Effect of component characteristics on mechanical properties of asphalt: A molecular dynamics study

Large-scale application of reclaimed asphalt and modifiers in asphalt admixtures make a claim for the component regulation mechanism of asphalt thus to improve the mechanical properties of asphalt admixtures. In this study, the effects of component characteristics on the micromechanical properties of three common asphalts (AAA-1, AAM-1 and AAK-1) collected in the Strategic Highway Research Program's Materials Reference Library were studied by using molecular dynamics simulation methods. The physical and mechanical properties of these asphalts were simulated, including density, glassy transition temperature (Tg), flow temperature (Tf), bulk modulus, shear modulus and Young's modulus. In addition, an aggregate-asphalt-aggregate model was constructed to simulate a confined shear case to explore the contribution of different components to the mechanical properties of the asphalt mixture. The results show that the densities of AAA-1, AAK-1 and AAM-1 asphalt models are 0.991 ± 0.005 g/cm3, 1.00 ± 0.005 g/cm3 and 0.968 ± 0.004 g/cm3, which verify the rationality of the models. The Tg of AAA-1, AAK-1 and AAM-1 asphalt models are 253.70 K, 268.74 K and 257.55 K, respectively, which are consistent with the experimental results of the Differential Scanning Calorimeter. The Tf of AAA-1, AAK-1 and AAM-1 asphalt models are 361.26 K, 374.48 K and 374.95 K, respectively. The diffusion of resin and aromatic are sensitive to temperature from mean squared displacement (MSD) analysis. The bulk modulus, shear modulus and Young's modulus of the AAM-1 asphalt model are 3.254 GPa, 0.757 GPa and 2.109 GPa, which are the highest among these three models due to its highest relative molecular mass and resin content. The confined shear simulation on the aggregate-asphalt-aggregate model shows that the shear strength between aggregate and AAM-1 asphalt is the strongest, followed by the case of AAA-1 and AAK-1, in keeping with the sequence of the shear modulus of three asphalts. Asphaltene has the largest MSD and contributes greatly to the adhesion between the asphalt and aggregate interface during the confined shear. These computed parameters could be the basis for the design of high-modulus asphalt admixture applicated in different environments.