Investigating the condition number approach to select probe liquids for evaluating surface free energy of bitumen.

Application of condition number (CN) approach is critical in selecting appropriate combination of probe liquids for evaluating the surface free energy (SFE) of bitumen. The CN approach recommends use of probe liquids with CN<10, however, several researchers have used probe liquid combinations having CN>10 without concerning its adverse effects on the SFE of bitumen. Inappropriate choice of probe liquids may result in incorrect SFE values of bitumen, thereby influencing its compatibility with aggregates. Therefore, the present study is strongly motivated to exhibit the application of CN approach for selecting appropriate probe liquids. Further investigating the impact of CN on aggregate-bitumen compatibility, the present research work also aims at validating CN approach. A polymer modified bitumen (i.e., PMB40) and two types of aggregates namely, quartzite, and basalt aggregates were selected in this study. Five probe liquids namely, water, formamide, diiodomethane, ethylene glycol and glycerol were selected, which formed ten different combinations of probe liquid triplets. The CN of probe liquid triplets was calculated based on singular value decomposition (SVD) method. Thereafter, using the SFE of aggregates and bitumen, compatibility of basalt-PMB40 and quartzite-PMB40 was evaluated using compatibility ratio (CR) parameter. Results revealed that except for probe liquids triplets with CN<10, the aggregate-bitumen compatibility was highly inconsistent when evaluated using probe liquids triplets having CN>10. Therefore, the present study addresses the adverse effect of inappropriate selection of probe liquids on aggregate-bitumen compatibility and also validates the CN approach. [ABSTRACT FROM AUTHOR]