# A Review of Nanomaterials' Effect on Mechanical Performance and Aging of Asphal Mixtures
## 5 Aging Resistance  
### Asphalt Binder  
The organic nature of the asphalt binder leads to a continuous non-reversible aging process. During the aging process, the chemical composition of the asphalt binder changes, generally, the asphaltenes content tend to increase, while resins and aromatics tend to decrease [1]. Regarding the properties of the binder, the aging process is most prominent in the form of hardening and brittleness. The aging of the asphalt mixtures is highly dependent on the aging of the asphalt binder thus, several methods were developed and standardized to simulate in laboratory the aging of the asphalt binder. Actually, the paving industry relies on such methods to establish criteria for the paving grade bitumen in Europe [105] and for the performance-graded asphalt binders in USA [106]. Also, due to its convenience, less time, and material consuming, researchers frequently only study aging at the binder level. The aging methods more frequently used are the rolling thin film oven test (RTFOT), thin film oven test (TFOT), and pressure aging vessel (PAV). The RTFOT is considered to be representative of the short-term aging (corresponding to the plant mixing and field compaction processes) and PAV is added to simulate long-term aging. After the aging simulation, the properties of the aged binder can be compared with those of the unaged binder. Generally, researchers consider parameters such as retained penetration--RP (Equation (1)), increase in softening point--ISP (Equation (2)), viscosity aging index--VAI (Equation (3)), DSR rutting parameter (G*/sin&), and DSR fatigue parameter (G*sin&). \[\text{RP}=\frac{\text{Aged penetration value}}{\text{Unaged penetration value}}\times 100 \tag{1}\]  
\[\text{ISP}=\text{Aged softening point value}-\text{Unaged softening point value} \tag{2}\]  
\[\text{VAI}=\frac{\text{Aged viscosity value}-\text{Unaged viscosity value}}{\text{Unaged viscosity value}}\times 100 \tag{3}\]  
Regarding the properties of the asphalt binder, the aging process causes an increase in viscosity and softening point and a reduction in penetration value. From the rheology perspective, the aging process causes an increase in the complex modulus and a decrease in the phase angle. Several authors highlight the positive contributions of nanomaterials to aging resistance. The presence of nanomaterials may play an important role in improving the asphalt mixture aging resistance by two mechanisms, first they may act as a barrier thus retarding the oxidation process and second as they can prevent the evaporation of light components of the asphalt [53]. [PERSON] and [PERSON] [34] studied the 60/70 asphalt binder modification using two types of organically modified nanoclay, cloisite, and nanofil, with the dosages of 2%, 4%, and 7%. The modifications lead to higher RP and lower ISP values, indicating less effect of aging in the binder. The enhancement in aging resistance was increasing according to the increase in nanoclay dosage (Figure 13). Regardless of both nanoclay were organically modified, the obtained effects were dependent of the nanoclay type. According with both parameters, RP and ISP, the modifications with nanofil were more effective in enhancing aging resistance. Other studies concerning nanoclay modifications, reported similar trends, increase in RP and reduction in ISP and VAI [79; 84; 107; 108; 109; 110]. [PERSON] [31] and [PERSON] et al. [99] studied the effects of organically modified nanoclay in the rheology of two asphalt binders. The authors selected 6% nanofill to modify the 70/100 asphalt binder and, 3% and 6% cloisite to modify the 40/60 asphalt binder. After short-term and long-term aging, in DSR testing the modified binders showed smaller variations (smaller increase in stiffness and smaller reduction of phase angle) when compared with the unaged modified binder, which means less  
Figure 13: Retained penetration and softening point increment of two nanomodified binders [34]. aging effect.