Angularity Number of Coarse Aggregate
Theory
The angularity number of an aggregate is defined as the amount by which the percentage of voids exceeds 33 after compacting the aggregate. Angularity refers to the lack of roundness of aggregate.
This test is very important to conduct since it determines the shape of aggregates. More the angularity number, the better the interlocking and inter friction, therefore better structural stability.
Angular aggregate is widely used in bituminous construction and flexible pavement because it provides a strong bond and good interlocking. These aggregates require more cement paste due to the presence of large number of voids.
Apparatus -
Metal cylinder- Metal cylinder with one end closed, having a capacity of 3 litres. The diameter and height of the cylinder should be approximately equal.
Tamping rod – The rod should be rounded at one end and have a circular cross-section of 16 mm diameter and a length of 60 cm.
Balance
Metal Scoop, of approximately 20×12×5 cm.
IS Sieves from the following sets: 20 mm & 16 mm, 16 mm & 12.5 mm, 12.5 mm & 10 mm, 10 mm & 6.3 mm, 6.3 mm & 4.75 mm.
Formulae - The angularity number shall be calculated by using the formula.
From the solids:
Angularity number = 67- (100*W) / (C*Ga)
Where,
W is the mean weight of aggregate in the cylinder in grams,
C is the weight of water required to fill the cylinder in grams,
Ga is the specific gravity of aggregate.
From the voids:
Angularity number = Volume of water added / (Total volume of cylinder) - 33