High temperature rheological properties of APAO and EVA compound modified asphalt

Construction and Building Materials 233 (2020) 117246

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

High temperature rheological properties of APAO and EVA compound modified asphalt Kezhen Yan a,b,⇑, Shan Tian a,b, Jinghao Chen a,b, Jun Liu a,b a b

College of Civil Engineering, Hunan University, Changsha 410082, China Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, Changsha 410082, China

h i g h l i g h t s
The addition of APAO and EVA increased the elasticity of asphalt.
In FTIR test, the additive reacted with asphalt.
The addition of EVA affected the rheological properties of compound modified asphalt at medium temperature.
The compound modification of EVA/APAO showed good crack resistance at low temperature.

a r t i c l e

i n f o

Article history: Received 1 June 2019 Received in revised form 21 September 2019 Accepted 12 October 2019

Keywords: Storage stability High temperature performance Temperature sensitivity Complex modulus

a b s t r a c t This study aims to explore the laboratory performance of APAO (Amorphous Poly Alpha Olefin) and EVA (ethylene-vinyl acetate copolymer) compound modified asphalt. Four EVA concentrations (i.e., 0%, 2%, 4%, and 6% by the weight of base asphalt) and four APAO concentrations (i.e., 0%, 2%, 4%, and 6% by the weight of base asphalt) were selected. Conventional tests (penetration, softening point, ductility and viscosity) were conducted. Frequency sweep, temperature sweep and multiple stress creep recovery (MSCR) tests were carried out to investigate the rheological properties of the asphalt binders and the storage stability was measured by cigar tube tests. The aging effect was evaluated by using dynamic shear rheometer (DSR) testing results. Fourier transform infrared spectroscopy (FTIR) test was used to study the chemical reaction of the asphalt. The results represented that the addition of additives (i.e., APAO and EVA) decreased the nonrecoverable creep compliance and aging index while increased softening point, elastic recovery, complex modulus and recovery rates, which indicating that APAO and EVA enhanced the high temperature properties of asphalt. Specially, in the ductility test at 5 , the addition of APAO/EVA greatly improved the crack resistance at low temperature. The increasing VTS (viscosity-temperature susceptibility) indicated the additives enhanced the resistance to temperature susceptibility of this compound modified asphalt. Besides, the binder with APAO is better than that with EVA alone, especially in the elastic recovery and aging effect. Besides, the storage stability test results showed that the increase of APAO improved the stability of asphalt and the compound modified asphalt binders showed good resistance to cracking at low temperature in ductility test at 5 °C. The FTIR test showed that chemical reactions might happen during the mixing process of asphalt. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Asphalt pavements in China are subjected to heavy traffic and adverse loading and environmental conditions. Distresses like cracking and rutting are often seen in the pavements in China. Therefore, the application to improve the properties of asphalt ⇑ Corresponding author at: College of Civil Engineering, Hunan University, Changsha 410082, China. E-mail address: [email protected] (K. Yan). https://doi.org/10.1016/j.conbuildmat.2019.117246 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

pavement and prolong its working life has become a major task in highway construction for Chinese engineers [1–3]. Polymer modified bitumen is one of the most common applications in the manufacture of good pavement [4–6]. Basically, polymers are divided into two categories, one is the plastomer, the other is thermoplastic elastomer. EVA is one of plastomer which have been used in road construction for 20 years and is second frequently used modifier [7]. Many researchers have studied the properties of EVA modified asphalt. This kind of polymer modifier can easily be blended with asphalt [7], and improve

2

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

performance of asphalt, especially rheological properties on high temperature and low temperature [5,8,9]. What’s more, EVA is economical, and it can be recycled from the waste plastic [10–12]. Through the study of EVA compound modified asphalt, EVA can be better applied and reduce the waste of related resources. However, in addition to these advantages, EVA also has its shortcomings [13]. The main problem of EVA modified asphalt is that it is easy to isolate with asphalt at high temperature. In M. Ameri’s research, the M. Ameri et al. (2013) compared the storage stability of 3% EVA asphalt and 1% EVA asphalt, and found that the higher EVA dosage in the asphalt, the greater the degree of segregation [6]. Moreover, the elastic recovery of EVA modified asphalt is poor which is easily to cause rutting in pavement [14]. So, in order to overcome these shortcomings, some researchers incorporated other additives to the modified asphalt, like SBS and crumb rubber [15,16]. And the new type of composite modified asphalt has become a new trend of the asphalt. In this study, APAO is selected to combine with EVA to generate compound modified asphalt. APAO is a kind of amorphous plastic body material with low molecular weight which is amorphous and irregular in microstructure [17]. Therefore, this material has many characteristics that crystalline polymers do not have such as easy workability and recyclable, so it can save resource and be helpful for environmental protection [18]. As a thermoplastic rubber modifier, not only can APAO improve the resistance of asphalt to deformation at high temperature, but also reduce the temperature sensitivity of asphalt and improve the anti-cracking ability of asphalt mixture at low temperature [19–21]. Specially, the storage stability of APAO modified asphalt is good if the content of APAO content is no more than 6% [22], and the elastic recovery increased with the increase of APAO in asphalt [23]. Therefore, APAO and EVA were used to add into the base asphalt to evaluate the modified effect of this combination (APAO and EVA) in this study. Then, the conventional, rheological FTIR test and the aging resistance properties were tested to research the properties of combination of APAO and EVA in different temperature. Multiply stress creep-recovery (MSCR) also were tested to assess the high temperature properties. Moreover, thermal stability and elastic

recovery also being researched in this study to evaluate the storage ability in high temperature and elastic property in loading condition. Finally, based on these researches, it is hoped that the best ratio of APAO/EVA on asphalt could be found to be salutary to the further researches.

