The influence of added coir (coconut) fibre of various lengths (from 2.5 mm to 10 mm) and dosages (up to 8 wt%) on the rheological properties of Trinidad Lake Asphalt (TLA) and Trinidad Petroleum Bitumen (TPB) was evaluated by measuring changes in the phase angle, δ (measure of the elasticity) and the complex modulus, G* (measure of the degree of stiffness). Results indicated that for both TLA and TPB, the highest values of G* (stiffest) and the lowest values of δ (most elastic) were observed for blends containing 2.5-mm coir fibre lengths for added coir concentrations of 6% and 8%, respectively. When compared to the unmodified TLA, the addition of 6 wt% of 2.5-mm coir fibre resulted in the largest significant increase in G* (7.3 times) as well as a significant decrease in δ (from 49.3° to 19.8°), representing a significant stiffening and increased elasticity of the modified blend. For TPB, the optimum concentration of added coir fibre occurred after the addition of 6 wt% of the 2.5-mm coir fibre, which resulted in the largest significant increase in G* of 5.4 times (stiffening) as well as a significant decrease in δ from 86.2° to 47.4° (increased elasticity as the material transformed from an almost viscous liquid to a semi-elastic solid) when compared to the unmodified pure TPB. The utilization of coir fibre for the rheological enhancement of Trinidad asphaltic materials can also provide an environmentally attractive option for solving the waste disposal issues associated with the dumping of waste coconut husk.

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