Glass beads for road markings and other industrial usage: Crystallinity and hazardous elements

Abstract

Road markings, a necessary road safety feature, always contain a layer of glass beads that deliver retroreflectivity for driving at night and simultaneously protect the underlying paint layer. Even though such glass beads were generally considered as harmless, their analysis for the presence of crystalline silica was not reported so far. To fill the knowledge gap and to confirm the common perception, representative types of glass beads (11 samples from 6 manufacturing plants worldwide) were evaluated for the presence of crystalline phases by X-ray diffraction and their surface was analysed under scanning electron microscope. The study has not indicated the presence of a crystalline phase in amount higher than environmental background and no irregular shard-like surface features were found under microscope. In addition, analysis with inductively coupled plasma – mass spectrometry revealed only marginal content of hazardous elements. The same results were obtained with glass beads manufactured in identical process but used for other industrial applications. This assessment confirmed that the analysed classes of industrial glass beads are fully annealed and amorphous material that is free from hazardous ingredients.