5. Recycling

Recycling of old pavements is becoming a widespread technique; in order to preserve the natural resources of aggregates and binder, the materials reclaimed from the damaged layers of the pavements maintained are generally reincorporated in the material for new maintenance layers. However, recycling induces some technical challenges. In the case of the Hot mix asphalt (HMA), the most commonly used road construction material, one of the main concerns is ageing. Along with the heterogeneity of the RA properties in stockpiles, it is one of the main factors limiting the recycling rates in HMA. Therefore, the characterisation of ageing through reliable ageing indexes and of its impact on the bitumen physical properties is of paramount importance to improve the recycling techniques. The RILEM TC 237 SIB TG5 inherited a database from the previous work of the RILEM TC 206 ATB TG5 on a protocol for bituminous mixture ageing in laboratory. Taking advantage of these data, the work of the Task Group was first dedicated to a state of the art and an evaluation of the chemical ageing characterization through indexes based on Fourier Transform Infrared Spectroscopy (FTIR). In a second step, an attempt was made, in order to bring out the essential trends of the rheological data with ageing, by using a Huet modified rheological model. Then, exploring the potential of a recently developed method, an interpretation of these trends in terms of asphalt structure is suggested. Finally, possible empirical relationships between the chemical ageing indexes and the rheological parameters are investigated.