2. Experimental materials and methods 2.1. Laboratory materials In this article, the asphalt with penetration grade of 60–80 is selected as base asphalt which will be modified by the additives. The basic properties of the base binder are prepared in Table 1. EVA is produced by DuPont in the USA and the physical nature is displayed in Table 2. The density of APAO (in Table 3) is 1.41 g/ cm3, and the softening point is 295 °C. 2.2. The process of making compound modified asphalt In this research, the compound modified binders were made by high-speed shear method. Firstly, the matrix binder was preheated at 170 ± 5 °C to liquid. According to M. Ameri’s study, the higher EVA dosage in the asphalt is, the greater degree of segregation is [6]. So, the dosage of EVA is not property too high, and the content of APAO which is according to J. Wei’s study was also selected [22]. Then, APAO (0, 2, 4 and 6 wt%) and EVA (0, 2, 4 and 6 wt%) were added to the matrix asphalt simultaneously, under 170 ± 5 °C with high speed shear of 3000 rpm for 30 min [5,24]. Finally, the mixes were stirred with a low speed (500 rpm, mechanical agitation) for ten minutes to remove the bubbles in mixture [25].

2.3. Test methods Following the preparation of the polymer modified asphalt, various rheological and conventional tests were carried out. Fig. 1 presents the experimental process.

Table 1 Properties of 70# Asphalt. Binder testing

Specification

Test temperature

Values

Specification

Penetration (100 g,5 s)/0.1 mm Softening point/ °C Ductility (5 cm/min)/cm

69.7 50.2 ＞150

25 °C – 15 °C

69.0 50.2 131.5

ASTM D5(ASTM 2013) ASTM D36(ASTM 2012) ASTM D113(ASTM 2007)

Table 2 Physical Properties of EVA. Product parameters

Test conditions

Units

Values

Specification

Density The melt flow rate VA content Melting point

190 °C/2.16 kg 190 °C/2.16 kg 190 °C/2.16 kg 190 °C/2.16 kg

g/cm3 g/10 min % °C(°F)

0.955 6 28 72(1 6 2)

ASTM D792(ISO 1183) ASTM D1238(ISO 1133) – ASTM D3418(ISO 3146)

Table 3 Physical Properties of APAO. Properties

Test conditions

Units

Values

Specification

Density Tensile strength Bending modulus Melting point

190 °C/2.16 kg 23 °C 23 °C 190 °C/2.16 kg

g/cm3 MPa MPa °C

0.955 210 9000 295

ASTM D792(ISO 1183) – – ASTM D3418(ISO 3146)

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

3

Fig. 1. Experimental design flow chart.

2.3.1. Conventional test In the study, physical properties tests such as penetration at 25 °C (ASTM D 5), softening point test (ASTM D 36), and ductility test at 5 °C (ASTM D 113) were carried out. 2.3.2. Rotational viscosity test Brookfield rotational viscometer DVII was used to measure the rotational viscosity of asphalt. Viscosity reflects the high temperature fluidity and workability of asphalt. The viscosity values at three temperatures (135 °C, 155 °C, and 175 °C) were measured following AASHTO T 316 [26] and the viscosity-temperature curves were drew up. Specially, the temperature sensitivity is studied by the indicator of VTS (viscosity-temperature susceptibility) [27,28]. Equation (1) shows the definition.

 log ½log ðgÞ

< 1:0945 ! log ½log ðgÞ ¼ A þ VTS  log ðT Þ  1:0945 ! log ½log ðgÞ ¼ 1:0945

ð1Þ

where g is the viscosity values of binder (cp), A is the intercept of the linear regression equation, T is the test temperature, VTS is the slope of the regression line and the value of 1.0945 is the vitrification of binder at low temperature. 2.3.3. Elastic recovery test According to Dimitrios G. Papageorgioua’s research [16], the interlocking effect in APAO prevents the plastic deformation which means the material has good mechanical strength. To measure the elasticity of asphalt, the elastic recovery tests were carried out (ASTM D 6084). This test process is similar to the ductility test. Firstly, the sample was bathed in water for 1.5 h at 25 °C. Then, the asphalt sample was stretched to 10 cm (5 cm/min) and cut in the middle. After that, keep the sample in water for 1 h with constant temperature, and measure the length of the sample. The elastic recovery value will be calculated in the end and the equation is as follows. Excellent elastic resilience means that asphalt will have excellent fatigue and cracking resistance. It’s an important indicator for polymer modified asphalt.

Recov ery; % ¼

EX  100 E

ð2Þ

where: E: original elongation of the specimen, cm; X: elongation of the specimen, at the completion of the specified recovery time, with severed ends just touching, cm.

