Question
Design of concrete structures, normally most aggregate sizes are adopted with scopes from 10mm to 20mm. Does an increase of most aggregate size advantage structures?

Answer
To answer this query, let's consider the example of a cube. Surface area to volume ratio of a cube is 6/b that b is the length of cube. This implies that surface area to volume ratio reduces with an increase in volume. Then, when size of maximum aggregate is improved, surface area to be soaked by water per unit volume is condensed. Consequently, water requirement of concrete mixes is reduced accordingly so water or cement ratio can be lowered, resulting in a rise in concrete power.

Though, increase of aggregate size is also accompanied by effect of reduced contact areas and discontinuities formed by these larger sized particles. In general, for utmost aggregate sizes less than 40mm, effect of lower water requirement could offset drawbacks brought about by discontinuities as recommended by Longman Scientific and Technical in 1987.