Performance of warm recycled mixtures in field trial sections

Over the last decade, many researchers focalized on new technologies for the production of Warm Mix Asphalt (WMA) at lower temperatures to significantly reduce pollutant emissions and energy costs. Among various WMA technologies currently available on the market, chemical additives demonstrated to provide suitable performance with respect to the main distresses that typically affect flexible pavements. However, so far research efforts have mainly addressed the laboratory optimization of WMAs with rare correlations with field trials. The lack of experience about in-situ behavior risks limiting the use of such technologies, especially when mixtures include both Styrene-Butadiene-Styrene modified bitumens and Reclaimed Asphalt (RA). Given this background, the paper describes the performance evaluation of full-scale trial sections built with open and dense graded recycled WMAs as part of maintenance activities of an Italian motorway. Two segments included WMA mixtures prepared with different chemical additives, whereas a third segment was constructed with hot mixtures typically adopted in pavement rehabilitation works. Volumetric and stiffness properties, rutting and cracking resistance as well as interface shear strength were investigated on in-situ cored samples. Results showed that WMAs did not compromise mixture stiffness counterbalancing stiffening effects due to the presence of RA. Such a behavior resulted beneficial in terms of fracture resistance and did not penalize the rutting aptitude. Moreover, the shear strength evaluation showed that lower lay-down temperatures of WMAs did not alter the bond between pavement layers.