Effect of recycling cycles on hot and warm bituminous mixtures with high rates of reclaimed asphalt

As road networks in most industrialised countries approach the end of their service lives, rehabilitation becomes critical. To minimise natural resource consumption, reclaimed asphalt (RA) is expected to be the primary material for reconstruction. This study focused on understanding how the manufacturing process affects the reusability of bituminous mixtures. The key variables analysed included the manufacturing temperature and process, RA content and number of recycling cycles, examining their effects on the geometrical properties, compactability, water sensitivity, stiffness modulus and cracking resistance. The results demonstrate that hot multi-recycling did not compromise the performance. However, lowering the manufacturing temperature (from 165 °C to 135 °C) increased the influence of recycling cycles, especially on water sensitivity. After three cycles, the indirect tensile strength ratio of the warm mix with 40% RA decreased from 95% (0 cycles) to 88%. The Fénix test highlighted the higher brittleness in warm mixtures with 70% RA, showing reduced ductility at 20 °C (0.36 mm compared to 0.63 mm for the same mixture without RA). Nevertheless, adding a biorejuvenator in the third cycle improved warm mixture behaviour, enhancing ductility and preventing excessive brittleness, notably at 5 °C.