Rheological and environmental characteristics of crumb rubber asphalt binders containing non-foaming warm mix asphalt additives

Construction and Building Materials 238 (2020) 117707

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

Rheological and environmental characteristics of crumb rubber asphalt binders containing non-foaming warm mix asphalt additives M. Reza Pouranian ⇑, Mohammad Ali Notani, Mahmood T. Tabesh, Behrokh Nazeri, Mehdi Shishehbor Lyles School of Civil Engineering, Purdue University, West Lafayette, IN 47907, USA

h i g h l i g h t s
WMA additives reduced CRM binder’s activation energy.
The total gas emission of CRM binders has a nonlinear relation with temperature.
Above 130 °C, CRM asphalt binders intensify the emission of hazardous gases.
WMA additives mitigate the environmental concern of CRM asphalt binders.

a r t i c l e

i n f o

Article history: Received 23 August 2019 Received in revised form 16 November 2019 Accepted 24 November 2019

Keywords: Crumb rubber modified asphalt Warm asphalt additives Rutting Fatigue Cracking Rheology Gas chromatography-mass spectrometry test

a b s t r a c t Introducing crumb rubber (CR) into asphalt binder can both provide environmental benefits such as conservation of natural resources and conservation of landfill space and significantly improve rheological and mechanical performance characteristics of asphalt binders. Incorporation of CR into asphalt binder demands some amount of kinematic energy to make modified asphalt binder sufficiently fluid for mixing and compaction purposes that liberates some greenhouse and fume emissions. By taking advantage of warm mix additives (WMA), it is possible to effectively reduce the production temperature of hot-mix asphalt mixtures to mitigate such environmental concerns. This study, Firstly, aims to investigate the CR dosage effect on the properties of asphalt binder containing different non-foaming warm mix additives: Sasobit and Evotherm M1. Secondly, the environmental concerns regarding CR inclusion into asphalt binder are evaluated by implementing gas chromatography-mass spectrometry (GC–MS) test. Rheological and mechanical tests have provided deep insight into the effects of such combinations of WMA and CR in asphalt binders and results indicated that a crumb rubber modified (CRM) asphalt binder with 15–20% CR yielded optimum performance concerning rutting, fatigue, and cracking performance. Furthermore, while both WMA additives can significantly improve the workability and enhance the rutting performance of CRM asphalt binders, they have a slightly negative effect concerning fatigue and cracking performance of CRM asphalt binders. From the environmental aspect, application of WMA additives also could potentially result in a 63–75% reduction in total emission of CRM asphalt mixtures containing 10–25% CR. Relationship between temperature and the total emission of CRM binders is not linear and it is more than likely a second-order polynomial relationship. Moreover, the results of emission analysis showed that CRM binders deliberate some hazardous fumes due to high temperature, which can be alleviated by incorporating WMA additives into the modified blend. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction For many years, because of their structural, functional, and economical benefits, conventional hot-mix asphalt (HMA) mixtures have been the most popular materials for use in pavement construction. Generally, all research efforts on asphalt materials have

⇑ Corresponding author. E-mail address: [email protected] (M.R. Pouranian). https://doi.org/10.1016/j.conbuildmat.2019.117707 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

tried to address one, two, or all three of the following categories: characterization and behavior assessment, economy, and environment impact. Since use of asphalt mixtures implies natural resources and energy consumption, any economic achievement is accompanied with positive inevitable environmental consequences. Achieving a longer life span as a result of improved performance of asphalt mixtures, for example, results in use of fewer natural resources and less fuel consumption [1]. It can be claimed that the current state of the art in pavement material

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engineering is almost exclusively focused on producing sustainable asphalt materials especially after the United Nations conference on sustainable development and the environment in 1992 [2]. Crumb rubber (CR) is a recycled material produced by grinding scrap tires, and for decades it has been widely used and investigated in the production of asphalt mixtures because benefits that include reducing need for scrap tires disposal and saving raw materials and cost [3]. Application of CR in the United States as a modifier introduced into asphalt binder in pavement industry goes back to the early 1960s [4,5]. Previous studies have reported that application of crumb-rubber-modified (CRM) asphalt binder in production of asphalt mixtures results in improvement of the mixture’s durability, in reduction of aging and oxidation, in higher resistance to rutting, fatigue, and reflective cracking, in lower maintenance costs and noise generation, and in improvement of skid resistance [1,6–10].There are, however, some concerns in using CR into asphalt material, including poor pumpability, mixability, and workability and also the need for more heat energy when preparing such mixtures in the asphalt plant production process [11]. CR particles absorb the lighter portion of binders that turn the asphalt blend into a high fluid resistance material, it has also been claimed that using asphalt binder with high penetration grade (lower viscosity) and higher aromatic fraction resulted in more swelling phenomena of CR particles in CRM asphalt binders [12]. Adding CR to the virgin binder mainly changes its structure in three ways: reducing the maltene potion of the base binder, increasing binder stiffness due to CR swelling phenomena, and microstructure changes in base binders [12]. The production of CRM asphalt binders involves a higher mixing and compaction temperature (15–20 °C higher than that of conventional asphalt binder) because of its high viscosity, so it also increases greenhouse gas emissions and production of fumes, odor, and volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene, xylenes and sulfur compounds [1,13]. Emergence of warm-mix additives has alleviated the high demand for heat energy in asphalt plant producer or in the paving process itself. Given this development, several studies have reported that utilization of warm mix asphalt (WMA) additives into asphalt mixture could reduce the required temperatures for mixing and compaction of asphalt mixtures by up to 20–40 °C through a reduction in binder viscosity and chemical interaction between WMA additives and neat asphalt binder [1,14]. In the same vein, combining CRM asphalt binders and WMA additives has recently focused research attention on mitigation of adverse environmental impact of incorporation of CR into asphalt mixture [15–18]. Some investigations have shown that combinations of different WMA additives and CRM asphalt binders can result in a 15– 30 °C reduction in mixing and compacting temperatures [19–21]. Although this seems to offer an appropriate solution for environmental issues related to using CRM asphalt binders, adding WMA additives to CRM asphalt binders can affect the performance of CRM asphalt mixtures at low, intermediate, and high service temperatures, and interactive effects of CRM asphalt binders and WMA additives on rheological characteristics of the final binder are still a matter of concern and argument. Yu and Wang [22] conducted a study to evaluate the effect of source properties and content of WMA additives on CRM asphalt properties. In that study, an asphalt binder with crumb rubber powder (40 mesh size) was mixed in a ratio of 18% CR by mass of the asphalt to prepare CRM asphalt binder. Combination of this CRM asphalt binder with two different WMA additives at various application rates (Sasobit and Evotherm) revealed that the types and contents of the WMA additives had a substantial impact on temperature sensitivity and high and low-temperature properties of CRM asphalt binder. They suggested 3% and 8%, respectively, as optimum percentages of Sasobit and Evotherm for 18%-CRM

