Asphalt is a dark brown to black viscous material that is mainly obtained from residue of petroleum distillation. It is widely used in pavement. The exact components of asphalt are difficult to define because crude petroleum varies in composition from source to source. We pursue the idea of creating a model mixture for asphalt, comprised of only 5-10 compounds. The model mixture should be able to replicate several physical properties of core asphalts for Strategic Highway Research Program (SHRP) while possessing chemical functionalities consistent with those of real asphalts, as based on experimental characterizations available from literature data. Model asphalts cannot replace asphalts in engineering applications. Instead they provide inputs for fundamental studies in order to elucidate why different asphalts exhibit different physical properties.

In my project, I investigate asphalt using "molecular simulation": statistical mechanics-based tools that can predict microscopic and macroscopic properties of a system based on the details of its molecule-molecule interactions. Two common molecular simulation approaches were used: Monte Carlo (MC) and molecular dynamics (MD). Monte Carlo method uses "random walks" (stochastic methods) to simulate and analyze molecular systems. In this method, samples are drawn from a probability distribution, often the classical Boltzmann distribution, to obtain thermodynamic properties, such as heat capacities, phase transition temperatures. For molecular dynamics, the basic ingredient is the calculation of the forces on each atom, and from that information, the position of each atom throughout a specified period of time (typically on the order of nanoseconds = 10^-9 seconds). Newton's equations are used in molecular dynamics to simulate atomic motion.

In my research work, I first chose naphthalene and 1-methylnaphthalene as two model components in core asphalt to learn how to use MC and MD to simulate their properties. The results from simulations were compared with literature data and they showed good agreement. In the future I will simulate other pure components of core asphalts and also mixture of them in order to find a way to improve the properties of asphalt.