Search Results (989)

This study developed a design framework for porous mixtures using a 100% sustainable non-bituminous epoxy–polyurethane binder system. Conventional design protocols for porous asphalt mixtures exhibit limitations in accurately controlling void content and mixture composition. This study proposed a novel design framework for porous mixtures containing 100% sustainable binder based on statistical analysis and theoretical calculations. The relationships among target air voids, binder content, and aggregate gradation were systematically analyzed, and calculation formulas for coarse aggregate, fine aggregate, and mineral filler contents were derived. A mix design framework was further established by applying the void-filling theory, where the combined volume of binder, fine aggregate, and filler equals the void volume of the coarse aggregate skeleton, thereby ensuring precise control of the target void ratio. Additionally, mixing procedures were investigated with emphasis on feeding sequence, compaction method, and mixing temperature. Results indicated that the optimized feeding sequence significantly improved binder distribution; specimens compacted using the Marshall double-sided compaction method achieved a density of 89.60%. Rheological analysis revealed that at 30 °C, the viscosities of sustainable binder and polyurethane filler were 1280 mPa·s and 6825 mPa·s, respectively, suggesting optimal mixture uniformity. The proposed methodology and process parameters provide essential technical guidance for engineering applications of porous mixtures containing 100% sustainable binder. Full article

Temperature homogeneity assumes a crucial role in the manufacture of asphalt mixtures due to its impact on mechanical formation and mixing homogeneity. The existence of reclaimed asphalt pavement (RAP) exacerbates its impact on temperature inhomogeneity. To address this, the RAP contents of 20%, 40%, and 60%, combined with RAP preheated temperatures of 353 K, 373 K, and 393 K, were taken into consideration to examine the thermal transition and evolution of temperature for the recycled asphalt mixtures in the mixing. Thermal images captured within the range of 30 s to 120 s were used to monitor the temperature evolution of the recycled asphalt mixtures during the mixing. To quantitatively assess the level of thermal non-uniformity, a Relative Thermal Equilibrium Temperature Index (RETI) was introduced. This index reflects the degree of deviation from ideal thermal equilibrium within the recycled mixtures. Based on the RETI calculation, complete temperature homogeneity cannot be attained until the end of the mixing of hot recycled asphalt mixtures. However, a prolongation of the mixing time or an elevation in the RAP preheated temperature can expedite the thermal equilibrium process of recycled asphalt mixtures. Additionally, the RAP contents also exerted a crucial influence on the thermal equilibrium process of the recycled asphalt mixtures. Full article

The aging of asphalt mixture is one of the primary factors influencing the durability and performance of pavements. This study analyzed the influence of short-term (STOA) and long-term (LTOA) aging on hot mix asphalt (HMA) with the incorporation of recycled concrete aggregates (RCAs). The effect of aging on these types of mixtures has not been previously evaluated. HMAs were produced with 0%, 12%, and 21% RCAs (by mass), referred to as HMA Control, HMA RCA12, and HMA RCA21. These replacement percentages correspond to particles ranging between 19 and 12.5 mm (12%) and 19 and 9.5 mm (21%). The Marshall test was employed to determine the optimal asphalt content, followed by indirect tensile strength, resilient modulus, and permanent deformation resistance tests on samples subjected to STOA and LTOA. Overall, the results demonstrate that the incorporation of RCAs could improve the durability of asphalt mixtures by reducing their susceptibility to aging. Specifically, HMA RCA12 exhibited the best balance between stiffness, deformability, and resistance to aging, suggesting a favorable technical potential for its application in sustainable pavements, although additional testing is required to validate its long-term performance. Despite this, high RCA contents may reduce resistance to rutting and moisture damage. The results suggest that the optimal performance is achieved by balancing binder content and aggregate absorption to minimize susceptibility to aging. Full article

