High-Performance Asphalt Binder Incorporating Trinidad Lake Asphalt and SBS Polymer for Extreme Climates

Abstract

This study investigates the development of high-performance asphalt binders modified with Trinidad Lake Asphalt (TLA) and styrene–butadiene–styrene (SBS) polymers to enhance pavement durability under extreme climate conditions. A comprehensive evaluation of physical, rheological, and mechanical properties was conducted using Superpave performance tests, Multiple Stress Creep Recovery (MSCR), and a Dynamic Shear Rheometer (DSR). The results indicate that integrating 20% TLA significantly increases stiffness and rutting resistance by 51.7% compared to unmodified PG 64-22 asphalt, while 10% SBS improves elasticity and enhances elastic recovery by 85.3%. However, at 15% SBS, excessive viscosity was observed, reaching 13,000 cP at 135 °C, posing workability challenges and sampling challenges in the lab environment. The MSCR test confirmed that binders modified with 20% TLA and 15% SBS exhibited over 88% recovery and reduced non-recoverable creep compliance (J_nr < 0.01 kPa⁻¹), demonstrating superior resistance to permanent deformation. Additionally, low-temperature rheological testing (BBR at −12 °C) revealed that SBS incorporation mitigates excessive stiffness caused by TLA, improving the binder’s flexibility. These findings underscore the potential of TLA-SBS modified binders in achieving long-lasting, traffic-resilient pavements for extreme climatic conditions. Field validation is recommended to assess long-term feasibility in real-world applications.

1. Introduction

Traffic volumes are continuously increasing, as evidenced by data from the US Federal Highway Administration, while sudden climate changes due to global warming exacerbate pavement deterioration. This dual impact of rising traffic loads and extreme weather accelerates pavement distress, reducing service life. Asphalt remains the predominant material used for pavement construction worldwide due to its versatility and performance characteristics. The quality of asphalt binder, which acts as the adhesive material in asphalt mixtures, plays a critical role in pavement performance. Consequently, selecting high-performance materials for asphalt pavements is a growing trend in road engineering. To achieve optimal performance under varying climatic and traffic conditions, researchers have explored incorporating modifiers and fillers into petroleum-based asphalt binders [1,2].

The natural asphalt Trinidad Lake Asphalt (TLA) differs greatly from petroleum asphalt in terms of composition—soluble asphalt and mineral matter makes all the difference. This composition imparts unique characteristics to TLA, such as rigidity, which limits its use as a standalone binder in asphalt mixtures; low penetration values and high softening points arise from the mineral and asphaltene content by weight of the asphalt component [3]; and TLA been used in asphalt products for over a century. A simple refining process ensures a consistent soluble bitumen content in TLA, and its combination of bitumen and mineral components contributes to its advantageous properties, such as outstanding water resistance, chemical stability, and temperature control [4].

Despite its benefits, the hardness of TLA makes it unsuitable as a sole binder in bitumen mixtures. Instead, it is commonly blended with crude oil distilled asphalt in specific ratios. This combination enables TLA to be included into bitumen mixtures without compromising performance even at high temperatures. TLA-modified binders are prevalent in applications such as bituminous concrete (BC), mastic asphalt (MA) pavements, and modern thin bridge pavement systems [5,6]. These blends demonstrate enhanced stiffness, adhesion, diminished thermal susceptibility, superior resistance to rutting, and improved oxidative aging characteristics. Nonetheless, the augmented rigidity may adversely affect workability, compaction, and could potentially result in premature failures in the field [7].

Researchers have included polymers into asphalt mixtures to help to offset these difficulties. By lowering temperature sensitivity and increasing resistance to permanent deformation, polymers—including plastometers and thermoplastic elastomers—improve asphalt’s performance. Early questions about the hot storage stability of bituminous mixtures modified with polymers were mostly answered by later field tests, notably conducted in Texas during the 1970s with interesting findings [8]. Evaluated for their ability to increase temperature and stress resistance in asphalt mixtures are several polymers; among these, SBS is widely preferred for its consistent performance across a broad temperature range [9,10,11,12,13,14].

SBS is a thermoplastic elastomer particularly effective in improving pavement performance due to its molecular structure, which forms a three-dimensional network through physical cross-linking. This structure imparts SBS-modified asphalt with excellent strength, elasticity, and enhanced performance under varying temperature conditions. While star-shaped SBS offers a superior high-temperature performance, linear SBS provides a better performance at medium and low temperatures [15,16,17,18,19].

Despite extensive research on TLA and SBS individually, studies combining PG 64-22 asphalt binder with higher replacement percentages of TLA and SBS remain limited. There is a need to establish the optimal proportions of TLA and SBS to produce high-performance asphalt with enhanced resistance to plastic deformation under heavy loads (3.2 kPa) for extreme climatic conditions. This work attempts to close this discrepancy by means of the Superpave test method and MSCR test validation of TLA and SBS-modified binders.

In this study, PG 64-22 was mixed with TLA in proportions of 10% and 20%, and styrene–butadiene–styrene (SBS) was added in proportions of 5%, 10%, and 15%. Previous studies have indicated a TLA content maximum threshold of 20% and 15% for SBS alternatives in corresponding combinations [20,21]. Mixing was performed using the wet process—more especially, McDonald Technology—the efficiency of which in reaching homogeneity [22] is well known. The mixing process took one hour at 177 °C with a blending mixer speed of 700 revolutions per minute. Figure 1 shows a thorough experimental framework.