2.3.4. Storage stability test The main problem of polymer modified asphalt is the lack of stability during long-term storage at high temperature. Following ASTM D 7173, the cigar tube tests (also named storage stability test) are used to test the separation tendency of the polymer. Before the test, the mixed asphalt was poured into the cigar tube and sealed storage. The segregation process involves heating the tube vertically for 48 h in a 163 °C oven. After that, when the tube was cooled, the upper and lower which was one third long of the cigar tube were tested for softening point test. In the storage stability test, the asphalt (6%APAO + 2%EVA) was tested to verify their stability. 2.3.5. Short-term aging of asphalt In this study, the asphalt was subjected to thin film oven aging process according to ASTM D1754. In this test, the asphalt sample was placed on thin film oven which was equipped with a thermostat and a rotating disc rack at 163 °C for 5 h. 2.3.6. Rheological properties tests In this research, the rheological properties were assessed by using dynamic shear rheometer (DSR), with the plate geometry with a 25-mm diameter plate and 1-mm gap [29]. Generally, the rheological indicators of temperature sweep and frequency sweep in the SHRP program is based on the material is in the range of linear viscoelastic range. The rheological properties of asphalt were studied from different temperature (temperature sweep), vehicle speeds (frequency sweep) and loads (multiple stress creep recovery), and the strain amplitude values for both the frequency sweep and temperature sweep were limited to the linear viscoelastic (LVE) response of the binder [30]. The linear viscoelastic condition, for DSR, refers to the area ensure that the decline range of complex modulus does not exceed 5% through measurement, which is shown in Fig. 2. The temperature sweep was performed between 30 and 90 °C at the constant frequency of 1.5 Hz which was consistent with the actual frequency of the pavement, and the recommendation strain values of LVE-test were adopted. Then complex modulus G* and phase angle d were obtained. G* is defined as the ratio of maximum stress to maximum strain, which indicates the resistance to deformation. d indicates the viscoelastic state of asphalt. When d equals to 0°, it means the material is purely elastic, whereas d of 90°

4

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

Fig. 2. The example of amplitude sweep.

corresponds to completely viscous [31,32]. G*/sind was calculated by these two parameters and it is a main parameter to evaluate the rutting resistance of asphalt. The higher G*/sind value, the better rutting resistance. Additionally, to simulate the different traffic speed, the frequency sweep will be carried out. The frequency was varied from 102 to 0.1 rad/s at 60 °C. It is believed that frequency of 1.5 Hz corresponds to traffic speed of 55 mph [31]. In this test, the parameters of G* and d were measured at different frequencies. The test mode of temperature sweep and frequency sweep is controlled-strain loading, whereas the mode of MSCR (multiple stress creep recovery) is controlled-stress loading. Therefore, MSCR test will evaluate the rheological properties and rutting resistance of asphalt from different perspectives. MSCR is aimed to evaluate the elastic response and the rutting resistance at different stress levels (0.1 kPa and 3.2 kPa). During the test the binder will be subjected to 10 times cycle of creep stress (1 s-duration one cycle) and recovery (9 s-duration one cycle). Then, two parameters (the creep recovery rate R100, R3200 and unrecoverable creep flexibility) will be calculated in the experiment. The test process and the sample preparation have been stated in ASTM D7405, and the test temperature was 58, 64 and 70 °C with TFOT-aged binders

Fig. 3. The penetration test result at 25 °C.

Fig. 4. Softening Point test results.

2.3.7. FTIR spectra analysis The molecular structure of the modified asphalt was analyzed by Fourier transform infrared spectroscopy (FTIR) characterization technologies. In this experiment, the bitumen sample were dissolved in carbon disulfide solvent at a mass percentage of 5%. Then a small amount of solution was dripped on the potassium bromide slide and the solvent was dried in infrared light. Finally, the slide was put into the instrument for experiment. 3. Results and discussions 3.1. Physical properties test results The effect of APAO/EVA additive on the penetration of asphalt are shown in Fig. 3. When the content of one additive is unchanged, the penetration of asphalt decreases with the increase of another additive. The change rate of penetration with the increase of every 2% APAO is larger than that the increase of every of 2% EVA. Furthermore, the minimum penetration value of compound modified asphalt is 33.3(0.1 mm), which decreases 52% compare to base asphalt.

In Fig. 4, the softening point result changed with the content of modifier. On basis of this result, it can be noticed that when the dosage of APAO is 0%, the values of softening point increased by 5%, 9.5%, and 6%, respectively with the increases of every 2% EVA. However, when the dosage of EVA is 0%, the values of softening point increased by 5%, 22%, and 3%, respectively with the increases of every 2% APAO. Besides, the maximum softening point value was showed when the content of EVA and APAO reach 6%. Therefore, the addition of APAO and EVA in asphalt increased the value of softening point which indicated the better high temperature performance. What’s more, as the content of EVA increased, the change rate of the softening point slowed down, it could be inferred that the content of EVA in the complex modified asphalt should not exceed 6% The ductility at 5 °C which represents the low temperature performance of asphalt are shown in Fig. 5. In Fig. 5, the ductility of asphalt with 6%APAO and 6%EVA is about 2.5 times than that of base asphalt. However, the effect of 6%APAO combined with 6% EVA is not the best. Compared to base asphalt, it is found that

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

5

When the content of APAO remains 2% or 4%, the values of the asphalt reached the maximum with 2% EVA. Good elastic resilience can reduce residual deformation and improve fatigue resistance of asphalt. Therefore, the result represents that addition of APAO and EVA can both improve the rutting resistance of asphalt, and the effect of APAO is more obvious. In this test, the content of APAO is recommended to be no more than 6%, because the recovery is too high to increase, and the dosage of EVA is recommended to be no more than 2% (by wt.) to increase the role of APAO in elastic recovery performance. 3.2. Viscosity test results

Fig. 5. Ductility results at 5 °C.

