Insights into the role of aggregate shape in enhancing rheology and reducing cement usage in concrete mixture design

Advancements in crushing techniques have significantly improved the particle shape of crushed stone, which should have a positive impact on concrete properties. This study employs micro-CT to compare the particle shapes of crushed stone and gravel, followed by the preparation of concrete having optimized flow properties with water-cement ratios of 0.4 and 0.5, incorporating varying excess paste thicknesses. The study investigates the relationships between excess paste thickness, rheology, and compressive strength. The results indicated that crushed stone based on the advanced crushing techniques has particle shape parameters comparable to gravel, occupying less volume for the same particle size. The test results exhibited that the concrete mix having crushed stone exhibited better flowability and lower yield stress compared with gravel based concrete, irrespective of excess paste thickness. No clear correlation was observed between slump and yield stress across different water-cement ratios and aggregate types. The excess paste thickness had no positive impact in reducing the plastic viscosity at w/c of 0.4. Initial yield stress decreased with an increase in excess paste thickness, and had a significant positive impact in reducing the structuration rate of crushed stone concrete, opposite to gravel concrete. Furthermore, no significant effect of excess paste thickness on the mechanical properties of the concrete was observed. Notably, well-shaped crushed stone concrete saved 20 kg/m3 to 55 kg/m3 of cement compared to gravel concrete, while maintaining similar workability and mechanical performance. These findings suggest the need to reconsider the effects of aggregate type on concrete rheology, providing valuable insights for developing eco-friendly, high-performance concrete mixtures.