In general a recycling process starting with development, planning, production, utilization and disposal of a product, e.g., of a building, during its lifetime may be regarded as a system of material cycles. The main object is to minimize the input of raw materials and the output of waste for every stage of a building. These material cycles may be designed by reprocessing the building material waste to valuables of high quality. To approach this aim a joint research project dealt with the liberation and separation of aggregates (d = 2–16 mm) from concrete waste. The liberation is accomplished by a pneumatic cannon to simulate the stressing in impact crushers. With this cannon spherical concrete samples (d = 150 mm) are comminuted. The comminution is evaluated by the liberation grade. Fully liberated, partially liberated and non‐liberated particles are distinguished. The experiments show an unexpectedly high liberation grade of up to 95% with a comparably small specific energy consumption of about 1 kWh/t. For separating both fully liberated and partially liberated aggregate, a pilot scale zigzag apparatus consisting of a zigzag channel, an air cyclone, a blower, a filter and a feeding system was used. If the diameter of the particles is kept nearly constant (e.g., by sieving) a multi‐stage density separation in a turbulent cross‐flow channel can be carried out. The separation performance may be evaluated by means of the separation function or grade efficiency curve, respectively. For the partially liberated aggregate a comparably good grade sharpness of about 0.74–0.84 is obtained for a 15‐stage zigzag apparatus with different particle size fractions and particle contents in air.
