- Email: [email protected]
Effect of LDHs on the aging resistance of crumb rubber modified asphalt
Construction and Building Materials xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of LDHs on the aging resistance of crumb rubber modified asphalt Ling Pang a,b, Kuangyi Liu a, Shaopeng Wu a,⇑, Min Lei b, Zongwu Chen a a b
State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China School of Sciences, Wuhan University of Technology, Wuhan 430070, China
h i g h l i g h t s LDHs improved the ageing resistance of crumb rubber modified asphalt (CRMA). LDHs present significant influences on properties of CRMA after UV aging. Less carbonyl groups appeared in the aged LDHs/CRMA than in the aged CRMA. LDHs modified CRMA has a better performance at both low and high temperatures.
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Crumb rubber modified asphalt Aging resistance Ultraviolet radiation aging LDHs
a b s t r a c t Layer double hydroxides (LDHs), a kind of ultraviolet light resistant material, was added into the Crumb Rubber Modified Asphalt (CRMA) and its effects on the aging resistance of the CRMA were investigated in this paper. The short-term and long-term aging processes of asphalt were simulated by Thin Film Oven Test (TFOT) and ultraviolet (UV) radiation test, respectively. With Fourier Transform Infrared Spectroscopy (FTIR) measurements, it was found that LDHs can slow down the formation of carbonyl groups during the aging process. The conventional physical properties test and Dynamic Shear Rheometer (DSR) test were used to evaluate the properties of the asphalt. The results showed that the softening point increases and G* ratios of CRMA decreases significantly, the ductility and the penetration retention rate increase after ultraviolet aging due to the introduction of LDHs. Besides, the results of both creep and relaxation test implied that the LDHs modified CRMA binder has a better UV aging resistance. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction With the development of motor transportation industry, the amount of discarded tires nearly reaches 10 million every year in the world [1]. A great number of waste rubber tires have caused serious environmental problems. Therefore, the utilization of waste rubber tires has attracted great interests of researchers in recent decades [2–4]. A lot of researches show that crumb rubber, made from waste rubber tires, can improve the temperature sensitivity, deformation resistance at high temperatures, crack resistance at low temperatures and fatigue resistance of asphalt as asphalt modifier. Therefore, the service life of crumb rubber modified asphalt (CRMA) pavement will be longer than unmodified ones [5–7]. In addition, CRMA can also reduce the traffic noise and improve the driving comfort [8]. So the utilization of waste crumb rubber as asphalt modifier is one of the most promising
⇑ Corresponding author. Tel./fax: +86 27 87162595.
ways to solve the problems caused by waste rubber tires considering the benefits of economy and environment [9]. Some researches on interaction mechanism of crumb rubber and base asphalt indicated that crumb rubber swells in asphalt by adsorbing the light components of asphalt [10–12]. However, just like other asphalt materials, the aging of CRMA during active time can induce the change of proportion of the components in the asphalt, the light components of asphalt volatilize, and micromolecules convert into large molecular size fractions by oxidation and polymerization [13–15]. The components of asphalt determine its properties, and the properties of CRMA binder are degraded with the decrease of light components and the structure destruction of asphalt [16], as a result, the CRMA pavement diseases take place. Therefore, it is important to improve the aging resistance of CRMA binder. LDHs have attracted a considerable attention as the UV light resistant materials to improve the properties of rubber, plastics, coating material in recent years. These layered materials are multi nestification layered structure. The inorganic layer sheets have the physical shield effect against UV light, and some metal elements of
E-mail address: [email protected] (S. Wu). 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.10.040
Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resistance of crumb rubber modified asphalt. Constr Build Mater (2013), http:// dx.doi.org/10.1016/j.conbuildmat.2013.10.040
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L. Pang et al. / Construction and Building Materials xxx (2013) xxx–xxx
layer sheets and negative ions between layer sheets will chemically absorb UV light. This kind of multi chemical absorbability and physical shield effect of LDHs result in excellent UV aging resistance in the organic material [17–19]. Wu et al. studied the effect of LDHs on the aging property of the asphalt and found that the LDHs can enhance the aging resistance of asphalt [20]. So, LDHs, as a kind of UV aging resistant materials, has the potential to improve the aging resistance of CRMA. In this paper, LDHs, were added into the CRMA at 0, 3, 5 wt% mass ratio, and the impact of the LDHs on the aging resistance of CRMA was investigated. Thin film oven (TFOT) test and UV light accelerated aging process were used to simulate the short-term aging and long-term field aging of asphalt, respectively. The rheological properties of asphalt before and after artificial UV aging were investigated by using Dynamic Shear Rheometer (DSR) through temperature sweep, creep tests and relaxation test. FTIR test result, conventional physical properties, complex modulus ratio, creep and relaxation curve of asphalt were used to evaluate the chemical and physical characteristics of asphalt before and after artificial UV aging.
2. Materials and experimental
2.4. Characterization methods 2.4.1. FTIR A Thermo Nicolet Model Nexus FTIR–Raman spectrophotometer was used to record FTIR spectra of rubber asphalt. A sample was prepared by casting an asphalt film onto a KBr thin plate from 5 wt% solution in carbon disulfide, then the solvent was dried for the FTIR analysis. 2.4.2. Conventional physical properties test The conventional physical properties tests including penetration, ductility, softening points and some other property indexes. They were conducted according to Chinese standard test methods of bitumen and bituminous mixtures for highway engineering JTG E20-2011. 2.4.3. DSR A MCR101 Dynamic Shear Rheometer (DSR) produced by Anton Paar Company was adopted to measure the rheological property of CRMA and LDHs/CRMA. DSR temperature sweep test was performed under the strain-controlled mode at a constant frequency of 10 rad/s. The tests were performed within the linear viscoelastic range of the tested asphalts. When the test temperature is higher than 30 °C, 25 mm diameter plates with 1 mm gap were used. When the test temperature is lower than 30 °C, 8 mm diameter plates with 2 mm gap were used. Furthermore, creep testing and relaxation testing were also used to evaluate the aging resistance of CRMA and LDHs/CRMA.
