The presence of which material is considered acceptable in a combination for fine aggregates?

Manufactured sand is considered an acceptable material in fine aggregates because it is specifically engineered to have the desired properties for concrete mixes. This type of sand is produced by crushing rocks and stones, which results in a material that can closely match the properties of natural sand, ensuring proper workability and strength in concrete.

Using manufactured sand allows for more control over the grading and particle shape, resulting in consistent performance in concrete applications. It can help improve the overall quality of the concrete by providing a good particle distribution and enabling the mix to achieve the required durability and strength.

On the other hand, while crushed concrete can be used in certain applications, it may introduce variability in quality and properties that are not always desirable. Fresh mortar is generally not included with fine aggregates as it can affect the setting and workability of the concrete mix negatively. Gravel, while acceptable as a coarse aggregate, does not meet the criteria for fine aggregates, as fine aggregates are typically defined by their grain size.