Low temperature cracking properties of asphalt mixtures containing rubber bitumen pellets

Abstract

This paper evaluates the effect of ground tyre rubber (GTR) bitumen pellets on the low temperature cracking properties of asphalt mixtures. Low temperature properties were evaluated at 0 °C using monotonic and cyclic three-point bending tests. Flexural strength was determined using beam specimens and fracture toughness was determined using two specimen geometries: single edge notched beam and semi-circular bending. Cyclic bending tests under controlled load conditions were also carried out using notched beams to determine crack propagation parameters. Dense surface course mixtures were produced with a paving grade binder, two different polymer modified binders and two pellets concentrations. It was found that the flexural strength increased when GTR bitumen pellets and polymer modified binders were used. Differences in fracture toughness between the mixtures were, however, relatively small. Only one of the mixtures with a polymer modified binder showed a significant higher fracture toughness value. Furthermore, good correlation was found between the fracture toughness values determined from the two specimen geometries. Cyclic test, on the other hand, showed that the mixtures produced with the bitumen pellets and with the polymer modified binders were able to sustain more load applications than the unmodified mixture. Furthermore, crack propagation parameters were affected by both the type of binder and the concentration of pellets in the mixture.