Improving pavement surface friction at high-crash-risk locations is a key strategy through which transportation agencies can enhance roadway safety. For an asphalt concrete (AC) mixture with a given gradation, the polishing resistance of the coarse aggregates is a critical indicator of microtexture, which governs the frictional behavior of AC mixes under low-speed trafficking. This study presents a comparative assessment of two laboratory-based aggregate polishing methods: one, using the Three-Wheel Polishing Device (TWPD) followed by measurement using the Dynamic Friction Tester (DFT), and the other using the British Wheel Polisher (BWP) with subsequent testing via the British Pendulum Tester (BPT) to determine the polished stone value (PSV). While previous studies have compared certain DFT and BPT results, none has directly evaluated both polishing procedures using the same set of coarse aggregate sources. This approach eliminates variability from differences in aggregate shipment times or production zones, allowing a more consistent comparison of polishing resistance and frictional behavior. Seven coarse aggregate sources were evaluated, including three sandstone types, three limestone types, and one rhyolite type. The BWP/BPT test results showed high variability among the aggregates, which was attributed to differences in material properties due to production processes and shipment timing, inconsistencies in sample preparation, and varying sensitivities of the polishing and measurement devices. In contrast, the TWPD/DFT method yielded more distinct and consistent polishing resistance results. Statistical analysis of the TWPD/DFT data, accounting for factors such as aggregate type, DFT speed, sample orientation, duplication, and operator effects, indicated that the DFT20 value (measured at 20 km/h) exhibited no statistically significant variation, confirming its reliability as an indicator of aggregate polishing resistance. Moreover, a comparison with field friction performance demonstrated a strong correlation between TWPD/DFT laboratory results and in situ aggregate behavior, whereas the BWP/BPT outcomes showed poor alignment. Based on these findings, the TWPD/DFT method is recommended as a more reliable and consistent alternative to the BWP/BPT method for laboratory evaluation of aggregate friction in AC mixture design.
Hungria et al. (2026) studied this question.