applied, and the strain control values of the asphalt samples before and after RTFO were 12% and 10%. The strain amplitude of the different tests for bio-binders was confined within the region of linear viscoelastic response of the binder [20].

4. Results and discussion 4.1. Infrared spectra of bio-oil before and after heating

Fig. 2. Physical appearance of the bio-oil.

3.3. SBS The SBS modifier used in this study is 1301-1 linear structure produced by a chemical company in Hunan province of China, as shown in Fig. 3. 3.4. Sample preparation Bio-oil concentrations of 5%, 10%, 15%, and 20% by weight of the SBS asphalt were applied in this study. The SBS modifier and base binder were homogeneously mixed using a high-speed shear emulsifying machine for approximately 15 min at 180 °C maintaining a rotational speed of 3000 r/min. Next, bio-oil was added into the SBS asphalt and stirred again using a high shear mixer for the duration of 20 min with the rotational speed of 3000 r/min. During this process, the mixing temperature used was lower than 140 °C to prevent the bio-oil from aging. The SBS content was added at 1% based on the weight of asphalt binder with the consideration of the modifier’s price. The contents of bio-oil were at 0%, 5%, 10%, 15% and 20% of total binder by weight, and the SBS modified bio-asphalts were named as S100, S105, S110, S115 and S120, respectively. The first number after S indicates 1% of SBS modifier, and the last two numbers indicate the percentage of bio-oil added. 3.5. Experimental program The changes in the behavior of bio-oil before and after heating at 163 °C were measured using TENSOR27 infrared spectrometer. The short-term aging of bio-binders was simulated by rolling thin

Fig. 4 shows the infrared spectra of bio-oil before and after heating, the heating temperature was 163 °C. After heating, the infrared spectra of the bio-oil showed a more obvious peak number of 1031 cm1, while the peak at 1088 cm1, 2962 cm1 and 3425 cm1 disappeared. According to the spectrum, 1031 cm1 is the fourth peak of acetal and ketal in the band, 1088 cm1 is the fourth peak of alcohol, phenol, ether, ester, etc. in the band, and 2962 cm1 is the band of saturated hydrocarbon radicals in the first peak region, which is the band of amines or amides. This shows that when the bio-oil was heated to 163 °C, alcohol, phenol, ether, ester, saturated hydrocarbon, amine or amide and other substances were reduced and a certain amount of acetal and ketal substances were generated. This result reveals the changes of bio-oil at this temperature, and the changes of bio-oil would also affect the properties of bioasphalt binders.

4.2. Complex shear modulus and phase angle analysis based on time sweep test The complex shear modulus (G⁄) and the phase angle (d) were obtained based on time sweep test from dynamic shear rheometer. The complex shear modulus (G⁄) is the ratio of the maximum stress to the maximum strain. It provides the total resistance of the material to deformation. The phase angle (d) is the time lag between the stress and strain of the asphalt during the test condition, and it is defined as the ratio of the elastic and viscous components. The G⁄ of unaged and RTFO-aged bio-binder with different concentrations of bio-oil are shown in Fig. 5. Based on the figure, it shows that the G⁄ of bio-binder is influenced by many factors, such as test temperature and bio-oil content.

Table 2 Elemental compositions and characteristics of bio-oils extracted from sawdust. Parameter

Test results

Mass fraction of elements /% C

H

O

N

54–56

5.5–7.2

35–45

0–0.2

Density/(gcm3)

pH

Viscosity at 135 °C/(Pas)

1.1

2.6

0.895

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Fig. 3. SBS modifier.

100 95 90 85 80 75 70 65 60 55 50 45 40 500

1000

1500

2000

2500

3000

3500

4000

Fig. 4. Infrared spectra of bio-oil before and after heating.

From Fig. 5(a) and (b), it can be concluded: (1) The complex shear modulus of 50#, S100, S105, S110, S115, S120 decreases gradually with the increase in temperature before and after RTFO aging. This indicates that the increase in temperature has reduced the rutting resistance of the asphalt. (2) Before RTFO aging, the complex shear modulus of S100 was the highest at the same temperature, followed by 50# and S105. In addition, regardless of the

