# Study on the Aging Behavior of Asphalt Binder Exposed to Different Environmental Factors
## 2 Materials and Methods
### Outdoor Exposure Test  
A comprehensive asphalt binder exposure test was conducted. The test site is situated in Dunhuang City, Gansu Province, characterized by a dry climate, minimal rainfall, significant day-night temperature fluctuations, prolonged sunshine hours, intense UV radiation, and radiation levels second only to Tibet. This region is famously referred to as \begin{table}
\begin{tabular}{c c c} \hline \hline
**Indictors** & **Results** & **Standard** \\ \hline Penetration (25 °C, 100 g, 5 s)/0.1 mm & 81.5 & 80–100 \\ Wax content/\% & 0.6 & \(\leq\)2.2 \\ Ductility (5 cm/min, 10 °C)/cm & 100 & \(\geq\)30 \\ Softening point/\({}^{\circ}\)C & 45 & \(\geq\)44 \\ Flashpoint/\({}^{\circ}\)C & 305 & \(\geq\)245 \\ Solubility (trichloroethylene)/\% & 99.8 & \(\geq\)99.5 \\ Mass change/\% & \(-\)0.13 & \(\leq\)\(\pm\)0.8 \\ Residual penetration & 64 & \(\geq\)57 \\ Aging test (163 °C, 5 h) & Residual ductility & 11 & \(\geq\)8 \\ Ratio/\% & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Fundamental properties of virgin asphalt binder. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Indictors** & **Results** & **Standard** \\ \hline Penetration (25 °C, 100 g, 5 s)/0.1 mm & 66 & 60–80 \\ Ductility (5 cm/min, 5 °C)/cm & 42 & \(\geq\)30 \\ Softening point/\({}^{\circ}\)C & 87.5 & \(\geq\)55 \\ Flashpoint/\({}^{\circ}\)C & 280 & \(\geq\)230 \\ Solubility (trichloroethylene)/\% & 99.5 & \(\geq\)99 \\ Elastic recovery (25 °C) & 80 & \(\geq\)65 \\ Storage stability (Softening point difference, 48 h) & 1.0 & \(\leq\)\(\pm\)2.5 \\ Mass change/\% & \(-\)0.4 & \(\leq\)\(\pm\)1.0 \\ Residual penetration & 75 & \(\geq\)60 \\ Aging test (163 °C, 5 h) & Residual ductility & \\ Ratio/\% & 30 & \(\geq\)20 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Fundamental properties of SBS modified asphalt binder. the \"World Wind Farm\", with maximum wind speeds reaching 25.2 m/s at 3 m, 24.16 m/s at 2 m, 18.76 m/s at 1 m, and a surface maximum of 12.85 m/s. Summers here scorch with temperatures exceeding 40 \({}^{\circ}\)C, and the average day-night temperature difference stands at 25.6 \({}^{\circ}\)C, peaking at 30 \({}^{\circ}\)C. Annual precipitation averages 39.9 mm, evaporation hits 2486 mm, and the yearly dryness index registers at 21.67, classifying it as an extremely arid climate zone. Sunshine hours exceed 3200 annually, with a cumulative annual radiation amount of 6800 MJ/m\({}^{2}\), earning it Class I status and a daily cumulative ultraviolet radiation value of 1.2347 MJ/m\({}^{2}\). These unique natural conditions, including extreme drought, frigid cold, strong winds, substantial temperature variations, and potent ultraviolet radiation, contribute to the intricate aging of asphalt binder, significantly impacting asphalt pavement performance. The exposure test involved positioning the samples 0.5 m above the ground, as depicted in Figure 1. After 3 months of outdoor exposure, the aged samples were recycled. The dimension of the samples exposed to outdoor was 16 cm \(\times\) 11.5 cm \(\times\) 0.32 cm. As illustrated in Figure 2, three distinct exposure modes were established. Mode 1 entailed a complete exposure test, where the asphalt binder samples remained unobstructed, fully exposed to the natural environment, and subjected to all environmental factors, including temperature, oxygen, light, wind, rain, dust, and more. This mode was also referred to as All-aging. Mode 2 involved covering the top of the samples by using a glass, exposing them to the effects of light, temperature, oxygen, and similar factors. This mode was labeled O+UV-aging. Mode 3 introduced a shade in the form of an impermeable plate above the asphalt binder samples, allowing them to experience only the effects of temperature, oxygen, and related factors, earning it the name O-aging. It is worth noting that the UV-transparent glass and the impermeable plate are not in direct contact with the binder. After aging from outdoor exposure, the surface of the aging sample was first rinsed with water.