What does a sieve size of No. 40 indicate?

A sieve size of No. 40 indicates that there are 40 openings per lineal inch. This classification is essential in material grading, particularly in construction and civil engineering. The specific size designation helps determine the particle size distribution of aggregates, which in turn affects the properties of materials such as concrete or asphalt.

When materials are passed through a No. 40 sieve, particles that are smaller than the sieve openings will pass through, while larger particles will be retained. This kind of classification is vital for ensuring the right consistency and quality in construction materials.

The other choices involve different measurements or percentages that do not correlate directly with the standard sieve size identification system. The options referring to microns, voids, or kilograms pertain to different concepts in material science and construction and would not accurately define what is meant by a No. 40 sieve.