asphalt binder. Another study showed that, while combinations of a CRM asphalt binder (20% by the weight of base binder) and four WMA additives (SasobitÒ, Asphaltan AÒ, Asphaltan BÒ, and LicomontÒ) at 2% and 4% content resulted in a significant reduction in production temperature, it also degraded the low-temperature characteristics of the final binders [6]. The rheological and chemical attributes of CRM asphalt binder (18% by weight of base binder) in conjunction with four non-foaming WMA additives (EvothermDATÒ, SasobitÒ, paraffin waxÒ, and combined Evotherm-DATÒ and SasobitÒ) were investigated by Yu et al. [11], with results indicating that all selected WMA additives enhanced the workability of the CRM binder, although using WMA additives could affect the suspension of CR particles in base asphalt binder. Some studies have shown that CRM asphalt has a good potential of energy saving due to the reduction of raw material and its longer service life [1,4,23–25].Wang et al. [23] indicated that adding rubberized material to asphalt binder resulted in net positive energy gaining between 310,267 and 566,109 kJ/kg. Also, Farina et al. [26] showed that application of CR materials in asphalt mixtures led to 43% to 46% reduction in the overall energy consumption. Furthermore, the other investigations have reported that CRM asphalt binders not only increase the amount of hazardous gas emissions due to high production temperature requirements, but also that the CR materials by themselves could release other gas emissions at high temperature [13,27,28]. Based on the literature, the authors found that most of the studies considered a constant percentage of CR (18–20%) when evaluating the interaction between different dosages of WMA additives and CRM asphalt binder, and studies on the combined effects of different CRM asphalt binders within recommended optimum percentage of WMA additives are reasonably limited. Moreover, the effect of warm-mix additives on concentrations of liberated gas from CRM asphalt binder during mixing and compacting process is unclear. Considering these knowledge gaps, the objectives of this study was to investigate the rheological properties of varying CRM asphalt binders with two non-foaming WMA additives, Sasobit and Evotherm-M1, and the emission of gas liberated from a combination of WMA additives and CR modified asphalt binders. To accomplish these objectives, asphalt binder rheological parameters, including penetration, softening point, viscosity, rutting factor, fatigue factor, and low-temperature performance were considered to characterize the interaction between four dosages of CRM into asphalt binder (10, 15, 20 and 25% CR by weight of base binder) with the two aforementioned nonfoaming WMA additives. A gas emission analysis was also conducted to determine the emission components of the CRM asphalt binders at different CR percentages using dynamic headspace gas chromatography–mass spectrometry (GC–MS) at three temperatures (130 °C, 150 °C, and 170 °C); this analysis could contribute understanding of the role of CR content in gas emission of CRM asphalt mixtures in plants. 2. Experimental plan 2.1. Materials The base asphalt binder used in this study was PG 67-22, obtained from a local asphalt supplier, whose conventional properties are shown in Table 1. To focus on the study’s objective, one single CR size (sieve No. 30 or 0.600 mm with mesh sieve residue of 6.2%) was blended with the base asphalt binder at four percentages: 10, 15, 20 and 25% by total weight of the base binder. According to the manufacturer, the crumb rubber particles were produced by mechanical grinding at ambient temperature. The results from thermal gravimetric analysis of the CR material are shown in Table 2.

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M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707 Table 1 Properties of base binder. Property

Test Method AASHTO

Original Binder SUPERPAVE Asphalt Binder Grade Flash Point, COC °C Rotational Viscosity, Pas Dynamic Shear, kPa (G*/sin d, 10 rad/sec) RTFO Residue: AASHTO T240 Mass Change, % Dynamic Shear, kPa (G*/sin d, 10 rad/sec) Pressure Aging Residue: AASHTO R28 Dynamic Shear, kPa (G*
sin d, 10 rad/sec) Creep Stiffness Stiffness, MPa (60 s) M-value

135 °C 64 °C

25 °C 12 °C

Table 2 Chemical and physical properties of crumb rubber. Property

Value

Polymer (rubber) (%) Carbon black (%) Plasticizer (%) Acetone extractive (%) Ash (%) Fiber content (%) Metal content (%) Moisture (%) Density (g/cm3)

54.85 31.45 2.89 3.90 6.54 0.40 0.01 0.40 1.09

The blending process of CR and base binder was performed using a high shear mixer with 4000 revolutions per minute (rpm) at 175 °C. To determine the appropriate mixing time for the CRM asphalt binders, the base asphalt binder was blended with different CR contents for three time durations (30, 45, and 60 min) and all specimens were studied through a temperature sweep (20– 80 °C) test result obtained by running a dynamic shear rheometer test. As an example, the result of the viscoelastic properties of CRM-25% are shown in Fig. 1 in terms of two main rheological parameters: complex modulus (G*) and phase angle (d). This result indicates that, although there are no significant differences in G* for different mixing times, phase angles begin to decrease as mixing time increases. Compared to a 30-minute mixing time, reduction of d at 45- and 60-minutes mixing times

Results

AASHTO M320 T48 T316 T315

230 min 3.0 max 1.0 min

PG67-22 358 °C 0.452 Pas 1.64 kPa

T 240 T315

1.0 max 2.2 min

0.028% 3.59 kPa

T315 T313

5,000 max 300 max 0.300 min

4750 kPa 234 MPa 0.307

reflects an increase in the elastic response portion of the binder due to thorough blending (absorption) of CR and oily components (maltene) of base asphalt binder. A comparison between the phase angle values of 45 and 60 min of mixing times also reveals insignificant difference between those values. The same behavior was observed for CRM asphalt binders with 15% and 20% CR. In the case of the binder containing 10% CR, since 30 min was found to be the optimum mixing time, a 45-minute mixing time seemed to be sufficient for complete blending of base binder with 15, 20, and 25% CR, and 30 min was sufficient for 10% CR. This study used the non-foaming WMA additives Sasobit and Evotherm-M1, whose properties are shown in Table 3. Sasobit is a wax-based organic additive with synthetic long-chain Fischer-Tropsch wax resulting from coal gasification [11]. Based on the literature, with lower viscosity than the binder at similar temperatures, a waxed-based WMA additive can reduce binder viscosity when substituted for only small portion (2–4%) of binder content [14]. Also, based on the manufacturer’s recommendation and previous studies, since the optimum dosage of Sasobit could be taken as between 0.8% and 3% by weight of asphalt binder [29–31], in this study 2% of Sasobit was selected. Evotherm M1 on the other hand is a chemical WMA additive considered to be a primary type of Evotherm 3G that can reduce the production temperature to a range of 85–115 °C [32]. The manufacturer’s recommended dosage is 0.25–0.75% by weight of the base binder, and most studies have recommended 0.5% as the optimum dosage [33–35], so 0.5% of Evotherm M1 by total weight of the base binder was chosen. To obtain consistent WMA modified binders, both WMA additives were added into CRM and base asphalt binders using a shear mixer for 5 min, as recommended by several studies [16,36]. In addition to the base binder and combination of the base binder with 2% Sasobit and 0.5% Evotherm-M1, eight other binders were then prepared as combinations the two WMA additives and the four CRM asphalt binders.

Table 3 Properties of WMA additives.

Fig. 1. Temperature sweep tests for CMR-25% at different mixing times.

a

Properties

Sasobit

Evotherm M1

Physical State Color Density (gr/cm3) Odor pH value Melting point (°C) Boiling point (°C) Flash point (°C) Solubility in water Vapor pressure (mmHg@25 °C) Mixing Temperature Range (°C) Recommended Dosage Ratea (%)

Pastilles and Prill Milky white 0.62 Odor free N/A 105–110 N/A 290 Insoluble N/A >120 0.8–3

Viscous Liquid Amber Dark 1 Amine-like 10–12 <30 >200 >204 Partially soluble <1  1010 >105 0.25–0.75

Percentage by weight of original asphalt binder.

