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

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