Int. J. Civ. Eng. DOI 10.1007/s40999-016-0040-3
RESEARCH PAPER
Laboratory Investigation of Crumb Rubber Modified Asphalt Binder and Mixtures with Warm-Mix Additives Tao Ma1 • Hao Wang2 • Yongli Zhao1 • Xiaoming Huang1 • Siqi Wang1
Received: 24 June 2015 / Revised: 2 November 2015 / Accepted: 25 January 2016 Iran University of Science and Technology 2016
Abstract This study evaluated the effects of warm mix asphalt (WMA) additives on the compaction temperature and properties of crumb rubber modified (CRM) asphalt binder and mixture. Two different WMA additives (named as Sas and Evm) were used to prepare warm-mix CRM asphalt binder and mixture. The viscosity of different warm-mix CRM asphalt binders and mastics was measured at different temperatures. The rheological and mechanical properties of different warm-mix CRM asphalt binders were tested. At the mixture level, the volumetric properties of different warm-mix CRM asphalt mixtures were experimented by Gyratory compactor at different temperatures and the performance of different warm-mix CRM asphalt mixtures were evaluated. It was found that both of the two WMA additives could lower the compaction temperatures of CRM asphalt mixtures by 10–20 C. However, they have different influences on rheological properties of CRM binder and performance of CRM mixture. The Sas warm-mix additive can improve the anti-rutting performance of CRM mixture but may degrade its low-temperature performance and moisture stability. The Evm warmmix additive has no adverse effects on the high-temperature and low-temperature performance of CRM asphalt mixtures and can improve its moisture stability.
& Tao Ma
[email protected] 1
School of Transportation, Southeast University, 2 Sipailou, Nanjing 210096, China
2
Civil and Environmental Engineering, Rutgers, State University of New Jersey, 96 Frelinguysen Rd, Piscataway, NJ 08854, USA
Keywords CRM binder WMA additive Rheological properties Mixture performance
1 Introduction The disposal of scrap tires has been a serious issue due to the lack of landfill space and environmental concerns [1]. Asphalt mixture has been commonly used in pavement construction and design of asphalt mixture with satisfactory performance is important to guarantee the service life of asphalt pavement [2–5]. On the other hand, the use of crumb rubber modified (CRM) binder has been of interest to the asphalt industry since 1980s due to many benefits such as increasing the resistance of asphalt pavements to permanent deformation and cracking, and reducing binder aging in the field [6]. It has been reported that the asphalt industry can recycle up to 40 % scrap tires if the CRM binder is widely used [7]. In general, tire rubber is comprised of natural and synthetic rubbers, carbon black and other mineral fillers. Currently, there are two different processes, the wet or dry process, to apply crumb rubber in CRM asphalt mixtures. In the dry process, crumb rubber is added to the aggregate before the asphalt binder is charged into the mixture. In the wet process, asphalt cement is pre-blended with the rubber at high temperatures and specific blending conditions. However, the wet process is considered as the more efficient way to improve the performance of asphalt binders and mixtures [8]. In recent years, the use of CRM asphalt mixtures has been increasing steadily. Previous studies have found that CRM asphalt binder could produce asphalt pavements with lower traffic noise, improved pavement performance and thus reduced maintenance costs [9–12]. It has been
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binder with WMA additives; and (3) the performance of CRM asphalt mixture with WMA additives.