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2.2. Experimental procedure 2.2.1. Convectional tests A graphical flowchart of experimental programs conducted in this study is shown in Fig. 2. After preparation of different modified binders, three initial asphalt binder tests for penetration, softening point, and viscosity were performed to assess the conventional physical properties of both the base and the modified binders in accordance with AASHTO T 49, AASHTO T53, and AASHTO T316, respectively. It should be noted that the viscosity test was performed at three test temperatures: 135 °C, 160 °C, and 175 °C. For each binder, three replicates were prepared and tested. Since asphalt binder is a viscoelastic material whose response is highly dependent on test temperature and loading frequency, at higher temperatures or lower frequencies the viscous portion of the asphalt binder is more prevalent than the elastic portion, so the viscous portion can be considered to result from a thermallyactivated process in which the molecules of the asphalt binders must overcome an intermolecular energy barrier to move to an

adjacent hole. In other words, when asphalt binder flows, a layer of asphalt molecules should slide on one another other, and in this process intermolecular forces cause resistance to flow. It has been proven that the minimum energy required to overcome this resistance, the so-called activation energy, can be described by the Arrhenius model (Eq.1). Ef

g ¼ AeRT

ð1Þ

where g is the viscosity of asphalt binder T is the temperature in degrees Kelvin, A is a model constant, Ef is the activation energy, and, finally, R is the universal gas constant, 8.314 J.mol1.K1. A simplified version of Eq.1 can be rewritten as follows:

lng ¼

Ef þ ln A RT

ð2Þ

Eq. (2) shows that the slope of ln(g) versus 1/T equals Ef/R because the trend is linear. Therefore, to find the activation energy, ln (g) versus 1/T should be plotted with the slope of this plot

Fig. 2. Flow chart of experimental plan procedure.

M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707

providing the value of Ef/R. Considering the universal gas constant (8.314 J.mol1.K1), Ef can be easily obtained. 2.2.2. High temperature evaluation method For assessing the effect of different CR contents on the high temperature performance of asphalt binder, Superpave rutting specification parameter (G*/sind) and multiple stress creep recovery (MSCR) tests conducted in accordance with AASHTO M320 and ASTM D7405, respectively. The emergence of modified asphalt binder in created some discrepancy with respect to Superpave permanent deformation parameters resulting in many researchers believing that it cannot adequately describe the elasticity of modified asphalt binders, so repeated creep and recovery (RCR) testing was introduced. One of the most significant challenges in analyzing the results of RCR test is that they do not describe the stress dependency of modified asphalt binders, so the MSCR test was introduced as a promising approach to investigating elasticity and stress dependency of modified asphalt binders [37–39]. Non-recoverable creep compliance (Jnr) and percentage of recovery (R%), the two main MSCR parameters, are used to show the amount of residual strain left and the portion of the sample’s recovery to its previous shape after loading and unloading [40]. The MSCR test was conducted at 64 °C on the RTFO-aged binders with two replicates, following AASHTO TP 70 and AASHTO MP 19 specifications, to evaluate the high-temperature binder. The non-recoverable creep compliance at 3.2 kPa (Jnr,3.2kPa) and percentage difference (Jnrdiff ¼ 100

Jnr;3:2kPa Jnr;0:1kPa ) Jnr;0:1kPa

was used to determine the various traffic

levels of the binders, in accordance with AASHTO MP19 (see Table 4). 2.2.3. Intermediate temperature evaluation methods The intermediate-temperature performance of binders was evaluated using three parameters. The first was the Superpave fatigue specification parameter (G*  sind) in accordance with AASHTPO M320. Some studies have also indicated that performing the MSCR test at intermediate-temperatures (20–30 °C) could appropriately describe the fatigue performance of asphalt binders, especially modified binders such as CRM asphalt binders [42–44]. Because of the high correlation between Jnr and R% values, it seems that percentage recovery (R %) alone is enough to clarify the fatigue behavior of binders. Furthermore, considering the two stress levels (0.1 and 3.2 kPa), the 3.2 kPa stress level is more critical for evaluating cracking performance [43], so in this study the MSCR test was conducted at the three intermediate temperatures of 20, 25, and 30 °C on RTFO-aged binders following AASHTO TP-70 and AASHTO M-322. R3.2kPa, the second parameter, was considered in comparing fatigue behaviors of all binders. For each test, two replicates were prepared and tested. Recently, using the Glover-Rowe parameter (G*cosd2/sind) has been given more attention as an efficacious fatigue and aging evaluation parameter [45]. Kandhal [46] proved that the Glower-Rowe parameter is in good agreement with asphalt binder ductility measurements, and it should be calculated at a test temperature of 15 °C and at a frequency of 0.005 rad/s. There is a zone in the black diagram based on the Glower-row parameter in which the curve obtained at values of 180 and 600 kPa correspond to damage onset

Table 4 Definition of traffic level based on the MSCR parameters [41]. Grade

Max Jnr 3.2 (k/Pa)

Max Jnr diff (%)

Traffic Level

S H V E

<4 <2 <1 <0.5

75 75 75 75

Standard Heavy Very Heavy Extremely Heavy

5

and significant damage, respectively [45,47,48]. It has been reported that performing DSR test at such a low frequency is impractical, as therefore it has been recommended that the DSR test can be performed for unmodified binders at 44.7 °C and the frequency of 10 rad/s [45,49]. Due to the complexity of DSRductility correlation for modified asphalt binders, it was decided to measure two main viscoelastic parameters (G* and d) at 44.7 °C and frequency of 10 rad/s on all specimens. 2.2.4. Low temperature evaluation method To deal with low-temperature performance, creep stiffness (S) and m-values of three PAV aged replicates were measured by using a bending-beam rheometer (BBR) testing method, in accordance with AASHTO T-313. The critical difference temperature, DTcr, is an indicator used by some investigators to evaluate cracking susceptibility of asphalt binders [47,48,50]. It is defined as the difference between the temperature at which the binder has a creep stiffness of 300 MPa (Ts(3 0 0)) and the temperature at which the m-value is 0.300 (Tm(0.300),) [47].

DTcr ¼ Tsð300Þ  Tmð0:300Þ

ð3Þ

A smaller DTcr value denotes higher susceptibility to cracking. To provide a better understanding of the thermal behavior of asphalt binders, Aflaki et al. [51] and Hajikarimi et al. [52] proposed a general power law model to describe the relationship between creep compliance and time, based on the main result of the BBR test, flexural creep stiffening (S(t)) and creep rate (mvalue). They introduced a description for creep compliance (DCC) as an indicator to explain low-temperature performance of modified binders.

