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Article

Synergistic Effects of Multi-Walled Carbon Nanotubes and SBS on Asphalt Binder Performance

by
Amjad H. Albayati
1,
Hasan M. Al-Mosawe
2,
Ahmed M. Mohammed
1,
Mayank Sukhija
3,
Aliaa F. Al-ani
1,
Mazen J. Al-Kheetan
4,* and
Mustafa M. Moudhafar
1
1
Department of Civil Engineering, University of Baghdad, Baghdad 10071, Iraq
2
Civil Engineering Department, Al-Nahrain University, Baghdad 10071, Iraq
3
School of Civil and Construction Engineering, Oregon State University, Corvallis, OR 97331, USA
4
Department of Civil and Environmental Engineering, Mutah University, Karak 61710, Jordan
*
Author to whom correspondence should be addressed.
Constr. Mater. 2026, 6(3), 34; https://doi.org/10.3390/constrmater6030034
Submission received: 24 March 2026 / Revised: 26 May 2026 / Accepted: 27 May 2026 / Published: 29 May 2026
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Abstract

The performance and durability of asphalt pavements are strongly influenced by the rheological properties of asphalt binders, particularly under severe climatic and traffic conditions. This study investigates the synergistic effects of incorporating multi-walled carbon nanotubes (CNTs) at dosages ranging from 0.25% to 1% into AC 40-50 asphalt binders modified with 4% Styrene–Butadiene–Styrene (SBS). A comprehensive experimental program involving physical, rheological, and chemical characterization tests was conducted, including penetration, softening point, viscosity, storage stability, a Dynamic Shear Rheometer (DSR), Multiple Stress Creep Recovery (MSCR), Linear Amplitude Sweep (LAS), Fourier Transform Infrared Spectroscopy (FTIR), and Glover-Rowe (G-R) analysis. Statistical inference using one-way ANOVA was also conducted to evaluate the significance of differences among the binder formulations investigated. The results showed a continuous increase in binder stiffness with increasing CNT content, as indicated by decreasing penetration values, higher softening points, and increased viscosity. Incorporating 1% CNT reduced the softening-point difference from 3.1 °C to 1.6 °C in SBS-modified binders, indicating improved storage stability. Rheological evaluations showed that 0.75% CNT increased the high-temperature performance grade from 82 °C to 88 °C and provided the best rutting resistance, as indicated by MSCR results. In contrast, the 0.5% CNT formulation exhibited superior fatigue resistance and the lowest Glover-Rowe index, indicating improved cracking resistance and durability. Overall, the findings demonstrate that CNTs can effectively enhance the performance of SBS-modified asphalt binders, with 0.75% CNT being optimal for hot-climate applications, while 0.5% CNT exhibited improved fatigue and cracking resistance under moderate-temperature conditions.

1. Introduction

Asphalt binders are critical components in asphalt mixtures, directly influencing pavement performance, durability, and resistance to environmental factors and increasing traffic loads. With the continuous evolution of road quality standards and the need for improved resistance to deformation and cracking, binder modification technologies have emerged as innovative solutions to enhance the physical and rheological properties of asphalt [1,2,3]. Among various modifiers, SBS is one of the most widely used polymers, known for its ability to improve crack resistance, increase flexibility at low temperatures, and enhance permanent deformation resistance at high temperatures [4,5,6]. However, SBS-modified binders face challenges related to storage stability, primarily due to phase separation during storage and transportation [7,8,9,10].
Several nanomaterials have been suggested in the past to improve the performance of asphalt binder [11,12,13,14,15,16,17,18,19]. Some nanomaterials enhance high-temperature performance, others improve low-temperature behavior, and a few are effective under both conditions. However, finding an ideal nanomaterial that balances both remains very challenging. Among different nanomaterials, CNTs have emerged as promising nanomaterials due to their exceptional mechanical and thermal properties [20,21,22]. Based on a comparative study, CNTs exhibit superior reinforcement ability through their nano-network and also aid in distributing stresses to retard the crack propagation, especially at extreme temperatures [23]. However, their effect varies with the change in base asphalt binders [11]. CNTs can be classified as single-walled (SW) or multi-walled (MW). In this study, multi-walled carbon nanotubes were selected for their superior mechanical strength, higher specific surface area, and relative ease of dispersion within the binder matrix. The importance of using CNTs in modifying SBS-modified asphalt binders lies in improving storage stability and reducing component separation, in addition to enhancing overall rheological and physical properties [24,25].
Studies have shown that adding CNTs to SBS-modified asphalt binders improves key performance indicators, including penetration, viscosity, and thermal susceptibility. It also improves storage stability metrics, including the separation index and the softening-point difference [26,27]. The combination of SBS and CNTs in asphalt binder modification represents a promising approach for developing high-performance asphalt mixtures with enhanced resistance to extreme service conditions, ultimately extending pavement service life and reducing maintenance costs. For instance, Goli et al. [28] investigated the effects of CNTs as a bond enhancer in asphalt binders and their influence on the storage stability of polymer-modified materials. Their study showed that CNTs improved the penetration index (PI), viscosity-temperature susceptibility (VTS), and temperature susceptibility (TS), while significantly enhancing the separation index (SI) and softening-point difference (SPD). Liu et al. [27] proposed a simplified method to improve compatibility by introducing SBS-modified CNTs, which promoted homogeneous dispersion and a three-dimensional network structure within the asphalt matrix, thereby enhancing thermal and mechanical properties. Similarly, Chen et al. [29] reported that CNT/SBS-modified asphalt exhibited excellent storage stability, with 7% and 28% improvements in rutting resistance relative to SBS-HVMA and TPS/SBS-HVMA, respectively, while only marginally reducing low-temperature performance by 5%.
Despite these promising findings, challenges remain. High-viscosity SBS asphalt exhibits poor workability, limited storage stability, and reduced high-temperature performance. Recent studies have shown that incorporating CNTs can significantly improve resistance to deformation and aging, particularly in hot climates, while only minimally affecting low-temperature performance. However, achieving an optimal balance between high-temperature rutting resistance and low-temperature flexibility, alongside improved workability and storage stability, remains an area of ongoing research. Accordingly, a summary of previous studies related to SBS- and CNT-modified asphalt binders, including the current study’s scope, is presented in Table 1.
As shown in Table 1, previous studies consistently reported that CNT incorporation improves the stiffness, rutting resistance, and storage stability of asphalt binders. However, the reported optimal CNT dosage varies with binder type and testing conditions. In addition, most previous studies have focused primarily on conventional physical and high-temperature rheological characterization, whereas integrated evaluations that combine fatigue, cracking resistance, and chemical characterization remain limited.

