Incorporation of postconsumer recycled (PCR) plastics in asphalt mixes is reported to improve the mechanical performance of asphalt mixes when used at a lower dosage. However, overstiffening of asphalt mixes due to the addition of higher amounts of plastic has been a serious concern. To this end, this study aims at increasing the percentage of plastic in asphalt mixes by incorporating a biorejuvenator. For this purpose, a control mix was designed using the balanced mix design (BMD) approach and then modified with two different types of PCR plastics, namely low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). The asphalt mixes were then further modified by adding a biorejuvenator. The volumetric properties were determined, and the mechanical performances (rutting, cracking, and moisture-induced damage resistance) of the asphalt mixes were evaluated using the Hamburg Wheel Tracking (HWT) and Indirect Asphalt Tensile Cracking Test (IDEAL-CT). The optimum dosage of plastics was determined using the BMD criteria. The optimum dose of LDPE was found to be 1.5% with 2% waste cooking oil (WCO)-modified binder. In addition, environmental impact analyses were performed on the plastic-modified mixes. A significant reduction in greenhouse gas emission was observed from the use of plastic in asphalt mixes. A minimum of 7.5% reduction in greenhouse gas generation was found by using optimum LDPE and WCO-modified asphalt mixes.

This study investigates the synergistic effects of combining polyphosphoric acid (PPA) and styrene–butadiene–styrene (SBS) as modifiers in asphalt binders to enhance their performance. The research focuses on optimizing the concentrations of PPA and SBS to improve the resistance to permanent deformation, cracking at intermediate and low temperatures, and resistance to aging. A series of empirical and rheological tests, including penetration, softening point, elastic recovery, dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), and bending beam rheometer (BBR), were conducted to evaluate the rheological and engineering properties of the modified binders. The results indicate that PPA can partially replace SBS, offering comparable improvements in high-temperature performance and creep resistance. The MSCR test revealed a statistically significant synergistic effect between PPA and SBS, resulting in improved recovery and reduced non-recoverable compliance. However, PPA alone shows limited effectiveness at low temperatures and in properties that are governed by elastic response. This study highlights the potential for optimizing asphalt modifiers by leveraging the complementary properties of PPA and SBS in hybrid systems, particularly regarding high-temperature properties and dynamic loading.

.

Influence of rice husk ash source variability on asphalt modification: Rheological and molecular insights

Performance enhancement of SBS modified asphalt using polyurethane precursor-based reactive modifiers

A novel DOA-pretreated Sasobit strategy for asphalt modification: Synergistic mechanism and molecular characterization

Thermoplastic polyurethanes (TPUs) synthesized from different monomers possess diverse chemical structures, leading to variations in asphalt modification performance and an incomplete understanding of the underlying mechanisms. To elucidate the effect of TPU chemical structure on asphalt modification, eight molecular models of asphalt modified by TPU with different chemical structures were constructed, and their mechanical behavior, microstructure, intermolecular interactions, compatibility, and interfacial interaction were systematically investigated by Molecular Dynamic Simulation. The results reveal that the soft segment type is the predominant factor governing the mechanical and interfacial interaction. Asphalt modified with PET-based TPU exhibited higher stiffness, with Young's modulus and shear modulus increasing by 65.04% and 67.44%, respectively, compared with those of PTMEG-based TPU. Moreover, PET-based TPU significantly strengthened the asphalt-aggregate interface, increasing interaction energy by 21.2% relative to PTMEG-based TPU. The maximum interfacial energy of 4165 kcal/mol was obtained for I-PE-M, which was 46% higher than the weakest system. Nevertheless, polyester-based TPUs showed slightly lower compatibility with the asphalt matrix than polyether-based counterparts, indicating a potential trade-off between interfacial enhancement and phase compatibility. These findings elucidate the fundamental colloidal and interfacial mechanisms governing polymer-asphalt systems, providing design principles for optimizing interfacial performance through segmental polarity engineering.

