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.

Importance of Aggregates

As at least three quarters of concrete is occupied by aggregates it is of great importance.

1.Cheaper than cement.Hence it reduces the cost of concrete.

2.Increases the binding capacity of cement.Cement alone can not be strong.

3.The chemical and thermal properties of aggregates effect the properties of concrete.

4.Durability of concrete depends on the characteristics of concrete.

Aggregates

The inert materials which are used in concrete is called aggregates.Such as sand,pebbles,cinder, gravel etc.But aggregates are not always inert. Recent study shows that the chemical and thermal properties of aggregates influence the quality of concrete.

Kinds of aggregates

Two kinds.

1.Fine aggregates:The aggregates which are smaller than 3/16 inch or 4.76 mm is called fine aggregates. Sand is the common fine aggregate.

2.Coarse aggregates:The aggregate which are bigger than 3/16 inch or 4.76 mm is called coarse aggregate. Broken brick,pebbles,gravel etc are coarse aggregates.