DCC ¼ abta1 

mðtÞ 1  SðtÞ t

ð4Þ

where t is time (s), and a and b are power law model parameters that can be determined using fitting curve techniques. Since it is clear that increasing m(t) and decreasing S(t) simultaneously could result in better low-temperature performance, a higher value of DCC reflects better cracking performance. In this study, DCC was also used to describe the low-temperature performance of asphalt binders. 2.2.5. Emission analysis method In this study the emission analysis of CRM binders was conducted using gas chromatography-mass spectrometry (GC–MS) with a quadrupole mass analyzer (QME200 Balzers Prisma 28510) and dynamic headspace. GC–MS is a popular laboratory method for determining different constituents of test material sample using emission analysis [13,53–55]. The emission analysis test was carried out at three headspace temperatures (130 °C, 150 °C, and 170 °C) to reflect the mixing temperatures of all CRM binders with/without WMA additives in a plant. The weight of each asphalt binder sample was 500 ± 5 mg. During gas chromatography analysis, the initial temperature was 45 °C maintained for 3 min, followed by a temperature increase to 270 °C with a step rate of 15 °C per minute. Similar to the work of Yang, et al., [14] the amount of agitation during the incubation period was 250 rounds per minute and the volume of gas injection was kept at 1 ml at a nozzle temperature of 150 °C. Fig. 3 shows the schematic setup for GC–MS. 110 ng of Hexanal analyte, one of the analytes in this study, as it was individually analyzed to determine the relationship between the corresponding peak area and the liberated gas concentration, considered a reference analyte in calculating the concentration of the other analyte using the following equation [13]:

Ca ¼

Ma MH ; ma ¼ Pa Ms pH

ð5Þ

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M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707

Fig. 3. GC–MS setup.

where Ca is the analyte concentration (ng/g), Ma is the analyte mass, Ms is the sample mass, Pa is the analyte peak area, MH is the mass of Hexanal analyte, and PH is the peak area for the Hexanal analyte. The results of emission analysis for CRM 10% asphalt binder at 170 °C is shown in Fig. 4 that also shows the analytes observed in this study. 3. Results and discussion 3.1. Conventional properties The penetration test results are shown in Fig. 5(a). Compared to the base binder, as expected, an increase of %CR in base binder results in a significant reduction in penetration values of the binders, indicating that a higher CR content in asphalt binders increases the asphaltene/resins ratio and may therefore improve the stiffening properties of CRM asphalt binders. Moreover, the results show that adding the Sasobit and Evotherm M1 to CRM

and base asphalt binders makes the binder stiffer (lower penetration value). Based on the t-test statistical analysis, the effect of Sasobit on the reduction of penetration values is more significant than that of Evotherm-M1. Fig. 5(b) shows the results of the softening point test for all binders. These results revealed that an increase of CR percentage in the base binder causes a higher softening point, while adding Sasobit and Evotherm M1 to CRM and base asphalt binders increases and decreases the respective softening points of the original binders. Statistical analysis (t-test) of softening point values of CRM asphalt binder with and without WMA additives indicated that a significant difference between softening points of those binders except for CRM-20% and CRM-25% binders. Fig. 5(c) shows the result of viscosity testing. Binder viscosity is important, and the viscosity of asphalt binders must be controlled to provide sufficient pumpability, mixability, and workability of asphalt binders at high construction temperatures (generally above 135 °C) [56]. It can be seen that increasing %CR in the base

Fig. 4. Results of dynamic headspace GC–MS chromatograms for CRM 10% asphalt binder at three temperatures of 130, 150 and 170 °C.

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M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707

60 Softening point (°C)

Penetration at 25°C (0.1mm)

70

50 40 30 20 10 0

90 80 70 60 50 40 30 20 10 0

(a)

(b)

Viscosity (Cntipoise)

7000 6000

135 °C

5000

160°C

4000

175°C

3000 2000 1000 0

(c) Fig. 5. Results of (a) penetration, (b) softening point and (c) viscosity tests.

binder significantly escalates the viscosity at all temperatures, especially for %CR higher than 15%. Incorporation of both WMA additives (Sasobit and Evotherm-M1) also effectively reduced the viscosity of CRM asphalt binders within the temperature range 135–175 °C. However, the viscosities of all CRM asphalt binders either with or without WMA additives at 135 °C were still higher than that of the base binder, and it was also observed that the viscosities of all binders except for those containing Evotherm-M1 decreased with increasing test temperature. For binders with Evotherm-M1, there was an increase of viscosity in the range 160 °C to 175 °C, probably due to the evaporation of Evotherm-M1 emulsion at test temperatures higher than 160 °C, so in the application of Evotherm-M1, the mixing temperature should not exceed 160 °C. Table 5 shows the percentage of viscosity reduction in CRM asphalt binders because of incorporation of both WMA additives. From this table, it can be seen that incorporation of Sasobit and Evotherm M1 in the base and CRM asphalt binders resulted in averages of 20% and 20%and 16% and 18%-respective reductions in viscosity of binders at 135 °C and 160 °C, respectively.

Fig. 6 is a plot of log Ln (g) versus 1/T. As mentioned in the test method section, the activation energy of each binder can be calculated based on the slope of this plot, so for each binder, Ef was calculated with the results shown in Table 6. The data from this table indicates that modifying asphalt binder with crumb rubber increases the thermally-activated resistance, implying that these modifiers reinforce the bands between asphalt molecules and thereby increase the fluid resistance of asphalt binder. On the other hand, it can be seen that adding a warm mix enhancement agent (Sasobit or Evotherm M1) into CRM asphalt binders significantly reduces the asphalt binder activation energy. This is implying that the resulted binders have lower viscosity as it can be supported by viscosity result. This can be related to enhanced swelling phenomena of CR particles in the asphalt binder containing warm mix [12]. It can be also be observed that, among two warm-mix enhancer agents, the effect of Evotherm M1 on reduction of activation energy is greater than that of Sasobit, suggesting that adding an Evotherm M1 warm mix agent significantly reduces the price of produced WMA since less kinematic energy is required to overcome the fluid resistance forces between the hydrocarbon chains.

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Table 5 Percentage of reduction in viscosity of CRM asphalt binders due to introduction of WMA additives. Binder Type

% reduction on viscosity Sasobit

Base CRM10 CRM15 CRM20 CRM25

Evotherm-M1

135 °C

160 °C

175 °C

135 °C

160 °C

175 °C

17 22 17 21 21

18 16 14 17 16

14 12 11 13 15

15 23 17 24 20

18 18 17 19 18

8 5 5 8 5

values, the binders with Evotherm–M1 are more sensitive to temperature change than those with Sasobit. The high failure temperature (HFT) is defined as the critical temperature when the rutting factor (G*/sind) is equal to 1.0 kPa for the unaged binder and 2.2 kPa for the RTFO-aged binder. Based on the linear regression equations, the HFT values of all binders could be determined (see Table 7). It can be seen that there is no significant difference between the high failure temperature of binders before (unaged) and after RTFO. All CRM asphalt binders exhibited higher failure temperatures (better rutting resistance) than the base binder, and adding Sasobit to them increases their high failure temperatures even further. Results of the MSCR test are summarized in Table 8. In this table, the recovery percentage at the stress level of 3.2 kPa (R3.2kPa) is a criterion suggested by AASHTO TP-70, so it should satisfy following equation: Fig. 6. Lng versus 1/T for all binders.

