Impact of sustainable additives on the thickness of the wearing course in flexible pavements: a comparison between design methodologies in Brazil

In Brazil, the traditional pavement design method by the National Department of Infrastructure and Transportation (DNIT) overlooks the mechanical performance of asphalt mixtures. As technological advancements in asphalt materials continue, understanding how variations in asphalt mixture compositions affect pavement durability and thickness using the new National Pavement Dimensioning Method (MeDiNa) is crucial. This study evaluates the impact of sustainable additives in asphalt mixtures (such as viscosity reducers, encapsulated rejuvenators, reclaimed asphalt pavement (RAP), and banana fibers) on wear layer design using both the empirical DNIT and mechanistic-empirical MeDiNa methodologies. Results indicate that wear layer thickness determined by DNIT is lower compared to the MeDiNa approach. This is evident from the analysis of asphalt mixtures with viscosity reducers and encapsulated rejuvenators, where most exhibit fatigue class zero, leading to thicker pavement layers compared to mixtures classified in fatigue classes 3 and 4. Mixtures incorporating sunflower oil, carnauba wax, canola oil, and beeswax failed to meet MeDiNa’s criteria for permanent deformation under medium traffic, indicating inadequate performance concerning plastic deformation. RAP-added asphalt mixtures predominantly exhibit fatigue classes 3 and 4, except those incorporating cottonseed oil, confirming that oil additions do not benefit asphalt pavement in terms of thickness and fatigue performance. Stone Matrix Asphalt (SMA) mixtures demonstrated superior fatigue resistance, with SMA mixtures containing banana fibers showing the thinnest layers and fatigue classes ranging from 2 to 4. This suggests better performance compared to other types, potentially reducing pavement construction costs.