Search Results (718)

With the increased application of porous asphalt, the recycling and reutilization of aged materials have become a critical issue for sustainable pavement engineering. This study investigates the evolution of the performance characteristics of porous asphalt mixtures under high-temperature heating conditions, with the aim of providing a theoretical basis for hot in-place recycling (HIR) technology in the rehabilitation of porous asphalt pavements. The heating states of asphalt, mortar and mixtures in HIR were simulated using controlled oven heating. Their microscopic, mechanical and thermal properties were evaluated under different aging conditions and with the incorporation of different rejuvenators. The results show that asphalt aging intensifies with the increasing heating temperature and time. The incorporation of bio-based rejuvenators significantly alleviates aging effects and demonstrates superior performance compared to conventional rejuvenators. Furthermore, aggregates and rejuvenators enhance the thermal conductivity of materials, while aging reduces the thermal conductivity coefficient and increases the risk of temperature gradient diseases. The rheological properties of asphalt are closely related to the degree of aging. While aging mitigation improves low-temperature cracking resistance and acoustic damping performance, it may compromise high-temperature deformation resistance. In conclusion, to achieve an optimal balance between performance recovery and aging control, it is recommended that the HIR of porous asphalt pavements be conducted at a heating temperature of 180 °C for 5 min, with the addition of 3% bio-based rejuvenator. Full article

Maintaining consistent quality performance of recycled aggregates is essential for their reliable use in construction applications. This study evaluated whether the regulatory revision permitting concurrent appointment of quality and environmental managers affected post-certification quality test performance within Korea’s recycled aggregate certification system. Extending a previous 2025 audit-based study, this research analyzed 311 certification-application-level follow-up quality test results obtained during the 2023 national post-certification management process. Statistical analyses, including chi-square tests, Fisher’s exact tests, odds ratio comparisons, and subgroup analyses, were conducted according to management structure, personnel change status, and recycled aggregate application type. The results showed that concurrent appointment and personnel changes were not associated with statistically significant deterioration in post-certification quality test performance. In contrast, the recycled aggregate application type showed substantially greater influence on pass/fail outcomes, with relatively higher failure risks observed in concrete and fine aggregate applications requiring stricter quality control conditions. Road construction and asphalt concrete applications generally maintained relatively stable pass rates regardless of management structure or personnel continuity conditions. The subgroup analyses additionally showed that concurrent appointment did not significantly increase failure risk within any recycled aggregate application category. These findings indicate that concurrent appointment did not significantly deteriorate actual post-certification quality performance within the analyzed national certification dataset. Full article

The incorporation of crumb rubber derived from waste tires in asphalt pavements has gained increasing attention as a strategy to enhance performance while reducing environmental impacts, particularly in cold regions such as the Midwestern United States, where pavements are subjected to severe thermal stresses and freeze–thaw cycles. Despite the numerous performance benefits observed in previous laboratory-scale studies, field demonstrations can play a critical role in validating the use of recycled waste tires as asphalt additives. This study examines the performance benefits and environmental impacts of incorporating recycled tire rubber into asphalt mixtures via a dry modification process for cold-climate applications. Building on these findings, this paper is based on a full-scale field demonstration of a dry-process rubber-modified asphalt pavement constructed in Ann Arbor, Michigan. Performance testing was conducted at both the binder and mixture levels, and field cores were collected during the construction of field sections. To complement the performance evaluation, a life-cycle assessment (LCA) was conducted to quantify the environmental impacts of rubber-modified asphalt and conventional asphalt. The results indicate that successful rubber incorporation, combined with improved low-, intermediate-, and high-temperature performance, enhances long-term durability compared with control sections. Moreover, despite slightly higher initial environmental impacts associated with rubber incorporation, improved durability and reduced maintenance frequency can lead to lower life-cycle impacts over the long term. The findings highlight the potential of rubber-modified asphalt as a sustainable, resilient solution for cold-region pavements, offering practical insights for agencies seeking to balance performance and environmental impacts in future infrastructure design. Full article