2. Research Novelty

Although the individual and combined effects of CNTs and SBS on asphalt binder performance have been reported in previous studies, as summarized in Table 1, most investigations primarily focused on conventional physical characterization and limited rheological evaluation. Previous studies have demonstrated the potential of CNTs to improve stiffness, rutting resistance, and storage stability; however, the reported findings vary with the CNT dosage and binder type selected. Comprehensive studies integrating advanced performance-related tests, such as MSCR, LAS, Glover-Rowe analysis, and FTIR within a unified experimental framework, remain limited. Therefore, the present study provides a systematic evaluation of 4% SBS-modified asphalt binders incorporating CNTs at varying dosages (0.25–1%) using integrated physical, rheological, and chemical characterization techniques. The findings are expected to contribute to the development of high-performance asphalt binders with improved resistance to cracking and deformation, ultimately supporting the construction of more resilient pavement structures under demanding service conditions.

3. Materials and Tests

3.1. Asphalt Cement

The asphalt binder used in this research was obtained from the Doura Oil Refinery in southwestern Baghdad, Iraq. Its physical properties, as determined by standard penetration grading tests, are detailed in Table 2. These results confirm that the binder meets the AC 40-50 penetration grade specifications outlined in AASHTO M20. Additionally, the binder’s rheological performance was assessed using the Superpave Performance Grading (PG) framework specified in AASHTO M320. As shown in Table 3, the binder satisfies the criteria for a PG 70-16 classification.

3.2. Modifiers

The modifiers used in this study include SBS and multi-walled carbon nanotubes (CNTs). The SBS employed, commercially known as Kraton® D1192, Kraton, Shanghai, China, is a linear elastomeric block copolymer consisting of rigid polystyrene end blocks and a flexible polybutadiene mid-block [53,54]. This molecular structure imparts both elasticity and toughness to the polymer. The SBS contains approximately 30% styrene by weight, contributing to its thermoplastic behavior and compatibility with asphalt binders. Multi-walled carbon nanotubes were selected for their exceptional mechanical properties, including high tensile strength, large specific surface area, and nanoscale dimensions, which enable them to act as effective reinforcing agents in the asphalt matrix. These CNTs exhibit a concentric cylindrical nanostructure composed of rolled graphene sheets, with a typical diameter of ~20 nm and a length of ~10 μm. The key physical and chemical properties of both SBS and MWCNTs are summarized in Table 4. Additionally, Figure 1 presents a photographic image of the materials, illustrating their physical form.

4. Testing Methods

A comprehensive experimental program was conducted to evaluate the physical, rheological, and chemical properties of CNT/SBS-modified asphalt binders. The testing program included conventional physical tests, storage stability evaluation, FTIR analysis, SEM imaging, DSR testing, MSCR, LAS, and G-R analysis. For all experimental procedures, three replicate measurements were conducted, and the reported results represent the average values to ensure reliability and repeatability.

4.1. Fundamental Properties

The fundamental physical properties of the asphalt binders were assessed to establish their fundamental characteristics and ensure compliance with relevant specifications. The tests conducted included penetration at 25 °C following the AASHTO T49, which indicates binder hardness and consistency; softening point in accordance with AASHTO T53, which identifies the binder’s temperature at which its state shifts from a semi-solid to a liquid state; and rotational viscosity at 135 °C (AASHTO T316), which assesses the flow behavior of the binder at mixing and compaction temperatures. Specific gravity at 25 °C (ASTM D70) was measured to determine the binder’s density for volumetric mix design purposes. Finally, storage stability (ASTM D7173) was conducted by evaluating the binder’s resistance to phase separation after 48 h of storage at 163 °C, based on the difference in softening points between the top and bottom sections of the binder sample. These tests provide essential baseline information on binder performance prior to further rheological characterization.

4.2. High Temperature PG

The asphalt binder’s high-temperature performance grade (PG) was determined according to the Superpave system outlined in AASHTO M320. The main parameter assessed was the rutting resistance factor (G*/sin δ), where G* represents the complex shear modulus (kPa) and δ denotes the phase angle in degrees. This parameter quantifies the binder’s ability to resist permanent deformation under high-temperature conditions and repeated loading. For unaged binders, the following Superpave specification applies:
G*/sin δ ≥ 1.00 kPa
Testing began at 64 °C and was conducted in 6 °C increments (i.e., 64 °C, 70 °C, 76 °C, etc.) until the binder failed to meet the specified rutting-resistance criteria. This procedure allowed the determination of the critical high temperature for each binder’s PG classification.

4.3. MSCR Test

The MSCR test was conducted following the AASHTO T350 guidelines using an Anton Paar DSR (SmartPave e102), Graz, Austria, to evaluate the permanent deformation resistance of the asphalt binders at a test temperature of 70 °C (the high-temperature PG for the unmodified asphalt binder). The test involved applying a sequence of 1 s creep and 9 s recovery cycles at stress levels of 0.1 kPa and 3.2 kPa on RTFO-aged samples. The procedure consisted of 30 cycles in total: 10 conditioning cycles at 0.1 kPa, followed by 10 cycles at 0.1 kPa, and 10 cycles at 3.2 kPa. The key outputs were percent recovery (R) and non-recoverable creep compliance (Jnr), calculated using the following relationships:
%   R =   ε r ε p × 100
J n r = ε n r τ
where εr is the recovered strain, εp is the peak strain, εnr is the non-recovered strain, and τ is the applied shear stress. These parameters provide critical insights into the binder’s elastic recovery behavior and rutting resistance under high-temperature loading conditions.

4.4. LAS Test

The Linear Amplitude Sweep (LAS) test was performed following the guidelines of AASHTO T391 to evaluate the fatigue resistance of asphalt binders at an intermediate temperature of 25 °C, which represents moderate pavement service conditions commonly associated with fatigue cracking under local environmental conditions [18,55]. Prior to testing, the binders were conditioned using RTFO aging (AASHTO T240) followed by PAV aging (AASHTO R28) to replicate field aging conditions. The experiment was performed using a Dynamic Shear Rheometer (DSR) with 8 mm parallel plates and a 2 mm gap, in accordance with AASHTO T315 specifications. The Linear Amplitude Sweep (LAS) procedure consists of two primary phases:
  • Frequency Sweep (undamaged condition): A low strain amplitude of 0.1% is applied across frequencies ranging from 0.2 to 30 Hz. This step is used to determine the undamaged α-parameter, which is essential for the Viscoelastic Continuum Damage (VECD) analysis.
  • Amplitude Sweep: Performed at a constant frequency of 10 Hz, during which the strain amplitude is gradually increased from 0% to 30% over 3100 loading cycles.
During the test, parameters including shear strain, dynamic modulus (|G*|), phase angle (δ), and shear stress are continuously monitored at 1 s intervals. Fatigue failure is determined as the point at which the initial value of |G*|sin δ decreases by 35%. The damage accumulated at the point of failure ( D f ) is subsequently calculated using the following equation:
D f   =   ( 0.35   C 0 / C 1 ) ^ ( 1 / C 2 )
where C 0 represents the mean value of |G*|sin δ measured over the 0.1% strain range, expressed in MPa, and C 1 and C 2 are the coefficients obtained by fitting the data to Equation (4) [56]:
l o g ( C 0   −   | G * | s i n   δ )   =   l o g ( C 1 )   +   C 2   l o g ( D )
where D represents damage accumulation in the specimen, the fatigue life ( N f ) at a certain strain level, γ (equal to 5% for thinner layers of asphalt concrete and 2.5% for thicker layers) is evaluated through Equation (5) [56].
N f = A 35   ·   ( γ ) ^ B
where A35 and B are material-specific factors used to determine the fatigue life ( N f ) of the bitumen, as defined in Equations (6) and (7):
A 35 = f D f k k π C 1   C 2 α
B = −2α
where α is an undamaged material property, f denotes the loading frequency (typically 10 Hz), and k is determined according to the following Equation (8):
k = 1 + 1 − C 2 α

