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Development of a novel binder rejuvenator composed by waste cooking oil and crumb tire rubber
Construction and Building Materials 236 (2020) 117621
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Development of a novel binder rejuvenator composed by waste cooking oil and crumb tire rubber Yi Xingyu b, Dong Ruikun a,b, Tang Naipeng a,b,⇑ a b
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, PR China School of Civil Engineering, Chongqing University, Chongqing 400045, PR China
h i g h l i g h t s Optimized preparation time of WRO rejuvenator is 70 min. Enhanced rejuvenation effect with developed WRO rejuvenator was observed. Sulfoxide intensity decreased with developed WRO rejuvenator. Improved aging resistance with WRO rejuvenator was found.
a r t i c l e
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Article history: Received 29 August 2018 Received in revised form 9 November 2019 Accepted 13 November 2019
Keywords: Aged asphalt Crumb tire rubber Waste cooking oil Rejuvenator DTc value Multiple stress creep and recovery (MSCR) Fourier transform infrared spectrometer (FTIR)
a b s t r a c t In order to improve the performance of recycled mixture containing reclaimed asphalt pavement (RAP), it is usually necessary to add the rejuvenators. Waste cooking oil (WCO) has been used to rejuvenate recycled binder materials, and some studies have proposed adding virgin polymers to improve fatigue performance of recycled mixture. The output of crumb tire rubber (CTR) is large and the price of it is cheap. However, the compatibility between CTR and the aged binder is poor. In this paper, the CTR was mixed with WCO for pre-desulfurization to prepare the waste rubber/oil (WRO) rejuvenator. The high and low temperature rheological properties before or after aging of the rejuvenated binders were tested by dynamic shear rheometer (DSR) and bending beam rheometer (BBR), and the functional groups of rejuvenated binders was detected by fourier transform infrared spectrometer (FTIR). Multiple stress creep and recovery (MSCR) test was conducted to measure rutting resistance. A WCO-based rejuvenator and an aromatic oil were chosen as control groups. It was found that WRO had the potential to be used as an asphalt rejuvenator. The 70 min reaction time of the WRO rejuvenator was determined by viscosity curve and infrared spectrograms. WRO rejuvenator significantly improved the low temperature properties of aged binder, and partially retaining the high temperature properties of aged binder. With 10% WRO rejuvenator, the performance grade of the artificial aged binder was recovered from 82–16 to 70–28. After aging, the high and low temperature continuous grading of the WRO rejuvenated binder did not change much. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction After long-term service of the asphalt pavement, the asphalt material undergoes severe ageing under the combined action of ultraviolet rays, heat, oxygen and water. The ageing hardening of asphalt materials leads to pavement distress such as cracking on the road surface. When the pavement distress develops to a certain extent, the original road surface needs to be overhauled, and a large amount of reclaimed asphalt pavement (RAP) is produced. ⇑ Corresponding author at: Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, PR China. E-mail address: [email protected] (N. Tang). https://doi.org/10.1016/j.conbuildmat.2019.117621 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
According to a survey conducted by the Ministry of Transport in 2012, China produces more than 160 million tons of RAP annually. Under this circumstance, a large amount of research has been carried out on the recycling of waste asphalt pavement mixtures. In the US, the average dosage of RAP for recycled mixture was 20.5% in 2016 [1]. In Japan, the average dosage of RAP in asphalt pavement was 47% in 2014. The mixture manufacturer in Japan first dries RAP, then mixes it with the rejuvenator for several hours, and finally mixes it with the new aggregates and virgin binder [2]. After years of development, China’s road industry has formed a variety of recycling technology, but the recycling efficiency of RAP is still low. According to the ‘‘Technical Specification for Road Asphalt Pavement Recycling” issued by the Ministry of Transport in
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2008, rejuvenator may not be used when the RAP dosage does not exceed 20% of the recycled mixture. A wide variety of rejuvenators were used to improve the performance of recycled binder. The aromatic extracts were used as rejuvenator with the characteristics of small molecular mass, low viscosity and good permeability [3]. However, these rejuvenators contain high aromatic fraction, which is volatile and leads to poor ageing resistance of recycled blends [4]. Ali et al. [5] compared the rejuvenation effect of an aromatic extracts, a naphthenic oil, a paraffinic oil, a tall oil, and an oleic acid produced from vegetable oils. It was mentioned that aromatic extracts have less recovery on low temperature performance of RAP binders. Zaumanis et al. [6] examined the rejuvenation effect of nine rejuvenators, including plant oils, waste derived oils, engineered products, as well as traditional and non-traditional refinery base oils. It was noted that the refined tallow is the most effective rejuvenator to reduce the viscosity of aged binder and the binder rejuvenated by using waste engine oil bottoms showed a considerably higher viscosity value. Since many countries produced large amounts of waste cooking oil (WCO) each year [7], the handling of WCO was particularly important. The use of WCO as an asphalt rejuvenator was an interesting attempt, and many studies shown that WCO has good rejuvenation effect [8–11]. However, the acid value and viscosity of WCO has significantly influence on the rejuvenation effect [12], therefore the quality control of WCO is an important problem [13]. In addition, the binders rejuvenated by WCO showed the high moisture susceptibility due to poor adhesion [14]. The rubber-modified asphalt has good adhesion property [15]. The use of crumb tire rubber (CTR) in asphalt mixtures containing RAP can achieve effective elastic improvement and good economy [16–19]. However, for rubberised asphalt mixtures containing RAP, the addition of crumb rubber has a slightly negative effect in the moisture susceptibility [20]. In addition, rubber macromolecules have poor compatibility with binders [21]. Differences in molecule size, polarity and solubility for rubber and asphalt cause incompatibility and sedimentation of rubber particles [22]. Billiter et al. [23] found that asphalt with a high aromatic content can dissolve more crumb rubber. Aged asphalt has fewer aromatic components compared with neat asphalt [24]. As a result, the compatibility between rubber and aged asphalt is worse. Therefore, when adding the CTR to aged binder, it is necessary to improve the compatibility. Ding et al. [25] mixed the CTR with aromatic extract oil and desulfurized the CTR by microwave treatment. Then an antiager was added to the mixture to prepare rejuvenator. Under the action of additives and microwaves, the macromolecular network structure of the CTR was destroyed, and the small molecule polymer produced by the desulfurization and pyrolysis of CTR were mixed with additives and oil to form a rejuvenator solution. Since the aromatic extract oil is volatile, an antiager was added during the preparation of the rejuvenator, which increases the cost of the rejuvenator. In order to solve the problems mentioned previously and improve the performance of mixture containing RAP, this paper aims to develop an oil/rubber two-phase dispersion system formed by CTR and WCO as a rejuvenator. Therefore, the objectives of this study are to: (1) develop asphalt rejuvenator based on crumb tire rubber/waste cooking oil mixtures and investigate the rejuvenation effect; (2) compare the newly developed rejuvenator with commercial available products.
