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Effect of warm mixture asphalt (WMA) additives on high failure temperature properties for crumb rubber modified (CRM) binders
Construction and Building Materials 35 (2012) 281–288
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Effect of warm mixture asphalt (WMA) additives on high failure temperature properties for crumb rubber modified (CRM) binders Hainian Wang a,⇑, Zhengxia Dang a,1, Zhanping You b,2, Dongwei Cao c,3 a
Highway School, Chang’an University, South Erhuan Middle Section, Xi’an, Shanxi 710064, China Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, United States c Research Institute of Highway Ministry of Transport, Beijing 100088, China b
a r t i c l e
i n f o
Article history: Received 16 January 2012 Received in revised form 7 April 2012 Accepted 16 April 2012
Keywords: Rubber asphalt Warm mixture asphalt additive Rheological property Dynamic shear rheometer Complex modulus
a b s t r a c t This paper investigates the effect of three warm mixture asphalt (WMA) additives on the high temperature rheological properties of both unaged and rolling thin film oven (RTFO) aged crumb rubber modified (CRM) binders. The WMA additives used in this study include Sasobit, RH and Advera. The ambient 40-mesh tire rubber with the concentrations of 10%, 15%, 20%, and 25% by the weight of asphalt binder, respectively, was used in this study. Dynamic shear rheometer (DSR) was employed to measure the complex modulus (G⁄) and phase angle (d) of CRM binders at various testing temperatures. The statistical analysis of variance (ANOVA) was applied to quantify the effects of WMA additives on the CRM binders’ rutting resistance properties. It was found in this study that, the three WMA additives could all improve the CRM binders’ resistance to rutting, and greatly improved high-temperature portion of the performance grade (PG) of CRM binders. It is found that Sasobit had the most remarkable effect on G⁄ of both unaged and RTFO-aged CRM binders, RH only had significant effect on G⁄ of RTFO-aged binders, Advera’s effect was indistinctive. Furthermore, WMA additives’ effect on d was not conclusive. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction 1.1. Background Tire rubber is widely used as an environmental friendly material with good performance in pavement engineering since Charles McDdonald employed the dry processes to produce a rubberized asphalt mixture called Overflex TM 60 years ago [1–3]. There are many benefits from applying crumb rubber modified (CRM) binders into asphalt pavements, such as reducing the thickness of asphalt overlays but increasing pavement life, decreasing traffic noise and maintenance costs, increasing resistance to rutting and cracking [4–7]. For this reason, CRM binders attract more and more attentions recently. Rutting is one of the main pavement distresses mainly due to traffic loading, especially under hot climatic conditions. In Superpave binder testing procedure, dynamic shear rheometer (DSR) can comprehensively consider the two factors and is adopted to characterize the rheological properties of asphalt binders at intermediate to high temperatures. Since the rheological property ⇑ Corresponding author. Tel.: +86 29 82334798; fax: +86 29 82334824. E-mail addresses: [email protected] (H. Wang), zhaofengwuying@ 163.com (Z. Dang), [email protected] (Z. You), [email protected] (D. Cao). 1 Tel.: +86 29 82334824. 2 Tel.: +1 906 487 1059. 3 Tel.: +86 13910287728. 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.04.004
of asphalt binder has been applied by many researchers to evaluate the rheological properties of rubber asphalt [8–10]. It is found that adding crumb rubber into binders can significantly increase the rutting resistance parameter, which meant a better resistance of high temperature susceptibility than the unmodified binders. Meanwhile, the rutting resistance parameters of CRM binders improved as the CRM percentage increased. Compared with cryogenic CRM binders, the ambient CRM was found to be a better modifier in producing the CRM binder, which was less sensitivity to rutting at high pavement temperature [11–13]. Wang et al. tested the CRM binder viscosity at different high temperatures using rotational viscosity. It was found that the addition of crumb rubber can greatly increase the binder viscosity, and the temperature need to rise to 147 °C, 162 °C and 174 °C for 15%, 20% and 25% rubber asphalt ratio binders to meet the 3 Pa s requirement respectively, in Superpave specification [14]. Therefore the mixing temperatures and compaction temperatures of rubberized asphalt binders were much higher than those of ordinary asphalt mixtures, then caused some problems in the construction schedule [15]. The ‘‘warm mixture asphalt’’ (WMA) refers to the technologies which allow a considerable reduction of mixing and compaction temperatures of asphalt mixes through lowing the viscosity of asphalt binders by use of organic additives, chemical additives, or foaming processes. If the technologies are incorporated well with CRM binders, it can produce rubberized asphalt mixtures with good properties. In recent years, the rheological properties of
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asphalt binders at intermediate or high temperature effect on rubberized WMA binders attract more and more focus. For example, studies found a further enhancement of softening point after adding Sasobit into CRM binder [16]. AKisetty applied the DSR to determine the high failure temperature for each rubberized WMA binders (the WMA additives were Aspha-min and Sasobit) both in the original state and after short-term aging in the rolling thin film oven (RTFO). It was also predicted that the rubberized binders containing the inorganic additive had better rutting resistance compared with the control CRM binders. In addition, the difference of failure temperature values between rubberized binders with Aspha-min and Sasobit was not significant at the 5% level within each binder source [17]. Previous studies focused more on the rheological property of CRM binders, but there are very limited work done on rubberized WMA binders. Since the implementation of SHRP, the DSR has been widely used for the determination of rutting resistance parameter as well as the high failure temperature of the binder. Results obtained from the DSR are vital to pavement performance when determining its resistance to rutting. As the WMA additives types and rubber concentrations are various in different studies, their modifying effects on the rheological properties of rubberized WMA binders are different. However there is no comprehensive study in comparing the rheological property of unaged and RTFO-aged rubberized WMA binders with different additives types. Considering the technical and economic issues, how to select a suitable warm mix asphalt additive for CRM binders from great varieties is worthy for further study.
Table 1 The properties of virgin asphalt. Aging states
Test properties
Test results
Unaged binders
Rotational viscosity@ 135 °C (Pa s) G⁄/sin d @ 64 °C (kPa) G⁄/sin d @ 64 °C (kPa) G⁄sin d @ 25 °C (kPa) Stiffness @ 12 °C (mPa) m-value @ 12 °C
0.435 1.367 3.906 1171 187 0.316
RTFO aged residue RTFO + PAV aged residue
Table 2 Crumb rubber properties (by weight of crumb rubber). Crumb rubber
40 mesh (0.425 mm) (%)
Specific gravity Moisture content Ash content Carbon black content Acetone content Fibre content Sulfur content
1.165 0.67 5.42 31.98 5.62 0.01 1.47
Sasobit, RH and Advera, then artificially short-term aged using RTFO procedure [18]. The complex modulus (G⁄) and phase angle (d) for the rubberized WMA binders in the original state and after RTFO-aged process were evaluated. Fig. 1 shows a flow chart of the experimental design used in this study. 2. Materials and test program 2.1. Materials
1.2. Objective and scope The main objective of this study is to evaluate the effects of WMA additives on high temperature properties via selected Superpave binder tests. The CRM binders were produced in the laboratory incorporating one CRM source (ambient) and four CRM percentages (10%, 15%, 20% and 25% by the weight of asphalt binder) into one base binder. The rubberized WMA binders were manufactured with and without three different WMA additives:
2.1.1. Asphalt binders The Superpave performance grade (PG) 64–22 virgin asphalt taken from a Detroit construction site in Michigan was used in this study. Table 1 shows the properties of the PG 64–22 binders. 2.1.2. Crumb rubber modifier (CRM) The CRM produced by mechanical shredding at the ambient temperature was obtained from one source: 40 mesh (0.425 mm), and came from Beijing, China. The rubber characteristics are given in Table 2. Four rubber concentrations, 10%, 15%, 20% and 25% by weight of asphalt binder, were used in this study, and the CRM binders were used as the control binders.