discovered that the reaction that occurs between the rubber and the asphalt is not a chemical reaction, but rather a diffusion process that includes the physical absorption of aromatic oils from the asphalt into the polymer chain of the rubber [13, 14]. However, the production of CRM asphalt mixture requires much higher mixing and compacting temperatures compared to conventional asphalt mixtures. This increases the effort of quality control in the field construction. If the rubberized asphalt pavement is not paved and compacted at the preferred temperature range, it will have inadequate volumetric properties and poor longterm performance [15]. In addition, production and compaction of CRM asphalt mixtures at relatively high temperatures restrict their placement on cold bases in the cold regions or during cold weather. Warm mix asphalt (WMA) technologies have gained increasing popularity in recent years because of its unique property to allow the reduction in mixing and compaction temperatures of asphalt mixtures without compromising the quality of mixture [16–19]. A number of WMA additives have been used by the asphalt industry in recent years. These techniques are typically classified into three categories: organic or wax additives; emulsified additives; and foaming techniques [20–22]. Typically, the mixing and compaction temperatures of WMA range from 100 to 140 C (212–280 F), compared to the 150–180 C (300–350 F) for Hot-mix asphalt (HMA). Due to the reduction of mixing and compaction temperatures, WMA technologies can reduce carbon dioxide emissions, consume less energy and reduce dust emissions compared to conventional HMA. Therefore, the use of WMA technology in conjunction with CRM asphalt binder has the potential to decrease the high temperature requirements for mixing and compaction while maintaining the performance benefits brought by CRM asphalt mixtures. The main objectives of this study are to evaluate (1) the effect of WMA additives on reducing the viscosity of CRM binder or mastic at mixing and compacting temperatures; (2) the rheological and mechanical properties of CRM
2 Experimental Procedures 2.1 Materials Base asphalt binder with penetration grade of 70 was used in this study. Table 1 summarizes the properties of the base asphalt binder. The crumb rubber modifier was produced by mechanical shredding of passenger car tires at the ambient temperature. The size of crumb rubber modifier is 40 mesh (0.425 mm) with a gradation as shown in Table 2. The binder mixing used in this study was the wet process, in which the crumb rubber modifier was added to the base asphalt binder before introducing it into the asphalt mixture. Based on previous studies and trial tests [23], the CRM binder was produced in the laboratory at 180 C for 45 min by an open blade mixer at a speed of 1000 rpm and then kept in the oven at 180 C for another 45 min. The percentage of crumb rubber was 25 % by weight of the base binder. Two types of WMA additives were used in this study: One, named as Sas, is a solid polyolefin additive. The other one, named as Evm, is a liquid surfactant. The solid additive can reduce the high-temperature viscosity of binder while the liquid additive mainly plays the role of lubrication between binder and aggregate. Based on previous studies and trial tests [20], the Sas additive was added into the CRM binder at different concentrations (1.5, 2.25, 3, 3.75 and 4.5 % by weight of the CRM binder) followed by mixing with a shear mixer at 180 C and 1000 rpm for 5 min to achieve a consistent mixing. Based on previous studies and trial tests [21], the Evm additive was added at different concentrations (0.3, 0.45, 0.6, 0.75 and 0.9 % by weight of the CRM binder) followed by mixing with a shear mixer at 180 C and 1000 rpm for 5 min to disperse the additives throughout the CRM binder.
Table 1 Properties of base asphalt binder Penetration (25 C, 0.1 mm)
67
Softening point (C)
[100
48.5
Table 2 Gradation of crumb rubber
Ambient CRM
Retained (%)
123
Ductility (15 C, cm)
Density (g/cm3)
1.037
RTFO aged residual (163 C, 85 min) Mass loss (%)
Residual penetration ratio (%)
0.28
86.6
Sieve no. (lm) 30 (600)
40 (425)
50 (300)
80 (180)
100 (150)
200 (75)
0
8.5
31.9
32.9
7.6
18.6
Int. J. Civ. Eng. 100 90
70 60 50 40 30
Passing Ratio (%)
80
20 10 0 0.075 0.15
0.3
0.6
1.18 2.36 4.75
9.5
12.5
16
Seiving Sizes (mm) Fig. 1 Gradation for CRM asphalt mixture
Asphalt mastics were produced by mixing the binder with mineral filler at the weight ratio of 1:1. And then the asphalt mastics of CRM asphalt binder were prepared with different concentrations (0, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9 % by weight of CRM binder) of Evm for viscosity test. Mix design for CRM asphalt mixture was conducted to prepare CRM asphalt mixture with or without WMA additives for performance evaluation [24]. The bitumenaggregate ratio was determined to be 6.5 % and the gradation is shown in Fig. 1. 2.2 Testing Procedures 2.2.1 Asphalt Binder Test The Brookfield rotational viscometer [25] was used to test the high-temperature viscosity of different binders and mastics. Penetration test, softening point test and ductility test were conducted to evaluate the basic rheological properties of different binders. The dynamic shear rheometer (DSR) [26] was used to measure the mechanical properties of different binders. The multiple stress creep recovery (MSCR) test [27] was conducted for different binders to measure the resistance of binder to permanent deformation. The frequency sweep test [28] was conducted to evaluate the dynamic shear modulus and phase angle of different binders. The test procedures for the asphalt binder and mastic follow the Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011) in China [29].
