Development and Evaluation of Functional Open Graded Friction Courses (FOGFC) Mixtures for in Situ Highway Runoff Treatment: Heavy Metals Removal using Inorganic Substances
The highways attributes to a general source of various pollutants and available studies suggested that commonly found heavy metals are Cu, Zn, Pb, Cr etc. In this regard, Permeable Friction Courses (PFC) or Open Graded Friction Courses (OGFC) has been recognized over the last few decades as surfacing material for its attribute in improvements of highway runoff water quality. Typically it is produced by removing fine aggregates from asphalt mix and by placing approximately 50 mm thick layer overlay on top of existing conventional concrete or asphalt surface. The permeable friction course has a typical range of pore space about 18% to 22%. Based on several previous studies it is noted that permeable friction course has a noticeable contribution for removal of particulate pollutants from stormwater runoff. However, removal of dissolved (non-particulate) pollutants, especially heavy metals, has little or no significant effect with permeable frictional courses.
The objective of this study is to develop and evaluate an innovative Functional Open Graded Frictional Courses (FOGFC) by adding inorganic substances for removing heavy metals in highway runoffs, with preliminary focus in removal of copper and zinc. Based on literature review, typical range of copper and zinc concentration in highway runoff was found to be .022 – 7.033 mg/l and .056 - .929 mg/l respectively. A range of inorganic material was used by various studies for removal of Cu and Zn, including Sodium and Calcium bentonites in clay form, Silica gel, TiO2, Zeolites in various form, fly ash and regular hydrotalcite. For the present study, based on the review and comparison of the inorganic absorptive materials based on commercial availability, cost applicability for using in OGFC, Silica gel, Zeolite and Bentonites are selected. A series of batch experiment will be conducted using these three materials to measure their absorption capacity from copper and zinc aqueous solution, and the results of the absorption capacity of Cu and Zn will be checked whether they comply with the previous studies. Based on the feedback from batch experiment and suitable modification, the selected materials will be used in OGFC sample and subsequent test will be conducted to evaluate the performance of the proposed materials for removal of Cu and Zn in OGFC, and the result will be used to select a material and development of Functional OGFC (FOGFC).
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