2. Materials and methods 2.1. Materials CTR and WCO were selected to develop asphalt rejuvenator in this study. One PG64-22 base binder was aged through standard
Rolling Thin Film Oven (RTFO) and 40 h Pressure Ageing Vessel (PAV) to obtain artificial aged binder. The temperature selected for the PAV ageing process is 100 °C. The artificial aged binder was chosen rather than extracted RAP binder for that artificial aged binder can provide consistent properties through this study. And the performance grade of artificial aged binder is PG82-16. CTR is 40 mesh radial tire. Table 1 shows the results of component and elemental analysis of CTR. WCO was collected from a WCO processing company by filtering, dehydrating and physically distilling the raw material of the waste oil. Fatty acids were tested by GC– MS. Basic properties and major fatty acid contents of WCO are shown in Table 2. A commercial available waste cooking oil-based (WCO-based) rejuvenator and a commercial available aromatic oil (85.5% aromatic content) were chosen as control groups. The infrared spectrograms of WCO and WCO-based rejuvenator were shown in Fig. 1. The infrared spectrogram of WCO-based rejuvenator was similar to that of WCO except the peak at 1710 cm1, which means they have similar chemical compositions. The peak at 1710 cm1 characterizes the carbon@oxygen (C@O) bond of ketones, and the peak here may be due to the different sources of WCO. 2.2. Preparation of crumb rubber/waste cooking oil blends The pre-study on waste rubber/oil (WRO) has been completed by this research group [26]. The CTR and WCO were accurately weighed by an electronic balance in a ratio of 2:8, and placed for 2 h at ambient temperature after mixing evenly. The mixture was heated with home-made reactor for 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 120 min, 180 min and 240 min respectively, with the temperature rising rate of 8 °C/min and the stirring speed of 250–300 rpm. When the temperature reaches 260 °C, start timing and keep the temperature at 260 °C ± 10 °C. The temperature required for desulfurization and degradation of CTR is usually above 250 °C, but too high temperature will cause Table 1 Component and element composition of crumb tire rubber. Items
Values
Component Operating oil (%) Rubber hydrocarbon (%) Carbon black (%) Mineral filler (%)
6.82 53.24 29.24 10.70
Elemental composition C (%) H (%) N (%) S (%)
80.41 5.75 0.68 2.38
Table 2 Basic properties and major fatty acid contents of waste cooking oil. Property
Values
Physical and chemical Acid value (mg(KOHg1)) Flash point (°C) Density (gcm3)
0.5–1 304 0.90–0.91
Fatty acid composition Tetradecanoic acid (%) 9-Hexadecenoic acid (%) Hexadecanoic acid (%) 9-Octadecenoic acid (%) Ethyl oleate (%)
1.00 0.56 15.56 45.64 36.95
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Fig. 1. Spectroscopic comparison of WCO with commercial available rejuvenator.
excessive evaporation of light components in WCO. Therefore, 260 °C was selected as the processing temperature. The WRO mixtures were stirred to make them heated uniformly and capped to prevent volatilization of light components during heating process, and finally the WRO rejuvenators were obtained. 2.3. Preparation of rejuvenated binders WRO rejuvenator (6% or 10% by the weight of the artificial aged binder) was mixed slowly with artificial aged binder. One commercial aromatic oil and one commercial WCO-based rejuvenator were mixed with artificial aged binder at a dosage of 10%. All blends were heated for 1 h with the stirring speed of 300–350 rpm at a temperature of 175 °C ± 5 °C. 2.4. Rheological tests Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were used to evaluate the rheological properties of rejuvenated binders at both high and low temperature according to AASHTO T315 and AASHTO T313. RTFO-ageing was implemented at 163 °C for 85 min according to AASHTO T240. PAVageing was implemented according to AASHTO R28. Continuous grades of all tested samples were determined based on AASHTO M320. The Multiple Stress Creep and Recovery (MSCR) test were conducted to evaluate the high temperature properties and elastic response of asphalt binders according to AASHTO TP-70. Brookfield viscometer rotation method can be used to determine the ratio of shear stress and shear rate of non-Newtonian fluid, i.e. apparent viscosity [27]. The viscosity test of the WRO and WCO was done using Brookfield viscometer according to ASTM D4402. 21# rotor models, 50 rpm rotating speed and 25 °C test temperature was adopted in this test due to the low viscosity of WRO and WCO at ambient temperature. The temperature of specimen and rotor in the tube was maintained at 25 °C for more than 1.5 h. WRO samples with a reaction time of 0 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 120 min, 180 min and 240 min were tested. WCO samples with a heat time of 0 min, 30 min, 60 min, 90 min, 120 min, 180 min and 240 min were tested. All WCO samples and WRO samples have the same reaction temperature. 2.5. FTIR test Fourier transform infrared spectrometer (FTIR) can be used to analyze the functional groups of CTR [28]. This study used FTIR to analyze WRO samples with, by Nicolet iS5 Fourier transform
infrared spectrometer. And infrared analysis of rejuvenated binder and artificial aged binder was also carried out. The WRO and WCO sample was analyzed by transmission mode, and the binder sample was analyzed by attenuated total reflectance (ATR) mode. The thickness of the sample affects the absorbance, so in order to facilitate the comparison, the peak with less variation among the samples was taken as a reference. The sulfoxide, carbonyl and butadiene index were calculated by the following equations:
IC¼O ¼ A1700 =An
ð1Þ
IS¼O ¼ A1030 =An
ð2Þ
IPB ¼ A965 =An
ð3Þ
where IC¼O is carbonyl index, IS¼O is sulfoxide index, IPB is butadiene index, A1700 is carbonyl peak area, A1030 is sulfoxide peak area, A965 is butadiene peak area, and An is the peak area used as a reference. 3. Development of rejuvenator 3.1. Viscosity test of WCO and WRO samples WRO samples at different reaction times and original WCO samples at different heating times were tested by a Brookfield viscometer at 25 °C. The results are shown in Fig. 2. At high temperature, the CTR has a certain degree of swelling. This may result in an obvious viscosification effect of the WRO sample with 30 min reaction compared with the WRO sample at ambient temperature (0 min reaction). After 30 min of reaction, with the desulfurization and pyrolysis of the CTR in WRO, the viscosity of WRO samples decreased rapidly and reached the lowest point at 70 min. After 70 min of reaction, the viscosity of WRO sample increased significantly, and the slope of WCO curve was similar to that of WRO. This indicated that the increase of WRO viscosity after 70 min was mainly caused by the viscosification of WCO in WRO. 3.2. FTIR analysis of WRO samples This test was carried out by transmission mode. After the desulfurization of CTR in WCO, the components released in the oil phase were captured by the spectrometer. The peak at 965 cm1 characterizes the functional group of butadiene produced after the desulfurization of CTR. The peak at 721 cm1 was chosen as reference. And the butadiene index, shown in Fig. 3, was calculated by Eq. (3). During the four hours of the reaction, the rubber powder was continuously desulfurized and pyrolyzed to release the polymer, which increased the butadiene index. And a platform region was
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facial blending zone develops between RAP and virgin asphalt binder [29]. Part of the binder covering the surface of RAP aggregates will undergo re-ageing. After the re-ageing, the PG of artificial aged binder was 82–16, and the ageing was more serious. For aromatic oil rejuvenated binder, high temperature PG decreased by 6 °C, whereas low temperature PG has not changed. This indicated that the rejuvenation effect of aromatic oil was not obvious under the dosage of 10%. At the same dosage, WRO rejuvenator and WCObased rejuvenator both reduced the high temperature and low temperature PG of artificial aged binder by two grades, which had better rejuvenation effect. With the increase of WRO rejuvenator content, the high and low temperature PG of WRO rejuvenated binder had a significant drop. Fig. 2. Viscosity curve of the WRO and WCO at 25 °C.
Fig. 3. Butadiene index of WROs at different reaction time.
formed at 1–1.5 h. It can be concluded that the CTR has been in the state of desulfurization and pyrolysis for 4 h. Retaining part of the rubber particles can provide elasticity to the rejuvenated binder, which makes the rejuvenated binder have better pavement performance. Therefore, based on the viscosity test results, 70 min was taken as the reaction time of the WRO rejuvenator.
