The stiffness of an asphalt layer is an important characteristic affecting the performance of the layer. This stiffness is affected by temperature and time, as the bituminous component of the asphalt layer ages. As the stiffness increases, the distribution of traffic loads will be affected, as described in multi-layered linear elastic theory. In addition, the increasingly aged condition of the asphalt layer will allow cracking, as a mode of failure, to become increasingly likely. The ageing processes can be characterized as occurring in two phases, namely, Short Term Ageing and Long Term Ageing. Short Term Ageing represents the ageing that an asphalt mix undergoes during manufacture, storage, transport and placement. Long Term Ageing represents the ageing an asphalt mix undergoes after placement, and over the lifetime of the pavement. This paper reviews the different reaction mechanisms of ageing of bituminous binder as well as the effects of oxidation accelerators such as heat and ultraviolet light. There is also an overview of the physical and chemical properties of bituminous binders that can be used to monitor the rate of ageing.
Papers presented at the 36th Southern African Transport Conference, CSIR International Convention Centre, Pretoria, South Africa on 10-13 July 2017.