4.5. Glover-Rowe Index

The Glover-Rowe (G-R) parameter is a rheological indicator used to assess the cracking resistance of PAV-aged asphalt binders. It combines the complex shear modulus (G*) and phase angle (δ) into a single parameter, providing insight into the binder’s tendency towards brittleness and cracking. The G-R parameter is calculated using the following relationship:
G − R = G *   × ( cos δ ) 2 / sin δ
The test is performed using the DSR with an 8 mm specimen and a 2 mm gap at a temperature of 15 °C and a frequency of 0.005 rad/s. A higher G-R value indicates increased stiffness and reduced flexibility, which corresponds to a greater risk of thermal cracking. Anderson [57] suggests that a G-R value of approximately 180 kPa is associated with the onset of cracking, while a value of 600 kPa indicates severe cracking potential.

5. Asphalt Binder Modification Process

The modified asphalt binder was prepared following the method proposed by Tang et al. [45]. The reference binder (AC 40-50) was first heated in an oven at 160 °C for 1.5 h to ensure full liquefaction. Approximately 500 g of molten asphalt was then transferred to a mixing vessel maintained at 160 °C. For the polymer modification, 4% SBS pellets (by binder weight) were gradually added to the base binder and then blended in a high-speed shear mixer at 5000 rpm for 45 min to achieve uniform dispersion. Subsequently, CNTs were incorporated into the SBS-modified asphalt at binder-weight dosages of 0.25%, 0.5%, 0.75%, and 1.0%. Each blend was subjected to additional high shear mixing at 3000 rpm for 45 min at 160 °C. Upon completion of mixing, the modified binders were allowed to cool to room temperature and then stored in sealed containers for later testing. To facilitate reference in the Section 6, the binders are designated according to the labels shown in Table 5.

6. Results and Discussion

6.1. Fourier Transform Infrared Spectroscopy (FTIR)

The FTIR analysis provided valuable insights into the chemical interactions and structural modifications of the asphalt binder (AC 40-50) upon incorporating SBS and CNT modifiers. The unmodified AC 40-50 sample exhibited characteristic absorption peaks typical of asphalt binder, dominated by strong saturated hydrocarbon stretching vibrations in the 2800–3000 cm−1 region, indicative of abundant aliphatic structures, as shown in Figure 2a. Irrespective of the asphalt binders, a symmetric bending of CH3 was observed at around 1377 cm−1, and asymmetric bending in CH3 was depicted around 1460 cm−1. Pronounced aromatic vibrations were identified around 1600 cm−1, highlighting the intrinsic aromatic-rich composition of the asphalt binder. The presence of moderate absorption peaks at approximately 1700 cm−1 (carbonyl groups, C=O stretching) and 1030 cm−1 (sulfoxide groups, S=O stretching) indicated mild oxidative products inherent to petroleum-derived asphalt binders. These peaks were clearly shown in Figure 2b.
Upon modifying the binder with 4% SBS, subtle yet noteworthy spectral alterations were observed. As seen in Figure 2c, a few new peaks were developed around 699 cm−1, 910 cm−1, and 966 cm−1, indicating the composition of SBS in terms of styrene and butadiene [58]. The incorporation of SBS resulted in minor intensity variations, particularly within the aromatic and carbonyl absorption bands, reflecting possible interactions between the polymer molecules and the asphalt matrix. This suggests a molecular-level enhancement in structural integrity, potentially contributing to improved mechanical and rheological properties. Further modifying the SBS-enhanced binder with CNT at concentrations ranging from 0.25% to 1% introduced nuanced variations in absorption intensities and calculated spectral indices, as indicated in Figure 3. Specifically, CNT incorporation led to modest reductions in the aromaticity index (1600 cm−1) and the carbonyl index (1700 cm−1), indicating potential interactions between CNT particles and asphalt aromatic structures, possibly forming physical entanglements or reinforcing networks at the nanoscale. Such interactions are hypothesized to enhance the mechanical robustness and durability of the modified asphalt binders.
The consistent sulfoxide indices observed across all samples indicate that the modifications with SBS and CNT did not significantly alter the initial sulfoxide content or introduce substantial oxidation during preparation and mixing processes. The limited variation in carbonyl indices across samples further suggests that SBS-CNT modifications may provide subtle enhancements or stabilization against oxidative degradation, potentially prolonging the binder’s service life. Collectively, the FTIR spectra and corresponding indices indicate that the strategic incorporation of SBS and CNT modifiers into an AC 40-50 asphalt binder produces subtle yet beneficial molecular-scale changes. These changes imply enhanced interactions within the asphalt matrix, potentially translating into improved performance characteristics, particularly in durability, stiffness, and resistance to initial oxidation, without compromising the binder’s inherent chemical stability.