29:371J0:2633 nr;3:2kPa < R3:2kPa

Table 6 Activation Energy of base and modified asphalt binders. Binder Type

Ef

A

Base Base + Sasobit Base + Evotherm M1 CRM10% CRM15% CRM20% CRM25% CRM10 + Sasobit CRM10 + Evotherm M1 CRM15 + SasobitÒ CRM15 + Evotherm M1 CRM20 + Sasobit CRM20 + Evotherm M1 CRM25 + Sasobit CRM25 + Evotherm M1

6.57E+04 6.37E+04 6.20E+04 7.34E+04 7.78E+04 7.86E+04 7.96E+04 6.83E+04 6.62E+04 6.77E+04 6.82E+04 6.01E+04 6.64E+04 6.73E+04 6.38E+04

3.06E-06 1.32E-07 1.22E-07 2.94E-05 3.03E-06 8.11E-06 4.42E-05 3.38E-05 6.28E-05 3.34E-06 5.38E-05 6.21E-05 1.71E-04 2.11E-04 5.74E-04

3.2. Performance tests 3.2.1. High-temperature tests Figs. 7 and 8 show the Superpave rutting specification parameters for the unaged and RTFO specimens at temperature sweep from 46 °C to failure temperature (maximum 94 °C), respectively. As expected, CRM asphalt binders with a higher CR content exhibited greater rutting resistance than the base binder, with CRM25+ Sasobit having the highest rutting resistance. Compared to original CRM asphalt binders, incorporation of Sasobit in CRM asphalt binders can help to significantly increase the rutting factor of CRM asphalt binders. Adding the Evotherm-M1 to CRM asphalt binders also has an adverse effect on the rutting resistance of CRM asphalt binders, with regression analysis also revealing that the relationship between the logarithm of the G*/sin d and temperature could be expressed by a linear model. Table 7 shows the slope values of the obtained regression equation for all binders. Based on these

ð6Þ

To indicate whether or not the results for a particular binder meet equation (6) a value of ‘‘Yes” or ‘‘No” is shown in column 8 of Table 8, while the value ‘‘N/A” in this column represents an insignificant recovery if Jnr, 3.2 kPa > 2 kPa1 in accordance with AASHTO TP-70. Based on the MSCR results, except for the base binder, the base binder + Sasobit, and the base binder + Evotherm-M1, the other binders met the criteria of Equation (6). All CRM asphalt binders (with or without WMA additives) also surpassed the maximum allowable Jnr difference (Jndiff), i.e., 75% mainly due to the extremely low Jnr,0.1kPa values. However, the low Jnr 0.1kPa and Jnr 3.2kPa values for all CRM asphalt binders (with or without WMA additives) still confirm their adequate resistance to permanent deformation. Based on the criteria presented in Table 4, although all original CRM and CRM + Sasobit binders met the requirements for the extreme traffic level ‘‘E”, the CRM + Evotherm-1M with % CR less than 20% passed the requirement of high traffic level ‘‘H” and CRM25 + Evotherm-M1 met the very high traffic level ‘‘V”. Therefore, among the two WMA additives, only Sasobit exhibited a positive effect on the rutting resistance property, in a good agreement with Superpave rutting specification results. 3.2.2. Intermediate-temperature tests Fig. 9(a) shows the relationship between the logarithm of the Superpave fatigue criterion and temperatures for all binders, showing that, with increasing temperature, the fatigue factors of all binders proportionally decrease, and the threshold temperatures of all binders are less than 25 °C. Threshold temperature is defined as the critical temperature when the fatigue factor (G*  sind) is equal to 5000 kPa. For CRM asphalt binders without WMA additives, increasing the CR content can result in reducing the fatigue factor, corresponding to higher fatigue resistance. Compared to the base binder, the fatigue factor value decreases at approximately 40% and 20% when %CR increases from 0% to 10%, and 10% to 20%, respectively, for temperatures of 25 and 22 °C. A statistical analysis of variance (ANOVA) was also applied at a 5% significance level to

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Fig. 7. Results of logarithmic rutting factor vs. temperature for unaged CRM binders with (a): Evotherm-M1 and (b): Sasobit.

Fig. 8. Results of logarithmic rutting factor vs. temperature for RTFO aged binders with (a): Evotherm-M1 and (b): Sasobit.

Table 7 Results of high failure temperature and slope of linear equations for unaged and short-term aged specimens. Binder Type

Base Base + Sasobit Base + Evotherm M1 CRM10% CRM15% CRM20% CRM25% CRM10 + Sasobit CRM10 + Evotherm M1 CRM15 + Sasobit CRM15 + Evotherm M1 CRM20 + Sasobit CRM20 + Evotherm M1 CRM25 + Sasobit CRM25 + Evotherm M1

Slope

High Failure Temperature (°C)

Unaged

After RTFO

Unaged

After RTFO

0.068 0.065 0.071 0.062 0.051 0.048 0.045 0.066 0.069 0.058 0.06 0.049 0.052 0.05 0.051

0.06 0.059 0.063 0.054 0.047 0.041 0.042 0.052 0.055 0.047 0.049 0.045 0.045 0.042 0.044

67.4 73.5 64.2 75.6 85.1 89.5 91.1 78.6 71.8 86.2 78.1 92.9 84.7 95.6 87.4

69.6 73.7 65.9 79.3 83.7 90.2 92.4 82.7 74.5 90 81.9 93.2 87.6 96.7 88.2

investigate the effects of testing temperature, % CR, and type of WMA additives on the fatigue factor of the binders. The results of the ANOVA analysis revealed that testing temperature had more

influence than two other parameters (% CR and type of WMA additive). Although CR content has a significant influence on fatigue behavior of CRM asphalt binder with 15%, 20%, and 25% CR, there

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Table 8 Results of MSCR test. Binder Type

Jnr

Base Base + Sasobit Base + Evotherm M1 CRM10% CRM15% CRM20% CRM25% CRM10 + Sasobit CRM10 + Evotherm M1 CRM15 + Sasobit CRM15 + Evotherm M1 CRM20 + Sasobit CRM20 + Evotherm M1 CRM25 + Sasobit CRM25 + Evotherm M1

3.651 1.457 2.241 0.211 0.185 0.164 0.119 0.105 0.367 0.088 0.489 0.061 0.332 0.045 0.298

Jnr,0.1

kPa

Jnr,3.2 3.857 2.687 3.913 0.384 0.366 0.314 0.303 0.204 1.457 0.278 1.654 0.245 1.384 0.277 0.974

kPa

Jnr

Stress Sensitivity (Meets AASHTO MP 19)