4.2. High temperature properties 4.2.1. Phase angle The phase angle can characterize the viscoelastic ratio of binders. Binder materials with lower phase angle have more elasticity and deformation recovery capability. Fig. 4 shows the phase angle of unaged rejuvenated binder (10% rejuvenator by weight of artificial aged binder) and artificial aged binder. The phase angle was greatly improved owing to the supplement of viscous components. All other curves can be approximated as the translation of the artificial aged binder curve. The improvement in the phase angle of artificial aged binder with the addition of the WRO rejuvenator was the smallest amongthe three rejuvenators. This can be explained by the fact that the effective oil content of WRO rejuvenator was 8% by the weight of artificial aged binder. Moreover, the rubber components in WRO rejuvenator improved the elastic property to some extent. Fig. 5 shows the phase angle change of artificial aged binder and rejuvenated binders (10% rejuvenator by weight of artificial aged binder) at 70 °C after RTFO-ageing. The high PG of WRO rejuvenated binder and WCO-based rejuvenated binder is 70. The high PG of other two binders is greater than 70. In order to better compare the performance of binders, we chosen 70 °C as test temperature. After RTFO-ageing, the phase angle of artificial aged binder
4. Binders properties characterization 4.1. Performance grade Table 3 shows the results of PG, upper and lower continuous grading temperatures of artificial aged binder and rejuvenated binders (10% rejuvenator by weight of artificial aged binder). Like all the rejuvenated binders, the artificial aged binder also undergone RTFO-ageing and 20 h PAV-ageing to simulate the re-ageing of RAP binder during hot recycling and service. Full blending may not occur during the rejuvenation process in the field, and an inter-
Fig. 4. Phase angle of unaged artificial aged binder and rejuvenated binders.
Table 3 Properties of artificial aged binder and rejuvenated binders. Binders
Unaged (high temp.) RTFO (high temp.) Unaged (low temp.) PAV (low temp.) Performance grade (PG) Penetration (25 °C) Softening point
Units
°C °C °C °C – 0.1 mm °C
Artificial aged binder
86.3 85.7 24.4 16.7 82–16 20.1 67.5
Rejuvenated binders 6% WRO rejuvenator
10% WRO rejuvenator
10% WCO-based rejuvenator
10% Aromatic oil
79.4 77.9 33.7 26.4 76–22 39.9 61.4
74.0 70.8 37.8 33.7 70–28 63.0 54.8
72.3 71.6 36.2 30.3 70–28 61.9 53.4
80.7 80.2 27.1 20.6 76–16 29.9 61.6
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the modulus of the WRO rejuvenated binder was slightly less than that of the WCO-based rejuvenated binder after RTFO-ageing.
Fig. 5. Phase angle change of artificial aged binder and rejuvenated binders at 70 °C after RTFO-ageing.
decreased the most, and ageing degree was the most serious. The addition of aromatic oil slightly improved the ageing properties of artificial aged binder. However, due to its volatility, the ageing resistance of aromatic oil rejuvenated binder was still not good, and the phase angle was seriously decreased after ageing. In all rejuvenated binder, the WRO rejuvenated binder had the lowest phase angle reduction. Compared to WCO-based rejuvenated binder, WRO rejuvenator contained less light oil after preparation at high temperature. Furthermore, the light components absorbed by CTR in WRO rejuvenator were released slowly along with the ageing process, supplementing some of the lost light components. Therefore, the WRO rejuvenated binder has better RTFO-ageing resistance.
4.2.2. Complex shear modulus |G*| Fig. 6 shows the complex shear modulus |G*| value of artificial aged binder and rejuvenated binders (10% rejuvenator by weight of binder) after RTFO-ageing. Smaller |G*| value means worse resistance to deformation of material, larger viscosity and less elasticity. Compared to the artificial aged binder, the |G*| and the temperature susceptibility of all the rejuvenated binder decreased. Aromatic oil had the least change in modulus and temperature susceptibility of artificial aged binder among the three rejuvenators. Vegetable and bio-based oils required less dosages than aromatic oil to reach the same PG [30]. Therefore, when the dosage of aromatic oil is same as WRO rejuvenator or WCO-based rejuvenator, aromatic oil rejuvenated binder will show poorer performance. The most obvious improvement occurred in samples containing WCO-based rejuvenator or WRO rejuvenator. Despite the elastic supplement of the CTR and the relatively low light oil content,
Fig. 6. Complex shear modulus of artificial aged binder and rejuvenated binders after RTFO-ageing.
4.2.3. Multiple stress creep and recovery High percent recovery means good elasticity and large recoverable strain of the binders under stress. Fig. 7(a) shows the percent recovery of rejuvenated binders and artificial aged binder under the stress of 0.1 kPa. The inaccurate measured data has a negative value, due to sample damage at higher temperature. Therefore, this paper used the data of lower temperature for comparison. The percent recovery R0.1 of artificial aged binder was the largest, indicating that the rutting resisitance of artificial aged binder was good, which was mainly caused by ageing. WCO-based rejuvenated binder sample had the smallest R0.1, which indicated that WCO-based rejuvenated binder had greater viscosity and lower rutting resisitance due to the addition of WCO-based rejuvenator. R0.1 of WRO rejuvenated binder was closer to that of aromatic oil rejuvenated binder, and the two rejuvenators retained some of the high temperature properties of artificial aged binder. Fig. 7(b) shows the percent recovery R3.2 of rejuvenated binders and artificial aged binder. Under the stress of 3.2 kPa, more negative value data appeared. This is due to the flowability of the asphalt increased at higher temperatures. And if a larger stress were applied in this case, the sample will be more susceptible to damage, resulting in more inaccurate data. When the test temperature was lower, the results of R3.2 were similar to that of R0.1. However, comparing with the results of R0.1, the R3.2 of the WRO rejuvenated binder was much closer to that of WCO-based rejuvenated binder, which indicated that the addition of CTR has not significantly improve the elasticity under the stress of 3.2 kPa. The main reason for the small increase in elasticity at 3.2 kPa may be due to the fact that the rubber content in the binder is only 2%, and less rubber content leads to less elastic increase.
Fig. 7. Percent recovery of rejuvenated binders and artificial aged binder after RTFO-ageing; (a) under 0.1 kPa stress, (b) under 3.2 kPa stress.
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The non-recoverable creep compliance value Jnr3.2 has been proved by many studies to have a good correlation with the rutting performance of the mixtures [31–34]. Higher non-recoverable creep compliance value of binder means worse rutting performance of the mixture. Fig. 8(a) shows the non-recoverable creep compliance value Jnr0.1 under the stress of 0.1 kPa and Fig. 8(b) shows the Jnr3.2 under the stress of 3.2 kPa. The variation trend of the compliance value curve of all binders in Fig. 8(a) was similar to that in Fig. 8(b). Under 3.2 kPa or 0.1 kPa stress, the nonrecoverable creep compliance value of WCO-based rejuvenated binder and WRO rejuvenated binder reached a relatively close level. Compared to the other two types of rejuvenated binder, aromatic oil rejuvenated binder had better rutting resistance. The curve of WRO rejuvenated binder was quite different from the base binder, which indicated that the addition of WRO rejuvenator partly retained the rutting resistance of artificial aged binder at the content of 10%. D’Angelo et al. [35] proposed to determine high temperature performance grading at a certain temperature according to Jnr3.2. According to AASHTO MP19-10, the high temperature performance grading of asphalt samples is as follows: artificial aged binder is PG64E, WRO rejuvenated binder is PG64H, WCOBased rejuvenated binder is PG64H and aromatic oil rejuvenated binder is PG64E.
4.3. Low temperature properties Fig. 9 shows the change in continuous grading low temperature of artificial aged binder and rejuvenated binders after PAV-ageing. The artificial aged binder had the highest rise in the low temperature grade, indicating further ageing of the asphalt. The addition of aromatic oil has not significantly improved the low temperature grade before or after PAV-ageing. WRO rejuvenated binder had the lowest low temperature grade and the lowest temperature rise
Fig. 8. The non-recoverable creep compliance value of base binder, rejuvenated binders and artificial aged binder after RTFO-ageing; (a) under 0.1 kPa stress, (b) under 3.2 kPa stress.