6.2. Morphological Characteristics

Scanning Electron Microscopy (SEM) was used to examine the morphological evolution of the asphalt binder upon CNT incorporation and to evaluate how these structural changes vary with CNT dosage. Figure 4 illustrates the SEM images of unmodified, SBS-modified, and CNT-modified asphalt binders. A distinct morphological difference is observed between the base (RB) and SBS-modified binders (Figure 4a,b). While the reference binder appears relatively homogeneous, the SBS-modified binder exhibits a well-defined polymeric network composed of styrene and butadiene phases.
With the incorporation of CNTs into the SBS binder, the microstructure becomes more interlocked and compact, indicating an enhanced polymer network. The CNTs display a tubular morphology, and their dispersion density increases with dosage (Figure 4c–f). At CNT contents exceeding 0.5%, agglomeration becomes evident, thereby increasing binder stiffness. This increase in stiffness is associated with higher viscosity and can significantly affect the binder’s resistance to rutting and cracking. As evident from Figure 4f, the 1% CNT-modified SBS binder exhibits poor dispersion, leading to the formation of excessive agglomerated clusters. This clustering disrupts the polymeric network and diminishes the reinforcing efficiency of the CNTs. The formation of agglomerations and poor dispersion was also observed in a previous study, highlighting the need for an optimal dosage for achieving desired performance [23].
Therefore, while CNT inclusion can enhance the binder’s structural integrity, excessive dosages may adversely affect workability and fatigue resistance. Performance evaluations are essential for optimizing CNT content and ensuring balanced performance. The observed morphological evolution underscores the importance of selecting appropriate dosages to achieve desirable behavior in pavement applications.

6.3. Basic Properties

The basic physical properties of the asphalt binders are presented in Figure 5a–e. The penetration results (Figure 5a) showed a consistent decrease upon modification, with values decreasing from 41 (0.1 mm) for the reference binder (RB) to 27 for the SBS-modified binder (PMB), corresponding to a 34.15% reduction. The addition of CNTs further reduced penetration progressively to 25, 24, 22, and 21 for CNT0.25, CNT0.5, CNT0.75, and CNT1, respectively, corresponding to a 48.78% decrease for CNT1 relative to RB. This stiffening effect is attributed to the synergistic interaction between SBS and CNTs, in which CNTs act as nanofillers, restricting polymer chain mobility and thereby forming a denser microstructure. The softening point (Figure 5b) increased substantially from 50.2 °C for RB to 71.7 °C for PMB, and further to 74.9 °C for CNT1, reflecting a 48.9% improvement. This enhancement is linked to the thermal stability imparted by CNTs, which impede molecular mobility and promote network formation within the binder, as also noted by Sun et al. [59] and Liu et al. [60]. In the same context, Li et al. found that CNTs induce wax crystallization and lead to the reorganization of the colloidal structure of the asphalt binder [61]. It is noteworthy, however, that although the trends in penetration and softening point suggest continuous improvement with increasing CNT content, the extent of improvement may diminish at higher CNT dosages due to potential CNT aggregation (as observed in SEM images). Viscosity results at 135 °C (Figure 5c) showed a significant increase: from 724 mPa.s for RB to 2728 mPa.s for PMB, and further to 3246–3360.7 mPa.s for the CNT-modified binders, indicating an overall viscosity gain of 360.77%. This trend aligns with previous reports [33,60], where CNTs increase viscosity by enhancing internal friction and restricting binder flow. As per Shams et al., the pronounced increase in viscosity upon the addition of CNTs is due to the formation of a strong CNT nanonetwork, which restricts molecular mobility [23]. However, the increased viscosity of the CNT-modified binders may require higher mixing and pumping temperatures to maintain adequate workability and handling characteristics. The specific gravity results (Figure 5d) showed a slight decrease with modification, from 1.028 for RB to 1.025 for PMB and down to 1.022 for CNT1, reflecting a modest change of −0.58% due to the incorporation of lower-density modifiers. Storage stability results (Figure 5e) highlighted the stabilizing effect of CNTs, with the softening-point difference (ΔT) between the top and bottom sections decreasing from 3.1 °C for the SBS-modified binder (PMB) to 1.6 °C for CNT1, indicating a 48% reduction in phase separation. This improvement is consistent with findings by Liu et al. [60] and Sun et al. [59], who demonstrated that CNTs mitigate polymer migration during storage by forming physical entanglements and enhancing the compatibility between SBS and the asphalt matrix.

6.4. High Temperature PG

The asphalt binder’s high-temperature rheological properties, as assessed by the Dynamic Shear Rheometer (DSR), are presented in Figure 6a–c. The G*/sin δ is a critical indicator of rutting resistance at elevated temperatures, with the Superpave specification requiring a minimum value of 1.00 kPa. As shown in Figure 6a, G*/sin δ values for the unmodified reference binder (RB) were significantly lower than those for the modified binders, confirming the limited rutting resistance of the RB binder. The addition of 4% SBS (PMB) increased G*/sin δ across the temperature range, indicating improved stiffness and elastic response. The incorporation of CNTs into the SBS-modified binder further increased G*/sin δ values, with the most pronounced improvements observed at 0.75% and 1% CNT dosages. This trend suggests that CNTs enhance the binder’s load-bearing capacity by reinforcing the polymer network, restricting molecular mobility, and increasing stiffness at elevated temperatures. This behavior of CNT was also reported in a couple of previous studies [23,62]. However, it is noteworthy that while the 1% CNT formulation shows slightly higher G*/sin δ values than the 0.75% formulation, the gains beyond 0.75% are marginal, indicating a performance plateau at higher CNT dosages.
The phase angle (δ), shown in Figure 6b, complements the G*/sin δ results by illustrating the viscoelastic character of the binders. Lower δ values indicate more elastic behavior, which is desirable for rutting resistance. The RB binder exhibited the highest δ values across the temperature range, reflecting its predominantly viscous response. In contrast, the SBS- and CNT-modified binders displayed lower δ values, indicating enhanced elastic response. The δ values decreased progressively as CNT content increased, with the lowest phase angle observed in the 1% CNT formulation. However, the differences between 0.75% and 1% CNT were relatively small, suggesting that the incremental improvements in elasticity diminish at higher CNT contents.
The true high-temperature performance grade (failure temperature), presented in Figure 6c, further confirms these trends. The RB binder had a failure temperature of 74.8 °C, whereas the SBS-modified binder increased it to 85.1 °C. The incorporation of CNTs raised the failure temperatures to 86.0 °C for CNT0.25, 86.1 °C for CNT0.5, and 88.0 °C for both CNT0.75 and CNT1. This indicates that the maximum improvement in high-temperature PG is achieved at 0.75% CNT, with further increases in CNT content yielding limited additional benefits for PG enhancement. Overall, the results indicate that a CNT dosage of 0.75% effectively improves the high-temperature PG to PG 88-XX, whereas increasing the CNT content to 1% maintains the same PG level, indicating a performance plateau at higher CNT dosages. One grade improvement in the PG with the addition of CNT was also observed in a previous study [63].

