The Influence of Particle Size and Concentration of Recycled Tyre Rubber on the Rheological Properties of Trinidad Lake Asphalt and Petroleum Bitumen

This study investigated the influence of the particle size of waste tyre rubber on the rheological properties of Trinidad Lake Asphalt (TLA) and Trinidad Petroleum Bitumen (TPB). Modified TLA and TPB blends containing 0, 1, 2, 3, 4, 5, and 10 wt % waste tyre rubber of particle sizes ranges ≤250 μm, >250 μm to 355 μm, >355 μm to 500 μm and >500 μm to 710 μm were analyzed and the rheological properties of complex modulus (G*), storage modulus (G’), loss modulus (G″) and phase angle (δ) of the various blends were measured over the frequency range 0 Hz to 16 Hz at a temperature of 80 oC. The TLA blend containing 1% rubber additive had a relatively higher G* (stiffness). Blends containing between 1% and 4% were less elastic (higher δ) than pure TLA whereas the blend containing 5% was more elastic (lower δ). The dependency of the parent asphalt composition on the rheological properties of modified asphalt blends was evident. In the case of TPB, the incremental addition of the tyre rubber resulted in an increase in the values of G* and a general decrease in δ as the concentration of rubber was increased. Maximum values of G* and minimum values of δ were observed for both TLA and TPB blends when the particle size of the rubber was in the range > 355 μm to 500 μm. This also occurred for TLA and TPB blends containing rubber of particle size ≤ 250 μm but only at the 5% added rubber concentration. The measured values of G″ were always higher than those of G’ for both the TLA-rubber and TPB-rubber blends indicating that both blend types exhibit a viscoelastic liquid response under shear. Higher values of G’ were recorded for the TLA and TPB with the rubber particles of sizes in the ranges > 355 μm to 500 μm range and ≤ 250 μm at a rubber concentration of 5% suggesting that these mixtures exhibit a greater level of dispersion which can ultimately account for the unique rheological properties.