ECO-SUSTAINABLE OPTIMIZATION OF THE MIX-DESIGN METHODOLOGY IN MODIFIED BITUMINOUS MIXTURES WITH HIGH PERCENTAGE OF RECYCLED TIRE RUBBER

Abstract

The design of a reference dense-graded bituminous sub-ballast mixture (3% of air voids and a bitumen 4% over the total weight of the mix) and three rubber-aggregate mixtures containing ground rubber-aggregate by a dry process (RUMAC to 1,5 to 3% of rubber by total weight and 5-7% of binder) was evaluated. Using an eco-sustainable original approach based on experimental findings obtained in the laboratory with the Volumetric mix-design by gyratory compaction for a level 3 (high-traffic) design rail lines. This work proves that rubberized blends having ground rubber in bituminous asphalt mixtures behave better than conventional asphalt materials. By using the same method of volumetric compaction, the densification curves resulting from each mixture have been studied with the purpose to obtain a best empirical parameter multiplier of the number of gyrations necessary to reach the same compaction energy as in conventional mixes. It has provided experimental parameters evaluating the results obtained from the gyratory-compaction of bituminous mixtures with an HMA and rubber-aggregate blends as a sub-ballast layer in railway underlayment trackbed. By adopting this increase-parameters of compaction, called “beta” factor, uniform densification and higher workability are found in modified mixtures with rubber considering the usual bearing capacity requirements in rail track.