Effect of addition of pigments on thermal characteristics and the resulting performance enhancement of asphalt

Lower thermal conduction and higher specific heat of conventional black pavement result in extreme surface temperatures during summers. Asphalt being highly temperature-dependent and viscoelastic, is more vulnerable to damage under vehicular loading at these temperatures. It also contributes towards Urban Heat Island (UHI) effect, hence demanding for non-black pavement surfaces by use of coloring additives which could help in the surface temperature reduction. Iron oxide red and Titanium dioxide white pigments are used to decolor the black mixes. Asphalt and bitumen samples were thermally investigated in heat sinks at three different solar fluxes. Pigment dosage was kept at 4% by weight of total mix for all the types of pigments. Samples were heated and cooled for 3 and 2 h, respectively. The effect of change in temperature of pigmented samples was also verified through performance testing. Cooper wheel tracking and dynamic modulus tests were performed to assess the high-temperature performance while fatigue parameters were assessed with a four-point bending beam fatigue test. Rheology of binder was assessed using Dynamic Shear Rheometer (DSR). Moreover, Rolling Bottle Test and Bitumen Bond Strength Test were also performed to check moisture sensitivity. Results showed that pigmented binder remain 8–10 ⁰C cooler while pigmented asphalt mixtures remain 4–5 ⁰C cooler as compared to unmodified samples. Performance tests reflected higher permanent deformation resistance at higher temperatures without compromising the fatigue property at lower temperatures. Rheology also depicted an increase in stiffness of pigmented binder, indicating better performance at higher temperatures. Use of pigments also enhances the moisture resistance/adhesion of the binder.