The fine aggregate comprises the portion of the aggregate, which has a small particle size.
The DOE Method, used by Firstmix was developed for aggregates conforming to BS 882 (see References 5) and the fine aggregate is defined as containing a high proportion of particles passing a 5mm (0.197 in.) sieve. In the US and elsewhere a 4.75mm (0.187 in.) sieve is used as the limit, but this difference is not so great as to prevent the use of the DOE Method for aggregates which are so classified.
For concrete mix design the most significant properties of the fine aggregate are the type and grading.