Mechanical performance of dry process fine crumb rubber asphalt mixtures placed on the Portuguese road network

This paper evaluates the mechanical response of two gap-graded asphalt rubber mixtures manufactured by the dry process (ARdry). The observed behaviour is compared with that of a similar gap-graded mixture without rubber granulate, used as reference. The laboratory results are also compared with analogous asphalt rubber mixes produced elsewhere by the wet process (ARwet). The blends were produced in a plant and laid in trial sections and on the Portuguese road EN 370, in order to collect representative specimens for laboratory testing. The mechanical evaluation of the mixes was carried out by repetitive four-point bending tests and wheel-tracking tests. The laboratory results and the behaviour observed on the EN 370 allow us to conclude that mechanical performance of the tested ARdry is better than that measured for the reference blend, and is at the same level of performance as ARwet, provided that a proper mixture design and some construction directives are used.