The increase of volume of given weight of aggregates due to the presence of moisture is called bulking of aggregates. 5 to 8 percent of moisture of aggregate weight cause 20 to 30 percent volume increase. This because of the creation of thin film of water inside aggregates which cause interlocking air. This are tries to get out and cause volume increase. By adding of water in dry aggregates the volume in crease up to adding of 8 percent of water of aggregate weight. Further adding of water cause water move into the void of aggregates particle. This cause volume to decrease. When aggregates are saturated its volume is same as the dry condition. Five aggregates increase volume more than coarse aggregates.
The bulking is determined by following expression
Bulking, b = Vm/Vd x100
Where Vm is the volume with moist and Vd is the dry or fully saturated volume and b is the bulking percentage.