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Effect of nano-zinc oxide and organic expanded vermiculite on rheological properties of different bitumens before and after aging
Construction and Building Materials 146 (2017) 30–37
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of nano-zinc oxide and organic expanded vermiculite on rheological properties of different bitumens before and after aging Chongzheng Zhu a, Henglong Zhang a,⇑, Caijun Shi a, Sheng Li b a b
College of Civil Engineering, Hunan University, Changsha, China State Engineering Laboratory of Highway Maintenance Technology, Changsha University of Science & Technology, Changsha, China
h i g h l i g h t s Aging properties of different based bitumens with nano-ZnO and OEVMT were compared. The rheological properties of the binders were evaluated before and after TFOT, PAV, UV and NEA. The improvement effect in aging resistance of bitumen depends on the aging degree and nature of bitumen.
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Article history: Received 8 November 2016 Received in revised form 23 March 2017 Accepted 7 April 2017
Keywords: Bitumen Rheology Nano-zinc oxide Organic expanded vermiculite Thermal oxidation aging Photo oxidation aging
a b s t r a c t A novel anti-aging modifier containing surface modified nano-zinc oxide (nano-ZnO) and organic expanded vermiculite (OEVMT) was used to improve the aging properties of different bitumens (denoted as 70#, 90# and 110#). These aging methods include thin film oven test (TFOT), pressure aging vessel (PAV), ultraviolet (UV) radiation and natural exposure aging (NEA). The aging properties of the binders after different aging methods were evaluated by dynamic shear rheometer (DSR) test and bending beam rheometer (BBR) test. The result shows that the rutting resistance of three types of bitumens before the above aging methods is enhanced with the introduction of anti-aging modifiers. As a result of TFOT, PAV, UV and NEA, compared with corresponding blank samples, these modified bitumens containing antiaging modifier show the lower complex modulus and the higher phase angle, indicating their good thermal oxidation and photo oxidation aging resistance. Moreover, the improvement effect of anti-aging modifier is not only bound up with the aging degree of these bitumens, but also depends on the bitumen nature. Besides, the BBR test result manifests that the anti-aging modifier can improve the lowtemperature rheological performance of 90# bitumen after PAV aging, and has little influence on that of 70# bitumen and 110# bitumen after PAV aging. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Bituminous materials are vulnerable to aging in the process of construction and service time of pavement, which will seriously affect the service performance and service life of bitumen pavement [1,2]. Based on the different stages during construction and usage of asphalt pavement, the aging is divided into short-term aging and long-term aging. The short-term aging happens in the process of mixing, transportation, paving and compaction of bituminous mixture, which is also called for short-term thermal oxidation aging [3]. The short-term aging is usually simulated by TFOT or rolling thin film oven test (RTFOT). In addition, the long-term aging happens during the service time of pavement. On the basis ⇑ Corresponding author. E-mail address: [email protected] (H. Zhang). http://dx.doi.org/10.1016/j.conbuildmat.2017.04.062 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
of different causes of bitumen aging, the long-term aging is further classified into long-term thermal oxidation aging and long-term photo oxidation aging [4–6]. The PAV is used to simulate the long-term thermal oxidation aging, while the UV radiation is utilized to simulate the long-term photo oxidation aging. In order to enhance the aging resistance of bitumen, many studies have been conducted. Generally, adding anti-aging modifiers to bitumen for enhancing the aging resistance is the main method. The anti-aging modifiers mainly include antioxidant [7–9], UV absorber [9–12], layered silicates [12–15] and inorganic nanoparticles [16–20]. In terms of antioxidant and UV absorber, Martin et al. [7] found that though some antioxidants (eg. phenols, amine and aminophenol) could improve the anti-aging property of lubricating oil, resin, rubber and so on, they had no pronounced effect on the antiaging property of bitumen. What’s worse, these antioxidants in
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improving the anti-aging property of bitumen had a larger selectivity, sometimes even accelerated the aging of bitumen. Cong et al. [9] studied the influence of two UV absorbers (octabenzone and bumetrizole) and two antioxidants (zinc dialkyldithio phosphate and carbon black) on aging resistance of bitumen. The results showed that the single UV absorbers or antioxidants could not enhance simultaneously the photo and thermal aging resistance of bitumen. Moreover, the bumetrizole sometimes showed the opposite influence on thermal-oxidative aging or UV aging of bitumen. Feng et al. [11] found that two UV absorbers (octabenzone and bumetrizole) could remarkably improve the photo aging resistance of SK-70 bitumen, whereas they had a little effect on the thermal aging resistance of SK-70 bitumen. Furthermore, different UV absorbers had different influence on aging resistance of different bitumens. That was to say that an UV absorber could enhance the aging resistance of some bitumens, but it had reversed effect on aging resistance of else bitumens. With respect to layered silicates and inorganic nano-particles, Yu et al. [12] studied the effect of organo-montmorillonite (OMMT) on aging properties of bitumen, and found that OMMT could improve the physical and rheological properties of bitumen after thermal-oxidative aging. Lamya et al. [13] also found that OMMT could