50# S100 S105 S110 S115 S120

4

10

test temperatures, the complex shear modulus of S110, S115 and S120 are roughly identical. This shows that the addition of SBS modifier increased the resistance of 50# asphalt towards permanent deformation. The resistance to rutting of bio-asphalt with 5% bio-oil is low, but it is not different from the original asphalt. When the bio-oil content increased to 10%, its resistance to rutting is further decline; but when the bio-oil content increased to 20%, and the complex shear modulus basically remained unchanged. The results show that the effect of bio-oil content on complex shear modulus is not much when the content of bio-oil is more than 10% before RTFO. (3) After RTFO aging, the complex shear modulus of bio-asphalt increased with the increase in bio-oil content at the same temperature. Among all the bio-asphalt, the complex shear modulus of S120 was the highest and 50# asphalt was the smallest while the S110 and S115 were quite similar. This indicates that the incorporation of bio-oil after RTFO makes it relatively hard and its resistance to deformation increases due to the aging of the bio-asphalt. Fig. 6 illustrates the d of bio-asphalt binders with different content of bio-oil at a wide range of test temperatures. As can be seen from Fig. 6(a), the phase angles of S110 and S115 increase when tested at a higher temperature, which indicates that the viscous components increase gradually with the increase in temperature. While the phase angle of 50#, S100, S105, S120 reaches the maximum at 64 °C, which indicates that the viscous component reached its maximum at 64 °C. The phase angle of S100 was the smallest at the temperature of 64 °C compared to other asphalts. This indicates that the addition of SBS modifier increases the elastomeric content of the asphalt. Fig. 6(b) shows that the phase angle of 50#, S100, S105, S110, S115 and S120 increases with the increase in temperature, which indicates that as the temperature increases, the viscous composition of asphalt gradually increases. At the same temperature, the phase angle of each asphalt is ordered as 50# > S100 = S105 > S110 = S115 > S120; the results show that after RTFO aging the 50# asphalt still has a large viscous composition, and the phase angle of the asphalt mixed with 5% bio-oil is more consistent with that of the asphalt mixed with 1% SBS modifier. The phase angle of bio-asphalt with 10% bio-oil is more consistent with that of 15% bio-oil. With the increase in the content of bio-oil, the phase angle of bio-asphalt gradually decreased, and the aging of bio-asphalt increased. The recoverable amount of asphalt binder will increase with the decrease in the phase angle, which is beneficial to anti-rutting performance of asphalt mixture at high temperature.

5

50# S100 S105 S110 S115 S120

10

4

10 3

10

3

10 2

10

50

55

60

65

(a)unaged

70

75

80

85

50

55

60

65

70

75

80

85

(b) RTFO-aging

Fig. 5. G* of bio-binder with different bio-oil concentrations at testing frequency of 10 rad/s.

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J. Gao et al. / Construction and Building Materials xxx (2018) xxx–xxx 90

90

50# S100 S105 S110 S115 S120

88

86

50# S100 S105 S110 S115 S120

85

80

75

84

70 82

65 80

50

55

60

65

70

75

80

85

50

55

(a)unaged

60

65

70

75

80

85

(b) RTFO-aging

Fig. 6. d of bio-binder with different bio-oil concentrations at testing frequency of 10 rad/s.

50# S100 S105 S110 S115 S120

10

50# S100 S105 S110 S115 S120

100

10

1 1

0.1

0.1 50

55

60

65

70

75

80

85

(a)unaged

50

55

60

65

70

75

80

85

(b) RTFO-aging

Fig. 7. G*/sind of bio-binder with different bio-oil concentrations at testing frequency of 10 rad/s.

The bio-asphalt which bio-oil content is 20% has the smallest phase angle; this indicates that the bio-asphalt with the higher content of bio-oil is highly aged after RTFO aging. The rutting factor (G⁄/sind) was taken as an index to characterize the high performance of asphalt in AASHTO M320-05 (AASHTO, 2005) [21]. The G⁄/sind of bio-binders with different bio-oil contents was used to analyze their high temperature performance, as shown in Fig. 7. As can be seen that the rutting factor of 50#, S100, S105, S110, S115, S120 decreases gradually with the increase in temperature. This indicates that the rutting resistance decreases with the increase in temperature. Before RTFO aging, when the temperature is same, S100 asphalt has the maximum rutting factor, followed by 50#, S105, S110, S115 and S120 which has the rutting factor of roughly the same; this indicates that the addition of SBS modifier increases the resistance of 50# asphalt to rutting deformation, and on the basis of this, the anti-rutting ability is reduced because of the addition of bio-oil. After RTFO aging, at the same temperature, the rutting factor of each asphalt is ordered as S120 > S115 > S110 > S105 > S100 > 50#; this indicates that the resistance to rutting deformation increases with the increase of bio-oil content after RTFO aging, which is due to the aging caused by the incorporation of bio-oil, as shown in Fig. 4.

