Effect of Crumb Rubber Bituminous Mixes on Functional Characteristics of Road Pavements

The Road Research Laboratory of Spain's Technical University of Catalonia has conducted a study to determine the effects of adding crumb rubber on the functional characteristics of gap-graded mixtures–- particularly the effects on texture and noise. The evaluation was performed on the basis of full-scale measurements of several test sections. All sections were constructed with a gap-graded mixture in which three types of binders were used: bitumen with crumb rubber added by the wet process, the same bitumen with crumb rubber added by the dry process (1% and 2% crumb rubber content), and polymer-modified bitumen acting as the reference. The test sections were located on Road B-140 near Barcelona, Spain. Texture and skid resistance were measured by the side force coefficient routine investigation machine (SCRIM), and noise levels were quantified in a semi-anechoic chamber with the close proximity method. The use of different tires was also analyzed by the Laboratory of Acoustics Applied to Civil Engineering of the University of Castilla-La Mancha (Spain). The results revealed the impact of construction and service conditions on the surface characteristics of pavements and that, in general, the addition of crumb rubber by the dry process may slightly decrease the noise from tire–pavement interaction, while texture levels are decreased and skid resistance is increased, compared with the results obtained with the addition of crumb rubber by the wet process.