Abstract Manager

The LC 21-102 standard (CPP Test), employed in Quebec (Canada), uses an accelerated polishing by projection method to simulate maximum wear of pavement coarse aggregates. The residual friction coefficient, measured with a British pendulum, evaluates their suitability for high-traffic road surfaces in terms of skid resistance. However, after observing certain cases of premature wear due to excessive aggregate polishing in some pavement sections (for which the aggregates were initially considered satisfactory based on the CPP test), a study was initiated to re-evaluate the various critical parameters of the method. This research project investigates the impact of polishing by projection time and explores its underlying mechanisms by analyzing changes in aggregate microtexture. Four aggregates with distinct mineralogical compositions and polishing resistances were selected for the study. Their mineralogical and physico-mechanical properties were characterized by using techniques such as optical microscopy, X-ray diffraction (Rietveld),  Los Angeles and Micro-Deval tests. A high-precision 3D laser microprofilometer was employed to capture the surface relief of aggregates and measure their microtexture parameters, including peak density, shape, and height. A British pendulum was used to assess the residual friction coefficient. Tests were conducted before polishing and at various stages extending beyond the standard duration (40 cycles versus 20 cycles). The results indicate a continuous decrease in friction values after the standard polishing time for all aggregates tested, suggesting that extending the polishing duration is necessary to achieve maximum wear. Polishing by projection also appears to follow a distinct mechanism compared to other well-established methods like the vertical-wheel and the Wehner/Schulze: it operates more through indentation, digging the aggregate surface and creating a new microtexture with, on average, less dense but higher and sharper peaks. Additionally, aggregate properties like general and differential hardness seem to influence the microtexture formation and its evolution during polishing.