2. Materials and Experimental Methodology

2.1. Materials

Crude-oil-refined asphalt (PG 64-22) obtained from the TXAPA, TX, USA was the main/original binder used in this study.

Table 1. Original PG 64-22 binder properties.

Aging States	Test Properties	Test Result
Asphalt binder (before aging)	Viscosity @ 135 °C (cP) Viscosity @ 180 °C (cP)	757 284
	G*/sin δ @ 64 °C (kPa)	2.09
RTFO (short-term aged)	G*/sin δ @ 64 °C (kPa)	6.00
RTFO + PAV aged residual	G*sin δ @ 25 °C (kPa)	3405
	Stiffness @ −12 °C (MPa)	189
	m-value @ −12 °C	0.37

defines the overall characteristics. Considered for its adaptability and efficiency in many climatic conditions, this binder serves as a basic tool for research. The second modification used in the research was TLA, a naturally occurring asphalt straight from the prestigious Trinidad and Tobago pitch lake, particularly because of its unusual composition and natural origin. TLA’s special qualities are described in

Table 2. Trinidad Lake Asphalt (TLA) properties.

Properties	Test Method	Test Result
Penetration (25 °C)	ASTM D5 [23]	2–4
Density	ASTM D70 [24]	1.42–1.44 g/m3
Softening point	ASTM D36 [25]	94–100 °C
Flash point	ASTM D92 [26]	257–268 °C
Fire point	ASTM D92 (Cleveland open cup) [26]	308–312 °C

. The final modifier used was SBS, a polymer obtained from TSRC Specialty Materials LLC, Houston, TX, USA. With its characteristics stated in

Table 3. Properties of SBS polymer.

Parameter	Method	Test Result
Density	ISO 2781 [27]	0.94 g/cm3
Hardness	ASTM D2240 [28]	79 Shore A
Toluene solution viscosity	ASTM D445 [29]	13 cSt
Volatile matter	ASTM D1416 [30]	<0.7%
Yellow index	ASTM D1925 [31]	<7

, SBS is well known for increasing asphalt binders’ elasticity and durability. By adding SBS, asphalt’s mechanical qualities should be enhanced, thus raising its resilience under various stress loads.

2.2. Preparation of Samples

The combination was created using a multi-step sequential approach with a mechanical agitator at high temperatures and a low-speed shear mixer. Initially, separately at 10% and 20% ratios, 300 g of base PG 64-22 asphalt binder and TLA was heated and then completely softened in a container. Styrene–butadiene–styrene (SBS) was then added at three separate ratios of 5%, 10%, and 15%, respectively. To ensure complete mixing of the SBS with the modified bituminous binder with TLA, the combinations were next sheared for one hour at 700 rpm using a low-speed shearer. The temperature during mixing was constantly kept at 177 °C ± 2 °C throughout the process.

2.3. Physical Properties Test

The asphalt binder’s workability was evaluated using the rotational viscometer test outlined in ASTM D4402 [32]. Using a 10.5 g sample and spindle number 27, this evaluation was performed at two critical temperatures of −135 °C and 180 °C (2 samples). Twenty readings taken at one-minute intervals allowed us to faithfully replicate field conditions. Understanding the handling qualities of the binder and its efficiency during the mixing and compaction stages of pavement building depends on knowing the viscosity at these temperatures. The viscosity of the binder shows its flow behavior at high temperatures, which is essential for correct compaction in pavement layers and effective mixing with aggregates. Since this temperature corresponds with normal mixing and application conditions, testing at 135 °C offers an understanding of the binder’s performance during standard hot-mix asphalt processes. Evaluations at 180 °C, on the other hand, enable the analysis of the binder’s behavior under highly demanding circumstances, such those experienced when particular additives change their thermal characteristics; ensuring the binder keeps its workability in practical paving uses depends on these tests.

2.4. Asphalt High Temperature Aging: Mechanisms of Short-Term (RTFO) and Extended Aging (PAV)

The lifetime and performance of pavement materials depend greatly on the thermal aging of asphalt. The two main phases into which this process falls are RTFO and long-term PAV thermal aging. Every phase denotes several aspects of the aging asphalt experiences during its lifetime.

2.4.1. Short-Term Thermal Aging

This stage addresses the first aging brought on by bituminous mixture manufacturing. The Rolling Thin Film Oven (RTFO) of ASTM D2872-19 [33] mimics the conditions bitumen comes across when aggregates are heated. The RTFO test heats bitumen at 163 °C under a constant airflow for 85 min. This arrangement replicates the volatilization of smaller hydrocarbons and oxidation reactions typical of hot-mix asphalt manufacturing. This test offers an understanding of bitumen’s performance right after application by analyzing variations in viscosity and other physical characteristics.

2.4.2. Long-Term PAV Thermal Aging

As per ASTM D6521-19 [34], asphalt binders are subjected to extended aging in a Pressurized Aging Vessel (PAV) following the short-term aging simulated by the RTFO. Usually, covering five to ten years, the PAV test models the oxidative aging that takes place across the lifetime of a pavement. This test allows asphalt to be accelerated in the aging process by high temperatures and pressures, thus enabling the prediction of its long-term performance. The PAV approach replicates environmental stresses including heat, oxygen, and UV radiation, which helps asphalt to gradually harden, and embrittlement occurs. Assessing the resilience and durability of asphalt pavements depends on an awareness of long-term thermal aging, thus guaranteeing that they satisfy performance criteria over their expected lifetime.

