What is the Optimal Size of Aggregate Used in Concrete?

The usual range of aggregate used in construction is between 9.5 mm and 37.5 mm in diameter, with the most common size being 20 mm. Coarse-grained aggregates are particles larger than 9.5 mm. A larger size, 40 mm, is more commonly used in bulk concrete. The size distribution of fine to coarse-grained aggregates plays an important role in the workability and performance of concrete.

The use of slag is not limited to roads, but slag aggregates are widely used in all types of civil works. As a natural material, the aggregate may include worn or unstable particles in the supplied product. If there is a deficiency in a locally available fine aggregate, concrete may benefit from the addition of air entrainment, additional cement, or a supplemental cementitious material (SCM). Generally, the aggregate in concrete comprises 60% to 75% of the mix.

This is the optimal size aggregate used in PCC for constructing pavements, roads, walkways, or driveways. In contracts and agreements, “maximum aggregate size” refers to the smallest sieve that 100% of your aggregate can pass through. Good quality aggregate must be clean, hard, strong, and free of absorbed harmful chemicals, clay coatings, or other contaminants that may affect cement hydration or reduce paste-aggregate bonding. Optimized grading based on aggregate availability and project requirements will result in cost-effective concrete with good workability and finishability.

The absorption and surface moisture of aggregates are simple but critically important aspects of producing concrete that consistently achieves the specified or desired strength. Only 15-34% of the aggregates in zone 1 will pass through a 0.6 mm screen; 35-59% of the aggregates in zone 2 will; 60-79% of zone 3 will; and 80-100% of zone 4 will. In general, 40 mm size aggregate is used for normal strengths and 20 mm size is used for high strength concrete. To achieve a good concrete mix, the chosen aggregate must be clean, hard particles free of clay coatings and absorbed chemicals.

Aggregates are one of the most important components of concrete that give it body and reduce shrinkage. A track record of good performance of a local aggregate also provides an indication of its performance in service.