Sorting of mineral construction and demolition wastes by near-infrared technology

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Construction and demolition waste (CDW) from building constructions are heterogeneous mixtures, containing clay brick, mineral bounded building materials, like concrete, calcium silicate unit, aerated concrete and lightweight concrete, mortar, plaster, insulation material, wood, plastic etc. Even after processing – such as presorting by hand, single or double-stage crushing, separation of reinforcement by over belt magnetic separators, air sifter for the separation of light components, jigging machines and sieving - the recycled product often remains heterogeneous. In the building industry the amount of composite building materials is increasing nowadays, leading to a more difficult separation. The heterogeneity of recycled aggregates prevents the profitable reuse; therefore, it is necessary to reduce the heterogeneity. Sensor-based single particle sorting devices are the most promising techniques to sort efficiently usable material fractions and to discharge impurities and contaminants from the recyclable fractions. Main focus is the separation of gypsum attachments and composite particles, which cannot be avoided by mechanical crushing. In this project a sorting machine prototype based on a near-infrared technology, which is adapted to mineral building materials, was developed. Furthermore, the sorting rate for different material mixes was determined for different influencing factors, like moisture and pollutions on the surface.