These tests taken together give a thorough knowledge of asphalt’s thermal aging response. They greatly help to direct the choice and design of binders capable of meeting the demands of road service conditions as well as the difficulties of initial processing.

2.5. Rheological Characteristics at High and Ambient Temperatures

Using a Dynamic Shear Rheometer (DSR) test, the viscoelastic properties of the binder were evaluated following AASHTO T315 [35] at 64 °C. Determining the binder’s resistance to rutting under high temperatures—where these problems are most common—requires this test. Executed at 10 radians per second (1.59 Hz), the test produces fundamental performance measures including the phase angle (δ) and complex shear modulus (G%) (3 samples). To define baseline performance criteria, testing was first conducted on the unaged, modified binder. RTFO and PAV aging techniques were then applied to the binder to replicate field aging effects. Measuring the G*/sinδ parameter for both unaged and RTFO-aged binders at 64 °C revealed that they were inversely linked to rutting sensitivity: this value captures the binder elastic response and resistance against permanent deformation.

Also tested on the long-term aged binder at 25 °C was fatigue resistance, A key component guaranteeing the pavement lifetime, this test gauges the binder’s resistance to repeated loading cycles without cracking. And tested at a lower temperature to confirm the binder’s resilience and adaptability over its service life, the G*.sinδ value measures fatigue resistance. These tests taken together give a complete assessment of the binder’s performance under both high and ambient temperatures, thus guaranteeing its suitability for uses requiring resistance to rutting and wear damage.

2.6. Rheological Property at Low Temperature

Underlying AASHTO T 313 [36], the rheological characteristics of the asphalt at low temperatures were assessed using a Bending Beam Rheometer (BBR) at −12 °C (2 samples). To guarantee thermal balance, a 125 mm length, 12.5 mm width, 6.25 mm thickness modified asphalt specimen was submerged in methanol for one hour. The sample was then placed at both ends and 240 s of a constant force of 980 mN was applied at its midpoint. Throughout the test, the deflection of the sample (measured in millimeters) was recorded with precision. These observations helped us to determine the creep stiffness (S) and creep rate (m), thus offering vital information on the low-temperature resistance of the material. These parameters are key markers of the asphalt’s resistance to thermal stress and prevention of cracking under cold conditions—qualities essential for maintaining pavement durability in such surroundings.

2.7. Multiple Stress Creep and Recovery (MSCR) Examination

The MSCR test is designed to replicate the high-stress conditions road surfaces endure, particularly in the early stages of their service life when rutting is prevalent. This test precisely replicates the first field aging process using asphalt binders aged via RTFO. Thus, the MSCR test provides a better estimate of the rutting resistance of a binder.

The MSCR test data yield two fundamental parameters: % recovery, and non-recoverable creep compliance (J_nr) (3 samples). Equation (1) shows the J_nr, which, by means of the ratio of the unrecoverable shear strain to the applied stress, gauges the binder’s sensitivity to permanent deformation under continuous load. Computed as the percentage change in unrecovered strain from peak strain, percent recovery (rec%) measures the binder’s capacity for recovery following loading. Equation (2) details this [36].

$$J_{nr}={\displaystyle \frac{Unrecoverable shear strain}{Applied Stress}}$$

(1)

$$\mathrm{rec} (\%)=100 \times {\displaystyle \frac{Peak strain-Unrecovered strain}{Peak strain}}$$

(2)

Twenty stress cycles at 0.1 kPa and then ten cycles at 3.2 kPa comprise the MSCR test. Every cycle consists of a 1 s shear creep load then a 9 s recovery period. Whereas the higher stress level of 3.2 kPa evaluates the binder’s performance under non-linear conditions, the lower stress level of 0.1 kPa assesses its behavior within the linear viscoelastic range. Predicting long-term pavement performance depends on a thorough knowledge of the binder’s behavior over several stress levels, which this method guarantees. Equations (3)–(6) help us to determine the average values of J_nr and rec% [37].

$$J_{nr\left(0.1\right)} ={\displaystyle \frac{\sum _{n=11}^{20}{[J}_{nr}0.1n]}{10}}$$

(3)

$$J_{nr\left(3.2\right)} ={\displaystyle \frac{\sum _{n=21}^{30}{[J}_{nr}3.2n]}{10}}$$

(4)

$${rec}_{0.1} ={\displaystyle \frac{\sum _{n=11}^{20}{[rec}_{0.1}n]}{10}}$$

(5)

$${rec}_{3.2} ={\displaystyle \frac{\sum _{n=21}^{30}{[rec}_{3.2}n]}{10}}$$

(6)

Based on expected traffic loads, these criteria define the appropriate grade of high-temperature performance for bituminous binders. J_nr3.2 thresholds of 4.5 kPa⁻¹, 2.0 kPa⁻¹, 1.0 kPa⁻¹, and 0.5 k Pa⁻¹ define the PG classifications: Standard (S), Heavy (H), Very Heavy (V), and Extremely Heavy (E). Furthermore, the difference in J_nr diff between the 0.1 kPa and 3.2 kPa stress levels cannot be more than 75%, thus maintaining the stress sensitivity of the binder within reasonable limits.

