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S. Nahar, A. Schmets, A. Scarpas, G. Schitter:
"Temperature induced healing in strained bituminous materials observed by atomic force microscopy";
Talk: Fourth International Conference on Self-Healing Materials, Ghent, Belgium; 06-16-2013 - 06-20-2013; in: "Proceedings of the 4th International Conference on Self-Healing Materials", (2013), ISBN: 9789082073706; 489 - 493.

Bitumen is the binder in the composite material named asphalt concrete. Under cyclic
mechanical loading of traffic passing over the pavement, eventually damage will
initiate in the pavement, leading to eventual structural failure. This damaging process
is accelerated by time dependent change of the mechanical properties of asphalt
concrete due to ageing mechanisms like oxidation. Bitumen displays spatial
heterogeneity at the micrometer scale, which has been observed by atomic force
microscopy (AFM). The mechanical properties of the elliptical, microstructural
domains of bitumen are distinct from those of the continuous phase. This introduces
stiffness discontinuities in the material, which under mechanical loading will
concentrate stresses at the interfaces, and thus the locations where early stages of
damage will develop.
This work aims at in situ probing of the crack healing of bituminous materials as a
function of moderate temperature changes. The bitumen was prepared on a flexible
substrate which was mechanically strained to induce damage. AFM measurements of
the strained bitumen specimen provides evidence of the crack initiation at the
interface and the predominant propagation of cracks through the elliptical domain
phases. Healing of these cracks was observed after applying modest amounts of
heat to the material. Meanwhile the process was monitored in situ with AFM. With
increase of temperature one of the phases starts softening, while the material as a
whole remains solid. This allows the phases to rearrange and meanwhile eliminating
micro cracks at the interface.

Bitumen, microstructure, atomic force microscope