Asphalt concretes including bitumen modified with compounds based on crumb rubber from waste tires: A laboratory and field study

End-of-life tires represent one of the major waste streams in terms of volume generated annually, worldwide. One of the possible destinations for the waste rubber from end-of-life tires is asphalt concrete, but the many recycling techniques that are currently adopted in different countries present disadvantages (economic, logistic or performance) that hinder their diffusion. An innovative technology has been recently developed, dealing with the use of waste rubber in the production of compounds for bitumen modification, in partial or total replacement of the styrene-butadiene-styrene (SBS) polymers. The objective of the present paper is the characterization of hot-mix asphalt (HMA) made with compound-modified bitumen. The investigated mixes were produced in the laboratory and in the asphalt plant; the latter were laid on a trial highway section. The shear-gyratory compacted specimens and the cores taken from the trial section were analysed in terms of volumetric properties, indirect tensile strength, stiffness and fatigue performance. The experimental data were statistically validated through t-test. The results showed that the HMA with compound-modified bitumen, compared to the HMA with SBS-modified bitumen, had similar voids content, stiffness and strength, but a slightly improved fatigue performance (+15 % on both ε6 and σ6 parameters), which can be associated with a lower severity of the ageing experienced by the binder during the mixing. The combined use of SBS and compound modifiers may entail an increase (about 30 %) of the HMA stiffness.