Understanding influence of crushers on shape characteristics of fine aggregates based on digital image and conventional techniques

Shape characteristics of fine aggregates, namely angularity and form 2D are greatly associated with the types of rocks, mineralogical compositions, and allied crushing mechanism. Thus, for a given source and aggregate, the type of crusher may play a critical role in producing aggregates having different shape parameters. The present study was undertaken to compare shape parameters of fine aggregates produced from three different crushers, i.e. vertical shaft impactor (VSI), cone crusher (CC) and horizontal shaft impactor (HSI). Basaltic fine aggregates collected from three different crushers was divided into five sizes, namely FA1 (P4.75-R2.36: aggregate passing 4.75 mm and retaining on 2.36 mm), FA2 (P2.36-R1.18), FA3 (P1.18-R0.600), FA4 (P0.600-R0.300) and FA5 (P0.300-R0.150). The angularity and form 2D values of different sizes and types of fine aggregates were measured using Aggregate Image Measurement System (AIMS) in accordance with AASHTO TP 81. Further, conventional technique namely fine aggregate angularity (FAA) test was used to measure angularity of fine aggregates. Furthermore, Angle of Repose (AoR) test was conducted to identify influence of shape characteristics on particle packing behaviour. The study showed that both the techniques (i.e., AIMS and FAA) could differentiate among the quality of fine aggregates produced from different crushers. However, both techniques resulted in opposite trend in angularity of aggregates. The AIMS measurement showed that angularity and form 2D was highest for aggregates produced from HSI crusher followed by CC and VSI. On the other hand, FAA showed that aggregates produced from CC crusher had maximum angularity followed by VSI and HSI. Conclusively, the AIMS showed that HSI crusher could produce aggregates with highest angularity, while FAA showed that this type of crusher might produce aggregates with least angularity. Curiously, the AoR values showed no significant difference for the fine aggregates produced from different crushers. The interrelation between angularity and form 2D is also discussed in the paper.