enhance the short-term thermal oxidation aging resistance of bitumen. Zhang et al. [14] drew a conclusion that expanded vermiculite (EVMT) and organic expanded vermiculite (OEVMT) could improve the thermal-oxidative aging resistance of bitumen, while they had no obvious effect on the photo-oxidative aging resistance of bitumen. Zhang et al. [15] further investigated the effect of different organic layered silicates (eg. OMMT, organic rectorite (OREC) and OEVMT) on aging properties of bitumen, and found that OEVMT had more significant improvements effect in aging resistance of bitumen in comparison with OREC and OMMT. Additionally, Zhang et al. [16] also found that the softening point increment and viscosity aging index of bitumen after UV aging were decreased significantly with the introduction of different inorganic nanoparticles (nano-SiO2, nano-TiO2 and nano-ZnO). Moreover, nano-ZnO showed the better improvement effect in UV aging resistance of bitumen in comparison with nano-SiO2 and nano-TiO2. Ellie et al. [17] utilized dynamic shear rheometer and infrared spectrometer to investigate the effect of nano-SiO2 on aging performance of bitumen. The results showed that the rheological aging index and carbonyl aging index of nano-SiO2 modified bitumen were lower than those of blank sample, which indicated that the anti-aging properties of bitumen were improved. Zhang et al. [18] arrived at a result that nano-ZnO could remarkably enhance the UV aging resistance of bitumen, whereas it had no evident effect on the thermal-oxidative aging resistance of bitumen. However, the effect of OEVMT on aging resistance of bitumen was just the reversed. From all above, although these anti-aging modifiers can improve the aging resistance of bitumen by a certain extent, they still show some obvious defects. Antioxidants and layered silicates can enhance the thermal oxidation aging resistance of bitumen, while they have no obvious effect on the photo oxidation aging resistance of bitumen. However, the improvement of UV absorbers and inorganic nano-particles on the aging resistance of bitumen is just opposite. In addition, the bitumens from different crude oil vary obviously in constituents and properties, which in turn make the improvement effect of some anti-aging modifiers (e.g. antioxidants and UV absorbers) have a larger selectivity. Therefore, it is of significant importance to seek suitable anti-aging modifiers, which not only can improve both thermal oxidation and photo oxidation aging resistance of bitumen simultaneously, but also adapt to the vast majority of bitumens. According to the above introduction about layered silicates and inorganic nanoparticles, OEVMT and nano-ZnO can be compounded to develop a novel anti-aging mod-
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ifier, which can utilize both the effect of OEVMT on hindering the penetration of the oxygen molecules and the shield and absorption effect of nano-ZnO on UV radiation [19,21]. Thus it can be promising modifiers to improve both thermal oxidation aging and photo oxidation aging resistance of the bulk of bitumens simultaneously. In this paper, the anti-aging modifiers containing nano-ZnO and OEVMT were used to modify three types of bitumens from different origins. The binders were aged according to TFOT, PAV, UV and NEA, respectively. TFOT and PAV were used to simulate thermal oxidation process of bitumen, and UV and NEA were utilized to simulate photo oxidation of bitumen. The effects of the antiaging modifier on the rheological properties of these bitumens before and after aging were investigated.
2. Experimental 2.1. Materials Three types of base bitumens (70#, 90# and 110#) from different crude oil were used in this research. 70#, 90# and 110# bitumen are 60/80, 80/100 and 100/120 penetration grade bitumen, respectively. The 70# bitumen was supplied by China National Petroleum Corp., China. The 90# bitumen was manufactured by SK Energy Co. Ltd., South Korea. The 110# bitumen was obtained by Jiangsu Baoli Asphalt Co. Ltd., China. The physical properties and chemical compositions of these base bitumens are listed in Table 1. Expanded vermiculite (EVMT) was procured from Shijiazhuang kinley mining Co., Ltd. To prepare organic expanded vermiculite (OEVMT, 300 mesh), cetyltrimethyl ammonium bromide (CTAB) was used to modify EVMT, supported by Shanghai Zhanyun Chemical Co., Ltd., Shanghai, China. Surface modified nano-zinc oxide (Nano-ZnO) with c-(2,3-epoxypropoxy) propyltrimethoxysilane was supplied by Zhoushan tomorrow nano materials Co., Ltd, and the average particle size is 20 nm. 2.2. Preparation of modified bitumens containing nano-ZnO and OEVMT The liquated base bitumen (70#, 90# or 110# bitumen) was poured into an oil-bath heating container, the work temperature was controlled at 150 ± 5 °C. Then the anti-aging modifier containing 1% Nano-ZnO + 3% OEVMT by mass of base bitumen was added into the bitumen. Firstly the mixture was sheared by a high shear mixer at 4000 rpm for 60 min. Next it was stirred by a paddle agitator at a rotation speed of 2000 rpm for about 90 min, the control temperature was maintained at 150 ± 5 °C. The processed mixture was modified bitumen containing nano-ZnO and OEVMT. The same process was also conducted in the base bitumen in order to obtain blank sample. 2.3. Rheological properties test Dynamic shear rheometer (DSR) was used to test the dynamic shear rheological properties of bitumens according to ASTM D 7175 [22], such as complex modulus (G⁄) and phase angle (d). The range of sweeping temperature was 40–90 °C with 0.5 °C intervals. Bending Beam Rheometer (BBR) was utilized to test the low temperature rheological performance of bitumens after PAV aging according to ASTM D 6648 [23], such as stiffness modulus (S) and stiffness change rate (m-value). The test temperatures were 6 °C and 12 °C, the S and m-value at 60 s were identified as the test result.