The performance of recycled hot-mix asphalt mixtures (RHAM) is strongly governed by the extent and uniformity of interactions between the aged binder in reclaimed asphalt pavement (RAP) and the virgin binder. However, in current engineering practice, it remains difficult to accurately evaluate the blending degree of aged and virgin asphalt during RHAM production, where the blending degree refers to the extent and uniformity of binder interaction during hot mixing. Moreover, influenced by various construction-related factors, the uniformity of interfacial diffusion between the two asphalt layers is also hard to control, which compromises the durability of RHAM. To address these issues, fluorescence microscopy was used to quantitatively characterize the blending behavior of aged and virgin asphalt, and Fourier transform infrared spectroscopy (FTIR) was employed to investigate the interfacial diffusion process and its evolution under time-temperature coupling conditions from plant production to field paving. The results indicate that, owing to the fluorescent characteristics of the Styrene-butadiene-styrene block copolymer (SBS) modifier in polymer-modified asphalt, the blending behavior during hot mixing can be quantitatively characterized by the fluorescent area and its areal proportion, providing a rapid solution for quantitative evaluation during RHAM production. Increasing the preheating temperature of RAP, extending mixing time, raising mixing temperature, and adopting Mixing Sequence I reduced the proportion of fluorescent area, suggesting improved blending between aged and virgin asphalt. After blending, the interfacial diffusion between aged and virgin asphalt occurs within the RHAM; the uniformity of this diffusion becomes more pronounced as the elapsed duration from production to paving increases. Nevertheless, excessively long duration may induce secondary aging of the blended binder. Accordingly, the duration is recommended to be controlled at approximately 90 min and should not exceed 180 min. By elucidating the blending and diffusion behaviors of aged and virgin asphalt, this study provides practical guidance for contractors in controlling production-process parameters for RHAM.

The use of resource-saving technology in road construction material production is a current problem, the solution of which will allow us to increase the environmental and economic efficiency of the road construction industry. Nowadays, secondary raw materials are widely used in highway construction, obtained both from the waste of old road construction materials and collected from other industries. During asphalt production, up to 90% of raw materials can be replaced by reclaimed asphalt pavement (RAP). This technology requires residual binder modification to reduce the negative impact on the technological and operational asphalt concrete properties. On the other hand, the use of rubber crumbs or granules obtained from the disposal of old car tires in asphalt–concrete mixtures is widespread. However, some types of car tires cannot be used as raw materials to produce an effective modifier. Truck tires and tires from special vehicles are suitable for use as a modifier for asphalt–concrete mixtures. Tires designed for passenger cars do not contain enough polymer. As an experiment on asphalt–concrete mixture production using secondary resources only, a testing facility was developed. The testing facility uses hot gas obtained by burning automobile tires in a special oven as a heat source. Rubber residues from the recycling of automobile tires are used as fuel, which cannot be used to produce rubber powder or granules. RAP obtained by cold milling of the pavements of city and public roads was used as the object of the research. When studying the characteristics of the asphalt–concrete-mixture-based binder, it was found that the sulfur compounds present in the composition of hot gases change the properties of the binder, leading to a serious deterioration in the technological characteristics of asphalt–concrete mixtures. The asphalt–concrete mixture obtained during RAP processing is characterized by a narrow temperature range in which it can be laid and compacted to the required density values. After laying the pavement, quality control revealed a significant variation (the number of air voids ranged from 0.8 to 5.5%) in the average density of samples taken from the compacted layer. In addition, there were significant violations of the longitudinal evenness of the finished coating. Experiments were carried out to extract the binder from asphalt–concrete mixtures before and after regeneration. The physico-mechanical and rheological characteristics were studied and qualitative analysis of the binder was realized by IR spectroscopy. The data obtained allow us to establish the mechanism of how sulfur-containing gases influence the bitumen binder’s properties in asphalt mixtures. Additionally, the features of thermo-oxidative degradation occurring during the hot recycling of asphalt–concrete mixtures were established. A justification is also given for the need to use anti-aging modifiers to restore the properties of the residual binder.

To enhance the thermo-oxidative aging resistance of asphalt while maintaining its excellent high- and low-temperature performance, polyurethane (PU) and graphene oxide (GO) were used for asphalt modification. The physical, rheological, and anti-aging properties of PU/GO composite modified asphalt were investigated, while the Fourier-transform infrared spectroscopy test and the molecular simulation were employed to explore the modification mechanism of PU and GO. Results show that PU and GO alter the viscoelastic fraction of asphalt, which provides it with excellent high-temperature stability and low-temperature performance. Moreover, PU can reduce the intermolecular gaps and strengthen van der Waals interactions within asphalt, which decreases its free volume and increases its cohesive energy. The addition of GO can promote the aggregation of asphaltenes, enhancing the stability of asphalt. The synergistic modification mechanism of PU and GO decreases the free volume and molecular gaps in asphalt, while suppressing oxygen diffusion and the formation of carbonyl and sulfoxide groups during thermo-oxidative aging. This synergistic effect improves the thermo-oxidative aging resistance of asphalt. These findings provide new insights and a promising strategy for developing durable asphalt through experimental and theoretical approaches.

