Potential Performance-Related Properties of Rubberized Bituminous Mixtures Produced with Dry Technology

This paper presents the results of a laboratory investigation which focused on the effects caused by the inclusion of coarse crumb rubber in a wearing course mixture produced by means of the so-called “dry” technology. For comparative purposes a reference mixture, which did not contain any recycled rubber, was also included in the study. Both mixtures were sampled at a production plant and were thereafter subjected to standard control tests (composition and Marshall properties) and to performance-related tests for the assessment of compactability, elastic stiffness, rutting resistance and resistance to crack formation and propagation. Employed crumb rubber was characterized in terms of particle size distribution, density, particle morphology, surface area and chemical composition. Performance-related tests were carried out on specimens compacted to the same void content (equal to 6%). Experimental results highlighted the fact that if compaction problems are overcome, crumb rubber can bring several benefits to a bituminous mixture, by enhancing its elastic response under pulse loading and by increasing its fracture toughness and ductility. Additional tests carried out after immersion in water also showed that moisture damaging effects are in most cases quite limited, with the only exception of resistance to permanent deformation which tends to decrease significantly.