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Table 1 Physical properties and chemical compositions of base bitumens. Physical properties and chemical compositions
70#
90#
110#
Physical properties
Penetration (25 °C, 0.1 mm) Softening point (°C) Ductility (15 °C, cm) Viscosity (135 °C, mPas) Viscosity (60 °C, Pas)
71 45.3 >150 590 600
86 42.3 >150 456 247
105 41.3 >150 327 325
Chemical compositions(%)
Saturates Aromatics Resins Asphaltenes
24.53 31.16 33.83 10.48
19.81 39.08 30.54 10.57
25.73 41.85 18.96 13.46
2.4. Aging procedures The short-term and long-term thermal oxidation aging of bitumen were simulated by thin film oven test (TFOT) (ASTM D1754) [24] and TFOT + pressure aging vessel (PAV) (ASTM D6521) [25], respectively. The standard aging condition of PAV was 100 °C, 2.1 MPa, and 20 h. In this research, the photo oxidation aging was simulated by accelerated ultraviolet (UV) aging and natural exposure aging (NEA). The procedure of UV aging was as follow: after TFOT, the residual bitumen was placed in a UV radiation draft oven for 6 days, the working temperature was controlled at 60 ± 5 °C, the UV lamp was 500 W, and the average intensity radiation on the bitumen surface was about 12 w/m2. In addition, the process of NEA was as follow: the standard TFOT sample disk containing 50 ± 0.5 g bitumen was exposed to natural light, and the time was 90 days. Glass board was placed on the sample disk to prevent the influence of rain. Meanwhile, in order to avoid the deposition of dust particles on the glass board reducing the influence of light on bitumen, the glass board need be wiped on time. It is worth to point out that the film thickness of all above-mentioned bitumens is about 3.2 mm. 3. Results and discussion 3.1. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens The complex modulus (G⁄) and phase angle (d) are usually utilized to characterize the dynamic shear rheological properties of bitumen. G⁄ is related to the ability to resist shear deformation of
bitumen material, while d is generally used to evaluate the ratio between elastic and viscous response during the shearing process. The G⁄ and d of all binders at whole scanning temperature region (40–90 °C) before aging is displayed in Fig. 1. As shown in Fig. 1, the addition of anti-aging modifier slightly augments the G⁄ and drops the d of three types of bitumens. It indicates that the antiaging modifier introduced in these base bitumens can enhance the shear deformation resistance and elastic behavior, while decrease the viscous behavior. The reason is due to the movement of bitumen molecules hindered by adding anti-aging modifier, leading to the hardness of these bitumens. In addition, there is no doubt that aging takes place during the mixing of anti-aging modifier to the bitumen, but this aging is rather slight, so the improvement of anti-aging modifier on aging properties of bitumen is also very slight. However, the increase in G⁄ and the decrease in d is more obvious with the anti-aging modifier introduced into these base bitumens. Consequently, compare with corresponding blank samples, the modified bitumens increase in G⁄ values and decrease in d values by a certain extent. Moreover, the test result in Fig. 2 illustrates the increment of G⁄ value of these bitumens before and after modification at 60 °C is 70# > 90# > 110#, that is 1.4, 0.4 and 0.3 kPa, respectively. G⁄/sind is defined as the rutting factor of bitumen according to Superpave system, which is the important parameter to evaluate rutting resistance of bitumen pavement at high temperature. The higher the rutting factor of bitumen material is, the better rutting resistance of bitumen pavement is. The G⁄/sind of bitumen versus temperature (40–90 °C) before aging is plotted in Fig. 3. After introducing the anti-aging modifier, the G⁄/sind of three bitumens is increased, illuminating that the rutting resistance of these bitumens is enhanced. In addition, the temperature when G⁄/sind less
Fig. 1. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens: (a) complex modulus, and (b) phase angle.
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Fig. 2. Effect of anti-aging modifier on complex modulus value (60 °C) of different bitumens. Fig. 4. Temperatures when G*/sind = 1 kPa of all bitumens.
than 1 kPa is generally regarded as the fail temperature of bitumen under high temperature condition. According to Fig. 4, it is clear that the fail temperatures of three bitumens are enhanced by adding anti-aging modifier, indicating the good high temperature stability. Moreover, relative to 90# and 110# bitumen, the enhanced degree of 70# bitumen is the most obvious.
3.2. Thermal oxidation aging properties 3.2.1. Short-term thermal oxidation aging The results of the dynamical shear rheological properties of all binders after TFOT aging are shown in Fig. 5. Obviously, it can be observed that the anti-aging modified bitumens show the lower G⁄ and the higher d than the corresponding blank samples. The result manifests that the anti-aging modifier results in the improvement of the short-term thermal oxidation aging resistance of these bitumens. The reason is due to the exfoliated nanostructures formed in OEVMT/bitumen compound [21]. This nanostructure can increase effectively the average path length of the oxygen molecules penetration and the light component volatiliza-
tion during thermal oxidation aging. Accordingly, the oxidation rate of bitumen is slowed down significantly. Besides, as the Fig. 6 shows, the decrement in the G⁄ of anti-aging modified bitumens relative to unmodified bitumen after TFOT aging at 60 °C are 110# > 90# > 70#, namely, 5.7, 1.7 and 0.7 kPa, respectively. It is thus clear that the improvement of anti-aging modifier on 110# bitumen after TFOT aging is the most obvious, which is related to the constituent of bitumen. According to the Table 1, it can be found that oil content in 110# bitumen is higher than 70# and 90# bitumen. Hence, the influence of TFOT aging on 110# bitumen is the most serious, which is consistent with the result in Fig. 6. 3.2.2. Long-term thermal oxidation aging The influence of anti-aging modifier on dynamic shear rheological properties of bitumens after PAV aging is illustrated in Fig. 7. It is noted that adding anti-aging modifier leads to decrease in G⁄ and increase in d of three types of bitumens after PAV aging. The results demonstrate that the anti-aging modifier can slow down the longterm thermal oxidation aging of bitumen significantly. This reason
Fig. 3. Effect of anti-aging modifier on rutting factor of different bitumens.
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Fig. 5. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens after TFOT aging: (a) complex modulus, and (b) phase angle.
Fig. 6. The complex modulus decrement (60 °C) of modified bitumens relative to unmodified bitumen after TFOT aging.
is the same as the explanation in TFOT aging. In addition, the G⁄ decrement of anti-aging modified bitumens to unmodified bitumen after PAV aging at 60 °C is displayed in Fig. 8. The decrement ranking is 110# 70# > 90#, that is 14.4, 14.3 and 7.7 kPa, respectively. Consequently, the improvement of anti-aging modifier on 70# and 110# bitumens after PAV aging is more obvious than 90# bitumen. Besides, the improving degrees of anti-aging modifier on the dynamic shear rheological properties of all bitumens after PAV aging are more obvious through making a comparison with the result after TFOT aging. Similarly, it also can be found that the influence of PAV aging on 110# bitumen is the most serious. Bending Beam Rheometer test is usually used to evaluate the low temperature cracking performance of bitumen materials. The predominant evaluation indexes include stiffness modulus (S) and stiffness change rate (m-value). Under a certain time and temperature, S is equal to the specific value of stress to total strain. The bigger S value shows that the bitumen material is more brittle under low temperature, and thus bitumen pavement is more prone to crack. m-value is related to relaxation rate of bitumen material. The smaller m-value manifests that the stress relaxation perfor-
Fig. 7. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens after PAV aging: (a) complex modulus, and (b) phase angle.
