Impact of hydrated lime on the durability of SMA mixtures: laboratory and field evaluation

The work presented in this paper describes the research activities of the task group Properties of filler aggregates' with respect to the durability of Stone Mastic Asphalt (SMA) mixtures, which was conducted recently at the Belgian Road Research Centre. The main objective of this study comprises the effect of hydrated lime on the durability of SMA mixtures. The methodology developed in this study includes in an initial phase the design in the laboratory of a critical' SMA10 mixture. Such a critical' SMA10 mixture was considered to be characterised by a high water sensitivity and, therefore, a low durability. During this process, attention was paid to both the SMA composition as well as to the compaction energy applied in order to provide suitable test samples. Subsequently, by making use of such a critical' SMA10 mixture, the effect of the filler nature on the durability of the SMA mixtures was established; in particular both the modification by as well as the optimal content of hydrated lime was studied. Additionally, the possible effect of hydrated lime on the workability of latter SMA mixtures was investigated. Finally, the results obtained in the laboratory were complemented by a field study and a monitoring campaign. This survey comprises the evaluation of the impact of hydrated lime on the compactibility and the water sensitivity on test sections as well as a yearly follow up of the performance of a series of SMA10 mixtures varying in the type of filler material used.