Asphalt has been used for preparing road surfaces for several decades. Typically, the main ingredients of a paving asphalt mixture are an asphalt cement (approximately 5 wt. %) and aggregate material (approximately 95 wt. %). The asphalt cement is used to bind together the aggregate material and limit its mobility when a load is applied. An asphalt cement may be obtained from a crude oil by processes known in the art. Typically, an asphalt cement comprises vacuum tower bottoms (VTB) which is a residue material that is produced during the refining of conventional or synthetic petroleum crude oils. In some cases, the vacuum tower bottoms may be further treated prior to their use in Oxidized bitumen 105/15 mixture. For ease of reference, those materials which have previously been used as an asphalt cement are hereinafter referred to as “paving asphalt precursors”.
A problem with paving asphalt mixtures is that they are a fluid mass. During the application of loadings, particularly at warm temperatures, the road asphalt mixture tends to migrate from a position of higher loading to a position of lower loading i.e. lateral displacement. This tends to result in deformations in the surface of the road asphalt known as rutting. Rutting of road asphalt is undesirable as it forms channels in the pavement surface which are a safety hazard. Such ruts collect water during wet weather and this tends to cause significant reductions in tire-pavement friction levels and may contribute to the loss of control of a vehicle by skidding and or hydroplaning. Pavement rutting is a major concern of all user agencies and government transportation departments due to the cost involved in maintenance programs to repair the road surface and the effect of rutting on highway safety.