6.5. Discussion on MSCR Results

The MSCR test results, presented in Figure 7 and Table 6, provide clear insights into the high-temperature rutting performance of the tested binders at 70 °C. The reference binder (RB) exhibited the highest accumulated creep strain and the highest non-recoverable compliance (Jnr3.2 = 6.0175 kPa−1) with an almost negligible recovery (R3.2 = 0.00%), indicating a severe susceptibility to permanent deformation under traffic loading. The polymer-modified binder (PMB) significantly improved these properties, achieving a Jnr3.2 of 1.9767 kPa−1 and an R3.2 of 17.85%, classifying it within the H grade (heavy traffic) category according to AASHTO M332. Further incorporation of carbon nanotubes (CNTs) into the PMB matrix enhanced the rutting resistance up to an optimal point, which can be attributed to the formation of a reinforcing nano-network that restricts molecular mobility and improves stress distribution within the binder matrix. The CNT0.75 binder achieved the best performance (Jnr3.2 = 0.8632 kPa−1, R3.2 = 22.33%), qualifying it for the V grade (very heavy traffic). The CNT0.25 and CNT0.5 binders also showed improvements over PMB, indicating that moderate CNT dosages effectively enhance the elastic response and creep recovery behavior of SBS-modified binders classified as H-grade (heavy-traffic) binders.
However, at a 1% CNT dosage (CNT1), performance declined: Jnr3.2 increased to 3.9387 kPa−1, and R3.2 dropped sharply to 0.02%, placing it back in the S grade (standard traffic) category. The reduction in rutting resistance at higher CNT contents is consistent with previous studies. Goli et al. [28] and Tang et al. [45] reported that excessive CNT addition can cause agglomeration due to strong van der Waals forces, leading to poor dispersion and cluster formation within the binder. This disrupts the uniform CNT distribution, creating localized stress concentrations that limit their reinforcing effect. Additionally, Shu et al. [33] and Wang et al. [64] noted that high CNT levels may saturate the binder’s molecular network, weakening interactions between SBS polymer chains and the asphalt matrix and thereby reducing overall performance. In summary, CNT incorporation improves high-temperature rutting resistance up to an optimal threshold of 0.75%, beyond which excessive CNTs can impair performance due to agglomeration and reduced intermolecular interactions. Based on the AASHTO M332 classification system, the binders are categorized as follows:
  • RB and CNT1 fall into the S grade (standard traffic);
  • PMB, CNT0.25, and CNT0.5 meet the H grade (heavy traffic);
  • CNT0.75 achieves the more stringent V grade (very heavy traffic).
These findings underscore the critical need to carefully optimize CNT dosage to maximize the reinforcing effects of nano-modifiers in polymer-modified asphalt binders, thereby enhancing rutting resistance and overall binder performance.

6.6. Discussion on LAS Results

The fatigue performance of the tested binders was assessed using the effective shear stress–strain response and fatigue life estimates obtained from the LAS test conducted at 25 °C. The strain level corresponding to the peak stress serves as an indicator of binder ductility. Higher peak strain values and a slower stress decline following the peak suggest enhanced flexibility and greater resistance to fatigue under cyclic loading conditions. Figure 8 illustrates the effective shear stress–strain relationships for all binder types, revealing distinct trends. The reference binder (RB) exhibited the highest peak stress but a rapid stress decay beyond the peak, indicating high initial stiffness but limited energy dissipation under cyclic loading, resulting in lower fatigue tolerance. In contrast, the polymer-modified binder (PMB) exhibited a lower peak stress and a more gradual decay, suggesting a more flexible and fatigue-tolerant response.
The incorporation of carbon nanotubes (CNTs) into the PMB matrix notably influenced the fatigue behavior. CNT0.5 exhibited the best fatigue performance, demonstrating a balanced stress–strain response with a moderate peak stress and the smoothest decay curve among all CNT-modified binders. This indicates that a 0.5% CNT dosage optimally enhances the binder’s fatigue resistance, likely due to improved stress-transfer efficiency and the formation of a well-dispersed nanonetwork within the SBS-modified asphalt matrix. At this dosage, CNTs appear to enhance the binder’s interfacial bonding and energy dissipation capacity without inducing agglomeration, which can negatively affect performance at higher dosages. The fatigue life estimates (Nf) at 2.5% and 5% strain levels, shown in Figure 9 and summarized in Table 7, reinforce these observations. At 2.5% strain, CNT0.5 achieved the highest fatigue life (Nf = 7172 cycles), outperforming all other binders, including PMB (Nf = 5387 cycles) and RB (Nf = 1991 cycles). Similarly, at 5% strain, CNT0.5 maintained superior fatigue resistance (Nf = 322 cycles), again exceeding PMB (Nf = 222 cycles) and RB (Nf = 102 cycles). The enhanced fatigue resistance of CNT0.5 can be attributed to the optimal CNT dosage, which improves binder toughness and flexibility while promoting a more uniform stress distribution within the SBS-modified matrix, thereby delaying crack initiation and propagation. In addition, the well-dispersed CNT network at this dosage may improve energy dissipation under repeated loading, thereby enhancing fatigue performance. Conversely, although higher CNT dosages (e.g., CNT1) still improved performance compared with RB, the benefits were reduced relative to CNT0.5, likely due to CNT agglomeration at higher contents, which can hinder uniform stress transfer and reduce the binder’s ability to dissipate strain energy effectively. The effect of agglomeration at higher dosages (especially >0.5% CNT) was also evident in the SEM images and has been reported in previous studies.
Overall, the LAS results demonstrate that CNT0.5 provides the most significant enhancement in fatigue resistance among the tested binders, underscoring the importance of optimizing CNT dosage to balance stiffness, flexibility, and crack resistance in polymer-modified asphalt binders.

6.7. G-R Index

The G-R index results, presented in Figure 10 (Black Space Diagram) and Table 8, provide valuable insights into the durability and cracking resistance of the tested binders. The G-R parameter is widely recognized as a reliable indicator of binder durability, with lower G-R values correlating with greater fatigue resistance and reduced susceptibility to cracking. A binder falling within the “safe zone” of the Black Space diagram is generally considered to have acceptable performance characteristics and a lower risk of durability issues. In this study, all binders, including the 1% CNT binder, fall within the safe zone, indicating that none of the tested binders are at immediate risk of cracking under typical service conditions. However, variations in G-R index values provide important distinctions in binder performance.
The CNT0.5% binder exhibited the lowest G-R index (2026 Pa), indicating an optimal balance of stiffness and flexibility and suggesting superior durability. The CNT0.25% and CNT0.75% binders showed intermediate G-R values of 2801 Pa and 2776 Pa, respectively, while the SBS-modified binder (PMB) and reference binder (RB) exhibited higher G-R indices of 4287 Pa and 3228 Pa, respectively. Notably, the 1% CNT binder, although still within the safe zone, recorded the highest G-R index (9011 Pa), reflecting a stiffer, less flexible network that could compromise long-term performance under fatigue loading. These results are consistent with the LAS test findings, which also demonstrated that the CNT0.5% binder exhibited the best fatigue resistance, further reinforcing the conclusion that a CNT content of 0.5% offers the most favorable balance of stiffness, flexibility, and durability for enhanced binder performance.
In summary, based on the overall experimental results, a clear trade-off exists between stiffness-related rutting resistance and fatigue-related cracking performance with increasing CNT dosage. Lower-to-moderate CNT contents (0.25–0.5%) improved fatigue resistance and durability-related behavior by maintaining a balanced viscoelastic response and effective stress dissipation within the binder matrix. In contrast, higher CNT dosages, particularly 0.75%, significantly enhanced stiffness, rutting resistance, and elastic recovery due to the formation of a stronger reinforcing nano-network. However, excessive CNT incorporation (1%) led to performance degradation, likely due to CNT agglomeration and reduced stress distribution efficiency. These findings highlight the importance of optimizing CNT dosage based on the targeted pavement performance requirements and climatic conditions.