PG 64-22 Asphalt binders
Rubber modified asphalt
15%
10%
25%
20%
WMA additives
Control CRM binders
unaged
RTFO
DSR @ 76, 70, 64, 58, 52ºC
DSR @ 76, 70, 64, 58, 52ºC
2%Sasobit
4%RH
same testing procedures as 5%Advera rubberized warm asphalt binders
same testing procedures as 5%Advera rubberized warm asphalt binders
5%Advera
unaged
RTFO
DSR @ 82,76, 70, 64, 58, 52ºC
DSR @ 82, 76, 70, 64, 58, 52ºC
Fig. 1. Flow chart of experimental design procedures.
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Fig. 2. The three WMA additives.
60 40 20 0
35
G* at 10rad/ s (kPa)
60
G* at 10rad/s (kPa)
80
The control binder Sasobit RH Advera
30 25
10%
15%
20%
50
30 20 10 20%
25%
(a)
(b) 18
The control binder Sasobit RH Advera
10 5 10%
15%
20%
The control binder Sasobit RH Advera
15 12 9 6 3
0
0
25%
10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(c)
(d)
The control binder Sasobit RH Advera
G* at 10rad/s (kPa)
G* at 10rad/s (kPa)
15%
Crumb rubber concentration
15
6
10%
Crumb rubber concentration
20
8
The control binder Sasobit RH Advera
40
0
25%
G* at 10rad/s (kPa)
G* at 10rad/s (kPa)
100
4
2
3
Sasobit RH Advera
2
1
0
0 10%
15%
20%
25%
10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(e)
(f)
Fig. 3. G⁄ values of unaged warm rubberized asphalt binders at different temperatures (a) 52 °C; (b) 58 °C; (c) 64 °C; (d) 70 °C; (e) 76 °C; (f) 82 °C. 2.1.3. WMA additives Sasobit, RH and Advera were selected as the available commercial WMA additives in producing the rubberized WMA binders. Fig. 2 shows the three WMA additives in the laboratory. RH, as a WMA additive, is a kind of white powder developed in China. In addition, the percentages used (by rubberized asphalt binders weight) of warm mix asphalt additives were generally based on the recommendations by the manufactures. As a result, 2% Sasobit, 4% RH, and 5% Advera were blended with rubberized asphalt binders in this research.
2.2. Production of rubberized WMA binders There are two major processes: the wet and dry processes when using recycled tires to produce rubberized asphalt mixtures. The wet process defines any method that adds CRM to asphalt, which is then well blended and interacted at high temperature under high agitation before incorporating the modified binder into the mix. The dry process defines any method which adds CRM directly into the hot mixture asphalt (HMA) [19,20].
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60
Sasobit
80
G* at 10rad/s (kPa)
G* at 10rad/s (kPa)
The control binder RH Advera
60 40 20
50
The control binder Sasobit RH Advera
40 30 20 10 0
0 10%
20%
25%
20%
25%
(a)
(b) 20
20
10
16
10%
15%
20%
The control binder Sasobit RH Advera
12 8 4
0
0
25%
10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(c)
(d)
8
G* at 10rad/s (kPa)
The control binder Sasobit RH Advera
10
G* at 10rad/s (kPa)
15%
Crumb rubber concentration
G* at 10rad/s (kPa)
30
10%
Crumb rubber concentration
The control binder Sasobit RH Advera
40
G* at 10rad/s (kPa)
15%
6 4 2
4
Sasobit RH Advera
3 2 1 0
0 10%
15%
20%
25%
10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(e)
(f)
Fig. 4. G⁄ values of RTFO- aged warm rubberized asphalt binders at different temperatures (a) 52 °C; (b) 58 °C; (c) 64 °C; (d) 70 °C; (e) 76 °C; (f) 82 °C.
Table 3 The WMA additives’ ANOVA on G⁄ of unaged CRM binders. Source
0 1 2 3
Binders (temperature < 64 °C)
Binders (temperature > 64 °C)
0
1
2
3
0
1
2
3
–
S –
N S –
N S N –
–
S –
S S –
S S N –
N: non-significant; S: significant. Rubberized WMA binders 0: Control; 1: Sasobit; 2: RH; 3: Advera. The significance level is 0.05.
The wet process was applied to modify the asphalt in this paper. The rubberized binder was produced in the laboratory at 350 °F (177 °C) for 30 min by an open blade mixer at a blending speed of 700 rpm [21,22]. The percentage of crumb rubber added for the CRM binders were 10%, 15%, 20% and 25% by weight of the based asphalt binder. As the moisture content of the crumb rubber in Table 2 was extremely small, only 0.67% by weight of crumb rubber, it did not need to
dry the rubber powders before blending with virgin binder. Then added WMA additives: Sasobit, RH and Advera into the binders followed by mixing with a shear mixer for 5 min to achieve consistent mixing [23]. The specified concentrations of the additives were 2%, 4%, and 5% by weight of the mixture respectively. The rubberized WMA binders were then artificially short-term aged through (RTFO) aging process for 85 min at 163 °C [18]. 2.3. Superpave binder tests In this study each rubberized WMA binder sample (both unaged and RTFO aged) were tested with DSR (AASHTO T 315: with the plate gap adjusted to 2 mm) to evaluate its high temperature properties [24]. For the CRM binders without WMA additives, the DSR test was operated at five different temperature conditions: 52 °C, 58 °C, 64 °C, 70 °C and 76 °C, and the temperatures were 52 °C, 58 °C, 64 °C, 70 °C, 76 °C, and 82 °C for the rubberized WMA binders. All the DSR tests were carried out in accordance with ASHTO T 315. The high-temperature portion of the PG grade is determined by measuring the temperature at which the unaged and RTFO-aged asphalt binder’s G⁄/sin d values are at least 1.0 kPa and 2.2 kPa, respectively, when measured at a frequency of 10 radian per second (rad/s) [25]. G⁄ represents the total resistance to deformation un-
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H. Wang et al. / Construction and Building Materials 35 (2012) 281–288 Table 4 The WMA additives’ ANOVA on G⁄ of RTFO-aged CRM binders. Source
0 0 0 1 1 2
VS VS VS VS VS VS
1 2 3 2 3 3
RTFO-aging rubberized warm asphalt F
P-value
36.696 34.305 0.7633 11.242 24.535 8.2596
7.9453 10 1.2179 10 0.3932 0.00275 5.2368 10 0.00857
F crit 6
4.3807 4.3807 4.3807 4.2793 4.2793 4.2793
5
5
tween an in-phase component and an out-of-phase component. The in-phase component is an elastic component and can be related to energy stored in a sample for every loading cycle, while the out-of-phase component represents the viscous component and can be related to energy lost per cycle in permanent flow. The relative distribution of these components is a function of the composition of the material, loading time and temperature. When the value of d is 0°, it represents the completely elastic nature of the binders, while the d value approach 90° for all binders, it reflects the approach to complete viscous behavior.
3. Results and discussions
der dynamic loading. It reflects that the higher rigidity is favorable at high temperatures for the rubberized WMA binder. Usually as the temperature increases or the frequency decreases, G⁄ decreases continuously, which reflects a decrease in resistance to deformation. The elasticity of the rubberized WMA binders may be measured with d. To resist rutting and fatigue damage, more elasticity is favorable at high temperatures. d represents the relative distribution of this total response be-
The influence of different WMA additives on the G⁄ values of rubberized WMA binders with different crumb rubber concentrations is discussed in this section. Figs. 3 and 4 show the G⁄ values measured by the DSR tests at different temperatures for both the unaged and RTFO-aged rubberized WMA binders with different crumb rubber concentrations, respectively.
