How is "fine aggregate" defined?

Fine aggregate is defined as the material that passes through the 4.75 mm sieve. This classification is important in construction and civil engineering because fine aggregates play a critical role in the workability, strength, and durability of concrete. They typically consist of sand and smaller particles that help fill voids between larger coarse aggregates, contributing to a denser and more stable concrete mix.

The significance of this size-based definition is rooted in how aggregates behave in a concrete matrix. Aggregates that pass through the sieve can fill gaps and provide a smooth finishing surface, which is essential for various applications, including pavements and structural elements. By focusing on those particles that are smaller than 4.75 mm, standards for concrete mix designs ensure that proper proportions of fine aggregates are included, which helps in meeting specifications for strength and structural integrity.

In comparison, aggregates larger than 4.75 mm are classified as coarse aggregates and serve different functions in a concrete mix. Options that suggest mixes of coarse and fine aggregates or limit the definition to natural aggregates fail to accurately describe fine aggregates by focusing more on composite materials rather than the individual classification based on particle size.