7. Statistical Inferences

Based on the experimental results discussed in the previous sections, the incorporation of CNTs significantly affects the physical and rheological properties of SBS-modified asphalt binders. Since multiple CNT dosages were investigated, a one-way analysis of variance (ANOVA) was conducted to assess the statistical significance of differences among binder formulations. The null hypothesis assumed that no significant differences exist among the investigated binder types for the selected performance parameters. A 95% confidence level was adopted, with a p-value < 0.05 indicating a statistically significant difference and leading to rejection of the null hypothesis.
Table 9 summarizes the ANOVA results for the evaluated properties. The analysis showed statistically significant differences (p < 0.05) for most measured parameters, including softening point, penetration, viscosity, true failure temperature, Jnr3.2, R3.2, fatigue life (Nf), and G-R index. These findings confirm that CNT incorporation and dosage significantly affect the rheological and durability-related behavior of SBS-modified asphalt binders. In contrast, the specific gravity (GS) results showed no statistically significant differences among the investigated binders (p > 0.05), indicating that the addition of CNTs had only a minimal influence on binder density. Overall, the ANOVA results support the experimental observations and highlight the importance of optimizing CNT dosage to achieve balanced binder performance.

8. Conclusions

The following key conclusions are drawn from the experimental results and analyses:
  • FTIR analysis indicated beneficial molecular interactions between SBS, CNTs, and the binder, suggesting improved structural integrity. SEM images showed that the addition of CNTs strengthens the polymeric network of SBS binders, increasing stiffness up to an optimal dosage. At higher contents, CNTs form dense agglomerated clusters (notably at 1%).
  • Basic physical tests indicated that adding CNTs to SBS-modified binders progressively increased stiffness, reflected by lower penetration, higher softening point, and increased viscosity. CNTs also improved storage stability by reducing phase separation, with the softening-point difference (ΔT) decreasing from 3.1 °C for the SBS-modified binder to 1.6 °C at 1% CNT.
  • High-temperature PG results indicated that incorporating CNTs enhanced rutting resistance, with the 0.75% CNT formulation increasing the high-temperature PG from 82 °C for the SBS-modified binder to 88 °C. However, increasing CNT content to 1% did not yield further improvements in PG, suggesting a performance plateau at higher CNT dosages.
  • MSCR results indicated an optimal CNT dosage of 0.75% for balancing stiffness and recovery, while LAS fatigue tests showed the best fatigue resistance at 0.5% CNT, highlighting a trade-off between stiffness and flexibility at higher dosages.
  • Glover-Rowe index analysis and Black Space diagram confirmed that all binders remained within the safe zone for durability, with the 0.5% CNT binder exhibiting the lowest G-R index.
  • A CNT dosage of 0.75% is recommended for improving rutting resistance in hot climates, while the 0.5% CNT formulation exhibited improved fatigue and cracking resistance under moderate-temperature conditions based on LAS and Glover-Rowe analyses. However, the high-temperature PG evaluation in this study was conducted mainly for comparative purposes using original binder measurements, and additional RTFO-aged evaluation, low-temperature characterization, workability assessment, and field validation are required to further assess the suitability of these binders under different climatic and construction conditions.

Author Contributions

A.H.A.: Investigation, Formal analysis, Project administration, Resources, Writing—original draft. H.M.A.-M.: Data curation, Investigation, Methodology, Writing—original draft. A.M.M.: Methodology, Data curation, Writing—original draft. M.S.: Visualization, Formal analysis, Writing—review and editing. A.F.A.-a.: Formal analysis, Data curation, Writing—review and editing. M.J.A.-K.: Conceptualization, Methodology, Writing—review and editing. M.M.M.: Investigation, Methodology, Data curation. All authors have read and agreed to the published version of the manuscript.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data Availability Statement

All data, models, and code generated or used during the study appear in the submitted article.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