Foamed asphalt cold recycling technology is one of the key engineering approaches to address the accumulation of large quantities of reclaimed asphalt pavement (RAP) in road maintenance and rehabilitation. However, a systematic design methodology that simultaneously accounts for long-term fatigue resistance and toughness has not yet reached a unified consensus or widespread application. Existing studies have investigated the effects of fine aggregate gradation or cement content on individual performance aspects of mixtures, but studies incorporating both factors into a unified experimental framework for parallel comparison of multiple performance indicators remain limited. To this end, this study designed three mineral aggregate gradations with significantly different fine aggregate contents and systematically evaluated the effects of gradation composition, foamed asphalt content, and cement dosage on the mechanical properties, moisture stability, high-temperature stability, and fatigue performance of the mixtures. Indirect tensile fatigue tests under a stress-controlled mode were conducted to determine the fatigue life of different gradations at four stress ratio levels. The results indicate that sufficient fine aggregate content, particularly particles smaller than 0.075 mm, is a key factor in enhancing mixture compactness, indirect tensile strength, and resistance to moisture damage. The effect of cement on fatigue performance exhibits stress-level dependency: at low stress ratios, the addition of cement improves fatigue life, whereas at high stress ratios, the increased brittleness of the material reduces fatigue resistance, which is consistent with findings reported in previous studies. Furthermore, this study provides comparative experimental data for different fine aggregate gradations. The optimal gradation scheme demonstrated superior overall performance across all evaluated indicators, verifying the feasibility of achieving a balance between strength and toughness through gradation optimization. Compared with conventional design methods guided by a single strength index, this study offers a more comprehensive basis for mix design optimization of foamed asphalt cold recycled mixtures and provides engineering references for their application in long-life pavement maintenance. Full article

The growing demand for sustainable and economically efficient road maintenance solutions has driven the development of materials that reduce the use of natural aggregates and promote waste valorization. In this context, this study evaluates the use of reclaimed asphalt pavement (RAP) and greywacke aggregates derived from Panasqueira mining by-products as partial or total substitutes for granite aggregates in cold asphalt mixtures intended for rapid pothole repair. Reference mixtures and recycled mixtures were produced with controlled proportions of RAP and greywacke, using cationic bituminous emulsion and hydrated lime, as well as an additional mixture composed only of RAP with a fluxing cold binder. Three commercial mixtures, identified as CCM1, CCM2, and CCM3, were also evaluated. Performance was analyzed through Cantabro particle loss, Marshall stability and flow, indirect tensile stiffness modulus, and water sensitivity (ITSR). The results show that greywacke provides a robust granular skeleton, while RAP content and binder type influence stiffness, cohesion, and moisture resistance. Overall, the combination of RAP and greywacke proved to be technically viable and, in several cases, superior to the commercial mixtures studied. Full article

This study examined the foaming characteristics of asphalt and their effects on the performance of cold recycled mixtures. The expansion ratio and half-life were used to evaluate effects of asphalt type, foaming temperature, and water content. The influence of asphalt content, gradation, cement content, curing time, and mixing water on mechanical properties and water stability was analyzed. The results indicate that asphalt type is the key factor affecting foaming performance. CNOOA asphalt showed optimal foaming at 160 °C with 2% water, achieving an expansion ratio of 27 and a half-life over 30 s. Optimal asphalt contents for gradations A and B are 3.5% and 2.5%, respectively. A 1.5% cement content provides the best performance balance. Dry and wet indirect tensile strengths increased by 91.18% and 205.56% after 3-day curing. The optimal mixing water ranges are 60–90% and 70–80% of optimum moisture content for gradations A and B. Curing time has the most significant influence on performance, followed by cement and asphalt content. This study provides a theoretical basis for optimizing foamed asphalt cold recycling. Full article

