Quantitative Evaluation of Microtexture Frictional Properties of Aggregates and Reclaimed Asphalt Pavement

The frictional properties of aggregates play a significant role in determining pavement skid resistance. To preserve natural aggregates, reclaimed asphalt pavement (RAP) has been widely used for decades. However, its use in pavement surface courses is often limited due to its unknown frictional properties. Therefore, this research aimed to quantitatively investigate both aggregates and RAP to develop a quick evaluation method for frictional properties. Nine types of aggregates from Tennessee were selected for relative frictional tests. X-ray fluorescence was utilized to quantify the silica dioxide (${\mathrm{SiO}}_2$) contents, establishing correlations with polish stone value (PSV), micro-Deval (MD) abrasion loss, and surface morphological characteristics of aggregates tested via the aggregate image measurement system. Subsequently, to develop a quick way to measure the ${\mathrm{SiO}}_2$ of RAP, laboratory-produced RAP and field-sampled RAP were compared. Laboratory-produced RAP was fabricated and compared with chemical trichloroethylene (TCE) and a hammer-crushed processing method to accurately measure the ${\mathrm{SiO}}_2$ content for the application of field-sampled RAP. Field pavement friction tests were conducted to correlate the laboratory findings to field measurements. Results show that the coefficients of determination (${\mathrm{R}}^2$) of ${\mathrm{SiO}}_2$ from raw aggregates with PSV, MD loss, and texture loss are 0.81, 0.60, and 0.78, respectively. Field-sampled RAP washed by TCE three times could provide more accurate ${\mathrm{SiO}}_2$ content compared with hammer crushing. The field pavement friction test demonstrates that pavements with lower ${\mathrm{SiO}}_2$ contents exhibit reduced skid resistance due to texture loss caused by traffic polishing. These findings offer a straightforward method for evaluating pavement friction and selecting RAP with high skid resistance, where higher ${\mathrm{SiO}}_2$ content provides higher friction properties. As a result, this research provides a valuable strategy for the rapid evaluation of aggregates and RAP for skid resistance.