Upcycling waste tires and recycled polyethylene (rPE) into asphalt offers a sustainable solution. However, poor compatibility between crumb rubber (CR), rPE and asphalt limits practical application. Accordingly, the size characteristics of modifiers is critical to polymer-asphalt interaction and the resulting rheological behavior, yet remains insufficiently understood in rubber-polyethylene elastomers. In this study, CR and rPE were extruded and cryogenically pulverized to obtain the thermo-mechanical rubber-polyethylene elastomers (TRPE) and micronized elastomers (mRPE). The microphase interaction, phase separation, and rheological behavior of modified asphalt were evaluated. The results indicate that TRPE already establishes a relatively well-dispersed polymeric phase in asphalt, while further micronization improves microstructural uniformity and reduces the softening point difference to 0.8 degrees C. Rheological analysis reveals a progressive enhancement in polymer-asphalt interaction of TRPE modified asphalt (TRPEA) and mRPE modified asphalt (mRPEA), as evidenced by a reduction in rheological interaction index (h value) from 0.87 to 0.14. The results show that the Cole-Cole plots are insufficient to distinguish the compatibility of TRPEA and mRPEA under the specific test conditions. Due to the dissolution of large elastic particles, TRPEA and mRPEA exhibit a pronounced shift toward viscous behavior. Moreover, mRPEA shows improved deformation resistance at high temperature and highest fatigue life with 5.66 & times; 106 at 2.5% strain. Overall, this work provides valuable insights in optimizing waste-derived modifiers for sustainable pavement materials.

Fume released from asphalt pavement threaten workers' health and the atmosphere environment. While many studies have focused on its composition analysis, influencing factors and suppression methods, the origins of different fume compositions remain unclear. In this study, 70# base asphalt was separated into four fractions including saturate, aromatic, resin and asphaltene (SARA). Their volatile species at 150 degrees C were analyzed through SPME-GC x GC-MS, meanwhile TG, GPC and SEM were adopted to investigate their thermal losses, molecule weight distributions and micro-morphology. Results show that aromatic released for nearly 80 % of polycyclic aromatic hydrocarbons (PAHs), single-ring benzenes, and sulfur-containing volatiles, while saturate contribute 84.7 % of alkanes. Except for pyrene, aromatic generated 66.8-99.4 % of single-ring benzenes and 2-4 ring PAHs. To elucidate molecular reaction pathways, reactive molecular dynamics (ReaxFF-MD) simulations of fume generation were performed. MD results indicated that aromatic mainly yielded 2-4 ring PAHs and saturate produced alkanes, and resin generated partial PAHs and heteroatom compounds, while asphaltene decomposed into less-volatile macromolecules with minor small molecules. These findings clarify the specific sources of asphalt fume species and provide insights for understanding fume molecules generation mechanism.

The value-added recycling of waste plastics as modifiers in asphalt could efficiently dispose of the solid waste and achieve economic modification. However, there remains a research gap in the comparison of the modification effect of various recycled plastics on asphalt. Therefore, this study illustrated the potential application of seven different recycled plastics (RPs) pellets in improving asphalt performance. The chemical structure and rheological performance of recycled plastics modified asphalt (RPMA) were investigated through the Fourier transform infrared (FTIR) test, gel permeation chromatography (GPC) test, X-ray diffraction (XRD) test and dynamic rheological test. The results showed that the recycled polyvinyl chloride, recycled ethylene-vinyl acetate, recycled polystyrene and recycled acrylonitrile butadiene styrene introduced new functional groups in RPMA, derived initially from the plastics. However, the modification of RPMA is mainly the physical process. Due to the macromolecular from RPs, it showed a significant increase in large molecules of RPMA. The crystalline structure of the binders was observably enhanced by recycled polyethylene, leading to the restriction of molecular chain movement and improvement in deformation resistance. As indicated, the incorporation of RPs increased the elastic component and stiffness, which significantly improved the deformation resistance, especially in recycled polyethylene. This study would support the selection of plastic recycling and promote the application of RPs in asphalt modifiers for sustainable materials in road infrastructure.