%Recovery

Yes No Yes No No No No No No No No No No No No

4.8 24.5 3.4 40.2 59.2 72.3 85.8 51.4 32.4 68.9 42.6 85.5 68.4 92.1 84.5

R0.1

%Diff

6 84 75 82 98 91 155 94 297 214 238 302 317 515 227

is no significant difference between a fatigue factor of 20% and 25% CRM asphalt binders, so it can be concluded that increasing CR content can improve the fatigue performance of CRM binder. Although the impact of both WMA additives on the fatigue factor of CRM asphalt binders is negative, the adverse effect of Evotherm-M1 is more significant than that of Sasobit on fatigue resistance of CRM asphalt binders. Fig. 9(b) shows the threshold temperature for all binders based on fatigue factor values. Generally, lower fatigue temperature thresholds implying the idea that the binder indicates a higher fatigue resistance. From Fig. 9(b), it can be found that adding CR to the neat binder decreases the temperature thresholds implying the idea that CRM binders present a better fatigue resistance. Moreover, the result of temperature threshold is in a good agreement with explanation provided for Fig. 9(a). The ANOVA results also indicated that, except for CRM10, the adverse effects of both WMAs on CRM asphalt binders are significant, although all CRM asphalt binders with WMA additives showed better fatigue resistance than did the base binder. Fig. 10 displays comparison among MSCR R3.2 values, and it can be observed that the all CRM asphalt binders without WMA additives were less sensitive to temperature change, especially for more than 15% content of CR. However, inclusion of WMA additives to CRM asphalt binders resulted in higher temperature sensitivity of CRM asphalt binders. Compared to Evotherm-M1, the Sasobit exhibited a less negative effect on CRM asphalt binders in term of fatigue resistance (higher R3.2) and temperature sensitivity. The base + Evotherm-M1 binder exhibited the lowest R3.2 values and highest temperature sensitivity among of all binders. Fig. 11 shows the black diagram for all specimens. In this figure, the asphalt binders are plotted at three different stages of aging (unaged, RTFO, and PAV). In the black diagram, the damage area is defined by two boundaries: The Glover-Rowe parameter of G*(cos2d/sind) = 180 kPa which indicates the onset of cracking and G*(cos2d/sind) = 600 kPa which indicates when surface cracking is apparent. The area between these two limits indicates where some damage has occurred, but no surface cracking is observed. As can be seen, increasing CR content, shifting the curve to the right section of the diagram which implies better fatigue resistance. And also, as can be seen, increasing CRs content from 10 to 25% enhances fatigue resistance by maintaining distance from G-R = 600 kPa, attribute to the high flexibility index of CRs-modified asphalt binders. Moreover, adding warm mix agent to the CRs-modified asphalt binders changed the fatigue behavior of CRs-modified asphalt binders, i.e., CRM + Sasobit blends exhibited better fatigue resistance than CRM + Evotherm-M1. A CRs-modified asphalt blend

kPa

R3.2

% Recovery (Meets AASHTO TP 70)

Traffic Level

N/S N/S N/S Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

S S S E E E E E H E H E H E V

kPa

2.14 12.8 1.98 36.7 48.7 56.4 59.1 33.2 24.1 45.8 22.9 52.1 37.4 63.7 48.6

containing warm mix asphalt agents presented a low degree of success through crack resistance definition, since it was located in the damage zone of the black diagram. Among them, only the CRs 25% + warm mix agent exhibited a better fatigue behavior, below of the crack appearance zone (In the PAV condition). Considering both CRs-modified asphalt binder containing warm mix agents, the one dosed with Sasobit is placed to the right of the one that included Evotherm M1, implying the greater effectiveness of adding Sasobit over Evotherm M1 on fatigue resistance of asphalt binder. 3.2.3. Low-temperature tests Table 9 shows the creep stiffness and creep rate results (mvalue) of all binders obtained from the BBR testing. AASHTO T313 specifies that the stiffness value and m-value should be less than 300 MPa and larger than 0.3 for a specific temperature grade, respectively, and based on the BBR test results, all binders met the AASHTO T-313 requirements at 12 °C and incorporation of CR could significantly reduce the creep stiffness of the base binder. The statistical ANOVA results at the 5% significance level revealed that testing temperature, CR content, and their interaction had a very significant effect on creep stiffness and m-value of CRM asphalt binders. However, comparison between CRM asphalt binders with 20% and 25% CR content revealed no significant difference, with a confidence level of 95%, between creep stiffness and m-value of two CRM asphalt binders; this means that the lowtemperature performances of CRM25 and CRM20 were identical. In the case of WMA additive incorporation, although the Evotherm-M1 decreased the creep stiffness and increases the m-value of CRM asphalt binders, adding Sasobit to CRM asphalt binders resulted in increasing creep stiffness and reduced the m-values of the CRM asphalt binders. The ANOVA results also indicated that neither WMA additive had no significant effect on low-temperature parameters of CRM asphalt binders. The values of DTcr are presented in Fig. 12. Anderson, et al. [48] and Rowe [49] recommended two temperature thresholds, 2.5 °C and 5 °C, as cracking warning and cracking limit, respectively, to describe cracking susceptibility of asphalt binders using DTcr. As can be seen in this figure, CRM asphalt binders are less susceptible to thermal cracking than the base binder or the CRM binder + WMA additives, and higher %CR results in less susceptibility to cracking. Although all binders exceeded the warning limit, only CRM asphalt binders could pass the cracking limit. Furthermore, both WMA additives had an adverse effect on low-temperature cracking resistance, although the adverse impact of Sasobit is less than that of Evotherm-M1.

M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707

11

(a) 30

Threshold Temperature (°C)

25

20

15

10

5

0

(b) Fig. 9. Results of (a) logarithmic fatigue factor vs. temperature for RTFO and PAV aged binders; (b) Threshold temperature based on the fatigue factor.

Temperature gradients cause shrinkage in asphalt layers, resulting in thermal tensile stress between aggregate and asphalt binder phases. A low-stiffness binder exhibits a high rate of altering stiffness and as a result the binder has a chance to experience a stress relaxation phase. With respect to the anticracking features of an ideal asphalt binder, low flexural creep compliance is more desirable. In the same vein, a binder with higher creep rate achieves greater stress relaxation. Derivation of creep compliance (DCC) presents a relationship between flexural creep stiffness and creep rate in which a high value of DCC implies a high thermal crack resistance of asphalt binders.

Table 10 shows the estimated power-law model (Eq. (4)) parameters (a and b) that were used to determine DCC indicators for all binders. The DCC indicator results for asphalt binders are shown in Fig. 13, revealing that incorporation of CRs into asphalt blends increases the DCC value, implying improvement in thermal crack resistance compared with base binders, especially a the 12 °C test temperature. This is to be expected since crumb rubber particles compared to the asphalt binder are relatively insensitive because of the low glass-transition temperature of crumb rubber. A comparison of the CRs modified binders including warm mix agents

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M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707

90

20°C

25°C

30°C

80

R 3.2kPa (%)

70 60 50 40 30 20

CRM 25+ Evotherm M1

CRM 25+Sasobit

CRM 20+ Evotherm M1

CRM 20+ Sasobit

CRM 15+ Evotherm M1

CRM15+Sasobit

CRM10+Evotherm M1

CRM10 +Sasobit

CRM 25%

CRM 20%

CRM 15%

CRM 10%

Base+ Evotherm M1

Base +Sasobit

0

Base

10

Fig. 10. R3.2 values of RTFO aged binders at three intermediate temperatures.

