Active Mineral Fillers Arrest Migrations of Alkane Acids to the Interface of Bitumen and Siliceous Surfaces

Moisture damage is one of the most intractable and costly pavement damage problems. Acid compounds in bitumen are implicated in the increased risk of moisture damage at the bitumen-aggregate interface, especially in cases where siliceous aggregates are used in pavement structure. This paper examines the efficacy of using active mineral powders as dopants in bitumen to control the migration of alkane acids to the interface of bitumen and siliceous stone aggregates. Results from combined atomic force microscopy and infrared spectroscopy (AFM-IR) confirm that alkane acids accumulate at the bitumen-silica interface which in turn negatively affect adhesion specially under wet conditions. Mineral powders including silica or alumina effectively reduced the accumulation and crystallization of alkane acids at the silica interface, but dry calcium carbonate powder was ineffective. Due to their polar surface and high surface area, the oxide particles create internal competition to draw alkane acids away from the interface. The study results help explain the essential role of active mineral fillers in controlling the migration of detrimental alkane acids to the interface of bitumen and siliceous aggregates which are known to be susceptible to moisture damage.