Low-noise friction courses containing treated and un-treated crumb rubber to mitigate tyre/road noise in urban contexts

Tyre/road interaction is one of the main causes of traffic noise. This generates health, social, and environmental issues. Low-NMAS mixtures containing crumb rubber (CR) can be used to mitigate the aforementioned issues both in the short and long period. The main objective of the study presented in this paper is to investigate the variation of volumetric, surface, mechanical, and acoustical properties of friction courses due to the presence of treated and un-treated CR. Low-noise mixtures were designed during the ongoing project "E-VIA" (LIFE18 ENV/IT/000201) and were used to pave a street in Florence. Several samples were created using the Superpave Gyratory Compactor (AASHTO T-312, UNI EN 12697-31). The first set of specimens, consisting of asphalt concrete, with NMAS=6 mm and bitumen in the range 5-7%, have been used as a reference. Other two sets of specimens were created adding treated and un-treated CR to the reference mixture and using the dry method. Results show how the different compositions taken into account affect the properties and performance of the mixtures under investigation. Correlations, equations, and main trends were derived. Future studies will include the comparison between the in-lab produced specimens (herein analysed) and the cores extracted from the aforementioned street.