76
The control binder Sasobit RH Advera
72 68 64 60 56 52 10%
15%
20%
25%
Phase angle at 10rad/s (degree)
3.1. High temperature complex shear modulus (G⁄)
Phase angle at 10rad/s (degree)
F: the F value; F crit, the F critical value. Rubberized WMA binder 0: Control; 1: Sasobit; 2: RH; 3: Advera. The significance level (a) is 0.05.
76
The control binder Sasobit RH Advera
72 68 64 60 56 52 10%
15%
The control binder Sasobit RH Advera
72 68 64 60 56 52 10%
15%
20%
25%
80
The control binder Sasobit RH Advera
76 72 68 64 60 56 52 10%
Crumb rubber concentration
15%
70 65 60 55 10%
15%
20%
25%
Crumb rubber concentration
(e)
Phase angle at 10rad/s (degree)
Phase angle at 10 rad/s (degree)
75
25%
(d) The control binder Sasobit RH Advera
80
20%
Crumb rubber concentration
(c) 85
25%
(b) Phase angle at 10rad/s (degree)
Phase angle at 10rad/s (degree)
(a) 76
20%
Crumb rubber concentration
Crumb rubber concentration
Sasobit RH Advera
85 80 75 70 65 60 55 50
(f) 10%
15%
20%
25%
Crumb rubber concentration
(f)
Fig. 5. d values of unaged warm rubberized asphalt binders at different temperatures (a) 52 °C; (b) 58 °C; (c) 64 °C; (d) 70 °C; (e) 76 °C; (f) 82 °C.
H. Wang et al. / Construction and Building Materials 35 (2012) 281–288
Phase angle at 10rad/s (degree)
Fig. 3 indicated that as expected, the G⁄ values of all kinds of unaged CRM binders (with or without additives) decreased when the DSR temperature rose at any rubber concentration, meaning that the resistance to deformation under dynamic loading would decline continually as the testing temperature rose constantly. However, with increasing percentage of crumb rubber, the unaged binder’s G⁄ increased significantly at each test temperature. Take the rubberized WMA binder with Sasobit tested at 70 °C for example, when the concentration changed from 10% to 15, 15% to 20%, 20% to 25%, the G⁄ could increased to 169%, 163% and 132% respectively. Furthermore, a general trend was found from the result that the addition of Sasobit into CRM binders greatly increased the binders’ rigidity at high temperatures, when compared with the control CRM binders. The most remarkable effect was that when the CRM percentage was 25%, the G⁄ values of rubberized WMA binder with Sasobit increased 136% and 134% at 70 °C and 76 °C respectively by the control CRM binder. However, when the test temperature was lower than 64 °C, RH and Advera had no significant influence on the resistance to deformation of CRM binders. Compared to the control CRM binders, the G⁄ decreased or increased with different CRM T he control binder Sasobit RH A dvera
68 64 60 56 52 10%
15%
20%
25%
concentrations at different temperatures when added RH and Advera into CRM binders. Therefore, it was quite difficult to find a regular result for all rubberized WMA binders with RH and Advera. Moreover, when the test temperature was higher than 64 °C, RH and Advera could enhance the G⁄ values at different crumb rubber concentrations, even the CRM binder’ G⁄ with RH was higher than it with Sasobit when the test temperature was 82 °C and the crumb rubber concentrations was 10% and 15%. This indicated that there was no significant effect on G⁄ values of CRM binders for RH and Advera when the temperatures were lower than 64 °C, however, the two WMA additives played a positive role as the temperature rose for the unaged CRM binders. As shown in Fig. 4, at the same temperature, crumb rubber concentration and WMA additive, RTFO-aged binder had a higher G⁄ in comparison to unaged binder. Furthermore, the RTFO-aged binders with Sasobit and RH both had higher rigidity than the control RTFO-aged binders, as the two additives could increase the binders’ G⁄ at any rubber concentration and test temperature. Take the binder with 25% rubber concentration and tested at 76 °C as an example, the G⁄ of the rubberized WMA binder with Sasobit and
Phase angle at 10rad/s (degree)
286
T he control binder Sasobit RH A dvera
64 60 56 52 48 10%
Crumb rubber concentration
15%
60 56 52 10%
15%
20%
25%
Phase angle at 10rad/s (degree)
T he control binder Sasobit RH A dvera
64
25%
(b) T he control binder Sasobit RH A dvera
68 64 60 56 52 10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(c)
(d)
72
T he control binder Sasobit RH A dvera
68 64 60 56 52 10%
15%
20%
25%
Phase angle at 10rad/s (degree)
Phase angle at 10 rad/s (degree)
Phase angle at 10rad/s (degree)
(a) 68
20%
Crumb rubber concentration
76
Sasobit RH A dvera
72 68 64 60 56 52 10%
15%
20%
25%
Crum rubber concentration
Crumb rubber concentration
(e)
(f)
Fig. 6. d values of RTFO-aged warm rubberized asphalt binders at different temperatures (a) 52 °C; (b) 58 °C; (c) 64 °C; (d) 70 °C; (e) 76 °C; (f) 82 °C.
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100
the control Sasobit RH Advera
88
94
o
94
Failure Temperature ( C)
o
Failure Temperature ( C)
100
82 76 70 64
88
the control Sasobit RH Advera
82 76 70 64 58
58
52
52 1
2
3
4
Crumb Rubber Concentration
10%
15%
20%
25%
Crumb Rubber Concentration
(a)
(b)
Fig. 7. Failure temperature of all CRM binders with different WMA additives (a) the unaged binders; (b) the RTFO-aged binders.