low-temperature beading beam test, immersion Marshall test and freeze–thaw splitting test were conducted to evaluate the performances of CRM asphalt mixtures with different WMA additives. The test procedures for the asphalt mixtures follow the Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011) in China [29]. Wheel tracking test was conducted at 60 C to evaluate the rutting resistance of different asphalt mixtures. Slab specimen with dimensions of 300 9 300 9 50 mm3 (length 9 width 9 thickness) was used during wheel tracking test. The dynamic loading of 0.7 MPa was applied on the slab specimen through a rubber wheel with contact width of 50 mm. Linear variable differential transformers (LVDTs) were used to measure the vertical displacement of the slab specimen along the wheel path. The unrecoverable displacement (rutting depth) was recorded one time per 20 s during the test. The dynamic stability (DS) was defined in Eq. (1). At least three replicates should be used for each test. And the variation coefficient of the test results should be lower than 20 %. DS ¼
15N 42 15 ¼ ; d60 d45 d60 d45
ð1Þ
where N is the number of wheel loading cycles per minute, (N = 42 cycles/min in this study), and d45 and d60 are the rutting depths measured at 45 and 60 min, respectively. Low temperature bending beam test was conducted at -10 C to evaluate the low-temperature anti-cracking performance of different asphalt mixtures. Beam specimen with dimensions of 250 9 30 9 35 mm3 (length 9 width 9 height) was prepared for low-temperature bending beam test. The constant loading was applied on the span center of the beam specimen to get vertical deflection at 50 mm/min until the beam was broken. The applied load and the corresponding vertical deflection at the span center of the beam specimen were recorded by loading sensor and LVDTs. According to the testing curve of applied load–vertical deflection, the failure strain for the test specimen can be calculated based on Eq. (2). At least three replicates should be used for each test. And the test results during each test should follow the statistical acceptance criterion shown in Eq. (3): eb ¼
6hd ; L2
ð2Þ
2.2.2 Asphalt Mixture Test
where eb and d are the failure strain and vertical deflection when the test beam is broken, and h and L are the height and length of the test beam.
Gyratory compactor [30] was used to determine the applicable compaction temperature for CRM asphalt mixtures with different WMA additives. Wheel tracking test,
jei ev j k SD ðk; nÞ ¼ ð1:15; 3Þ; ð1:46; 4Þ; ð1:67; 5Þ; ð1:82; 6Þ;
ð3Þ
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where ei is the failure strain of the ith test specimen while i equals 1, 2…n; ev is the mean value of the failure strain of all specimens; SD is the standard deviation of the failure strain of all specimens; n is the number of the test specimens, and k is the reliability coefficient. The immersion Marshall test and freeze–thaw splitting test were performed to evaluate the moisture susceptibility of different asphalt mixtures. Cylindrical specimens with height of 150 mm and diameter of 100 mm were used in both immersion Marshall test and freeze–thaw splitting test. During immersion Marshall test, the Marshall testing device was used to determine the Marshall strength of asphalt mixture under the vertical loading which was applied on the Marshall specimen to keep a constant deformation rate of 50 mm/min until the specimen was broken, and its load was recorded. The Marshall strength ratio (MSR) was used to evaluate the moisture stability of asphalt mixture, which is the strength of specimen after immersed in 60 C water for 48 h compared to the strength of specimen after immersed in 60 C water for 30 min. The MSR can be calculated according to Eq. (4). At least three replicates should be tested to get the average Marshall strength during each test, and the test results should follow the statistical acceptance criterion shown in Eq. (5). MSR ¼
MS2 100; MS1
ð4Þ
where MS2 is the average Marshall strength of all specimens immersed in water for 48 h, and MS1 is the average Marshall strength of all specimens immersed in water for 30 min. jMSi MSv j k SD ðk; nÞ ¼ ð1:15; 3Þ; ð1:46; 4Þ; ð1:67; 5Þ; ð1:82; 6Þ;
TSR ¼
R2 100; R1
ð6Þ
where R2 is the average tensile strength of specimens with freeze–thaw conditioning, and R1 is the average tensile strength of specimens without freeze–thaw conditioning. jRi Rv j k SD ðk; nÞ ¼ ð1:15; 3Þ; ð1:46; 4Þ; ð1:67; 5Þ; ð1:82; 6Þ;
ð7Þ
where Ri is the tensile strength of the ith test specimen while i equals 1, 2…n; Rv is the mean value of the tensile strength of all specimens; SD is the standard deviation of the tensile strength of all specimens; n is the number of the test specimens, and k is the reliability coefficient.
