Laboratory-based Investigation into the Removal Behaviour of Asphalt in Porous Asphalt Mixture on Zinc Ions from Road Runoff

Abstract

This paper was to investigate the removal behaviour of asphalt in pore-space on dissolved zinc from road runoff based on laboratory experiments. Asphalt films were soaked with different initial concentrations of Zn2+ solutions over 720 h. The surface chemical state of asphalt films before and after experiment were examined by X-ray photoelectron spectroscopy(XPS), while solution samples were analysed for Zn2+ concentrations by an inductively coupled plasma atomic emission spectrometer(ICP-AES). Experimental data were further analysed using both kinetics and adsorption isotherms. It confirmed that Zn2+ in solution had been adsorbed to the asphalt film. The initial stage of adsorption matched both the first-order equation and the parabolic diffusion equation; whereas the entire adsorption process was found fit the second-order equation. Moreover, the adsorptive behaviour satisfied the Freundlich model. These provide evidence to support the adsorption ability of asphalt on the pore-walls in porous asphalt with regard to Zn2+ in road runoff.