# 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 that conducted studies about nanosilica modified asphalt mixtures, reported important improvements in the mechanical performance of the mixture. To evaluate the asphalt mixture performance, the mechanical tests most found in literature were Marshall stability, water sensitivity (using the indirect tensile strength ratio or the retained Marshall stability), permanent deformation, and stiffness. The Figures 2-6 present the results found in several studies. \"Control\" refers to the mixtures with 0% of nanosilica and, \"Modified\" refers to the modification performed by each author. [PERSON] [95] studied an asphalt concrete, AC 14 Surf 35/50, using limestone filler, basalt aggregate, and considering two binder contents, 5.5% and 6.5%, with three nanosilica modifications, 2%, 4%, and 6%, respectively. From Marshall tests results the author observed, for both binder contents, that the peak of Marshall stability corresponded to the 4% nanosilica modification and, across the dosage range, a decrease of the Marshall flow related with the increase of the nanosilica dosage. The results of [PERSON] [95] presented in Figure 2 correspond to the 6.5% binder content mixture with 4% nanosilica modification, that caused an increase of 19% in Marshall stability. [PERSON] et al. [96] performed Marshall tests in cores from two test tracks, (1) using as binder a neat bitumen AH-70 (penetration grade 60/70) modified with 5% of styrene-butadiene-styrene (SBS), and (2) using as binder the same neat bitumen (AH-70) modified with 5% styrene-butadiene-rubber (SBR), 0.5% nanosilica, and 1% polyethylene. The formula of the nanosilica-polymers modified mixture was determined through an orthogonal experiment. The authors concluded that a small amount of nanosilica could enhance significantly the performance of the polymer-modified binder. Regarding the Marshall stability results, with the nanosilica-polymers modification an increase of 28% was obtained (Figure 2). [PERSON] et al. [21] studied a stone matrix asphalt (SMA), with aggregate maximum nominal size 19 mm and 6.3% binder content, modified with various percentages of nanosilica (0.5%, 1.0%, 1.5%, and 2.0%). The control binder used in the study was a 60/70 penetration grade bitumen modified with 5% SBS. The authors tested the asphalt mixtures for Marshall stability, indirect tensile strength, and indirect tensile stiffness modulus. The effects obtained in the tests increased according with the increase of nanosilica dosage. Thus, the mixture with 2% nanosilica had the most improved mechanical behavior. Regarding the 2% nanosilica modification, the Marshall stability increased 68% (Figure 2), indirect tensile strength increased 19% (Figure 3), and indirect tensile stiffness modulus increased 47%. Figure 2: Marshall stability of control and nanosilica modified asphalt mixtures. [PERSON] et al. [62] studied an asphalt mixture modified with 3% silane silica (nanosilica modified with silane coupling agent). The neat binder was the Panjin 90 (penetration grade 70/100) and alkaline aggregates were used for the mixtures production. The modified mixture presented 24% increase in Marshall stability (Figure 2) and 26% increase in dynamic stability number (rutting test). To address water sensitivity, the authors performed Marshall tests in specimens conditioned for 48 h immersion (IM) and for 48 h vacuum saturation (VS) and determined the respective retained Marshall stability. With both conditioning methods, the modified mixture performed better than the control (Figure 4). [PERSON] et al. [58] studied an asphalt mixture (NMAS 19 mm) with PG 76 polymer-modified binder and modified with 2% and 4% nanosilica. For the mixture production, granitic aggregates were used, and the selected binder content was 7.5%. The effects obtained with the modifications were sensitive to the nanosilica dosage. Thus, the 4% modification had the highest effects in the mechanical performance.