Assessing the impact of ultra-thin diamond nanothreads on the glass transition temperature of a bituminous binder

Abstract

Low-temperature cracking and rutting are the most destructive problems of bitumen that hinder the application of high-performance bitumen engineering, which is dependent on its glass transition temperature (T_g). Through in silico studies, this work has systematically investigated the T_g of a bituminous binder with the addition of diamond nanothread (DNT) fillers with varying filler content, alignment, distribution, and functional groups. In general, the glass transition phenomenon of the bitumen is determined by the mobility of its constituent molecules. T_g is found to increase gradually with the increase in the weight percentage of DNT and then decreases when the weight percentage exceeds 5.05 wt%. The enhancement effect on T_g is weakened when DNTs are distributed vertically or functionalized with functional groups. Specifically, DNT fillers induce inhomogeneity, which promotes the motion of small molecules while hindering the motion of large molecules. The aggregation of DNTs and the molecular environment in the vicinity of DNTs directly affect T_g. In summary, aggregation and adhesion are the dominant mechanisms affecting the mobility of the constituent molecules in the DNT/bitumen system and thus its glass transition temperature. This work provides in-depth insights into the underlying mechanisms for the glass transition of a bituminous binder, which could serve as theoretical guidance for tuning the low-temperature performance of the bituminous binder.