Fig. 9. Change in low temperature continuous grading of artificial aged binder and rejuvenated binders after PAV-ageing.
after ageing, which indicated that WRO rejuvenated asphalt had excellent low temperature property and ageing resistance. Only 80% of WCO was used in the preparation of WRO rejuvenator, but the continuous grading temperature of WRO rejuvenated binder was lower than that of WCO-based rejuvenated binder. In terms of low temperature continuous grading, the presence of CTR led to better low temperature behavior of WRO rejuvenated binder. For asphalt binder, the difference in the continuous grading low temperature calculated by m-value and S-value, respectively, is DTc value. For aged asphalt, the low temperature grade tends to be controlled by the m value. The more negative DTc value, the more serious the ageing. Therefore, DTc can be used to indicate the aging status of asphalt binder. As such, in this paper, DTc values can be used from two aspects. One is to examine the rejuvenation effect but not to evaluate the low temperature performance. Second is to monitor the aging evolution of rejuvenated binders. In other words, during the RTFO and PAV procedures of rejuvenated binders, if DTc value changed little, the binder is considered to behave better in terms of anti-aging. Fig. 10 shows the change in DTc value of artificial aged binder and rejuvenated binders after PAV-ageing. The DTc value of aromatic oil rejuvenated binder and WCO-based rejuvenated binder was largest. But the DTc value of aromatic oil rejuvenated binder droped rapidly after the PAVageing. Although the DTc value of WCO-based rejuvenated bidner decreased after PAV-ageing, it was still the largest among all samples. DTc value of WRO rejuvenated binder was smaller than the other two types of asphalt, and after ageing, it was still smaller than WCO-based rejuvenated binder. This indicated that, in terms of DTc value, the rejuvenation effect of WCO-based rejuvenator was more stable, and the WRO rejuvenator needed further improvement.
Fig. 10. DTc change of artificial aged binder and rejuvenated binders after PAVageing.
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Fig. 11. Spectroscopic comparison of unaged artificial aged binder and rejuvenated binders.
4.4. FTIR analysis of rejuvenated binders
5. Conclusions
The infrared spectrograms for unaged rejuvenated binders (10% rejuvenator by weight of binder) and artificial aged binder at the wavenumbers between 4000 cm1 and 500 cm1 are shown in Fig. 11. New absorption peaks appeared in WCO-based rejuvenated binder and WRO-rejuvenated binder sample at 1744 cm1 and 1166 cm1 belong to ester carbonyl functional group and C–O stretching, respectively [11,12]. The new absorption peak is the characteristic peak of WCO. The increase in sulfoxide and carbonyl is related to the ageing of the asphalt [36–38]. The WCO also contains a carbonyl group [39], mixing with the artificial aged binder results in an inaccurate measurement of the carbonyl index. Therefore, the sulfoxide index, shown in Fig. 12, was used to observe the ageing of the binders. It can be seen from Fig. 12 that the sulfoxide index of aromatic oil rejuvenated binder had the smallest difference from artificial RAP asphalt, which indicated that the rejuvenation effect of aromatic oil was not as good as WCO-based and WRO at the dosage of 10%. The sulfoxide index of WCO-based rejuvenated binder was the lowest, which was close to that of WRO rejuvenated binder. The polymer produced by the desulfurization of CTR contains sulfur–oxygen functional groups [40], the sulfoxide index of WRO rejuvenated binder was slightly higher than that of WCO-based rejuvenated binder. At the same dosage, the aromatic oil rejuvenated binder had a large difference in sulfoxide index compared to WCO-based rejuvenated binder and WRO rejuvenated binder.
In this paper, the CTR was mixed with WCO for predesulfurization to prepare the WRO rejuvenator. The reaction time of the WRO rejuvenator was determined by viscosity curve and infrared spectrograms. The high and low temperature rheological properties before or after aging of the rejuvenated binders were tested by DSR and BBR, and the change of functional groups of rejuvenated binders was tested by FTIR. The MSCR test was conducted to measure rutting resistance. WRO has the potential to be used as an asphalt rejuvenator. CTR reacted and released polymer during the reaction time. In order to retain a portion of the rubber particles to provide elasticity, the recommended process is a reaction at 260 °C for 70 min based on the viscosity results. The newly developed WRO rejuvenator significantly improved the low temperature properties of aged binder in terms of low temperature continuous grading. However, for the DTc value, the WCO-based rejuvenator has better rejuvenation effect. The high temperature properties of aged binder partially retained with the addition of WRO. The viscous behavior of the aged binder increased. The elasticity supplement was not obvious under the stress of 3.2 kPa during the MSCR test. This may be due to the small dosage of rubber. The developed WRO rejuvenator and the commercial available WCO-based rejuvenator show similar rejuvenation effect with respect to high and low temperature properties. Meanwhile, WRO rejuvenated binder offers better aging resistance than that rejuvenated with the commercial available WCO-based rejuvenator. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements
Fig. 12. Sulfoxide index of unaged rejuvenated binders and artificial aged binder.
This work was financially supported by National Natural Science Foundation of China (No. 51578097), China Postdoctoral Science Foundation (Grant Number: 2018M633319) and the Fundamental Research Funds for the Central Universities (Project Number: 2018CDXYTM0003).
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Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.conbuildmat.2019.117621.
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[19] M. Fakhri, E. Amoosoltani, The effect of reclaimed asphalt pavement and crumb rubber on mechanical properties of roller compacted concrete pavement, Constr. Build. Mater. 137 (2017) 470–484. [20] F. Xiao, S.N. Amirkhanian, Laboratory investigation of moisture damage in rubberised asphalt mixtures containing reclaimed asphalt pavement, Int. J. Pavement Eng. 10 (5) (2009) 319–328. [21] R. Dong, M. Zhao, N. Tang, Characterization of crumb tire rubber lightly pyrolyzed in waste cooking oil and the properties of its modified bitumen, Constr. Build. Mater. 195 (2019) 10–18. [22] M. García-Morales, P. Partal, F.J. Navarro, F.J. Martínez-Boza, C. Gallegos, Processing, rheology, and storage stability of recycled EVA/LDPE modified bitumen, Polym. Eng. Sci. 47 (2) (2007) 181–191. [23] T.C. Billiter, R.R. Davison, C.J. Glover, J.A. Bullin, Physical properties of asphaltrubber binder, Petrol Sci. Technol. 15 (3–4) (1997) 205–236. [24] R. Tauste, F. Moreno-Navarro, M. Sol-Sánchez, M.C. Rubio-Gámez, Understanding the bitumen ageing phenomenon: a review, Constr. Build. Mater. 192 (2018) 593–609. [25] Z. Ding, C. Shen, J. Jiang, S.Y. He, Research on comprehensive utilization of waste rubber and aged asphalt, Appl. Mech. Mater. 34–35 (2010) 1526–1531. [26] R. Dong, M. Zhao, Research on the pyrolysis process of crumb tire rubber in waste cooking oil, Renew. Energ. 125 (2018) 557–567. [27] A. Jamshidi, B. Golchin, M.O. Hamzah, P. Turner, Selection of type of warm mix asphalt additive based on the rheological properties of asphalt binders, J. Clean. Prod. 100 (2015) 89–106. [28] L. He, Y. Ma, Q. Liu, Y. Mu, Surface modification of crumb rubber and its influence on the mechanical properties of rubber-cement concrete, Constr. Build. Mater. 120 (2016) 403–407. [29] M.D. Nazzal, S.S. Kim, A. Abbas, L.A. Qtaish, E. Holcombe, Y.A. Hassan, Fundamental evaluation of the interaction between RAS/RAP and virgin asphalt binders, No. FHWA/OH-2017-24, Ohio Department of Transportation, Office of Statewide Planning & Research, 2017. [30] E. Arámbula-Mercado, A. Epps Martin, F. Kaseer, F. Yin, Development of a dosage selection methods for recycling agents used in asphalt mixtures with high recycled binder ratios, in: TRB 96th Annual Meeting, No.17-00720, 2017. [31] J. D’Angelo, The relationship of the MSCR test to rutting, Road Mater. Pavement Des. 10 (2009) 61–80. [32] E. DuBois, D.Y. Mehta, A. Nolan, Correlation between multiple stress creep recovery (MSCR) results and polymer modification of binder, Constr. Build. Mater. 65 (2014) 184–190. [33] J. Zhang, L.F. Walubita, A.N.M. Faruk, P. Karki, G.S. Simate, Use of the MSCR test to characterize the asphalt binder properties relative to HMA rutting performance – a laboratory study, Constr. Build. Mater. 94 (2015) 218–227. [34] N. Tang, W. Huang, M. Zheng, J. Hu, Investigation of Gilsonite-, polyphosphoric acid- and styrene–butadiene–styrene-modified asphalt binder using the multiple stress creep and recovery test, Road Mater. Pavement Des. (2017). [35] J. D’Angelo, R. Kluttz, R.N. Dongre, K. Stephens, L. Zanzotto, Revision of the superpave high temperature binder specification: the multiple stress creep recovery test, in: Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions 76, 2017, pp. 123–162. [36] P.R. Herrington, J.E. Patrick, G.F.A. Ball, Oxidation of roading asphalts, Ind. Eng. Chem. Res. 33 (2002) 2801–2809. [37] J.C. Petersen, R. Glaser, Asphalt oxidation mechanisms and the role of oxidation products on age hardening revisited, Road Mater. Pavement Des. 12 (2011) 795–819. [38] W. Zeng, S. Wu, J. Wen, Z. Chen, The temperature effects in aging index of asphalt during UV aging process, Constr. Build. Mater. 93 (2015) 1125–1131. [39] R. Zhang, Z. You, H. Wang, M. Ye, Y.K. Yap, C. Si, The impact of bio-oil as rejuvenator for aged asphalt binder, Constr. Build. Mater. 196 (2019) 134–143. [40] N. Tang, W. Huang, F. Xiao, Chemical and rheological investigation of highcured crumb rubber-modified asphalt, Constr. Build. Mater. 123 (2016) 847– 854.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Development of a novel binder rejuvenator composed by waste cooking oil and crumb tire rubber Yi Xingyu b, Dong Ruikun a,b, Tang Naipeng a,b,⇑ a b
