Characterization of the Optical and Mechanical Properties of Innovative Multifunctional Thermochromic Asphalt Binders

Abstract

Conventional asphalt binder material strongly absorbs solar energy due to its black color. The consequent high surface temperature of asphalt pavement during the summer accelerates rutting, impairs long-term durability, and causes undesirable environmental impacts (i.e., heat island effects and volatile gas emissions). The black surface of asphalt also leads to high thermal emissivity and a fast rate of temperature drop under severe cold weather conditions. Thermochromic materials are substances that can reversibly change their colors in response to temperature variations. This study presents innovative, multifunctional thermochromic asphalt binder that is designed to modulate the surface temperature of asphalt pavement, i.e., to reduce the surface temperature of pavement during hot summers and to increase the surface temperature during cold winters. Optical measurements are conducted on the thermochromic asphalt binder, which is found to be more reflective than conventional asphalt binders, and the reflectance additionally increases with temperature. Such properties were found to significantly reduce the pavement surface temperature at a typical summer day in Cleveland, Ohio. To study the effects of thermochromic materials on the mechanical performance of the asphalt binder, the thermochromic asphalts are characterized using Superpave binder performance tests. Typical testing methods have been conducted on the asphalt binders at three stages: unaged, rolling thin-film oven (RTFO) residues, and RTFO + pressure aging vessel residuals. Experimental results indicated that the penetration, phase angle, and creep rate of asphalt binder was decreased, while the softening point, viscosity, complex modulus, rutting parameter, fatigue parameter, and stiffness of the asphalt binder was increased when thermochromic powder was added into conventional asphalt binder. Furthermore, increasing the content of thermochromic powder leads to reduction in the penetration depth and creep rate and an increase of the softening point, viscosity, complex shear modulus, rutting parameter, fatigue parameter, and stiffness. Additionally, the high-temperature performance grades of the asphalt binder were enhanced with blending 3–6% black, 6% blue and red thermochromic powders. Therefore, the incorporation of thermochromic materials into asphalt pavement will potentially improve its performance and durability, especially in hot regions.