Sustainability assessment of road pavements requires the combined consideration of environmental and mechanical performance, since conventional mass-based Life Cycle Assessment (LCA) may lead to misleading conclusions. This study proposes a multi-criteria decision-support framework that integrates LCA results with key mechanical indicators through structural normalisation, enabling the comparison of asphalt mixtures on an equivalent structural basis. Three sustainable asphalt mixtures were analysed, namely Hot Recycled Mix Asphalt (HRMA), Half-Warm Mix Asphalt (HWMA), and Cold Recycled Mixture (CRM), and compared with a reference Hot Mix Asphalt (HMA). Environmental impacts were quantified using a cradle-to-gate LCA, while mechanical performance was characterised through stiffness, fatigue resistance, rutting, and moisture susceptibility. These indicators were integrated into a Structural Contribution index and a Material Environmental Impact Ratio. The results show that, although CRM benefits from cold production and high recycling rates, its lower structural performance reduces its advantage when equivalent thickness is considered. HWMA emerges as the most favourable compromise within the adopted framework, combining lower environmental impacts with competitive structural performance, while HRMA offers the greatest structural contribution with competitive environmental performance. Sensitivity analysis confirms the robustness of the framework under realistic variations in weighting assumptions. The study demonstrates that incorporating structural performance into environmental assessment is essential to avoid misleading conclusions and to support more reliable decision-making in sustainable pavement design. Full article

The heating efficiency of hot in-place recycling for asphalt pavements directly depends on parameters such as hot air temperature, hot air velocity, and heating machinery travel speed. However, the interactions among these parameters and their influence mechanism on deep-layer temperature remain unclear. In this study, a three-dimensional transient heat transfer model of an asphalt pavement was established to simulate the effects of different parameters under intermittent heating conditions, including hot air temperature, hot air velocity, and travel speed, on the pavement surface temperature and temperature at a depth of 4 cm. The results indicate that travel speed exhibits the most sensitive effect on temperature, with an absolute regression coefficient of 8.5 °C·min/m. A reduction of 0.5 m/min in travel speed increases the deep-layer temperature by approximately 4.25 °C. Every 50 °C increase in hot air temperature raises the deep-layer temperature by about 5.75 °C. The effect of hot air velocity on temperature is relatively small within the range of 12 to 14 m/s. The heat penetration efficiency increases monotonically as the hot air temperature and velocity increase or the travel speed decreases. This study reveals the quantitative relationship between heating parameters and temperature responses, providing a theoretical basis for parameter optimization in hot in-place recycling processes. Full article

To address the rapid performance deterioration and secondary maintenance challenges of highway asphalt pavements that have undergone a first-round hot in-place recycling, this study investigates the feasibility of secondary recycling. Using the Yangzhou section of the G40 Expressway (Class II mild aging) and the Lianyungang section of the G30 Expressway (Class VI severe aging) as engineering backgrounds, three recycling schemes were designed and evaluated: Scheme A (100% RAP control), Scheme B (RAP with rejuvenator and virgin aggregate), and Scheme C (Scheme B reinforced with toughening basalt fibers). A comprehensive multi-dimensional testing protocol—including dynamic stability, semi-circular bending (SCB), low-temperature beam stripping, and Hamburg wheel-tracking—was employed to systematically evaluate the pavement performance of the second-time hot in-place recycled asphalt mixtures. The results indicate that while secondary recycled mixtures (Schemes A and B) maintain acceptable high-temperature stability, their intermediate-to-low temperature cracking resistance serves as the critical bottleneck, failing to meet standard specifications. In contrast, compared with Scheme A (100% RAP control), Scheme C (with basalt fibers) increased the flexibility index by 646.2–946.7%, the low-temperature fracture energy by 96.7–261.0%, and the Hamburg wheel-tracking stripping point by 48.1–62.2%, effectively mitigating the brittle fatigue common in aged recycled binders. According to the Jiangsu Expressway Maintenance Design Guidelines, the incorporation of basalt fibers elevated the comprehensive performance grade of the mixture from below Grade C to Grade A. This research provides a robust scientific basis and a “digital filter” for the large-scale engineering application of sustainable secondary recycling technology in heavy-traffic environments. Full article

