Benchmarking Contiguous Aggregate Ratios with Asphalt Compactability and Rut Resistance

ABSTRACT Aggregate packing is the primary determinant of the shear strength, stiffness, and durability of asphalt mixes. The current asphalt mix design practices emphasize using aggregate gradation envelopes as control mechanisms to achieve an enhanced aggregate packing structure with optimum shear strength, durability, and stiffness, and to guarantee rutting resistance. However, experience in South Africa has shown that the bias toward rut-resistant mix designs often leads to compactability problems. The significant knowledge embedded in the basic aggregate gradation curve has the potential to improve the understanding of the compactability and rut resistance of asphalt mixes. Based on the well-known Bailey method, the basic aggregate grading curve is used in this paper to determine various revised rational Bailey ratios (RBRs) that adhere to the contiguous aggregate fractions (i.e., aggregate with consecutive sizes). The determined ratios demonstrated a better description of the aggregate packing. The subsequent correlations analysis performed in this paper indicated that the revised RBRs exhibit strong relationships with compactability (i.e., R2 up to 0.99) and rutting resistance (i.e., R2 up to 0.81) of asphalt mixes. The research work presented in this paper indicates that the revised RBRs can be used to optimize asphalt mix designs via benchmarking methodology. Ranges of the revised rational Bailey parameters for such a benchmarking methodology are proposed to enhance the asphalt grading selection and mix design process.