RH were 134% and 48% higher than that of the control RTFO-aged binders respectively. Nevertheless, for rubberized WMA binders, Sasobit typically had a greater enhancement on CRM binder’s resistance to deformation than RH. Similar to unaged rubberized WMA binders, Advera had no consistent influence on RTFO-aged rubberized WMA asphalt binder’s G⁄ at any temperature and crumb rubber concentration when compared with the control CRM binder. When the test temperature was lower than 64 °C, the addition of RH could enhance or weaken the high failure temperature properties of RTFO-aged rubberized WMA binders. But when the temperature rose, compared with the control CRM binders, binders with RH had higher G⁄ values. It can also be found from Fig. 4 that when refer to the influence of rubber concentration on different CRM binders containing or not containing additives, conclusions came different. The G⁄ could be improve constantly as the rubber concentration increased for binders with Sasobit. However the phenomenon didn’t exist in the control CRM binder or the binders with RH and Advera. 3.2. ANOVA analysis on G⁄ The statistical analysis of variance (ANOVA) was applied to investigate the G⁄ of rubberized WMA binders with different crumb rubber concentrations as functions of the WMA additives (Control, Sasobit, RH, Advera) at different temperatures. In this study, ANOVA was conducted by the Excel program, the accuracy of the various models was evaluated by identifying 95% confidence intervals (a = 0.05). The statistical significance of G⁄ values as functions of the WMA additives at all temperatures and crumb concentrations was examined. The results are shown in Table 3 and Table 4. Then ANOVA results in the tables were employed to evaluate whether the three WMA additives had or not had significant effect on G⁄ of the unaged and RTFO-aged CRM binders. Based on the results, it was predicted that the addition of WMA additives generally caused different statistically significant effects on rutting properties for both unaged and RTFO-aged rubberized WMA binder. It was found that when the test temperature was lower than 64 °C, Sasobit had a significant effect on G⁄ of the unaged CRM binders, however RH and Advera had no significant influence on the unaged CRM binders’ high temperature performances. In general, ANOVA results in Table 3 also indicate that the three WMA additives all had significant effects on G⁄ values as the test temperature rose. However even then, there was no observable difference between the unaged CRM binders with RH and Advera. When it mentioned RTFO-aged CRM binders, it was verified in Table 4 that both Sasobit and RH had a good influence on G⁄, however, Advera’ effect was not
significant on CRM binders. Therefore, when it requires rubberized WMA binder with high resistance to deformation at high temperatures, the research suggested that Sasobit is a good WMA additive to meet the requirement. 3.3. Phase angle (d) The main objective of this part is to discuss the different WMA additives influence on phase angle (d) of crumb rubbers, that is, to analysis the relation between WMA additives and the elasticity of rubberized WMA binders at high temperatures. As it is seen in Figs. 5 and 6, d values of unaged and RTFO-aged CRM binders with different additives under various crumb rubber concentrations and temperatures were confirmed. Findings suggested that d increased with the increasing of test temperature and the decreasing of CRM concentration for unaged binders. This indicated that, for rubberized WMA binder, the properties of elasticity for binders were enhanced with the addition of crumb rubber or when temperature drop. While the WMA additives had different influences on the unaged CMR binders, the trend was not consistent. Compared with the unaged rubberized WMA binder, d decreased continuously with crumb rubber concentration increasing no more than 20% for RTFO-aged binder. So it is suggested to apply the rubber concentration no more than 20% for CRM binder at high temperature. In addition, Advera could enhance d when contrasted with the control binder. 3.4. The failure temperature of the CRM binders with WMA additives In general, the failure temperature in Fig. 7 indicated that the high failure temperatures of the unaged rubberized WMA binders were significantly greater than that of the control binders. The addition of RH had the most positive influence on the rutting resistance of unaged CRM binders. However Sasobit and Advera had a less significant effect on the failure temperature. When refer to the RTFO-aged binders, the CRM binders with Sasobit had the highest failure temperatures. RH and Advera had less remarkable effects on the binders’ failure temperature. 4. Summary and conclusion To evaluate the high temperature properties of CRM binders with WMA additives, CRM binders were manufactured using one ambient CRM (40#), four crumb rubber concentrations (10%, 15%, 20% and 25% by the asphalt binder weight). The rubberized WMA binders were produced with three WMA additives (Sasobit, RH and Advera), and artificially short-term aged (RTFO test) in the laboratory. The
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parameters (complex shear modulus and phase angle) used to describe rutting properties for the binders were measured by DSR. Besides, the ANOVA technique was applied to quantify the effect of WMA additive on the rubberized WMA binders’ resistance to deformation under dynamic loading properties at high temperatures. Based on the limited study, the following conclusions were reached from the experimental data obtained in this study: (1) The addition of WMA additives had different effects on high failure temperature properties of unaged and RTFO-aged CRM binders with different crumb rubber concentrations and test temperatures. WMA additives can improve the CRM binders’ resistance to rutting. (2) Compared to the control CRM binders, the unaged rubberized WMA binders with Sasobit had higher G⁄ values. When the crumb rubber concentration was 25%, the G⁄ values of CRM binder with Sasobit were 136% and 134% higher than the values of the control binders at 70 °C and 76 °C, respectively. This is indicated that Sasobit significant enhances the rutting resistance properties of CRM binders. However, Advera do not significantly influence the high temperature rheological performance of unaged CRM binders. When the test temperature was lower than 64 °C, the addition of RH could enhance or weaken the high failure temperature properties of RTFO-aged rubberized WMA binders. But when the temperature rose, compared with the control CRM binders, binders with RH had higher G⁄ values. (3) After RTFO-aged, rubberized WMA binder had a higher G⁄ in comparison to unaged binder. The analysis results indicated that for RTFO-aged CRM binders, the addition of Sasobit and RH could significantly increase the G⁄ of CRM binders when compared with the RTFO-aged control binders. Take the binder with 25% rubber concentration at 76 °C as an example, the G⁄ of the rubberized WMA binders with Sasobit and RH were 234% and 148% of that of RTFO-aged control binders respectively. But Advera had not significant effect on the binders’ G⁄ values. (4) When referring to d of all kinds of both unaged and RTFOaged rubberized WMA binders, compared with the control binders, there was great variability between the effects of different WMA additives on the d values: increase or decrease. The trend was not consistent. (5) When considering the rutting resistance parameter, G⁄/sin d, to characterize the high-temperature portion of the PG grade, unaged CRM binders with RH had the highest failure temperature, moreover, the addition of Sasobit was the most positive for the failure temperature for the RTFO-aged CRM binders.
Acknowledgements The research is supported by the funds of National Natural Science Foundation of China (NSFC) (Nos. 51178056 and 51110105018) and the Shaanxi Provincial Natural Science Foundation (2011JQ7007). The experimental work was completed in the Transportation Materials Research Center at Michigan Technological University. References [1] Roberts FL, Kandhal PS, Brown ER, Dunning RL. Investigation and evaluation of ground tire rubber in hot mix asphalt. National Center for Asphalt Technology, Report 89–3; 1989. [2] Ding Zhan, Jiang Jun, He Shaoying, Shen Cheng. Research on physical and chemical behavior of crumb rubber in asphalt rubber. In: International conference on civil engineering and building materials; 2011. p. 3411–5.
