Chemical Characterization of Rubber Seed Oil-Rejuvenated Bitumen for Reclaimed Asphalt Pavement Applications in Tropical Climates

Abstract

Road pavements in tropical climates deteriorate faster due to average surface temperatures exceeding 55 °C and annual rainfall above 1,500 mm, which accelerate oxidative ageing and moisture damage. Aged bitumen typically shows penetration values as low as 22 dmm, softening points above 55 °C, and viscosity exceeding 5,200 cP, confirming severe stiffness and brittleness. This study investigates Rubber Seed Oil (RSO) as a bio-based rejuvenator for Reclaimed Asphalt Pavement (RAP) mixtures under these tropical stresses. Fourier Transform Infrared Spectroscopy (FTIR) spectra revealed strong carbonyl (1700 cm⁻¹) and sulfoxide (1030 cm⁻¹) peaks in aged binder; incorporation of 4% RSO approximately reduced carbonyl intensity by 35% and sulfoxide by 28%, restoring functional groups critical for flexibility. Elemental analysis, Carbon, hydrogen, Nitrogen and Sulfur (CHNS) analysis showed aged binder contained approximately 84% carbon, 10% hydrogen, and 6% heteroatoms; RSO addition increased hydrogen content by 2% and reduced oxygen-related heteroatoms by 1.5%, replenishing maltene fractions. X-ray Diffraction (XRD) analysis revealed crystalline phases decreased from 22% (aged binder) to 14% at 4% RSO, signifying enhanced amorphous content and improved resilience under tropical thermal cycles. Complementary physical tests confirmed viscosity reduction from 5,200 cP to 3,100 cP and penetration increase from 22 dmm to 46 dmm at 4% RSO dosage. These improvements directly address tropical pavement weaknesses: reduced brittleness under high heat and improved cohesion under heavy rainfall. The findings justify adoption of RSO as a sustainable rejuvenator, with implications for extending pavement lifespan by 30–40%, reducing maintenance costs by up to 25%, and lowering virgin bitumen demand by 20%. This work establishes a scientific basis for incorporating RSO into RAP recycling specifications, advancing resilient and circular road infrastructure in tropical regions.