In this study atomic force microscopy (AFM) creep indentations were performed to extract viscoelastic properties of the different domains (defined as microrheology) observed in bitumen samples from two different sources. The microrheology and geometry obtained using the AFM were used to perform finite element (FE) simulations to study the effect of bitumen microstructure on internal stress distribution. FE analyses suggest that microstructures with varying mechanical properties cause localised stress amplification that can lead to cracking/phase separation. A custom-made loading frame in conjunction with an AFM was used to examine the effects of tensile strain on bitumen microstructure. FE simulation and experimental results show that applying strain resulted in damage/phase separation concentrated in the interstitial zone between neighbouring bee structures, defined as load-induced phase separation. This study suggests that evaluating the bitumen microstructure and microrheology is critical to understanding the mechanisms of damage evolution in bitumen and engineering binders with higher inherent durability.

This paper presents findings from a study conducted to evaluate changes in the microstructure of asphalt binder resulting from aging as well as the effect of these changes on the evolution of damage resulting from tensile deformations. Two types of asphalt binders were aged with the rolling thin film oven and pressure aging vessel aging techniques. The microstructure and the microrheology of the six binders were obtained with atomic force microscopy (AFM) imaging and creep indentation experiments. This information was then used to perform numerical simulations to examine the effect of tensile strains on the internal stress distribution in the binder. Experimentally, a microloading apparatus was used to induce tensile strains in the samples of the asphalt binder while the binder was observed for damage with the use of AFM. The damage and changes in the binder microstructure resulting from the tensile load observed experimentally were compared with the results from the numerical simulations. Results suggest that localized regions of high stress intensity between different domains act as damage nucleation sites. Results also suggest that the differences in the rheological properties of the microdomains reduce with aging. As a result, the internal distribution of stresses becomes less heterogeneous, the magnitude of stress localization decreases, and there are fewer sites where damage nucleates.