Bulking of sand

The increase in the volume of a given mass of fine aggregate caused by the presence of water is known as bulking. The bulking of sand is caused by the films of water which posh the particles apart. The bulking of sand depend upon the percentage of moisture present in the sand and its fineness. It is seen that bulking increases gradually with moisture content up to a certain point and then begins to decrease with the further addition of water due to the merging of films when the sand is inundated. In ordinary sand, the bulking usually varies between 15% to 30%.

The course aggregates do not bulk owing to the fact that the voids between the particles are too large to form films that set the particles apart.