## 1 Aim of the Work  
This work is far from being a review of the state-of-the art technologies, methods and materials used for using nanoparticles-containing bitumens and asphalts. For this, specialised textbooks, good reviews, and interesting research articles are present. They can furnish all the necessary information. This work is, instead, a critical presentation of this field, introducing the reader to the properties of nanoparticles and their use to improve the properties of bitumens and asphalt concretes. For this purpose, the various kinds of nanoparticles (nanosilica, nanoceramics, nanoclays, and even organic nanoparticles or inorganic nanoparticles surface-functionalised) used in this field will be rationally classified and presented. The added-value properties they confer to bituminous materials will be critically discussed, highlighting at the same time both positive and negative aspects, costs included. The purpose is to furnish useful and critic comparisons, suggestions and perspectives. This work is therefore a thought commentary on all the aspects involved in this topic, from the physical origin of the emergence of novel properties, to the principles to be followed to choose the most appropriate technique of investigation, according to the complex nature of the material involved and according to the specific chemical aspect needing investigation. The aim of the work is then to provide a panoramic view of the state-of-the art, making useful criticisms and giving comments and suggestions, to make researchers conscious of several hidden aspects that can be hardly found in standard research articles (for instance how to analyse IR spectra, how to improve the excitonic absorption to make bitumens resistant to UV radiation, how to investigate the distribution of nanoparticles in the bulk state rather than in the surface as usually done by standard microscopies, the eternal costs/benefits struggle, need of interdisciplinary works etc.). To do so, the work will follow this logical scheme: we first show (Sections 2 and 3) the peculiar properties of bitumens and how they can be improved by the use of nanoparticles and why; then we present the problems to be faced: the issue of nanoparticle stabilization and the cost involved. To show how to face these problems, we will present the possible solutions to obtain a reasonable cost/benefit equilibrium, in order, from the cheapest solution (use of inorganic nanoparticles), gradually moving to surface-functionalized nanoparticles up to the use of organic nanostructures (Sections 4-6). Then, we will comment the added values conferred by the nanoparticles (Section 7) and the experimental methods for a proper characterization (Section 8), to finally conclude with future perspectives as we see them (Section 9).  
It is our conviction that literature is quite rich in experimental works related to the use of nanoparticles in bitumens, but it is still relatively poor in works critically commenting the state-of-the art and offering different points of view especially on the basis of the fascinating fields of molecular physics and the physics of complex systems. We hope that this contribution could finally tickle researchers' curiosity and stimulate their imagination in the piloted design of material for road pavements with ever-increasing performances.