3. Results and discussion
2.1. Materials
3.1. FTIR characterization analysis
The CRMA used in this paper was provided by Hubei Guochuang Hi-tech Material Co., Ltd. The diameter of crumb rubber power modifier was smaller than 0.3 mm and the content was 15% by weight. The basic properties of CRMA are exhibited in Table 1. Mg–Al layered double hydroxides complex metallic material was used to modify the CRMA. The LDHs was produced by Rui Fa Chemical Company Limited, Jiang Su, China. The density of the LDHs was 1.7 g/cm3 and the moisture content was less than 0.3%.
2.2. Preparation of LDHs modified asphalt Many researchers suggested the blending temperature of crumb rubber and base asphalt should be more than 160 °C and less than 200 °C [21]. In China, the most commonly used blending temperature for CRMA is 175–185 °C. Although this temperature range may lead to the degradation of base asphalt, it is good for the swelling process of crumb rubber. Therefore, LDHs was blended into CRMA binder using a shear blender at 180 °C in this research. The rotation speed of the blender was 5000 r/min and 60 min of blending was used to ensure a good distribution of LDHs. The CRMA without LDHs was also processed under the same conditions as the reference group.
2.3. Aging procedures TFOT was employed to simulate the short-term oxidation that occurs during the hot-mix process according to Chinese standard test methods of bitumen and bituminous mixtures for highway engineering JTG E20-2011(T0609-2011) [22]. After TFOT aging, the asphalt samples with film thickness of 1 mm were prepared for further UV aging to simulate the photodegradation that occurs during the service life. The UV aging performed on the asphalt samples lasted for 10 days in a UV light accelerated aging oven, the radiation strength of the UV light was set at 26.5 W/ m2 with the wavelength of 360 nm, and the test temperature was controlled at 60 °C.
Table 1 Properties of base asphalt and CRMA. Index
Base asphalt
CRMA
Specification
Penetration at 25 °C (0.1 mm) Ductility of base asphalt at before TFOT 15 °C, CRMA at 5 °C (cm) after TFOT Softening point (°C) Education, softening point difference (°C) Elasticity resume at 25 °C (%)
72 65
51 12
T0604-2011 T0605-2011
19 44.5 –
8.5 68 2
T0605-2011 T0606-2011 T0661-2011
–
79
T0662-2000
FTIR was applied to study the effect of LDHs on the aging resistance of the CRMA. The aging of asphalt includes thermal oxygen and light oxygen aging. The occurrence of carbonyl groups is the result of the oxidation aging of base asphalt. According to the precious research, the carbonyl (C@O) index can be used as an indicator to evaluate the aging extent of asphalt [23,24]. It was computed as the following formula [25]:
Area of the carbonyle band centered around 1700 cm1 IC@O ¼ P Area of the spectral bands between 2000 and 600 cm1 The FTIR spectrums of asphalts without aging and asphalts with UV aging were shown in Fig. 1. As an indicator of the aging extent, the corresponding functional groups indices were listed in Table 2. Fig. 1 shows no obvious absorbance peak can be observed for asphalts without aging, while carbonyl clearly appeared after UV aging for 10 days. The intensity of carbonyl absorption peaks of LDHs/CRMA were lesser than that of CRMA. Table 2 shows more details about these changes discussed above. The carbonyl index of CRMA is 0.013, larger than that of LDHs/CRMA after UV aging for 10 days, which means less carbonyl groups formation after the introduction of LDHs, indicating that LDHs modified asphalts had better resistant to the formation of carbonyl and hence might getting more stable. Therefore, the LDHs can improve the aging resistance of CRMA binder. 3.2. Conventional physical properties Figs. 2–4 showed the conventional properties test results of CRMA and LDHs/CRMA before and after aging. It is obvious that LDHs provide increased soft points and decreased penetration of CRMA before UV aging, therefore LDHs is good for deformation resistance of asphalt at high temperatures although it degrades the ductility of CRMA slightly. After subjected to UV aging, there would be a great difference in conventional properties, the softening points decreased, the penetration and ductility increased with the addition of LDHs, especially when 5 wt% of LDHs was added. Table 3 lists the softening point increment, ductility retention rate and penetration retention rate after UV aging using original values as references. The softening point increment, ductility retention rate and penetration retention rate can be used to evalu-
Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resistance of crumb rubber modified asphalt. Constr Build Mater (2013), http:// dx.doi.org/10.1016/j.conbuildmat.2013.10.040
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0.4
14 CRMA
CRMA-UV
3%LDHS/CRMA
3%LDHS/CRMA-UV
5%LDHS/CRMA
5%LDHS/CRMA-UV
0.3
UV
10
Ductility (cm)
Absorbance
Fresh
12
1700cm-1
0.2
8 6 4
0.1
2 0 CRMA
0 600
800
1000
1200
1400
1600
1800
3%LDHs/CRMA
5%LDHs/CRMA
2000 Fig. 4. Ductility of asphalts at 5 °C.
Wavenumber (cm-1) Fig. 1. FTIR analysis of asphalts before and after aging.