The viscosity values of different types modifier are shown in Fig. 7. It can be noticed the viscosity values increase with the increase of APAO and EVA. As shown in Fig. 7(a) and (b), adding 2% EVA or 2% APAO to base asphalt, and the viscosity increased slightly. When the proportion of APAO or EVA remained, and another additive increased from 0% to 4%, the viscosity of asphalt was almost the same, which mean APAO and EVA both ameliorate the viscosity properties in different temperature, even there were the same influence when the content of additives was less than

the asphalt with 2% EVA has the largest value (12.5 cm). It indicates that the modifier-EVA indeed improves the low temperature performance, but the performance isn’t increased with the increase of EVA. When the EVA is constant (0%), with the increase of every 2%APAO, the ductility values increase 123%, 27% and 133%, respectively, and the 6% APAO has the maximum of ductility. However, under the compound modification of EVA and APAO, when the dosage of EVA remained constant, the ductility isn’t always increased as the content of APAO increases, and it will be decrease slightly when the dosage of APAO is 4% or 6%. According to the data analysis above, the effect of APAO on asphalt performance at low temperature is greater than that of EVA. According to the elastic recovery test in Fig. 6, it can be noticed that the recovery value of the base asphalt is the minimum (20%) and the elastic recovery value increases with the increase of dosage under the action of single modifier. As the content of EVA remains 2% and the APAO increases from 0% to 6%, the percentage of elastic recovery is close to 95% which is equivalent to the role of SBS [25]. Specially, the value of asphalt only with 6%APAO even reaches 96%. Maybe, the addition of EVA reduced the space for APAO to play, so the recovery value wasn’t bigger than the asphalt with 6%APAO.

Fig. 6. Elastic recovery test result.

Fig. 7. Viscosity values of asphalt at different temperatures.

6

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

4% (by wt.) . As the APAO or EVA increases to 6%, the viscosity values were 2.8 Pas and 2.2 Pas. The results showed that the improvement of asphalt viscosity by adding APAO was greater than EVA. If the asphalt is too sticky, it would affect the workability of asphalt. Hence, in the technical standards stipulated, the viscosity of polymer modified asphalt shouldn’t be greater than 3 Pas at 135 °C and these kinds of asphalt all meet the requirement. Aim to assess the temperature sensitivity of asphalt, the relationship between log(Temperature) and log(log(Viscosity)) are figured out in Fig. 8. According to the Eq. (1), the parameter VTS which represents the temperature sensitivity of asphalt will be calculated. The VTS is larger, the gradient is smaller which means the viscosity have smaller changes with the temperature increase, and the temperature sensitivity is lower. In Fig. 8(a) and (b), the VTS value of the asphalt (6%APAO + 2%EVA) is 0.9363, compare to base asphalt (1.2399), it increases 32%. Therefore, VTS values increases with the increase content of additives. And the VTS value of asphalt (6%APAO + 2%EVA) is greater than the asphalt (2%APAO + 6%EVA), which means the improvement of resistance to temperature sensitivity after the addition of APAO is greater than that of EVA. 3.3. Storage stability test The purpose of this test is to simulate the separation process of asphalt after long time and high temperature. If the temperature difference between the upper and bottom is larger, the modified

Fig. 8. Relationships between log(T) and log(log(Viscosity)).

Table 4 Storage stability test results. Types of modifier

Top (°C)

Bottom (°C)

Temperature difference

2%EVA 2%APAO 6%APAO 6%APAO + 2%EVA

53.1 52.3 67.9 72.8

49.7 53.5 68.2 71.9

3.4 1.2 0.3 0.9

asphalt would not be endurable to high temperature and perennial loading conditions. In terms of the specification JTG-F40-2004, the temperature difference should not more than 2.5 °C. As shown in Table 4, the performance of APAO modified asphalt was more stable and its temperature difference was no more than 2.5 °C. It may due to the uniform distribution of APAO. On the contrary, EVA modified asphalt was easy to separate of which temperature difference was 3.4 °C. However, the storage stability of compound modified asphalt was greatly improved. In Table 4, after adding 6% APAO and 2%EVA into asphalt, the temperature difference decreased to 0.9 °C. According to the data above, it is concluded that plenty of APAO with irregular structure were uniformly distributed in asphalt, which reduced the flow space of other modifier and prevented the EVA from separating. Therefore, APAO is a good stabilizer to improve the stability of asphalt, which is helpful to the development of compound modified asphalt. 3.4. Rheological properties test results 3.4.1. Temperature sweep results To evaluate the rheological properties of compound asphalt, Figs. 9 and 10 show the relationship curves between the complex modulus, phase angle, rutting factor and temperature. In this test, two different types modified asphalt are selected: One is to change the amount of APAO with 2% EVA [6], the other is to change the amount of EVA when APAO content is 2% (by wt.). The temperature dependence of G* and d for the compound modified asphalt have been evaluated in Fig. 9. It can be seen from the Fig. 9 that, as the temperature increases, the parameter G* decreases and the parameter d increases, which indicated that increased fluidity of asphalt binder and the transition from elastomer to viscoelastic. However, in Fig. 9(a), it is obviously that the G* of all the modified asphalt are lager than the base asphalt, indicating that a greater shear deformation resistance. Furthermore, when the content of EVA remains 2%, the G* ascends and d descends with the augmentation of APAO. It indicates that the accretion of APAO increases resistance of deformation of bitumen and it can coexists well with EVA in asphalt. Specially, the effect of EVA are different from APAO. In Fig. 9(b), it is evident that the four curves have an intersection point which is around 54 °C. Compared to the asphalt with 2%APAO, as the increase of EVA, the G* decreases between 30 °C and 54 °C. After 54 °C, the G* increased as the dosage of EVA increase and the values are bigger than the APAO single modified asphalt. However, with the increase of EVA, the phase angle is decreased which indicated the addition of EVA improved the elasticity of asphalt. According to Yang et al. [33], the apparent elasticity or viscosity of asphalt is determined by the 75° phase angle of asphalt in rheological analysis. When the phase angle of asphalt is bigger than 75°, the asphalt shows viscosity and elastic instead. In the Fig. 9(a) and (b), after 30 °C, the phase Angle of matrix asphalt is greater than 75°, which means that it gradually loses elasticity. The modified asphalt gradually loses elasticity after 45 °C, and the temperature of losing elasticity gradually increases with the increase content of modifier, implying both APAO and EVA can make asphalt more resilient. In addition, according to A. Yuliestyan [34], when the temperature access to the fusion point of EVA, the crystal area collapses. As

