MICA - is its problem reputation deserved?

Abstract

Mica in road building aggregates was first identified as a potential problem in the 1960s. Since then, numerous specification requirements minimising mica contents have been incorporated in aggregate specifications over the years, unfortunately becoming more severe with time. The current COTO (2020) requirements exclude many potentially useful materials, probably unnecessarily, due to an apparent misunderstanding of the mineralogical, identification and engineering properties and behaviour of micas in road layers. This paper considers the history of mica problems and specifications and makes recommendations regarding their testing and evaluation for road aggregates. A proposed test method for their assessment is suggested.