The increase in surface area with the decrease in aggregate particle size is demonstrated below:

(a) (b) (c)

Figure (a) shows: one 25.0 mm  cube of aggregate [surface area= 6 x 25.0 x 25.0 = 3750 mm² ]

Figure (b) shows: eight 12.5 mm  cubes of aggregate [surface area= 6 x 12.5 x 12.5 x 8 = 7500 mm²] and

Figure (c) shows: sixty-four 6.25 mm  cubes of aggregate [surface area= 6 x 6.25 x 6.25 x 64 = 15,000 mm²

If a large coarse aggregate particle is reduced to fine sand size particles, the same volume would have a surface area about 100 times greater than that of the original cube.