Laboratory study to evaluate the influence of reclaimed asphalt content on performance of recycled porous asphalt

Road-pavement maintenance and rehabilitation are more frequently performed on porous asphalt (PA) surface layers because of their inherent low durability. Such activities lead to the production of a considerable amount of reclaimed asphalt (RA), mainly from PA layers and from the heavy use of virgin non-renewable natural resources, because of the fact that the use of RA is not usually allowed in PA. In this sense, the use of milled materials from old PA wearing courses in new PA layers promotes an important cycle of re-use that should be encouraged. The experimental study aims to investigate the performance of recycled PA mixtures prepared by partly substituting virgin aggregates with selected coarse RA from a milled PA wearing course. A reference PA mixture (without RA) and six recycled PA mixtures prepared with two amounts of RA (20 % and 25 %) and three total binder contents (5.25 %, 5.50 %, and 5.75 %) were investigated in terms of compactability, durability, and water resistance. In this sense, indirect tensile strength (ITS) tests, particle loss (Cantabro) tests, semicircular bending (SCB) tests, and repeated indirect tensile tests were carried out in both dry and wet conditions. Moreover, compactability properties of the reference PA mixture and the recycled PA mixtures were compared. Results showed that recycled PA mixtures with 20 % and 25 % of RA can perform as well as the reference PA mixture in terms of moisture resistance and durability if an accurate mix design is performed. The optimum total binder content was found to increase as the amount of RA increases, because of the fact that a prominent part of the aged binder acts as “black aggregate.” Finally, on the basis of a performance-based equivalence principle, a reliable approach for a practical method able to predict the amount of “re-activated” binder within the RA is proposed.