Table 2 FTIR absorbance indices of asphalts after UV aging for 10 days. Asphalt
CRMA–UV
3% LDHs/CRMA–UV
5% LDHs/CRMA–UV
Carboyl index
0.013
0.009
0.008
ductility retention rate and penetration retention rate compared to the CRMA, indicating LDHs can significantly improve the aging resistance of CRMA. Compared with CRMA, properties of CRMA/ LDHs was much retained after UV aging, which indicated the LDHs/CRMA had better UV aging resistance than CRMA. 3.3. Temperature sweep test
60 Fresh
UV
Penetration (0.1mm)
50 40 30 20 10 0 CRMA
3%LDHs/CRMA
5%LDHs/CRMA
Fig. 2. Penetration of asphalts at 25 °C.
100 Fresh
90
UV
Softening point (°C)
80 70
The temperature sweep conducted by DSR can characterize the variation of complex modulus and phase angle of asphalt in a wide range of temperature. Figs. 5 and 6 respectively showed the complex modulus and phase angle of CRMA and LDHs/CRMA before and after aging, and also showed the effect of LDHs on the aging resistance. The complex modulus (G*) of LDHs/CRMA was higher and phase angle was smaller than that of CRMA at all test temperatures before aging. It means that the addition of LDHs increased the G* and reduced the phase angle. The increase of G* and the decrease of phase angle caused by aging, which induced more solidlike and hardening [23]. However, after UV aging for 10 days, the G* and phase angle curve of all asphalts tended to get closer with the deepened aging of asphalts, but the G* of LDHs/CRMA was lower and phase angle was higher than that of CRMA. This means that the LDHs/CRMA binder suffered less hardening and it was more viscous than CRMA. Table 4 displays the G* ratios at different temperatures using original modulus as reference value. From Table 4, it can be seen that the G* ratios of 3% and 5% LDHs modified asphalts were lower than that of CRMA after UV 10 days. The more the G* value of asphalt increase, the more aging the asphalts suffer. So, the aging degree of the LDHs modified asphalt was not as serious as CRMA. It implied that the addition of LDHs improved the aging resistance of CRMA.
60
3.4. Creep and relaxation test 50
The effect of LDHs modifier on the aging properties of CRMA binder was also studied by shear creep test. Fig. 7 gave the creep strain response curve of CRMA and LDHs/CRMA. The creep testing was conducted at 60 °C by DSR. A constant shear stress of 5 Pa was
40 30 20 10 0
CRMA
3%LDHs/CRMA
5%LDHs/CRMA
Fig. 3. Softening points of asphalts.
ate the aging resistance [26]. According to Table 3, the 3% and 5% LDHs/CRMA exhibited lower softening point increment, higher
Table 3 The softening point increment, ductility and penetration retention rate after UV aging for 10 days. Asphalt
CRMA
3% LDHs/CRMA
5% LDHs/CRMA
Softening point increment (°C) Ductility retention rate (%) Penetration retention rate (%)
11.0 41.7 64.7
8.5 46.4 72.9
7.0 55.6 76.6
Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resistance of crumb rubber modified asphalt. Constr Build Mater (2013), http:// dx.doi.org/10.1016/j.conbuildmat.2013.10.040
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10
120
CRMA
3%LDHs/CRMA
5%LDHs/CRMA 3%LDHs/CRMA-UV
CRMA-UV 5%LDHs/CRMA-UV
8
Creep strain (%)
Complex modulus (MPa)
160
80
CRMA
CRMA-UV
3%LDHs/CRMA
5%LDHs/CRMA
3%LDHs/CRMA-UV
5%LDHs/CRMA-UV
6 4
40 2 0 -10
-5
0
5
10
15
20
25
0
30
0
100
200
Temperature (°C)
300
400
500
Time (s)
Fig. 5. Complex modulus curves of asphalts before and after aging.
Fig. 7. Creep strain curve at 60 °C.
60 CRMA 5%LDHs/CRMA 3%LDHs/CRMA-UV
1.E+05
3%LDHs/CRMA CRMA-UV 5%LDHs/CRMA-UV
1.E+05
Shear stress (Pa)
Phase angle (°)
50
40
30
CRMA
3%LDHs/CRMA
5%LDHs/CRMA
CRMA-UV
3%LDHs/CRMA-UV
5%LDHs/CRMA-UV
8.E+04 6.E+04 4.E+04
20 -10
2.E+04 0 -5
0
5
10
15
20
25
30
50
100
150
200
250
300
Time (s)
Temperature (°C) Fig. 8. Stress relaxation curves at 5 °C. Fig. 6. Phase angle curves of asphalts before and after aging.