One of the main obstacles to producing natural rubber-modified asphalt is the difficulty of mixing Technical Specification Natural Rubber (TSNR) or its compounds with asphalt, leading to long mixing times and high costs. This study aims to evaluate the use of 60/70 penetration asphalt as a plasticizer to accelerate the mixing process and improve the rheological properties of modified asphalt using Technical Specification Natural Rubber (TSNR). The production process for technical specification natural rubber-modified asphalt involves two stages: the production of the technical specification natural rubber compound (CTSNR) and the production of CTSNR-based modified asphalt (CTSNRMA). The CTSNR production process begins with mastication of technical specification natural rubber (TSNR), followed by the addition of activators (zinc oxide, stearic acid), accelerators (Mercaptobenzothiazole sulfenamide (MBTS)), antioxidants (2,2,4-Trimethyl-1,2-dihydroquinoline (TMQ)), and 60/70 penetration asphalt as a plasticizer (at concentrations of 30%, 40%, and 50%). After homogeneous mixing for 30–60 min, the CTSNR is diluted 5–10 mm for the next mixing stage with hot asphalt at 160–170 °C. The best results of this study showed that CTSNR-modified asphalt with 4% rubber content and 50% plasticizer (CTSNRM-450) successfully reduced the mixing time to 16 min, making it more efficient than the traditional method, which takes up to 180 min. The addition of asphalt plasticizer decreased penetration to 35.6 dmm and increased the softening point to 55.4 °C. The CTSNRMA-440 formula, with 4% rubber content and 40% plasticizer, produced the best results in terms of storage stability, meeting the ASTM D5892 standard with a softening-point difference of 0.95 °C, which is well below the threshold of 2.2 °C. The CTSNRMA-440 sample achieved a Performance Grade (PG) of 76, suitable for hot-climate conditions, with a significant reduction in mixing time, greater stability, and increased resistance to high temperatures. Full article

In Mediterranean cities, high solar radiation combined with limited shading and vegetation intensifies the urban heat island (UHI) phenomenon. As the road network often covers a large portion of the cities’ surfaces and is mostly constructed using asphalt pavements, it can significantly affect the urban microclimate, leading to low thermal comfort and increased energy consumption. Recycled and waste materials are increasingly used in the construction of pavements in accordance with the principle of sustainability for minimizing waste and energy to produce new materials based on a circular economy. The scope of this study is to evaluate the effect of recycled or waste materials used in road pavements on the urban microclimate. The surface and ambient temperature of urban pavements constructed with conventional asphalt and recycled/waste-based mixtures are assessed through simulation. Two study areas comprising large street junctions near metro stations in the city of Thessaloniki, in Greece, are examined under three scenarios: a conventional hot mix asphalt, an asphalt mixture containing steel slag, and a high-albedo mixture. The results of the research suggest that the use of steel slag could reduce the air temperature by 0.9 °C at 15:00, east European summer time (EEST), while the high-albedo scenario could reduce the ambient temperature by 1.6 °C at 16:00. The research results are useful for promoting the use of recycled materials, not only as a means of sustainably using resources but also for the improvement of thermal comfort in urban areas, the mitigation of the UHI effect, and the reduction of heat stress for human health. Full article

The incorporation of reclaimed asphalt pavement (RAP) offers significant environmental benefits; however, its use is often limited by an increased susceptibility to cracking due to the insufficient elasticity of the severely aged RAP binder. This limitation is conventionally mitigated using polymers such as styrene–butadiene styrene, which, despite their effectiveness, are costly and carbon intensive. This paper introduces a low-carbon sulfur-based ternary polymer developed through TiO₂-catalyzed inverse vulcanization of elemental sulfur to be used as a modifier to address the abovementioned challenge at the asphalt mixture level. The sulfur polymer containing waste cooking oil and metal-rich biochar was incorporated into hot-mix asphalt having 25% RAP. The mixture specimens were evaluated before and after accelerated thermal and ultraviolet aging. Cracking resistance was measured using the Indirect Tensile Asphalt Cracking Test (IDEAL-CT), while resistance to rutting and moisture damage were assessed through the Hamburg Wheel Tracking Test (HWT). IDEAL-CT findings showed improved ${\mathrm{C}\mathrm{T}}_{\mathrm{I}\mathrm{n}\mathrm{d}\mathrm{e}\mathrm{x}}$ values for the modified mixture under unaged conditions and after three days of thermal aging, with smaller variations noted after prolonged thermal aging and during the combined thermal–ultraviolet aging process. Results from the HWT test revealed that the addition of the sulfur polymer did not negatively impact resistance to rutting or moisture damage; all mixtures remained significantly below rutting failure thresholds. Furthermore, a simplified environmental analysis indicated that substituting 10 wt% of petroleum binder with the sulfur polymer lowered the binder’s cradle-to-gate global warming potential by around 11%. In summary, study results showed that the newly developed sulfur polymer system has the potential to improve cracking resistance even when exposed to select accelerated aging protocols while decreasing embodied carbon, thus endorsing its viability as a sustainable modifier for asphalt mixtures. Full article

