Analysis and identification of elongated mineral particles in road coated aggregates.

The issue of Elongated Mineral Particles (EMP) in building materials has been revealed during roadworks in 2013 in France. In fact, road coating aggregates are made of specific rock gravels that can contain Naturally Occurring Asbestos (NOA), which is mainly actinolite. The legislation refers to six regulatory asbestos, that consist in asbestiform habitus of the six minerals. The current technical standard is not adapted for analyzing natural material, as it cannot distinguish the asbestiform fibers and the cleavage fragments fibers. Therefore, the Eichrom Laboratories developed an internal method for analyzing rock gravel and identifying the different kind of EMP. This analytical method is based on an accurate sample preparation and three techniques at different resolutions: a petrological analysis with a stereomicroscope, a mineralogical analysis with a Polarized Light Microscope (PLM) and structural and with a Transmission Electronic Microscope (TEM). This innovative procedure is reinforced by the expertise of geologists, which is not necessary for the manufactured products. Putting the process in a national standard is essential for result homogenization of the asbestos testing laboratories.