Laboratory Mix Design Procedure for Foamed Bitumen Mixtures

The primary objective of this study was to propose a practical and consistent mix design procedure for foamed bitumen mixture (FBM). The main focus of the proposed methodology was the use of the gyratory compaction method. The study maximized the mix design parameters, such as mixing water content (MWC) and compaction effort. The study was initially carried out on FBMs with virgin limestone aggregate without reclaimed asphalt pavement (RAP) material, and a mix design procedure was proposed. The proposed methodology was validated on FBMs with 50% RAP and 75% RAP. Efforts were also made to optimize the foamed bitumen (FB) content in FBMs with and without RAP. Optimum MWC was achieved by optimizing mechanical properties such as indirect tensile stiffness modulus and indirect tensile strength (ITS-dry and ITS-wet). A rational range of 75% to 85% optimum water content was obtained by the modified Proctor test and found to be the optimum range of MWC that gave optimum mechanical properties for FBMs. The study used a gyratory compactor for FBM compaction and found that a unique, mixture-specific number of gyrations that was independent of the FB content could be established. The study also found that the presence of RAP influenced the design's FB content: treating RAP as black rock in FBM mix design was not appropriate.