3 Results and Discussion 3.1 Viscosity of CRM Binder and Mastic The viscosities of different CRM binders were tested at different temperatures as shown in Table 3. Figure 2 shows the viscosity–temperature curves for the original CRM binder, CRM binder with 3 % Sas and CRM binder with 0.6 % Evm, respectively. It shows that Sas has significant influence on the viscosity of CRM binder, while Evm has no obvious influence on the viscosity of CRM binder. The viscosity of CRM binder decreases as the concentration of Sas increases while it almost keeps constant with the concentration of Evm increasing. For instance, the 150 C
ð5Þ
where MSi is the Marshall strength of the ith test specimen while i equals 1, 2…n; MSv is the mean value of the Marshall strength of all specimens; SD is the standard deviation of the Marshall strength of all specimens; n is the number of the test specimens, and k is the reliability coefficient. The splitting test was used to determine the tensile strength of asphalt mixtures at biaxial stress states. During the freeze–thaw splitting test, tensile strength ratio was used to evaluate the moisture stability of asphalt mixture. It is defined as tensile strength of specimen after freeze–thaw conditioning compared to tensile strength of specimen at ambient temperature. During the freeze–thaw conditioning, the specimen was immersed in water under vacuum state for 15 min, then frozen at -18 C in refrigerator for 16 h and then immersed in 60 C water for 24 h. The tensile strength ratio (TSR) can be calculated based on Eq. (6). At
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least three replicates should be tested to get the average tensile strength during each test, and the test results should follow the statistical acceptance criterion shown in Eq. (7).
Table 3 Viscosity of different binders at different temperatures (Pa s) Temperature (C)
135
150
165
180
Binders Original CRM binder
24
9
4.9
2.5
With 1.5 % Sas
16.6
7
3.3
1.9
With 2.25 % Sas
12.5
6.4
3.4
1.6
With 3 % Sas
10.2
5.6
2.6
1.5
With 3.75 % Sas
9.6
5.5
2.5
1.4
With 4.5 % Sas With 0.3 % Evm
8.1 19.4
4.2 8.9
2.3 4.4
1.3 2.5
With 0.45 % Evm
19.4
8.6
4.4
2.5
With 0.6 % Evm
20.1
8.7
4.5
2.3
With 0.75 % Evm
20.3
8.5
4.3
2.4
With 0.9 % Evm
19.5
8.1
4.1
2.2
Int. J. Civ. Eng. 140
30 Original CRM binder
120
with 3%Sas
100
Viscosity (Pa.s)
Viscosity (Pa.s)
25 with 0.6%Evm
20 15 10
Original CRM asphalt mastic with 0.3%Evm with 0.4%Evm with 0.5%Evm with 0.6%Evm with 0.7%Evm with 0.8%Evm with 0.9%Evm
80 60 40 20
5
0 130
140
150
160
170
180
190
Temperature (oC)
0 130
140
150
160
170
180
190
Temperature ( ) Fig. 2 Viscosity–temperature curves for the CRM binder and the warm-mix CRM binders (with 3 % Sas or 0.6 % Evm)
viscosities of the CRM binders with 1.5, 3 and 4.5 % Sas were 77.8, 62.2 and 46.7 % of the 150 C viscosity of the original CRM binder. To further confirm the influences of Sas on the viscosity of CRM binder, the viscosity of the original CRM binder was tested at 170 C while the CRM binders with 3 and 4 % Sas were tested at 160 and 155 C, respectively. It is found that the 170 C viscosity of the CRM binder is about 4.13 Pa s while the 160 C viscosity of the CRM binder with 3 % Sas is about 4.09 Pa s and the 155 C viscosity of the CRM binder with 4 % Sas is about 4.21 Pa s. It indicates that 3–4 % Sas in the CRM binder can lower the testing temperature by 10–15 C for the warm-mix CRM binder to reach the same viscosity of the original CRM binder at 170 C. It is mainly because that Sas is a long-chain aliphatic hydrocarbon which has much lower viscosity than asphalt binder at liquid state, while Evm is a surfactant which mainly lowers the interfacial tension of asphalt binder but has no obvious interference to the viscosity of asphalt binder. The viscosities of asphalt mastics with different concentrations of Evm in the CRM binder were measured at different temperatures. Figure 3 shows the viscosity-temperature curves for the asphalt mastics. It indicates that Evm has obvious influence on the viscosity of asphalt mastics. The viscosity of asphalt mastics decreases with the concentration of Evm in the CRM binder increasing. For instance, the 150 C viscosities of the CRM asphalt mastics with 0.3, 0.6 and 0.9 % Sas were 82.4, 62.7 and 49.0 % of the 150 C viscosity of the original CRM asphalt mastic. To further confirm the influences of Evm on the viscosity of CRM asphalt mastic, the viscosity of the original CRM asphalt mastic was tested at 170 C while CRM asphalt mastic with 0.6 and 0.8 % Evm were tested at 160 and
