Dominant effect of fine-scale particle shape in aggregates on the rheology of cement-based mortar: Experimental and DEM study of particle size–shape interactions

Rheological behavior governs the fresh and hardened performance of cementitious materials. Fine aggregate characteristics can strongly alter it, yet the coupled effect of fine aggregate size and shape on shear behavior and mortar rheology remains insufficiently understood. In this study, glass-derived fine aggregates are intentionally produced with prescribed size–shape combinations to isolate size–shape interaction and provide direct experimental evidence at the aggregate scale. High-speed imaging quantifies overall shape parameters of fine aggregate and serves as input to the discrete element method (DEM) model. Direct shear tests are conducted on the glass sands, and rheology is measured on fresh mortars made with the same aggregates. Distinct size and shape combinations yield three characteristic shear stress–displacement responses, demonstrating that fine-scale particles govern shear mobilization by supporting the granular skeleton. Mortar rheology further shows that fine-scale particle shape dominates both Bingham yield stress and plastic viscosity. Peak shear stress of the sands correlates with mortar yield stress, establishing a shear–rheology linkage that predicts fresh mortar rheology from aggregate shear properties and informs sustainable mix design.