Effect and mechanism of warm mix agent on the rheological properties of styrene–butadiene–styrene-modified asphalt

Abstract

Introduction:

The objective of this study was to investigate the effect and reaction mechanism of warm mix agent PN2217 on the rheological properties of styrene-butadiene-styrene (SBS) asphalt.

Methods:

Fourier transform infrared (FT-IR) spectroscopy and atomic force microscope (AFM) were conducted to reveal the reaction mechanism between PN2217 and SBS asphalt. Dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), and bending beam rheometer (BBR) tests were performed to analyze the rheological properties of SBS asphalt modified with 1, 3, and 5 wt% PN2217.

Results:

The addition of PN2217 changed the component proportions, reducing phase separation and promoting the formation of a more homogeneous microstructure via crosslinked long-chain molecules. PN2217 improved the temperature sensitivity and permanent deformation resistance of SBS asphalt at high temperatures, mainly by increasing the elastic components. However, the addition of PN2217 reduced the cracking resistance potential of SBS asphalt by 7%–19% and increased stress sensitivity by 4.8%–8.3% at low temperatures.

Discussion:

This deterioration at low temperature may be attributed to the loss of light-weight components.

1 Introduction

The construction of asphalt pavement has a great impact on the environment. One impact is the large amount of fuel consumption and greenhouse gas emission due to high production temperatures (Zhao et al., 2021; Valdés-Vidal et al., 2020; Kalyan et al., 2021). Another is that the large amount of toxic gas produced in the construction process can cause irreversibly harmful effects on the health of construction personnel. Therefore, increasing attention has been paid to the environmental problems caused by asphalt pavement in the production process (Kendall et al., 2008; Jamshidi et al., 2013).

Warm-mix asphalt can be mixed and compacted at relatively lower temperatures than hot-mix asphalt (Rubio et al., 2012; Topal et al., 2014; Rodríguez-Alloza et al., 2013). The commonly used method is to add warm mix agent into the asphalt to reduce production temperature. The application of warm mix agent can reduce greenhouse gas emissions by 10%–50% and fuel consumption by 11%–35% (Topal et al., 2014). In addition, the energy required by warm-mix asphalt production is approximately 300% less than hot-mix asphalt, further reducing the impact on the environment.

Commonly used warm-mix technologies are organic or wax additives, foaming techniques, and chemical additives (Liu et al., 2012; Liu et al., 2011; He et al., 2023). Classical organic or wax additives are Sasobit, Asphaltan B, and Licomont BS (Liu et al., 2011; Button et al., 2007; Kheradmand et al., 2017; Transportation Research Record, 2011). The second technology is foaming techniques. Cold water is injected into the hot asphalt binder or asphalt mixing chamber, thus producing foams with large volumes (Anderson et al., 2008; Mohd et al., 2017; Masson et al., 2015), which may cause a reduction in asphalt mixing temperature of 20–30 °C (Masson et al., 2015). The commonly used chemical additives are Evotherm (Middleton and Forfylow, 2009; Fakhri et al., 2013; Puchard and Gorgenyi, 2012; Al-Rawashdeh and Sargand, 2014; Vincent et al., 2018) and Cecabase RT (Cheraghian et al., 2020; Wasiuddin et al., 2007; Goh et al., 2011; Taher and Aman, 2020; Perkins, 2009). There are three types of Evotherm products: Evotherm ET, DAT, and 3G (Sargand et al., 2012; Goh et al., 2011), which can reduce construction temperature by 55 °C, 45–55 °C, and 33–45 °C, respectively (Yu et al., 2019).

Recently, PN2217 technology has been gradually introduced into highway engineering. The addition of PN2217 reduces the construction temperature of asphalt mixture and can extend the service life of asphalt pavement. However, there has been little research into the influence and reaction mechanism of PN2217 on the rheological properties of asphalt. Asphalt, as a viscoelastic material, plays an important role in the pavement performance of asphalt mixture. The rheological properties of asphalt are essential for evaluating its viscoelastic behaviors (Mallick et al., 2008; Lu X. et al., 2021; Hurley and Prowell, 2006; Capitão et al., 2012; Goh et al., 2008). Therefore, it is necessary to investigate the effect and mechanism of PN2217 warm-mix agent on the rheological properties of asphalt.

The object of this study was to conduct a multi-scale investigation into the effect and modified mechanism of PN2217 on the rheological properties of SBS asphalt. The modified mechanism was analyzed by FT-IR and AFM tests. DSR, MSCR, and BBR tests were conducted to investigate the rheological properties of SBS asphalt with different contents of warm mix agent.

2 Materials and experimental methods

2.1 Raw materials

SBS (I-C) modified asphalt produced by Jilin Jiarui Asphalt Technology Co. Ltd. was applied. The main technology indexes are shown in Table 1.

Warm mixing agent PN2217 produced by Shandong Paini New Materials Co., Ltd., was selected as the warm mixing agent. Its main chemical composition is a diamine ethylene oxide admixture; its basic performance indexes are shown in Table 2.

2.2 Preparation of PN2217 modified asphalt

The warm-mix asphalts were made using a high-speed shear mixer (Xiao et al., 2009a; Xiao et al., 2009b; Banerjee et al., 2012). SBS asphalt was heated to 175 °C before PN2217 was added. The PN2217 content was 1, 3, and 5 wt% of SBS asphalt, after which the specimens were stirred at 3000 rpm for 45 min (Goh et al., 2011). The warm-mix asphalt was prepared at 135 °C. Four types of specimen were prepared to investigate the effects of warm mix agent on SBS asphalt: control sample (SBS asphalt), PN2217-1 (SBS asphalt with 1 wt% PN2217), PN2217-3 (SBS asphalt with 3 wt% PN2217), and PN2217-5 (SBS asphalt with 5 wt% PN2217).

2.3 Mechanism

2.3.1 Fourier transform infrared spectrum test

A German Brooke TENSOR Fourier infrared spectrum analyzer was used to investigate the changes in the molecular structure of the control group and warm-mix asphalts with different PN2217 contents. The asphalt sample (1–2 mg) was fully ground with dried KBr powder (100–200 mg) and pressed into a transparent pellet for testing. The FT-IR test was performed with a resolution of 4 cm^-1, a scanning frequency of 32 scans, and a scanning wavenumber range of 4000 cm^-1 to 400 cm^-1.

