# Effect of Nano Hydrolcite on the Aging Resistance of a High Binder Content Stone Mastic Asphalt
## 1 Introduction  
Asphalt pavements are a key element of the transport infrastructure, usually, being the dominant structure of the road network. During service life, pavements have to withstand a variety of traffic loads and environmental conditions (e.g., temperature variation, solar radiation, moisture, and oxidation) that will degrade their initial performance. Besides costly, the maintenance of these infrastructures is challenging due to the consequent disruptions in mobility and safety risks. Recent research in pavement engineering is focusing in improving the performance of the materials from economic, environmental and mechanical standpoints. The surface courses are particularly important because of the direct contact with traffic. The asphalt mixtures applied in surface layer must perform well to provide adequate safety and comfort, coping with exigent requirements for skid resistance and permanent deformation, among others. Moreover, aging is particularly severe in pavement surface courses because they are directly exposed to the environmental conditions. Besides the conventional asphalt concrete (AC), over the years, other types of asphalt mixtures have been developed, for instance, the Stone Mastic Asphalt (SMA) and the Porous Asphalt (PA). In addition, to enhance the performance of these mixtures during the pavement service life, a variety of additives was studied. In particular, SMA is a gap-graded asphalt mixture that exhibits good performance, especially for application in surface courses due to their high resistance to cracking andrutting. The key factor contributing to SMA improved performance is the aggregate interlocking that promotes stone-on-stone contacts in the coarse particles, which does not occur in conventional dense mixes with continuous gradations, and increases resistance to permanent deformation [1; 2; 3]. In addition, the high bitumen mastic fulfilling the SMA voids can also enable durability in the long-term pavement life cycle. The improved mechanical and surface characteristics of SMA are responsible for the increased gain of interest in this type of asphalt mixture for application in pavement construction, mainly in heavy-trafficked areas. The asphalt binder, also designated as bitumen, is a material prone to aging that suffers a deterioration of its properties over the time which affects the performance of respective asphalt mixture [4]. As in many cases conventional bitumen no longer ensures acceptable performance and to address environmental and economic concerns, several modifications (i.e., additives) were developed: temperature reduction (warm mix technology), elasticity (polymers), adhesion improvers, rejuvenators, fibers, and rubber [5; 6; 7; 8; 9; 10; 11; 12]. Recently, in attempt to enhance aging resistance, the self-healing technology is being developed. Three self-healing technologies are currently available: nanoparticles, reheating, and rejuvenation [7; 13; 14; 15; 16; 17]. The use of nanomaterials as additives for asphalt mixtures already demonstrated several benefits regarding mechanical performance and aging resistance [13; 18; 19; 20; 21]. Generally, the nanomaterials more frequently studied are the nanosilica and nanoclays. Hydrotalcite is considered a layered double hydroxide (LDH) [22; 23]. The LDH are ionic lamellar materials composed by positively charged brucite-like layers of organic-inorganic or inorganic nanomaterials. Compared to conventional clays mineralogical structure, the LDH possess stronger interactions interlayers thus becoming less prone to delamination. Some research studies have already identified potential applications of LDH in concrete materials [24; 25]. Regarding asphalt binders, the use of LDH has also been investigated in last recent years, especially due to the barrier properties. Such property can give protection against ultraviolet radiation, delay oxidation, and retard the loss of volatiles, consequently enhancing the aging resistance of the binder [26; 27; 28; 29; 30; 31; 32; 33; 34].