Author: Zou, Fuliao
Title: Quantitative assessment of the leaching of heavy metals and PAHs from asphalt pavements and its impact
Advisors: Leng, Zhen (CEE)
Degree: Ph.D.
Year: 2023
Subject: Pavements, Asphalt -- Environmental aspects
Pavements, Asphalt
Hong Kong Polytechnic University -- Dissertations
Department: Department of Civil and Environmental Engineering
Pages: xvii, 197 pages : color illustrations
Language: English
Abstract: Asphalt pavements are widely used in road and highway constructions, but environmental concerns have been raised recently regarding their potential leaching of chemical components, i.e., the wear and tear of asphalt pavements can potentially release hazardous components into the environment, posing a threat to the environment and the health of living organisms. However, there are insufficient quantitative studies and data on the pollutant leaching from asphalt pavements and its potential impacts to support or release these concerns.
To fill this research gap, this study aims to systematically investigate the leaching behaviors of asphalt pavements and comprehensively characterize their potential toxicological influences on the aquatic environment. A multi-scale experimental method was proposed to comprehensively investigate the leaching behaviors, including leaching capacity and kinetics at the following three scales: asphalt binder, loose mortar, and compacted mixture. The findings indicated consistency in the leaching behavior of the samples across the three testing scales, with the mixture scale providing a more reliable representation of the actual conditions of asphalt pavements and offering greater precision in estimating long-term leaching. It was revealed that the overall leaching capacity of polycyclic aromatic hydrocarbons (PAHs) from asphalt pavements was generally at low levels, but the leaching of heavy metals may pose a significant environmental hazard. Moreover, the aging of bitumen was found to increase the leaching capacity of heavy metals over time. Therefore, greater attention should be directed towards the leaching of heavy metals to mitigate their potential impact on the environment.
The results of leaching kinetic simulations at the mixture scale revealed that heavy metal leaching from asphalt pavements followed both first and second-order kinetic models, with the latter model offering an appropriate description of the more complex initial stages of the leaching process, while the former model demonstrated precise predictions of the long-term leaching performance. It was identified that the toxicological potential of heavy metals was primarily attributed to their leaching kinetics. Given the finding of a notably high leaching rate during the initial stage, greater focus should be directed toward monitoring the leaching process at this stage. Dense-graded asphalt pavements exhibited a lower leaching rate than open-graded asphalt pavements. However, the reduced leaching rate may not necessarily indicate a lower toxicological potential, highlighting the significance of considering both the leaching kinetics and capacity in evaluating the potential impacts of pollutant leaching from asphalt pavements.
Further investigations were conducted to evaluate the toxicological effects of asphalt pavement leachate on zebrafish by examining their immune, genetic, and inflammatory responses to leachate exposure. The findings suggest that the leaching of pollutants from asphalt pavements, particularly those that incorporate hazardous waste materials, can lead to harmful health effects on zebrafish, including reduced longevity, inflammation, oxidative damage, and possible carcinogenicity. To address this issue, biochar was employed as a metal immobilization agent in asphalt and found to be effective in reducing heavy metal leaching. However, relying solely on biochar may be inadequate in ensuring the safe application of pavements with high leaching capacities.
In summary, this study characterized the leaching behaviors of asphalt pavements, considering both leaching capacity and kinetics, and evaluated the associated environmental impacts. The research emphasizes the importance of monitoring and regulating the pollutant leaching from asphalt pavements to mitigate adverse environmental effects. The findings offer valuable insights into improving the selection of asphalt materials for road construction and maintenance, as well as implementing measures to minimize potential environmental impacts.
Rights: All rights reserved
Access: open access

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