# 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
### Nanoclay  
In the studies of asphalt mixtures modified with nanoclays, several improvements in the mechanical performance were identified. Generally, the effect reported by the authors were: Increase in Marshall stability, reduction in permanent deformation, lower water sensitivity (increase in indirect tensile strength ratio and/or retained Marshall stability), increase in stiffness modulus/resilient modulus, and better resistance to fatigue. Although the findings are generally consistent, the big variety of materials leads to different effects in mechanical performance. The nanoclay type, the modification of raw nanoclay with organo-modifiers, the nanoclay dosage and the original asphalt binder properties can have a strong influence in the results. The following paragraphs describe the most relevant studies found in the literature and their more important conclusions. [PERSON] et al. [94] studied an asphalt mixture (NMAS 12.5 mm) with 5.7% binder content, using two different binders, PG 58-28 and PG 64-28 (control binders), and modified with an organically modified nanoclay (cloisite) with the dosages of 1%, 3%, and 5%. The authors tested for permanent deformation using the asphalt pavement analyzer rut test (APA), and concluded that the resistance to permanent deformation increased with the nanoclay dosage (Figure 7). The effect of the modifications in the softer binder (PG 58-28) was stronger that in the harder binder (PG 64-28). The modifications with 5% nanoclay presented a reduction of 57% and 38% with the PG 58-28 and PG 64-28, respectively. [PERSON] [40] studied the effects of three nanoclay modifications in the performance of a SMA mixture. The SMA mixture (NMAS 12.5 mm) was produced with 6.1% binder content and, basalt aggregates and asphalt binder 50/70 (control binder) were used. The author introduced the nanoclay as a partial substituent of the mineral filler, and not by previously blending with the asphalt binder. In this case, the nanoclay dosages were 2%, 3.5%, and 5% by mass of dry aggregates. The author modified raw bentonite clay with three organic modifiers, obtaining three organically modified clays: Nanoclay A--modified with dimethyl, dehydrogenated tallow, quaternary ammonium (NC A); nanoclay B--modified with methyl, tallow, bis 2 hydroxyethyl quaternary ammonium (NC B); and nanoclay C--modified with dimethyl, benzyl, hydrogenated tallow, quaternary ammonium (NC C). The author evaluated water sensitivity using the modified Lottman test at 25 \({}^{\circ}\)C, and observed: With nanoclay A the indirect tensile strength increased by 14%, 20%, and 3%; with nanoclay B the indirect tensile strength increased by 11%, 20%, and \(-\)2%; and with nanoclay C the indirect tensile strength decreased by 11%, 14%, and 17%, for 2%, 3.5%, and 5% dosages, respectively. The indirect tensile strength results corresponding to the 2% modifications are presented in Figure 8. Regarding the indirect tensile strength ratio, for all the nanoclays, the highest ratio corresponded to the 2% dosage (Figure 9). The ratio presented a trend of decrease with the increase in dosage, in such way, with 5% dosage all nanoclays performed worse that the control mixture. The author evaluated permanent deformation at 40 \({}^{\circ}\)C using the dynamic creep test, applying 100 kPa load for 21,600 pulses. The nanoclay A enhanced the resistance to permanent deformation, presenting a reduction of 9%, 10%, and 36% for 2%, 3.5%, and 5% dosages, respectively. The mixture modified with nanoclay B performed worse that the control mixture, presenting an increase in permanent deformation of 30%, 40%, and 51% for 2%, 3.5%, and 5% dosages, respectively. The behavior of the mixture modified with nanoclay C was more complex, presenting 12% increase with 2% dosage, 29% reduction with 3.5% dosage, and similar to control with 5% dosage. Figure 8: Indirect tensile strength of control and nanoclay modified asphalt mixtures. Figure 7: Effect of nanoclay dosage on rut depth [94]. [PERSON] [31] and [PERSON] et al.