## 4 Conclusions  
This study aimed to evaluate the influence of the aggregate skeleton gradation on the cracking resistance of asphalt concrete mixtures, especially those used in thin overlays. To investigate the effect of aggregate skeleton gradation, it was considered that aggregate gradation can be divided into two main factors: (1) fine fraction content and (2) nominal maximum aggregate size (NMAS). For each stage, different gradations were designed and manufactured with two different types of asphalt binders, a conventional binder, B35/50, and a polymer modified binder, PMB 45/80-65, and Fenix tested in a temperature range between \(-5\) and \(20\)\({}^{\circ}\)C. Based on the findings, the following conclusions can be drawn:  
* The Fenix test showed enough sensitivity to compare cracking performance between the designed gradations. This test allowed the performance of all the mixtures to be evaluated under different test temperatures and relatively quickly. Figure 11: Displacement at 50% of post-peak load versus temperature. * The correlation between the aggregate skeleton gradation and the cracking performance of asphalt concrete mixtures was established. Not only temperature and asphalt binder nature have a strong influence on the cracking resistance of asphalt mixtures, but also aggregate skeleton gradation. * Asphalt concrete manufactured with PMB 45/80-65 presented an enhanced performance due to its greater ductility but as temperature drops, the performance of all the mixtures tends to converge due to the hardening process that asphalt binders suffer. * Regarding the fine particles content, the results show a significant correlation between the fine fraction content and the measured cracking parameters. For the same asphalt binder content, asphalt mixtures manufactured with a lower content of fines aggregates resulted in a further improvement of the toughness of the mixture. Accordingly, it can be stated that the asphalt mastic and the fine fraction content have a considerable influence on the cracking resistance of asphalt concrete for thin layers. * Regarding the influence of the NMAS, a correlation between the NMAS and cracking response of asphalt concrete has also been obtained. Indeed, as the NMAS increases so does the stiffness of the mixtures. * It should be noted that the established correlations shall not be used to describe the cracking behavior of asphalt concrete mixtures, but to compare the relevance between the studied properties. Based on the obtained equations for the displacement at 50% of post-peak load and comparing the regression coefficients of each equation, it can be concluded the fine fraction content exerts a stronger influence on the ductility of the mixture compared to the NMAS. The obtained results reflect the importance of considering not only the effect of the asphalt binder nature and the environmental conditions but also the aggregate skeleton gradation in the design of asphalt concrete mixtures, especially those used in thin overlays, to achieve a desirable cracking performance. In particular, special attention should be paid to the fine fraction content when designing an asphalt concrete mixture. According to the results, mixtures designed with a reduced NMAS and a low content of fine aggregated experienced a further improvement of their toughness. Formal analysis, L.G.-G.; Investigation, L.G.-G.; Methodology, R.M. ; Project administration, R.M. ; Supervision, R.M., and F.E.P-J. ; Validation, R.M. ; Visualization, L.G.-G.; Writing original draft, L.G.-G.; Writing review and editing, R.M.