2.3.2 Atomic force microscope test

An INNOVA atomic force microscope (AFM) was utilized to measure the surface morphology of the control group and warm-mix asphalts with different PN2217 contents. The asphalt samples for AFM testing were prepared by hot melt casting: the asphalt was heated to a molten state (135 °C) under anhydrous and oxygen-free conditions, and then a small amount of molten asphalt was uniformly cast on a clean silicon wafer (1 × 1 cm) and placed in a constant temperature and humidity chamber (25 °C, 50% RH) for 24 h to cool and form a smooth film with a thickness of ∼50 μm for testing.

The test was conducted using an INNOVA atomic force microscope in tapping mode with a silicon nitride probe (spring constant: 40 N/m; resonance frequency: 300 kHz). The scanning parameters were strictly controlled: scanning range 30 × 30 μm, scanning speed 0.999 Hz, gain value 0.5, pre-pressure 300 mV, and image resolution 512 × 512 pixels. A random selection method was adopted for scanning points (five replicate points per sample), and the AFM images obtained were processed by the instrument’s supporting software (NanoScope Analysis) for noise reduction and roughness parameter calculation to ensure the accuracy of microscopic morphology and quantitative data.

2.4 Rheological properties

2.4.1 Dynamic shear rheometer test

The DSR test was conducted using an AR 1500ex rheometer to describe the elastic-viscous behaviors of the control group and warm-mix asphalts with different PN2217 contents. The diameter of the test plates and the gap between parallel plates were set at 25 mm and 1 mm, respectively. The test configurations for frequency and temperature sweep tests are displayed in Table 3.

The complex (), elastic (), and viscous () modulus at different applied frequencies and temperatures were obtained to establish the master curves of essential rheological parameters and determine the viscoelastic properties of control specimen and warm-mix asphalts over the entire temperature and frequency range through the time–temperature superposition principle (Pamplona et al., 2012), as shown in Equations 1, 2.where and are test and reference temperature and and are reduced angular and angular frequency.

2.4.2 Multiple stress creep recovery test

The high-temperature anti-rutting properties of all specimens pretreated in a rotary thin film oven (RTFOT), as described by AASHTO T350-19, were evaluated by an MSCR test using an AR 1500ex rheometer in a continuous manner at stress levels of 0.1 and 3.2 KPa for 10 cycles at approximately 64 °C. Each cycle consisted of 1 s creep stress loading and 9 s stress unloading recovery. The elastic recovery percentage, R, and non-recoverable creep compliance in each cycle are calculated in accordance with Equations 3, 4.where , , and are the peak, residual, and initial strains in each cycle, respectively, and is the corresponding stress level.

The mean value of and from 10 cycles of applied stress level on the specimen was divided during those cycles to acquire R and . Much research has revealed that the relationship of to measured rutting depth is much better than that of the rutting factor (Zhang et al., 2015; Bastos et al., 2017). R represents the ratio of recoverable to total strain in each cycle (Azarhoosh and Koohmishi, 2020).

2.4.3 Bending beam rheometer test

The bending beam rheometer (BBR) test was applied to evaluate the low-temperature anti-cracking performance of control specimen and warm-mix asphalts with different PN2217 contents. The ultimate stiffness temperature and creep strain rate obtained from BBR testing have a good relationship with the breaking temperature obtained from temperature stress experiments (TSRSTs) (Walubita et al., 2021; Lu G. et al., 2021).

According to ASTM D6648-01, specimens with dimensions of 125 12.5 6.25 mm were prepared in a silicone rubber test mode. The BBR test was conducted on a TE-BBR-R bending beam rheometer. The test temperature was set as −6 °C, and a constant load of 0.98 N was applied to the specimen. Creep stiffness S and creep rate m, as shown in Equations 5, 6, at 60 s are obtained to evaluate the rheological properties at low asphalt temperature:where b, h, and L are width, height, and span of the beam, respectively; P is the load applied to it; and is its middle span deflection.

3 Results and discussion

3.1 Reaction mechanism

3.1.1 FT-IR analysis

The FT-IR control specimen and warm-mix asphalts are shown in Figure 1. It can be concluded that the addition of PN2217 changed the component of SBS asphalt.

FIGURE 1

The characteristic peak at 720 cm^-1 results from the vibration of long-chain alkanes. The characteristic peak from 750 to 900 cm^-1 may be attributed to the presence of aromatic compounds. It can be concluded that the long-chain alkanes increased after the addition of PN2217, which may be attributed to the recombination of some branched chain molecular structures. An increase of C=C can be observed at 1,600 cm^-1, which may promote a uniform distribution of asphaltene, resulting in the generation of stable and uniform microstructures formed by the crosslinking of long-chain molecules. The light component in SBS asphalt may be gradually transformed into a heavy component. Therefore, PN2217 may lower the possibility of phase separation, thus enhancing the stability and uniformity of the microstructure.

After the addition of PN2217, the variation region of the characteristic peaks is mainly concentrated at 400–2,000 cm^-1. These peaks are therefore important for characterizing and identifying warm-mix asphalt. The peak strength of each characteristic peak also had some changes with different PN2217 contents. Functional group indexes at 720, 750–900, and 1,600 were calculated to quantitatively analyze the influence of PN2217 content on the FT-IR characteristic peak of modified asphalt. The corresponding characteristic peak functional group index calculation formula is as follows (Equations 7–10):

where , , and are the functional group indexes at 720, 750–900, and 1,600 cm^-1, respectively; , , and are the areas of characteristic peak at 720, 750–900, and 1,600 cm^-1, respectively; and is the total area of all characteristic peaks from 400 to 2,000 cm^-1.

The functional group index of all asphalt samples is shown in Table 4. It can be observed that quantitative analysis results were consistent with a variational tendency of FT-IR spectrums. Therefore, typical characteristic peaks at 720 cm^-1, 750–900 cm^-1, and 1,600 cm^-1 can be used to identify the presence of PN2217 and quantitatively characterize the PN2217 content in warm-mix asphalt.

