A study carried out at the Belgian Road Research Centre has shown that it is possible to monitor the development of bituminous binders in wearing courses (plus-minus 5 cm thick) of pavements of different ages by separately considering the bitumen extracted and recovered from the top 0.5 cm and that from the underlaying part of the course. The generic composition of binders as determined by high performance liquid chromatography and checked by infrared spectography provides an insight into the effect of ageing on chemical constitution, which may be expressed by the following scheme: Cyclics->Resins->Asphaltenes. It then becomes possible to simulate and monitor the phenomenon in the laboratory under operating conditions (500 g of bitumen, more than 100 centrigrades and flow of oxygen) that produce a similar development as that observed in the field, i.e. mainly the formation of resins at the expense of cyclics and, to a smaller extent, an increase in asphaltenes. By simulated ageing tests in the laboratory, it is also possible to study the retarding effect of antioxidants on bitumen ageing. (A)
Abstract