Analysis of the nanoscale phase characteristics of bitumen and bitumen in mastics and mixtures via AFM.

A peak force quantitative nanomechanical mode (PF-QNM) can be used to simultaneously measure the topographical and nanomechanical property maps of samples. Currently, few studies used this mode to investigate the phase characteristics of bitumen in mastics and mixtures. The present study adopted hot-bitumen-pouring methods to prepare base bitumen surface samples and further used frozen-storage and low-temperature-cutting methods to prepare the internal samples of base bitumen in mastics and mixtures. Then, the atomic force microscopy (AFM) PF-QNM mode was used to collect data on the topographical and nanomechanical properties of bitumen and bitumen in mastics and mixtures. The results indicated that a typical bee structure only appeared on the bitumen surface. In contrast to the bitumen surface, the bitumen interior showed two phases, A- and B-phase, which were close in some properties to the periphase and paraphase of the bitumen surface, respectively. Furthermore, the addition of mineral aggregates affected the phase characteristics of the free bitumen interior. With an increase in the mineral aggregate surface area, the proportion of A-phase decreased and that of B-phase increased in the free bitumen interior. LAY DESCRIPTION: Bitumen is a complex mixture of hydrocarbons primarily applied for pavement materials. In the pavement industry, the bituminous mixture is a multilevel system, in which bitumen acts as a binder binding the aggregates and fillers to form bituminous mixture. Currently, atomic force microscopy (AFM), which is an advanced microscopy technology, has been used to investigate bitumen surface phase characteristics at the nanoscale. However, few studies have directly explored the nanoscale phase characteristics of bitumen in mastics or mixtures. Recently, with the progress of technology, a peak-force-quantitative-nanomechanical mode (PF-QNM) can be used to simultaneously measure the topographical and nanomechanical property maps of samples. Relying on this advanced mode, this study analyzed the nanoscale phase characteristics of the bitumen surface and interior, and further explored the effect of mineral aggregates on bitumen interior phase characteristics. In detail, we used hot-bitumen-pouring methods to prepare bitumen surface samples and adopted frozen-storage and low-temperature-cutting methods to prepare the internal samples of bitumen in mastics and mixtures. Subsequently, AFM PF-QNM mode was used to collect topographical and nanomechanical property maps of bitumen and bitumen in mastics and mixtures. The results indicated that the bitumen interior only consisted of two phases, where the A-phase presented low adhesion, deformation, and dissipation, while the B-phase presented high adhesion, deformation, and dissipation. A-phase and B-phase of the bitumen interior were close to the periphase and paraphase of the bitumen surface, respectively. Furthermore, the addition of mineral aggregates significantly affected the bitumen interior phase characteristics.