Self-assembly of amorphous sulphur in bitumen-sulphur mixtures and its impact on properties

- Sulphur agglomeration in sulphur-bitumen mixtures was observed.
- The agglomeration of sulphur progresses with time, influencing properties.
- Potential insights to increased stiffness of sulphur extended asphalt mixtures.

The inclusion of elemental sulphur in asphalt mixtures imparts an increased stiffness to the resultant asphalt pavements i.e. sulphur extended asphalt mixtures (SEAM), increasing the pavement performance. In the past, studies have been conducted which have attributed the increase in asphalt mixture stiffness to the formation of sulphur crystals in the voids of the compacted asphalt mixture. However, there are a limited number of studies which have investigated the influence of sulphur on the bitumen-sulphur mixture. This study investigates the fate of elemental sulphur in a bitumen-sulphur mixture over time and the impact of the sulphur to properties of the bitumen-sulphur mixture. It was seen that the sulphur added to bitumen could dissolve in the bitumen, exist as an amorphous phase or a crystalline phase, depending on the concentration of elemental sulphur present in the mixture. The stiffness of the bitumen-sulphur mixture was seen to increase with time, above a threshold sulphur concentration. This increase in the stiffness of the bitumen-sulphur mixture could be attributed to the observed aggregation of the amorphous sulphur over time. These findings provide an alternative theory to explain the increase stiffness of asphalt pavements containing SEAM.