Pavement surface deformations are related to design deficits, or problems of stability of the materials pavement. To have a sustainable material that ensures a long enough life for the pavement, several research have been developed. This work focuses on the effect of crumb rubber on the static creep behavior of asphalt mixtures, aiming to improve their mechanical performances and rutting resistance on the one hand, and to contribute to environmental sustainability on the other. Crumb rubber was incorporated into asphalt mixtures at varying percentages (0.25%, 0.5%, and 0.75%) using a dry process. Samples of asphalt mixture compacted with gyratory compactor and Marshall Method were tested at two temperature levels, (20°C and 60°). The modification of asphalt, temperature and mode of compaction are parameters that influence creep properties and rutting resistance. During the static creep test, total deformation (εTot), initial deformation (εIn), permanent deformation (εPer), creep stiffness and Creep compliance were recorded. Results showed that the presence of crumb rubber at low content in asphalt mixture improve their performances, while at high content of crumb rubber, a decrease in the performance of the asphalt mixtures was observed. Also, the properties of static creep recorded during the creep test are better for the specimens compacted with Gyratory compactor comparing with those compacted with Marshall Method. Aiming to predict creep stiffness and creep compliance as a function of crumb rubber content and Axial micro deformation, a model was developed using adaptive neuro-fuzzy inference system (ANFIS) approach. The results demonstrate that the developed ANFIS models provide accurate predictions with strong agreement with experimental results.

Thermosetting polyurethane (PU) has recently been introduced as an asphalt modifier to improve the mechanical strength and durability of pavements. However, the permanent crosslinked network of thermosetting PU makes the material difficult to repair once damage accumulates. In contrast, self-healing asphalt technologies rely on either extrinsic healing agents or intrinsic dynamic bonds to restore stiffness and delay cracking. Dynamic disulfide bonds are a promising class of reversible covalent bonds that can rearrange at moderate temperatures and have been widely used to build self-healing polyurethane networks. This study investigates a disulfide-crosslinked polyurethane-modified asphalt binder (DP10) and compares its fatigue and healing performance with base asphalt (BA), thermosetting PU-modified asphalt (P10), and styrene-butadiene-styrene (SBS)-modified asphalts (S3 and S10). A dynamic shear rheometer (DSR) was used to conduct time sweep fatigue tests, linear amplitude sweep (LAS) tests, and fatigue-healing-fatigue protocols. Fourier transform infrared spectroscopy (FTIR) was employed to confirm the formation of polyurethane and disulfide structures. Results show that DP10 significantly increases fatigue life at small to medium strain levels compared with BA and P10 and performs competitively with SBS-modified binders. More importantly, DP10 exhibits a much higher healing index than P10 and maintains strong healing capability over repeated fatigue-healing cycles, approaching the intrinsic healing level of base asphalt. These findings demonstrate that incorporating dynamic disulfide bonds into thermosetting PU networks provides a practical route to binders that combine high strength with recoverability, which is attractive for long-life, self-healing pavement design.

This study investigates the synergistic and fineness-dependent modification of base asphalt using rice husk biochar (RHB) and styrene-butadiene-styrene (SBS), aiming to achieve the efficient utilization of agro-waste resources while markedly improving the high-temperature performance and durability of green pavement materials and sustainable transportation infrastructure. Through conventional performance tests, rheological measurements, and microstructural analyses, the performance behavior of RHB-SBS composite-modified asphalt and the interaction mechanisms between the modifiers were systematically examined. The results indicate that the fineness of RHB has a significant effect on the performance of the composite-modified asphalt, with 300 mesh identified as the optimal particle size that provides the best balance between high-temperature stiffness, low-temperature ductility, and storage stability. When the RHB fineness is fixed at 300 mesh, increasing the RHB content from 0 to 16 wt% markedly enhances the high-temperature performance of the composite asphalt, while its low-temperature performance slightly decreases. Scanning electron microscopy (SEM) analysis reveals that the porous structure and large specific surface area of RHB enable it to form a stable spatial network within the asphalt matrix, thereby improving high-temperature stability. Fourier-transform infrared spectroscopy (FTIR) results show that the incorporation of RHB alters the chemical structure of the asphalt and increases the degree of crosslinking, while thermogravimetry-differential scanning calorimetry (TG-DSC) analysis further confirms that the thermal stability of the composite-modified asphalt is significantly enhanced.

