In 1925, Duff Abrams introduced the concept of fineness modulus (FM) for estimating the proportions of fine and course aggregates in concrete mixtures. The premise: "aggregate of the same fineness modulus will require the same quantity of water to produce a mix of the same consistnecy and give a concrete of the same strength."
Before calculating FM, lab technicians perform a sieve analysis to determine the particle size distribution, or grading, of the aggregate sample. FM is the sum of the total percentages retained on each specified sieve divided by 100. ASTM C 33 requires the FM of fine aggregate to be between 2.3 and 3.1. The higher the FM, the coarser the aggregate. Fine aggregate affects many concrete properties, including workability and finishability. Usually, a lower FM results in more paste, making concrete easier to finish. For the high cement contents used in the production of high-strength concrete, coarse sand with an FM around 3.0 produces concrete with the best workability and highest compressive strength.