[3] Misra A, Niu HP, Lee Y-H. Behavior of crumb rubber modified hot mix asphalt. Proc Mater Eng Conf 1996;1:144–53. [4] Huang Baoshan, Mohammad Louay N, Graves Philip S, Chris Abadie. Louisiana experience with crumb rubber-modified hot-mix asphalt pavement. Transport Res Rec: J Transport Res Board 2002;1789:1–13. [5] Soon-Jae Lee, Amirkhanian Serji N, Putman Bradley J. Characterization of recycled aged rap binders containing crumb rubber modifier using gel permeation chromatography. J Mater Civ Eng 2009;21(8):382–91. [6] Liang Robert Y, Lee Suckhong. Short-term and long-term aging behavior of rubber modified asphalt paving mixture. Transport Res Rec: J Transport Res Board 1996;1530:11–7. [7] Shen Junan, Amirkhanian Serji, Lee Soon-Jae. The effect of rejuvenating agents on recycled aged asphalt rubber modified binders. Int J Pavement Eng 2005;6(4):273–9. [8] Xiao Feipeng, Amirkhanian Serji N, Zhang Rengen. Rheological investigation of non-foaming WMA additives at mid-temperature. In: Proceedings of the 2011 GeoHunan international conference, Human, China; 2011. p. 1–3. [9] Shatanawi Khaldoun, Biro Szabolcs, Thodesen Carl, Amirkhanian Serji. Effects of water activation of crumb rubber on the properties of crumb rubbermodified binders. Int J Pavement Eng 2009;10(4):289–97. [10] Akisetty Chandra, Xiao Feipeng, Gandhi Tejash, Amirkhanian Serji. Estimating correlations between rheological and engineering properties of rubberized asphalt concrete mixtures containing warm mix asphalt additive. Constr Build Mater 2009;25(2):950–6. [11] Lee Soon-Jae, Akisetty Chandra K, Amirkhanian Serji N. The effect of crumb rubber modified (CRM) on the performance properties of rubberized binders in HMA pavements. Constr Build Mater 2008;22(7):1368–73. [12] Xiao Feipeng, Amirkhanian Serji N. Laboratory investigation of utilizing high percentage of rap in rubberized asphalt mixture. Mater Struct 2010;43:223–33. [13] Liu Shutang, Cao Weidong, Fang Jianguo, Shang Shujie. Variance analysis and performance evaluation of different crumb rubber modified (CRM) asphalt. Constr Build Mater 2009;23(7):2701–8. [14] Wang Hainian, You Zhanping, Mills-Beatle Julian, Hao Peiwen. Laboratory evaluation on high temperature viscosity and low temperature stiffness of asphalt binder with high percent scrap tire rubber. Constr Build Mater 2012;26(1):583–90. [15] Hurley Graham C, Prowell Brian D. Evaluation of aspha-min zeolite for use in warm mix asphalt. Natl Center Asphalt Technol. Auburn, Alabama: Auburn University; 2006. [16] Li Meiling, Lv Anling, Ran Jin, Li Qingguang. Testing and evaluation of Sasobit on the performances of asphalt rubber. In: Proceedings of the 11th international conference of Chinese transportation professionals; 2011. p. 3502–09. [17] Akisetty Chandra K, Lee Soon-Jae, Amirkhanian Serji N. High temperature properties of rubberized binders containing warm asphalt additives. Constr Build Mater 2009;23(1):565–73. [18] AASHTO T 240-09. Standard method of test for effect of heat and air on a moving film of asphalt (rolling thin-film oven test). American Association of State Highway Transportation Officials, 2009. [19] Wong Cheuk Ching, Wong Wing-gun. Effect of crumb rubber modifiers on high temperature susceptibility of wearing course mixtures. Constr Build Mater 2007;21(8):1741–5. [20] Bressette Terrie, Zhou Haiping, Stonex Anne, Hicks R. Gary. Asphalt rubber and its potential use in China. In: Proceedings of the seventh international conference of Chinese transportation professionals congress; 2007. p. 766–85. [21] Soon-Jae Lee, Amirkhanian Serji N, Shatanawi Khaldoun, Kim Kwang W. Shortterm aging characterization of asphalt binders using gel permeation chromatography and selected Superpave binder tests. Constr Build Mater 2008;22(11):2220–7. [22] Shen Junan, Amirkhanian Serji, Lee Soon-Jae, Putman Brad. Recycling of laboratory-prepared reclaimed asphalt pavement mixtures containing crumb rubber-modified binders in hot-mix asphalt. J Transport Res Board 2007;1962:71–8. [23] Gandhi T, Amirkhanian S. Laboratory investigation of warm asphalt binder properties-a preliminary analysis. In: The fifth international conference on maintenance and rehabilitation of pavements and technological control (MAIREPAV5), Park City, Utah, USA; 2007. p. 475–80. [24] AASHTO T 315-10. Standard method of test for determining the rheological properties of asphalt binder using a dynamic shear rheometer (DSR). American association of state highway transportation officials, 2010. [25] AASHTO M 320-09. Standard specification for performance-graded asphalt binder. Association of state highway transportation officials, 2009.
Contents lists available at SciVerse ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of warm mixture asphalt (WMA) additives on high failure temperature properties for crumb rubber modified (CRM) binders Hainian Wang a,⇑, Zhengxia Dang a,1, Zhanping You b,2, Dongwei Cao c,3 a
Highway School, Chang’an University, South Erhuan Middle Section, Xi’an, Shanxi 710064, China Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, United States c Research Institute of Highway Ministry of Transport, Beijing 100088, China b
a r t i c l e
i n f o
Article history: Received 16 January 2012 Received in revised form 7 April 2012 Accepted 16 April 2012
Keywords: Rubber asphalt Warm mixture asphalt additive Rheological property Dynamic shear rheometer Complex modulus
a b s t r a c t This paper investigates the effect of three warm mixture asphalt (WMA) additives on the high temperature rheological properties of both unaged and rolling thin film oven (RTFO) aged crumb rubber modified (CRM) binders. The WMA additives used in this study include Sasobit, RH and Advera. The ambient 40-mesh tire rubber with the concentrations of 10%, 15%, 20%, and 25% by the weight of asphalt binder, respectively, was used in this study. Dynamic shear rheometer (DSR) was employed to measure the complex modulus (G⁄) and phase angle (d) of CRM binders at various testing temperatures. The statistical analysis of variance (ANOVA) was applied to quantify the effects of WMA additives on the CRM binders’ rutting resistance properties. It was found in this study that, the three WMA additives could all improve the CRM binders’ resistance to rutting, and greatly improved high-temperature portion of the performance grade (PG) of CRM binders. It is found that Sasobit had the most remarkable effect on G⁄ of both unaged and RTFO-aged CRM binders, RH only had significant effect on G⁄ of RTFO-aged binders, Advera’s effect was indistinctive. Furthermore, WMA additives’ effect on d was not conclusive. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction 1.1. Background Tire rubber is widely used as an environmental friendly material with good performance in pavement engineering since Charles McDdonald employed the dry processes to produce a rubberized asphalt mixture called Overflex TM 60 years ago [1–3]. There are many benefits from applying crumb rubber modified (CRM) binders into asphalt pavements, such as reducing the thickness of asphalt overlays but increasing pavement life, decreasing traffic noise and maintenance costs, increasing resistance to rutting and cracking [4–7]. For this reason, CRM binders attract more and more attentions recently. Rutting is one of the main pavement distresses mainly due to traffic loading, especially under hot climatic conditions. In Superpave binder testing procedure, dynamic shear rheometer (DSR) can comprehensively consider the two factors and is adopted to characterize the rheological properties of asphalt binders at intermediate to high temperatures. Since the rheological property ⇑ Corresponding author. Tel.: +86 29 82334798; fax: +86 29 82334824. E-mail addresses: [email protected] (H. Wang), zhaofengwuying@ 163.com (Z. Dang), [email protected] (Z. You), [email protected] (D. Cao). 1 Tel.: +86 29 82334824. 2 Tel.: +1 906 487 1059. 3 Tel.: +86 13910287728. 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.04.004
of asphalt binder has been applied by many researchers to evaluate the rheological properties of rubber asphalt [8–10]. It is found that adding crumb rubber into binders can significantly increase the rutting resistance parameter, which meant a better resistance of high temperature susceptibility than the unmodified binders. Meanwhile, the rutting resistance parameters of CRM binders improved as the CRM percentage increased. Compared with cryogenic CRM binders, the ambient CRM was found to be a better modifier in producing the CRM binder, which was less sensitivity to rutting at high pavement temperature [11–13]. Wang et al. tested the CRM binder viscosity at different high temperatures using rotational viscosity. It was found that the addition of crumb rubber can greatly increase the binder viscosity, and the temperature need to rise to 147 °C, 162 °C and 174 °C for 15%, 20% and 25% rubber asphalt ratio binders to meet the 3 Pa s requirement respectively, in Superpave specification [14]. Therefore the mixing temperatures and compaction temperatures of rubberized asphalt binders were much higher than those of ordinary asphalt mixtures, then caused some problems in the construction schedule [15]. The ‘‘warm mixture asphalt’’ (WMA) refers to the technologies which allow a considerable reduction of mixing and compaction temperatures of asphalt mixes through lowing the viscosity of asphalt binders by use of organic additives, chemical additives, or foaming processes. If the technologies are incorporated well with CRM binders, it can produce rubberized asphalt mixtures with good properties. In recent years, the rheological properties of
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asphalt binders at intermediate or high temperature effect on rubberized WMA binders attract more and more focus. For example, studies found a further enhancement of softening point after adding Sasobit into CRM binder [16]. AKisetty applied the DSR to determine the high failure temperature for each rubberized WMA binders (the WMA additives were Aspha-min and Sasobit) both in the original state and after short-term aging in the rolling thin film oven (RTFO). It was also predicted that the rubberized binders containing the inorganic additive had better rutting resistance compared with the control CRM binders. In addition, the difference of failure temperature values between rubberized binders with Aspha-min and Sasobit was not significant at the 5% level within each binder source [17]. Previous studies focused more on the rheological property of CRM binders, but there are very limited work done on rubberized WMA binders. Since the implementation of SHRP, the DSR has been widely used for the determination of rutting resistance parameter as well as the high failure temperature of the binder. Results obtained from the DSR are vital to pavement performance when determining its resistance to rutting. As the WMA additives types and rubber concentrations are various in different studies, their modifying effects on the rheological properties of rubberized WMA binders are different. However there is no comprehensive study in comparing the rheological property of unaged and RTFO-aged rubberized WMA binders with different additives types. Considering the technical and economic issues, how to select a suitable warm mix asphalt additive for CRM binders from great varieties is worthy for further study.