Fig. 3 Viscosity–temperature curves for the original asphalt mastic and asphalt mastics with different concentrations of Evm in the CRM binder
155 C, respectively. It is found that the 170 C viscosity of the original CRM asphalt mastic is about 19.12 Pa s, while the 160 C viscosity of the CRM asphalt mastic with 0.6 % Evm is 19.53 Pa s and the 155 C viscosity of the CRM asphalt mastic with 0.8 % Evm is 18.72 Pa s. It indicates that 0.6–0.8 % Evm in the CRM binder can lower the testing temperature by 10–15 C for the warm-mix CRM asphalt mastic to reach the same viscosity of the original CRM asphalt mastic 170 C. It is mainly because Evm can lower the interfacial tension of asphalt binder and plays the role of lubricant at the interface between asphalt binder and mineral filler. 3.2 Rheological Properties of CRM Binder Table 4 summarizes the rheological properties including penetration, softening point and ductility for different binders. It is clearly shown that Sas has more significant influence on the rheological properties of CRM binder than Evm. As the content of Sas in the CRM binder increases, the penetration and ductility decrease while the softening point increases. It indicates that Sas additive has positive influence on the temperature sensitivity and high-temperature performance of the CRM binder but negative influence on the ductility. Meanwhile, Evm additive has no obvious influences on the rheological properties of CRM binder. It is mainly related to the different material properties of Sas and Evm. As a long-carbochain paraffin with crystal structure, Sas is much stiffer than asphalt binder at solid state. As a combination of different polar functional groups, Evm has no obvious interference to the microstructure of asphalt binder especially at low concentrations.
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Int. J. Civ. Eng. Table 4 Rheological properties of different binders
Penetration (25 C, 0.1 mm)
Indices
Softening point (C)
Ductility (5 C, mm)
Binders Original CRM binder
40.3
76
With 1.5 % Sas
35.2
76
45
With 2.25 % Sas
32.7
84
38
With 3 % Sas
30.2
89
33
With 3.75 % Sas
28.9
[90
22
With 4.5 % Sas
25.9
[90
15
With 0.3 % Evm
39.2
77
75
With 0.45 % Evm
39.2
76
79
With 0.6 % Evm
38.9
80
78
With 0.75 % Evm
38.5
80
72
With 0.9 % Evm
38.1
80
71
1.8
Percent recoverable strain (%)
9
Creep ompliance (1/kPa)
1.6 1.4 1.2 1.0 0.8
Original CRM binder With Sas With Evm
0.6 0.4 0.2
8.4
8 6.8
7 6
5.0
5 4 3 2 1 0 Original CRM
0.0 470
78
480
490
500
510
520
Time (s)
With Sas Binders
With Evm
Fig. 5 Percent recoverable strain for different binders
3.3 Mechanical Properties of CRM Binder Multiple stress creep recovery tests were conducted for the original CRM binder, CRM binder with 3.5 % Sas and CRM binder with 0.7 % Evm. Figure 4 shows the MSCR curves for different binders. It indicates that the CRM binder with Sas has much smaller creep compliance than the original CRM binder, while the CRM binder with Evm has similar creep compliance with the original CRM binder. Figures 5 and 6 show the percent recoverable strain and the non-recoverable creep compliance at the end of the repeated creep test for different binders, respectively. The data show that the CRM binder with Sas has the highest percent recoverable strain and the lowest non-recoverable creep compliance, while the CRM binder with Evm has similar percent recoverable strain and non-recoverable creep compliance with the original CRM binder. Frequency sweep tests were also conducted for the original CRM binder, CRM binder with 3.5 % Sas and
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Non-recovrable compliance (1/kPa)
Fig. 4 Repeated creep curves for different binders 1.6
1.45
1.40 1.4 1.2 1 0.8 0.6 0.38
0.4 0.2 0 Original CRM
With Sas Binders
With Evm
Fig. 6 Non-recoverable compliance for different binders
CRM binder with 0.7 % Evm. Figure 7 shows the elastic and viscous shear modulus for different binders. Figure 8 shows the G*/sind for the different binders. It can be seen that Sas can increase both the elastic and viscous modulus leading to a higher G*/sind, while Evm has no obvious
Int. J. Civ. Eng.