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Figure 1. (a) Photograph of SBS and CNT, and (b) Transmission Electron Microscopy of CNT.
Figure 1. (a) Photograph of SBS and CNT, and (b) Transmission Electron Microscopy of CNT.
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Figure 2. FTIR characteristics peaks: (a) Full FTIR spectrum, (b) Representation of characteristics indices, and (c) Characteristics peaks of asphalt binder and SBS.
Figure 2. FTIR characteristics peaks: (a) Full FTIR spectrum, (b) Representation of characteristics indices, and (c) Characteristics peaks of asphalt binder and SBS.
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Figure 3. Value of Sulfoxide, Aromatics, and Carbonyl Indices.
Figure 3. Value of Sulfoxide, Aromatics, and Carbonyl Indices.
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Figure 4. SEM images for unmodified, SBS, and CNT modified asphalt binders: (a) RB, (b) SBS, (c) CNT0.25, (d) CNT0.5, (e) CNT0.75, and (f) CNT1.
Figure 4. SEM images for unmodified, SBS, and CNT modified asphalt binders: (a) RB, (b) SBS, (c) CNT0.25, (d) CNT0.5, (e) CNT0.75, and (f) CNT1.
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Figure 5. Variation in the basic properties for different asphalt binder types: (a) Penetration value, (b) Softening point, (c) Rotational viscosity, (d) Specific gravity, and (e) Storage stability.
Figure 5. Variation in the basic properties for different asphalt binder types: (a) Penetration value, (b) Softening point, (c) Rotational viscosity, (d) Specific gravity, and (e) Storage stability.
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Figure 6. Variation in the rheological properties for different binder types: (a) Rutting parameter, (b) Phase angle (δ), and (c) True failure temperature.
Figure 6. Variation in the rheological properties for different binder types: (a) Rutting parameter, (b) Phase angle (δ), and (c) True failure temperature.
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Figure 7. Creep strain for different binder types.
Figure 7. Creep strain for different binder types.
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Figure 8. Relationships between effective stress and strain for various binder types.
Figure 8. Relationships between effective stress and strain for various binder types.
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Figure 9. Fatigue life for different binder types.
Figure 9. Fatigue life for different binder types.
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Figure 10. Black Space Diagram with G-R parameter.
Figure 10. Black Space Diagram with G-R parameter.
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Table 1. Summary of studies on asphalt modification using SBS and CNT.
Table 1. Summary of studies on asphalt modification using SBS and CNT.
StudyYearBinder TypeCNT and SBS RatioMixing ConditionsMain FindingsMian Tests
Conventional Physical TestsFTIRSEMGRPGMSCRLAS
[30]201250/70 Pen.0.1, 0.5, 1% CNT1550 rpm, 40 min, 160 °CImproves its rheological properties, enhances resistance to rutting and thermal cracking, and reduces oxidative aging.✓ ✓
[31]201560/70 Pen.0.1, 0.5, 1.0% CNT1550 rpm, 160 °C, 40 min.Improve rutting resistance and thermal cracking resistance.✓ ✓ ✓
[32]201560/70 Pen.0, 0.3, 0.6, 0.9, 1.2, 1.5% CNTThree different kinds of mixers (mechanical mixer, high shear mixer, and ultrasonic device).Improved bitumen’s high- and low-temperature performance by increasing stiffness and reducing phase angle.✓ ✓
[21]201660/70 Pen.0.2–1.5%ultrasonic 60 WImproves fracture resistance and fatigue performance of asphalt mixtures.✓ ✓
[28]201760/70 Pen.CNT + SBSUltrasound 60 W, 15 Min, 120 °CImproved storage stability and rheological performance✓ ✓
[33]201790 A3.5% SBS+
0.5–3% CNTs		5000 rpm, 30 min, 160 °CImproved thermal stability also improved SBS dispersion and binder storage stability with CNTs.✓✓✓ ✓
[34]201860/70 Pen.0.5, 1, 1.5, 3% CNT3000 rpm, 45 min, 158 ± 5 °CImproved the higher temperature performance and permanent deformation resistance in both binder and mixtures.✓✓✓ ✓
[35]2018PG58-16(0.3, 0.6, 0.9, 1.2, 1.5)% CNT65-watt ultrasonic mixer, 160 °CEnhanced the rutting performance and rheological behavior of the asphalt binder.✓✓✓ ✓
[36]201860/80 Pen.6% SBS-Improved rheological properties, as evidenced by an enhanced complex modulus and a reduced phase angle, indicate better viscoelastic behavior.✓
[37]2019AC 30/45(1–5)% SBS-SBS was efficient in decreasing the creation of carbonyl and sulphoxide compounds at higher✓ ✓ ✓
[38]202050/70 Pen.(0.5–1)% CNT
(2–4)% HDPE		4000 rpm, 30 min, 160 °CTemperatures, chain segments of butadiene are reduced due to chain scission, resulting in degradation of binder properties.✓ ✓ ✓✓
[39]202140/50,60/70 Pen.(0.5, 1, 1.5, 2)% CNT1500 rpm, 45 min, 163 °CSignificant enhancement in complex modulus, viscosity, and creep recovery of the binder at high temperatures and a great decrease in compliance, indicating great resistance to permanent deformation.✓ ✓ ✓
[40]202180/100 Pen.0.5–1% CNT + 3–5% SBS4000 rpm, 50 min, 180 °CAt 1.5% CNT, 40/50 grade bitumen improved rutting resistance by 61% and stability by 35%, while 60/70 grade bitumen needed 2.0% CNT for similar results.✓ ✓ ✓
[41]202180/100 Pen.(0.5–2.5)% MWCNTs5000 rpm, 60 min, 155 °CHigher viscosity, fatigue resistance, and thermal aging resistance.✓ ✓✓
[42]202135/50 Pen.(6–8)% SBS-The modified binder is more rut-resistant.✓
[22]202260/70 Pen.(0.1, 0.5, 1)% CNThigh shear mechanical mixer, 1 h, 150 °CCNTs added to the asphalt binder were found to be stable under high-temperature storage conditions.✓
[43]202340/50 Pen.1, 3, 5% CNT
1, 3, 5% SBS		2220 rpm, 3.5 h, 180 °CImproved long-term performance and moisture resistance comparable to PMA-based PFC mixtures.✓ ✓
[44]202390#0.5–1% CNT,
5% SBS,
5% furfural-extracted oil doping.		4000 rpm, 50 min, 180 °CEnhances pavement performance in both hot and cold conditions, extending service life and reducing maintenance costs.✓ ✓✓✓
[45]2023SK90#0.3, 0.6, 0.9, 1.2, 1.5% CNTs + 4% SBS.5000 rpm, 45 min for SBS followed by 3000 rpm, 45 min for CNT, both at 160 °CThe rutting parameter (G*/sin) increased by 10%, 73%, and 208% with 1%, 3%, and 5% SBS, and by 18% and 130% with 3% and 5% CNTs.✓ ✓✓
[46]2023VG-301.6 SBS-Enhances the fatigue resistance of asphalt sealants—also better relaxation properties, preventing secondary cracking, and excellent deformation resistance under heavy traffic.✓✓
[47]2024-(0.4–0.6)% CNTs
SBS		-CNTs enhanced the high-temperature performance and rutting resistance of SBS-modified asphalt.✓ ✓
[48]202570#(4, 6, 8)% SBS
(4, 6, 8)% SBS-T
(4, 6, 8, 10, 12)% ER-SBS-T		4500 rpm, 30 min, 160 °CImproving high-temperature performance, with the best results at a 5% doping level.✓ ✓✓
[49]2025PG64-16CNTSMA
SBSMA
CNTS/SBSMA		5000 rpm, 50 min,
170 °C		CNTs enhanced interactions among components, with the effect most pronounced at a CNT content of 0.6%.✓✓ ✓✓
[50]2025AH-90(2–4)% SBS
(3–5)% SBR		5000 rpm, 40 min, 160 °CEnhances the high-temperature behavior of the asphalt binder. The high-temperature properties of fast-melting SBS-T-modified asphalt are similar to those of conventional SBS-modified asphalt. Performance is further improved when the ER-SBS-T modifier content exceeds 6%.✓✓ ✓✓
[51]2025PG58-22(4, 6, 8)% SBS30 Min, 180 °CBetter complex modulus (G\*), phase angle (δ), rutting factor (G\*/sin δ), creep recovery rate (R), and non-recoverable compliance (Jnr), indicating that the synergy of SBS and carbon nanotubes enhanced the high-temperature properties of asphalt.✓✓ ✓
[52]2025VG 10%3 SBS
(2, 4, 6)% LDPE		2500 rpm, 90 min, 180 °CSBS shows better resistance to aging compared to BA and SBR, with stiffness modulus increases of 21% for BA, 10% for SBS, and 39% for SBR after aging.✓✓ ✓✓✓
Current study202540/50 Pen.4% SBS, (0.25–1%) CNT5000 rpm, 45 min for SBS followed by 3000 rpm, 45 min for CNT, both at 160 °C ✓✓✓✓✓✓✓
Table 2. Conventional asphalt binder properties.
Table 2. Conventional asphalt binder properties.
PropertyOriginal BinderRTFO Aged Binder
Penetration at 25 °C, 0.1 mmDuctility at 25 °C, cmSoftening Point, °CSpecific GravityRetained Penetration, %Ductility, cm
Test MethodAASHTO T49AASHTO T51AASHTO T53ASTM D70AASHTO T49AASHTO T51
Test Result42 110 50.21.0286170
Specification Limit (ASTM D946)40–50≥100--≥55≥25
Table 3. Performance grading results of the Asphalt binder.
Table 3. Performance grading results of the Asphalt binder.
BinderPropertiesTemp.
Measured,
°C		Measured ParametersSpecification Limits, AASHTO M320-05
OriginalDSR, G/sinδ at 10 rad/s (kPa)643.922
701.738
760.879
Viscosity at 135 °C (Pa.s)-7243000 m Pa.s, max
Flash Point (°C)-309230 °C, min
RTFO AgedDSR, G/sinδ at 10 rad/s (kPa)646.4882.2 kPa, min
703.187
761.466
Mass Loss (%)-0.2781%, max
PAV
Aged		DSR, G.sinδ at 10 rad/s (kPa)2834205000 kPa, max
255176
BBR, Creep Stiffness (MPa)−6188300 MPa, max
Slope m-value−60.3240.3, min
Table 4. Modifiers key properties.
Table 4. Modifiers key properties.
PropertySBS (Kraton® D1192)CNTs (Multi-Walled)
Physical FormGranular (white powder)Black powder
Chemical Formula(C8H8-C4H6)nC
Bulk Density (25 °C, g/cm3)0.40.126
Particle Size1.18–0.075 mm (dia.)20 nm (dia.), 10 µm length
Tensile Strength (MPa)33–
Elongation at Break (%)1000–
Hardness (Shore A)70–
Table 5. Specimen’s key legend.
Table 5. Specimen’s key legend.
Binder CodeDescription
RBReference binder, unmodified AC40-50
PMBPolymer-modified binder (AC40-50 + 4% SBS)
CNT0.25AC40-50 + 4% SBS + 0.25% CNT
CNT0.5AC40-50 + 4% SBS + 0.5% CNT
CNT0.75AC40-50 + 4% SBS + 0.75% CNT
CNT1AC40-50 + 4% SBS + 1.0% CNT
Table 6. Mean values and standard deviations of MSCR test results at 70 °C.
Table 6. Mean values and standard deviations of MSCR test results at 70 °C.
Binder TypeJnr, kPa−1R, %
0.1 kPa3.2 kPa0.1 kPa3.2 kPa
RB5.829 ± 0.116.018 ± 0.140.04 ± 0.010.00 ± 0.00
PMB1.189 ± 0.051.977 ± 0.0843.98 ± 1.2517.85 ± 1.05
CNT0.251.128 ± 0.061.675 ± 0.0934.34 ± 1.4110.12 ± 0.79
CNT0.51.137 ± 0.051.592 ± 0.0739.23 ± 1.1810.85 ± 0.86
CNT0.750.287 ± 0.020.863 ± 0.1542.70 ± 1.3622.33 ± 1.09
CNT13.338 ± 0.133.939 ± 0.277.94 ± 0.480.02 ± 0.01
Table 7. LAS test results for fatigue life (Nf) of different binder types (mean and standard deviation).
Table 7. LAS test results for fatigue life (Nf) of different binder types (mean and standard deviation).
Binder TypeNf at the Strain Level of
2.5%5%
RB1991 ± 84102 ± 5
PMB5387 ± 176222 ± 16
CNT0.255327 ± 171216 ± 10
CNT0.57172 ± 204322 ± 19
CNT0.755361 ± 171237 ± 12
CNT14437 ± 150184 ± 8
Table 8. G-R parameter for different binder types (mean and standard deviation).
Table 8. G-R parameter for different binder types (mean and standard deviation).
Binder TypeG-R Index, Pa
RB3228 ± 118
PMB4287 ± 146
CNT0.252801 ± 97
CNT0.52026 ± 81
CNT0.752776 ± 92
CNT19011 ± 265
Table 9. ANOVA results.
Table 9. ANOVA results.
PropertyF-Statisticp-ValueSignificant Difference at α = 0.05, (Yes/No)
Softening point (°C)1054<0.0001Yes
Penetration890.0015Yes
Viscosity1861<0.0001Yes
GS0.360.867975No
Storage stability9110.000041Yes
True failure temperature1730.0001Yes
Jnr3.25020.00013Yes
R3.24080.00009Yes
Nf at 2.5% strain level3240.00011Yes
G-R index, Pa9040.00004Yes
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MDPI and ACS Style

