# A Review of Nanomaterials' Effect on Mechanical Performance and Aging of Asphal Mixtures
## 5 Aging Resistance
### Asphalt Mixtures
#### 5.2.2 Nanosilica  
[PERSON] et al. [58] aged the asphalt mixture using STOA and LTOA methods and, tested aged specimens for resilient modulus (RM) at 25 \({}^{\circ}\)C and 40 \({}^{\circ}\)C, and permanent deformation using the dynamic creep test. The authors found that the 4% nanosilica modification provided some aging resistance particularly at the long-term aging. Figure 15 presents the aging sensitivity of the parameters considered by the authors and under both aging methods.  
Figure 14: Example of the evolution of aging index.  
Figure 15: Aging sensitivity of the parameters considered in the study [58].  
[PERSON] et al. [24] produced LTOA aged specimens and conducted flexural tensile strength tests (three-point bending at -10 \({}^{\circ}\)C) and fatigue tests (four-point bending at 1000 \(\upmu\)m/m constant strain). To study the effects of aging the authors compared the results of flexural strength, flexural strain, and fatigue life of the unaged and LTOA aged specimens and, concluded that the 1% nanosilica modification had a positive effect in aging resistance. Figure 16 presents the aging sensitivity of the parameters considered.  
[PERSON] et al. [131] studied the effects of aging in the asphalt mixture using the TEAGE method [132], tuned to simulate seven years of field aging due to environmental conditions (UV radiation and precipitation) in the region of Lisbon. The aged mixtures were tested for indirect tensile strength (ITS), stiffness modulus, and fatigue, and the results were compared with those obtained under unaged conditions. The 4% nanosilica modified mixture presented lower aging sensitivity in all parameters, indicating an enhanced aging resistance (Figure 17).  
[PERSON] et al. [62] produced STOA aged specimens and compared their performance to that of unaged specimens. The authors evaluated the retained Marshall stability (RMS), using two conditioning methods: (1) 48 h immersion (IM) and (2) 48 h vacuum saturation (VS), and the tensile strength ratio (TSR). Analyzing the aging sensitivity of these parameters (Figure 18) it can be concluded that the modified mixture (3% silane silica) suffered less variation in these ratios. This indication is positive, although would be not sufficient to property conclude about aging resistance, as it would be possible that both specimens conditioned/unconditioned suffer intense aging thus maintaining approximately similar ratio under aged and unaged conditions. The analysis of Marshall stability or indirect tensile strength would be preferable.  
Figure 16: Aging sensitivity of the parameters considered in the study [24].  
Figure 17: Aging sensitivity of the parameters considered in the study [131].  
[PERSON] et al. [98] evaluated the abrasion of a porous asphalt mixture (NMAS 12.5 mm), under aged and unaged conditions, using the Cantabro test. The asphalt mixtures were produced with limestone aggregates, limestone filler, lime (0.5% by weight of mixture), and 60/70 asphalt binder modified with 4.5% SBS. The binder contents of the asphalt mixture were 5% and 6%. The authors used 0.2% glass fiber and 0.2 basalt fiber to modify the asphalt mixture and, following, studied the modification with 2% nanosilica. The specimens were conditioned for aging in a draft oven at 60 \({}^{\circ}\)C for seven days. In the mixture with 0.2% glass fiber, the modification with 2% nanosilica presented a reduction in Cantabro loss from 10.1% (control) to 4.4% (modified) and, from 7.7% (control) to 3.5% (modified), for binder content of 5% and 6%, respectively. In the mixture with 0.2% basalt fiber, the modification with 2% nanosilica presented a reduction in Cantabro loss from 10.7% to 5.5% and, from 8.9% to 4.7%, for binder content of 5% and 6%, respectively.  
Under a variety of mechanical tests and aging methods, the asphalt mixtures modified with nanosilica presented systematically lower aging sensitivity if compared to the correspondent control mixture, indicating enhanced aging resistance.