Study on modification mechanism of nano-ZnO/polymerised styrene butadiene composite-modified asphalt using density functional theory

The modification mechanism between nano-zinc oxide (nano-ZnO), polymerised styrene butadiene (PSB) and asphalt were studied by first-principles calculation, revealed the modification mechanism from the molecular scale. The asphalt was divided into four components: saturate, aromatic, resin and asphaltene, used nano-ZnO and PSB as modifiers for asphalt, constructed systems of asphalt modifiers and asphalt components, then geometric optimisation of each system. Density functional theory (DFT) was used to calculate the binding energy and the number of charges transferred between saturate, aromatic, resin and nano-ZnO, PSB. Calculated results show that nano-ZnO has chemical modification of hydroxylation to asphalt. Meanwhile, the nano-ZnO has a physical adsorption effect based on van der Waals force for each component of asphalt, which can be stably combined with asphalt. PSB can form aromatic-ring stacking with asphalt, making PSB combined with asphalt, the interaction of this accumulation is not strong, and the combination of PSB and asphalt is unstable. When nano-ZnO and PSB were simultaneously added into the asphalt, the absolute value of the binding energy between saturate, aromatic, resin and PSB all increased, nano-ZnO acts as a medium for attracting asphalt and PSB, the addition of nano-ZnO can effectively enhance the binding stability of PSB and asphalt.