 After reading this article you’ll understand better the terms like 1.54 in concrete and 1.30 in mortar.

##### Definition of 1.54 in concrete

While water is included in the dry mixture (cement+sand+aggregate) as well as wet concrete mixture is arranged in shuttering, the particles reorganize themselves into pores and voids which decreased the volume of the wet mixture.

##### Void percentage compressibility

Aggregate: 33 to 34% (voids are filled up and particles are reduced)
Sand: 20% (voids are filled up particles are reduced)
Cement: Inconsiderable (because of fine particles)
By summing up the percentage of aggregate and sand, we get 34% + 24% = 54%
Dry Volume is greater than 54% of wet volume
= 100/100 + 54/100 = 1 + .54 = 1.54
Because of that, Dry Volume = 1.54 x wet volume

##### Definition of 1.30 in the mortar

Mortar is formed with cement and sand.

##### Void percentage compressibility

Sand: 20%
Cement: Inconsiderable (because of fine particles)
= 20%
Dry volume is greater than 20% of wet volume
= 100/100 + 20/100 = 1 + .20

As engineers select an additional 5% to 10% for wastages and weak workmanship so that the quantities of cement and sand are not reduced, the mortar ratio is taken as follow:

= 1.20+ .1 = 1.30
Because of that, dry volume = 1.30 x wet volume