Papers by Author: Bo Li

Abstract: It is currently interesting to use thermal or electrical conductive asphalt mixtures for snow-melting and maintenance of asphalt pavements in winter or strain-sensing application. Graphite is the principal conductive filler for asphalt mixtures. The addition of Graphite not only makes asphalts conductive but also has effects on other properties. Considering the visco-elastic property of asphalt, the effects of graphite on rheological properties of asphalt binders were investigated by Viscosity Test(VT) and Dynamic Shear Rheometer(DSR). The results of Viscosity Test indicate that viscosity of asphalt binder increases with an increasing amount of graphite. And the effect is more prominent at higher amount and lower temperature. It means that graphite makes asphalt binders stiffer. The results from DSR tests present that the values of complex modulus increase while phase angles decrease under a proper amount of graphite. It infers that proper amount of graphite can make asphalt a more elastic like material. And the results of rutting parameter point out that graphite can improve the rutting resistance of asphalts.

Abstract: Flexible pavement plays an important role in the primary concrete bridges at present. However, climate environment, to which pavement is exposed, significantly impact pavement stability and long-term performance. Especially, low temperature cracking of asphalt pavement in cold region is a common existing problem. In order to improve the pavement’s crack resistance it is necessary to predict the temperature stress distribution within the asphalt layers. A two-dimensional finite element model of a concrete bridge in thermal and thermal-structural couple analysis is developed to predict temperature and temperature stress variation of asphalt layers in cold region. The temperature stress variation is analyzed at seasonal temperature, different cooling rate and the different thickness of asphalt layers. The model considers a set of primary thermal environmental conditions. Ultimately, the model is aimed at providing pavement engineers with an efficient computational tool that attempts to increase the prediction accuracy of temperature in asphaltic pavement of cold region for more reliable pavement design.

Abstract: Asphalt pavement serving as solar collector has been developed for the heating and cooling of adjacent buildings as well as to keep the pavement ice-free directly. Material parameters such as thermal conductivity and heat capacity are some of the critical parameters related to the efficiency of the asphalt collector. Graphite powders were utilized as thermal conductive fillers to make asphalt collector conductive so as to improve the efficiency of the asphalt collector. The material parameters change with the addition of graphite consequently. In order to access the solar energy absorbability of conductive asphalt collector, it is necessary to predict the temperature distribution within the asphalt layers. A transient, two-dimensional finite element model is developed to predict temperature distributions in conductive asphalt solar collector due to material parameters. The ability of accurately predict asphalt pavement temperature at different depths will greatly help pavement engineers in determining the solar energy potential of conductive asphalt collector. The results from the prediction model show that the surface temperature of pavement decreases slightly with addition of graphite. The differential maximum asphalt temperature variation at a depth of 10cm is significantly more than that at the surface. Higher temperature and lower temperature gradient can also be observed at the depth of 10cm because the heat conduction is accelerated by the addition of graphite.

Abstract: It is currently interesting to use thermal or electrical conductive asphalt concrete for snow-melting and maintenance of asphalt pavements in winter. The addition of conductive fillers may have negative effects on the mechanical properties of asphalt concrete. The performance of conductive asphalt concrete is greatly affected by the initial crack and its propagation. Laboratory tests for neat and conductive asphalt concrete include Dynamic Modulus Test (DMT) and Indirect Tensile Fatigue Test (ITFT). DMT tests indicates that the value of dynamic modulus of asphalt concrete decreases with the increasing graphite content. It means that the conductive asphalt concrete achieves lower stiffness. It can be concluded from ITFT tests that the fatigue life (load cycle times) of conductive asphalt concrete is more than neat ones when stress level is under 1.0 MPa. Meanwhile higher fatigue resistance of conductive asphalt concrete is observed when carbon fibers (2 weight % of total aggregate) were added together with 22% graphite, especially at low stress levels.