7

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

Fig. 9. G* and d for base asphalt and compound modified asphalt.

the increase of temperature, the crystal area of EVA gradually collapses. What’s more, the change rate of G* decreases with the increase of temperature, implying that EVA has good stability at high temperature. Compared to the base asphalt, after the fusion point temperature, the G* of asphalt increased with the increase of EVA. Furthermore, the rutting factor G*/sind of asphalt has been calculated by G* and d in Fig. 10. According to the specification AASHTO M320, the rutting factor is defined as the rutting resistance of binders. As depicted in Fig. 10(a), G*/sind increases as the increase of APAO at the range from 30 °C to 90 °C, indicating that APAO has a good effect on asphalt rutting resistance at medium and high temperatures. However, as the increase of EVA in Fig. 10(b), G*/sind decreased until the melting point temperature of EVA. After the melting point temperature, it can be observed that G*/sind increases as the increase of EVA. It means that EVA is not conducive to improving the anti-rutting ability of asphalt at medium temperature and increase the value of G*/sind at high temperature. Moreover, in Table 5, it displays the failure temperature (G*/sind = 1.0 kPa) of different binders. It is clearly that the failure temperatures were increased as the addition of additives and the failure temperatures of asphalt (6%APAO + 2%EVA) is 82.9 °C which is larger than base asphalt (66.5 °C). Therefore, the addition of APAO and EVA greatly improves the high temperature performance

Fig. 10. Rutting factor for base asphalt and modified asphalt.

Table 5 The failure temperature (G*/sind = 1.0 kPa) for different bitumens. Additives

0%EVA 2%EVA 4%EVA 6%EVA

Failure temperatures/°C 0%APAO

2%APAO

4%APAO

6%APAO

66.5 71.8 – –

71.8 74.2 76.7 78.6

– 80.8 – –

– 82.9 – –

of asphalt. Compared the asphalt 6%APAO + 2%EVA and 2%EVA + 6% APAO, the failure temperature of 6%APAO is only 5% larger than the asphalt with 6%EVA. Above all, both APAO and EVA can ameliorate the high temperature properties of composite modified asphalt, but the addition of EVA is better at improving high temperature performance 3.4.2. Frequency sweep test results According to the Fig. 11, it can be noticed that the G* increases and the d decreases as the angular frequency increases. It means

8

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

Fig. 11. Frequency sweep results at 60 °C.

that with the increase of vehicle speed, asphalt shows more rigid and elastic. When the content of EVA remains 2% and increases the content of APAO, G* increased evidently when the addition of APAO increased from 2% to 4%, and the d decreases. Moreover, the asphalt with 6%APAO and 2%EVA shows fully elasticity whose d is blow than 75° between 1 rad/s and 100 rad/s. It proves that the addition of APAO plays a significant role in improving the strength and elasticity of asphalt. Besides, when only change the content of EVA and the content of APAO is 2%, the improvement of G* is not obvious and the d is decrease with the increase of EVA. It indicates that the modifiers APAO and EVA can change the transformation from elasticity to viscosity, but APAO is more prominent in improving shear resistance of asphalt. Therefore, it is further concluded that the content of EVA in asphalt does not need to be used too much which is also verified in ductility and elastic recovery tests.

3.4.3. MSCR results In the MSCR test, the creep recovery rate (R100 and R3200) and unrecoverable creep flexibility (J nr3:2 ) of asphalt are two required parameters by applying different loads to asphalt. The creep recovery shows the elasticity of binders and the unrecoverable creep represents the ability of anti-permanent deformation of bitumens which undergo different repeated traffic loads.

Fig. 12. Results of elastic recovery values under 100 Pa and 3200 Pa stress.