By ensuring the choice of bituminous binders with enough resilience and stability under various stress levels, this strong assessment system guarantees the lifetime and durability of pavement constructions are improved [37].

2.8. Statistical Analysis

Using the SPSS version 29.0.0 program, performed an analysis of variance using the ANOVA method; then, a post hoc test (LSD method) was performed with a confidence interval of 95%. Different sample means were found to be statistically significant using ANOVA. With a significance level of 0.05, a five-percent risk is implied of a Type I error—in which a difference is concluded to exist, where in fact none exists.

ANOVA showed notable variations; then, the LSD test pinpointed the particular groups with notable variations. This test determines the smallest necessary difference between 2 sample means such that their respective population means vary statistically. Any two sample means whose absolute difference exceeds this threshold points to a notable variation between the population means. Under the supposition that the null hypothesis is true, the significance level of 95% indicates a 5% probability of observing the data, or more extreme results. It does not show a 95% confidence of the alternative hypothesis being valid. Initially used to highlight general significant variations, ANOVA was next used with Fisher’s LSD test to identify pairwise changes between individual groups [38].

3. Results and Discussion

3.1. Physical Properties

As shown in Figure 2, the viscosity features of PG 64-22 bituminous binders modified with TLA and SBS polymers were evaluated at 135 °C and 180 °C to assess their workability and performance for pavement engineering uses. Statistical analysis results (

Table 4. Results of statistical analysis on the viscosity of modified bituminous binders at 135 °C and 180 °C based on several combinations under original conditions (α = 0.05).

Viscosity at 135 °C and 180 °C
		135C									180C
	Combination	P64-22	PG64-22 + 10% TLA	PG64-22 + 20% TLA	PG64-22 + 10% TLA + 5% SBS	PG64-22 + 20% TLA + 5% SBS	PG64-22 + 10% TLA + 10% SBS	PG64-22 + 20% TLA + 10% SBS	PG64-22 + 10% TLA + 15% SBS	PG64-22 + 20% TLA + 15% SBS	PG64-22	PG64-22 + 10% TLA	PG64-22 + 20% TLA	PG64-22 + 10% TLA + 5% SBS	PG64-22 + 20% TLA + 5% SBS	PG64-22 + 10% TLA + 10% SBS	PG64-22 + 20% TLA + 10% SBS	PG64-22 + 10% TLA + 15% SBS	PG64-22 + 20% TLA + 15% SBS
135 °C	PG64-22	-	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA	-	-	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 20%TLA	-	-	-	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA + 5% SBS	-	-	-	-	S	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 20%TLA + 5%SBS	-	-	-	-	-	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA + 10%SBS	-	-	-	-	-	-	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 20%TLA + 10%SBS	-	-	-	-	-	-	-	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA + 15%SBS	-	-	-	-	-	-	-	-	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 20%TLA + 15%SBS	-	-	-	-	-	-	-	-	-	S	S	S	S	S	S	S	S	S
180 °C	PG64-22	-	-	-	-	-	-	-	-	-	-	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA	-	-	-	-	-	-	-	-	-	-	-	S	S	S	S	S	S	S
	PG64-22 + 20%TLA	-	-	-	-	-	-	-	-	-	-	-	-	S	S	S	S	S	S
	PG64-22 + 10%TLA + 5% SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	S	S	S	S	S
	PG64-22 + 20%TLA + 5%SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	-	S	S	S	S
	PG64-22 + 10%TLA + 10%SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	S	S	S
	PG64-22 + 20%TLA + 10%SBS	-	-	-	-	-	-			-	-	-	-	-	-	-	-	S	S
	PG64-22 + 10%TLA + 15%SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	S
	PG64-22 + 20%TLA + 15%SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-

S—significant; N—non-significant.

) were carried out at a 95% confidence level (α = 0.05) to determine the significance of differences in viscosity among the modified combinations.

The unmodified PG 64-22 binder guaranteed good workability by displaying viscosities of 757 cP at 135 °C and 282 cP at 180 °C, far below the recommended limit of 3000 cP. With the addition of 10% TLA, the viscosity increased slightly to 856 cP (135 °C) and 303 cP (180 °C), and for 20% TLA, values further rose to 872 cP and 311 cP. Statistical analysis showed that these increases were significant (S) compared to the base binder, indicating that TLA enhances viscosity while maintaining workability at these levels.

When SBS was introduced, the viscosity increased considerably, particularly with a higher SBS content. For instance, with 5% SBS, the viscosities were 2087.5 cP (135 °C) and 787.5 cP (180 °C) for 10% TLA and increased to 2512.5 cP and 1025 cP for 20% TLA. Statistical analysis confirmed that the addition of 5% SBS led to significant (S) differences compared to the TLA-only blends. While the viscosities remained below the 3000 cP threshold, they indicated improved stiffness and deformation resistance, making these blends suitable for high-performance pavements.

At 10% SBS, viscosities exceeded acceptable workability limits, reaching 7212 cP (135 °C) and 1562.5 cP (180 °C) for 10% TLA and rising further to 8687.5 cP and 1812.5 cP for 20% TLA. These increases were statistically significant (S) compared to lower SBS blends, confirming the substantial impact of SBS on binder viscosity. At 15% SBS, the viscosities surged drastically, reaching 13,000 cP (135 °C) and 2387.5 cP (180 °C) for 10% TLA, which further escalated for 20% TLA. Statistical analysis indicated that these combinations were significantly different (S) from all other blends, stressing the compromise between lowered workability and better performance.

