A multi-scale approach to interpret Hot Mix Asphalt (HMA) creep behaviour at intermedate temperatures

Abstract

Nowadays, heavy traffic levels and climatic changes combination can lead to a premature pavement failure. This phenomenon is usually due to the accumulation of permanent deformations. In the last few years, the aptitude of hot mix asphalt (HMA) pavements to accumulate the permanent deformation has been linked to the asphalt binder behaviour. But, as it is deeply-rooted into the pavement-scientific community, the HMAs' "glue", the so called mastic, plays a key role on the mechanical and cracking behaviour of HMAs. The mastic is defined as the combination between filler (up to 0.075 mm) and the asphalt binder. Consequently, this dissertation try to open the possibility of studying the accumulation of the permanent deformations directly on mastics using a new tensile creep test. The pursuit of the proposed objective aims at introducing a multi-scale approach for the creep behaviour. Therefore, the mastics properties have been compared with the HMA cracking and mechanical behaviours to understand and distinguish the role of the mastic phase and its components on the performance level of the HMAs. In order to achieve the targeted aim, three different categories of fillers (by-product, conventional, and reclaimed) were involved in the research activities. The mentioned filler groups represent the Ladle Furnace Steel (LFS) slags, which were hydrated and not hydrated, the limestone and the limestone-based materials, and the Reclaimed Asphalt Pavement (RAP) (50\% and 20\% by the weight of the aggregates were used), respectively. Those were combined with two asphalt binders, neat and SBS modified, to prepare mastics and HMAs. To obtain the creep parameters, mastics were evaluated using the standard test MSCR at 64 °C, applying 3.20 kPa and 0.10 kPa as shear stresses, and a new experimental testing method performed at 7 °C using 60 N as tensile load, which was applied for 180 seconds. While, the HMAs were tested performing the Superpave protocol at 10 °C. Successively, the obtained parameters of mastics were compared with the energetic and the creep parameters of HMAs. The energetic characterization was done using the HMA fracture mechanic framework. The interpretation of the results showed that the mastic creep behaviour highly effects the dissipative capability of HMAs, especially when the by-product materials are used.