applied and the creep strain of asphalts was recorded during 100 s of the loading stage and 400 s of the unloading stage. As indicated in Fig. 7, the total creep strain of LDHs/CRMA was lower than that of CRMA binder before aging, which indicates that the introduction of LDHs increases the resistance to creep of CRMA at high temperatures. After UV aging for 10 days, the total creep strains of asphalts were lower than that of asphalts without UV aging, however among asphalts of having suffered UV aging, the total creep strains increased with the addition of LDHs, which indicates that LDHs can lower hardening of CRMA when subjected to UV aging, therefore the aging resistance of LDHs/CRMA is superior to CRMA. The shrinkage stress of asphalts with aging is higher than that of ones without aging, because the aging process has hardened asphalts. It is well known that the pavement will crack when the shrinkage stress is higher than the tensile strength. The shear relaxation testing was used to evaluate the low temperature performance of asphalt with the application of DSR instrument under strain-controlled model. The applied shear strain level was kept to 5%. Fig. 8 presented the relaxation test results of CRMA and LDHs/ CRMA before and after aging at 5 °C. It indicated that the
Table 4 G* ratio of asphalts after UV aging for 10 days. Asphalts
CRMA 3% LDHs/CRMA 5% LDHs/CRMA
G* ratio 10 °C
0 °C
10 °C
20 °C
30 °C
1.36 1.17 1.05
1.43 1.18 1.05
1.58 1.27 1.12
1.69 1.40 1.20
1.60 1.48 1.26
inclusion of LDHs into CRMA resulted in a higher shear stress, mainly because LDHs enhanced the elasticity of CRMA. Compared to CRMA, the shear stress of the LDHs/CRMA was lower after UV aging, especially 5% LDHs/CRMA had the lowest shear stress. The results implied that LDHs can lower hardening of CRMA with the addition of LDHs during aging process. Therefore LDHs can improve the UV aging resistance of CRMA. The reason why aged LDHs/CRMA had a lower shear stress is that LDHs could retard the oxidation of asphalt through the multi chemical absorbability and physical shield effect, slowing down the reduction of viscous component during the aging process. The more the viscous component, the better the low temperature property is. 4. Conclusions In this research, LDHs was added into the CRMA binder and the effects of LDHs on the UV aging resistance of the CRMA were investigated by means of FTIR analysis, conventional physical properties test and DSR test. Based on these test results, the following conclusions can be drawn: (1) The carbonyl groups, occurred after UV aging, was used as an aging index to evaluate the effect of LDHs on the aging resistance of CRMA. It was found that less carbonyl groups appeared in the aged LDHs/CRMA than in the aged CRMA, indicating that the CRMA binder would get less sensitive to UV aging when LDHs was introduced. (2) LDHs stiffened CRMA by increasing its softening points and decreasing its penetration. However, the softening point increment of LDHs/CRMA decreased and the penetration and ductility retention rate increased after UV aging, which
Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resistance of crumb rubber modified asphalt. Constr Build Mater (2013), http:// dx.doi.org/10.1016/j.conbuildmat.2013.10.040
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implied that LDHs can lower hardening speed of CRMA when subjected to UV aging. Therefore LDHs can improve the UV aging resistance of CRMA. (3) The G* ratio of LDHs/CRMA was lower and phase angle was higher than that of CRMA after aging. It means that the LDHs/CRMA binder suffered less hardening and it was more viscous than CRMA after UV aging. (4) The results of creep and relaxation test also supported the conclusions that LDHs can slow down the hardening speed of CRMA when subjected to UV aging. Therefore LDHs can improve UV aging resistance of CRMA and it can slow down the degradation of CRMA when LDHs/CRMA was subjected to UV aging.
Acknowledgements This work is supported by the Ministry of Science and Technology of China (2011BAE28B03) and the National Instrumentation Program (2013YQ160501). The authors gratefully acknowledge their support. References [1] Yu QX. The recycling and reuse of waste tire worldwide. World Rubber Ind 2010;37(2):50–4. [2] Zhang SL, Zhang ZX, Xin ZX, Pal K, Kim JK. Prediction of mechanical properties of polypropylene/waste ground rubber tire powder treated by bitumen composites via uniform design and artificial neural networks. Mater Des 2010;31(4):1900–5. [3] Gupata VK, Gupata B, Rastogi A, Agarwal S. A comparative investigation on adsorption performances of mesoporous activated carbon prepared from waster rubber tire and activated carbon for a hazardous azo dye-Acid Blue 113. J Hazard Mater 2011;186(1):891–901. [4] Xiang L, Cheng J, Que GH. Microstructure and performance of crumb rubber modified asphalt. Constr Build Mater 2009;23(12):3586–90. [5] Yetkin Yildirim. Polymer modified asphalt binders. Constr Build Mater 2007;21(1):66–72. [6] Mo LT, Shu DL, Li X, Huurman M, Wu SP. Experimental investigation of bituminous plug expansion joint materials containing high content of crumb rubber powder and granules. Mater Des 2012;37:137–43. [7] Lee SJ, Akisetty CK, Amirkhanian SN. Recycling of laboratory-prepared longterm aged binders containing crumb rubber modifier. Constr Build Mater 2008;22(9):1906–13.
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[8]. December 18, 2008. [9] Huang Y, Bird RN, Heidrich O. A review of the use of recycled solid waste materials in asphalt pavements. Resour Conserv Recy 2007;52(1):58–73. [10] Dong DW, Huang XX, Li XL, Zhang LQ. Swelling process of rubber in asphalt and its effect on the structure and properties of rubber and asphalt. Constr Build Mater 2012;29:316–22. [11] Liu ST, Cao WD, Fang JG, Shang SJ. Variance analysis and performance evaluation of different crumb rubber modified (CRM) asphalt. Constr Build Mater 2009;23(7):2701–8. [12] Magdy AA. Engineering characterization of the interaction of asphalt with crumb rubber modifier (CRM). Sci Eng 1997;57(8):51–97. [13] Ruan Y, Davison RR, Glover CJ. Oxidation and viscosity hardening of polymermodified asphalt. Energy Fuels 2003;17(4):991–8. [14] Lu XH, Isacsson U. Effect of ageing on bitumen chemistry and rheology. Constr Build Mater 2002;16(1):15–22. [15] Siddiqui MN, Ali MF. Studies on the aging behavior of the Arabian asphalts. Fuel 1999;78(9):1005–15. [16] Wu SP, Pang L, Mo LT, Chen YC, Zhu GJ. Influence of Aging on the evolution of structure, morphology and rheology of base and sbs modified bitumen. Constr Build Mater 2009;23(2):1005–10. [17] Chai H, Xu XY, Lin YJ, Evans DG, Li DQ. Synthesis and UV absorption properties of 2, 3-dihydroxynaphthalene-6-sulfonate anion-intercalated Zn–Al layered double hydroxides. Polym Degrad Stabil 2009;94(4):744–9. [18] Zhang LY, Lin YJ, Tuo ZJ, Evans DG, Li DQ. Synthesis and UV absorption properties of 5-sulfosalicylate-intercalated Zn–Al layered double hydroxides. J Solid State Chem 2007;180(4):1230–5. [19] Ay AN, Zümreoglu-Karan B, Temel A, Mafra