The mechanical performance of dry-process crumb rubber modified hot bituminous mixes: The influence of digestion time and crumb rubber percentage

The use of crumb rubber from scrap tires in hot bituminous mixes in order to improve their performance has become a technique of great potential in recent years. The two techniques used to add crumb rubber to bituminous mixes are the wet process and the dry process. Of the two, the dry process is somewhat less popular because it initially produced poorer results. The objective of the research presented in this paper is to improve the application of this technique by analyzing the influence of the variables digestion time and percentage of crumb rubber on the mechanical performance of bituminous mixes. This research project had two phases. The first phase studied the influence of these variables on the mix design, whereas the second phase analyzed how the variables affected the mechanical performance of the mixes. This paper presents the results of the second phase which analyzed the mechanical performance of dry-process crumb rubber mixes, more specifically, their response to moisture sensitivity and plastic deformations. The results obtained indicated that the determining factor in mix performance was the amount of crumb rubber added. In contrast, the influence of digestion time was found to be negligible. The study showed that in reference to moisture sensitivity and plastic deformations, the best performances were achieved with a digestion time of 45 min and a crumb rubber percentage of 0.5% and 1.0% of the total weight of the mix.

► The amount of crumb rubber has more impact than digestion time on the mechanical performance of the mixes.
► Increasing the crumb rubber content cause a reduction in the density of the mixes.
► The addition of crumb rubber to the mix improves its response to plastic deformations.
► Increasing the crumb rubber content over 1.0% causes a reduction in the resistance to water.