In order to better analyze the effect of bio-oil content on rutting factor, ANOVA analysis was conducted on the difference between rutting factor of unaged and RTFO-aging bio-asphalt at 64 °C and the accuracy of the various models were evaluated at a significance level of 0.05, as shown in Table 3. It was found that the p-values of bio-asphalt were less than .05 before and after RTFO aging, indicating that the content of bio-oil has a significant effect on the rutting factor of bio-asphalt. The Fvalue of the bio-asphalt before aging is bigger than of the aged, so the effect of bio-oil on rutting factor of bio-asphalt before aging is bigger than that after aging.

4.3. Frequency sweep and master curve generation based on frequency sweep test 4.3.1. Frequency sweep Frequency sweep test was carried out at different frequencies within a certain temperature range and the master curve can be constructed by frequency sweep results. In this paper, 50#, S100, S105, S110, S115, S120 were tested by frequency sweep test, and the storage modulusG0 , loss modulus G0 and complex shear modu-

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Table 3 The ANOVA on the difference between rutting factor of unaged and RTFO-aging bio-asphalt. Unaged

Between Groups Within Groups Total

RTFO-aging

SS

df

MS

F

p-value

SS

df

MS

F

p-value

3.098 0.001 3.099

4 10 14

0.775 0.000

7428.2

0.001

173.440 0.201 173.641

4 10 14

43.360 0.020

2157.928

0.002

1

10

100

10

100

104 104 10

3

103 102 102 101

101

100

10-1

100

0.01

0.1

1

10

100

10-1

0.01

0.1

(b) RTFO-aging

( a)unaged

Fig. 8. Storage modulus of bio-binder with different bio-oil concentrations at 64 °C.

10 5 10 4 10 4

10 3

10 3

10 2

10 2

10 1

0.01

0.1

1

10

100

(a)unaged

10 1

0.01

0.1

1

(b) RTFO-aging

Fig. 9. Loss modulus of bio-binder with different bio-oil concentrations at 64 °C.

lus G0 were obtained at 64 °C in consideration of the actual situation of road surface temperature and then the high temperature viscoelasticity of bio-asphalt was analyzed. As can be seen from Fig. 8, (1) the storage modulus of bioasphalt increased with the increase of frequency at 64 °C. It is shown that as the frequency increases, the asphalt exhibits more elastic properties. The shorter the time of vehicle loading, the higher the elastic properties of the asphalt pavement and the better is the anti-deformation performance. (2) Before RTFO, when the frequency is lower than 0.5 Hz, the storage modulus of different asphalt changes drastically, and does not show obvious regularity. When the frequency is higher than 0.5 Hz, with the increase in frequency, the storage modulus of the bio-asphalt with 15% bio-oil is

lower than other asphalt at the beginning and then higher than other asphalt at the end, this is because the bio-asphalt S115 is relatively sensitive to the change of storage modulus. (3) After RTFO, the storage modulus of bio-asphalt increased with the increase in bio-oil content at the same frequency. This indicated that the addition of bio-oil could increase the elastic properties of asphalt after RTFO. It can be seen from Figs. 9 and 10, (1) at a temperature of 64 °C, the loss modulus and the complex modulus of the asphalt increased with the increase in the frequency, which was consistent with the deformation of the storage modulus. (2) Before RTFO, the loss modulus and complex modulus of bio-asphalt S115 were lower than those of other asphalts while the other asphalts loss

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5

10 4

10

4

10 3

10

3

10 2

10

2

10

1

10

1

0.01

0.1

1

10

100

10

0.01

0.1

(a)unaged

1

10

100

(b) RTFO-aging

Fig. 10. Complex modulus of bio-binder with different bio-oil concentrations at 64 °C.

10 5 10 5 10 4 10 4 10 3 10 3 10 2

10 2

10 1

1E-3

10 1

0.01

0.1

1

10

100

1,000

1E-3

0.01

(a)unaged

0.1

1

10

100

1,000

(b) RTFO-aging Fig. 11. Master curve of G*/sind of bio-asphalt.

modulus and complex modulus were consistent. This indicates that the viscous of bio-asphalt with 15% bio-oil was weaker than any other asphalt. (3) After RTFO, the loss modulus and complex modulus increased with the increase of bio-oil content at the same frequency, which indicates that the addition of bio-oil could increase the anti-deformation ability of asphalt after RTFO.

