Time-Dependent Microstructure of Bitumen and Its Fractions by Modulated Differential Scanning Calorimetry

Bitumen fractions were analyzed by modulated differential scanning calorimetry (MDSC) before and after annealing at room temperature. MDSC allowed for separating glass transitions (Tg's) from order−disorder transitions. All fractions showed at least two Tg's and different states of order. Saturates were semicrystalline, aromatics were amorphous, resins, and asphaltenes were mesophasic. In bitumen, the fractions order in four stages upon cooling from the melt. In the first stage, all fractions order rapidly into a weakly organized phase. In the second stage, low molecular weight saturated segments crystallize. In the third stage, high molecular weight saturated segments crystallize. In the fourth stage, resins and asphaltenes order into a mesophase. The third and fourth stages are responsible for the room-temperature (steric) hardening of bitumen.