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mance of bitumen material is worse, thus bitumen pavement is also more likely to crack under low temperature. The stiffness and m-value of different bitumens after PAV aging is listed in Table 2. Under 6 °C and 12 °C, compared with corresponding blank sample, the S value of 70# or 110# modified bitumen is slightly increased, while that of 90# modified bitumen is decreased. In addition, the m-value of all modified bitumens is increased. It means that the anti-aging modifier can improve the stress relaxation performance of three types of bitumens after PAV aging, but slightly increase the brittle behavior of 70# and 110#. The conclusion indicates that the anti-aging modifier has little influence on the low temperature rheological performance of
Fig. 8. The complex modulus decrement (60 °C) of modified bitumens relative to unmodified bitumen after PAV aging.
70# and 110# bitumen after PAV aging. Besides, it shows a certain improved effect on that of 90# bitumen after PAV aging. Totally, based on the results of DSR and BBR test, it can be concluded that the long-term thermal oxidation aging resistance of these bitumens is enhanced by adding the anti-aging modifier. 3.3. Photo oxidation aging properties 3.3.1. Accelerated UV aging In Fig. 9, comparison of modified bitumens and unmodified bitumens, the apparent decrease in G⁄ and increase in d of the bitu-
Fig. 10. The complex modulus decrement (60 °C) of modified bitumens relative to unmodified bitumen after UV aging.
Table 2 Effect of anti-aging modifier on stiffness and m-value of different bitumens after PAV aging. Bitumen samples
S (MPa) m-value
6 °C 12 °C 6 °C 12 °C
70#
70#+ 1%Nano-ZnO +3%OEVMT
90#
90#+ 1%Nano-ZnO +3%OEVMT
110#
110#+ 1%Nano-ZnO +3%OEVMT
70.9 141.1 0.36 0.27
80 150.2 0.44 0.30
82.1 164.4 0.33 0.28
68.3 141.4 0.35 0.28
52.8 73.4 0.26 0.20
54.4 79.5 0.29 0.21
Fig. 9. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens after UV aging: (a) complex modulus, and (b) phase angle.
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Fig. 11. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens after NEA: (a) complex modulus, and (b) phase angle.
mens containing anti-aging modifier after UV aging can be observed. The result suggests that the resistance of bitumen to photo oxidation aging is enhanced evidently with the introduction of anti-aging modifier. The reason is that nano-ZnO has a good absorbance of the UV light. The highest absorbance value is 1.4, which means that UV radiation can be effectively absorbed by nano-ZnO during UV aging [19]. Consequently, the influence of UV radiation on bitumen molecules can be weakened obviously. Meanwhile, as shown Fig. 10, the decrement in G⁄ of anti-aging modified bitumens relative to unmodified bitumen after UV aging at 60 °C is 110# > 90# > 70#, namely, 7.8, 2.1 and 1.6 kPa, respectively. It implies that the improvement of anti-aging modifier on 110# bitumen is more remarkable than 70# and 90# bitumens. Refer to Fig. 6 and Fig. 8, it can be found that the improvement of anti-aging modifier on UV aging resistance of bitumens is located in between the improvement on TFOT aging resistance and the improvement on PAV aging resistance. Besides, it also can be observed in Fig. 10 that the influence of UV aging on 110# base bitumen is the most serious. 3.3.2. Natural exposure aging After natural exposure aging (NEA) test, all binders will take place aging, but the aging degree is slight due to the short time of bitumen samples exposure to sun. As depicted in Fig. 11, for 90# and 110# types of bitumens, anti-aging modified bitumens after NEA show slightly lower G⁄ and higher d than unmodified
bitumens. The result indicates that anti-aging modifier can enhance the photo oxidation aging resistance of bitumen. However, for 70# type of bitumen, modified bitumen have higher G⁄ and lower d than unmodified bitumen. The reason is considered that the hardening effect of anti-aging modifier on bitumen exceeds the improvement effect of it on aging resistance of bitumen. Furthermore, as displayed in Fig. 12, the decrement in G⁄ of anti-aging modified bitumens relative to unmodified bitumen after NEA at 60 °C is 110# > 90# > 70#, that is 0.4, 0.1 and 0.9 kPa, respectively. Besides, the influence of NEA on 110# base bitumen is the most serious. 4. Conclusions Based on the results of this investigation of the effects of the anti-aging modifier containing nano-ZnO and OEVMT on the rheological properties of three types of bitumens before and after different aging methods, the following conclusions were made: (1) The rutting resistance of three types of bitumens before aging is enhanced with the introduction of anti-aging modifiers. Moreover, the enhanced degree of 70# bitumen is the most obvious. (2) On the basis of TFOT, PAV, UV and NEA test results, the antiaging modifier can improve both good thermal oxidation and photo oxidation aging resistance of three bitumens simultaneously. (3) The improvement of anti-aging modifier on aging resistance of three types of bitumens is more and more remarkable as aging degree of these bitumens worsen. In addition, compared with 70# and 90# bitumens, the enhancement in aging resistance of 110# bitumen after various aging methods is the most remarkable. (4) The bending beam rheometer test result indicates that the anti-aging modifier can improve the low-temperature rheological performance of 90# bitumen after PAV aging, and has slightly influence on that of 70# and 110# bitumen after PAV aging.
Acknowledgments Fig. 12. The complex modulus decrement (60 °C) of modified bitumens relative to unmodified bitumen after NEA.
