1. IntroductionAging in asphalt mixtures is a phenomenon that starts from the time of construction in the factory and by passing the time, it will progress and finally it leads to stiffening of the asphalt and deterioration of the mixture. Asphalt undergoes hardening primarily due to two factors: loss of volatiles and oxidation of asphalt. The main loss of volatiles occurs in asphalt-aggregate mixtures between the time of mixing and final placement, when the mixture is at elevated temperatures. This is referred to as short-term aging. The longer, never-ending process of oxidation occurs partially throughout the short-term aging time frame, but much more extensively over time, while the mixture is in service and exposed to the environment. This is referred to as long-term aging [1]. Aging does not progress among different types of asphalts at the same rate, and also aggregate types are effective in this phenomenon [2]. Aging is not negative completely, because a small amount of this leads to improvement of the characteristics of the mixture [3].

Effects of Polyphosphoric Acid (PPA) on the ultraviolet (UV) aging properties of asphalt and asphalt mixture were studied. The morphologies of these binders were characterized by Fourier Transform Infrared Spectroscopy (FTIR) spectra and Thermo-Gravimetric (TG) analysis. Then, the e ects of PPA on asphalt and its mixture before and after UV aging were investigated in terms of the physical properties and pavement performances. Results showed that the mechanisms of PPA-modified asphalt were physical and chemical reactions; both UV aging and PPA additive could prompt the polycondensation of light components in asphalt. Compared to control samples, the introduction of PPA enhances the asphalt properties and intensifies the asphalt mixture performance. Furthermore, the asphalt performance aging variations (penetration aging index, softening point increment, ductility aging index, and G*/sin aging index) decreased signi cantly due to the introduction of PPA. It was shown that the effects of UV aging on the behaviors of asphalt and asphalt mixture were constrained with the addition of PPA by inhibiting the increase of carbonyl in the oxidation process.

Incorporating recycled asphalt pavement (RAP) into asphalt mixtures is a common practice for sustainability. However, aging and hardening of the RAP binder can compromise performance. Aged RAP is stiffer, less flexible, and more prone to cracking. This research investigates the combined effects of RAP content, RAP age, and nano-silica (SiO₂) addition on asphalt performance, focusing on fracture resistance, fatigue resistance, and moisture susceptibility. Asphalt mixtures containing 25%, 50%, and 75% RAP were evaluated using RAP aged 5 and 10 years. Nano-SiO₂was incorporated at 0%, 1%, 1.5%, and 2%. Performance evaluations included semi-circular bending test for fracture resistance, indirect tensile fatigue test for fatigue resistance, and tensile strength ratio (TSR) test for moisture susceptibility. The findings indicated that nano-SiO₂significantly enhanced fracture and fatigue resistance, especially at lower RAP content. At 25% RAP, 1.5% and 2% nano-SiO₂improved both fracture and fatigue resistance by 15%-20%. Notable enhancements were observed for mixtures with 50% and 75% RAP, with optimal results at 2% nano-silica. Furthermore, nano-SiO₂improved moisture resistance, increasing TSR values above 80%. Nano-silica effectively mitigated aging effects, particularly in mixtures with higher RAP content. Based on this analysis, utilizing 25%-50% RAP combined with 1.5% nano-SiO₂is advisable for producing high-performance asphalt mixtures.

The internal structure of a molecule can be presented in terms of intra-molecular (i.e., inter atomic) and inter-molecular energies such as van der Waals, bond and bending, torsion, and inversion energy. In this study, changes in molecular energies of individual asphalt components are evaluated as a function of physical aging factors. The factors for physical aging such as temperature and pressure are considered in a molecular dynamics simulation framework. The simulations are carried out by varying temperatures within the range from -35oC to 75oC and pressures within the range from 0.95 atm to 1.1 atm. The outputs of the simulations give a clear idea about the internal structure of molecules in liquid state. Simulation results show that physical aging process causes increase in bond stretching, angle bending, and torsion energy. Application of high temperatures results in high stretching of asphalt atoms. At high temperature intermolecular van der Waals repulsion increases. Pressure variation has negligible effects on intra and inter-molecular energy changes. From inversion energy values, the geometry of the molecules is found.

Using recycled asphalt pavement (RAP) in asphalt mixtures is common for improving sustainability, but it can lower performance because of the aging and hardening of RAP binder. Aged RAP is stiffer, less flexible, and more prone to cracking. The performance decreases with the age of RAP. Adding materials like nano-materials can help reduce these issues. This study investigates the combined impact of RAP content, RAP age, and Nano-silica (SiO₂) on asphalt performance, focusing on fracture resistance, fatigue resistance, and moisture susceptibility. Asphalt mixtures with 25%, 50%, and 75% RAP were tested using two types of RAPs with different ages (5 and 10 years). Nano-SiO₂ was added in varying percentages (0%, 1%, 1.5%, and 2%) to evaluate its effects. The performance was assessed using the semi-circular bending test for fracture resistance, the indirect tensile fatigue test for fatigue resistance, and the tensile strength ratio (TSR) test for moisture susceptibility. Results showed that Nano-SiO₂ improved the fracture and fatigue resistance of mixtures, especially those with lower RAP content. At 25% RAP, the addition of 1.5% and 2% Nano-SiO₂ enhanced fracture and fatigue resistance by 15-20%. For mixtures with 50% and 75% RAP, Nano-SiO₂ led to significant improvements, with the best results seen at 2% nano-silica. Nano-SiO₂ also enhanced moisture resistance, increasing TSR values above the 80% threshold. Nano-silica mitigated the effects of aging, particularly in mixtures with higher RAP content. According to this comprehensive evaluation, it is recommended to use 25-50% of RAP using 1.5% of Nano-SiO₂ to achieve high-performance mixtures.

