On the homogeneity of a thick layer of mixed granules in optical quality inspection

Abstract

Optical inspection of a thick layer of granules for foreign particles does not directly reveal their true number and the more so if the layer is not homogenous. This raises questions such as “how do I know if the layer is homogenous?” and “what is the relation between the observable particles and the true number?” In this work a theory is proposed for granules with a minority of flat plates that explains their statistical properties under the homogenous condition. Moreover, it offers a simple test for homogeneity or, vice-versa, a way to calculate the true contents in a thick homogenous layer from surface observations of the number of plates. The theory is tested successfully on a uniform ball batch and on dry and moist 2-8 mm gravel batches. The latter served as scaled labsimulations of a concrete demolition waste stream.