This study investigates the industrial validation of a granular additive derived from waste tire textile fibers (WTTF) developed to replace the conventional cellulose stabilizing additive in stone mastic asphalt (SMA) mixtures while enhancing their mechanical performance. Building on previous laboratory-scale findings, this work evaluates the feasibility and mechanical behavior of this recycled-fiber additive under real asphalt-plant production conditions, advancing a sustainable solution aligned with circular economy principles. Three asphalt mixtures were fabricated in a batch plant: a reference SMA (SMA-R) containing a commercial cellulose additive, an SMA incorporating the WTTF additive (SMA-F), and a reference hot mix asphalt (HMA-R). The WTTF additive was incorporated in a 1:1 proportion relative to the cellulose additive. Performance was assessed through tests of cracking resistance (Fénix test), stiffness modulus, fatigue resistance (four-point bending test), moisture susceptibility (ITSR), and resistance to permanent deformation (Hamburg wheel tracking). Industrial validation results showed that the SMA-F mixture met the design criteria and achieved superior mechanical performance relative to the reference mixtures. In particular, SMA-F exhibited greater ductility and toughness at low temperatures, reduced susceptibility to moisture-induced damage, and higher fatigue resistance, with an increase in fatigue durability of up to 44% compared to SMA-R. The results confirm that the WTTF additive is both feasible and scalable for industrial production, offering a solution that not only improves pavement mechanical performance but also promotes the valorization of a challenging waste material. Full article

The growing environmental effect of asphalt pavements has fueled interest in sustainable alternatives including the application of recycled materials and self-healing systems. This research investigates the synergistic possibilities of steel slag aggregates and steel wool fibers in hot-mix asphalt compositions to increase sustainability and let crack healing via electromagnetic induction heating. Using either recycled steel slag or natural porphyritic aggregates, two kinds of AC16 Surf S mixtures with 35/50 bitumen were created incorporating two levels of steel fiber content (2% and 4%). Based on repeated semi-circular bending (SCB) testing following regulated induction heating and confinement, a committed self-healing evaluation plan was developed. The results verified that combinations including recycled steel slag met or outperformed traditional mixes in terms of mechanical behavior. Induction heating successfully set off partial recovery of fracture toughness, with more fiber content and repeated heating cycles producing better healing values. Recovery levels ran from 14.6% to 40%, therefore proving the practicality of this approach. These results encourage the creation of asphalt mixtures with improved endurance and environmental advantages. The research offers both an approved approach for assessing healing and real-world recommendations for the construction of low-maintenance, round pavements utilizing induction-based techniques. Full article

The growing use of reclaimed asphalt pavement (RAP) in warm-mix asphalt (WMA) presents significant challenges when RAP originates from aged polymer-modified binder (PMB) pavements, where severe oxidation and polymer degradation lead to excessive stiffness and poor cracking resistance. This study presents a multi-scale evaluation of a hybrid modification strategy combining recycled engine oil waste (REOW, 3 wt.%) and styrene–butadiene–styrene (SBS, 1–4 wt.%) to restore aged PMB-containing RAP systems under controlled binder conditions. Three binders (control, REOW-modified, and REOW–SBS hybrid) were prepared using a fixed 70/30 virgin-to-RAP binder blend and characterized through rheological analysis, and multiple stress creep recovery (MSCR). The findings show that REOW softened the binder but reduced elastic recovery, whereas SBS modification restored elastic response. Corresponding WMA mixtures with 30 wt.% RAP and 5.0 wt.% total binder content were evaluated for moisture damage, raveling, rutting, and cracking resistance. At the mixture scale, the hybrid system achieved a TSR of 83%, reduced Hamburg rut depth by ~20%, and increased SCB fracture energy by ~30% compared with the control. These findings demonstrate that combined rejuvenation–reinforcement effectively re-mobilizes aged PMB chemistry and restores polymer elasticity, enabling high-performance WMA production with RAP derived from polymer-modified pavements. Full article

