Mechanical characterization of asphalt rubber – wet process

In many countries all over the world, bitumen modified with crumb rubber from ground tires is widely and successfully used, as binder in hot mix asphalt (HMA). Asphalt Rubber is commonly used as wearing course for HMA pavements in order to improve smoothness and skid resistance and to reduce cracking and traffic noise. As extra benefit, this bituminous mixture allows to recycle rubber from waste tires. In Italy, to date, this kind of mixture is not employed yet, except for some isolated situations, in spite of the encouraging results obtained all over the world. This paper focuses on the mechanical characterization of a wet process asphalt rubber. This material was taken from the first experimental pavement section in Italy and then analyzed in laboratory. For this evaluation, Asphalt Rubber was subjected to dynamic Indirect Tensile Stiffness Modulus test (ITSM), Indirect Tensile Fatigue Test (ITFT), Repeated Loading Axial Test (RLAT) and Wheel Tracking Test (WTT). For a better evaluation, the results obtained for ARFC were compared with those obtained with different mixes subjected to the same tests. In particular, two HMA mixes manufactured in laboratory with the same gradation curve and bitumen content of Asphalt Rubber (the first with a traditional pen70/100 binder and the second with a SBS modified binder), a SplittMastixAsphalt and a dense graded HMA with expanded clay taken from a plant mix, were used. Results clearly showed that the use of Asphalt Rubber can noticeably improve the mechanical properties of asphalt mixtures suggesting potential advantageous applications also for the Italian road network.