L. Layered double hydroxides with interlayer borate anions: a critical evaluation of synthesis methodology and pH-independent orientations in nano-galleries. Appl Clay Sci 2011;51(3):308–16. [20] Wu SP, Han J, Pang L, Yu M, Wang T. Rheological properties for aged bitumen containing ultraviolate light resistant materials. Constr Build Mater 2012;33:133–8. [21] Mohammadi Iman, Khabbaz Hadi. Challenges associated with optimisation of blending, mixing and compaction temperatures for asphalt mixture modified with crumb rubber modifier (CRM). Appl Mech Mater 2013;256– 259:1837–44. [22] JTG E20-2011. Standard test methods of bitumen and bituminous mixtures for highway engineering. Beijing: People’s Commuication Press; 2011. p. 21-33, 38–42. [23] Ouyang CF, Wang SF, Zhang Y, Zhang YX. Improving the aging resistance of asphalt by addition of zinc dialkyldithiophosphate. Fuel 2006;85(7– 8):1060–6. [24] Lu XH, Isacsson U. Chemical and rheological evaluation of ageing properties of SBS polymer modified bitumens. Fuel 1998;77(9–10):961–72. [25] Lamontagnea J, Dumas P, Mouillet V, Kister J. Comparison by Fourier transform infrared (FTIR) spectroscopy of different aging techniques: application to road bitumen. Fuel 2001;80(4):483–8. [26] Yu JY, Feng PC, Zhang HL, Wu SP. Effect of organo-montmorillonite on aging properties of asphalt. Constr Build Mater 2009;23(7):2636–40.
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Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of LDHs on the aging resistance of crumb rubber modified asphalt Ling Pang a,b, Kuangyi Liu a, Shaopeng Wu a,⇑, Min Lei b, Zongwu Chen a a b
State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China School of Sciences, Wuhan University of Technology, Wuhan 430070, China
h i g h l i g h t s LDHs improved the ageing resistance of crumb rubber modified asphalt (CRMA). LDHs present significant influences on properties of CRMA after UV aging. Less carbonyl groups appeared in the aged LDHs/CRMA than in the aged CRMA. LDHs modified CRMA has a better performance at both low and high temperatures.
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Crumb rubber modified asphalt Aging resistance Ultraviolet radiation aging LDHs
a b s t r a c t Layer double hydroxides (LDHs), a kind of ultraviolet light resistant material, was added into the Crumb Rubber Modified Asphalt (CRMA) and its effects on the aging resistance of the CRMA were investigated in this paper. The short-term and long-term aging processes of asphalt were simulated by Thin Film Oven Test (TFOT) and ultraviolet (UV) radiation test, respectively. With Fourier Transform Infrared Spectroscopy (FTIR) measurements, it was found that LDHs can slow down the formation of carbonyl groups during the aging process. The conventional physical properties test and Dynamic Shear Rheometer (DSR) test were used to evaluate the properties of the asphalt. The results showed that the softening point increases and G* ratios of CRMA decreases significantly, the ductility and the penetration retention rate increase after ultraviolet aging due to the introduction of LDHs. Besides, the results of both creep and relaxation test implied that the LDHs modified CRMA binder has a better UV aging resistance. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction With the development of motor transportation industry, the amount of discarded tires nearly reaches 10 million every year in the world [1]. A great number of waste rubber tires have caused serious environmental problems. Therefore, the utilization of waste rubber tires has attracted great interests of researchers in recent decades [2–4]. A lot of researches show that crumb rubber, made from waste rubber tires, can improve the temperature sensitivity, deformation resistance at high temperatures, crack resistance at low temperatures and fatigue resistance of asphalt as asphalt modifier. Therefore, the service life of crumb rubber modified asphalt (CRMA) pavement will be longer than unmodified ones [5–7]. In addition, CRMA can also reduce the traffic noise and improve the driving comfort [8]. So the utilization of waste crumb rubber as asphalt modifier is one of the most promising
⇑ Corresponding author. Tel./fax: +86 27 87162595.
ways to solve the problems caused by waste rubber tires considering the benefits of economy and environment [9]. Some researches on interaction mechanism of crumb rubber and base asphalt indicated that crumb rubber swells in asphalt by adsorbing the light components of asphalt [10–12]. However, just like other asphalt materials, the aging of CRMA during active time can induce the change of proportion of the components in the asphalt, the light components of asphalt volatilize, and micromolecules convert into large molecular size fractions by oxidation and polymerization [13–15]. The components of asphalt determine its properties, and the properties of CRMA binder are degraded with the decrease of light components and the structure destruction of asphalt [16], as a result, the CRMA pavement diseases take place. Therefore, it is important to improve the aging resistance of CRMA binder. LDHs have attracted a considerable attention as the UV light resistant materials to improve the properties of rubber, plastics, coating material in recent years. These layered materials are multi nestification layered structure. The inorganic layer sheets have the physical shield effect against UV light, and some metal elements of
E-mail address: [email protected] (S. Wu). 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.10.040
Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resistance of crumb rubber modified asphalt. Constr Build Mater (2013), http:// dx.doi.org/10.1016/j.conbuildmat.2013.10.040
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L. Pang et al. / Construction and Building Materials xxx (2013) xxx–xxx
layer sheets and negative ions between layer sheets will chemically absorb UV light. This kind of multi chemical absorbability and physical shield effect of LDHs result in excellent UV aging resistance in the organic material [17–19]. Wu et al. studied the effect of LDHs on the aging property of the asphalt and found that the LDHs can enhance the aging resistance of asphalt [20]. So, LDHs, as a kind of UV aging resistant materials, has the potential to improve the aging resistance of CRMA. In this paper, LDHs, were added into the CRMA at 0, 3, 5 wt% mass ratio, and the impact of the LDHs on the aging resistance of CRMA was investigated. Thin film oven (TFOT) test and UV light accelerated aging process were used to simulate the short-term aging and long-term field aging of asphalt, respectively. The rheological properties of asphalt before and after artificial UV aging were investigated by using Dynamic Shear Rheometer (DSR) through temperature sweep, creep tests and relaxation test. FTIR test result, conventional physical properties, complex modulus ratio, creep and relaxation curve of asphalt were used to evaluate the chemical and physical characteristics of asphalt before and after artificial UV aging.
