SPATIAL ARRANGEMENTS AND PHYSICAL PROPERTIES OF GRANULAR MINERAL MATERIALS AND COMPOSTED GREEN WASTE IN GREEN ROOF GROWING MEDIA

Green roofs create unique challenges for growing media development. It is important for the growing media to supply green roof vegetation with sufficient oxygen and water to encourage plant growth and development. Green roof growing media must be able to maintain a low bulk density in order to minimise the impact on load bearing capacity of the supporting building. The water holding capacity of green roof growing media also has an important role in relation to the water retention function of a green roof system. A greater understanding of the processes that occur in the structural matrix of green roof growing media could inform substrate material selection and lead to improvements in the environmental functions and performance of a green roof system. Green roof growing media mixes were prepared using 80% (v/v) of either; crushed brick, crushed tile or pelletised power station fly ash (Lytag^®) mixed with 20% (v/v) composted green waste. Physical properties such as particle size distribution, air filled porosity and water holding capacity were analysed using tradi¬tional methods for composted materials. Polished block and thin sectioning techniques were also used to observe the spatial arrangements between particles and the pore space architecture. The formation of stable aggregates created between the different mineral materials and the composted green waste is discussed in relation to the prevention of physical degradation of the growing media. In addition, the effect of spatial arrangements on pore space architecture and physical properties of green roof growing media is considered.