What comprises fine aggregates in construction?

Fine aggregates in construction primarily consist of particles that are smaller than 4.75 mm in diameter. Sand is the most common form of fine aggregate used in construction and is essential for making concrete, mortar, and plaster. It plays a critical role in providing bulk, strength, and stability to these materials. Sand also helps to fill voids between larger particles, ensuring a more cohesive mixture.

Gravel, while also an aggregate, is categorized as a coarse aggregate because its particles are larger than those of sand. Concrete blocks, on the other hand, are prefabricated construction elements made from concrete, and recycled materials refer to previously used materials repurposed for new construction. Therefore, sand stands out as the definitive example of fine aggregates used in the field, aligning with the correct answer.