4.3.2. Master curve generation The master curve was used to describe the rheological properties of bio-binder in this study. The master curve of G⁄/sind was generated by the applying of the time–temperature superposition principle. Different loading times and frequencies can be shifted to each other to obtain a single master curve. The required shift at a given temperature was defined by the shift factor a(T) and a constant was multiplied to get a reduced frequency n for the master curve, as shown in Eq. (1)

n ¼ faðTÞor logðnÞ ¼ logðf Þ þ logðaðTÞÞ

ð1Þ

Master curve can be constructed and any temperature can be selected as the reference temperature T0 to which all data are shifted [22–24]. At the reference temperature, the shift factor was defined as that a(T0) = 1 or log[a(T0)] = 0. A 64 °C reference

temperature was selected to generate the master curve for biobinders. A sigmoidal function was adopted to fit the dynamic shear test data of bio-binder, as shown in Eq. (2) [25].

logðG = sin dÞ ¼ d þ

a

1 þ ebþc logðnÞ

ð2Þ

where d is the minimum modulus value, n is the reduced frequency at reference temperature, a is the span of G⁄/sind values, and b, c are the shape parameters. The master curve was generated by nonlinear least squares fitting according to the time–temperature superposition principle [26]. The master curves of G⁄/sind of unaged and RTFO-aged binders with different bio-oil concentrations were shown in Fig. 11. From the constructed master curves in Fig. 11(a), the following observations could be obtained. (1) The bio-asphalt with different bio-oil content has similar tendency to the asphalt S100 with 1% SBS modifier and 50# asphalt from the low frequency to the high frequency, and the rutting factor increases with the increase in frequency. (2) In the lower frequency range, the rutting factor of bioasphalt S110 and S120 is higher than that of 50# and S100, while bio-asphalt S105 and S115 are smaller; this indicates that the bioasphalt S110 has better rutting resistance. (3) In the higher frequency range, the rutting factor of S110 and S120 of bio-asphalt is

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more consistent with that of 50# and S100, which indicates that it is roughly equivalent to the low-temperature anti-cracking performance of matrix asphalt; and rutting factors of S105 and S115 are smaller, which have a good low temperature cracking performance. It can be seen from Fig. 11(b), (1) Rutting factor of bio-asphalt and 50#, S100 from low to high frequency range has a similar trend, the rutting factor increases with the increase in frequency, which is consistent with the changes before RTFO. (2) In the lower frequency range, bio-asphalt rutting factor of 50# and S100 are large; this shows that after RTFO, bio-asphalt has a better resistance to rutting deformation. (3) In the higher frequency range, the rutting factor of bio-asphalt S110 is larger than 50# and S100, which indicates that the performance of bio-asphalt has been affected to a certain extent after aging but has only little effect on it. 5. Conclusions In this paper, to evaluate the rheological performance of bioasphalt, the G⁄ and d were tested by the dynamic shear rheometer at different bio-oil contents, testing temperatures and aging condition. The master curves of G⁄/sind of different bio-asphalt were constructed according to the time–temperature superposition principle. From these test results, the following conclusions were drawn: 1. The addition of bio-oil extracted from sawdust has significantly increased the complex shear modulus of asphalt binder at the same frequency conditions after rolling thin film oven (RTFO), which is desirable for rutting prevention of asphalt mixtures. The rheological properties of bio-binders are more influenced by RTFO aging compared with reference binder. 2. This result indicates that the viscosity of bio-asphalt with 15% bio-oil was weaker than other asphalt after RTFO based on the frequency sweep. After RTFO, the loss modulus and complex modulus increased with the increase in bio-oil content at the same frequency, which indicates that the addition of bio-oil could increase the anti-deformation ability of asphalt after RTFO. 3. It is feasible to characterize the rheological properties of bioasphalt binders by using the master curve of G⁄/sind in a wide range of loading frequency and testing temperature. 4. The master curve of rutting factor of bio-binder shows that the G⁄/sind of bio-asphalt increased with the increase in frequency and it also changes within the low and high frequency range before and after RTFO. After RTFO, with the addition of bio-oil into the SBS modified asphalt (1% SBS), the rutting factor was greatly increased at each loading frequency. However, the degree of enhancement was affected by bio-oil content and aging condition. Acknowledgments The authors appreciate the support from National Natural Science Foundation of China (NSFC) (No. 51378074, 51578075), the Fundamental and Applied Research Project of the Chinese National Transportation Department (2014319812180) and the Special Fund for Basic Scientific Research of Central Colleges, Chang’an University (CHD 310821153503). The authors also gratefully acknowledge the financial support from China Scholarship Council (No. 201706560009).

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Please cite this article in press as: J. Gao et al., Research on properties of bio-asphalt binders based on time and frequency sweep test, Constr. Build. Mater. (2018), https://doi.org/10.1016/j.conbuildmat.2018.01.048