G-R =600

kPa

e ge Zon Dama

Zone Damage

0 kPa

G-R = 18

Fig. 11. Black diagram of base and modified asphalt binders.

reveals that adding Sasobit to the CRs blend slightly decreases the DCC values compared to Evotherm M1, suggesting that while adding Sasobit or Evotherm M1 degrades the thermal anti-cracking capability, the thermal crack resistance of those is still higher than base binder at all test temperatures. 3.3. Emission analysis Fig. 14 shows the emission concentrations of 15 observed analytes of all CRM asphalt binders from 130 °C to 150 °C and to 170 °C, with results showing temperature to be a significant factor in production of all compound emissions. As expected, significantly increasing the temperature surges the emission of all analytes, possibly because the higher temperature could result in higher molec-

ular movement and more analyte consequently discharged from the headspace of the GC–MS. The data presented in Fig. 14 shows some of the analytes, Acetone and Meta/Para-xylene, are highly concentrated. Acetone and M/P-xylene, among others, are very flammable emitted gases whose presence near the binder surface diminishes safety because it may reduce the flash point of CRM asphalt binder. Extending CR content into the blend increases the amount of emitted Acetone and M/P-xylene, so increasing temperature from 130 to 170 °C increases the emission of Acetone and M/ P-xylene more than ten times and three times, respectively. Fig. 15 displays the variation of total emission due to temperature change for all CRM binders. It can be observed in the figure that the rate of change in total emission between 150 and 170 °C is much higher than that between 130 and 150 °C. For example,

13

M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707 Table 9 Results of BBR test. Stiffness (MPa)

m-value

CRM 25+ Evotherm M1

CRM 25+Sasobit

CRM 20+ Evotherm M1

CRM 20+ Sasobit

CRM 15+ Evotherm M1

CRM 10%

CRM15+Sasobit

0.147 0.138 0.166 0.161 0.186 0.212 0.234 0.154 0.182 0.175 0.201 0.175 0.232 0.208 0.249

CRM10+Evotherm M1

24 °C

0.238 0.211 0.223 0.256 0.268 0.295 0.301 0.227 0.239 0.237 0.249 0.247 0.265 0.268 0.283

CRM10 +Sasobit

18 °C

0.307 0.291 0.305 0.325 0.346 0.358 0.369 0.289 0.308 0.305 0.326 0.305 0.341 0.332 0.349

CRM 25%

12 °C

486 512 498 420 382 342 329 598 465 480 414 509 375 431 363

CRM 20%

24 °C

308 317 310 255 228 176 164 309 185 308 211 287 146 234 137

CRM 15%

18 °C

234 213 201 165 138 125 112 192 126 170 111 146 91 141 116

Base+ Evotherm M1

12 °C

Base

Base Base + Sasobit Base + Evotherm M1 CRM 10% CRM 15% CRM 20% CRM 25% CRM10 + Sasobit CRM10 + Evotherm M1 CRM15 + Sasobit CRM15 + Evotherm M1 CRM20 + Sasobit CRM20 + Evotherm M1 CRM25 + Sasobit CRM25 + Evotherm M1

Base +Sasobit

Binder Type

0

ΔTcr (°C)

-2

-4

-6

Crack Warning Crack Limit

-8 Fig. 12. Results of critical difference temperature (DTcr).

Table 10 Estimated parameters of DCC indicator. Binder Type

Temperature (°C) 12

Base Base + Sasobit Base + Evotherm M1 CRM10% CRM15% CRM20% CRM25% CRM10 + Sasobit CRM10 + Evotherm M1 CRM15 + Sasobit CRM15 + Evotherm M1 CRM20 + Sasobit CRM20 + Evotherm M1 CRM25 + Sasobit CRM25 + Evotherm M1

18

24

a

b

a

Β

a

b

2.34E03 2.25E03 2.30E03 3.85E03 4.56E03 4.63E03 4.75E03 3.65E03 3.71E03 4.34E03 4.49E03 4.40E03 4.52E03 4.56E03 4.63E03

0.342 0.325 0.334 0.351 0.367 0.382 0.389 0.345 0.348 0.357 0.361 0.371 0.376 0.376 0.381

1.34E03 1.25E03 1.29E03 2.65E03 2.86E03 2.93E03 2.90E03 2.43E03 2.53E03 2.75E03 2.80E03 2.81E03 2.86E03 2.80E03 2.87E03

0.273 0.269 0.272 0.281 0.289 0.306 0.31 0.276 0.278 0.281 0.286 0.297 0.301 0.302 0.308

8.24E04 8.15E04 8.20E04 1.38E03 1.57E03 1.61E03 1.63E03 1.27E03 1.31E03 1.43E03 1.48E03 1.52E03 1.57E03 1.53E03 1.60E03

0.205 0.189 0.195 0.238 0.256 0.261 0.26 0.229 0.231 0.247 0.25 0.253 0.258 0.252 0.258

the total emission of CRM 15% increased from 2189 ng/g to 3671 ng/g when the temperature changed from 130 to 150 °C

(an increase rate of 67%), while total emission increased from 3671 ng/g to 7260 ng/g when the temperature changed from 150

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M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707

Derivation of Creep Compliance

3.50E-05

-12°C 3.00E-05

-18°C 2.50E-05

-24°C

2.00E-05 1.50E-05 1.00E-05 5.00E-06 0.00E+00

Fig. 13. Derivation of Creep compliance of all specimens at different test temperatures.

to 170 °C (an increase rate of 98%). This implies that relationship between the total emission and temperature is not linear and it is more than likely a second-order polynomial relationship (see Fig. 15). Previous studies have revealed that a combination of WMA additives and CRM asphalt binders can result in reducing the mixing temperature of traditional CRM asphalt mixtures (usually above 160 °C) by 30–40 °C [1,14]. Therefore, by comparing the total emission of CRM binders at two temperatures of 130 °C and 170 °C, it can be seen that application of WMA additives can potentially result in a 63–75% reduction in total emission of CRM asphalt mixtures containing 10–25% CR. Table 11 also shows the effect of increased CR content on the emission of each observed analyte. It can be seen that there is no direct relationship between the amount of CR content and

emission of CRM asphalt binders, in other words, higher CR content does not necessarily mean higher emission. Although increasing the CR content could result in higher emission of some analytes such as 2-Methylheptane, 2,5-diethylthiophene, Benzothiazole, Cyclohexanone, Methyl isobutyl, and m-/pXylene, emission rates of other analyte such as Decane, Hexen1-ol, Toluene and Undecane are reduced. For other emission compounds, no specific trend was observed, probably because of different emission analytes from the base asphalt binder and CR materials. For example, Decane, Hexen-1-ol, Toluene, and Undecane are emission compounds that have been reported for asphalt binder emission in previous studies, while Benzothiazole, Cyclohexanone, Methyl isobutyl, and m-/p-Xylene have been observed in CRM binder emission [54,55]. Therefore, only

Fig. 14. Results of emission for all CRM binders.