Figs. 12 and 13 show the creep recovery results under 0.1 kPa and 3.2 kPa. In these diagrams, the results show that with the rise of the stress, the elastic recovery of all binders decreased. In addition, with the rise of temperature, the elastic recovery value of asphalt was greatly reduced. It was contributed that the high temperature made the asphalt sticky and lost some of its elasticity. When the APAO content remained unchanged, the recovery rate augmented until the EVA content increases to 4% in 0.1 kPa and 3.2 kPa. Moreover, the maximum R100 value (2%APAO + 4%EVA) is 33.63% which is ten times the base pitch. Similarly, as the increase of APAO and the content of EVA remained 2% in Fig. 13, the recovery values increased exponentially and the maximum R100 (6%APAO + 2%EVA) value is even as high as 72%, implying an elastic characteristic of this binders. This kind of binder (6% APAO + 2%EVA) also showed good elastic in the elastic recovery test. Compare the effect of the two additives, it can be found that the effect of APAO on asphalt is more obvious than EVA which makes asphalt more elastic. In Fig. 14, the graphs show the nonrecoverable creep compliance (J nr ) for these binders at three test temperatures. Normally, with the increase of temperature, the asphalt is gradually converted into viscous. Therefore, the J nr value exhibits increased with the rise of temperature. When the content of APAO remained, the J nr of asphalt presented a parabolic growth trend and the asphalt with 4%EVA has the minimum value. Such results suggest that

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

9

Fig.13. Results of elastic recovery values under 100 Pa and 3200 Pa stress.

4%EVA maybe the best content to reduce the permanent deformation of pavement under repeated traffic loads. However, when the EVA content is constant, the larger APAO content is, the lower J nr values is. When the proportion of APAO reach 6%, the asphalt has the minimum value which is even smaller than the binder with 2%APAO and 4%EVA. Therefore, based on the data analysis of the R and J nr , it suggests that the addition of APAO has better effect to the asphalt which significantly reduce the permanent deformation of pavement under repeated traffic loads. 3.5. Aging effect In the process of using asphalt, it is hard to avoid the influence of high temperature, external load and other natural factors, which causes the physical or chemical changes of asphalt. In order to ensure the asphalt meets the requirements of a certain period time, the durability of asphalt has been studied. It’s also known as the anti-aging of asphalt. In this research, the aging index (AI) is an indicator which aging level evaluation of asphalt, and it is displayed in Eq. (3) [4].

AI ¼

G =sinðdÞaged G =sinðdÞunaged

ð3Þ

Fig. 14. Variations in J nr with changes in additive content at three test temperatures.

G*/sin(d) is the rutting parameter of asphalt binders which are respectively TFOT aged and unaged in temperature sweep. When the AI values are greater than 1, it indicates a degree of hardening of the asphalt after the process of TFOT. Furthermore, the larger proportion of AI, the greater the degree of hardening of asphalt. (The value of AI may change due to the degradation of the polymer or oxidation of the asphalt [35]) Table 6 lists the aging effect results of different kinds of asphalt binders at various temperatures. In Table 5, the AI value of the original aging asphalt is the highest, reach to 2.4. After adding EVA to asphalt, the AI values did not change. However, the asphalt shows excellent durability when 4% APAO mixed with 2% EVA (around 1.0). When more APAO was mixed, the AI of asphalt didn’t increase compared with 4% APAO. Therefore, it indicates that APAO can improve the stability of asphalt and 4% is the best content. Similarly, when the content of APAO is constant, it shows the similar trend as the rise of EVA. The AI value of asphalt with 2%APAO and 4%EVA is minimum, but the AI value is still smaller than the asphalt with 4%APAO and 2%EVA. Therefore, the asphalt with 4%APAO had the least impact after short-term aging.

10

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

Table 6 AI values evaluated for various asphalt binders at different temperatures. Binders

0%APAO + 0%EVA + 70# 0%APAO + 2%EVA + 70# 2%APAO + 2%EVA + 70# 4%APAO + 2%EVA + 70# 6%APAO + 2%EVA + 70# 2%APAO + 0%EVA + 70# 2%APAO + 2%EVA + 70# 2%APAO + 4%EVA + 70# 2%APAO + 6%EVA + 70#

Aging indices at different temperatures 52 °C

58 °C

64 °C

70 °C

76 °C

2.4 2.3 2.3 0.9 1.4 2.8 2.3 1.9 4.4

2.3 2.3 2.3 1.0 1.5 2.8 2.3 1.8 3.9

2.3 2.3 2.3 1.0 1.6 2.8 2.3 1.7 3.7

2.2 2.3 2.3 1.0 1.7 2.8 2.3 1.8 3.5

2.2 2.2 2.2 1.0 1.7 2.7 2.2 1.8 3.3

It can be seen from the Fig. 15(a) and (b) that, all absorption peaks became weaker. Furthermore, two new peaks (1243 cm1 and 1740 cm1) appeared in 2%EVA modified asphalt. This means that the chemical reaction might occur during the mixing process. Compared the base asphalt and APAO-modified asphalt, two new peaks (739 cm1 and 968 cm1) appeared and the transmissivity peaks of 2916 cm1 and 2850 cm1 were strengthened. In addition to showing that APAO was reacting with these two groups, according to Liu’s research, there are two double bonds at the end of each APAO molecular chain and the bending vibration of CAH generates the peak 968 cm1[37]. In Fig. 15d, it can be found that the new peaks generated by APAO and EVA still existed in the composite modified asphalt. It means that APAO and EVA can react with asphalt to some extent.

