Grey energy impact of building material recycling – a new assessment method based on process chains

The manufacture of building materials consumes vast quantities of raw materials and accounts for a large proportion of global material flows and GHG emissions. Recycling demolition waste is thus a useful and practical way to conserve resources in the construction sector. For climate protection, it is important to investigate the material-induced grey energy of the recycling process. In this study we ask how grey energies induced by construction products based on secondary differ from equivalent products based on virgin materials. To evaluate this, we use a novel multi-stage assessment method presented in this paper. With this method, for the first time, we are able to calculate grey energy of entire recycling process chains starting from construction and demolition waste and ending with the new secondary material based building product, taking into account all the adjustments necessary to guarantee its functional equivalence to primary material based products. In 15 of the 19 process chains analysed, the use of RC material leads to in part rather significant positive grey energy impacts i.e. energy savings. In nine cases, the savings are over 50%, in six cases they are lower. The most important influential factors is the quality of both, the initial demolition material and the final construction product, defined by the product requirements. Furthermore, we conclude that an integrated recycling system is essential to ensure the recycling of co-products discharged during individual processing steps and provide evidence for further scientific discussion on how recycling can contribute to climate-neutral construction.