3.1.1.1 Epoxy ring-opening reaction between PN2217 and SBS/asphalt polar components

The epoxy groups in PN2217 undergo a nucleophilic ring-opening reaction with the active hydrogen-containing groups (e.g., hydroxyl (-OH) in asphalt asphaltenes, carboxyl (-COOH) in polar aromatics, and unsaturated C-H bonds in the SBS styrene–butadiene segment) under test preparation temperature (135 °C). This reaction breaks the stable epoxy ring structure, generates new hydroxyl and ether bonds, and forms covalent connections between PN2217 molecules and asphalt/SBS macromolecules. The ring-opening reaction increases the number of polar functional groups in the asphalt system, promotes the uniform dispersion of asphaltenes (the core skeleton of asphalt structure), and reduces the phase separation tendency of the SBS–asphalt composite system.

3.1.1.2 Amine hydrogen bonding formation and intermolecular force enhancement

The primary/secondary amine groups in PN2217 are strong hydrogen bond donors, which can form intermolecular hydrogen bonds with the hydrogen bond acceptors in asphalt (e.g., carbonyl C=O in asphaltenes and ether bond C-O in colloids) and SBS (e.g., ester groups in the SBS modified chain). The hydrogen bond network thus formed is a reversible physical crosslinking point, which significantly enhances the intermolecular force of the asphalt system without changing the main molecular chain structure of SBS. This is the key reason for the increase of elastic components in asphalt (verified by DSR test G′ rise), and it can hinder the thermal movement of molecular chains at high temperature, thus improving the high-temperature rutting resistance and temperature stability of SBS asphalt.

3.1.1.3 Mild crosslinking of long-chain molecules driven by functional group reactions

The new functional groups generated by the epoxy ring-opening reaction (e.g., multi-site hydroxyl groups) can react with the amine groups of other PN2217 molecules and the polar groups of asphalt asphaltenes to form mild long-chain crosslinking structures. Meanwhile, the hydrogen bond network acts as a “physical crosslinking bridge” to connect the crosslinked long-chain molecules, forming a stable “covalent crosslinking + hydrogen bond network” dual structure in the asphalt system. This structure makes the asphalt microstructure gradually evolve into a homogeneous two-phase system (verified by AFM and Han curve analysis), increases the content of long-chain alkanes (720 cm^-1 characteristic peak increase in FT-IR), and promotes the formation of a three-dimensional network structure, which further improves the structural stability and high-temperature deformation resistance of SBS asphalt.

3.1.2 AFM analysis

The 2D and 3D morphologies of SBS asphalt and PN2217 warm-mix asphalts are shown in Figure 2. The results indicate that the microscopic surface structure of asphalt changes and that the phenomenon of gathering, dispersing, and blending is evident, thus affecting the macro performance of SBS asphalt.

FIGURE 2

As shown in Figure 2, with an increase in the dosage of PN2217, the number and size of bee structures in the microstructure of modified asphalt gradually increase. PN2217 may serve as a nucleating agent, contributing to the heterogeneous nucleation of asphaltenes and wax crystals during the cooling process (Pauli et al., 2001), thus increasing the number of bee structures. The distribution of the bee structure in the asphalt system improved, and the internal structure of the warm mix asphalt was more stable (Jäger et al., 2004). The 3D structural side view and 2D morphology chromatographic column can, to some extent, represent the four components of asphalt (Song et al., 2021; Dong et al., 2017) (Figure 3). The prominent white part, prominent yellow part, the horizontal part, and the concave black part can, respectively, represent the contents of asphaltene, colloid, aromatic, and saturate. After the addition of PN2217, asphaltene and colloid content increased, accompanied by a decrease in the contents of saturate and aromatic, consistent with the results of the FT-IR test.

FIGURE 3

The root-mean-square roughness () and arithmetic-mean roughness () used to evaluate the flatness of rubber asphalt were calculated fromwhere N is the number of scan points and is the scan point height. The and values of rubber asphalt before and after acid rain immersion are shown in Figure 4.

FIGURE 4

As shown in Figure 4, the variation trends of and were similar. The surface roughness of SBS asphalt increased with increasing PN2217 content, indicating that the fluctuation degree of the surface topography of warm-mix asphalt increased. This may be because the addition of PN2217 makes SBS asphalt gradually develop into a homogeneous system.

Asphalt is composed of different phase structures. There are commonly three different phases in the surface morphology of asphalt: bee structure, peri-phase, and para-phase (Masson et al., 2006). The height variation in the characteristic areas in the surface morphology of the control specimen and warm-mix asphalts was statistically analyzed, and the statistical results of the height values of each typical region are shown in Figure 5.

FIGURE 5

As observed in Figure 5, after the addition of PN2217, the internal phase structures of SBS asphalt begin to converge, the boundary between the peri- and para-phase becomes blurred, and the height difference gradually decreases. With an increase in PN2217 content, the three-phase structure gradually becomes two-phase.

The peri-phase can be integrated with the para-phase. The appearance of the peri-phase on the microscopic surface of asphalt may be due to the long-chain alkyl eutectic of wax crystals and asphaltene. The polar groups are adsorbed onto the surface of wax crystals, thus weakening the adsorption of wax crystals on light components (Pauli et al., 2011; Das et al., 2016; Davis and Castorena, 2015). Moreover, an electric double layer is formed by polar groups on a wax crystal surface and asphaltene and colloid, which is not absorbed in asphalt. Therefore, the wax crystal surface solvation layer is conducive to stable dispersal in asphalt (Allen et al., 2014).

With an increase in PN2217 content, the asphaltene in asphalt increases and began to aggregate, and the bee structure gradually increases. The corresponding solvent layers increase and overlap. When the overlap reaches a certain extent, a two-phase structure appears on the microscopic surface of the asphalt.

The addition of PN2217 may absorb the light components into the asphalt, thus reducing the para-phase content. Meanwhile, the cross-linking of macromolecules provides a larger crystal nucleus for wax crystallization, resulting in an increase in the bee structure, and the corresponding solvation layers gradually increase and overlap, thus forming a two-phase structure. We reason that with the addition of PN2217, the multicomponent polymer system spontaneously diffused to the high concentration phase after its energy decreased, forming a stable two-phase system (Badri et al., 2021).

3.2 Rheological properties

3.2.1 DSR test

The time–temperature superposition principle was adopted to determine the frequency and temperature dependencies in the viscoelastic properties of the control specimen and warm-mix asphalts (Williams et al., 1955). The curves obtained at the reference temperature are fixed, and all the other curves are shifted horizontally by the value of corresponding shift factor, parallel to the logarithmic frequency axis, to form a single master curve. The value of rheological parameters measured at different temperatures and loading frequencies are used to create master curves at a reference of 60 °C based on the TTSP. The master curves of the control specimen and warm-mix asphalts are depicted in Figure 6.

