Leaching of polycyclic aromatic hydrocarbons from reclaimed asphalt : an assessment using standard and novel laboratory tests and a newly developed leaching model

Reclaimed asphalt (RA) is a valuable resource derived from bituminous materials removed from roads during pavement repair and reconstruction. It is a material which is not currently used to its full potential due to the mechanical and environmental uncertainties surrounding it, including concerns about leaching of chemicals that may eventually reach groundwater. The work for this thesis comprises three major parts: a laboratory leaching study using established leaching tests, the development of a novel leaching test procedure - the “Sawtooth Test” and the development of a new numerical leaching model. When road construction materials are in contact with water, there is potential for leaching to occur. Asphalt, for instance, has inherent contaminants associated with the aggregates and binder. With recycled materials such as RA, there is an increased uncertainty surrounding their polluting potential. This uncertainty lies in the possible increased range and quantity of contaminants to be released due to the previous service life of the material and the presence of coal tar in older materials. Three different types of leaching tests were applied to a range of asphalt mixes containing RA during the course of this work. They are (i) a batch test at a liquid to solid (L/S) ratio of 10 l/kg, (ii) an upflow percolation test which is terminated once a cumulative L/S ratio of 10 l/kg is achieved, and (iii) a new procedure - the “Sawtooth Test”. The ‘Sawtooth Test’ was developed in order to avoid the disadvantages associated with the up-flow percolation test, whilst providing a more complete assessment of leaching behaviour than the batch test. Finally, a numerical, conceptual model was developed to simulate leaching from RA during leaching tests. The model can simulate both the “Sawtooth Test” and the percolation test. Most importantly, with further work, the use of the model and the “Sawtooth Test” in combination may reduce the need for conducting the more expensive and time-consuming percolation tests.