3.6. FTIR spectra test In Fig. 15, it displays the FTIR test results about the base asphalt, 2% EVA-modified asphalt, 6% APAO-modified asphalt and the complex asphalt (6%APAO and 2%EVA). The transmissivity peaks at 739 cm1 and 968 cm1 represented CAH bend (ortho) out of plane deformation vibration[24]. The peak at 1243 cm1 stood for (CH3)3C-R stretching vibrations [36]. The transmissivity peaks at 1460 cm1 and 1380 cm1 represented CAH symmetric deforming in CH3 vibrations. Carboxylic acid (C@O)vibrations were observed at 1740 cm1. The absorption peaks at 2916 cm1 and 2850 cm1 were the results of asymmetric stretching vibration and symmetrical vibration of CAH in bitumen methylene (ACH2A), respectively.

4. Summary and conclusions In this study, the effects of APAO and EVA on the properties of asphalt binder were studied. The conventional tests (such as penetration and softening point tests), temperature sweep test, frequency sweep test, short-term aging rheological property test, FTIR test and storage stability test were conducted. Based on the testing results, the following conclusions can be drawn: (1) The addition of APAO and EVA enhanced the resistance to temperature susceptibility of asphalt. What’s more, the effect of APAO/EVA can both ameliorate the low and high temperature performance. However, APAO played a more significant role in improving performance at low temperatures. And the FTIR test showed that the chemical reactions might happen during the mixing of the APAO/EVA. (2) In the temperature sweep test, the effect of APAO/EVA can improve the rutting resistance of asphalt at high temperature, but the performance of EVA is weakened to a certain extent at medium temperature. The frequency sweep test showed that, with the increase of APAO/EVA, the rutting resistance of APAO/EVA modified asphalt increased under different traffic speeds. (3) In the MSCR test, it suggests that the APAO/EVA can both improve the resistance to rutting under repeated traffic loads. Similarly, in the elastic recovery test, the compound modified asphalt (6%APAO + 2%EVA) showed excellent recovery rate. The aging effect test showed that, the addition of APAO could greatly resist the influence of asphalt aging process, especially at the dosage of 4%APAO. However, the addition of EVA showed little effect. (4) Make a comparison of the asphalt modified by EVA alone, the addition of APAO can further improve the high temperature rutting resistance and resistance to cracking at low temperature of asphalt. After considering the high-medium temperature performance, storage stability, elastic recovery and ductility test, the best content of EVA is 2%–4% and the addition of APAO should be no more than 6%. In this study, the incorporation of APAO/EVA show better in ductility test which indicates the better low temperature performance. So more low temperature tests are recommended, such as the BBR test.

Declaration of Competing Interest

Fig. 15. FTIR analysis: base asphalt; 2% EVA-modified asphalt; 6% APAO-modified asphalt; complex modified asphalt.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

K. Yan et al. / Construction and Building Materials 233 (2020) 117246

Acknowledgements This research was financed by the National Natural Science Foundation of China (No. 51278188, 51778224), National Key R&D Program of China (No. 0505400). The authors sincerely thank them for their support. References [1] B. Brule, Y. Brion, A. Tanguy, Paving asphalt polymer blends: relationships between composition, structure and properties, Association of Asphalt Paving Technologists Proc, 1988. [2] S.F. Brown, R.D.Rowlett, J.L.Boucher, In: Proceedings of the Conference on US SHRP Highway Research Program: Sharing the Benefits, (1990). [3] U. Isacsson, X. Lu, Testing and appraisal of polymer modified road bitumens— state of the art, Mater. Struct. 28 (3) (1995) 139–159. [4] E.A.A. Siddig, C.P. Feng, L.Y. Ming, Effects of ethylene vinyl acetate and nanoclay additions on high-temperature performance of asphalt binders, Constr. Build. Mater. 169 (2018) 276–282. [5] W.-Q. Luo, J.-C. Chen, Preparation and properties of bitumen modified by EVA graft copolymer, Constr. Build. Mater. 25 (4) (2011) 1830–1835. [6] M. Ameri, A. Mansourian, A.H. Sheikhmotevali, Laboratory evaluation of ethylene vinyl acetate modified bitumens and mixtures based upon performance related parameters, Constr. Build. Mater. 40 (2013) 438–447. [7] M. Liang, S. Ren, W. Fan, X. Xin, J. Shi, H. Luo, Rheological property and stability of polymer modified asphalt: effect of various vinyl-acetate structures in EVA copolymers, Constr. Build. Mater. 137 (2017) 367–380. [8] W. Stark, M. Jaunich, Investigation of Ethylene/Vinyl Acetate Copolymer (EVA) by thermal analysis DSC and DMA, Polym. Test. 30 (2) (2011) 236–242. [9] M. Ameri, A. Mansourian, A.H. Sheikhmotevali, Investigating effects of ethylene vinyl acetate and gilsonite modifiers upon performance of base bitumen using Superpave tests methodology, Constr. Build. Mater. 36 (2012) 1001–1007. [10] K. Yan, L. You, D. Wang, High-Temperature Performance of Polymer-Modified Asphalt Mixes: Preliminary Evaluation of the Usefulness of Standard Technical Index in Polymer-Modified Asphalt, Polymers 11 (9) (2019) 1404. [11] M.B. García-Morales, P. Partal, F.J. Navarro, F.J. Martínez-Boza, C. Gallegos, Linear viscoelasticity of recycled EVA-modified bitumens, Energy Fuels Am. Chem. Soc. J. 18 (2) (2004) 357–364. [12] N. Moumita, T.K. Chaki, K.R. Sudhakar, Effect of recycled EVA as modifier on the various properties of bituminous binder for road application, Adv. Mater. Res. 214 (2011) 339–343. [13] J. Zhu, B. Birgisson, N. Kringos, Polymer modification of bitumen: advances and challenges, Eur. Polym. J. 54 (5) (2014) 18–38. [14] O. González, M.E. Muñoz, A. Santamarı´a, M. Garcı´a-Morales, F.J. Navarro, P. Partal, Rheology and stability of bitumen/EVA blends, Eur. Polym. J. 40 (10) (2004) 2365–2372. [15] N. Saboo, R. Kumar, P. Kumar, A. Gupta, Ranking the rheological response of SBS- and EVA-modified bitumen using MSCR and LAS tests, J. Mater. Civ. Eng. 30 (8) (2018) 04018165. [16] R. Yu, X. Liu, M. Zhang, X. Zhu, C. Fang, Dynamic stability of ethylene-vinyl acetate copolymer/crumb rubber modified asphalt, Constr. Build. Mater. 156 (2017) 284–292.

