Characterization of leachates from drainage asphalt pavement under multi-factor environmental treatments

Pavement leachates could cause considerable environmental contamination. However, the influence of multiple environmental factors on the compositions of pavement leachates is still ill-understood. Therefore, it is necessary to analyse the variation of bitumen leachates with environmental factors and accordingly clarify the leaching mechanism. For this reason, a multi-environment device was invented to perform single-factor, two-factor and full-climate environmental treatments on open-graded friction courses (OGFC) asphalt mixtures. Subsequently, the acidity and alkalinity (pH) value, metal element composition and conductivity of the bitumen leachates with varying environmental treatments were characterized and analysed. Based on this, the leaching mechanism of bitumen leachates dissolved in water was proposed. The results indicated that the bitumen compositions were influenced by different environmental treatments, inducing the variation of pavement leachates. The primary substances of pavements leachates were composed of the organic acid substances and minor metal element ions. Accordingly, the experiment results demonstrated the increase of conductivity, and partial metal element concentration with the extension of treatment time. In terms of the pH value, an initial increase followed by a progressive decrease was observed.