Aging and rupture phenomena are important factors which decrease the useful life of asphalt. During the recent decade, by using the images with high spatial accuracy (less than 10 cm) the qualitative monitoring of roads’ surfaces has been achieved. The present study has been performed to evaluate the aging and rupture phenomena on asphalt surface and to evaluate the DSM, extracted from drone images, in asphalt quality control in Alvar-e-Sofla village, Tabriz, Iran. Hyperspectral imaging for three kinds of asphalt (less than 2 years, 4 to 7 years and more than 10 years old) revealed that the 2-year old asphalt has always lower graph than the others because, after a while, the asphalt bitumen losses its quality and gets lighter and thus its surface reflection increases. Calibration of selected learning points for distress shows overall accuracy of 95% and CAPA coefficient of 95, which reveals the high accuracy and correctness of the results. Also, high spatial accuracy (7. 5 cm) shows the ability to study type 2 and 3 ruptures, in addition to cracking-depth evaluation and stress via these images at centimeter scale. Results showed that the obtained DSM from overlapping of drone images has the ability to extract lateral slopes of pedestrian and streets, which are applicable in evaluation of asphalt subduction amount during the time. If this problem is fixed and the road slope is standardized, practically the flooding events in cold seasons will be reduced and useful life of asphalt will be increased.

Bitumen aging is one of the factors causing and spreading cracks and moisture damage in asphalt pavements. Aging can occur during the production, transportation, and construction stages (short-term aging) or the operation period (long-term aging) and can cause bitumen to harden. Today, various methods are defined to simulate short-term and long-term aging. In this study, the effect of long-term aging of AASHTO R30 (as the most common standard method) and NCHRP 9-54 (as the latest method) on the fatigue performance of asphalt mixtures was investigated at strain levels of 500 and 1000 microstrains, loading frequencies of 5,10,15, and 25 Hz and temperature of 200c using a 4-point bending beam test. The results showed that both aging methods increased the initial stiffness and decreased the fatigue life of the samples at the strain levels and loading frequencies tested. Also, by comparing the fatigue life of the tested samples, it was found that the greatest reduction in fatigue life was related to the aged samples by the AASHTO R30 aging method. According to these results, it can be said that AASHTO  R30 is a conservative method in comparison with NCHRP 9-54.

Factors such as bitumen volatile materials’ evaporation and oxidation during mixing with stone grains, its transport to the project site and also during pavement servicing will result in bitumen aging and could lead to some failures in asphalt pavements. As a consequence of aging, the bitumen will become brittle and some cracks can be observed on the pavement which lowers the driving quality and increases the repair and maintaining costs. Rutting is also one of failures which will result in decrease of travel safety, and increase of roads’ maintenance costs. Knowing about the characteristics of asphalt composition (bitumen and stone material) could be useful in design of pavements with longer life. Regarding this subject and also this fact that a few studies have addressed the effect of mixture’s physical properties on the resistance parameters of asphalt, in this study, the impact of stone material’s type on creep abilities of aged warm asphalt mixture is investigated. In this context, asphalt samples with two types of limestone and silica stone materials were fabricated and put under aging trend based on standard methods. Then, the samples underwent dynamic creep test in 100 and 300 kPa and temperature of 50 and 60oC and their stable strains were measured. Finally, the results were analyzed using MATLAB software and an empirical model for creep behavior of aged asphalt concrete with stone material type consideration was presented. The results showed that lime samples, in comparison with silica samples, are more resistant against time-dependent deformation.

Aging is one of the factors affecting the physical and chemical properties of bitumen. This factor can lead to moisture damage in the asphalt mixture. The objective of this study is to investigate the effect of short- and long-term aging on the moisture damage mechanisms of hot mix asphalt containing Wetfix using the Pull-off method. Two types of bitumen with different performance grades (PG 58-22 and PG 64-16) modified with Wetfix BE additive and two types of aggregate (limestone and granite) were used. First, the rheological properties of bitumens and the physical characteristics of aggregates were determined, and then the chemical compositions of aggregates were obtained through an X-ray fluorescence (XRF) test. After modifying the bitumens with Wetfix, the pull-off test was performed to determine the cohesion strength of bitumen and the adhesion strength of bitumen to aggregate on aged and unaged samples in dry and wet conditions. Short-term aging increased the cohesion strength and long-term aging caused a decrease in cohesion strength in wet conditions. Therefore, long-term aging leads to a decrease in bitumen performance in wet conditions and as a result, a decrease in pavement resistance against moisture damage. However, adding Wetfix increased the cohesion strength between 20-32% and 26-48% in short and long-term aging, respectively, and adhesion strength between 43-26% and 57-38% in short- and long-term aging, respectively. Comparing the effects of aging of base and modified bitumen on the reduction of adhesion and cohesion strengths shows that the addition of Wetfix not only eliminates the negative effects of aging on these parameters, but also improves the resistance of modified bitumen compared to base bitumen against moisture damage.