Classify aggregates according to size by determining which particles pass through a standard 4-inch square sieve. Any particles that do pass through the sieve are fine aggregates, while those that stay behind in the sieve are coarse aggregates.
Fine aggregates are those stone and sand particles that pass through a Number 4 sieve but do not pass through a much finer Number 200 sieve. In the concrete industry, fine aggregates are used to fill spaces between larger coarse aggregate particles, reducing costs by lowering the amount of more expensive cement required in forming a consistent concrete. In road construction, fine aggregates are used in the top paving layer, providing a flat, smooth surface for vehicles.
Coarse aggregates are any stone particles that pass through a Number 3 sieve but are retained by finer meshes. Coarse aggregates are more affordable than fine aggregates, as they are more abundant in nature and because manufacturing them requires less crushing and grinding. In concrete, large amounts of coarse aggregates reduce costs, but overuse of these stones results in an inconsistent, weak product.
Smaller coarse aggregates also find use in road construction, where these stones make up lower foundational layers. The coarsest aggregates are unsuitable for either concrete or paving applications, but they find use as fill stones in low-lying areas.