Table 1 The properties of virgin asphalt. Aging states
Test properties
Test results
Unaged binders
Rotational viscosity@ 135 °C (Pa s) G⁄/sin d @ 64 °C (kPa) G⁄/sin d @ 64 °C (kPa) G⁄sin d @ 25 °C (kPa) Stiffness @ 12 °C (mPa) m-value @ 12 °C
0.435 1.367 3.906 1171 187 0.316
RTFO aged residue RTFO + PAV aged residue
Table 2 Crumb rubber properties (by weight of crumb rubber). Crumb rubber
40 mesh (0.425 mm) (%)
Specific gravity Moisture content Ash content Carbon black content Acetone content Fibre content Sulfur content
1.165 0.67 5.42 31.98 5.62 0.01 1.47
Sasobit, RH and Advera, then artificially short-term aged using RTFO procedure [18]. The complex modulus (G⁄) and phase angle (d) for the rubberized WMA binders in the original state and after RTFO-aged process were evaluated. Fig. 1 shows a flow chart of the experimental design used in this study. 2. Materials and test program 2.1. Materials
1.2. Objective and scope The main objective of this study is to evaluate the effects of WMA additives on high temperature properties via selected Superpave binder tests. The CRM binders were produced in the laboratory incorporating one CRM source (ambient) and four CRM percentages (10%, 15%, 20% and 25% by the weight of asphalt binder) into one base binder. The rubberized WMA binders were manufactured with and without three different WMA additives:
2.1.1. Asphalt binders The Superpave performance grade (PG) 64–22 virgin asphalt taken from a Detroit construction site in Michigan was used in this study. Table 1 shows the properties of the PG 64–22 binders. 2.1.2. Crumb rubber modifier (CRM) The CRM produced by mechanical shredding at the ambient temperature was obtained from one source: 40 mesh (0.425 mm), and came from Beijing, China. The rubber characteristics are given in Table 2. Four rubber concentrations, 10%, 15%, 20% and 25% by weight of asphalt binder, were used in this study, and the CRM binders were used as the control binders.
PG 64-22 Asphalt binders
Rubber modified asphalt
15%
10%
25%
20%
WMA additives
Control CRM binders
unaged
RTFO
DSR @ 76, 70, 64, 58, 52ºC
DSR @ 76, 70, 64, 58, 52ºC
2%Sasobit
4%RH
same testing procedures as 5%Advera rubberized warm asphalt binders
same testing procedures as 5%Advera rubberized warm asphalt binders
5%Advera
unaged
RTFO
DSR @ 82,76, 70, 64, 58, 52ºC
DSR @ 82, 76, 70, 64, 58, 52ºC
Fig. 1. Flow chart of experimental design procedures.
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Fig. 2. The three WMA additives.
60 40 20 0
35
G* at 10rad/ s (kPa)
60
G* at 10rad/s (kPa)
80
The control binder Sasobit RH Advera
30 25
10%
15%
20%
50
30 20 10 20%
25%
(a)
(b) 18
The control binder Sasobit RH Advera
10 5 10%
15%
20%
The control binder Sasobit RH Advera
15 12 9 6 3
0
0
25%
10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(c)
(d)
The control binder Sasobit RH Advera
G* at 10rad/s (kPa)
G* at 10rad/s (kPa)
15%
Crumb rubber concentration
15
6
10%
Crumb rubber concentration
20
8
The control binder Sasobit RH Advera
40
0
25%
G* at 10rad/s (kPa)
G* at 10rad/s (kPa)
100
4
2
3
Sasobit RH Advera
2
1
0
0 10%
15%
20%
25%
10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(e)
(f)
Fig. 3. G⁄ values of unaged warm rubberized asphalt binders at different temperatures (a) 52 °C; (b) 58 °C; (c) 64 °C; (d) 70 °C; (e) 76 °C; (f) 82 °C. 2.1.3. WMA additives Sasobit, RH and Advera were selected as the available commercial WMA additives in producing the rubberized WMA binders. Fig. 2 shows the three WMA additives in the laboratory. RH, as a WMA additive, is a kind of white powder developed in China. In addition, the percentages used (by rubberized asphalt binders weight) of warm mix asphalt additives were generally based on the recommendations by the manufactures. As a result, 2% Sasobit, 4% RH, and 5% Advera were blended with rubberized asphalt binders in this research.
2.2. Production of rubberized WMA binders There are two major processes: the wet and dry processes when using recycled tires to produce rubberized asphalt mixtures. The wet process defines any method that adds CRM to asphalt, which is then well blended and interacted at high temperature under high agitation before incorporating the modified binder into the mix. The dry process defines any method which adds CRM directly into the hot mixture asphalt (HMA) [19,20].
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60
Sasobit
80
G* at 10rad/s (kPa)
G* at 10rad/s (kPa)
The control binder RH Advera
60 40 20
50
The control binder Sasobit RH Advera
40 30 20 10 0
0 10%
20%
25%
20%
25%
(a)
(b) 20
20
10
16
10%
15%
20%
The control binder Sasobit RH Advera
12 8 4
0
0
25%
10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(c)
(d)
8
G* at 10rad/s (kPa)
The control binder Sasobit RH Advera
10
G* at 10rad/s (kPa)
15%
Crumb rubber concentration
G* at 10rad/s (kPa)
30
10%
Crumb rubber concentration
The control binder Sasobit RH Advera
40
G* at 10rad/s (kPa)
15%
6 4 2
4
Sasobit RH Advera
3 2 1 0
0 10%
15%
20%
25%
10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(e)
(f)
Fig. 4. G⁄ values of RTFO- aged warm rubberized asphalt binders at different temperatures (a) 52 °C; (b) 58 °C; (c) 64 °C; (d) 70 °C; (e) 76 °C; (f) 82 °C.
Table 3 The WMA additives’ ANOVA on G⁄ of unaged CRM binders. Source
0 1 2 3
Binders (temperature < 64 °C)
Binders (temperature > 64 °C)
0
1
2
3
0
1
2
3
–
S –
N S –
N S N –
–
S –
S S –
S S N –
N: non-significant; S: significant. Rubberized WMA binders 0: Control; 1: Sasobit; 2: RH; 3: Advera. The significance level is 0.05.
