Evaluation of coarse aggregate morphological characteristics affecting performance of heavy-duty asphalt pavements

Abstract

To further understand the effects of coarse aggregate morphological characteristics on performance of heavy-duty HMA pavements, aggregates with ideal spread morphological properties were prepared by hand sorting. Experimental methods were conducted to quantify the F&E ratio, Fractured Particle Percentage, and Particle Index. Image technique was also utilized to characterize the shape indices of Elongation Ratio (ER), Flatness Ratio (FR), Flatness & Elongation Coefficient (FEC), Sphericity Coefficient (SC) and angularity indices of Angularity Index (AI), Equivalent Ellipse Perimeter Ratio (EEPR). Aggregates and mixture performance were evaluated by Crushing Value test, Volumetric analysis, Wheel-Tracking test, and Uniaxial Penetration Shear test. Then all the acquired indices were correlated with the performance results. It was found that the requirement of F&E ratio in current specifications presented some defects for heavy-duty pavements, and a weighted average FEC value of less than 2.0 was proposed as the shape property indicator to control the Flatness & Elongation particles in coarse aggregates. Since Particle Index was rather sensitive to shape properties, it should be careful to use it as an angularity indicator, especially when 100% crushed aggregates were used.