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, PR China School of Civil Engineering, Chongqing University, Chongqing 400045, PR China
h i g h l i g h t s Optimized preparation time of WRO rejuvenator is 70 min. Enhanced rejuvenation effect with developed WRO rejuvenator was observed. Sulfoxide intensity decreased with developed WRO rejuvenator. Improved aging resistance with WRO rejuvenator was found.
a r t i c l e
i n f o
Article history: Received 29 August 2018 Received in revised form 9 November 2019 Accepted 13 November 2019
Keywords: Aged asphalt Crumb tire rubber Waste cooking oil Rejuvenator DTc value Multiple stress creep and recovery (MSCR) Fourier transform infrared spectrometer (FTIR)
a b s t r a c t In order to improve the performance of recycled mixture containing reclaimed asphalt pavement (RAP), it is usually necessary to add the rejuvenators. Waste cooking oil (WCO) has been used to rejuvenate recycled binder materials, and some studies have proposed adding virgin polymers to improve fatigue performance of recycled mixture. The output of crumb tire rubber (CTR) is large and the price of it is cheap. However, the compatibility between CTR and the aged binder is poor. In this paper, the CTR was mixed with WCO for pre-desulfurization to prepare the waste rubber/oil (WRO) rejuvenator. The high and low temperature rheological properties before or after aging of the rejuvenated binders were tested by dynamic shear rheometer (DSR) and bending beam rheometer (BBR), and the functional groups of rejuvenated binders was detected by fourier transform infrared spectrometer (FTIR). Multiple stress creep and recovery (MSCR) test was conducted to measure rutting resistance. A WCO-based rejuvenator and an aromatic oil were chosen as control groups. It was found that WRO had the potential to be used as an asphalt rejuvenator. The 70 min reaction time of the WRO rejuvenator was determined by viscosity curve and infrared spectrograms. WRO rejuvenator significantly improved the low temperature properties of aged binder, and partially retaining the high temperature properties of aged binder. With 10% WRO rejuvenator, the performance grade of the artificial aged binder was recovered from 82–16 to 70–28. After aging, the high and low temperature continuous grading of the WRO rejuvenated binder did not change much. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction After long-term service of the asphalt pavement, the asphalt material undergoes severe ageing under the combined action of ultraviolet rays, heat, oxygen and water. The ageing hardening of asphalt materials leads to pavement distress such as cracking on the road surface. When the pavement distress develops to a certain extent, the original road surface needs to be overhauled, and a large amount of reclaimed asphalt pavement (RAP) is produced. ⇑ Corresponding author at: Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing 400045, PR China. E-mail address: [email protected] (N. Tang). https://doi.org/10.1016/j.conbuildmat.2019.117621 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
According to a survey conducted by the Ministry of Transport in 2012, China produces more than 160 million tons of RAP annually. Under this circumstance, a large amount of research has been carried out on the recycling of waste asphalt pavement mixtures. In the US, the average dosage of RAP for recycled mixture was 20.5% in 2016 [1]. In Japan, the average dosage of RAP in asphalt pavement was 47% in 2014. The mixture manufacturer in Japan first dries RAP, then mixes it with the rejuvenator for several hours, and finally mixes it with the new aggregates and virgin binder [2]. After years of development, China’s road industry has formed a variety of recycling technology, but the recycling efficiency of RAP is still low. According to the ‘‘Technical Specification for Road Asphalt Pavement Recycling” issued by the Ministry of Transport in
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2008, rejuvenator may not be used when the RAP dosage does not exceed 20% of the recycled mixture. A wide variety of rejuvenators were used to improve the performance of recycled binder. The aromatic extracts were used as rejuvenator with the characteristics of small molecular mass, low viscosity and good permeability [3]. However, these rejuvenators contain high aromatic fraction, which is volatile and leads to poor ageing resistance of recycled blends [4]. Ali et al. [5] compared the rejuvenation effect of an aromatic extracts, a naphthenic oil, a paraffinic oil, a tall oil, and an oleic acid produced from vegetable oils. It was mentioned that aromatic extracts have less recovery on low temperature performance of RAP binders. Zaumanis et al. [6] examined the rejuvenation effect of nine rejuvenators, including plant oils, waste derived oils, engineered products, as well as traditional and non-traditional refinery base oils. It was noted that the refined tallow is the most effective rejuvenator to reduce the viscosity of aged binder and the binder rejuvenated by using waste engine oil bottoms showed a considerably higher viscosity value. Since many countries produced large amounts of waste cooking oil (WCO) each year [7], the handling of WCO was particularly important. The use of WCO as an asphalt rejuvenator was an interesting attempt, and many studies shown that WCO has good rejuvenation effect [8–11]. However, the acid value and viscosity of WCO has significantly influence on the rejuvenation effect [12], therefore the quality control of WCO is an important problem [13]. In addition, the binders rejuvenated by WCO showed the high moisture susceptibility due to poor adhesion [14]. The rubber-modified asphalt has good adhesion property [15]. The use of crumb tire rubber (CTR) in asphalt mixtures containing RAP can achieve effective elastic improvement and good economy [16–19]. However, for rubberised asphalt mixtures containing RAP, the addition of crumb rubber has a slightly negative effect in the moisture susceptibility [20]. In addition, rubber macromolecules have poor compatibility with binders [21]. Differences in molecule size, polarity and solubility for rubber and asphalt cause incompatibility and sedimentation of rubber particles [22]. Billiter et al. [23] found that asphalt with a high aromatic content can dissolve more crumb rubber. Aged asphalt has fewer aromatic components compared with neat asphalt [24]. As a result, the compatibility between rubber and aged asphalt is worse. Therefore, when adding the CTR to aged binder, it is necessary to improve the compatibility. Ding et al. [25] mixed the CTR with aromatic extract oil and desulfurized the CTR by microwave treatment. Then an antiager was added to the mixture to prepare rejuvenator. Under the action of additives and microwaves, the macromolecular network structure of the CTR was destroyed, and the small molecule polymer produced by the desulfurization and pyrolysis of CTR were mixed with additives and oil to form a rejuvenator solution. Since the aromatic extract oil is volatile, an antiager was added during the preparation of the rejuvenator, which increases the cost of the rejuvenator. In order to solve the problems mentioned previously and improve the performance of mixture containing RAP, this paper aims to develop an oil/rubber two-phase dispersion system formed by CTR and WCO as a rejuvenator. Therefore, the objectives of this study are to: (1) develop asphalt rejuvenator based on crumb tire rubber/waste cooking oil mixtures and investigate the rejuvenation effect; (2) compare the newly developed rejuvenator with commercial available products.