Polymers are widely used to enhance asphalt pavement performance and extend service life. Polyurethane (PU) has attracted increasing attention due to its flexible formulation and adjustable properties. However, the quantitative relationship between the chemical architecture of PU and the performance of the modified binder remains to be fully elucidated. This study systematically investigates the effects of hard-segment content and isocyanate index on the structural evolution, thermal stability, and mechanical properties of PU. Based on spectroscopic, thermal, and morphological analyses, a formulation with 20% hard-segment content and an isocyanate index of 1.0 was identified as the optimal modifier, achieving a balance between strength, flexibility, and thermal stability. Subsequently, polyurethane-modified asphalt (PUMA) binders with varying dosages were prepared and evaluated. A critical phase transition was observed when the PU content exceeded 30 wt%, where the dispersed PU domains evolved into a continuous crosslinked network within the asphalt matrix. Compared to conventional SBS-modified asphalt, the optimized PUMA exhibits significantly superior performance: the elastic recovery rate is improved by over 60%, and the non-recoverable creep compliance exhibits extremely small nonrecoverable strain accumulation under repeated loading, indicating exceptional rutting resistance. Simultaneously, the low-temperature stiffness modulus decreases by over 90%, significantly enhancing cracking resistance. These findings provide theoretical guidance for the molecular design of high-performance PUMA and support its broader application in sustainable pavement engineering.

A common challenge in asphalt is low-temperature hardening due to wax crystallization, causing cracking and elevated internal stress-induced fractures. The asphalt binder modification with crumb rubber (CR) has been extensively studied to improve asphalt pavement performance and sustainability. However, conflicting findings have been reported regarding the impact of CR on the ductility of asphalt binder, specifically at low temperatures. This study investigates the low-temperature performance of rubberized asphalt modified with CR treated using the KH-151 coupling agent. Conventional, untreated CR modified, and KH-151-treated CR modified asphalt samples were evaluated through force ductility tests at 5 ℃ and bending beam rheometer (BBR) tests. The asphalt binders were modified using 25% CR by weight of asphalt, with CR treated at KH-151 concentrations ranging from 1% to 2%. KH-151 treatment improved compatibility, reducing the softening point difference from 12.7 ℃ for untreated to 1.8 ℃ for 1.6% KH-151-treated CR modified asphalt, ensuring even CR particle distribution in asphalt. The viscosity reduced from 5.1 Pa⋅s for untreated CR modified asphalt to 2.6 Pa⋅s for 1.6% KH-151-treated CR modified asphalt, improving workability. Force ductility tests at 5 ℃ showed superior flexibility for 1.6% KH-151-treated CR modified asphalt, with elongation reaching 17.2 cm before aging and 12.2 cm after short-term aging. BBR tests at -24 ℃ showed creep stiffness reduced from 298 MPa for untreated CR modified asphalt to 221 MPa for 1.6% KH-151-treated CR modified asphalt, and m-values increased from 0.238 to 0.305. Correlation analysis confirmed strong relationships between BBR m-values and force ductility parameters (R2 > 0.8).

Despite significant research on diatomite and red mud as individual asphalt modifiers, a comprehensive review evaluating their synergistic potential as multifunctional fillers for sustainable pavements, integrating technical performance, waste valorisation, and circular economy principles, remains lacking. This gap hinders a full understanding of how these materials can optimize pavement performance and promote sustainability. Therefore, this review examines the physicochemical properties, preparation methods, and environmental benefits of diatomite and red mud in alignment with the United Nations Sustainable Development Goals (SDGs). Diatomite enhances pavement durability and aids in removing over 90 % of suspended solids from stormwater, supporting SDGs 6 (Clean Water and Sanitation) and 11 (Sustainable Cities and Communities). Red mud, a by-product of bauxite processing, improves rheological properties by reducing non-recoverable creep compliance by up to 70 %, contributing to SDG 9 (Industry, Innovation, and Infrastructure), though its high alkalinity requires leaching management. Life-cycle assessments show 5–15 % reductions in CO2 emissions and lower reliance on virgin materials, advancing SDG 12 (Responsible Consumption and Production). Trade-offs include diatomite-induced low-temperature brittleness and red mud's reduced moisture resistance. Based on these insights, this review identifies future research priorities in hybrid filler design, long-term validation, and contaminant mitigation, proposing a circular economy framework for cleaner, eco-efficient road infrastructure.