This work was supported by the National Natural Science Foundation of China (No. 51308203) and the Open Fund of State Engi-
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Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of nano-zinc oxide and organic expanded vermiculite on rheological properties of different bitumens before and after aging Chongzheng Zhu a, Henglong Zhang a,⇑, Caijun Shi a, Sheng Li b a b
College of Civil Engineering, Hunan University, Changsha, China State Engineering Laboratory of Highway Maintenance Technology, Changsha University of Science & Technology, Changsha, China
h i g h l i g h t s Aging properties of different based bitumens with nano-ZnO and OEVMT were compared. The rheological properties of the binders were evaluated before and after TFOT, PAV, UV and NEA. The improvement effect in aging resistance of bitumen depends on the aging degree and nature of bitumen.
a r t i c l e
i n f o
Article history: Received 8 November 2016 Received in revised form 23 March 2017 Accepted 7 April 2017
Keywords: Bitumen Rheology Nano-zinc oxide Organic expanded vermiculite Thermal oxidation aging Photo oxidation aging
a b s t r a c t A novel anti-aging modifier containing surface modified nano-zinc oxide (nano-ZnO) and organic expanded vermiculite (OEVMT) was used to improve the aging properties of different bitumens (denoted as 70#, 90# and 110#). These aging methods include thin film oven test (TFOT), pressure aging vessel (PAV), ultraviolet (UV) radiation and natural exposure aging (NEA). The aging properties of the binders after different aging methods were evaluated by dynamic shear rheometer (DSR) test and bending beam rheometer (BBR) test. The result shows that the rutting resistance of three types of bitumens before the above aging methods is enhanced with the introduction of anti-aging modifiers. As a result of TFOT, PAV, UV and NEA, compared with corresponding blank samples, these modified bitumens containing antiaging modifier show the lower complex modulus and the higher phase angle, indicating their good thermal oxidation and photo oxidation aging resistance. Moreover, the improvement effect of anti-aging modifier is not only bound up with the aging degree of these bitumens, but also depends on the bitumen nature. Besides, the BBR test result manifests that the anti-aging modifier can improve the lowtemperature rheological performance of 90# bitumen after PAV aging, and has little influence on that of 70# bitumen and 110# bitumen after PAV aging. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Bituminous materials are vulnerable to aging in the process of construction and service time of pavement, which will seriously affect the service performance and service life of bitumen pavement [1,2]. Based on the different stages during construction and usage of asphalt pavement, the aging is divided into short-term aging and long-term aging. The short-term aging happens in the process of mixing, transportation, paving and compaction of bituminous mixture, which is also called for short-term thermal oxidation aging [3]. The short-term aging is usually simulated by TFOT or rolling thin film oven test (RTFOT). In addition, the long-term aging happens during the service time of pavement. On the basis ⇑ Corresponding author. E-mail address: [email protected] (H. Zhang). http://dx.doi.org/10.1016/j.conbuildmat.2017.04.062 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
of different causes of bitumen aging, the long-term aging is further classified into long-term thermal oxidation aging and long-term photo oxidation aging [4–6]. The PAV is used to simulate the long-term thermal oxidation aging, while the UV radiation is utilized to simulate the long-term photo oxidation aging. In order to enhance the aging resistance of bitumen, many studies have been conducted. Generally, adding anti-aging modifiers to bitumen for enhancing the aging resistance is the main method. The anti-aging modifiers mainly include antioxidant [7–9], UV absorber [9–12], layered silicates [12–15] and inorganic nanoparticles [16–20]. In terms of antioxidant and UV absorber, Martin et al. [7] found that though some antioxidants (eg. phenols, amine and aminophenol) could improve the anti-aging property of lubricating oil, resin, rubber and so on, they had no pronounced effect on the antiaging property of bitumen. What’s worse, these antioxidants in
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improving the anti-aging property of bitumen had a larger selectivity, sometimes even accelerated the aging of bitumen. Cong et al. [9] studied the influence of two UV absorbers (octabenzone and bumetrizole) and two antioxidants (zinc dialkyldithio phosphate and carbon black) on aging resistance of bitumen. The results showed that the single UV absorbers or antioxidants could not enhance simultaneously the photo and thermal aging resistance of bitumen. Moreover, the bumetrizole sometimes showed the opposite influence on thermal-oxidative aging or UV aging of bitumen. Feng et al. [11] found that two UV absorbers (octabenzone and bumetrizole) could remarkably improve the photo aging resistance of SK-70 bitumen, whereas they had a little effect on the thermal aging resistance of SK-70 bitumen. Furthermore, different UV absorbers had different influence on aging resistance of different bitumens. That was to say that an UV absorber could enhance the aging resistance of some bitumens, but it had reversed effect on aging resistance of else bitumens. With respect to layered silicates and inorganic nano-particles, Yu et al. [12] studied the effect of organo-montmorillonite (OMMT) on aging properties of bitumen, and found that OMMT could improve the physical and rheological properties of bitumen after thermal-oxidative aging. Lamya et al. [13] also found that OMMT could enhance the short-term thermal oxidation aging