2. Materials and methods 2.1. Materials CTR and WCO were selected to develop asphalt rejuvenator in this study. One PG64-22 base binder was aged through standard
Rolling Thin Film Oven (RTFO) and 40 h Pressure Ageing Vessel (PAV) to obtain artificial aged binder. The temperature selected for the PAV ageing process is 100 °C. The artificial aged binder was chosen rather than extracted RAP binder for that artificial aged binder can provide consistent properties through this study. And the performance grade of artificial aged binder is PG82-16. CTR is 40 mesh radial tire. Table 1 shows the results of component and elemental analysis of CTR. WCO was collected from a WCO processing company by filtering, dehydrating and physically distilling the raw material of the waste oil. Fatty acids were tested by GC– MS. Basic properties and major fatty acid contents of WCO are shown in Table 2. A commercial available waste cooking oil-based (WCO-based) rejuvenator and a commercial available aromatic oil (85.5% aromatic content) were chosen as control groups. The infrared spectrograms of WCO and WCO-based rejuvenator were shown in Fig. 1. The infrared spectrogram of WCO-based rejuvenator was similar to that of WCO except the peak at 1710 cm1, which means they have similar chemical compositions. The peak at 1710 cm1 characterizes the carbon@oxygen (C@O) bond of ketones, and the peak here may be due to the different sources of WCO. 2.2. Preparation of crumb rubber/waste cooking oil blends The pre-study on waste rubber/oil (WRO) has been completed by this research group [26]. The CTR and WCO were accurately weighed by an electronic balance in a ratio of 2:8, and placed for 2 h at ambient temperature after mixing evenly. The mixture was heated with home-made reactor for 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 120 min, 180 min and 240 min respectively, with the temperature rising rate of 8 °C/min and the stirring speed of 250–300 rpm. When the temperature reaches 260 °C, start timing and keep the temperature at 260 °C ± 10 °C. The temperature required for desulfurization and degradation of CTR is usually above 250 °C, but too high temperature will cause Table 1 Component and element composition of crumb tire rubber. Items
Values
Component Operating oil (%) Rubber hydrocarbon (%) Carbon black (%) Mineral filler (%)
6.82 53.24 29.24 10.70
Elemental composition C (%) H (%) N (%) S (%)
80.41 5.75 0.68 2.38
Table 2 Basic properties and major fatty acid contents of waste cooking oil. Property
Values
Physical and chemical Acid value (mg(KOHg1)) Flash point (°C) Density (gcm3)
0.5–1 304 0.90–0.91
Fatty acid composition Tetradecanoic acid (%) 9-Hexadecenoic acid (%) Hexadecanoic acid (%) 9-Octadecenoic acid (%) Ethyl oleate (%)
1.00 0.56 15.56 45.64 36.95
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Fig. 1. Spectroscopic comparison of WCO with commercial available rejuvenator.
excessive evaporation of light components in WCO. Therefore, 260 °C was selected as the processing temperature. The WRO mixtures were stirred to make them heated uniformly and capped to prevent volatilization of light components during heating process, and finally the WRO rejuvenators were obtained. 2.3. Preparation of rejuvenated binders WRO rejuvenator (6% or 10% by the weight of the artificial aged binder) was mixed slowly with artificial aged binder. One commercial aromatic oil and one commercial WCO-based rejuvenator were mixed with artificial aged binder at a dosage of 10%. All blends were heated for 1 h with the stirring speed of 300–350 rpm at a temperature of 175 °C ± 5 °C. 2.4. Rheological tests Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were used to evaluate the rheological properties of rejuvenated binders at both high and low temperature according to AASHTO T315 and AASHTO T313. RTFO-ageing was implemented at 163 °C for 85 min according to AASHTO T240. PAVageing was implemented according to AASHTO R28. Continuous grades of all tested samples were determined based on AASHTO M320. The Multiple Stress Creep and Recovery (MSCR) test were conducted to evaluate the high temperature properties and elastic response of asphalt binders according to AASHTO TP-70. Brookfield viscometer rotation method can be used to determine the ratio of shear stress and shear rate of non-Newtonian fluid, i.e. apparent viscosity [27]. The viscosity test of the WRO and WCO was done using Brookfield viscometer according to ASTM D4402. 21# rotor models, 50 rpm rotating speed and 25 °C test temperature was adopted in this test due to the low viscosity of WRO and WCO at ambient temperature. The temperature of specimen and rotor in the tube was maintained at 25 °C for more than 1.5 h. WRO samples with a reaction time of 0 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 120 min, 180 min and 240 min were tested. WCO samples with a heat time of 0 min, 30 min, 60 min, 90 min, 120 min, 180 min and 240 min were tested. All WCO samples and WRO samples have the same reaction temperature. 2.5. FTIR test Fourier transform infrared spectrometer (FTIR) can be used to analyze the functional groups of CTR [28]. This study used FTIR to analyze WRO samples with, by Nicolet iS5 Fourier transform
infrared spectrometer. And infrared analysis of rejuvenated binder and artificial aged binder was also carried out. The WRO and WCO sample was analyzed by transmission mode, and the binder sample was analyzed by attenuated total reflectance (ATR) mode. The thickness of the sample affects the absorbance, so in order to facilitate the comparison, the peak with less variation among the samples was taken as a reference. The sulfoxide, carbonyl and butadiene index were calculated by the following equations:
IC¼O ¼ A1700 =An
ð1Þ
IS¼O ¼ A1030 =An
ð2Þ
IPB ¼ A965 =An
ð3Þ
where IC¼O is carbonyl index, IS¼O is sulfoxide index, IPB is butadiene index, A1700 is carbonyl peak area, A1030 is sulfoxide peak area, A965 is butadiene peak area, and An is the peak area used as a reference. 3. Development of rejuvenator 3.1. Viscosity test of WCO and WRO samples WRO samples at different reaction times and original WCO samples at different heating times were tested by a Brookfield viscometer at 25 °C. The results are shown in Fig. 2. At high temperature, the CTR has a certain degree of swelling. This may result in an obvious viscosification effect of the WRO sample with 30 min reaction compared with the WRO sample at ambient temperature (0 min reaction). After 30 min of reaction, with the desulfurization and pyrolysis of the CTR in WRO, the viscosity of WRO samples decreased rapidly and reached the lowest point at 70 min. After 70 min of reaction, the viscosity of WRO sample increased significantly, and the slope of WCO curve was similar to that of WRO. This indicated that the increase of WRO viscosity after 70 min was mainly caused by the viscosification of WCO in WRO. 3.2. FTIR analysis of WRO samples This test was carried out by transmission mode. After the desulfurization of CTR in WCO, the components released in the oil phase were captured by the spectrometer. The peak at 965 cm1 characterizes the functional group of butadiene produced after the desulfurization of CTR. The peak at 721 cm1 was chosen as reference. And the butadiene index, shown in Fig. 3, was calculated by Eq. (3). During the four hours of the reaction, the rubber powder was continuously desulfurized and pyrolyzed to release the polymer, which increased the butadiene index. And a platform region was
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facial blending zone develops between RAP and virgin asphalt binder [29]. Part of the binder covering the surface of RAP aggregates will undergo re-ageing. After the re-ageing, the PG of artificial aged binder was 82–16, and the ageing was more serious. For aromatic oil rejuvenated binder, high temperature PG decreased by 6 °C, whereas low temperature PG has not changed. This indicated that the rejuvenation effect of aromatic oil was not obvious under the dosage of 10%. At the same dosage, WRO rejuvenator and WCObased rejuvenator both reduced the high temperature and low temperature PG of artificial aged binder by two grades, which had better rejuvenation effect. With the increase of WRO rejuvenator content, the high and low temperature PG of WRO rejuvenated binder had a significant drop. Fig. 2. Viscosity curve of the WRO and WCO at 25 °C.