The utilization of waste materials such as high-content crumb rubber (CR), waste cooking oil (WCO), and low-density polyethylene (LDPE) in asphalt binder significantly reduces environmental waste while providing sustainable environmental and economic advantages for asphalt pavement applications. This paper aims to evaluate the effect of WCO-pretreated CR on the properties of LDPE-modified high-content crumb rubber asphalt binder (HCRMAB) to establish a linear correlation between chemical composition and storage stability. The viscosity tests demonstrated significant reductions in binder viscosity when incorporating 20% pretreated high-content crumb rubber (PHCR) compared to 20% untreated high-content crumb rubber (UHCR). The viscosity decreased by 56.77% at 135 °C, with substantial reductions of 41.73%, 30.84%, 44.12%, and 53.79% observed at 150 °C, 165 °C, 180 °C, and 195 °C, respectively. Storage stability tests indicated that 20% PHCR-modified asphalt binder showed a 93.83% lower softening point variation than 20% UHCR-modified asphalt binder. These results indicate that waste oil pretreatment significantly improves the workability and storage stability of pretreated high-content crumb rubber asphalt binder (PHCRMAB). Moreover, the addition of LDPE to PHCR-modified asphalts binder, particularly the addition of 20% PHCR+4% LDPE+0.60% sulfur, showed enhanced storage stability. Fourier transform infrared spectroscopy (FTIR) confirmed chemical interactions during modification, with a strong correlation (R2 = 0.96) between storage stability and chemical properties. Results from dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests revealed LDPE improved high-temperature properties but reduced low-temperature cracking resistance. These findings promote the practical application of pretreated high-content crumb rubber-modified asphalt (PHCRMA) in sustainable pavement construction.

The incorporation of waste tires into asphalt mixes for pavement construction offers a sustainable solution to both resource conservation and environmental pollution mitigation. Used tires yield crumb rubber (CR), which we can blend with asphalt binder through a wet process to enhance the rheological properties of asphalt by acting as a polymer modifier. This study aims to comprehensively review the existing literature, exploring the interrelationship between the preparation process, interaction mechanisms, and compatibility between CR and asphalt and the subsequent performance of asphalt treated using CR (CRMA). The characteristics of CR, such as its composition and microstructure, and the mixing conditions of asphalt, such as shear speed, time, and temperature, significantly influence the service performance of CRMA. Various pretreatment technologies, such as gamma irradiation, microwave, and different types of chemical additives, can alter the chemical bonding and microstructure of CR particles, leading to distinct effects on CRMA rheological properties. The interaction between CR particles and asphalt involves a two-stage process: initial light component penetration, referred to as CR swelling, followed by particle breakage, referred to as CR degradation. Careful adjustment of mixing parameters can regulate the degree of CR swelling and subsequent degradation, thereby influencing the rheological response of CRMA. Review demonstrates that CRMA performs at its best when the CR particles achieves an equilibrium swelling condition, characterized by peak viscosity under controlled mixing conditions. This equilibrium indicates maximum absorption of the asphalt’s light fractions without significant degradation of the CR structure.

Warm rubberized bitumen (WRB) shows great potential for achieving sustainable pavement engineering in Europe and United States. At present, potential mechanism for coupling effects of macro and micro factors on fatigue resistance of WRB remains unclear. This paper systematically investigates fatigue performance of WRB with combined effects of oxidative aging, wax structures, and crumb rubber (CR) desulfurization. The results show that oxidative aging nearly has no effects on phase separation for desulfurization crumb rubber modified bitumen (DCRMB) but enhance agglomeration of non-desulfurization CR (NCR). The short-chain C18 wax enhances interaction between CR and bitumen better than long-chain Sasobit wax, and combined additives of desulfurized CR and short-chain wax additives have better anti-aging performance at whole working temperatures. The crack lengths from multi-level time sweep test have good negative correlation with fatigue life determined by linear amplitude sweep test at strain level of 2.5 %. CR desulfurization improves fatigue resistance of CRMB, which can be relataed to enhanced interaction between CR and bitumen. The short-chain C18 wax improves fatigue resistance of NCRMB and DCRMB before and after oxidative aging, while addition of Sasobit wax has opposite effect due to wax crystallization. Oxidative aging deteriorates fatigue resistance of CRMB and WRB samples at higher strain levels, while opposite effect occurs at lower strain levels. The fatigue resistance of WRB deteriorates after CR desulfurization, which is attributed to dominant role in dispersion effect of wax-based additives on NCR. This investigation can provide theoretical insights into multi-factor coupling mechanisms of fatigue resistance for WRB.

