How modern petrographic analysis of roadstone aggregate can provide a better understanding of their frictional properties

The overall frictional performance of road wearing courses is directly related to the microtexture of the included stone particles. This study develops a detailed understanding of how mineralogy, petrography, and microstructure in different rock types, used as high polished stone value (hPSV) surfacing in Ireland, is related to the provision of frictional resistance. Whilst the surface microtexture of any stone particle is predominantly a function of grainsize, it is mostly the distribution and shape of surface topographic peaks and dales (asperities) that determines its frictional properties. These features are investigated using traditional microscopy in tandem with digital metrology and 3D Raman spectroscopy. The study follows the development of microtexture during artificial wear using standard PSV test specimens on an Accelerated Polishing Machine (APM). Measurements and analysis are conducted on raw aggregate (before polishing) and then at regular intervals in the polishing process at 3, 4.5, 6, 7.5 and 9 hours. The measurements follow the evolution of the microtexture, its relation to a selected set of metrological parameters and the petrography of the stone particle. In addition, road cores extracted from the oil track and wheel track of variably trafficked sites provide details on the wear of in-service stone particles for direct comparison with the laboratory worn samples. This work demonstrates that by combining traditional engineering tests, such as and PSV and AAV (Aggregate Abrasion Value), with novel modern methodologies, such as digital metrology and Raman spectroscopy, we can develop a better understanding of how the petrography of stone particles affects surface microtexture and by extension its potential frictional properties. As a result, this data can be utilised by road engineers to design sustainable surfaces by matching frictional demand with available local resources.