2. Materials and experimental
2.4. Characterization methods 2.4.1. FTIR A Thermo Nicolet Model Nexus FTIR–Raman spectrophotometer was used to record FTIR spectra of rubber asphalt. A sample was prepared by casting an asphalt film onto a KBr thin plate from 5 wt% solution in carbon disulfide, then the solvent was dried for the FTIR analysis. 2.4.2. Conventional physical properties test The conventional physical properties tests including penetration, ductility, softening points and some other property indexes. They were conducted according to Chinese standard test methods of bitumen and bituminous mixtures for highway engineering JTG E20-2011. 2.4.3. DSR A MCR101 Dynamic Shear Rheometer (DSR) produced by Anton Paar Company was adopted to measure the rheological property of CRMA and LDHs/CRMA. DSR temperature sweep test was performed under the strain-controlled mode at a constant frequency of 10 rad/s. The tests were performed within the linear viscoelastic range of the tested asphalts. When the test temperature is higher than 30 °C, 25 mm diameter plates with 1 mm gap were used. When the test temperature is lower than 30 °C, 8 mm diameter plates with 2 mm gap were used. Furthermore, creep testing and relaxation testing were also used to evaluate the aging resistance of CRMA and LDHs/CRMA.
3. Results and discussion
2.1. Materials
3.1. FTIR characterization analysis
The CRMA used in this paper was provided by Hubei Guochuang Hi-tech Material Co., Ltd. The diameter of crumb rubber power modifier was smaller than 0.3 mm and the content was 15% by weight. The basic properties of CRMA are exhibited in Table 1. Mg–Al layered double hydroxides complex metallic material was used to modify the CRMA. The LDHs was produced by Rui Fa Chemical Company Limited, Jiang Su, China. The density of the LDHs was 1.7 g/cm3 and the moisture content was less than 0.3%.
2.2. Preparation of LDHs modified asphalt Many researchers suggested the blending temperature of crumb rubber and base asphalt should be more than 160 °C and less than 200 °C [21]. In China, the most commonly used blending temperature for CRMA is 175–185 °C. Although this temperature range may lead to the degradation of base asphalt, it is good for the swelling process of crumb rubber. Therefore, LDHs was blended into CRMA binder using a shear blender at 180 °C in this research. The rotation speed of the blender was 5000 r/min and 60 min of blending was used to ensure a good distribution of LDHs. The CRMA without LDHs was also processed under the same conditions as the reference group.
2.3. Aging procedures TFOT was employed to simulate the short-term oxidation that occurs during the hot-mix process according to Chinese standard test methods of bitumen and bituminous mixtures for highway engineering JTG E20-2011(T0609-2011) [22]. After TFOT aging, the asphalt samples with film thickness of 1 mm were prepared for further UV aging to simulate the photodegradation that occurs during the service life. The UV aging performed on the asphalt samples lasted for 10 days in a UV light accelerated aging oven, the radiation strength of the UV light was set at 26.5 W/ m2 with the wavelength of 360 nm, and the test temperature was controlled at 60 °C.
Table 1 Properties of base asphalt and CRMA. Index
Base asphalt
CRMA
Specification
Penetration at 25 °C (0.1 mm) Ductility of base asphalt at before TFOT 15 °C, CRMA at 5 °C (cm) after TFOT Softening point (°C) Education, softening point difference (°C) Elasticity resume at 25 °C (%)
72 65
51 12
T0604-2011 T0605-2011
19 44.5 –
8.5 68 2
T0605-2011 T0606-2011 T0661-2011
–
79
T0662-2000
FTIR was applied to study the effect of LDHs on the aging resistance of the CRMA. The aging of asphalt includes thermal oxygen and light oxygen aging. The occurrence of carbonyl groups is the result of the oxidation aging of base asphalt. According to the precious research, the carbonyl (C@O) index can be used as an indicator to evaluate the aging extent of asphalt [23,24]. It was computed as the following formula [25]:
Area of the carbonyle band centered around 1700 cm1 IC@O ¼ P Area of the spectral bands between 2000 and 600 cm1 The FTIR spectrums of asphalts without aging and asphalts with UV aging were shown in Fig. 1. As an indicator of the aging extent, the corresponding functional groups indices were listed in Table 2. Fig. 1 shows no obvious absorbance peak can be observed for asphalts without aging, while carbonyl clearly appeared after UV aging for 10 days. The intensity of carbonyl absorption peaks of LDHs/CRMA were lesser than that of CRMA. Table 2 shows more details about these changes discussed above. The carbonyl index of CRMA is 0.013, larger than that of LDHs/CRMA after UV aging for 10 days, which means less carbonyl groups formation after the introduction of LDHs, indicating that LDHs modified asphalts had better resistant to the formation of carbonyl and hence might getting more stable. Therefore, the LDHs can improve the aging resistance of CRMA binder. 3.2. Conventional physical properties Figs. 2–4 showed the conventional properties test results of CRMA and LDHs/CRMA before and after aging. It is obvious that LDHs provide increased soft points and decreased penetration of CRMA before UV aging, therefore LDHs is good for deformation resistance of asphalt at high temperatures although it degrades the ductility of CRMA slightly. After subjected to UV aging, there would be a great difference in conventional properties, the softening points decreased, the penetration and ductility increased with the addition of LDHs, especially when 5 wt% of LDHs was added. Table 3 lists the softening point increment, ductility retention rate and penetration retention rate after UV aging using original values as references. The softening point increment, ductility retention rate and penetration retention rate can be used to evalu-
Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resistance of crumb rubber modified asphalt. Constr Build Mater (2013), http:// dx.doi.org/10.1016/j.conbuildmat.2013.10.040
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0.4
14 CRMA
CRMA-UV
3%LDHS/CRMA
3%LDHS/CRMA-UV
5%LDHS/CRMA
5%LDHS/CRMA-UV
0.3
UV
10
Ductility (cm)
