Performance of styrene-butadiene-rubber modified bitumen for sustainable pavement constructions in tropical regions

Abstract

Pavements in tropical regions are affected by high temperatures and ageing, and are susceptible to rutting, which reduces their resilience and durability. Hence, this study investigates the modification of bitumen with Styrene–Butadiene Rubber (SBR) at 0%, 3%, 6%, and 9% by weight. Conventional tests showed that SBR modification improved high-temperature properties up to 6%, followed by a sudden reduction at 9% modification, as evidenced by increased softening point and reduced penetration. At 6% modification, the SBR-modified bitumen would remain uniform and stable during storage. It would not affect performance upon use after storage, demonstrating its suitability as a performance-enhancing polymer for hot-climate applications. Multiple Stress Creep Recovery (MSCR) testing shows reductions in non-recoverable creep compliance and enhanced elastic recovery, making the modified bitumen. The 6% SBR modified binder showed a significantly higher Jnr diff value with a Jnr diff value of 53.42%. Similarly, the SBR-modified binders showed improved recovery, with %R 0.1 values of 14.89% to 18.45% at 64 °C and %R 3.2 values of 0.32% to 1.71%. Linear Amplitude Sweep (LAS) results showed that a 9% modification yielded the highest N_f value, but beyond 6%, the improvement was negligible. Considering cost and optimal performance, 6% SBR content modification should be considered. Glover–Rowe parameters showed that SBR-modified binders retained their elasticity and reduced the brittleness of bitumen, unlike unmodified binders, which shifted towards brittle behaviour. Pearson correlation analysis shows a strong positive cluster among fatigue life, % recovery, Fail Temperature (Unaged and Aged), G*/sin δ, softening point, elastic recovery, and rutting parameters, with correlation values exceeding 0.90 in most cases. Grey Relational Analysis (GRA) shows that a 6% SBR with a Grey Relational Grade (GRG) of 0.843 was ranked highest among all modifications. Principal Component Analysis (PCA) shows that a 6% SBR modification of the bitumen is optimal, providing a balance among rutting resistance, fatigue performance, and ageing durability. These findings highlight the potential of SBR-modified bitumen to enhance pavement performance and service life in tropical climates.