Microstructural properties of warm mix asphalt before and after laboratory-simulated long-term ageing

This paper presents microstructural analysis of two original and their respective warm mix asphalt (WMA) binders, obtained with the addition of Advera^® and Sasobit^®. The binders were analysed before and after long-term ageing with the aid of atomic force microscopy (AFM). The AFM images highlighted the effect of ageing using rolling thin film oven (RTFO) followed by pressure ageing vessel (PAV) on the binders’ microstructure. Ageing of original binders generally increased the size of the “bee” structures. The ageing effect on the microstructure morphology of WMA binders was found to be negligible. However, ageing could affect the mechanical properties without morphology variations. The high variability inside each sample analysed makes the analysis complex. Sasobit^® changed the original binders’ microstructure considerably, while Advera^® did not affect it. For the original and Advera^® binders, 24 hours after sample preparation, the dispersed phase expanded, and this effect was generally more pronounced for unaged than for aged binders. This could indicate a lower mobility of the species forming microstructures in aged samples. The reduced mobility of these species during heat treatment also affects the microstructure of the samples. A hypothesis on the development of “bee” structures starting from dendritic structures was proposed.