FIGURE 6

reflects the resistance to permanent deformation of asphalt subjected to repeated vehicle loading. The master curves of all specimens present similar tendency. increased as frequency increases. As shown in Figure 6a, higher values of for warm-mix asphalts than for the control specimen were observed. This effect was more pronounced at the low frequency area, equivalent to the high temperature region. In the low frequency region, the order of is PN2217-5>PN2217-3>PN2217-1>control specimen. The larger the , the stronger the ability of the asphalt to resist permanent deformation at high temperature. This may be because the addition of PN2217 makes the modified asphalt tend to be a two-phase system so as to prevent molecular chain migration at high temperature and improve its deformation resistance at high temperature.

Figures 6b, c present the and master curves of SBS asphalt binder and warm mix asphalts. The change in of asphalt binder mainly results from the variation of and viscous modulus . PN2217 mainly affects the of SBS asphalt in the low frequency region. The test results of the of all specimens are similar those of the complex modulus. In the low frequency region, the order of the elastic modulus is PN2217-5>PN2217-3>PN2217-1>control specimen. According to Figure 6c, PN2217 has no significant effect on the of SBS asphalt, indicating that PN2217 mainly improves resistance to permanent deformation by increasing the elastic modulus of SBS asphalt. The higher the content of PN2217, the more obvious the improvement of the elastic modulus of SBS modified asphalt.

The theory of polymer physics shows that stress relaxation occurs in viscoelastic polymers with the change of time. Han and Kim (1989) adopted molecular models of the viscoelasticity of homogeneous polymers to analyze the relationship curve of logG′ to logG’’, called the “Han curve”. The viscoelastic response in the high temperature (equivalent to low frequency) area is shown in Equations 13, 14:

where k is the slope of the Han curve, is the plateau moduli of the polymer (Pa), is the z-average molecular weight (g/mol), and is the average molecular weight (g/mol).

The Han curve has been used to investigate the phase structure of modified asphalt. Research has shown that when the slope at the end of the Han curve of asphalt material is close to 2, it is close to a homogeneous polymer. For the multi-phase asphalt system, the slope at the end of the Han curve is generally less than 2. In this study, the phase structure and the compatibility between PN2217 and SBS asphalt are analyzed by a frequency sweep test. The Han curves for the control specimen and warm-mix asphalts with different PN2217 contents are shown in Figure 7.

FIGURE 7

Linear fitting was used to fit and analyze the frequency scanning results of each modified asphalt at 75 °C. The fitting results are shown in Table 5.

As observed in Table 5, with an increase in PN2217 content, the slope at the end of the Han curve of modified asphalt is closer to 2, indicating that the degree of disorder inside SBS asphalt decreases after the addition of PN2217, and the asphalt gradually approaches the homogeneous polymer. This is consistent with the results of the FT-IR test. This may be due to the increase in asphaltene content in SBS asphalt under the action of PN2217.

A temperature sweep test was used for the temperature scan to investigate the temperature dependency of asphalt binders. The variation tendencies of for SBS asphalt and warm mix asphalt modified with different PN2217 contents are shown in Figure 8.

FIGURE 8

As depicted in Figure 8a, the fluidity of bitumen increases with the increase in temperature, and the complex shear modulus of all the bitumen decreases gradually. At the same temperature, the complex modulus of warm-mixed bitumen is lower than that of SBS bitumen. Compared with PN2217 warm-mix asphalt, SBS asphalt is more likely to produce large deformations under the same stress level. The rutting factor () is used to evaluate the resistance to permanent deformation for asphalt binder; with higher , asphalt binder has better high-temperature performance. The values of for all asphalt samples are shown in Figure 8b. The variation tendency of the rutting factor is consistent with the complex modulus. The addition of PN2217 can significantly improve the rutting factor of modified asphalt to improve its high-temperature rutting resistance. This may be because the addition of PN2217 forms a stable three-dimensional network structure in SBS asphalt, which lengthens and blocks the path of heat diffusion and plays a good barrier role in heat diffusion, thus significantly improving the high-temperature performance of modified asphalt.

Linear regression analysis was carried out on the logarithms of the rutting factor and temperature under different test temperatures to investigate the temperature sensitivity of different asphalt samples (Equation 15): can be used to evaluate the temperature sensitivity of asphalt. With higher , asphalt has higher temperature sensitivity in high temperature regions, and its high temperature performance is poor.

Linear regression analysis was conducted on the rutting factor measured at 52, 58, 64, 70, 76, and 82 according to the abovementioned equation. The results are shown in Figure 9.

FIGURE 9

As observed in Figure 9, there is a good linear relationship between the logarithm of all the modified asphalt rutting factors and the test temperature. The absolute value of the GTS of warm-mix asphalt decreases to varying degrees after the addition of PN2217 compared to SBS asphalt, indicating that the addition of PN2217 reduces the temperature sensitivity of SBS asphalt, thus increasing the temperature stability of SBS asphalt in the high temperature region; the higher the dosage of PN2217, the more obvious the improvement effect. This may be because the addition of PN2217 forms a good three-dimensional network structure in the asphalt, which limits the migration of asphalt molecules under high temperature conditions and significantly improves the high-temperature stability of SBS asphalt (Shi et al., 2020).

3.2.2 MSCR test

There are some limitations in using the rutting factor () to evaluate asphalt’s ability to resist deformation. Therefore, according to NCHRP9-10, an MSCR test can been considered a good index for the evaluation of high-temperature asphalt (Zhang et al., 2019). The cumulative strain versus time curves for all asphalts are shown in Figure 10. With increasing loading time, the cumulative strain gradually increased. The higher the stress level, the greater the cumulative strain value of asphalt. The cumulative strain value at 3.2 kPa (Figure 10b) was significantly higher than that at 0.1 kPa (Figure 10a) (Lei et al., 2020).

FIGURE 10

The cumulative strain values at different stress levels were in the order of the control specimen, PN2217-1, PN2217-3, and PN2217-5. The higher the cumulative strain value, the lower the creep recovery ability of modified asphalt, and the lower its high-temperature performance. The accumulated strain values of PN2217 warm-mix asphalt were significantly lower than that of control specimen, indicating that PN2217 can significantly enhance deformation recovery ability.

