Effect of Coarse Aggregate Sizes on Properties of Concrete

Concrete, the most commonly used material in construction, owes its strength, durability, and versatility to its constituents, particularly coarse aggregates, which significantly influence its mechanical and durability properties. This research investigates the effect of coarse aggregate sizes (14 mm, 20 mm, and a 50/50 blend of both) on the performance of concrete with a nominal mix ratio of 1:2:4 and a water-cement ratio of 0.55. A total of 36 cubes (100 x 100 x 100 mm) and 36 beams (400 x 100 x 100 mm) were cast to evaluate compressive and flexural strengths, respectively, at curing ages of 7, 14, 21, and 28 days. Additional tests, including slump, water absorption, dry density, aggregate crushing value (ACV), aggregate impact value (AIV), and particle size distribution, were conducted per British and ASTM standards to assess material properties and workability. Results revealed that the 50/50 blend exhibited the highest 28-day compressive strength (16.39 N/mm²), attributed to optimized particle packing, while the 14 mm aggregate mix achieved the highest flexural strength (4.26 N/mm²) due to enhanced stress distribution. The 50/50 blend also demonstrated the lowest water absorption (2.59% at 28 days), indicating superior durability per water absorption. Conversely, the 20 mm aggregate mix showed higher water absorption and lower flexural strength, suggesting a more porous microstructure. The study highlights trade-offs in aggregate sizes. The 50/50 blend optimized compressive strength (16.39 N/mm²) and durability (2.59% water absorption), while 14 mm aggregates gave the highest flexural strength (4.26 N/mm²). These findings show that each aggregate mix performed to standard and the samples tested offered good results for various applications in the construction industry.