Absorbance
Fresh
12
1700cm-1
0.2
8 6 4
0.1
2 0 CRMA
0 600
800
1000
1200
1400
1600
1800
3%LDHs/CRMA
5%LDHs/CRMA
2000 Fig. 4. Ductility of asphalts at 5 °C.
Wavenumber (cm-1) Fig. 1. FTIR analysis of asphalts before and after aging.
Table 2 FTIR absorbance indices of asphalts after UV aging for 10 days. Asphalt
CRMA–UV
3% LDHs/CRMA–UV
5% LDHs/CRMA–UV
Carboyl index
0.013
0.009
0.008
ductility retention rate and penetration retention rate compared to the CRMA, indicating LDHs can significantly improve the aging resistance of CRMA. Compared with CRMA, properties of CRMA/ LDHs was much retained after UV aging, which indicated the LDHs/CRMA had better UV aging resistance than CRMA. 3.3. Temperature sweep test
60 Fresh
UV
Penetration (0.1mm)
50 40 30 20 10 0 CRMA
3%LDHs/CRMA
5%LDHs/CRMA
Fig. 2. Penetration of asphalts at 25 °C.
100 Fresh
90
UV
Softening point (°C)
80 70
The temperature sweep conducted by DSR can characterize the variation of complex modulus and phase angle of asphalt in a wide range of temperature. Figs. 5 and 6 respectively showed the complex modulus and phase angle of CRMA and LDHs/CRMA before and after aging, and also showed the effect of LDHs on the aging resistance. The complex modulus (G*) of LDHs/CRMA was higher and phase angle was smaller than that of CRMA at all test temperatures before aging. It means that the addition of LDHs increased the G* and reduced the phase angle. The increase of G* and the decrease of phase angle caused by aging, which induced more solidlike and hardening [23]. However, after UV aging for 10 days, the G* and phase angle curve of all asphalts tended to get closer with the deepened aging of asphalts, but the G* of LDHs/CRMA was lower and phase angle was higher than that of CRMA. This means that the LDHs/CRMA binder suffered less hardening and it was more viscous than CRMA. Table 4 displays the G* ratios at different temperatures using original modulus as reference value. From Table 4, it can be seen that the G* ratios of 3% and 5% LDHs modified asphalts were lower than that of CRMA after UV 10 days. The more the G* value of asphalt increase, the more aging the asphalts suffer. So, the aging degree of the LDHs modified asphalt was not as serious as CRMA. It implied that the addition of LDHs improved the aging resistance of CRMA.
60
3.4. Creep and relaxation test 50
The effect of LDHs modifier on the aging properties of CRMA binder was also studied by shear creep test. Fig. 7 gave the creep strain response curve of CRMA and LDHs/CRMA. The creep testing was conducted at 60 °C by DSR. A constant shear stress of 5 Pa was
40 30 20 10 0
CRMA
3%LDHs/CRMA
5%LDHs/CRMA
Fig. 3. Softening points of asphalts.
ate the aging resistance [26]. According to Table 3, the 3% and 5% LDHs/CRMA exhibited lower softening point increment, higher
Table 3 The softening point increment, ductility and penetration retention rate after UV aging for 10 days. Asphalt
CRMA
3% LDHs/CRMA
5% LDHs/CRMA
Softening point increment (°C) Ductility retention rate (%) Penetration retention rate (%)
11.0 41.7 64.7
8.5 46.4 72.9
7.0 55.6 76.6
Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resistance of crumb rubber modified asphalt. Constr Build Mater (2013), http:// dx.doi.org/10.1016/j.conbuildmat.2013.10.040
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10
120
CRMA
3%LDHs/CRMA
5%LDHs/CRMA 3%LDHs/CRMA-UV
CRMA-UV 5%LDHs/CRMA-UV
8
Creep strain (%)
Complex modulus (MPa)
160
80
CRMA
CRMA-UV
3%LDHs/CRMA
5%LDHs/CRMA
3%LDHs/CRMA-UV
5%LDHs/CRMA-UV
6 4
40 2 0 -10
-5
0
5
10
15
20
25
0
30
0
100
200
Temperature (°C)
300
400
500
Time (s)
Fig. 5. Complex modulus curves of asphalts before and after aging.
Fig. 7. Creep strain curve at 60 °C.