resistance of bitumen. Zhang et al. [14] drew a conclusion that expanded vermiculite (EVMT) and organic expanded vermiculite (OEVMT) could improve the thermal-oxidative aging resistance of bitumen, while they had no obvious effect on the photo-oxidative aging resistance of bitumen. Zhang et al. [15] further investigated the effect of different organic layered silicates (eg. OMMT, organic rectorite (OREC) and OEVMT) on aging properties of bitumen, and found that OEVMT had more significant improvements effect in aging resistance of bitumen in comparison with OREC and OMMT. Additionally, Zhang et al. [16] also found that the softening point increment and viscosity aging index of bitumen after UV aging were decreased significantly with the introduction of different inorganic nanoparticles (nano-SiO2, nano-TiO2 and nano-ZnO). Moreover, nano-ZnO showed the better improvement effect in UV aging resistance of bitumen in comparison with nano-SiO2 and nano-TiO2. Ellie et al. [17] utilized dynamic shear rheometer and infrared spectrometer to investigate the effect of nano-SiO2 on aging performance of bitumen. The results showed that the rheological aging index and carbonyl aging index of nano-SiO2 modified bitumen were lower than those of blank sample, which indicated that the anti-aging properties of bitumen were improved. Zhang et al. [18] arrived at a result that nano-ZnO could remarkably enhance the UV aging resistance of bitumen, whereas it had no evident effect on the thermal-oxidative aging resistance of bitumen. However, the effect of OEVMT on aging resistance of bitumen was just the reversed. From all above, although these anti-aging modifiers can improve the aging resistance of bitumen by a certain extent, they still show some obvious defects. Antioxidants and layered silicates can enhance the thermal oxidation aging resistance of bitumen, while they have no obvious effect on the photo oxidation aging resistance of bitumen. However, the improvement of UV absorbers and inorganic nano-particles on the aging resistance of bitumen is just opposite. In addition, the bitumens from different crude oil vary obviously in constituents and properties, which in turn make the improvement effect of some anti-aging modifiers (e.g. antioxidants and UV absorbers) have a larger selectivity. Therefore, it is of significant importance to seek suitable anti-aging modifiers, which not only can improve both thermal oxidation and photo oxidation aging resistance of bitumen simultaneously, but also adapt to the vast majority of bitumens. According to the above introduction about layered silicates and inorganic nanoparticles, OEVMT and nano-ZnO can be compounded to develop a novel anti-aging mod-
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ifier, which can utilize both the effect of OEVMT on hindering the penetration of the oxygen molecules and the shield and absorption effect of nano-ZnO on UV radiation [19,21]. Thus it can be promising modifiers to improve both thermal oxidation aging and photo oxidation aging resistance of the bulk of bitumens simultaneously. In this paper, the anti-aging modifiers containing nano-ZnO and OEVMT were used to modify three types of bitumens from different origins. The binders were aged according to TFOT, PAV, UV and NEA, respectively. TFOT and PAV were used to simulate thermal oxidation process of bitumen, and UV and NEA were utilized to simulate photo oxidation of bitumen. The effects of the antiaging modifier on the rheological properties of these bitumens before and after aging were investigated.
2. Experimental 2.1. Materials Three types of base bitumens (70#, 90# and 110#) from different crude oil were used in this research. 70#, 90# and 110# bitumen are 60/80, 80/100 and 100/120 penetration grade bitumen, respectively. The 70# bitumen was supplied by China National Petroleum Corp., China. The 90# bitumen was manufactured by SK Energy Co. Ltd., South Korea. The 110# bitumen was obtained by Jiangsu Baoli Asphalt Co. Ltd., China. The physical properties and chemical compositions of these base bitumens are listed in Table 1. Expanded vermiculite (EVMT) was procured from Shijiazhuang kinley mining Co., Ltd. To prepare organic expanded vermiculite (OEVMT, 300 mesh), cetyltrimethyl ammonium bromide (CTAB) was used to modify EVMT, supported by Shanghai Zhanyun Chemical Co., Ltd., Shanghai, China. Surface modified nano-zinc oxide (Nano-ZnO) with c-(2,3-epoxypropoxy) propyltrimethoxysilane was supplied by Zhoushan tomorrow nano materials Co., Ltd, and the average particle size is 20 nm. 2.2. Preparation of modified bitumens containing nano-ZnO and OEVMT The liquated base bitumen (70#, 90# or 110# bitumen) was poured into an oil-bath heating container, the work temperature was controlled at 150 ± 5 °C. Then the anti-aging modifier containing 1% Nano-ZnO + 3% OEVMT by mass of base bitumen was added into the bitumen. Firstly the mixture was sheared by a high shear mixer at 4000 rpm for 60 min. Next it was stirred by a paddle agitator at a rotation speed of 2000 rpm for about 90 min, the control temperature was maintained at 150 ± 5 °C. The processed mixture was modified bitumen containing nano-ZnO and OEVMT. The same process was also conducted in the base bitumen in order to obtain blank sample. 2.3. Rheological properties test Dynamic shear rheometer (DSR) was used to test the dynamic shear rheological properties of bitumens according to ASTM D 7175 [22], such as complex modulus (G⁄) and phase angle (d). The range of sweeping temperature was 40–90 °C with 0.5 °C intervals. Bending Beam Rheometer (BBR) was utilized to test the low temperature rheological performance of bitumens after PAV aging according to ASTM D 6648 [23], such as stiffness modulus (S) and stiffness change rate (m-value). The test temperatures were 6 °C and 12 °C, the S and m-value at 60 s were identified as the test result.