ABSTRACT To address the dual challenges of waste polyethylene (WPE) recycling and the demand for road asphalt modifiers, asphalt was modified by constructing covalent crosslinking networks within the WPE, thereby enhancing its high‐temperature performance. A covalently crosslinked polyethylene waste plastic (CP) was synthesized via chemical modification of WPE. The structural characteristics and mechanical performance of CP were characterized by Fourier Transform Infrared spectroscopy (FTIR), proton nuclear magnetic resonance, gel content determination, and tensile test. The interaction mechanism between CP and asphalt components was analyzed by using fluorescence microscopy and FTIR. The basic performances of modified asphalt were evaluated based on the penetration, ductility, softening point, and Brinell rotational viscosity tests. The high‐temperature rheological performance was evaluated through a dynamic shear rheometer and multiple stress creep recovery. Results showed that the CP demonstrated superior mechanical properties relative to pristine WPE. The high‐temperature rheological performance of CP‐modified asphalt was significantly improved, peaking at a 5 wt% CP dosage. This improvement was attributed to the formation of a covalent cross‐linked network, in which ester bonds served as the covalent cross‐linking sites. This strategy achieves a synergistic improvement in asphalt performance and plastic reutilization, contributing to sustainable and low‐carbon goals.

ABSTRACT Waste tire rubber powder has become a widely used and sustainable replacement for asphalt modification. The traditional waste tire rubber‐modified asphalt exhibits poor low‐temperature performance, leading to frequent cracking in regions with lower temperatures. To effectively reutilize waste rubber tires and enhance the crack resistance of asphalt pavement, this study utilized styrene‐butadiene‐styrene (SBS) and waste tire rubber powder treated with activated desulfurization to prepare anti‐cracking composite modified asphalt (ACA). ACA was synthesized using the response surface method (RSM). Subsequently, the basic properties and anti‐aging performance were tested and compared, showing that ACA demonstrates superior high‐ and low‐temperature performance and aging resistance. Rheological tests confirmed ACA's outstanding high‐temperature rutting resistance and low‐temperature crack resistance. Notably, ACA exhibited a self‐healing capacity 3.9 times greater than SBS‐modified asphalt, showcasing superior fatigue resistance. Moreover, characterization of ACA's microstructure and morphology revealed that the rubber powder showed good compatibility with asphalt, SBS, and flexibilizer, forming a stable cross‐linked network within ACA. This structural feature is a key factor contributing to ACA's superior overall performance and crack resistance. Finally, pavement performance tests validated ACA's performance in asphalt mixtures, demonstrating a novel approach utilizing SBS and rubber powder to enhance asphalt's anti‐crack performance while recycling waste rubber tires.

Owing to climatic and environmental conditions, conventional asphalt pavements often fail to demonstrate the expected performance, resulting in surface deteriorations. Asphalt binders are modified using various additives to mitigate these deteriorations and enhance pavement performance. The excessive consumption of polymers as modifiers has recently raised environmental concerns, increasing interest in bio-based alternatives. In this study, a novel bio-based asphalt modifier, the boron-added resin compound (BARC), derived from resin and boron oxide, was utilized under laboratory conditions to enhance asphalt performance. Rheological tests, including dynamic shear rheometer (DSR), multi-stress creep recovery (MSCR), linear amplitude sweep (LAS), and bending beam rheometer (BBR) tests, were conducted on both unmodified and BARC-modified asphalt binders. The findings indicated that BARC significantly improved asphalt's resistance to rutting at high temperatures, extended fatigue life, and expanded its application range according to traffic loads, with optimal performance observed at 1% BARC content. Specifically, the fatigue life of the 1% BARC-modified binder increased by 11.13 times at a 5% strain level compared to the unmodified binder, exhibiting more elastic behavior and suitability for extremely heavy traffic conditions. Consequently, the novel bio-based additive, characterized by a short production process and low cost, is considered a promising alternative modifier for asphalt pavements.

