Search Results (207)

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

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 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

Rutting is a predominant distress in asphalt pavements, particularly in hot climatic regions. This study systematically investigated the high-temperature performance of hot mix asphalt modified with five nanomaterials, namely, nano-silica (NS), nano-alumina (NA), nano-titanium (NT), nano-zinc (NZ), and carbon nanotubes (CNTs), under consistent laboratory conditions. Modification dosages were selected up to 10% for NS, NA, and NT, and up to 5% for NZ and CNTs. The experimental methodology comprised the following: (i) binder rheological characterization through rotational viscosity, G*/sinδ, and multiple stress creep recovery (MSCR) to quantify rutting susceptibility; (ii) chemical and microstructural assessments using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM); (iii) mixture-level evaluation via repeated-load axial testing coupled with digital image correlation (DIC) to monitor permanent microstrain evolution; and (iv) rutting performance over a 20-year period using the VESYS 5W predictive model. A cost–performance analysis was further incorporated to assess the economic viability of each nanomaterial. The results demonstrated that nanomodification substantially improved rutting resistance, consistent with reductions in non-recoverable creep compliance and permanent microstrain. Among additives, the 8% NS mixture exhibited the most favorable performance, maintaining a present serviceability index (PSI) of 2.5 after 20 years, whereas the un-modified mixture dropped below the failure threshold within a few years. These findings confirm that nanomaterial selection and dosage can meaningfully enhance the structural and performance of asphalt pavements. Full article

Severe asphalt ageing and the difficulty in dispersing agglomerated particles within reclaimed asphalt pavement (RAP) hinder the uniform blending of virgin and aged mineral aggregates during plant-mixed hot recycling, compromising the durability of the recycled asphalt mixture. To accurately quantify the degree of blending between virgin and aged aggregate during thermal recycling and to optimise the mix design and mixing process for thermally recycled asphalt mixtures, a test method has been proposed. This method comprises key steps, including the preparation of asphalt mixtures, separation of virgin and aged materials, separation of the binder from aggregate, and calculation of the blending degree. It analyses the impact of varying mixing conditions on the blending degree of virgin and aged aggregate during the thermal recycling process. The results indicate that complete homogenization of virgin and aged aggregates during mixing is unattainable, with blending efficiency ranging from 40% to 60%. Increasing the amount of RAP has a negligible effect on blending efficiency. Appropriate increases in the amount of rejuvenating agent, mixing temperature, mixing time, and asphalt content enhance blending efficiency by 10% to 30%. The mixing sequence where RAP is first blended with virgin aggregate before incorporating virgin asphalt further enhances the blending efficiency of virgin and aged aggregates by approximately 20%. However, mixing temperatures exceeding 160 °C and mixing times exceeding 270 s caused secondary ageing of the asphalt, adversely affecting the blending degree of virgin and aged aggregates. Full article

This paper presents the effect of modifiers on the properties of a mixture of asphalt concrete with bitumen emulsion (ACBE). The mineral-asphalt mixture is the only one that can be produced using the cold-mix technology (CMA). The theoretical part of the article details the characteristics of the methods for producing mineral-asphalt mixtures in terms of their production temperature. Thus, hot (HMA), half-warm (H-WMA), warm (WMA) and cold (CMA) mixtures are discussed. The research section presents the design of the asphalt concrete composition with bitumen emulsion, the research methods, the experiment design and the research results. The design of the mixture of asphalt concrete with bitumen emulsion was carried out in accordance with the guidelines set out in EN 13108-31. In the experiment, Portland cement (C), bitumen emulsion (A), synthetic latex (styrene-butadiene rubber SBR) (B) and redispersible polymer powder EVA (polyethylene-co-vinyl acetate) (P) were used as modifiers. Twenty-four mixtures were designed as part of the experiment, according to the 3⁴ experiment design. The following physical and mechanical properties were assessed in the design of the research: air void content V_m, water ab-sorption n_w, indirect tensile strength ITS and IT-CY stiffness modulus. When analysing the research results, the authors observed a noticeable impact of the content of asphalt (A) and synthetic latex (B) on the air void content V_m. A significant effect was also observed for the interaction of Portland cement (C) and redispersible polymer powder (P) on the indirect tensile strength ITS. The next step was the optimisation of the ACBE mixture composition, which effect made it possible to identify the optimum amounts of modifiers in the mixture of asphalt concrete with bitumen emulsion (ACBE), which constituted recommendations for the requirements for mixtures of asphalt concrete with bitumen emulsion. Full article

This study investigates the feasibility of using Kraft lignin in Hot and Warm Mix Asphalt (HMA and WMA), with a particular focus on its integration alongside Sasobit^®. The research aims to evaluate the impact of Kraft lignin and Sasobit, individually and in combination, on the construction temperatures, compactability, and physical properties of asphalt mixtures. The experimental program included a reference HMA and modified mixes with 20% Kraft lignin, 3% Sasobit, and their combinations. These mixes were designed and subjected to tests to assess their volumetric and mass properties and to determine the construction temperatures using the Superpave Gyratory Compactor (SGC). The results demonstrated that adding Kraft lignin increased construction temperatures, while Sasobit effectively reduced these temperatures by lowering binder viscosity. When used together, Sasobit offset the increase in construction temperatures caused by Kraft lignin, resulting in compaction temperatures similar to the reference HMA mix. Additionally, Kraft lignin increased air voids, leading to reduced compactability at higher gyration levels. It also exhibited indications of a dual role, functioning as both a binder replacement and a filler. In conclusion, the combination of 20% Kraft lignin with 3% Sasobit offers a promising solution for enhancing the sustainability of asphalt mixtures. Full article