The statistical results for viscosity at 180 °C mirrored the trends observed at 135 °C (Table 4). Significant increases were noted for all SBS-modified blends compared to the base PG 64-22 and TLA-only combinations. However, at elevated SBS levels (10% and 15%), the viscosities became impractically high, compromising binder workability despite enhanced stiffness and elasticity.

Overall, the results demonstrate that the combination of 5% SBS with 10–20% TLA is optimal at a temperature of 135 °C, achieving an acceptable workability for practical pavement applications. Higher SBS content, although beneficial for improving binder performance, introduces significant workability challenges, as reflected in both viscosity data and statistical analysis, and a higher temperature is required to mitigate this issue of workability. These findings underscore the importance of optimizing TLA and SBS proportions to generate excellent asphalt binders fit for long-lasting pavements under high-temperature conditions. Further field studies and construction techniques are recommended to validate the performance of these blends in real-world pavement engineering scenarios.

3.2. Rheological Characteristics at High Temperature

The results of the DSR test and corresponding statistical analysis for G*/sin δ (kPa) at 64 °C are presented in Figure 3 and

Table 5. Results of statistical analysis for the G*/sin δ parameter at 64 °C for modified bituminous binders under many combinations in their original and RTFO conditions (α = 0.05).

Viscoelasticity Original and RTFO Condition at 64 °C
		Original									RTFO
	Combination	PG64-22	PG64-22 + 10% TLA	PG64-22 + 20% TLA	PG64-22 + 10% TLA + 5% SBS	PG64-22 + 20% TLA + 5% SBS	PG64- 22 + 10% TLA + 10% SBS	PG64- 22 + 20% TLA + 10% SBS	PG64-22 + 10% TLA + 15% SBS	PG64-22 + 20% TLA + 15% SBS	PG64-22	PG64-22 + 10% TLA	PG64-22 + 20% TLA	PG64-22 + 10% TLA + 5% SBS	PG64-22 + 20% TLA + 5% SBS	PG64-22 + 10% TLA + 10% SBS	PG64-22 + 20% TLA + 10% SBS	PG64-22 + 10% TLA + 15% SBS	PG64- 22 + 20% TLA + 15% SBS
Original	PG64-22	-	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA	-	-	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 20%TLA	-	-	-	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA + 5% SBS	-	-	-	-	S	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 20%TLA + 5%SBS	-	-	-	-	-	S	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA + 10%SBS	-	-	-	-	-	-	S	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 20%TLA + 10%SBS	-	-	-	-	-	-	-	S	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA + 15%SBS	-	-	-	-	-	-	-	-	S	S	S	S	S	S	S	S	S	S
	PG64-22 + 20%TLA + 15%SBS	-	-	-	-	-	-	-	-	-	S	S	S	S	S	S	S	S	S
RTFO	PG64-22	-	-	-	-	-	-	-	-	-	-	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA	-	-	-	-	-	-	-	-	-	-	-	S	S	S	S	S	S	S
	PG64-22 + 20%TLA	-	-	-	-	-	-	-	-	-	-	-	-	S	S	S	S	S	S
	PG64-22 + 10%TLA + 5% SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	S	S	S	S	S
	PG64-22 + 20%TLA + 5%SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	-	S	S	S	S
	PG64-22 + 10%TLA + 10%SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	S	S	S
	PG64-22 + 20%TLA + 10%SBS	-	-	-	-	-	-			-	-	-	-	-	-	-	-	S	S
	PG64-22 + 10%TLA + 15%SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	S
	PG64-22 + 20%TLA + 15%SBS	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-

S—significant; N—non-significant.

to evaluate the high-temperature rheological performance of PG64-22 bituminous binders altered with TLA and SBS under both original and RTFO-aged conditions. This value shows the binder’s rutting resistance, which is important for asphalt performance in hot climates and under heavy loads.

The base binder, PG64-22, exhibited the lowest G*/sin δ values of 2.03 kPa (original) and 5.38 kPa (RTFO). The addition of 10% and 20% TLA improved rutting resistance moderately, with values increasing to 2.57 kPa and 3.08 kPa for the original condition and 5.96 kPa and 6.52 kPa for the RTFO-aged condition, respectively. However, statistical analysis shows that these increases are significant (S) compared to PG64-22, indicating that TLA alone positively impacts rutting resistance.

The incorporation of SBS alongside TLA produced substantial improvements in rutting resistance. For 5% SBS, the results were as follows:

• PG64-22 + 10% TLA + 5% SBS achieved 10.10 kPa in the original condition and 19.70 kPa during the RTFO-aged condition.
• PG64-22 + 20% TLA + 5% SBS exhibited 14.54 kPa (original) and 25.18 kPa (RTFO). Statistical analysis confirms these improvements as significant compared to the PG64-22 and PG64-22 + TLA combinations, highlighting the effectiveness of SBS in enhancing binder performance.
• Further increasing SBS content to 10% and 15% showed remarkable gains as described below.
• PG64-22 + 10% TLA + 10% SBS reached 32.40 kPa (original) and 45.40 kPa (RTFO).
• PG64-22 + 20% TLA + 15% SBS recorded the highest values of 74.79 kPa (original) and 94.62 kPa (RTFO). Statistical analysis indicates that these combinations demonstrate significant differences (S) compared to all other binders, reinforcing the superiority of SBS-modified binders in achieving excellent rutting resistance.