influence on the modulus and G*/sind of CRM binder. According to the application of DSR results [31, 32], CRM binder becomes stiffer when Sas is added but barely changes with addition of Evm. This suggests that Sas additive can improve the CRM binder’s elastic properties and the resistance to permanent deformation. Meanwhile, Evm additive has no obvious influence on the CRM binder’s mechanical properties. This confirms the findings of the test of rheological properties.
1.E+05 Original CRM binder with Sas
G' (Pa)
with Evm
1.E+04
3.4 Volumetric Properties of CRM Asphalt Mixture 1.E+03 1.E-01
1.E+00
1.E+01
Frequency (Hz)
(a) 1.E+05 Original CRM binder with Sas
G'' (Pa)
with Evm
1.E+04
1.E+03 1.E-01
1.E+00
1.E+01
Frequency (Hz)
(b) Fig. 7 a Elastic shear modulus and b viscous shear modulus of different bindersat different frequencies
Mixtures were prepared with CRM binder, CRM binder with Sas and CRM binder with Evm, respectively, using Gyratory compactor at different temperatures. Figure 9 shows the air voids of mixtures prepared by the CRM binder and CRM binders with 3, 3.5 and 4 % Sas at different temperatures. Figure 10 shows the air voids of mixtures prepared by CRM binder and CRM binders with 0.6, 0.7 and 0.8 % Evm at different temperatures. It can be seen that the air voids of all the mixtures increase with the decreasing compaction temperature. However, the air voids of the CRM asphalt mixtures with warm-mix additives are lower than the CRM asphalt mixtures at the same compaction temperature. It proves the warm-mix effects of Sas and Evm for improved compact ability at the same temperature. The data in Figs. 9 and 10 show that, in order to reach the same air voids, the compaction temperatures of the CRM mixture with 3, 3.5 and 4 % Sas are 10, 15 and 20 C than the compaction temperature of the original CRM mixture, respectively. On the other hand, 0.6, 0.7 and 6.00
1.E+05
CRM binder
with 3%Sas
with 3.5%Sas
with 4%Sas
Original CRM binder with Sas 5.50
VV (%)
G*/sinδ (Pa)
with Evm
1.E+04
5.00
4.50
1.E+03 1.E-01
1.E+00
Frequency (Hz)
Fig. 8 G*/sind of different binders at different frequencies
1.E+01
4.00 130
140
150
160
170
180
Temperature ( ) Fig. 9 Air voids of CRM binders with Sas at different temperatures
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CRM binder
with 0.6%Evm
with 0.7%Evm
with 0.8%Evm
Dynamic stability(mm-1)
6.00
VV (%)
5.50
5.00
7000 6000 5000 4000 3000 2000 1000 0
4.50
CRM
with 3%Sas
with 3.5%Sas
with 4%Sas
with with with 0.6%Evm 0.7%Evm 0.8%Evm
Mixtures 4.00 130
140
150
160
170
180
Fig. 11 Testing results of wheel tracking test for different CRM asphalt mixtures
Temperature (℃) 5000
Table 5 Volumetric parameters of different CRM mixtures
Failure strain (με)
4500
Fig. 10 Air voids of CRM binders with Evm at different temperatures
4000 3500 3000 2500 2000
Mixtures
VV (%)
VMA (%)
VFA (%)
Original CRM mixture
4.50
18.01
75.01
500
CRM mixture with 3 % Sas
4.53
18.05
74.90
0
CRM mixture with 3.5 % Sas
4.49
17.97
75.01
CRM mixture with 4 % Sas
4.54
18.11
74.93
CRM mixture with 0.6 % Evm
4.48
18.03
75.15
CRM mixture with 0.7 % Evm
4.51
17.95
74.87
CRM mixture with 0.8 % Evm
4.56
18.11
74.82
1500 1000
3.5 Performances of CRM Asphalt Mixture Wheel tracking test, low-temperature bending beam test, immersion Marshall test and freeze–thaw splitting test
123
with 3%Sas
with 3.5%Sas
with 4%Sas
with with with 0.6%Evm 0.7%Evm 0.8%Evm
Mixtures
Fig. 12 Testing results of low-temperature bending beam test for different CRM asphalt mixtures
95 94 93
MSR (%)
0.8 % Evm in the CRM binder can lower the temperatures by 10, 15 and 20 C, respectively, as compared to original CRM mixture. To further confirm the previous analysis, the original CRM mixture was prepared at 170 C while CRM mixtures with 3, 3.5 and 4 % Sas additive were prepared at 160, 155 and 150 C, respectively, and CRM mixtures with 0.6, 0.7 and 0.8 % Evm were also prepared at 160, 155 and 150 C, respectively. The important volumetric parameters including air voids (VV), voids of mineral aggregates (VMA) and voids filled with asphalt (VFM) for the different CRM mixtures are summarized in Table 5. It can be seen that all of the mixtures have similar volumetric parameters. It confirms well the previous conclusions about the compaction temperature reduction by warm-mix additives.
