Introduction

1. 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.

2. 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.

3. 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.

Formulas

The angularity number shall be calculated by using the formula.

From the solids:

$$ \text{Angularity Number} = 67 - \frac{100 \times W}{C \times G_a} $$

Where:

• $W$ = mean weight of aggregate in the cylinder (g)
• $C$ = weight of water required to fill the cylinder (g)
• $G_a$ = specific gravity of aggregate

From the voids:

$$ \text{Angularity Number} = \frac{\text{Volume of water added}}{\text{Total volume of cylinder}} - 33 $$