Improved durability of recycled porous asphalt

Porous asphalt mixtures are extensively used as highway surface layer due to their benefit in improving skid resistance and reducing spray and splash effects during wet conditions. Moreover, porous asphalts (PA) are also oriented towards the reduction of road traffic noise thanks to enhanced sound absorption capabilities. Nevertheless, the limited durability of porous asphalt layers leads to frequent maintenance and rehabilitation activities. In this study, the use of course reclaimed asphalt (RA), obtained by milling old porous surface layers, as aggregate in new PA mixtures was evaluated. Preliminary, Binder Bond Strength tests on coated and uncoated basalt aggregate substrates showed encouraging results in terms of adhesion properties between unaged polymer modified bitumens and substrates coated with aged bitumens, simulating RA aggregates. Thus, five porous asphalt mixtures prepared with 15% course RA aggregates and different total binder contents were studied in the laboratory. A reference PA mixture containing only virgin aggregates was also investigated for comparison purposes. Indirect tensile strength tests, particle loss (Cantabro) tests, semi circular bending (SCB) tests and repeated indirect tensile tests were carried out in both dry and wet conditions in order to evaluate acceptability, durability, fracture resistance and water sensitivity of recycled mixtures. Results showed that recycled porous asphalt mixtures can perform as well as (or even better than) reference one. In particular, recycled mixtures at equal or higher binder contents than the reference mixture demonstrated an improvement in moisture resistance and durability.