This study investigates the influence of synthetic fibers and rubber powder derived from end-of-life tires (ELTs) on the rheological behavior of asphalt mastics composed of paving-grade bitumen and mineral filler. Nine asphalt mastic formulations were prepared with varying fiber and rubber contents, reflecting the composition of stone mastic asphalt mixtures. Dynamic shear rheometer tests were conducted to assess dynamic stiffness modulus, phase angle, non-recoverable creep compliance, and elastic recovery. The results demonstrated that ELT-derived additives significantly enhanced high-temperature stiffness and elasticity, while maintaining satisfactory viscoelastic balance at lower temperatures. Synergistic effects between fibers and rubber were observed, improving both non-recoverable compliance and percent recovery, particularly at elevated shear stresses. Prolonged exposure to production temperatures (175 °C) confirmed the thermal stability of the modified mastics, with the most notable performance gains occurring during the first hour of heating. Based on the findings, it was concluded that ELT-based fiber–rubber additives can improve high-temperature performance of asphalt mastics without negative effects in intermediate and, possibly, also low service temperatures. This permits expanding the use cases for these kinds of additives beyond the role of inert stabilizers in stone mastic asphalt to an active modifier for extending asphalt mix performance. Full article

This study investigated the synergistic mechanisms of flame retardancy and smoke suppression exhibited by a novel ternary additive in warm-mix asphalt (WMA). The ternary additive consisted of aluminum hydroxide (ATH), organic montmorillonite (OMMT), and expandable graphite (EG). A comprehensive experimental program was conducted, encompassing limiting oxygen index (LOI) testing, cone calorimeter testing, thermogravimetric analysis (TGA), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS). The results showed that incorporation of 6 wt% of the ternary additive (by mass of the asphalt binder) markedly improved the fire resistance of the WMA. The LOI increased from 19.8% (neat asphalt) to 25.2%. Cone calorimeter tests revealed a 23.9% increase in time to ignition, a 24.2% reduction in peak heat release rate, and a 47.5% decrease in total smoke production. These improvements are attributed to a synergistic mechanism involving the endothermic decomposition of ATH, the char-promoting effect of OMMT, and the intumescent expansion of expandable graphite (EG) forming a compact insulating barrier, which collectively inhibit combustion and smoke release. The ternary additive exhibits considerable promise as an effective flame-retardant modifier for enhancing the fire safety of warm-mix asphalt pavements, especially in high-risk scenarios such as tunnels. Full article

The increasingly stringent environmental requirements, as well as the tendency to achieve significant savings of energy products in HMA production processes, prompted researchers to investigate the possibility of reducing the moisture of the stone aggregate which is used in production of hot asphalt mixtures. The goal of this paper is to determine the effect of various drying parameters on the aggregate moisture loss. The parameters which were analyzed and observed in various combinations were selected on the basis of the production process of an asphalt plant, and they are as follows: the air flow speed (3.86 m/s, 4.53 m/s and 5.94 m/s), the drying temperature (basic temperatures 33.1 °C, 50.4 °C and 71.7 °C) and the time of exposure of the aggregate to drying (30, 45 and 60 s). In order to research the effect of reduction in moisture of the stone material, a laboratory model of a belt dryer (chamber with a cover) was conceived and made with a drying device that can control the air flow speed from 3.86 m/s to 6.32 m/s and the temperature, ranging from 33 °C to 110 °C. Tests were carried out in order to determine the moisture loss of different aggregate fractions, namely 0/2, 2/4, 4/8, 8/11, from the total (natural) moisture of fractions that are used as aggregate in the production of hot mix asphalt (HMA). In all, there were 162 samples of aggregate prepared and tested. Results showed that for different aggregate fractions, the ranges of the value of the moisture loss are considerably different and that they depend on the parameters of drying and the natural moisture of the aggregate. It was noticed that there was less moisture loss in fractions at a lower air flow speed (3.86 m/s) than there was at higher speeds, while the highest aggregate moisture loss was noticed at an air flow speed of 5.94 m/s. For all duration times of drying, regardless of the drying temperature or speed, it is noticed that, with the prolongation of the drying time, the aggregate moisture loss becomes more intense. The drying temperature directly affects the reduction in the aggregate moisture; the higher the air flow temperature is, the more significant the moisture loss is during drying of the aggregate. The results of the linear regression and the coefficient of determination R² indicate a very firm connection between the loss of the aggregate moisture and the duration of the drying time. From the obtained equations, it is possible to calculate the reduction in the aggregate moisture for different lengths of drying duration and different drying temperatures. Full article

