An experimental study of the effect of mineral hardness contrast in aggregates on long-term pavement friction

This study emphasises the significance of aggregate hardness contrast in influencing long-term pavement friction. Eight types of aggregates with varying quartz content were tested. Mosaics built with the selected aggregates, representing pavement layers, underwent polishing tests to evaluate their long-term friction. The results revealed a parabolic variation, peaking at 50% quartz, confirming that the Aggregate Hardness Parameter is crucial for long-term pavement friction. Consequently, long-term pavement friction relies on significant hardness variation among aggregate minerals, rather than solely their average hardness. This finding contradicts the well-established view that a higher quartz content in aggregates consistently enhances their long-term friction retention.