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Table 1 Physical properties and chemical compositions of base bitumens. Physical properties and chemical compositions
70#
90#
110#
Physical properties
Penetration (25 °C, 0.1 mm) Softening point (°C) Ductility (15 °C, cm) Viscosity (135 °C, mPas) Viscosity (60 °C, Pas)
71 45.3 >150 590 600
86 42.3 >150 456 247
105 41.3 >150 327 325
Chemical compositions(%)
Saturates Aromatics Resins Asphaltenes
24.53 31.16 33.83 10.48
19.81 39.08 30.54 10.57
25.73 41.85 18.96 13.46
2.4. Aging procedures The short-term and long-term thermal oxidation aging of bitumen were simulated by thin film oven test (TFOT) (ASTM D1754) [24] and TFOT + pressure aging vessel (PAV) (ASTM D6521) [25], respectively. The standard aging condition of PAV was 100 °C, 2.1 MPa, and 20 h. In this research, the photo oxidation aging was simulated by accelerated ultraviolet (UV) aging and natural exposure aging (NEA). The procedure of UV aging was as follow: after TFOT, the residual bitumen was placed in a UV radiation draft oven for 6 days, the working temperature was controlled at 60 ± 5 °C, the UV lamp was 500 W, and the average intensity radiation on the bitumen surface was about 12 w/m2. In addition, the process of NEA was as follow: the standard TFOT sample disk containing 50 ± 0.5 g bitumen was exposed to natural light, and the time was 90 days. Glass board was placed on the sample disk to prevent the influence of rain. Meanwhile, in order to avoid the deposition of dust particles on the glass board reducing the influence of light on bitumen, the glass board need be wiped on time. It is worth to point out that the film thickness of all above-mentioned bitumens is about 3.2 mm. 3. Results and discussion 3.1. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens The complex modulus (G⁄) and phase angle (d) are usually utilized to characterize the dynamic shear rheological properties of bitumen. G⁄ is related to the ability to resist shear deformation of
bitumen material, while d is generally used to evaluate the ratio between elastic and viscous response during the shearing process. The G⁄ and d of all binders at whole scanning temperature region (40–90 °C) before aging is displayed in Fig. 1. As shown in Fig. 1, the addition of anti-aging modifier slightly augments the G⁄ and drops the d of three types of bitumens. It indicates that the antiaging modifier introduced in these base bitumens can enhance the shear deformation resistance and elastic behavior, while decrease the viscous behavior. The reason is due to the movement of bitumen molecules hindered by adding anti-aging modifier, leading to the hardness of these bitumens. In addition, there is no doubt that aging takes place during the mixing of anti-aging modifier to the bitumen, but this aging is rather slight, so the improvement of anti-aging modifier on aging properties of bitumen is also very slight. However, the increase in G⁄ and the decrease in d is more obvious with the anti-aging modifier introduced into these base bitumens. Consequently, compare with corresponding blank samples, the modified bitumens increase in G⁄ values and decrease in d values by a certain extent. Moreover, the test result in Fig. 2 illustrates the increment of G⁄ value of these bitumens before and after modification at 60 °C is 70# > 90# > 110#, that is 1.4, 0.4 and 0.3 kPa, respectively. G⁄/sind is defined as the rutting factor of bitumen according to Superpave system, which is the important parameter to evaluate rutting resistance of bitumen pavement at high temperature. The higher the rutting factor of bitumen material is, the better rutting resistance of bitumen pavement is. The G⁄/sind of bitumen versus temperature (40–90 °C) before aging is plotted in Fig. 3. After introducing the anti-aging modifier, the G⁄/sind of three bitumens is increased, illuminating that the rutting resistance of these bitumens is enhanced. In addition, the temperature when G⁄/sind less
Fig. 1. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens: (a) complex modulus, and (b) phase angle.
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Fig. 2. Effect of anti-aging modifier on complex modulus value (60 °C) of different bitumens. Fig. 4. Temperatures when G*/sind = 1 kPa of all bitumens.
than 1 kPa is generally regarded as the fail temperature of bitumen under high temperature condition. According to Fig. 4, it is clear that the fail temperatures of three bitumens are enhanced by adding anti-aging modifier, indicating the good high temperature stability. Moreover, relative to 90# and 110# bitumen, the enhanced degree of 70# bitumen is the most obvious.
3.2. Thermal oxidation aging properties 3.2.1. Short-term thermal oxidation aging The results of the dynamical shear rheological properties of all binders after TFOT aging are shown in Fig. 5. Obviously, it can be observed that the anti-aging modified bitumens show the lower G⁄ and the higher d than the corresponding blank samples. The result manifests that the anti-aging modifier results in the improvement of the short-term thermal oxidation aging resistance of these bitumens. The reason is due to the exfoliated nanostructures formed in OEVMT/bitumen compound [21]. This nanostructure can increase effectively the average path length of the oxygen molecules penetration and the light component volatiliza-
tion during thermal oxidation aging. Accordingly, the oxidation rate of bitumen is slowed down significantly. Besides, as the Fig. 6 shows, the decrement in the G⁄ of anti-aging modified bitumens relative to unmodified bitumen after TFOT aging at 60 °C are 110# > 90# > 70#, namely, 5.7, 1.7 and 0.7 kPa, respectively. It is thus clear that the improvement of anti-aging modifier on 110# bitumen after TFOT aging is the most obvious, which is related to the constituent of bitumen. According to the Table 1, it can be found that oil content in 110# bitumen is higher than 70# and 90# bitumen. Hence, the influence of TFOT aging on 110# bitumen is the most serious, which is consistent with the result in Fig. 6. 3.2.2. Long-term thermal oxidation aging The influence of anti-aging modifier on dynamic shear rheological properties of bitumens after PAV aging is illustrated in Fig. 7. It is noted that adding anti-aging modifier leads to decrease in G⁄ and increase in d of three types of bitumens after PAV aging. The results demonstrate that the anti-aging modifier can slow down the longterm thermal oxidation aging of bitumen significantly. This reason
Fig. 3. Effect of anti-aging modifier on rutting factor of different bitumens.
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Fig. 5. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens after TFOT aging: (a) complex modulus, and (b) phase angle.
Fig. 6. The complex modulus decrement (60 °C) of modified bitumens relative to unmodified bitumen after TFOT aging.
is the same as the explanation in TFOT aging. In addition, the G⁄ decrement of anti-aging modified bitumens to unmodified bitumen after PAV aging at 60 °C is displayed in Fig. 8. The decrement ranking is 110# 70# > 90#, that is 14.4, 14.3 and 7.7 kPa, respectively. Consequently, the improvement of anti-aging modifier on 70# and 110# bitumens after PAV aging is more obvious than 90# bitumen. Besides, the improving degrees of anti-aging modifier on the dynamic shear rheological properties of all bitumens after PAV aging are more obvious through making a comparison with the result after TFOT aging. Similarly, it also can be found that the influence of PAV aging on 110# bitumen is the most serious. Bending Beam Rheometer test is usually used to evaluate the low temperature cracking performance of bitumen materials. The predominant evaluation indexes include stiffness modulus (S) and stiffness change rate (m-value). Under a certain time and temperature, S is equal to the specific value of stress to total strain. The bigger S value shows that the bitumen material is more brittle under low temperature, and thus bitumen pavement is more prone to crack. m-value is related to relaxation rate of bitumen material. The smaller m-value manifests that the stress relaxation perfor-
Fig. 7. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens after PAV aging: (a) complex modulus, and (b) phase angle.
