Question

Do you think coarse aggregates or fine aggregate have a large surface area per unit weight? Why is the concept important

Answer 1

Choose always FINE aggregate for larger surface are per unit weight.

The more pulverized the material is, then the more surface are you will have; this is due to the fact that the smaller the particles, the less "void" space we have, that is, the more "bulk" density we will have and therefore, more area.

Imagine beans vs. tennis balls in the same volume (imagine a milk galon)

You will have pleny of beans and not so may tennis balls, then there will be plenty of space between balls, and not so many in beans

the total mass in the same volume will be higher in the beans, and the area of each beans, may be small, but we have plenty!