Exploring Aggregate Morphological Characteristics under Laboratory Polishing for Enhanced Pavement Skid Resistance

As the use of recycled asphalt pavement (RAP) in pavement construction grows for sustainable development, it becomes essential to investigate potential frictional deterioration over time. This study evaluated the friction properties of recovered RAP material aggregates compared with raw aggregates across various polishing cycles. The micro-Deval test was employed to simulate aggregate loss of texture, while morphological and friction properties were measured using an aggregate imaging measurement system (AIMS-II), along with a British pendulum tester (BPT) and dynamic friction tester (DFT). Additionally, Fourier transform infrared spectroscopy (FTIR) was employed to assess its potential in determining the origin and composition of RAP material aggregates. A simple method was used to fabricate custom aggregate rings, allowing for accurate testing in the DFT setup. The aggregate testing results revealed notable variations across the measurement techniques. AIMS-II analysis showed that traprock (maroon-colored) exhibited the highest surface texture, while DFT and BPT results indicated that certain limestones outperformed traprock in friction properties. Additionally, the testing results demonstrated that the RAP materials were comparable to, or even outperformed, certain limestone sources. However, because of potential variability within RAP stockpiles, careful quantification is necessary to assess their suitability. FTIR analysis demonstrated its ability to distinguish between carbonate-rich and silica-rich aggregates; however, further research is needed to build a library of aggregate sources. Finally, a machine learning algorithm identified the loss of aggregate DFT 20 values as the most significant aggregate property representing friction loss in asphalt mixtures.