According to the above analysis, the addition of PN2217 makes SBS asphalt a homogeneous system. The greater the amount of PN2217, the more obvious the effect. The uniformly dispersed components in SBS asphalt will precipitate long-chain molecules in the asphalt, and these crosslink with each other to form a more uniform and stable microstructure which effectively hinders the thermal movement of the asphalt chain. It also shows that the modified asphalt has excellent anti-deformation ability (Wang et al., 2020).

Elastic recovery percentage (R) and non-recoverable creep compliance () for all asphalt samples at 0.1 and 3.2 kPa are shown in Figure 11.

FIGURE 11

R can reflect on the ability of asphalt to recover applied strains after loading. As shown in Figure 11a, the variation tendencies for control specimens and warm-mix asphalts were similar at different stress levels. R decreased with increasing applied stress level. The addition of PN2217 increased the share elastic strain, thus improving the flexibility of SBS asphalt, and this effect is obvious when the PN2217 content is 10%. R slightly decreased at a stress level of 3.2 kPa, for SBS, PN2217-1, PN2217-3, and PN2217-5 at 3.03%, 0.67%, 0.50%, and 0.48%, respectively. Therefore, PN2217 can reduce the stress sensitivity of SBS asphalt at high temperature.

Figure 11b indicates that all asphalt samples at 0.1 and 3.2 kPa. reflect, to some extent, the resistance of asphalt binder against permanent deformation. The higher value demonstrates better performance for asphalt binder against permanent deformation at high temperature. The test results for are contrary to R. The value of increases with increasing stress level. At the same stress level, for SBS asphalt is the highest, indicating that cumulative strain and permanent rutting is easily produced for SBS asphalt at high temperature. By adding PN2217 warm mix agent, the value of is considerably decreased compared to SBS asphalt binder. Stress sensitivity in warm-mix asphalts was significantly lower than SBS asphalt binder. Increment ranges for SBS, PN2217-1, PN2217-3, and PN2217-5 are 265%, 13.2%, 19.8%, and 15.2%, respectively.

3.2.3 BBR test

The values of the stiffness (S) and creep rate (m-value) for the control specimen and warm-mix asphalts extracted from the BBR test at −6 are depicted in Figure 12. S demonstrates asphalt against loading at low temperature, and the m-value represents the sensitivity of creep to time and stress relaxation characteristics. The higher the S parameter, the better the cracking resistance potential of the asphalt, and vice versa for the m-value. The S value of asphalt material should be less than 300 MPa, and the m-value should not be less than 0.3 (Wen et al., 2020; Walubita et al., 2021).

FIGURE 12

The creep stiffness modulus S-value data in Figure 12a shows a double increasing characteristic: as the test temperature decreases, the S-values of all asphalt samples significantly increase; as the PN2217 content increases from 0 to 5 wt% at the same low temperature, the S-value of asphalt shows a gradual upward trend. From −6 °C to −24 °C, the S-value of the matrix SBS asphalt increases from 125.6 MPa to 589.7 MPa, and the S-value of PN2217-5 modified asphalt increases from 150.5 MPa to 689.5 MPa. This is because at low temperatures, the thermal motion of asphalt molecules weakens, the material exhibits brittle hardening characteristics, the stiffness against external deformation increases, and the creep stiffness modulus increases accordingly, which conforms to the basic characteristics of asphalt low-temperature rheology. Compared with the matrix SBS asphalt, the S-values of PN2217-1, PN2217-3, and PN2217-5 increased by 7.0%, 10%, and 19% at −6 °C, respectively, and the increase remained consistent at lower temperatures. From a performance perspective, the S-value characterizes the ability of asphalt to resist load deformation at low temperatures, but a higher S-value is not necessarily better, because then the asphalt material has stronger low-temperature brittleness, poorer deformability, and is prone to brittle cracking due to stress concentration under external forces. This directly indicates that the addition of PN2217 reduces the low-temperature flexibility of SBS asphalt and has a negative effect on low-temperature crack resistance.

The creep rate m-value in Figure 12b exhibits a double decreasing characteristic that is completely opposite to the S-value: as the test temperature decreases, the m-values of all asphalt samples continue to decrease. At the same low temperature, as the dosage of PN2217 increases, the m-value of the asphalt shows a gradually decreasing trend.

From −6 °C to −24 °C, the m-value of matrix SBS asphalt decreased from 0.410 to 0.265, and the m-value of PN2217-5 modified asphalt decreased from 0.375 to 0.233. This is because the stress relaxation ability of asphalt decreases significantly at low temperatures, while the sensitivity of creep to time decreases. It is difficult for the material to release internal stress through slow creep, which can easily lead to stress accumulation and cracking. Compared with the matrix SBS asphalt, the m values of PN2217-1, PN2217-3, and PN2217-5 at −6 °C decreased by 4.8%, 5.9%, and 8.3%, respectively. The m value is the core indicator for evaluating the low-temperature stress relaxation performance of asphalt. The higher the m-value, the stronger the stress relaxation ability of asphalt, and the better the low-temperature crack resistance. On the other hand, a decrease in m-value means that it is difficult for the asphalt to release the internal stress generated by the load at low temperatures, so the risk of cracking is significantly increased. This further confirms the deteriorating effect of PN2217 on the low-temperature crack resistance of SBS asphalt, and the degree of deterioration increases with the increase of dosage.

3.3 Correlation analysis between microscopic molecular structure and macro-performance

The change of microscopic molecular structure may result in the variation of macro-performance. The addition of PN2217 causes a series of physical and chemical actions affecting the rheological properties of SBS asphalt. The functional group index was selected to quantify and characterize the microscopic molecular structure of asphalt. Correlation analysis was adopted to investigate the relationship between the functional group index and , S, m, and . The linear fitting results are shown in Figure 13.

FIGURE 13

As shown in Figure 13, the adjusted R² values are all greater than 0.8, indicating a good linear relationship between the functional group index and the properties of warm-mix asphalt. Furthermore, the variation tendencies of all parameters are consistent with the results of the rheological properties. Due to the addition of PN2217, the number of long-chain alkanes increases, and the molecular structure of some branch chains recombines to the long-chain molecular structure. This led to the migration of components with small molecular weight to components with large molecular weight, resulting in the change of the surface morphology, with the asphalt gradually changing into a homogeneous structure. The long-chain molecular structure is crosslinked to form a stable network structure, thus increasing the elastic component of the asphalt. The ability to resist permanent deformation and recoverable strain at high temperature increases, and the low temperature performance of asphalt decreases due to the decrease of components with small molecular weight.