This study evaluates the performance of recycled, long-term-aged rubber-modified asphalt (RMA) mixtures rejuvenated with soybean oil. Crumb rubber is widely used in asphalt mixtures for its ability to enhance elasticity, crack resistance, and durability. However, long-term aging leads to oxidative hardening, increased stiffness, and reduced cracking resistance, creating a need for effective rejuvenation strategies. To simulate extended field aging, plant-produced RMA mixtures were conditioned at 85 °C for five and ten days and subsequently treated with 10% soybean oil by binder weight. Mechanical performance was assessed using the Disc-Shaped Compact Tension test, Indirect Tensile Asphalt Cracking Test, Hamburg Wheel Tracking Test, and Rapid Shear Rutting Test. Rejuvenation effectively reversed aging-related deterioration, increasing fracture energy by 137–211% and improving cracking tolerance indices by 22–104%, thereby restoring or surpassing the cracking performance of unaged RMA mixtures. This improvement in flexibility was accompanied by reduced rutting resistance, with rutting tolerance indices decreasing by 52–70%, consistent with the softening effect of bio-based oils. Performance space diagrams further illustrated the trade-off between enhanced cracking resistance and increased rut susceptibility. Overall, the results demonstrate that soybean oil provides strong restorative capabilities for aged RMA mixtures, but achieving balanced field performance requires optimization of rejuvenator dosage. Full article

The sustainable utilization of multiple reclaimed pavement materials is a critical pathway toward green highway construction. This study investigates the performance and synergistic mechanisms of cold-recycled mixtures incorporating both Reclaimed Asphalt Pavement (RAP) and Reclaimed Cement-Stabilized Base (RCSB), using emulsified asphalt as the primary binder. A comprehensive experimental program was conducted to evaluate the effects of reclaimed material proportions, mixing sequences, and curing ages on the mechanical strength, moisture susceptibility, and high-temperature stability of the mixtures. Microscopic characterization via Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) were employed to elucidate the Interfacial Transition Zone (ITZ) evolution. Results indicate that an optimal RCSB incorporation range of 20–40% establishes a robust “stone-to-stone” rigid skeleton, significantly enhancing the splitting strength (up to 0.87 MPa) and durability (Splitting Strength Ratio, TSR > 91%). SEM observations confirm the formation of a dense interpenetrating network structure within this range, where cement hydration products and asphalt films achieve optimal chemo-physical bonding. Exceeding 40% RCSB leads to a moisture-starved state and a sharp decline in dynamic stability due to insufficient binder coating. Micro-morphological characterization reveals that the transition from macro-interfacial debonding to a robust cohesive failure mode is the fundamental driver for the performance peak at 20–40% RCSB. SEM observations confirm the formation of a dense interpenetrating network structure, where cement hydration products successfully anchor into the asphalt film. This optimized ITZ effectively eliminates the stress concentration and aggregate crushing seen in high-RAP mixtures, thereby ensuring superior mechanical integrity. Furthermore, a pre-wetting mixing sequence ensures a high-energy mineral surface that promotes the heterogeneous nucleation of cement. SEM results show that this prevents the competitive adsorption between cement and asphalt, transforming the ITZ from a friable, loose state into a densified crystalline adhesive matrix. Full article

