Low-Temperature Performance of Asphalt Mixtures Under Static and Oscillatory Loading

Abstract

Nominal Maximum Aggregate Size (NMAS) significantly affects several mechanical properties of asphalt pavement both at low and high temperatures. Currently, aggregates with two NMAS, 9.5 and 12.5 mm, are widely used for surface layer in asphalt pavement. During the past decades, many agencies in the US have investigated the effect of NMAS aggregates on the field performance of asphalt mixtures. However, little research was performed to simultaneously evaluate the material behavior under static and oscillatory loading. This paper presents an experimental, laboratory-based, investigation to address the effect of two different NMAS aggregates, 9.5 and 12.5 mm, on the low-temperature properties of Hot Mix Asphalt (HMA). Two test types were selected for this purpose: Bending Beam Rheometer (BBR) mixture creep test, which is based on static loading, and Dynamic Shear Rheometer (DSR) mixture Complex Modulus test, which uses oscillatory loading. Based on the experimental data, Creep Stiffness, m-value (slope of logarithmic Creep Stiffness vs. time curve), Thermal Stress, Critical Cracking Temperature and Complex Modulus are calculated and, then, statistically and graphically compared. Significant differences in mechanical performance were observed between NMAS 9.5 and 12.5 mm HMA mixtures under static loading conditions. However, in case of oscillatory loading, mixtures prepared with softer binder showed smaller differences in Shear Complex Modulus, |G*|, between mixtures having NMAS 9.5 and 12.5 mm compared to mixtures with a stiffer binder. Air voids content (4 and 7 %) did not affect the measurement obtained with BBR and DSR except when aggregates with NMAS 9.5 mm and stiffer binders were used.