Conventional slope stability analyses typically incorporate stress dependent nonlinear strength effects through posterior equivalence or correction, which limits their direct role in identifying critical failure mechanisms. This study proposes a slope stability analysis approach in which nonlinear strength is incorporated in a front end, continuously parameterized manner within a discrete upper bound framework. Based on a power law nonlinear strength criterion, the equivalent friction angle along the slip surface is represented using B spline functions, enabling the simultaneous determination of the critical slip surface, strength distribution, and factor of safety within a unified optimization framework. Validation against linear degenerative cases and nonlinear benchmark examples shows that the proposed method produces safety factors and failure mechanisms consistent with existing upper bound solutions and finite element limit equilibrium analyses. Stress field back analysis further confirms the mechanical plausibility of the continuously evolving equivalent strength representation. Parametric investigations indicate that slope stability is governed by four key parameters, namely stress level, strength scale ratio, nonlinear exponent, and slope angle. These parameters control the global stability scale, spatial non uniformity and stress sensitivity of strength, and geometric effects, respectively. The proposed approach captures nonlinear strength behavior with a limited number of degrees of freedom and provides an efficient computational framework for slope stability analysis under nonlinear strength conditions.

Upcycling of end-of-life tires and polyethylene plastic enables sustainable reuse while upgrading asphalt, yet their thermodynamic incompatibility with asphalt has hindered application. Here, this paper demonstrated a thermo-mechanical activation method that synthesizes a homogeneous thermoplastic rubber-polyethylene elastomer (TRPE). The physicochemical structure of TRPE and rheological behavior of asphalt were evaluated to map the relations between activation, modifier and asphalt. The cradle-to-construction GHG emission was evaluated. The results show that thermo-mechanical activation disrupts sulfur networks, shortens polymer chains and enriches polar groups, with temperature emerging as the dominant factor. These changes remodel TRPE structure and influence binder rheological behavior within wide temperature and frequency range. Growing degree of activation increases the temperature susceptibility of asphalt, while moderate activation delivers a viscoelastic balance and well-rounded enhancement of physical properties. GHG assessment shows TRPE exhibits 20 % lower emissions than SBS at the modifier level, and a 7.5 % reduction at the pavement level.

Polyurethane can significantly improve the asphalt’s high-temperature performance, mechanical properties, and water stability. However, aging is an unavoidable process for asphalt binders during construction. This study employed hydroxyl-terminated polybutadiene (HTPB) polyurethane as a polymer modifier to examine the impact of aging on the microstructure and rheological properties of polyurethane-modified asphalt (PUMA). Fluorescence microscopy and Fourier transform infrared spectroscopy were used to analyze the microstructural changes before and after aging. In addition, the high- and low-temperature performance, fatigue resistance, and adhesion properties of HTPB-PUMA were systematically evaluated and compared with those of base asphalt and styrene-butadiene-styrene (SBS) modified asphalt. Results indicated that the aging behavior of HTPB-PUMA was similar to that of SBS-modified asphalt, characterized by asphalt phase aging and polymer phase degradation. The incorporation of polyurethane mitigated the negative effects of aging on high-temperature properties, low-temperature relaxation, fatigue resistance, and pull-off strength, thereby improving the overall aging resistance of asphalt. This study provides scientific guidance for advancing the anti-aging performance of PUMA in pavement applications.

The addition of high-content crumb rubber (HCCR) in asphalt can effectively address waste tire pollution and provide sustainable environmental and economic advantages. However, the practical application of conventional rubberized binders is significantly limited by high viscosity and poor storage stability. To address these issues, researchers have pretreated crumb rubber (CR) with oil, but high-temperature performance remains insufficient. Therefore, this study aimed to optimize the viscosity, storage stability, and rheological properties of high-content crumb rubber-modified asphalt (HCCRMA) by varying the pretreatment levels of CR and incorporating various additives, including styrene-butadiene-styrene (SBS), deoiled asphalt (DA), or recycled low-density polyethylene (RLDPE). In addition, CR was pretreated with waste cooking oil (WCO) at various ratios, pre-swelling temperatures, and times. The results show that DA exhibits excellent storage stability and lower viscosity compared with other modifiers in HCCRMA, and the 4% RLDPE with pretreated HCCR has the greatest high-temperature rutting resistance. The inclusion of RLDPE increases the stiffness and elasticity of the modified asphalt, which results in greater high-temperature performance. Additionally, the fluorescence microscopy (FM) test confirms that SBS exhibits better dispersion than other modifiers and forms a more homogeneous phase separation in the HCCRMA. All in all, this research achieved an optimal balance of storage stability and rheological properties in asphalt modified with pretreated HCCR and 6% SBS, which provides a valuable reference for performance improvement of HCCR-modified binders.