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M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707

8000

CRM10%

y = 1.46x2 - 337x + 21364

CRM15%

y = 2.6338x2 - 663.35x + 43914

Total emission (ng/g)

7000 6000 5000 4000

CRM20% y = 3.9538x2 - 1044.2x + 70678 CRM25% y = 3.3338x2 - 853.4x + 56524

3000 2000 1000 110

130

150

170

190

Temperature (°C) Fig. 15. Total emission of four CRM binders at three different temperatures.

increased CR content results in escalating the emission of analytes from CR materials. 4. Conclusions




This study, firstly, set out to investigate interactions between a combination of non-foamed warm mix additives, i.e., Evotherm M1 and Sasobit, and CRM-modified asphalt binders using experimental and analytical approaches. Secondly, the environmental repercussions of crumb rubber inclusion into asphalt binder were investigated using gas chromatography-mass spectrometry testing at high temperatures. This study presents the following conclusions and contributions to the state of the art of sustainable asphalt material engineering as:











Both WMA additives reduced CRM binder mixing and compaction temperatures due to a reduction in activation energy of CRM binders.
Sasobit had a positive effect on CRM binder high temperature performance, while adverse effect was observed for CRM




binders containing Evotherm M1. However, in comparison with base binder, CRM binder contacting WMA additives still presented better rutting performance. Both WMA additives produced negative effects with respect to fatigue and cracking performance of CRM asphalt binders. Evotherm M1 had also a higher negative impact than Sasobit did. However, both CRM binders containing WMA additives showed fatigue resistance enhancement compared to the base binder Although CRM binders containing WMA additives presented better performance than the base binder, both WMA additives reduced thermal crack resistance of CRM binders. CRM asphalt binder liberated several hazardous gases like Acetone and Meta/Para-xylene at temperatures elevated above 130 , significantly intensifying the concentration of such gases. The total gas emission of CRM binders is highly dependent on temperature as it shows a nonlinear behavior. WMA additives are a good alternative for mitigating environmental concern related to CRM asphalt binder by significantly reducing mixing and compaction temperature.

Table 11 Effect of CR content on emission of each observed analyte. Analyte

130 °C

1

1

Acetone Benzothiazole Cyclohexanone Decane Heptanal Hexanal Hexen-1-ol Methyl isobutyl ketone m-/p-Xylene Pentanal Toluene Undecane 1:

: increase in emission;

150 °C

1

2-Methylheptane 2,5-Diethylthiophene Acetic acid

: decrease in emission;

: not specific trend observed.

170 °C

General Trend

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M.R. Pouranian et al. / Construction and Building Materials 238 (2020) 117707

Authors contribution statement The authors confirm contribution to the paper as follows: study conception and design: Dr. M. Reza Pouranian, Mr. Mohammad Ali Notani, and Dr. Mehdi Shishehbor. Data curation: Mr. Behrokh Nazeri and Dr. M.Reza Pouranian. Analysis and interpretation of results: Dr. M.Reza Pouranian, Mr. Mohammad Ali Notani, Dr. Mehdi Shishehbor. Original Manuscript preparing: Dr. M.Reza Pouranian, Mr. Mahmood T. Tabesh. Review and Editing: Dr. M. Reza Pouranian and Mr. Mahmood T. Tabesh. All authors reviewed and discussed the results and contributed to the final version of revised manuscript. Declaration of Competing Interest 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. References [1] M.R. Pouranian, M. Shishehbor, Sustainability assessment of green asphalt mixtures: a review, Environments 6 (2019) 73, https://doi.org/10.3390/ environments6060073. [2] T.J. Van Dam, J. Harvey, S.T. Muench, K.D. Smith, M.B. Snyder, I.L. Al-Qadi, H. Ozer, J. Meijer, P. Ram, J.R. Roesler, Towards Sustainable Pavement Systems: A Reference Document, Federal Highway Administration, United States, 2015. [3] D. Lo Presti, Recycled tyre rubber modified bitumens for road asphalt mixtures: a literature review, Constr. Build. Mater. 49 (2013) 863–881. [4] H.U. Bahia, R. Davies, Effect of crumb rubber modifiers (CRM) on performance related properties of asphalt binders, Asph. Paving Technol. 63 (1994) 414. [5] D.I. Hanson, K.Y. Foo, E.R. Brown, R. Denson, Evaluation and characterization of a rubber-modified hot mix asphalt pavement, Transp. Res. Rec. (1994). [6] A.M. Rodríguez-Alloza, J. Gallego, I. Pérez, A. Bonati, F. Giuliani, High and low temperature properties of crumb rubber modified binders containing warm mix asphalt additives, Constr. Build. Mater. 53 (2014) 460–466. [7] L.P.T.L. Fontes, G. Trichês, J.C. Pais, P.A.A. Pereira, Evaluating permanent deformation in asphalt rubber mixtures, Constr. Build. Mater. 24 (2010) 1193– 1200. [8] H.I. Ozturk, F. Kamran, Laboratory evaluation of dry process crumb rubber modified mixtures containing Warm Mix Asphalt Additives, Constr. Build. Mater. 229 (2019) 116940. [9] V. Venudharan, K.P. Biligiri, N.C. Das, Investigations on behavioral characteristics of asphalt binder with crumb rubber modification: Rheological and thermo-chemical approach, Constr. Build. Mater. 181 (2018) 455–464. [10] J. Gong, Y. Liu, Q. Wang, Z. Xi, J. Cai, G. Ding, H. Xie, Performance evaluation of warm mix asphalt additive modified epoxy asphalt rubbers, Constr. Build. Mater. 204 (2019) 288–295. [11] H. Yu, Z. Leng, F. Xiao, Z. Gao, Rheological and chemical characteristics of rubberized binders with non-foaming warm mix additives, Constr. Build. Mater. 111 (2016) 671–678. [12] H. Wang, X. Liu, P. Apostolidis, S. Erkens, T. Scarpas, Numerical investigation of rubber swelling in bitumen, Constr. Build. Mater. 214 (2019) 506–515. [13] X. Yang, Z. You, D. Perram, D. Hand, Z. Ahmed, W. Wei, S. Luo, Emission analysis of recycled tire rubber modified asphalt in hot and warm mix conditions, J. Hazard. Mater. 365 (2019) 942–951. [14] M.C. Rubio, G. Martínez, L. Baena, F. Moreno, Warm mix asphalt: an overview, J. Clean. Prod. 24 (2012) 76–84. [15] F. Xiao, P.E.W. Zhao, S.N. Amirkhanian, Fatigue behavior of rubberized asphalt concrete mixtures containing warm asphalt additives, Constr. Build. Mater. 23 (2009) 3144–3151. [16] H. Wang, Z. Dang, Z. You, D. Cao, Effect of warm mixture asphalt (WMA) additives on high failure temperature properties for crumb rubber modified (CRM) binders, Constr. Build. Mater. 35 (2012) 281–288. [17] H. Yu, Z. Leng, Z. Zhou, K. Shih, F. Xiao, Z. Gao, Optimization of preparation procedure of liquid warm mix additive modified asphalt rubber, J. Clean. Prod. 141 (2017) 336–345. [18] A.M. Rodríguez-Alloza, J. Gallego, Mechanical performance of asphalt rubber mixtures with warm mix asphalt additives, Mater. Struct. 50 (2017) 147. [19] F. Moreno, M. Sol, J. Martín, M. Pérez, M.C. Rubio, The effect of crumb rubber modifier on the resistance of asphalt mixes to plastic deformation, Mater. Des. 47 (2013) 274–280. [20] H.H. Kim, S.-J. Lee, Effect of crumb rubber on viscosity of rubberized asphalt binders containing wax additives, Constr. Build. Mater. 95 (2015) 65–73. [21] Z. Leng, H. Yu, Z. Zhang, Z. Tan, Optimizing the mixing procedure of warm asphalt rubber with wax-based additives through mechanism investigation and performance characterization, Constr. Build. Mater. 144 (2017) 291–299.

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