4 Conclusion

References

• 1

  Al-RawashdehA. S.SargandS. M. (2014). The effect of chemical composition of aggregate on the performance of hot and warm mix asphalt in presence of water. Adv. Civ. Eng. Mater.3 (1), 20–56. 10.1520/acem20130064

  • CrossRef
  • Google Scholar
  • View reference in article

• 2

  AllenR. G.LittleD. N.BhasinA.GloverC. J. (2014). The effects of chemical composition on asphalt microstructure and their association to pavement performance. Int. J. Pavement Eng.15 (1), 9–22. 10.1080/10298436.2013.836192

  • CrossRef
  • Google Scholar
  • View reference in article

• 3

  AndersonR. M.BaumgardnerG.MayR.ReinkeG. (2008). Engineering properties, emissions, and field performance of warm mix asphalt technology. Natl. Coop. Highw. Res. Program (NCHRP).

  • Google Scholar
  • View reference in article

• 4

  AzarhooshA.KoohmishiM. (2020). Investigation of the rutting potential of asphalt binder and mixture modified by styrene-ethylene/propylene-styrene nanocomposite. Constr. Build. Mater.255, 119363. 10.1016/j.conbuildmat.2020.119363

  • CrossRef
  • Google Scholar
  • View reference in article

• 5

  BadriR. M.AlkaissiZ. A.SutantoM. (2021). Physical, rheological and morphological characterization of modified asphalt binder with differing crumb rubber contents. Mater. Today Proc.42, 3028–3034. 10.1016/j.matpr.2020.12.819

  • CrossRef
  • Google Scholar
  • View reference in article

• 6

  BanerjeeA.de Fortier SmitA.ProzziJ. A. (2012). The effect of long-term aging on the rheology of warm mix asphalt binders. Fuel97, 603–611. 10.1016/j.fuel.2012.01.072

  • CrossRef
  • Google Scholar
  • View reference in article

• 7

  BastosJ.BabadopulosL.SoaresJ. B. (2017). Relationship between multiple stress creep recovery (MSCR) binder test results and asphalt concrete rutting resistance in Brazilian roadways. Constr. and Build. Mater.145 (AUG.1), 20–27. 10.1016/j.conbuildmat.2017.03.216

  • CrossRef
  • Google Scholar
  • View reference in article

• 8

  ButtonJ. W.EstakhriC.WimsattA. (2007). A synthesis of warm mix asphalt. Texas: Southwest Region University Transportation Center, Texas Transportation Institute.

  • Google Scholar
  • View reference in article

• 9

  CapitãoS. D.Picado-SantosL. G.MartinhoF. (2012). Pavement engineering materials: review on the use of warm-mix asphalt. Constr. Build. Mater.36, 1016–1024. 10.1016/j.conbuildmat.2012.06.038

  • CrossRef
  • Google Scholar
  • View reference in article

• 10

  CheraghianG.Cannone FalchettoA.YouZ.ChenS.KimY. S.WesterhoffJ.et al (2020). Warm mix asphalt technology: an up to date review. J. Clean. Prod.268, 122128. 10.1016/j.jclepro.2020.122128

  • CrossRef
  • Google Scholar
  • View reference in article

• 11

  DasP. K.BaajH.TigheS.KringosN. (2016). Atomic force microscopy to investigate asphalt binders: a state-of-the-art review. Road Mater. Pavement Des.17 (3), 693–718. 10.1080/14680629.2015.1114012

  • CrossRef
  • Google Scholar
  • View reference in article

• 12

  DavisC.CastorenaC. (2015). Implications of physico–chemical interactions in asphalt mastics on asphalt microstructure. Constr. Build. Mater.94, 83–89. 10.1016/j.conbuildmat.2015.06.026

  • CrossRef
  • Google Scholar
  • View reference in article

• 13

  DongZ.LiuZ.WangP.GongX. (2017). Nanostructure characterization of asphalt-aggregate interface through molecular dynamics simulation and atomic force microscopy. Fuel189, 155–163. 10.1016/j.fuel.2016.10.077

  • CrossRef
  • Google Scholar
  • View reference in article

• 14

  FakhriM.GhanizadehA. R.OmraniH. (2013). Comparison of fatigue resistance of HMA and WMA mixtures modified by SBS. Procedia - Soc. Behav. Sci.104, 168–177. 10.1016/j.sbspro.2013.11.109

  • CrossRef
  • Google Scholar

• 15

  GohS. W.YouZ. (2011). “Evaluation of warm mix asphalt produced at various temperatures through dynamic modulus testing and four-point beam fatigue testinged,” in Pavements and materials: recent advances in design, testing and construction ASCE, 123–130.

  • Google Scholar

• 16

  GohS. W.YouZ. (2008). “Mechanical properties of warm mix asphalt using asphamin,” in Proceedings of 2008 annual transportation research board meeting (Washington, D.C: National Research Council).

  • Google Scholar

• 17

  HanC.KimJ. K. (1989). Molecular theory for the viscoelasticity of compatible polymer mixtures. 1. A tube model approach. Macromolecules22 (4), 1914–1921. 10.1021/ma00194a067

  • CrossRef
  • Google Scholar
  • View reference in article

• 18

  HeX.TanM.YangD.ZhuX.TanS.YangX. (2023). Rheological properties of SBS-Modified asphalt containing aluminum hydroxide and organic montmorillonite. Case Stud. Constr. Mater19, e02491. 10.1016/j.cscm.2023.e02491

  • CrossRef
  • Google Scholar
  • View reference in article

• 19

  HurleyG.ProwellB. (2006). Evaluation of Evotherm for use in warm mix asphalt. NCAT Rep.2, 15–35.