Fig. 3. Butadiene index of WROs at different reaction time.
formed at 1–1.5 h. It can be concluded that the CTR has been in the state of desulfurization and pyrolysis for 4 h. Retaining part of the rubber particles can provide elasticity to the rejuvenated binder, which makes the rejuvenated binder have better pavement performance. Therefore, based on the viscosity test results, 70 min was taken as the reaction time of the WRO rejuvenator.
4.2. High temperature properties 4.2.1. Phase angle The phase angle can characterize the viscoelastic ratio of binders. Binder materials with lower phase angle have more elasticity and deformation recovery capability. Fig. 4 shows the phase angle of unaged rejuvenated binder (10% rejuvenator by weight of artificial aged binder) and artificial aged binder. The phase angle was greatly improved owing to the supplement of viscous components. All other curves can be approximated as the translation of the artificial aged binder curve. The improvement in the phase angle of artificial aged binder with the addition of the WRO rejuvenator was the smallest amongthe three rejuvenators. This can be explained by the fact that the effective oil content of WRO rejuvenator was 8% by the weight of artificial aged binder. Moreover, the rubber components in WRO rejuvenator improved the elastic property to some extent. Fig. 5 shows the phase angle change of artificial aged binder and rejuvenated binders (10% rejuvenator by weight of artificial aged binder) at 70 °C after RTFO-ageing. The high PG of WRO rejuvenated binder and WCO-based rejuvenated binder is 70. The high PG of other two binders is greater than 70. In order to better compare the performance of binders, we chosen 70 °C as test temperature. After RTFO-ageing, the phase angle of artificial aged binder
4. Binders properties characterization 4.1. Performance grade Table 3 shows the results of PG, upper and lower continuous grading temperatures of artificial aged binder and rejuvenated binders (10% rejuvenator by weight of artificial aged binder). Like all the rejuvenated binders, the artificial aged binder also undergone RTFO-ageing and 20 h PAV-ageing to simulate the re-ageing of RAP binder during hot recycling and service. Full blending may not occur during the rejuvenation process in the field, and an inter-
Fig. 4. Phase angle of unaged artificial aged binder and rejuvenated binders.
Table 3 Properties of artificial aged binder and rejuvenated binders. Binders
Unaged (high temp.) RTFO (high temp.) Unaged (low temp.) PAV (low temp.) Performance grade (PG) Penetration (25 °C) Softening point
Units
°C °C °C °C – 0.1 mm °C
Artificial aged binder
86.3 85.7 24.4 16.7 82–16 20.1 67.5
Rejuvenated binders 6% WRO rejuvenator
10% WRO rejuvenator
10% WCO-based rejuvenator
10% Aromatic oil
79.4 77.9 33.7 26.4 76–22 39.9 61.4
74.0 70.8 37.8 33.7 70–28 63.0 54.8
72.3 71.6 36.2 30.3 70–28 61.9 53.4
80.7 80.2 27.1 20.6 76–16 29.9 61.6
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the modulus of the WRO rejuvenated binder was slightly less than that of the WCO-based rejuvenated binder after RTFO-ageing.
Fig. 5. Phase angle change of artificial aged binder and rejuvenated binders at 70 °C after RTFO-ageing.
decreased the most, and ageing degree was the most serious. The addition of aromatic oil slightly improved the ageing properties of artificial aged binder. However, due to its volatility, the ageing resistance of aromatic oil rejuvenated binder was still not good, and the phase angle was seriously decreased after ageing. In all rejuvenated binder, the WRO rejuvenated binder had the lowest phase angle reduction. Compared to WCO-based rejuvenated binder, WRO rejuvenator contained less light oil after preparation at high temperature. Furthermore, the light components absorbed by CTR in WRO rejuvenator were released slowly along with the ageing process, supplementing some of the lost light components. Therefore, the WRO rejuvenated binder has better RTFO-ageing resistance.
4.2.2. Complex shear modulus |G*| Fig. 6 shows the complex shear modulus |G*| value of artificial aged binder and rejuvenated binders (10% rejuvenator by weight of binder) after RTFO-ageing. Smaller |G*| value means worse resistance to deformation of material, larger viscosity and less elasticity. Compared to the artificial aged binder, the |G*| and the temperature susceptibility of all the rejuvenated binder decreased. Aromatic oil had the least change in modulus and temperature susceptibility of artificial aged binder among the three rejuvenators. Vegetable and bio-based oils required less dosages than aromatic oil to reach the same PG [30]. Therefore, when the dosage of aromatic oil is same as WRO rejuvenator or WCO-based rejuvenator, aromatic oil rejuvenated binder will show poorer performance. The most obvious improvement occurred in samples containing WCO-based rejuvenator or WRO rejuvenator. Despite the elastic supplement of the CTR and the relatively low light oil content,
Fig. 6. Complex shear modulus of artificial aged binder and rejuvenated binders after RTFO-ageing.
4.2.3. Multiple stress creep and recovery High percent recovery means good elasticity and large recoverable strain of the binders under stress. Fig. 7(a) shows the percent recovery of rejuvenated binders and artificial aged binder under the stress of 0.1 kPa. The inaccurate measured data has a negative value, due to sample damage at higher temperature. Therefore, this paper used the data of lower temperature for comparison. The percent recovery R0.1 of artificial aged binder was the largest, indicating that the rutting resisitance of artificial aged binder was good, which was mainly caused by ageing. WCO-based rejuvenated binder sample had the smallest R0.1, which indicated that WCO-based rejuvenated binder had greater viscosity and lower rutting resisitance due to the addition of WCO-based rejuvenator. R0.1 of WRO rejuvenated binder was closer to that of aromatic oil rejuvenated binder, and the two rejuvenators retained some of the high temperature properties of artificial aged binder. Fig. 7(b) shows the percent recovery R3.2 of rejuvenated binders and artificial aged binder. Under the stress of 3.2 kPa, more negative value data appeared. This is due to the flowability of the asphalt increased at higher temperatures. And if a larger stress were applied in this case, the sample will be more susceptible to damage, resulting in more inaccurate data. When the test temperature was lower, the results of R3.2 were similar to that of R0.1. However, comparing with the results of R0.1, the R3.2 of the WRO rejuvenated binder was much closer to that of WCO-based rejuvenated binder, which indicated that the addition of CTR has not significantly improve the elasticity under the stress of 3.2 kPa. The main reason for the small increase in elasticity at 3.2 kPa may be due to the fact that the rubber content in the binder is only 2%, and less rubber content leads to less elastic increase.
