# A Review of Nanomaterials' Effect on Mechanical Performance and Aging of Asphal Mixtures
## 4 Effect of the Modification with Nanomaterials in the Mechanical Performance of Asphalt Mixtures
### Nanosilica
The authors evaluated water sensitivity using the tensile strength ratio and concluded that the 4% nanosilica modification enhanced significantly the behavior of the mixture, raising TSR from 82% to 98% (Figure 5). Regarding resilient modulus, the 4% modification lead to 74% and 142% of increase (Figure 6), at the temperatures of 25 \({}^{\circ}\)C and 40 \({}^{\circ}\)C, respectively. Testing for dynamic creep, a 42% reduction in permanent deformation was observed. [PERSON] and [PERSON] [20] studied an asphalt mixture (NMAS 12.5 mm) modified with 2%, 4%, 6%, and 8% nanosilica. The control binder was the 60/70. The optimum binder content (OBC) was calculated using the Marshal methodology, and the results showed a decrease in OBC proportional to the increase in nanosilica dosage. The OBC values were 5.5%, 5.3%, 5.2%, 5.0%, and 4.9% for the 0% (control mixture), 2%, 4%, 6%, and 8% nanosilica modified, respectively. Regarding the performance tests, the effects obtained with the modifications were sensitive to the nanosilica dosage thus, the 8% nanosilica modification had the highest effects. Concerning the 8% modification, the modified mixture presented 31% increase in Marshall stability (Figure 2), 37% increase in resilient modulus (Figure 6),  
Figure 4: Retained Marshall stability of control and nanosilica modified asphalt mixtures. Figure 3: Indirect tensile strength of control and nanosilica modified asphalt mixtures. 30% increase in indirect tensile strength, decrease in indirect tensile strength ratio from 98% to 73% (Figure 5), 71% increase in flow number (lower permanent deformation), and better fatigue resistance (18% increase in the strain for 10\({}^{5}\) cycles). As the authors produced the modified mixtures using the respective OBC, the decrease in water sensitivity (indirect tensile strength ratio) can be partially explained by the higher air void content of the nanosilica-modified mixtures (4.47% air void content in control mixture versus 5.93% air void content in 8% nanosilica modification). [PERSON] et al. [22] studied an asphalt mixture with PG 58-34 with acrylonitrile-butadiene-styrene (control binder) and modified with 4% and 6% nanosilica. The effects obtained were dependent of the nanosilica dosage. Thus, the 6% modification had the highest effects in the mechanical performance. Regarding the 6% modification, the authors reported 30% increase in the dynamic modulus, 34% reduction in permanent deformation (evaluated with the asphalt pavement analyzer rutting test) and 27% increase in resilient modulus (Figure 6). [PERSON] et al. [25; 36] studied an asphalt mixture (AC 14) with granitic aggregates, limestone filler, and 4.5% binder content. The selected binder was the 35/50 penetration grade (control binder) and the nanosilica dosage was 4%. The author concluded that the 4% nanosilica modification enhanced the mechanical performance of the mixture and reported the following effects: 11% increase in Marshall stability (Figure 2); improvement in retained Marshall stability from 77% to 98% (Figure 4); 59% increase in indirect tensile strength (Figure 3); improvement in indirect tensile strength ratio from 57% to 70% (Figure 5); better affinity aggregate-binder (more 10% of binder coverage); 34% reduction in permanent deformation; 4% and 18% average increase in stiffness modulus at the temperature of 20 \({}^{\circ}\)C and 30 \({}^{\circ}\)C, respectively; and better fatigue resistance (4% increase in the strain for 10\({}^{6}\) cycles). [PERSON] et al. [24] produced an asphalt mixture (AC 16) with limestone aggregates and 60/70 penetration grade bitumen and studied the modification with 1% nanosilica. The authors reported the following effects: 27% increase in Marshall stability (Figure 2); 14% reduction in permanent deformation;  
Figure 5: Indirect tensile strength ratio of control and nanosilica modified asphalt mixtures. Figure 6: Resilient modulus of control and nanosilica modified asphalt mixtures.