# A Review of Nanomaterials' Effect on Mechanical Performance and Aging of Asphal Mixtures
## 7 Concluding Remarks  
This review addressed the effects of the modifications with nanomaterials: Nanosilica, nanoclay, and nanioron, on the mechanical properties of the asphalt mixtures. The studies about modification of asphalt binders with nanomaterials showed that if a correct dispersion of the nanomaterials in the asphalt matrix is attained, several properties can be improved. Regarding the properties of the asphalt binders, the modifications with nanomaterials brought a reduction in penetration value and an increase of viscosity and softening point, as well as, increase in complex modulus and a decrease in phase angle. The effects of the modifications are dependent on the type and dosage of the nanomaterial, as well as, on the properties of the original asphalt binder to be modified. The optimum nanomaterial dosage may be dependent on the mechanical property to be enhanced, as well as the cost of the modification. For example, softer binders attained higher gains in resistance to permanent deformation with the nanomaterials modification than harder binders. The effects of the nanomaterial modifications in the properties of the asphalt mixtures conducted to similar trends than for binders, meaning that the consideration of the type of modification is connected to the goal in terms of performance achieved for the best cost. The review carried out allows for the following conclusions:  
* For asphalt mixtures, the modifications with nanosilica present higher Marshall stability, higher indirect tensile strength, higher stiffness modulus, lower permanent deformation, enhanced fatigue resistance, and higher resistance to moisture damage. The studies found in literature covered the dosage range of 0.5% to 8%, and the effects of the modifications increase according with the increase in dosage. Nevertheless, the cost of the modification should be taken into account, as the use of high dosages can return not economical. * The effects of the modifications with nanoclays were dependent of the type of nanoclay. Besides the particle size distribution and the specific surface area, the type of treatment, raw (hydrophilic) or organically modified (hydrophobic), can have particular importance in the obtained effects. Generally, the effects of nanoclays modifications are higher Marshall stability, lower permanent deformation, higher stiffness modulus at high temperatures, better fatigue resistance, and higher resistance to moisture damage. The studies found in literature covered the dosage range of 1% to 7% and, the effects of the modifications increase according with the increase in dosage. Nevertheless, in the case of some organically modified nanoclays, the performance enhancement peaked at relatively low dosages (e.g. 2%) and a further increase in dosage worsened the performance. As the cost of organically modified nanoclays can be roughly double the cost of raw nanoclay, the use of such modifications should be careful optimized to ensure maximum performance with lowest dosage possible. * Currently, the modifications with nanioron are not as explored as those with nanosilica and nanoclays, nevertheless, several studies reported important improvements in the mechanical performance of the modified asphalt mixture, such as, higher Marshall stability, higher indirect tensile strength, higher resistance to moisture damage, lower permanent deformation, enhanced fatigue resistance, and fracture resistance. The optimum dosage of nanioron particles seems to be in the range of 0.8% to 0.9%, where the performance gains peak and, further increase in dosage worsens the performance. Comparatively to other nanomaterials, the lower optimum dosage of nanioron particles can make them more competitive from economic point of view. * Besides the improvements in mechanical performance, the nanomaterials also gave good indications regarding an enhanced aging resistance.