Laboratory Evaluation of Biochar-Modified Bitumen for its Application in Road Construction

Abstract

This research seeks to assess the potential for modifying VG40 bitumen by implementing biochar extracted from rice straw. The addition of biochar would help address India’s reliance on bitumen imports and the issue of agricultural residue burning. The employed method for the mixture preparation was highshear mixing, where the components were combined at various percentages of biochar incorporation: 0%, 5%, 10%, and 15% by weight of bitumen (VC0, VC5, VC10, VC15). The obtained mixtures were characterized by several techniques providing information on physical properties such as ductility, softening point, viscosity, penetration and specific gravity of the obtained biochar-modified binders. The following tests were applied for rheological evaluation: temperature sweep, frequency sweep, PG grading, multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) tests. The evaluation of the produced asphalt mixtures was performed in line with the Marshall mix design, indirect tensile strength (ITS), tensile strength ratio (TSR), resilient modulus, IDEAL-CT index, Hamburg wheel rut test, dynamic creep, and indirect tensile fatigue tests. The findings show biochar consistently improved binder rigidity, softening point, and viscosity, while FTIR and SARA analyses indicated that the changes were predominantly physical or chemical. Rheological examinations showed significant improvements in rutting resistance and elastic recovery with increasing biochar concentration, with the highest effectiveness at 10% biochar (VC10), while performance decreased only slightly at 15% due to excessive rigidity. From the perspective of mixture analysis, biochar incorporation raised Marshall stability by up to 37.6%, raised ITS and TSR indices (demonstrating the enhancement in moisture resistance), strengthened cracking resistance (IDEAL-CT index raised by 30.4% at 10% dosage), and decreased rutting and fatigue strains, with VC10 again positioned between the other dosages. Overall, the inclusion of 10% biochar provides the ideal solution by offering a good balance of stiffness, durability, water resistance, and fatigue resistance, while higher percentages yield little or no additional benefit due to over-stiffening. Therefore, it has been shown that rice straw biochar is a technically sound, low-cost, and sustainable bitumen additive capable of both improving pavements' performance and providing an effective use of otherwise wasted agricultural materials.