The Influence of Aggregate Grading on the Workability and Strength of High-Strength Concrete

High-strength concrete (HSC) is widely used in structural applications because of its superior mechanical properties and durability. However, its extensive use is often associated with high cement consumption and a greater environmental burden. This study evaluates the influence of coarse aggregate size distribution on the performance of sustainable high-strength concrete (HSC) incorporating a 40% ternary SCM replacement (metakaolin, GGBS, and silica fume). To achieve a target compressive strength of 100 MPa, three mixtures were tested with varying aggregate gradings: 5–10 mm (M1), 10–20 mm (M2), and 5–20 mm (M3). Results at 28 days showed that M3 (continuous grading) achieved the highest compressive strength (114 MPa), followed by M2 (111 MPa) and M1 (104 MPa). While all mixes exceeded the 100 MPa threshold, workability was highly sensitive to aggregate size; M1 exhibited the lowest slump (20 mm), whereas M3 achieved 90 mm, indicating that continuous grading significantly improves particle packing and fluid behaviour in high-binder systems. These findings demonstrate that a 40% reduction in Portland cement is viable for 100 MPa applications when aggregate skeletons are selected to minimize void ratios, though the low workability of smaller fractions (M1) requires increased dosage of high-range water reducers.