60 CRMA 5%LDHs/CRMA 3%LDHs/CRMA-UV
1.E+05
3%LDHs/CRMA CRMA-UV 5%LDHs/CRMA-UV
1.E+05
Shear stress (Pa)
Phase angle (°)
50
40
30
CRMA
3%LDHs/CRMA
5%LDHs/CRMA
CRMA-UV
3%LDHs/CRMA-UV
5%LDHs/CRMA-UV
8.E+04 6.E+04 4.E+04
20 -10
2.E+04 0 -5
0
5
10
15
20
25
30
50
100
150
200
250
300
Time (s)
Temperature (°C) Fig. 8. Stress relaxation curves at 5 °C. Fig. 6. Phase angle curves of asphalts before and after aging.
applied and the creep strain of asphalts was recorded during 100 s of the loading stage and 400 s of the unloading stage. As indicated in Fig. 7, the total creep strain of LDHs/CRMA was lower than that of CRMA binder before aging, which indicates that the introduction of LDHs increases the resistance to creep of CRMA at high temperatures. After UV aging for 10 days, the total creep strains of asphalts were lower than that of asphalts without UV aging, however among asphalts of having suffered UV aging, the total creep strains increased with the addition of LDHs, which indicates that LDHs can lower hardening of CRMA when subjected to UV aging, therefore the aging resistance of LDHs/CRMA is superior to CRMA. The shrinkage stress of asphalts with aging is higher than that of ones without aging, because the aging process has hardened asphalts. It is well known that the pavement will crack when the shrinkage stress is higher than the tensile strength. The shear relaxation testing was used to evaluate the low temperature performance of asphalt with the application of DSR instrument under strain-controlled model. The applied shear strain level was kept to 5%. Fig. 8 presented the relaxation test results of CRMA and LDHs/ CRMA before and after aging at 5 °C. It indicated that the
Table 4 G* ratio of asphalts after UV aging for 10 days. Asphalts
CRMA 3% LDHs/CRMA 5% LDHs/CRMA
G* ratio 10 °C
0 °C
10 °C
20 °C
30 °C
1.36 1.17 1.05
1.43 1.18 1.05
1.58 1.27 1.12
1.69 1.40 1.20
1.60 1.48 1.26
inclusion of LDHs into CRMA resulted in a higher shear stress, mainly because LDHs enhanced the elasticity of CRMA. Compared to CRMA, the shear stress of the LDHs/CRMA was lower after UV aging, especially 5% LDHs/CRMA had the lowest shear stress. The results implied that LDHs can lower hardening of CRMA with the addition of LDHs during aging process. Therefore LDHs can improve the UV aging resistance of CRMA. The reason why aged LDHs/CRMA had a lower shear stress is that LDHs could retard the oxidation of asphalt through the multi chemical absorbability and physical shield effect, slowing down the reduction of viscous component during the aging process. The more the viscous component, the better the low temperature property is. 4. Conclusions In this research, LDHs was added into the CRMA binder and the effects of LDHs on the UV aging resistance of the CRMA were investigated by means of FTIR analysis, conventional physical properties test and DSR test. Based on these test results, the following conclusions can be drawn: (1) The carbonyl groups, occurred after UV aging, was used as an aging index to evaluate the effect of LDHs on the aging resistance of CRMA. It was found that less carbonyl groups appeared in the aged LDHs/CRMA than in the aged CRMA, indicating that the CRMA binder would get less sensitive to UV aging when LDHs was introduced. (2) LDHs stiffened CRMA by increasing its softening points and decreasing its penetration. However, the softening point increment of LDHs/CRMA decreased and the penetration and ductility retention rate increased after UV aging, which
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L. Pang et al. / Construction and Building Materials xxx (2013) xxx–xxx
implied that LDHs can lower hardening speed of CRMA when subjected to UV aging. Therefore LDHs can improve the UV aging resistance of CRMA. (3) The G* ratio of LDHs/CRMA was lower and phase angle was higher than that of CRMA after aging. It means that the LDHs/CRMA binder suffered less hardening and it was more viscous than CRMA after UV aging. (4) The results of creep and relaxation test also supported the conclusions that LDHs can slow down the hardening speed of CRMA when subjected to UV aging. Therefore LDHs can improve UV aging resistance of CRMA and it can slow down the degradation of CRMA when LDHs/CRMA was subjected to UV aging.
Acknowledgements This work is supported by the Ministry of Science and Technology of China (2011BAE28B03) and the National Instrumentation Program (2013YQ160501). The authors gratefully acknowledge their support. References [1] Yu QX. The recycling and reuse of waste tire worldwide. World Rubber Ind 2010;37(2):50–4. [2] Zhang SL, Zhang ZX, Xin ZX, Pal K, Kim JK. Prediction of mechanical properties of polypropylene/waste ground rubber tire powder treated by bitumen composites via uniform design and artificial neural networks. Mater Des 2010;31(4):1900–5. [3] Gupata VK, Gupata B, Rastogi A, Agarwal S. A comparative investigation on adsorption performances of mesoporous activated carbon prepared from waster rubber tire and activated carbon for a hazardous azo dye-Acid Blue 113. J Hazard Mater 2011;186(1):891–901. [4] Xiang L, Cheng J, Que GH. Microstructure and performance of crumb rubber modified asphalt. Constr Build Mater 2009;23(12):3586–90. [5] Yetkin Yildirim. Polymer modified asphalt binders. Constr Build Mater 2007;21(1):66–72. [6] Mo LT, Shu DL, Li X, Huurman M, Wu SP. Experimental investigation of bituminous plug expansion joint materials containing high content of crumb rubber powder and granules. Mater Des 2012;37:137–43. [7] Lee SJ, Akisetty CK, Amirkhanian SN. Recycling of laboratory-prepared longterm aged binders containing crumb rubber modifier. Constr Build Mater 2008;22(9):1906–13.
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Please cite this article in press as: Pang L et al. Effect of LDHs on the aging resistance of crumb rubber modified asphalt. Constr Build Mater (2013), http:// dx.doi.org/10.1016/j.conbuildmat.2013.10.040