Effect of Composition on Basic Properties of Engineered Media for Living Roofs and Bioretention

Engineered media used in living roofs and bioretention plays a crucial role in determining stormwater mitigation performance. Engineered media with compositions varying in four aggregates, volumetric ratio of compost (0, 10, and 20%) and three amendments (zeolite, paving sand, and topsoil) were prepared in the laboratory. Media basic properties including particle-size distribution (PSD), dry bulk density, particle density, porosity, and saturated hydraulic conductivity (K-s), were characterized and investigated as a function of the varying composition. All media are classified as poorly-graded sand (SP), exhibiting porosity greater than 0.51, with magnitudes of K-s ranging from 10(-2) to 10(-1) cm/s. Media with pumice-based aggregates have particle densities between 2.21 and 2.48 g/cm(3). The K-s of a pure aggregate classified as SP is positively related to the particle size corresponding to 50% fines on the cumulative PSD curve. K-s values of four aggregates either remain unchanged or decrease by 73% at most with the addition of the compost. An amendment to an aggregate-compost mixture can alter K-s in different ways, depending on its particle shape, coarseness, and organic material. (C) 2016 American Society of Civil Engineers.