Fig. 7. Percent recovery of rejuvenated binders and artificial aged binder after RTFO-ageing; (a) under 0.1 kPa stress, (b) under 3.2 kPa stress.
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The non-recoverable creep compliance value Jnr3.2 has been proved by many studies to have a good correlation with the rutting performance of the mixtures [31–34]. Higher non-recoverable creep compliance value of binder means worse rutting performance of the mixture. Fig. 8(a) shows the non-recoverable creep compliance value Jnr0.1 under the stress of 0.1 kPa and Fig. 8(b) shows the Jnr3.2 under the stress of 3.2 kPa. The variation trend of the compliance value curve of all binders in Fig. 8(a) was similar to that in Fig. 8(b). Under 3.2 kPa or 0.1 kPa stress, the nonrecoverable creep compliance value of WCO-based rejuvenated binder and WRO rejuvenated binder reached a relatively close level. Compared to the other two types of rejuvenated binder, aromatic oil rejuvenated binder had better rutting resistance. The curve of WRO rejuvenated binder was quite different from the base binder, which indicated that the addition of WRO rejuvenator partly retained the rutting resistance of artificial aged binder at the content of 10%. D’Angelo et al. [35] proposed to determine high temperature performance grading at a certain temperature according to Jnr3.2. According to AASHTO MP19-10, the high temperature performance grading of asphalt samples is as follows: artificial aged binder is PG64E, WRO rejuvenated binder is PG64H, WCOBased rejuvenated binder is PG64H and aromatic oil rejuvenated binder is PG64E.
4.3. Low temperature properties Fig. 9 shows the change in continuous grading low temperature of artificial aged binder and rejuvenated binders after PAV-ageing. The artificial aged binder had the highest rise in the low temperature grade, indicating further ageing of the asphalt. The addition of aromatic oil has not significantly improved the low temperature grade before or after PAV-ageing. WRO rejuvenated binder had the lowest low temperature grade and the lowest temperature rise
Fig. 8. The non-recoverable creep compliance value of base binder, rejuvenated binders and artificial aged binder after RTFO-ageing; (a) under 0.1 kPa stress, (b) under 3.2 kPa stress.
Fig. 9. Change in low temperature continuous grading of artificial aged binder and rejuvenated binders after PAV-ageing.
after ageing, which indicated that WRO rejuvenated asphalt had excellent low temperature property and ageing resistance. Only 80% of WCO was used in the preparation of WRO rejuvenator, but the continuous grading temperature of WRO rejuvenated binder was lower than that of WCO-based rejuvenated binder. In terms of low temperature continuous grading, the presence of CTR led to better low temperature behavior of WRO rejuvenated binder. For asphalt binder, the difference in the continuous grading low temperature calculated by m-value and S-value, respectively, is DTc value. For aged asphalt, the low temperature grade tends to be controlled by the m value. The more negative DTc value, the more serious the ageing. Therefore, DTc can be used to indicate the aging status of asphalt binder. As such, in this paper, DTc values can be used from two aspects. One is to examine the rejuvenation effect but not to evaluate the low temperature performance. Second is to monitor the aging evolution of rejuvenated binders. In other words, during the RTFO and PAV procedures of rejuvenated binders, if DTc value changed little, the binder is considered to behave better in terms of anti-aging. Fig. 10 shows the change in DTc value of artificial aged binder and rejuvenated binders after PAV-ageing. The DTc value of aromatic oil rejuvenated binder and WCO-based rejuvenated binder was largest. But the DTc value of aromatic oil rejuvenated binder droped rapidly after the PAVageing. Although the DTc value of WCO-based rejuvenated bidner decreased after PAV-ageing, it was still the largest among all samples. DTc value of WRO rejuvenated binder was smaller than the other two types of asphalt, and after ageing, it was still smaller than WCO-based rejuvenated binder. This indicated that, in terms of DTc value, the rejuvenation effect of WCO-based rejuvenator was more stable, and the WRO rejuvenator needed further improvement.
Fig. 10. DTc change of artificial aged binder and rejuvenated binders after PAVageing.
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Fig. 11. Spectroscopic comparison of unaged artificial aged binder and rejuvenated binders.
4.4. FTIR analysis of rejuvenated binders
5. Conclusions
The infrared spectrograms for unaged rejuvenated binders (10% rejuvenator by weight of binder) and artificial aged binder at the wavenumbers between 4000 cm1 and 500 cm1 are shown in Fig. 11. New absorption peaks appeared in WCO-based rejuvenated binder and WRO-rejuvenated binder sample at 1744 cm1 and 1166 cm1 belong to ester carbonyl functional group and C–O stretching, respectively [11,12]. The new absorption peak is the characteristic peak of WCO. The increase in sulfoxide and carbonyl is related to the ageing of the asphalt [36–38]. The WCO also contains a carbonyl group [39], mixing with the artificial aged binder results in an inaccurate measurement of the carbonyl index. Therefore, the sulfoxide index, shown in Fig. 12, was used to observe the ageing of the binders. It can be seen from Fig. 12 that the sulfoxide index of aromatic oil rejuvenated binder had the smallest difference from artificial RAP asphalt, which indicated that the rejuvenation effect of aromatic oil was not as good as WCO-based and WRO at the dosage of 10%. The sulfoxide index of WCO-based rejuvenated binder was the lowest, which was close to that of WRO rejuvenated binder. The polymer produced by the desulfurization of CTR contains sulfur–oxygen functional groups [40], the sulfoxide index of WRO rejuvenated binder was slightly higher than that of WCO-based rejuvenated binder. At the same dosage, the aromatic oil rejuvenated binder had a large difference in sulfoxide index compared to WCO-based rejuvenated binder and WRO rejuvenated binder.
In this paper, the CTR was mixed with WCO for predesulfurization to prepare the WRO rejuvenator. The reaction time of the WRO rejuvenator was determined by viscosity curve and infrared spectrograms. The high and low temperature rheological properties before or after aging of the rejuvenated binders were tested by DSR and BBR, and the change of functional groups of rejuvenated binders was tested by FTIR. The MSCR test was conducted to measure rutting resistance. WRO has the potential to be used as an asphalt rejuvenator. CTR reacted and released polymer during the reaction time. In order to retain a portion of the rubber particles to provide elasticity, the recommended process is a reaction at 260 °C for 70 min based on the viscosity results. The newly developed WRO rejuvenator significantly improved the low temperature properties of aged binder in terms of low temperature continuous grading. However, for the DTc value, the WCO-based rejuvenator has better rejuvenation effect. The high temperature properties of aged binder partially retained with the addition of WRO. The viscous behavior of the aged binder increased. The elasticity supplement was not obvious under the stress of 3.2 kPa during the MSCR test. This may be due to the small dosage of rubber. The developed WRO rejuvenator and the commercial available WCO-based rejuvenator show similar rejuvenation effect with respect to high and low temperature properties. Meanwhile, WRO rejuvenated binder offers better aging resistance than that rejuvenated with the commercial available WCO-based rejuvenator. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements
Fig. 12. Sulfoxide index of unaged rejuvenated binders and artificial aged binder.
This work was financially supported by National Natural Science Foundation of China (No. 51578097), China Postdoctoral Science Foundation (Grant Number: 2018M633319) and the Fundamental Research Funds for the Central Universities (Project Number: 2018CDXYTM0003).
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Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.conbuildmat.2019.117621.
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