Measurement of Water Diffusion in Asphalt Binders Using Fourier Transform Infrared-Attenuated Total Reflectance

The presence of moisture in asphalt mixtures deteriorates their structural integrity. Moisture also acts as a catalyst to promote other forms of pavement distresses. Two critical factors influence the rate and intensity of moisture-induced damage: (a) the speed of moisture transport within the asphalt mixture and binder and (b) the influence of moisture on the cohesive and adhesive properties of the constituent materials. Quantifying these factors is essential to understand, model, and mitigate moisture-induced damage in asphalt mixtures. The experimental and analytical procedures used to measure diffusivity of the asphalt binder are presented. Fourier transform infrared-attenuated total reflectance spectroscopy was used to monitor the diffusion of water into thin films of asphalt binder. The diffusion process was characterized by changes in the portions of the spectra that correspond to the presence of water. Two models were used to fit the data obtained: a diffusion model that followed Fick's second law and a dual mode diffusion model with two diffusion coefficients (D-1 and D-2) and weighting factor X-1. Four asphalt binders were evaluated (AAB, AAD, AAF, and ABD), and all presented better fitting under the dual mode diffusion. Diffusivities of asphalt binders AAB, AAD, and AAF were statistically similar, but diffusivity of asphalt binder ABD was different from that of the others.