Lignin, an abundant and renewable biopolymer, holds significant potential for asphalt modification owing to its unique aromatic structure and reactive functional groups. This review summarizes the main lignin preparation routes and key physicochemical attributes and assesses its applicability for enhancing asphalt performance. The physical incorporation of lignin strengthens the asphalt matrix, improving its viscoelastic properties and resistance to oxidative degradation. These enhancements are mainly attributed to the cross-linking effect of lignin’s polymer chains and the antioxidant capacity of its phenolic hydroxyl groups, which act as free-radical scavengers. At the mixture level, lignin-modified asphalt (LMA) exhibits improved aggregate bonding, leading to enhanced dynamic stability, fatigue resistance, and moisture resilience. Nevertheless, excessive lignin content can have a negative impact on low-temperature ductility and fatigue resistance at intermediate temperatures. This necessitates careful dosage optimization or composite modification with softeners or flexible fibers. Mechanistically, lignin disperses within the asphalt, where its polar groups adsorb onto lighter components to boost high-temperature performance, while its strong interaction with asphaltenes alleviates water-induced damage. Furthermore, life cycle assessment (LCA) studies indicate that lignin integration can substantially reduce or even offset greenhouse gas emissions through bio-based carbon storage. However, the magnitude of the benefit is highly sensitive to lignin production routes, allocation rules, and recycling scenarios. Although the laboratory research results are encouraging, there is a lack of large-scale road tests on LMA. There is also a lack of systematic research on the specific mechanism of how it interacts with asphalt components and changes the asphalt structure at the molecular level. In the future, long-term service-road engineering tests can be designed and implemented to verify the comprehensive performance of LMA under different climates and traffic grades. By using molecular dynamics simulation technology, a complex molecular model containing the four major components of asphalt and lignin can be constructed to study their interaction mechanism at the microscopic level.

Improving both the high- and low-temperature performance of asphalt is still difficult in modern pavement applications. This performance imbalance has motivated the development of new modification strategies that can enhance temperature stability while maintaining construction workability. In this research, a low-molecular-weight elastic polyolefin (POL) with inherent compatibility was introduced as a novel asphalt modifier. POL was incorporated at five dosages (0%, 2%, 4%, 6%, and 8% by weight of asphalt) to investigate its effects on the fundamental physical, rheological, and low-temperature properties of the asphalt. The rheological behavior was characterized by dynamic shear rheometer (DSR) and bending beam rheometer (BBR), while the modification mechanism and dispersion morphology were analyzed through Fourier-transform infrared spectroscopy (FT-IR) and fluorescence microscopy (FM). The results reveal that POL markedly improves the high-temperature performance and workability of asphalt, with the rutting factor increasing by two- to eightfold. POL modification improved the thermal stability of asphalt, shifting the maximum decomposition temperature from 455.2 °C for the base binder to 461-463 °C, while the total mass loss remained nearly constant at 80-83%. Microscopic observations confirm that POL forms a physically blended network within the asphalt matrix, exhibiting a green fluorescent structure that becomes progressively continuous with increasing dosage. The most homogeneous dispersion and optimal compatibility occur at a POL dosage of 6%, beyond which phase segregation emerges and low-temperature properties deteriorate. Accordingly, a 6% POL dosage is recommended for achieving balanced performance. These findings provide theoretical and practical guidance for the development of balanced performance and thermally stable POL-modified asphalt materials.

Functionalized recycling of waste polypropylene into low-carbon asphalt modifier towards circularity: From mechanochemical preparation to structural and performance evaluations

Recycling waste rubber is essential for promoting circular economy practices, reducing environmental pollution, and conserving resources. This study examines the performance of crumb rubber-modified asphalt mixtures incorporating two light oils (aromatic oil and tall oil) to alleviate the high viscosity and poor workability of asphalt with high rubber content. Mixtures were prepared using a neat asphalt modified with 20% crumb rubber and 5% light oil (by mass of the neat asphalt), combined with basalt aggregate in an AC-13 gradation. High-temperature performance was evaluated via Marshall stability and wheel tracking tests at 60 °C, moisture sensitivity through immersion Marshall and freeze-thaw splitting tests, and low-temperature cracking resistance using semi-circular bending (SCB) tests at 15 °C. Tensile strength and fatigue life were measured by splitting tests at 25 °C and fatigue tests at 15 °C, respectively. Results indicate that the rubber-modified mixtures showed significant improvements: the total deformation decreased by 44.7% and 64.1% for aromatic oil- and tall oil-modified mixtures, respectively, compared to the neat asphalt. Fracture toughness increased by 46.5% and 71.9%, and tensile strength improved by 40.2% and 63.6%, respectively. At a low stress ratio (0.281), mixtures with tall oil exhibited a 47.9% longer fatigue life than those with aromatic oil. Tall oil demonstrated superior performance, attributed to enhanced rubber swelling and crosslinked network formation, which improved viscosity and aggregate coating. The findings confirm that light oil-modified rubber asphalt mixtures, especially those containing tall oil, present a viable approach for developing high-performance and environmentally sustainable road pavements.