To address the challenges of decarbonization in the global transportation sector and disposal of waste tires, warm asphalt rubber (WAR) with low viscosity and high performance was prepared. In particular, the preparation and rheological behavior of WAR incorporating composite warm mix systems at relatively high crumb rubber contents have not been thoroughly documented. In this study, WAR prepared under such conditions was systematically examined. A five-factor, three-level segmented orthogonal experimental design (OED) was employed to investigate the effects of preparation parameters on hot mix asphalt rubber (AR) properties. Based on the optimized AR formulation, a composite warm mix system combining Ultra-Warm Mix additive (UWM) and Sasobit was developed, and control groups containing 5% UWM only and 1.5% Sasobit only were prepared for comparison. Conventional physical tests together with rheological characterization, including Dynamic Shear Rheometer (DSR), Multiple Stress Creep Recovery (MSCR), and Bending Beam Rheometer (BBR) tests, were conducted to evaluate the high- and low-temperature performance of WAR. Results show that the optimal preparation process consisted of aromatic oil content 5%, crumb rubber content 30%, shear temperature 220 °C, shear time 120 min, and reaction time 90 min. The composite warm mix system notably enhanced WAR performance, with the WAR-5U1.5S group exhibiting the most balanced properties. A marked reduction in rotational viscosity was achieved while maintaining a stable softening point, and satisfactory ductility and elastic recovery were also retained. DSR and MSCR tests confirmed improved high-temperature deformation resistance, an increase in percent recovery R, and a decrease in non-recoverable creep compliance J_nr. BBR test further verified that the composite system maintained good low-temperature cracking resistance, meeting all specification requirements. Overall, these results indicate that, compared with the optimized AR, WAR can reduce mixing viscosity without sacrificing rutting or cracking performance, while alleviating the limitations observed for single warm mix additives. This study provides essential technical support for promoting WAR that integrates low-carbon construction with superior pavement performance. Full article

The global production of electronic waste (e-waste) has increased due to the quick turnover of electronic devices, creating urgent problems for resource management and environmental sustainability. As a result, e-waste-derived materials (EWDMs) are being explored in pavement engineering research as sustainable substitutes in line with Sustainable Development Goals (SDGs), specifically SDG 9 (Industry, Innovation, and Infrastructure), 11 (Sustainable Cities and Communities), 12 (Responsible Consumption and Production), and 13 (Climate Action). Therefore, to assess global research production and the effectiveness of EWDMs in asphalt applications, this review combines scientometric mapping and systematic evidence synthesis. A total of 276 relevant publications were identified via a thorough search of Web of Science, Scopus, and ScienceDirect (2010–2025). These were examined via coauthorship structures, keyword networks, and contributions at the national level. The review revealed that China, India, and the United States are prominent research hubs. Additionally, experimental studies have shown that EWDMs, such as printed circuit board powder, fluorescent lamp waste glass, high-impact polystyrene, and acrylonitrile–butadiene–styrene, improve the fatigue life, Marshall stability, rutting resistance (up to 35%), and stiffness (up to 28%). However, issues with long-term field durability, microplastic release, heavy metal leaching, and chemical compatibility still exist. These restrictions highlight the necessity for standardised toxicity testing, harmonised mixed-design frameworks, and performance standards unique to EWDMs. Overall, the review shows that e-waste valorisation can lower carbon emissions, landfill build-up, and virgin material extraction, highlighting its potential in the circular pavement industry and promoting sustainable paving practices in accordance with SDGs 9, 11, 12, and 13. This review suggests that further studies on large-scale field trials, life cycles, and technoeconomic assessments are needed to guarantee the safe, long-lasting integration of EWDMs in pavements. It also advocates for coordinated research, supportive policies, and standardised methods. Full article

This study develops and assesses a hydrophobized fly ash mineral powder as a filler for dense fine-graded asphalt mixtures in Kazakhstan. Fly ash from a local TPP was dry co-milled with a stearate-based modifier to yield a free-flowing, hydrophobic powder that meets the national limits for moisture, porosity, and gradation. SEM shows cenospheres and broken shells partially armored by adherent fines, suggesting an increased micro-roughness and potential sites for binder–filler bonding. Three mixes were produced: a carbonate reference and two fly ash variants, all designed at the same optimum binder content. Compared with the reference, fly ash fillers delivered a markedly higher compressive strength (up to about five times at 20 °C), improved adhesion, and high internal friction, while the mixture density rutting resistance was essentially unchanged. Water resistance indices remained high and stable despite only modest changes in water saturation, and crack resistance improved, especially for the dry ash mixture. The convergence of microstructural, physicochemical, and mechanical results shows that surface-engineered fly ash from a Kazakhstani TPP can technically replace natural carbonate filler while enhancing durability-critical performance and supporting the more resource-efficient use of industrial by-products in pavements. Full article