  • Google Scholar
  • View reference in article

• 20

  JägerA.LacknerR.Eisenmenger-SittnerC.BlabR. (2004). Identification of four material phases in bitumen by atomic force microscopy. Road Mater. Pavement Des.5 (Suppl. 1), 9–24. 10.1080/14680629.2004.9689985

  • CrossRef
  • Google Scholar
  • View reference in article

• 21

  JamshidiA.HamzahM. O.YouZ. (2013). Performance of warm mix asphalt containing sasobit®: State-of-the-art. Constr. Build. Mater.38, 530–553. 10.1016/j.conbuildmat.2012.08.015

  • CrossRef
  • Google Scholar
  • View reference in article

• 22

  KalyanG.RameshA.Venkat RamayyaV. (2021). Performance evaluation of warm mix asphalt mixture with partial inclusion of reclaimed asphalt pavement materials. Mater. Today Proc.38, 2919–2926. 10.1016/j.matpr.2020.09.242

  • CrossRef
  • Google Scholar
  • View reference in article

• 23

  KendallA.KeoleianG. A.LepechM. D. (2008). Materials design for sustainability through life cycle modeling of engineered cementitious composites. Mater. Struct.41 (6), 1117–1131. 10.1617/s11527-007-9310-5

  • CrossRef
  • Google Scholar
  • View reference in article

• 24

  KheradmandB.MuniandyR.LawT. H.BtR. (2017). An overview of the emerging warm mix asphalt technology. Int. J. Pavement Eng.15 (1), 7–9. 10.1080/10298436.2013.839791

  • CrossRef
  • Google Scholar
  • View reference in article

• 25

  LeiJaZhengN.XuX.WuC.LuD. (2020). High temperature rheological properties of warm mixed asphalt. Jianzhu Cailiao Xuebao/Journal Build. Mater.23 (4), 904–911. 10.3969/j.issn.1007-9629.2020.04.024

  • CrossRef
  • Google Scholar
  • View reference in article

• 26

  LiuJ.LiP. (2012). Low temperature performance of Sasobit-Modified warm-mix asphalt. J. Mater. Civ. Eng.24 (1), 57–63. 10.1061/(asce)mt.1943-5533.0000347

  • CrossRef
  • Google Scholar
  • View reference in article

• 27

  LiuJ.SaboundjianS.LiP.ConnorB.BrunetteB. (2011). Laboratory evaluation of Sasobit-Modified warm-mix asphalt for Alaskan conditions. J. Mater. Civ. Eng.23 (11), 1498–1505. 10.1061/(asce)mt.1943-5533.0000226

  • CrossRef
  • Google Scholar
  • View reference in article

• 28

  LuG.ZhangS.XuS.DongN.YuH. (2021). Rheological behavior of warm mix asphalt modified with foaming process and surfactant additive. Crystals11, 410. 10.3390/cryst11040410

  • CrossRef
  • Google Scholar
  • View reference in article

• 29

  LuX.SjvallP.SoenenH.BlomJ.MakowskaM. (2021). Oxidative aging of bitumen: a structural and chemical investigation. Road Mater. Pavement Des.23 (6), 1–16. 10.1080/14680629.2021.1871936

  • CrossRef
  • Google Scholar
  • View reference in article

• 30

  MallickR. B.KandhalP. S.BradburyR. L. (2008). Using warm-mix asphalt technology to incorporate high percentage of reclaimed asphalt pavement material in asphalt mixtures. Transp. Res. Rec. J. Transp. Res. Board2051, 71–79. 10.3141/2051-09

  • CrossRef
  • Google Scholar
  • View reference in article

• 31

  MassonJ. F.LeblondV.MargesonJ. (2006). Bitumen morphologies by phase-detection atomic force microscopy. J. Microsc.221 (1), 17–29. 10.1111/j.1365-2818.2006.01540.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 32

  MassonJ. F.PelletierL.CollinsP. (2015). Rapid FTIR method for quantification of styrene-butadiene type copolymers in bitumen. J. Appl. Polym. Sci.79 (6), 1034–1041. 10.1002/1097-4628(20010207)79:6<1034::aid-app60>3.0.co;2-4

  • CrossRef
  • Google Scholar
  • View reference in article

• 33

  MiddletonB.ForfylowR. W. B. (2009). Evaluation of warm-mix asphalt produced with the double barrel green process. Transp. Res. Rec. J. Transp. Res. Board2126 (1), 19–26. 10.3141/2126-03

  • CrossRef
  • Google Scholar
  • View reference in article

• 34

  MohdH. M. R.YouZ.YangX. (2017). A comprehensive review of theory, development, and implementation of warm mix asphalt using foaming techniques. Constr. Build. Mater.152, 115–133. 10.1016/j.conbuildmat.2017.06.135

  • CrossRef
  • Google Scholar
  • View reference in article

• 35

  PamplonaT.AmoniB.AlencarA.LimaA.RicardoN.SoaresJ.et al (2012). Asphalt binders modified by SBS and SBS/Nanoclays: effect on rheological properties. J. Braz. Chem. Soc.23, 639–647. 10.1590/s0103-50532012000400008

  • CrossRef
  • Google Scholar
  • View reference in article

• 36

  PauliA. T.BranthaverJ. F.RobertsonR. E.GrimesW. (2001). Atomic force microscopy investigation of SHRP asphalts. Am. Chem. Soc. Div. Petroleum Chem. Prepr.46 (2), 110–114.

  • Google Scholar
  • View reference in article

• 37

  PauliA. T.GrimesR. W.BeemerA. G.TurnerT. F.BranthaverJ. F. (2011). Morphology of asphalts, asphalt fractions and model wax-doped asphalts studied by atomic force microscopy. Int. J. Pavement Eng.12 (4), 291–309. 10.1080/10298436.2011.575942

  • CrossRef
  • Google Scholar
  • View reference in article

• 38

  PerkinsS. (2009). Synthesis of warm mix asphalt paving strategies for use in Montana highway construction. Mix Des.

  • Google Scholar

• 39

  PuchardZ.GorgenyiA. (2012). Experiences on Low Temperature (LT) asphalts in Hungarian road building. Procedia - Soc. Behav. Sci.48, 2029–2034. 10.1016/j.sbspro.2012.06.1176

  • CrossRef
  • Google Scholar
  • View reference in article

• 40

  Rodríguez-AllozaA. M.GallegoJ.PérezI. (2013). Study of the effect of four warm mix asphalt additives on bitumen modified with 15% crumb rubber. Constr. and Build. Mater.43 (3), 300–308. 10.1016/j.conbuildmat.2013.02.025

  • CrossRef
  • Google Scholar
  • View reference in article

• 41

  RubioM. C.MartínezG.BaenaL.MorenoF. (2012). Warm Mix Asphalt: an overview. J. Clean. Prod.24, 76–84. 10.1016/j.jclepro.2011.11.053

  • CrossRef
  • Google Scholar
  • View reference in article

• 42

  SargandS.NazzalM. D.Al-RawashdehA.PowersD. (2012). Field evaluation of warm-mix asphalt technologies. J. Mater. Civ. Eng.24 (11), 1343–1349. 10.1061/(asce)mt.1943-5533.0000434

  • CrossRef
  • Google Scholar
  • View reference in article

• 43

  ShiJ.FanW.ZhaoP.LuX.WangT. (2020). Effect of sasobit on rheological properties of high viscosity asphalt sasobit. Journal China Univ. Petroleum Ed. Nat. Sci.44 (6), 141–148. 10.3969/j.issn.1673-5005.2020.06.018

  • CrossRef
  • Google Scholar
  • View reference in article

• 44

  SongY.GaoP.LvP. (2021). Study on the low temperature properties and microscopic characteristics mechanism of warm mix asphalt. Cailiao Daobao/Materials Rep.3 (5), 10052–10060.