11

[17] J. Shen, F. Li, S. Li, Experimental research of APAO modified bitumen, Highway 4 (1997) 27–32. [18] D.G. Papageorgiou, D.N. Bikiaris, K. Chrissafis, Effect of crystalline structure of polypropylene random copolymers on mechanical properties and thermal degradation kinetics, Thermochim. Acta 543 (2012) 288–294. [19] L. You, K. Yan, D. Wang, D. Ge, X. Song, Use ofamorphous-poly-alpha-olefin as an additive to improve terminal blend rubberized asphalt, Constr. Build. Mater. 228 (2019) 116774. [20] L. Kong, J. Zhou, Q. Yan, The improvement of the APAO modified asphalt high temperature stability Kunming, China, in: Proceedings of the 9th Domestic Symposium of Petroleum Asphalt Technology, 2004, pp. 42–46. [21] L. Kong, J. Zhou, Q. Yan, Experimental research on APAO modified asphalt, Technol. Hwy. Trans. 10 (2005) 63–70. [22] J. Wei, Y. Li, F. Dong, H. Feng, Y. Zhang, Study on the amorphous poly alpha olefin (APAO) modified asphalt binders, Constr. Build. Mater. 66 (2014) 105– 112. [23] J. Wei, Z. Liu, Y. Zhang, Rheological properties of amorphous poly alpha olefin (APAO) modified asphalt binders, Constr. Build. Mater. 48 (2013) 533–539. [24] X. Zhao, K. Yan, W. He, C. Cai, Effects of Sasobit/Deurex on amorphous poly alpha olefin (APAO) modified asphalt binder, Constr. Build. Mater. 154 (2017) 323–330. [25] K. Yan, W. He, M. Chen, W. Liu, Laboratory investigation of waste tire rubber and amorphous poly alpha olefin modified asphalt, Constr. Build. Mater. 129 (2016) 256–265. [26] AASHTO, Standard Method of Test for Viscosity Determination of Asphalt Binder Using Rotational Viscometer, Washington, DC, (2013). [27] R.O. Rasmussen, R.L. Lytton, G.K. Chang, Method to predict temperature susceptibility of an asphalt binder, J. Mater. Civil Eng. 14 (3) (2002) 246–252. [28] J. Yuan, J. Wang, F. Xiao, S. Amirkhanian, J. Wang, Z. Xu, Impacts of multiplepolymer components on high temperature performance characteristics of airfield modified binders, Constr. Build. Mater. 134 (2017) 694–702. [29] G. Airey, A. Hunter, B. Rahimzadeh, The influence of geometry and sample preparation on dynamic shear rheometer testing, European Symposium on Performance of Bituminous & Hydraulic Materials in Pavements, 2002. [30] W. Cao, C. Wang, A new comprehensive analysis framework for fatigue characterization of asphalt binder using the Linear Amplitude Sweep test, Constr. Build. Mater. 171 (2018) 1–12. [31] S. Biro, T. Gandhi, S. Amirkhanian, Midrange temperature rheological properties of warm asphalt binders, J. Mater. Civ. Eng. 21 (7) (2009) 316–323. [32] G. Airey, Rheological properties of styrene butadiene styrene polymer modified road bitumensH, Fuel 82 (14) (2003) 1709–1719. [33] S. Yang, K. Yan, W. He, H. Wang, Laboratory evaluation of deurex-modified asphalt, J. Mater. Civ. Eng. 30 (1) (2018) 04017258. [34] A. Yuliestyan, A.A. Cuadri, M. García-Morales, P. Partal, Influence of polymer melting point and Melt Flow Index on the performance of ethylene-vinylacetate modified bitumen for reduced-temperature application, Mater. Des. 96 (2016) 180–188. [35] X. Lu, U. Isacsson, Chemical and rheological evaluation of ageing properties of SBS polymer modified bitumens, Fuel 77 (9) (1998) 961–972. [36] F. Zhang, C. Hu, The research for structural characteristics and modification mechanism of crumb rubber compound modified asphalts, Constr. Build. Mater. 76 (2015) 330–342. [37] W. Liu, K. Yan, D. Ge, M. Chen, Effect of APAO on the aging properties of waste tire rubber modified asphalt binder, Constr. Build. Mater. 175 (2018) 333–341.