Impact of crushing processes on aggregate morphology: evaluation using FAA and AIMS tests

This study evaluates the influence of lithology and crushing processes on the morphology of fine aggregates from five quarries of plutonic igneous and metamorphic origin. Three particle size fractions (0.30, 0.60, and 1.18 mm) were analyzed using the Aggregate Imaging Measurement System (AIMS) and the Fine Aggregate Angularity (FAA) test according to Brazilian standards DNIT 432/2020 and DNIT 415/2019, respectively. The originality of this study lies in the integrated evaluation of geological anisotropy, crushing technology, and aggregate morphology using both indirect (FAA) and image-based (AIMS) methods under real quarry operating conditions. The results demonstrated that geological features such as magmatic foliation, mineral orientation, gneissic banding, and cleavage planes influence aggregate shape and angularity by controlling preferential fracture mechanisms during crushing. However, the cone crusher (CC) and, especially, the vertical shaft impact crusher (VSI) were capable of partially mitigating these geological effects, producing predominantly semicircular and subrounded to subangular particles. Aggregates processed by VSI exhibited more uniform 2D shape distributions and lower shape variability than those produced by CC, particularly for metamorphic rocks. Statistical analysis (ANOVA) revealed significant differences (p < 0.05) between FAA and AIMS results, indicating that the indirect nature of FAA may lead to angularity interpretations that differ from those obtained through image-based measurements. The findings highlight the importance of considering both lithology and crushing technology in aggregate production, as well as the need for more reliable and standardized protocols for morphological characterization in civil engineering applications.