Thermal Properties of Thermochromic Asphalt Binders by Modulated Differential Scanning Calorimetry

Thermochromic materials are substances that can reversibly change their colors in response to temperature. These materials can be designed to have high solar reflectance at high temperature and low solar reflectance at low temperature. They are therefore potential new smart materials that can improve pavement thermal conditions. The innovation of this study was to develop thermochromic asphalt binders possessing dynamic solar reflectance in response to environmental temperature. The preliminary study indicated that the thermochromic binder coating achieved a temperature reduction as high as 6.4°C under the conditions of a typical summer day in Cleveland, Ohio. A comparison of measurements under cold conditions in Cleveland demonstrated that thermochromic asphalt binder could remain warmer than conventional asphalt binder. This attribute helps to improve the resistance of asphalt pavement to low- temperature cracking, delays ice formation on the road surface, and potentially improves the durability and safety of asphalt roads. The phase transition temperature and latent heat of thermochromic asphalt binders were characterized by standard differential scanning calorimetry (DSC). The specific heat capacity, thermal conductivity, and thermal diffusivity of thermochromic asphalt binders were determined by modulated DSC at temperatures ranging from –20°C to 50°C. Comparison measurements found that thermochromic asphalt binders presented higher specific heat capacity, lower thermal conductivity, and lower thermal diffusivity than conventional pure asphalt binders. Empirical models were proposed for the variations of specific heat capacity and thermal conductivity of various asphalt binders as a function of temperature. These models provided data for design and simulation of thermal responses of asphalt pavement incorporating thermochromic binder materials.