Bulking of Aggregate

The increase of volume of given weight of aggregate 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 air tries to get out and cause volume to increase.by adding of water in dry aggregates the volume increase up to adding of 8 percent of water of aggregate weight.Further adding of water cause water to move into the void of aggregate particle. This cause volume to decrease.When aggregates are saturated its volume is same as the dry condition.Fine aggregates increase volume more than coarse aggregates.

The bulking is determined by following expression
             
                    bulking, b=(Vm/Vd)*100
Where Vm is the volume with moisture and Vd is the dry or fully saturated volume and b is the bulking percentage.