This paper studies the selective adsorption and dewetting processes of various biomodifiers with respect to siliceous surfaces to determine dominant moisture damage mechanisms in bitumen doped with biomodifiers. Accordingly, it introduces four different biomodifiers made from various biomasses while explaining their differential effects on moisture susceptibility of bitumen when they are introduced to bitumen as a modifier to make commonly used biomodified binders. The biomodified binders studied here are made from extracts of biomass: wood pellets, miscanthus, corn stover, and animal waste. The moisture effect on biomodified bitumen was evaluated through contact angle measurement followed by molecular-level binding energy based on density functional theory (DFT). The change of contact angle between each biomodified bitumen and a silica surface when exposed to water was used as an indicator of the propensity for dewetting. The biomodifiers from animal waste showed the least change, followed by corn stover, wood pellet, and miscanthus. This aligns with our results of in situ Fourier transform infrared analysis, which showed that the biomodifier from miscanthus has the lowest adsorption affinity, while the one from animal waste has the highest adsorption onto siliceous stones. The higher adsorption efficiency of animal-based biomodifier is also verified by DFT-based molecular modeling, showing that the lipid and protein contents of animal waste, containing highly polar small compounds, exhibit a better adsorption to silica nanoparticles compared to carbohydrate of terrestrial plants.
Keywords: binding energy; biomass; biomodified binder; bitumen; contact angle; moisture damage; preferential adsorption.