Albayati, A.H.; Al-Mosawe, H.M.; Mohammed, A.M.; Sukhija, M.; Al-ani, A.F.; Al-Kheetan, M.J.; Moudhafar, M.M. Synergistic Effects of Multi-Walled Carbon Nanotubes and SBS on Asphalt Binder Performance. Constr. Mater. 2026, 6, 34. https://doi.org/10.3390/constrmater6030034

AMA Style

Albayati AH, Al-Mosawe HM, Mohammed AM, Sukhija M, Al-ani AF, Al-Kheetan MJ, Moudhafar MM. Synergistic Effects of Multi-Walled Carbon Nanotubes and SBS on Asphalt Binder Performance. Construction Materials. 2026; 6(3):34. https://doi.org/10.3390/constrmater6030034

Chicago/Turabian Style

Albayati, Amjad H., Hasan M. Al-Mosawe, Ahmed M. Mohammed, Mayank Sukhija, Aliaa F. Al-ani, Mazen J. Al-Kheetan, and Mustafa M. Moudhafar. 2026. "Synergistic Effects of Multi-Walled Carbon Nanotubes and SBS on Asphalt Binder Performance" Construction Materials 6, no. 3: 34. https://doi.org/10.3390/constrmater6030034

APA Style

Albayati, A. H., Al-Mosawe, H. M., Mohammed, A. M., Sukhija, M., Al-ani, A. F., Al-Kheetan, M. J., & Moudhafar, M. M. (2026). Synergistic Effects of Multi-Walled Carbon Nanotubes and SBS on Asphalt Binder Performance. Construction Materials, 6(3), 34. https://doi.org/10.3390/constrmater6030034

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