Microstructural self-healing of bituminous materials: Combined experimental and numerical study

Bituminous materials form a class of materials that possess the intrinsic ability to selfheal. This self-healing capability is evidenced by the observation that the service life of these materials \u91in the field\u92 exceeds the service life as predicted by standard mechanical laboratory tests. This mismatch between laboratory prediction and field service life is usually accounted for by applying a shift or healing factor. In this contribution we demonstrate a model that is based on the observation that bitumen possesses a microstructure on the micrometre length scale, as can be observed by atomic force microscopy (AFM). On this scale bitumen can be regarded as a two-phase material, where the phases have a distinct stiffness. . One of the phases has a very typical appearance and is often referred to as \u91bee-phase\u92 [1-3]. The interface between the phases can be regarded as a manifold that is defined by stiffness gradient in the material. From mechanical considerations damage will initiate within this manifold. Modest variations in thermodynamic conditions (thus without melting the material) will already lead to rearrangement of phases, and a new damage initiation manifold, meanwhile the accumulated damage is erased. Starting from two experimental microstructural arrangements, one before and one after phase rearrangement, a finite element mesh is produced. For both phases a viscoelastic constitutive model is implemented. The interface manifold is treated equally, but is allowed to acquire damage, as are the other phases, to a lesser extent. In this way, using experimental observations as a starting point, it is demonstrated that the effect of healing in bituminous materials can be treated micromechanically, and leads to quantitative results. This opens the way to quantify the healing potential of a bituminous material upon its microstructure. Optimal manifolds to accommodate the healing behaviour can then be derived. The experimental challenge will be to engineer the interface manifold in accordance with the desired healing potential of the material