In terms of statistical comparisons, all modified combinations (TLA and TLA + SBS) were significantly better than the base PG64-22 binder across both conditions. Particularly, SBS modification combined with 20% TLA produced significant improvements, with 15% SBS content yielding the most exceptional performance.

The results demonstrate a clear trend: while TLA enhances stiffness, the addition of SBS not only mitigates the potential brittleness introduced by TLA but also significantly increases the rutting resistance. This is critical for pavement engineering applications, where high resistance to permanent deformation ensures durability under extreme temperatures and heavy traffic. The highest-performing binder, PG64-22 + 20% TLA + 15% SBS, emerges as a prime candidate for pavements requiring extended service life and reduced maintenance costs. Statistical analysis further validates these findings, confirming the consistent and significant improvements brought about by TLA and SBS modification.

3.3. Rheological Characteristics Results (Ambient Temperature)

The performance of various asphalt binder formulations was evaluated using G*sinδ (kPa), and their statistical significance at 25 °C after undergoing RTFO + PAV aging is shown below in Figure 4 and

Table 6. Statistical analysis results for modified bituminous binders RTFO + PAV-aged at 25 °C assessed depending on different combinations with a significance level of α = 0.05.

PAV Condition at 25 °C
		RTFO + PAV
	Combination	PG64-22	PG64-22 + 10% TLA	PG64-22 + 20% TLA	PG64-22 + 10% TLA + 5% SBS	PG64-22 + 20% TLA + 5% SBS	PG64-22 + 10% TLA + 10% SBS	PG64-22 + 20% TLA + 10% SBS	PG64-22 + 10% TLA + 15% SBS	PG64-22 + 20% TLA + 15% SBS
25 °C	PG64-22	-	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA	-	-	S	S	S	S	S	S	S
	PG64-22 + 20%TLA	-	-	-	S	S	S	S	S	S
	PG64-22 + 10%TLA + 5% SBS	-	-	-	-	S	S	S	S	S
	PG64-22 + 20%TLA + 5%SBS	-	-	-	-	-	S	S	S	S
	PG64-22 + 10%TLA + 10%SBS	-	-	-	-	-	-	S	S	S
	PG64-22 + 20%TLA + 10%SBS	-	-	-	-	-	-	-	S	S
	PG64-22 + 10%TLA + 15%SBS	-	-	-	-	-	-	-	-	S
	PG64-22 + 20%TLA + 15%SBS	-	-	-	-	-	-	-	-	-

S—significant; N—non-significant.

. The analysis involved blends of PG 64-22 with TLA at 10% and 20%, and further modifications with SBS in varying proportions (5%, 10%, and 15%). The parameter G*sinδ is critical for assessing rutting resistance, while statistical analysis identifies significant performance improvements.

The baseline PG 64-22 binder exhibited a G*sinδ value of 3403 kPa, well below the Superpave limit of 5000 kPa, indicating moderate stiffness suitable for standard pavements. However, the addition of 10% TLA increased the G*sinδ value to 5692 kPa, and 20% TLA further increased it to 6551 kPa, significantly exceeding the permissible limit. These results demonstrate the stiffening effect of TLA, which improves rutting resistance but may lead to potential cracking due to reduced flexibility.

To address this, the inclusion of SBS modifiers effectively reduced the stiffness imparted by TLA. For instance, PG 64-22 + 10% TLA + 5% SBS achieved a G*sinδ value of 3865.12 kPa, within the acceptable range. Similarly, for 20% TLA, adding 5% SBS reduced G*sinδ to 5494.83 kPa, showing notable improvement but still slightly above the limit. Increasing the SBS content to 10% and 15% further optimized the performance, with values dropping to 3448.98 kPa and 4179.00 kPa for 10% and 20% TLA, respectively. The most significant results were observed at 15% SBS, where G*sinδ values fell drastically to 765.47 kPa and 1182.15 kPa for 10% and 20% TLA, respectively. These results indicate that SBS modification effectively balances stiffness and flexibility, enhancing binder performance.

The statistical analysis results further validate these findings. For the original condition, the baseline PG 64-22 showed significant differences (S) when compared with TLA and SBS-modified combinations, highlighting the influence of additives on binder properties. Notably, combinations involving 15% SBS consistently showed significant improvements (S) under both original and RTFO conditions, underscoring the effectiveness of SBS in mitigating the stiffness caused by TLA. The statistical analysis also showed significant differences across the majority of formulations, confirming that SBS-modified binders maintain their performance benefits even after long-term aging.

In summary, the addition of SBS modifiers to TLA-blended PG 64-22 binders significantly improves the balance between stiffness and flexibility, ensuring compliance with Superpave performance limits. The statistical analysis confirms the robustness of these improvements, particularly at higher SBS dosages. These findings emphasize the potential of SBS-modified binders for producing high-performance pavements capable of withstanding heavy traffic and environmental stress.

3.4. Results of MSCR Test on Original and RTFO-Aged Binders

The statistical analysis results from

Table 7. Statistical analysis of RTFO + PAV-aged, modified bituminous binders at 25 °C, evaluated over several combinations (α = 0.05).

