# Effect of Nano Hydrolcite on the Aging Resistance of a High Binder Content Stone Mastic Asphalt
## 4 Conclusions  
This study is a contribution to fill a gap in knowledge regarding the effects of the modification with nano hydrotalcite in the properties of an asphalt mixture, particularly, surface characteristics, mechanical performance, and aging resistance. The asphalt mixture under study was a binder-rich Stone Mastic Asphalt with an aggregate upper sieve size of 8 mm. The used binder was a polymer-modified bitumen (PMB 45/80-65) and the binder dosage was 7.5% by mass. Two asphalt mixtures were studied, one using the supplied binder, and other using the supplied binder modified by adding 3% of nano hydrotalcite. To evaluate the performance of the asphalt mixtures a laboratory study was conducted, involving testing for skid resistance, mean texture depth, indirect tensile strength, water  
Figure 5: Fatigue lines of the control (**a**) and modified (**b**) SMA 8 in unaged and aged conditions. Figure 6: Complementary results of the fatigue tests: \(\varepsilon_{5}\) (**a**) and slope of the fatigue line (**b**). sensitivity, stiffness, and resistance to fatigue. To evaluate the effects of aging, both asphalt mixtures were aged under the LTOA method and subsequently tested for indirect tensile strength, water sensitivity, stiffness, and resistance to fatigue. The obtained results indicated that the asphalt mixtures presented adequate surface characteristics and mechanical performance for application in surface courses. Regarding surface characteristics, the modified asphalt mixture presented approximately similar behavior to the control materials, having higher skid resistance and lower mean texture depth. Regarding the initial mechanical performance (unaged conditions), the modified asphalt mixture presented a softer behavior, as indicated by a lower stiffness modulus. The most relevant enhancement of the modification was the increase in the indirect tensile strength and water sensitivity (with an ITSR of 100%). The modification with nano hydrotalcite did not present clear contributions regarding a potential enhancement in aging resistance. To assess the effects of aging, the evolution of several mechanical performance parameters, between the unaged and aged conditions, was quantified. However the modified asphalt mixture presented smaller evolution in the fatigue resistance parameters, in the remaining tests the trends were not clear, or actually slightly worse than the control material. The aged asphalt mixtures presented a more stiff and brittle behavior. As expected, after the aging process, the indirect tensile strength and stiffness modulus increased, and, the phase angle and resistance to fatigue decreased. If compared to conventional surface course asphalt mixtures, the binder-rich SMA tended to present better initial mechanical performance (under unaged conditions). Regarding aging, the binder-rich SMA presented smaller variation in the parameters between unaged and aged conditions, which indicates enhanced durability if compared to conventional asphalt mixtures. Future studies will evaluate aging mechanisms under more field-like conditions, such as, the combined effects of temperature, solar radiation, and moisture damage. The paper intended to give a contribution to the research and development of the bituminous mixtures nanomodification. It is a very promising technology regarding more sustainable and long life transportation infrastructures. The results presented in the paper have validated the techniques implemented in laboratory concerning the production and testing of this type of modified bituminous mixtures. However, some important challenges must be faced in near future to promote the generalized development and implementation of this technology in engineering practice. It is the case of supply form and cost of nanomaterials. Conceptualization, J.C. and J.N. ; methodology, J.C. and J.N. ; investigation, J.C. and J.N. ; writing--original draft preparation, J.N. ; writing--review and editing, J.C. and J.N. ; supervision, J.C. and J.N.