Laboratory Mix Design of Asphalt Mixture Containing Reclaimed Material

This paper presents a study on the production of asphalt test specimens in the laboratory containing reclaimed asphalt. The mixtures considered were stone mastic asphalt concrete mixtures containing up to 30% of reclaimed asphalt. Specimens were compacted to the reference density obtained from the Marshall mix design. Gyration compaction method was used for preparing specimens for the experimental programme, while coring and cutting methods and X-ray computed tomography (CT) were used to investigate the change in properties within the specimens and to validate the selected methodology. The study concluded that gyratory compaction is suitable to produce homogeneous test specimens also for mixtures containing high amount of reclaimed asphalt. Nevertheless, preliminary trials for each material are mandatory, as well as final coring and trimming of the specimens due to side effects. 1. Introduction The use of gyratory compactor for producing asphalt mixture specimens has been used preferably over other methods such as the Marshall hammer largely on the basis that it has a better control on compaction which provides a reliable way to evaluate the density of the mix design. The gyratory compaction process changes by varying the number of gyrations. The angle of the plates and the pressure are fixed by the manufacturer of the gyratory compactor according to EN 12697-31:2007 [1]. The required target density (for the design air voids) is fixed as input and compactor automatically apply certain number of gyrations to achieve the required density. The size of gyratory mould, uniformity over the sample, and the height/diameter ratio influence the air voids distribution and the density. In addition, the vertical air void distribution within the gyratory compacted specimen is different between the core section and the section close to the circumference. Higher air voids are observed in the circumference and evenly distributed compared to those within the core section [2]. Hence, specimen manufactured through gyratory compactor usually presents issues concerning the specimen’s homogeneity [3]. This arises from the fact that two replicates from nominally identical test specimens sometimes show a variation in their performance and hence the requirement to produce at least three replicates for verification. A homogeneous specimen has the same proportions or properties throughout its volume to create a consistent mixture for testing purposes and performance evaluation. Although air voids possess no mechanical strength, their distribution is crucial in determining the