Physicochemical compatibility assessment of bio-additives and bitumen using solubility science-based approaches
Yongping Hu, Anand Sreeram, Abir Al‐Tabbaa, Gordon Airey
Abstract
• Evaluation of Hansen Solubility Parameter (HSP) based indices for screening highly effective bio-based additives for bitumen. • Evaluated bio-based additives lower the critical temperatures and reduce cracking susceptibility of bitumen. • Bio-based additives which have similar HSPs with bitumen could be more compatible with bitumen and perform better. Increasing environmental concerns necessitate the urgent investigation of alternative, sustainable resources as replacement for fossil fuel-derived bitumen; the primary material used for road construction. One of the promising approaches is the use of bio-based alternatives as partial or full bitumen substitutes in asphalt mixtures. Currently, the selection of bio-additives is subjective, resulting in significant variations in the quality of bio-based bitumen produced and its resulting utility as an engineering material. This study utilised solubility-based measurements using the Hansen solubility parameters (HSP) to assess the fundamental physicochemical compatibility between bitumen and two bio-based additives. Firstly, tall oil (bio-additive-1) and waste cooking oil (bio-additive-2) were employed as bio-sourced additives and bitumen was separated into its basic polarity-based building blocks i.e. maltenes and asphaltenes. Afterwards, the HSPs of bitumen, its subfractions and bio-additives were measured. Frequency sweep tests, linear amplitude sweep (LAS) tests and bending beam rheometer (BBR) tests were carried out to assess the rheological properties of blended bio-bitumen and its relation to solubility-based indices. Bio-additive-1 showed better performance and efficiency compared to bio-additive-2 in improving the low-temperature performance, fatigue life and durability of bio-bitumen. The HSP of bio-additive-1 was closer to those of bitumen and its subfractions compared to bio-additive-2, which likely contributes to increased compatibility. The overlapping ratios of Hansen spheres and bitumen subfractions were positively correlated with the rheological properties of the bio-bitumen. Overall, the findings represent a first step towards development of a robust framework for the scientific design of bio-bitumen in future paving applications.