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mance of bitumen material is worse, thus bitumen pavement is also more likely to crack under low temperature. The stiffness and m-value of different bitumens after PAV aging is listed in Table 2. Under 6 °C and 12 °C, compared with corresponding blank sample, the S value of 70# or 110# modified bitumen is slightly increased, while that of 90# modified bitumen is decreased. In addition, the m-value of all modified bitumens is increased. It means that the anti-aging modifier can improve the stress relaxation performance of three types of bitumens after PAV aging, but slightly increase the brittle behavior of 70# and 110#. The conclusion indicates that the anti-aging modifier has little influence on the low temperature rheological performance of
Fig. 8. The complex modulus decrement (60 °C) of modified bitumens relative to unmodified bitumen after PAV aging.
70# and 110# bitumen after PAV aging. Besides, it shows a certain improved effect on that of 90# bitumen after PAV aging. Totally, based on the results of DSR and BBR test, it can be concluded that the long-term thermal oxidation aging resistance of these bitumens is enhanced by adding the anti-aging modifier. 3.3. Photo oxidation aging properties 3.3.1. Accelerated UV aging In Fig. 9, comparison of modified bitumens and unmodified bitumens, the apparent decrease in G⁄ and increase in d of the bitu-
Fig. 10. The complex modulus decrement (60 °C) of modified bitumens relative to unmodified bitumen after UV aging.
Table 2 Effect of anti-aging modifier on stiffness and m-value of different bitumens after PAV aging. Bitumen samples
S (MPa) m-value
6 °C 12 °C 6 °C 12 °C
70#
70#+ 1%Nano-ZnO +3%OEVMT
90#
90#+ 1%Nano-ZnO +3%OEVMT
110#
110#+ 1%Nano-ZnO +3%OEVMT
70.9 141.1 0.36 0.27
80 150.2 0.44 0.30
82.1 164.4 0.33 0.28
68.3 141.4 0.35 0.28
52.8 73.4 0.26 0.20
54.4 79.5 0.29 0.21
Fig. 9. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens after UV aging: (a) complex modulus, and (b) phase angle.
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Fig. 11. Effect of anti-aging modifier on dynamic shear rheological properties of different bitumens after NEA: (a) complex modulus, and (b) phase angle.
mens containing anti-aging modifier after UV aging can be observed. The result suggests that the resistance of bitumen to photo oxidation aging is enhanced evidently with the introduction of anti-aging modifier. The reason is that nano-ZnO has a good absorbance of the UV light. The highest absorbance value is 1.4, which means that UV radiation can be effectively absorbed by nano-ZnO during UV aging [19]. Consequently, the influence of UV radiation on bitumen molecules can be weakened obviously. Meanwhile, as shown Fig. 10, the decrement in G⁄ of anti-aging modified bitumens relative to unmodified bitumen after UV aging at 60 °C is 110# > 90# > 70#, namely, 7.8, 2.1 and 1.6 kPa, respectively. It implies that the improvement of anti-aging modifier on 110# bitumen is more remarkable than 70# and 90# bitumens. Refer to Fig. 6 and Fig. 8, it can be found that the improvement of anti-aging modifier on UV aging resistance of bitumens is located in between the improvement on TFOT aging resistance and the improvement on PAV aging resistance. Besides, it also can be observed in Fig. 10 that the influence of UV aging on 110# base bitumen is the most serious. 3.3.2. Natural exposure aging After natural exposure aging (NEA) test, all binders will take place aging, but the aging degree is slight due to the short time of bitumen samples exposure to sun. As depicted in Fig. 11, for 90# and 110# types of bitumens, anti-aging modified bitumens after NEA show slightly lower G⁄ and higher d than unmodified
bitumens. The result indicates that anti-aging modifier can enhance the photo oxidation aging resistance of bitumen. However, for 70# type of bitumen, modified bitumen have higher G⁄ and lower d than unmodified bitumen. The reason is considered that the hardening effect of anti-aging modifier on bitumen exceeds the improvement effect of it on aging resistance of bitumen. Furthermore, as displayed in Fig. 12, the decrement in G⁄ of anti-aging modified bitumens relative to unmodified bitumen after NEA at 60 °C is 110# > 90# > 70#, that is 0.4, 0.1 and 0.9 kPa, respectively. Besides, the influence of NEA on 110# base bitumen is the most serious. 4. Conclusions Based on the results of this investigation of the effects of the anti-aging modifier containing nano-ZnO and OEVMT on the rheological properties of three types of bitumens before and after different aging methods, the following conclusions were made: (1) The rutting resistance of three types of bitumens before aging is enhanced with the introduction of anti-aging modifiers. Moreover, the enhanced degree of 70# bitumen is the most obvious. (2) On the basis of TFOT, PAV, UV and NEA test results, the antiaging modifier can improve both good thermal oxidation and photo oxidation aging resistance of three bitumens simultaneously. (3) The improvement of anti-aging modifier on aging resistance of three types of bitumens is more and more remarkable as aging degree of these bitumens worsen. In addition, compared with 70# and 90# bitumens, the enhancement in aging resistance of 110# bitumen after various aging methods is the most remarkable. (4) The bending beam rheometer test result indicates that the anti-aging modifier can improve the low-temperature rheological performance of 90# bitumen after PAV aging, and has slightly influence on that of 70# and 110# bitumen after PAV aging.
Acknowledgments Fig. 12. The complex modulus decrement (60 °C) of modified bitumens relative to unmodified bitumen after NEA.
This work was supported by the National Natural Science Foundation of China (No. 51308203) and the Open Fund of State Engi-
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