Strategies based on the use of recycled materials have been widely discussed as alternatives to reduce environmental impacts in transport infrastructure. In pavement engineering, the use of Reclaimed Asphalt Pavement (RAP) in base layers offers environmental benefits; however, its benefits depend on processing conditions and structural performance. Chemical stabilization techniques, although mechanically effective, tend to introduce environmental hotspots associated with binder production. In this study, controlled thermal conditioning of RAP is evaluated as a warm base solution without chemical stabilizers in the context of airport pavements. A comparative life cycle assessment was conducted under a production- and construction-stage scope (A1–A3 and A5, excluding transportation under equivalent logistical assumptions), considering untreated RAP, heated RAP, and RAP stabilized with emulsion and cement, and was integrated with mechanistic–empirical structural performance analyses. The results indicate that, although heated RAP presents intermediate absolute environmental impacts due to additional energy consumption, it achieves the highest eco-efficiency, expressed as the lowest ratio between global warming potential (IPCC 2023) and estimated structural service life. In the analyzed scenarios, the warm base showed approximately 71% lower environmental impact per year of service than untreated RAP and about 90% lower than the emulsion-stabilized alternative. These findings suggest that performance-based sustainability assessment can reveal environmental advantages in solutions that exhibit moderate increases in production-stage impacts but enhanced structural longevity. It should be noted that the conclusions are conditioned by the adopted production and construction system boundaries, which do not include the use, rehabilitation, or end-of-life phases. Full article

The disposal of waste tyres presents a significant environmental challenge, necessitating sustainable, high-value recycling solutions. This study explores the incorporation of waste tyre metal fibre (WTMF) into hot mix asphalt (HMA) to enhance mechanical performance while reducing its electrical resistivity as well as the landfill burden. The primary goal of this research is to apply response surface methodology (RSM) to experimental data for modelling and optimizing WTMF-modified HMA mixes by capturing the coupled effects of fibre reinforcement and binder content on mechanical and functional performance. The microstructural characteristics of WTMF were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). WTMF-modified mixes containing five WTMF dosages (from 0% to 1.50%) and bitumen contents from 4% to 6% were prepared and tested in the laboratory. The resulting dataset was used for RSM modelling, with WTMF and bitumen contents as input factors and Marshall stability, flow, porosity, and electrical resistivity as response variables. The central composite design (CCD) technique was employed to quantify interaction effects and to identify statistically significant trends. The developed models were validated using statistical indicators, and optimal mixture compositions were determined and experimentally verified. Microstructural analysis revealed WTMF’s irregular, rough surface with microcracks and pits, aiding crack-bridging and stress transfer. RSM results indicated 0.71% WTMF and 5.1% bitumen as an optimal combination of factors. Furthermore, high R² (>0.80) and adequate precision (>4.0) values from analysis of variance (ANOVA) underscore the significance of the proposed models, revealing a robust correlation between experimental and predicted data. This study demonstrated WTMF’s potential to be used in conventional HMA mixes, offering a sustainable recycling pathway for waste tyres. Full article

Road pavement rehabilitation increasingly incorporates innovative surface technologies aimed at improving pavement performance while reducing environmental impacts. In addition to conventional recycled asphalt pavement (RAP) maintenance strategies, advanced pavement surface systems such as reflective coatings, rejuvenator-based self-healing mixtures, and thin low-noise asphalt layers have been developed to enhance durability and functional performance. This study presents a comparative Life Cycle Assessment (LCA) of four pavement surface technologies using primary inventory data obtained from full-scale road sections. The systems evaluated include a conventional maintenance mixture and three alternative surface solutions: reflective pavement coatings, RAP mixtures incorporating rejuvenator-based self-healing systems, and thin low-noise asphalt layers. The assessment follows ISO 14040 and ISO 14044 standards and applies the ILCD 2011 midpoint+ (EF 2.0) method. To enable comparability between technologies with different durability, the functional unit was defined as 1 m² of rehabilitated pavement per year of service life. The results indicate that thin low-noise asphalt layers provide the highest environmental benefits across most impact categories due to significant material savings associated with reduced layer thickness. Reflective pavement coatings decrease several impacts, particularly fossil resource depletion and atmospheric emissions, although higher burdens are observed in some categories due to synthetic binder production. RAP mixtures incorporating rejuvenator-based self-healing systems improve resource efficiency and extend pavement durability but may increase impacts associated with binder manufacturing. Overall, the findings highlight relevant environmental trade-offs between different pavement surface technologies and demonstrate that parameters such as layer thickness, binder composition, recycled material content, and service life strongly influence environmental performance. The study illustrates how comparative Life Cycle Assessment supports the development and selection of more sustainable pavement surface systems. Full article