PAV Condition at 25 °C
		RTFO + PAV
	Combination	PG64-22	PG64-22 + 10% TLA	PG64-22 + 20% TLA	PG64-22 + 10% TLA + 5% SBS	PG64-22 + 20% TLA + 5% SBS	PG64-22 + 10% TLA + 10% SBS	PG64-22 + 20% TLA + 10% SBS	PG64-22 + 10% TLA + 15% SBS	PG64-22 + 20% TLA + 15% SBS
25 °C	PG64-22	-	S	S	S	S	S	S	S	S
	PG64-22 + 10%TLA	-	-	S	S	S	S	S	S	S
	PG64-22 + 20%TLA	-	-	-	S	S	S	S	S	S
	PG64-22 + 10%TLA + 5% SBS	-	-	-	-	S	S	S	S	S
	PG64-22 + 20%TLA + 5%SBS	-	-	-	-	-	S	S	S	S
	PG64-22 + 10%TLA + 10%SBS	-	-	-	-	-	-	S	S	S
	PG64-22 + 20%TLA + 10%SBS	-	-	-	-	-	-	-	S	S
	PG64-22 + 10%TLA + 15%SBS	-	-	-	-	-	-	-	-	S
	PG64-22 + 20%TLA + 15%SBS	-	-	-	-	-	-	-	-	-

S—significant; N—non-significant.

, alongside the graphical data from Figure 5, give a thorough assessment of the impact of incorporating TLA and SBS into PG64-22 asphalt binders. These findings focus on % recovery and non-recoverable compliance J_nr, offering insight into the potential for high-performance asphalt binders in pavement engineering.

The control binder, PG64-22, shows a poor performance with low % recovery and high J_nr values. Statistical analysis confirms these results as significant (S) when compared to binders with TLA and SBS additions, particularly under RTFO conditions. Adding 10% or 20% TLA alone improves performance but remains statistically non-significant (N) in most comparisons under original conditions. However, under RTFO conditions, the performance differences become statistically significant, showing the contribution of TLA to binder stability after aging.

Among the tested combinations, 10% TLA with 15% SBS and 20% TLA with 15% SBS show an almost identical performance in % recovery and J_nr. Both combinations achieve a % recovery exceeding 80% in the original condition and 88% after RTFO aging, along with negligible J_nr values < 0.01 kPa⁻¹. This similarity indicates that 15% SBS is the optimal threshold for achieving high-performance properties, regardless of whether 10% or 20% TLA is used. Statistical analysis supports this observation, showing no significant differences (N) between these two combinations, reinforcing their equivalence in performance. These findings emphasize the critical role of SBS in achieving high-performance asphalt binders suitable for heavy traffic and extreme climatic conditions.

In conclusion, the integration of TLA and SBS into PG64-22 produces high-performance asphalt binders capable of meeting the demands of modern pavement engineering. The combination of 20% TLA and 15% SBS is recommended as the optimal formulation, balancing elasticity, rutting resistance, and long-term durability, paving the way for resilient and sustainable road infrastructure.

3.5. Rheological Characteristics Results (Low Temperature)

The performance of modified high-performance bituminous binders modified with TLA and SBS was evaluated based on their stiffness, m-value, and statistical analysis. These analyses are crucial for ensuring flexibility, durability, and thermal resistance, which are essential for flexible pavements.

The stiffness graph (Figure 6) indicates that the unmodified PG64-22 bituminous binder demonstrates a stiffness value of 188 MPa, representing superior flexibility, a critical factor for high-performance binders. The incorporation of TLA slightly reduces stiffness and an increase in TLA content further increases stiffness (180 MPa for 10% TLA and 254 MPa for 20% TLA), showing a marginal compromise in flexibility to enhance durability. The addition of SBS at 5% and 10% further increases stiffness, with combinations such as PG64-22 + 10% TLA + 5% SBS exhibiting 243 MPa. However, these levels still remain acceptable within performance limits for flexible pavements. Interestingly, stiffness decreases significantly at higher SBS levels (e.g., 56.4 MPa for PG64-22 + 10% TLA + 15% SBS), which enhances flexibility but may compromise rutting resistance. The statistical analysis in

Table 8. Results of statistical analysis of the stiffness (RTFO + PAV) of modified asphalt binders at −12 °C was conducted, considering various combinations, with a significance level of α = 0.05.

Stiffness at −12 °C
		RTFO + PAV
	Combination	PG64-22	PG64-22 + 10%TLA	PG64-22 + 20%TLA	PG64-22 + 10%TLA + 5% SBS	PG64-22 + 20%TLA + 5% SBS	PG64-22 + 10%TLA + 10% SBS	PG64-22 + 20%TLA + 10% SBS
RTFO + PAV	PG64-22	-	S	S	S	S	S	S
	PG64-22 + 10%TLA	-	-	S	S	S	S	S
	PG64-22 + 20%TLA	-	-	-	S	S	S	S
	PG64-22 + 10%TLA + 5% SBS	-	-	-	-	S	S	S
	PG64-22 + 20%TLA + 5% SBS	-	-	-	-	-	S	S
	PG64-22 + 10%TLA + 10% SBS	-	-	-	-	-	-	S
	PG64-22 + 20%TLA + 10% SBS	-	-	-	-	-	-	-

S—significant; N—non-significant.

supports these findings, where combinations of TLA and SBS at −12 °C show significant differences (“S”) for stiffness at moderate additive levels, while higher SBS contents result in some non-significant (“N”) outcomes due to potential phase separation.

