Influence of Aggregate Grading on the Compressive Strength of M25 Concrete: An Experimental Study

Adjusting the particle-size distribution of aggregate raised the 28-day compressive strength of M25 concrete by about 37–38% at a fixed water–cement ratio and cement content. An M25 mix (water–cement ratio 0.50, cement 372 kg/m³, water 186 kg/m³) was designed to IS 10262:2009. Six blends of coarse aggregate (4.75–20 mm) and five blends of fine aggregate (0.3–2.36 mm) were prepared by recombining sieved fractions, and 150 mm cubes were tested in compression. For the coarse blends, 28-day strength rose from 25.4 to 34.8 MPa as the share of the 13.2 mm and 20 mm fractions increased from 30% to 80%, while the best 3-day and 7-day results came from a different blend, with 60% of those fractions. For the fine blends, 28-day strength rose from 29.5 MPa to a maximum of 40.6 MPa at a 28/18/32/22 blend of the 2.36 mm, 1.7 mm, 600 µm and 300 µm fractions, then fell slightly. The study is exploratory and used one set of materials, so the results should be confirmed with replicate specimens before use in design.