Validation of remote, on-line, near-infrared measurements for the classification of demolition waste

The classification performance, based on measurements obtained by a dedicated remote near-infrared sensor, is validated. Goal is the separation of demolition waste in three fractions: wood, plastic, and stone. In phase one, reference objects are collected and measured in order to develop the classification algorithm and to obtain reference classification results. In phases two and three, the validation performance and robustness are tested under laboratory and industrial conditions. In phase two, preliminary measurements are performed in the laboratory, indicating that some sensor hardware modifications are necessary. In phase three, measurements are performed on a pilot plant according to the following validation design. On the conveyor belt, objects are measured in the middle and at both borders, wet objects are measured in the middle, and a small set of objects is measured during 4 consecutive days. It is checked whether the classification performance obeys the predefined demands. The applied chemometrical techniques are well capable of separating dry demolition waste if the objects are positioned in the middle of the conveyor belt. It is recommended to overcome the sensor miniaturization-scale limitations by applying larger optical parts. The hardware sensor is not robust to wet objects, although this problem was accounted for during the development of the classification procedure. Including wet objects in the training set might overcome this restriction. (C) 2002 Elsevier Science B.V. All rights reserved.