CRM
92 91 90 89 88 87 86 85 CRM
with 3%Sas
with 3.5%Sas
with 4%Sas
with with with 0.6%Evm 0.7%Evm 0.8%Evm
Mixtures Fig. 13 Testing results of immersion Marshall test for different CRM asphalt mixtures
were conducted to evaluate the dynamic stability, failure strain, MSR and TSR of different CRM asphalt mixtures with or without warm-mix additives. Figures 11, 12, 13 and 14 summarize the test results for the original CRM asphalt mixture, CRM asphalt mixtures with 3, 3.5 and 4 %
Int. J. Civ. Eng.
4.
91 90
TSR (%)
89 88 87 86 85 84 83
CRM
with 3%Sas
with 3.5%Sas
with 4%Sas
with with with 0.6%Evm 0.7%Evm 0.8%Evm
Mixtures Fig. 14 Testing results of freeze–thaw splitting test for different CRM asphalt mixtures
Sas and CRM asphalt mixtures with 0.6, 0.7 and 0.8 % Evm, respectively. It can be seen that Sas can improve the anti-rutting performance of CRM asphalt mixture while jeopardizing its low-temperature performance. It is also shown that Sas has negative influences on the moisture stability of CRM asphalt mixture, although the effect is not significant. On the other hand, Evm shows no obvious influences on the high-temperature and low-temperature performance of CRM asphalt mixtures. But it improves moisture stability of CRM asphalt mixture. It is noted that the performance of the warm-mix CRM asphalt mixture was found better than the conventional asphalt mixture with the same base binder regardless of the type of warm mix additive.
4 Conclusions Based on the laboratory testing results, the main findings are as follows: 1.
2.
3.
The Sas warm-mix additive can improve the antirutting performance of CRM asphalt mixture while affecting its moisture stability negatively. The Evm warm-mix additive has no significant influence on high- and low-temperature performance of CRM asphalt mixture and improves its moisture stability.
The Sas warm-mix additive has significant influences on the high-temperature viscosity of CRM binder, while the Evm warm-mix additive has no obvious influences. However, Evm has significant influence on the viscosity of CRM asphalt mastic. Sas warm-mix additive has significant influence on both the rheological properties and mechanical properties of CRM binder while Evm warm-mix additive has no obvious influence. It is indicated that Sas can improve the temperature sensitivity and high-temperature performance of CRM binder while having negative influence on its ductility. With 3–4 % Sas in the CRM binder, the compaction temperature of warm-mix CRM asphalt mixture can be lowered by 10–20 C than the original CRM asphalt mixture to reach the same air voids. Adding 0.6–0.8 % Evm in the CRM binder has the same warm-mix effect.
The test results prove the feasibility of using CRM binder with warm-mix additives. It is promising to use warm-mix additives to lower construction temperatures while preserving the pavement performance. The findings presented in this study were based on one base binder and one CRM source. Further studies will be conducted with more material variations to validate the findings. Acknowledgments The study is financially supported by National Natural Science Foundation of China (No. 51378006), National Science and Technology Support Program of China (No. 2014BAG05B04), Huoyingdong Foundation of the Ministry of Education of China (No. 141076), Excellent Young Teacher Program of Southeast University (2242015R30027), and State Key Laboratory of High Performance Civil Engineering Materials.
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