The effect of progressive aging on the bond strength of bitumen to siliceous stones

Oxidative aging changes the composition of bitumen, and these changes affect the cohesive properties and adhesive properties of the bitumen. While cohesive properties of bitumen have been shown to be negatively impacted by aging, bitumen's bonding strength to stone aggregates can increase. Aging makes bitumen become more polar and gives rise to concentration of oxidized asphaltenes. It is hypothesized that oxidized asphaltenes show stronger interaction with siliceous substrates, promoting bitumen's bonding to siliceous stones such as quartz and granite. This study uses computational modeling and laboratory experiments to evaluate the interaction of progressively aged bitumen with siliceous substrates. To do so, asphalt samples aged from 20 to 60 hours were prepared, and their bonding properties were examined in dry conditions and wet conditions. The study results showed that as bitumen becomes aged and/or exposed to water, its shear thinning increases. Our computational modeling showed oxidation promotes the interaction between bitumen components and silica. In terms of bitumen's bonding to stones, our modeling results showed that oxidized compounds of bitumen such as asphaltene and resin have higher interaction energies with siliceous surfaces than non-oxidized counterpatrs. Our experiments found that siliceous stones (represented by glass beads in experiment) had greater interaction with aged bitumen than with unaged bitumen. Furthermore, aged bitumen showed even higher interaction with siliceous stones when exposed to water compared to dry conditions, as shown by the moisture-induced shear-thinning index (MISTI) test. The latter observations indicate that water could not diffuse into the interface of aged bitumen and siliceous stones to weaken their bond. The outcomes of the study provide insights pertaining to bitumen's adhering to stones. It further informs methods related to the extraction of bituminous compounds from reservoir rocks as well as removal of oxidized bitumen from stones when reclaiming old asphalt pavements.