Sustainable management of Construction and Demolition Waste (CDW) is key to the Circular Economy. Reusing crushed concrete as recycled concrete aggregates (RCAs) in hot-mix asphalt (HMA) is a viable CDW solution, although RCA’s high absorption can affect performance. This study evaluates the effect of partially replacing 0%, 10%, and 30% of virgin aggregate with RCA in a dense-graded HMA, assessing its moisture susceptibility and cracking resistance. Specimens were subjected to long-term water-immersion aging (3 and 6 months at 25 °C) and tested for Indirect Tensile Strength (ITS), Tensile Strength Ratio (TSR), and Cracking Tolerance Index (CT-index). RCA incorporation consistently increased ITS at all aging levels. In particular, the 30% RCA mixtures exhibited the highest strength, exceeding the absolute ITS thresholds required by various U.S. transportation agencies to ensure structural capacity. While TSR values remained below the 80% AASHTO T 283 threshold, 10% and 30% RCA mixes had higher TSR than the control, indicating a comparative improvement in moisture resistance. Conversely, the CT-index decreased with more RCA and longer immersion, particularly at 30% RCA, revealing a trade-off between strength gain and cracking tolerance under prolonged wet exposure. Overall, a 10% RCA replacement level provided the most balanced performance, supporting its technical feasibility for sustainable, performance-based mixture design. Full article

Despite being crucial for sustainable pavement construction, the widespread application of hot recycled asphalt mixtures in high-grade surface courses is hindered by concerns over their long-term performance, particularly regarding cracking resistance and moisture stability. This study systematically evaluates the road performance of hot central plant recycling (HCPR with 30% RAP) and hot in-place recycling (HIPR with 80% RAP) mixtures, benchmarked against virgin hot mix asphalt (SMA-13), through comprehensive laboratory simulations. The enhancing effect of basalt fibers (BFs) was thoroughly investigated. Results revealed a significant performance trade-off; while the recycled mixtures exhibited superior high-temperature stability (e.g., an 80.7% increase in dynamic stability for HIPR), their cracking resistance substantially decreased with higher RAP content (e.g., reductions of 60.8% in low-temperature flexural strain and 22.1% in intermediate-temperature fracture energy for HIPR). Both recycled mixtures also showed susceptibility to moisture damage, evidenced by stripping in Hamburg wheel-tracking tests. The incorporation of BFs effectively mitigated these deficiencies. It comprehensively improved the performance, enabling the HCPR mixture to meet specifications for severely cold regions and elevating the HIPR mixture to compliance level for cold regions. Furthermore, BF significantly enhanced rutting resistance under coupled hydrothermal conditions. These findings demonstrate that basalt fiber reinforcement can bridge the performance gap of recycled mixtures, thereby expanding their application scope and providing a robust technical basis for selecting and optimizing recycling strategies in high-grade pavement engineering. Full article

The primary aim of this study is to predict the Marshall stability and flow values of hot-mix asphalt samples prepared according to the Marshall design method using regression-based machine learning algorithms. To overcome the limited number of experimental observations, synthetic data generation was applied using the Conditional Tabular Generative Adversarial Network (CTGAN), while the structural consistency of the generated data was validated through Principal Component Analysis (PCA). Two datasets containing 17 physical and mechanical input variables were analyzed, and multiple regression models were compared, including Extra Trees, Random Forest, Gradient Boosting, AdaBoost, and K-Nearest Neighbors. Among these, the Extra Trees Regressor consistently achieved the best results with near-perfect accuracy in flow predictions (MAE ≈ 4.06 × 10⁻¹⁵, RMSE ≈ 4.97 × 10⁻¹⁵, Accuracy ≈ 99.99%) and high performance in stability predictions (MAE = 109.52, RMSE = 150.67, accuracy = 90.45%). Furthermore, model interpretability was ensured by applying SHapley Additive Explanations (SHAP), which revealed that parameters such as softening point, VMA, penetration, and void ratios were the most influential features. These findings demonstrate that regression-based ensemble models, combined with synthetic data augmentation and explainable AI methods, can serve as reliable and interpretable tools in asphalt mixture design. Full article

The construction sector has a prominent role in raw materials consumption and environmental depletion due to waste and emissions connected to the production of construction materials and construction/demolition operations. Thus, research is pushing to develop sustainable construction materials, mainly recycling waste and by-products. Following this trend, the present study explores the possible use of two different blends of cement-based waste powder and biomass ashes as filler for the production of asphalt concretes. The materials have been tested following the EN 13043 standard requirements for fillers for bituminous mixtures. Still, the basic performances of hot mix asphalts produced with the recycled materials have been evaluated on a laboratory scale. The physical, chemical, and mechanical characterization of the waste fillers and the bituminous mixtures showed advantages and downsides in the use of the recycled powders for hot mix asphalt production. Despite final performances in line with traditional hot mix asphalt, the chemical composition of the proposed fillers has a negative influence mainly on the water susceptibility of the mixture. However, the findings of the study open new perspectives on future possible applications of the recycled fillers in the road pavements sector. Full article