Preventing Assembly and Crystallization of Alkane Acids at the Silica-Bitumen Interface To Enhance Interfacial Resistance to Moisture Damage

The accumulation and crystallization of alkane acids at the interface of bitumen and siliceous aggregates are known to increase the propensity for moisture damage in bitumen-based composites such as asphalt pavement. This paper examines strategies for surface passivation of siliceous substrates to prevent alkane acid accumulation at the bitumen-silica interface. This study involves three parts: (1) direct imaging of model bitumen-silica interfaces by atomic force microscopy (AFM), (2) transmission electron microscopy (TEM) and in situ Fourier transform infrared spectroscopy (FTIR) of silica nanoparticles (SiO2 NPs) passivated with bioderived compounds, and (3) density functional theory (DFT) computational modeling of single-molecule binding energies to siliceous surfaces. AFM results suggest that acid crystallization at the bitumen- silica interface is initiated by acid molecules binding to active sites of siliceous surfaces and that acid accumulation can be effectively prevented by the passivation of these active sites. From a mixture of bioderived compounds, the primary molecules that bound to SiO2 NP were rich in polyaromatic and polar groups as determined by TEM and FTIR. DFT modeling identified specific bioderived molecules with high affinity for silica that could displace alkane acids from siliceous substrates while passivating active sites of siliceous surfaces. Accordingly, the study results demonstrate the feasibility of designing functional materials with built-in reinforcement mechanisms against moisture damage. Understanding the role of surface-active compounds and their adsorption mechanisms can help improve current design methodologies used for paving mixtures and develop adhesion promotors to enhance the resistance of bitumen-silica interface to moisture damage. The study results show that autonomous molecular migration can be exploited for the design of functional materials with built-in reinforcement mechanisms against moisture damage.