Influence of processing conditions on rheology of tyre rubber modified bitumens

Tyre Rubber Modified Binders (TR-MBs), produced through McDonald wet process and used worldwide (e.g. asphalt rubber), have been demonstrated to provide various benefits to pavements and, moreover, they represent a good opportunity for recycling tyre rubber. However this technology is still struggling to be fully adopted in Europe, mainly because of their poor stability during high temperatures storage, which leads to high initial costs in modifying existing asphalt plants. NO-agitation TR-MBs (also known as terminal blends) is proving to be a great option and its development could also be the key to spreading the recycling of tyre rubber in paving applications in Europe. This paper aims to enrich this field of research by presenting the results of a study focused on the optimisation of laboratory procedures to better understand the effect of varying processing conditions on the rheology TR-MBs. The experimental programme has been carried out by a preliminary selection of materials, followed by the production of the TR-MBs, via practical laboratory protocols. A continuous comparison between two commercially used SBS-MBs, with high and medium levels of modification, and the produced TR-MBs, helped to understand the effect of varying the selected processing conditions on binder properties. Results have shown that TR-MBs are a very effective alternative to commercially used SBS-MB. Although the rheology of TR-MBs is very sensitive to the varying of processing conditions, therefore an appropriate selection of materials and a superior binder design are mandatory to optimise the modification process to achieve the desired level of modification.