The wet process was applied to modify the asphalt in this paper. The rubberized binder was produced in the laboratory at 350 °F (177 °C) for 30 min by an open blade mixer at a blending speed of 700 rpm [21,22]. The percentage of crumb rubber added for the CRM binders were 10%, 15%, 20% and 25% by weight of the based asphalt binder. As the moisture content of the crumb rubber in Table 2 was extremely small, only 0.67% by weight of crumb rubber, it did not need to
dry the rubber powders before blending with virgin binder. Then added WMA additives: Sasobit, RH and Advera into the binders followed by mixing with a shear mixer for 5 min to achieve consistent mixing [23]. The specified concentrations of the additives were 2%, 4%, and 5% by weight of the mixture respectively. The rubberized WMA binders were then artificially short-term aged through (RTFO) aging process for 85 min at 163 °C [18]. 2.3. Superpave binder tests In this study each rubberized WMA binder sample (both unaged and RTFO aged) were tested with DSR (AASHTO T 315: with the plate gap adjusted to 2 mm) to evaluate its high temperature properties [24]. For the CRM binders without WMA additives, the DSR test was operated at five different temperature conditions: 52 °C, 58 °C, 64 °C, 70 °C and 76 °C, and the temperatures were 52 °C, 58 °C, 64 °C, 70 °C, 76 °C, and 82 °C for the rubberized WMA binders. All the DSR tests were carried out in accordance with ASHTO T 315. The high-temperature portion of the PG grade is determined by measuring the temperature at which the unaged and RTFO-aged asphalt binder’s G⁄/sin d values are at least 1.0 kPa and 2.2 kPa, respectively, when measured at a frequency of 10 radian per second (rad/s) [25]. G⁄ represents the total resistance to deformation un-
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H. Wang et al. / Construction and Building Materials 35 (2012) 281–288 Table 4 The WMA additives’ ANOVA on G⁄ of RTFO-aged CRM binders. Source
0 0 0 1 1 2
VS VS VS VS VS VS
1 2 3 2 3 3
RTFO-aging rubberized warm asphalt F
P-value
36.696 34.305 0.7633 11.242 24.535 8.2596
7.9453 10 1.2179 10 0.3932 0.00275 5.2368 10 0.00857
F crit 6
4.3807 4.3807 4.3807 4.2793 4.2793 4.2793
5
5
tween an in-phase component and an out-of-phase component. The in-phase component is an elastic component and can be related to energy stored in a sample for every loading cycle, while the out-of-phase component represents the viscous component and can be related to energy lost per cycle in permanent flow. The relative distribution of these components is a function of the composition of the material, loading time and temperature. When the value of d is 0°, it represents the completely elastic nature of the binders, while the d value approach 90° for all binders, it reflects the approach to complete viscous behavior.
3. Results and discussions
der dynamic loading. It reflects that the higher rigidity is favorable at high temperatures for the rubberized WMA binder. Usually as the temperature increases or the frequency decreases, G⁄ decreases continuously, which reflects a decrease in resistance to deformation. The elasticity of the rubberized WMA binders may be measured with d. To resist rutting and fatigue damage, more elasticity is favorable at high temperatures. d represents the relative distribution of this total response be-
The influence of different WMA additives on the G⁄ values of rubberized WMA binders with different crumb rubber concentrations is discussed in this section. Figs. 3 and 4 show the G⁄ values measured by the DSR tests at different temperatures for both the unaged and RTFO-aged rubberized WMA binders with different crumb rubber concentrations, respectively.
76
The control binder Sasobit RH Advera
72 68 64 60 56 52 10%
15%
20%
25%
Phase angle at 10rad/s (degree)
3.1. High temperature complex shear modulus (G⁄)
Phase angle at 10rad/s (degree)
F: the F value; F crit, the F critical value. Rubberized WMA binder 0: Control; 1: Sasobit; 2: RH; 3: Advera. The significance level (a) is 0.05.
76
The control binder Sasobit RH Advera
72 68 64 60 56 52 10%
15%
The control binder Sasobit RH Advera
72 68 64 60 56 52 10%
15%
20%
25%
80
The control binder Sasobit RH Advera
76 72 68 64 60 56 52 10%
Crumb rubber concentration
15%
70 65 60 55 10%
15%
20%
25%
Crumb rubber concentration
(e)
Phase angle at 10rad/s (degree)
Phase angle at 10 rad/s (degree)
75
25%
(d) The control binder Sasobit RH Advera
80
20%
Crumb rubber concentration
(c) 85
25%
(b) Phase angle at 10rad/s (degree)
Phase angle at 10rad/s (degree)
(a) 76
20%
Crumb rubber concentration
Crumb rubber concentration
Sasobit RH Advera
85 80 75 70 65 60 55 50
(f) 10%
15%
20%
25%
Crumb rubber concentration
(f)
Fig. 5. d values of unaged warm rubberized asphalt binders at different temperatures (a) 52 °C; (b) 58 °C; (c) 64 °C; (d) 70 °C; (e) 76 °C; (f) 82 °C.
H. Wang et al. / Construction and Building Materials 35 (2012) 281–288
Phase angle at 10rad/s (degree)
Fig. 3 indicated that as expected, the G⁄ values of all kinds of unaged CRM binders (with or without additives) decreased when the DSR temperature rose at any rubber concentration, meaning that the resistance to deformation under dynamic loading would decline continually as the testing temperature rose constantly. However, with increasing percentage of crumb rubber, the unaged binder’s G⁄ increased significantly at each test temperature. Take the rubberized WMA binder with Sasobit tested at 70 °C for example, when the concentration changed from 10% to 15, 15% to 20%, 20% to 25%, the G⁄ could increased to 169%, 163% and 132% respectively. Furthermore, a general trend was found from the result that the addition of Sasobit into CRM binders greatly increased the binders’ rigidity at high temperatures, when compared with the control CRM binders. The most remarkable effect was that when the CRM percentage was 25%, the G⁄ values of rubberized WMA binder with Sasobit increased 136% and 134% at 70 °C and 76 °C respectively by the control CRM binder. However, when the test temperature was lower than 64 °C, RH and Advera had no significant influence on the resistance to deformation of CRM binders. Compared to the control CRM binders, the G⁄ decreased or increased with different CRM T he control binder Sasobit RH A dvera
68 64 60 56 52 10%
15%
20%
25%
concentrations at different temperatures when added RH and Advera into CRM binders. Therefore, it was quite difficult to find a regular result for all rubberized WMA binders with RH and Advera. Moreover, when the test temperature was higher than 64 °C, RH and Advera could enhance the G⁄ values at different crumb rubber concentrations, even the CRM binder’ G⁄ with RH was higher than it with Sasobit when the test temperature was 82 °C and the crumb rubber concentrations was 10% and 15%. This indicated that there was no significant effect on G⁄ values of CRM binders for RH and Advera when the temperatures were lower than 64 °C, however, the two WMA additives played a positive role as the temperature rose for the unaged CRM binders. As shown in Fig. 4, at the same temperature, crumb rubber concentration and WMA additive, RTFO-aged binder had a higher G⁄ in comparison to unaged binder. Furthermore, the RTFO-aged binders with Sasobit and RH both had higher rigidity than the control RTFO-aged binders, as the two additives could increase the binders’ G⁄ at any rubber concentration and test temperature. Take the binder with 25% rubber concentration and tested at 76 °C as an example, the G⁄ of the rubberized WMA binder with Sasobit and
Phase angle at 10rad/s (degree)
286
T he control binder Sasobit RH A dvera
64 60 56 52 48 10%
Crumb rubber concentration
15%
60 56 52 10%
15%
20%
25%
Phase angle at 10rad/s (degree)
T he control binder Sasobit RH A dvera
64
25%
(b) T he control binder Sasobit RH A dvera
68 64 60 56 52 10%
15%
20%
25%
Crumb rubber concentration
Crumb rubber concentration
(c)
(d)
72
T he control binder Sasobit RH A dvera
68 64 60 56 52 10%
15%
20%
25%
Phase angle at 10rad/s (degree)
Phase angle at 10 rad/s (degree)
Phase angle at 10rad/s (degree)
(a) 68
20%
Crumb rubber concentration
76
Sasobit RH A dvera
72 68 64 60 56 52 10%
15%
20%
25%
Crum rubber concentration
Crumb rubber concentration
(e)
(f)
Fig. 6. d values of RTFO-aged warm rubberized asphalt binders at different temperatures (a) 52 °C; (b) 58 °C; (c) 64 °C; (d) 70 °C; (e) 76 °C; (f) 82 °C.