The m-value graph complements these observations by assessing the relaxation potential of the binders (Figure 7). The unmodified PG64-22 binder displays the highest m-value (0.35), indicating superior flexibility and stress relaxation capacity. However, adding TLA reduces the m-value slightly (e.g., 0.276 for 10% TLA and 0.295 for 20% TLA), reflecting the trade-off between increased stiffness and reduced relaxation potential. The addition of SBS further decreases the m-value, particularly at higher concentrations. For instance, PG64-22 + 10% TLA + 10% SBS has an m-value of 0.234, suggesting limited thermal relaxation.

Table 9. Results of statistical analysis of the m-value (RTFO + PAV) of modified bituminous binders at −12 °C as a function of various combination (α = 0.05).

m-Value at −12 °C
		RTFO + PAV
	Combination	PG64-22	PG64-22 + 10%TLA	PG64-22 + 20%TLA	PG64-22 + 10%TLA + 5% SBS	PG64-22 + 20%TLA + 5% SBS	PG64-22 + 10%TLA + 10% SBS	PG64-22 + 20%TLA + 10% SBS
RTFO + PAV	PG64-22	-	S	S	S	S	S	S
	PG64-22 + 10%TLA	-	-	S	N	S	S	S
	PG64-22 + 20%TLA	-	-	-	S	S	S	S
	PG64-22 + 10%TLA + 5% SBS	-	-	-	-	N	S	N
	PG64-22 + 20%TLA + 5% SBS	-	-	-	-	-	S	N
	PG64-22 + 10%TLA + 10% SBS	-	-	-	-	-	-	S
	PG64-22 + 20%TLA + 10% SBS	-	-	-	-	-	-	-

S—significant; N—non-significant.

confirms these trends statistically, showing significant results (“S”) for m-value reductions at moderate additive levels, while a higher SBS content leads to non-significant (“N”) results, indicating diminished performance at extreme modification levels.

The statistical analysis validates the experimental findings, emphasizing the importance of balancing stiffness and m-value for high-performance binders. Lower stiffness values and higher m-values are preferred for flexible pavements, as they ensure better flexibility and resistance to cracking. The results suggest that TLA and moderate SBS levels (5–10%) strike an optimal balance, providing enhanced durability without compromising flexibility. Excessive SBS content (15%) may improve flexibility but can introduce inconsistencies due to compatibility issues.

In conclusion, the combination of TLA and SBS modifiers offers a promising approach to developing high-performance asphalt binders. The statistical analyses and performance data confirm the effectiveness of these modifications in achieving the desired balance between flexibility and load resistance. These findings support the use of optimized TLA and SBS combinations for sustainable and durable flexible pavements, advancing pavement engineering practices to meet modern traffic and environmental demands.

4. Conclusions

This study on high-performance asphalt binders modified with Trinidad Lake Asphalt (TLA) and styrene–butadiene–styrene (SBS) polymers demonstrates the potential to achieve a robust balance between workability, flexibility, and durability. Comprehensive evaluations of physical, rheological, and mechanical properties underline the effectiveness of these modifications in enhancing the performance of TLA-modified binders for modern pavement engineering.

• The incorporation of TLA and SBS has a notable impact on binder viscosity. Moderate amounts of TLA (10–20%) combined with SBS (up to 5%) maintain satisfactory workability. However, a higher SBS content raises viscosity, reducing workability and necessitating increased mixing and compaction temperatures to address this issue.
• The DSR test results reveal substantial enhancements in rutting resistance with the addition of SBS, particularly at higher dosages. The optimal combination of 20% TLA and 15% SBS provides exceptional resistance to permanent deformation, making it a prime candidate for pavements subjected to high temperatures and heavy traffic loads.
• TLA increases stiffness and rutting resistance, but excessive rigidity is mitigated effectively by incorporating SBS. Moderate SBS levels restore flexibility while maintaining compliance with Superpave performance criteria, emphasizing the role of SBS in balancing stiffness and flexibility.
• The % recovery and non-recoverable compliance (J_nr) data indicate that binders with 15% SBS exhibit superior elastic recovery and minimal deformation under loading, even after RTFO aging. This confirms the suitability of these formulations for high-performance applications in heavy traffic and extreme climatic conditions.
• While an SBS above 7.5% is typically considered highly modified, this study investigated higher dosages (10–15%) due to the 20% TLA substitution limit. The results confirm that increasing SBS enhances elasticity and rutting resistance, with 15% SBS achieving >88% recovery and J_nr < 0.01 kPa⁻¹. However, increased viscosity at higher SBS contents necessitates careful consideration of workability.
• The combination of 20% TLA with 10% SBS emerges as the optimal formulation, providing a balance between performance and practical usability for high-traffic, extreme climate pavements.

Overall, the findings validate the use of TLA and SBS-modified binders as a sustainable solution for constructing durable and long-lasting flexible pavements. The combination of 20% TLA with 10% SBS emerges as the optimal formulation, balancing workability, durability, and high-temperature performance without compromising low-temperature flexibility. These results provide valuable insights for the design of high-performance asphalt binders, advancing the state of pavement engineering to address modern traffic and environmental challenges effectively. Further field studies are recommended to validate these results in real-world applications, ensuring the practical feasibility and reliability of these advanced binder formulations.