Assessment of the physical characteristics and stormwater effluent quality of permeable pavement systems containing recycled materials

Abstract

This paper evaluates the physical characteristics of two recycled materials and the pollutant removal efficiencies of four 0.2 m² tanked permeable pavement rigs in the laboratory, that contained either natural aggregates or these recycled materials in the sub-base. The selected recycled materials were Crushed Concrete Aggregates (CCA) and Cement-bounded Expanded Polystyrene beads (C-EPS) whilst the natural aggregates were basalt and quartzite. Natural stormwater runoff was used as influent. Effluent was collected for analysis after 7–10 mins of discharge. Influent and effluent were analysed for pH, Chemical Oxygen Demand (COD), Dissolved Oxygen (DO), Electroconductivity (EC), turbidity, Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Nitrate-Nitrogen (NO₃-N), reactive phosphorous (${\text{PO}}_4^{3-}$) and sulphates (${\text{SO}}_4^{2-}$). Both CCA and C-EPS had suitable physical properties for use as sub-base materials in PPS. However, C-EPS is recommended for use in pavements with light to no traffic because of its relatively low compressive strength. In terms of pollutant removal efficiencies, significant differences (p < 0.01) were found in pH, EC, TDS, DO, ${\text{PO}}_4^{3-}$ and ${\text{SO}}_4^{2-}$ across all rigs whereas no significant differences (p > 0.05) were found with respect to TSS, turbidity, COD and NO₃-N. Effluent from rigs containing CCA and C-EPS saw significant increases in pH, EC and TDS measurements whilst improvements in DO, TSS, turbidity, COD, ${\text{PO}}_4^{3-}$ and ${\text{SO}}_4^{2-}$ were observed. All mean values except pH were, however, within the Maximum Permissible Levels (MPLs) of water pollutants discharged into the environment according to the Trinidad and Tobago Environmental Management Authority (EMA) or the United States Environmental Protection Agency (US EPA). In this regard, the CCA and C-EPS performed satisfactorily as sub-base materials in the permeable pavement rigs. It is noted, however, that further analysis is recommended through leaching tests on the recycled materials.

Keywords:

• Permeable pavement
• crushed concrete aggregates
• pollutant removal
• small island developing states (SIDS)
• expanded polystyrene
• recycling

Acknowledgements

This research was supported by the University of the West Indies, St. Augustine Campus, the University of Trinidad and Tobago and international engineering firm AECOM. Special thanks to Dr. Denver Cheddie and Mrs. Vitra Ramjattan-Harry from the University of Trinidad and Tobago for their support. The support of Prof Chad Staddon, Director of the International Water Securities Network (University of the West of England, Bristol) is gratefully acknowledged.