  • Google Scholar

• 45

  TaherM.AmanM. Y. (2020). Resilient modulus of Advera warm mixture asphalt incorporating reclaimed asphalt pavement (RAP) materials. IOP Conf. Ser. Earth Environ. Sci.498, 012015. 10.1088/1755-1315/498/1/012015

  • CrossRef
  • Google Scholar
  • View reference in article

• 46

  TopalA.SengozB.KokB. V.YilmazM.Aghazadeh DokandariP.OnerJ.et al (2014). Evaluation of mixture characteristics of warm mix asphalt involving natural and synthetic zeolite additives. Biochimica Biophysica Acta57 (apr), 38–44. 10.1016/j.conbuildmat.2014.01.093

  • CrossRef
  • Google Scholar
  • View reference in article

• 47

  Transportation Research Record (2011). “Journal of the transportation Research board,” in Asphalt Materials and Mixtures 2011, 2.

  • Google Scholar
  • View reference in article

• 48

  Valdés-VidalG.Calabi-FloodyA.Sanchez-AlonsoE.DíazC.FonsecaC. (2020). Highway trial sections: performance evaluation of warm mix asphalt and recycled warm mix asphalt. Constr. Build. Mater.262, 120069. 10.1016/j.conbuildmat.2020.120069

  • CrossRef
  • Google Scholar
  • View reference in article

• 49

  VincentG.FrançoisO.BogdanC.ChantalR.EtienneB.JeanA. (2018). Laboratory investigations of mechanical performance of foamed bitumen mixes that use half-warm aggregates. Transp. Res. Rec.1998 (1), 89–95. 10.3141/1998-11

  • CrossRef
  • Google Scholar

• 50

  WalubitaL. F.FuentesL.TanvirH.ChunduriH. R.DessoukyS. (2021). Correlating the asphalt-binder BBR Test data to the HMA (ML-OT) fracture properties. J. Mater. Civ. Eng.33 (9), 04021230. 10.1061/(asce)mt.1943-5533.0003866

  • CrossRef
  • Google Scholar

• 51

  WangL.ZhangQ.FengL. (2020). Performance evaluation of warm-mixed crumb rubber asphalt based on rheological and microscopic characteristics analysis. Jianzhu Cailiao Xuebao/Journal Build. Mater.23 (6), 1458–1463. 10.3969/j.issn.1007-9629.2020.06.026

  • CrossRef
  • Google Scholar

• 52

  WasiuddinN. M.SelvamohanS.ZamanM. M.GueganM. L. T. A. (2007). Comparative laboratory study of Sasobit and Aspha-min additives in warm-mix asphalt. J. Transp. Res. Board1998, 82–88. 10.3141/1998-10

  • CrossRef
  • Google Scholar

• 53

  WenY.GuoN.WangL.GuW.YouZ. (2020). Analysis of rheological properties and micromechanism of foamed warm mix asphalt mastic. Cailiao Daobao/Materials Rep.34 (5), 10052–10060.

  • Google Scholar

• 54

  WilliamsM. L.LandelR. F.FerryJ. D. (1955). The temperature dependence of relaxation mechanisms in amorphous and other glass-forming liquid. J. Am. Chem. Soc.77 (14), 3701–3707. 10.1021/ja01619a008

  • CrossRef
  • Google Scholar

• 55

  XiaoF.JordanJ.AmirkhanianS. (2009a). Laboratory investigation of moisture damage in warm-mix asphalt containing moist aggregate. Transp. Res. Rec. J. Transp. Res. Board2126 (2126), 115–124. 10.3141/2126-14

  • CrossRef
  • Google Scholar

• 56

  XiaoF.ZhaoP.AmirkhanianS. N. (2009b). Fatigue behavior of rubberized asphalt concrete mixtures containing warm asphalt additives. Constr. and Build. Mater.23 (10), 3144–3151. 10.1016/j.conbuildmat.2009.06.036

  • CrossRef
  • Google Scholar

• 57

  YuH.ZhuZ.WangD. (2019). Evaluation and validation of fatigue testing methods for rubberized bituminous specimens. Transp. Res. Rec.2673 (8), 603–610. 10.1177/0361198119841308

  • CrossRef
  • Google Scholar

• 58

  ZhangJ.WalubitaL. F.FarukA. N. M.KarkiP.SimateG. S. (2015). Use of the MSCR test to characterize the asphalt binder properties relative to HMA rutting performance – a laboratory study. Constr. and Build. Mater.94 (sep.30), 218–227. 10.1016/j.conbuildmat.2015.06.044

  • CrossRef
  • Google Scholar

• 59

  ZhangC.WangH.YouZ.GaoJ.IrfanM. (2019). Performance Test on styrene-butadiene-styrene (SBS) modified asphalt based on the different evaluation methods. Appl. Sci.9 (3), 467. 10.3390/app9030467

  • CrossRef
  • Google Scholar

• 60

  ZhangH.WangY.YuT.LiuZ. (2020). Microstructural characteristics of differently aged asphalt samples based on atomic force microscopy (AFM). Constr. Build. Mater.255, 119388. 10.1016/j.conbuildmat.2020.119388

  • CrossRef
  • Google Scholar

• 61

  ZhaoP.RenR.ZhouH.OuyangJ.LiZ.SunD. (2021). Preparation and properties of imidazoline surfactant as additive for warm mix asphalt. Constr. Build. Mater.273, 121692. 10.1016/j.conbuildmat.2020.121692

  • CrossRef
  • Google Scholar