The engineering properties and the long-term performance of road asphalts can be improved significantly by the use of additives. A research project recently undertaken at the Christian Doppler Laboratory of the Institute for Road Construction and Road Maintenance, Vienna University of Technology and realised in close co-operation with the rubber-industry focused on the re-use of products recycled from old car tires as additives in road asphalt wearing courses. It aimed at an optimisation of the engineering properties of new types of high performing road asphalts by the use of modifiers recovered from waste car tires and, furthermore, their large-scale industrial production. For this purpose, performance-based test procedures at the bitumen scale as well as at the asphalt mix scale were assessed, using rheological and mechanical laboratory tests to quantify the effects of the new modifiers with regard to the improvement of the engineering properties in different load and climatic boundary conditions.
The test methods employed in the course of the project enabled, for the first time, systematic mix design and 0ptimisation for any type of asphalt material and proved to be a key prerequisite for the successful and scientifically sound development of modifiers from reclaimed waste tire products. As a result two products, i.e. rubber flour and rubber granulate, both recovered from waste car tires were specified for modifying road asphalts. These products were used for modifying new types of high-performing road asphalt wearing courses, which have been installed on highly trafficked road sections and are now under observation.