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100
the control Sasobit RH Advera
88
94
o
94
Failure Temperature ( C)
o
Failure Temperature ( C)
100
82 76 70 64
88
the control Sasobit RH Advera
82 76 70 64 58
58
52
52 1
2
3
4
Crumb Rubber Concentration
10%
15%
20%
25%
Crumb Rubber Concentration
(a)
(b)
Fig. 7. Failure temperature of all CRM binders with different WMA additives (a) the unaged binders; (b) the RTFO-aged binders.
RH were 134% and 48% higher than that of the control RTFO-aged binders respectively. Nevertheless, for rubberized WMA binders, Sasobit typically had a greater enhancement on CRM binder’s resistance to deformation than RH. Similar to unaged rubberized WMA binders, Advera had no consistent influence on RTFO-aged rubberized WMA asphalt binder’s G⁄ at any temperature and crumb rubber concentration when compared with the control CRM binder. When the test temperature was lower than 64 °C, the addition of RH could enhance or weaken the high failure temperature properties of RTFO-aged rubberized WMA binders. But when the temperature rose, compared with the control CRM binders, binders with RH had higher G⁄ values. It can also be found from Fig. 4 that when refer to the influence of rubber concentration on different CRM binders containing or not containing additives, conclusions came different. The G⁄ could be improve constantly as the rubber concentration increased for binders with Sasobit. However the phenomenon didn’t exist in the control CRM binder or the binders with RH and Advera. 3.2. ANOVA analysis on G⁄ The statistical analysis of variance (ANOVA) was applied to investigate the G⁄ of rubberized WMA binders with different crumb rubber concentrations as functions of the WMA additives (Control, Sasobit, RH, Advera) at different temperatures. In this study, ANOVA was conducted by the Excel program, the accuracy of the various models was evaluated by identifying 95% confidence intervals (a = 0.05). The statistical significance of G⁄ values as functions of the WMA additives at all temperatures and crumb concentrations was examined. The results are shown in Table 3 and Table 4. Then ANOVA results in the tables were employed to evaluate whether the three WMA additives had or not had significant effect on G⁄ of the unaged and RTFO-aged CRM binders. Based on the results, it was predicted that the addition of WMA additives generally caused different statistically significant effects on rutting properties for both unaged and RTFO-aged rubberized WMA binder. It was found that when the test temperature was lower than 64 °C, Sasobit had a significant effect on G⁄ of the unaged CRM binders, however RH and Advera had no significant influence on the unaged CRM binders’ high temperature performances. In general, ANOVA results in Table 3 also indicate that the three WMA additives all had significant effects on G⁄ values as the test temperature rose. However even then, there was no observable difference between the unaged CRM binders with RH and Advera. When it mentioned RTFO-aged CRM binders, it was verified in Table 4 that both Sasobit and RH had a good influence on G⁄, however, Advera’ effect was not
significant on CRM binders. Therefore, when it requires rubberized WMA binder with high resistance to deformation at high temperatures, the research suggested that Sasobit is a good WMA additive to meet the requirement. 3.3. Phase angle (d) The main objective of this part is to discuss the different WMA additives influence on phase angle (d) of crumb rubbers, that is, to analysis the relation between WMA additives and the elasticity of rubberized WMA binders at high temperatures. As it is seen in Figs. 5 and 6, d values of unaged and RTFO-aged CRM binders with different additives under various crumb rubber concentrations and temperatures were confirmed. Findings suggested that d increased with the increasing of test temperature and the decreasing of CRM concentration for unaged binders. This indicated that, for rubberized WMA binder, the properties of elasticity for binders were enhanced with the addition of crumb rubber or when temperature drop. While the WMA additives had different influences on the unaged CMR binders, the trend was not consistent. Compared with the unaged rubberized WMA binder, d decreased continuously with crumb rubber concentration increasing no more than 20% for RTFO-aged binder. So it is suggested to apply the rubber concentration no more than 20% for CRM binder at high temperature. In addition, Advera could enhance d when contrasted with the control binder. 3.4. The failure temperature of the CRM binders with WMA additives In general, the failure temperature in Fig. 7 indicated that the high failure temperatures of the unaged rubberized WMA binders were significantly greater than that of the control binders. The addition of RH had the most positive influence on the rutting resistance of unaged CRM binders. However Sasobit and Advera had a less significant effect on the failure temperature. When refer to the RTFO-aged binders, the CRM binders with Sasobit had the highest failure temperatures. RH and Advera had less remarkable effects on the binders’ failure temperature. 4. Summary and conclusion To evaluate the high temperature properties of CRM binders with WMA additives, CRM binders were manufactured using one ambient CRM (40#), four crumb rubber concentrations (10%, 15%, 20% and 25% by the asphalt binder weight). The rubberized WMA binders were produced with three WMA additives (Sasobit, RH and Advera), and artificially short-term aged (RTFO test) in the laboratory. The
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parameters (complex shear modulus and phase angle) used to describe rutting properties for the binders were measured by DSR. Besides, the ANOVA technique was applied to quantify the effect of WMA additive on the rubberized WMA binders’ resistance to deformation under dynamic loading properties at high temperatures. Based on the limited study, the following conclusions were reached from the experimental data obtained in this study: (1) The addition of WMA additives had different effects on high failure temperature properties of unaged and RTFO-aged CRM binders with different crumb rubber concentrations and test temperatures. WMA additives can improve the CRM binders’ resistance to rutting. (2) Compared to the control CRM binders, the unaged rubberized WMA binders with Sasobit had higher G⁄ values. When the crumb rubber concentration was 25%, the G⁄ values of CRM binder with Sasobit were 136% and 134% higher than the values of the control binders at 70 °C and 76 °C, respectively. This is indicated that Sasobit significant enhances the rutting resistance properties of CRM binders. However, Advera do not significantly influence the high temperature rheological performance of unaged CRM binders. When the test temperature was lower than 64 °C, the addition of RH could enhance or weaken the high failure temperature properties of RTFO-aged rubberized WMA binders. But when the temperature rose, compared with the control CRM binders, binders with RH had higher G⁄ values. (3) After RTFO-aged, rubberized WMA binder had a higher G⁄ in comparison to unaged binder. The analysis results indicated that for RTFO-aged CRM binders, the addition of Sasobit and RH could significantly increase the G⁄ of CRM binders when compared with the RTFO-aged control binders. Take the binder with 25% rubber concentration at 76 °C as an example, the G⁄ of the rubberized WMA binders with Sasobit and RH were 234% and 148% of that of RTFO-aged control binders respectively. But Advera had not significant effect on the binders’ G⁄ values. (4) When referring to d of all kinds of both unaged and RTFOaged rubberized WMA binders, compared with the control binders, there was great variability between the effects of different WMA additives on the d values: increase or decrease. The trend was not consistent. (5) When considering the rutting resistance parameter, G⁄/sin d, to characterize the high-temperature portion of the PG grade, unaged CRM binders with RH had the highest failure temperature, moreover, the addition of Sasobit was the most positive for the failure temperature for the RTFO-aged CRM binders.
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