The recycling of construction waste is an important stepping-stone towards the achievement of resource conservation and the reduction of environmental impacts through construction. Within the federal programme ProgRess II, it was decided to add an energetic perspective to the use of natural material resources in order to develop synergies as well as to reveal likely conflicts in aims. This also applies to the consideration of secondary materials. However, it has not yet been clarified how to implement such a combined analysis.
The aim of the research project was to extend material-oriented investigations on resource conservation potentials by energetic considerations and to develop an approach that allows the calculation and evaluation of energy consumption of recycling processes.
A method was developed which allows a uniform evaluation of different building products with regard to the energy consumption resulting from their production from construction and demolition waste. This was specified by means of the following building products as examples: Concrete, bricks, sand-lime bricks, gypsum, flat glass, stone wool, PVC profiles and PVC floor covering.
The method describes a sequence of three steps: Two steps for calculation of process energies for (1) the processing of demolition material to secondary material and (2) the conditioning of the secondary material to a useable recycling material with the same quality as corresponding products made by natural material. In the third step, the evaluation is carried out by comparing the process energies of construction products with recycled material with corresponding construction products made of natural materials.
Results indicate that recycled construction products can often be produced with less energy, in some cases with significantly less energy (plastics). This statement cannot be made with the same clarity for mineral materials. Depending on the type of application, recycled products are energetically advantageous (bricks, sand-lime brick), are of similar dimensions (concrete, flat glass) or require a higher energy input to produce (plasterboard, rock wool).
An evaluation of the energetic advantages of recycling products is therefore only reliably if the recycling process chains from demolition material to recycled material in new application are considered as a whole. The results provide important information for developing circular recycling business models in such a way that the potentials of raw material conservation and climate protection are consistently used in an integrative manner.