Draining asphalt experience in Italy

Asphalts developed to offer better performances than the traditional asphalts are termed “special”. Used for different applications within the road pavement, they perform complementary, integrative or substitutive functions with respect to the traditional mixes. Non-skid and “high modulus” bituminous mixtures, splittmastix asphalt (SMA), cold micro-surfacings (slurry seal), single-layer surface treatments and most especially porous (draining and sound-absorbing) asphalts all come into this category. A decisive development breakthrough in the performance of materials for road construction was signalled by the introduction of modified bitumens, particularly as regards improvement of the characteristics of cohesion and resistance to loadings from vehicular traffic. The indispensable condition for the development of these technologies was therefore the ”invention” of modified bitumen, in other words the binder which, with the addition of different types of polymers, in suitable plants and under controlled conditions, modifies its structure with “inversion of phase”, greatly enhancing the performance. The basic concepts specifically regarding porous asphalt are discussed in the paper.