Determination of Bulk density of Course Aggregates

This method is used to determine the bulk density of given specimen during the concrete mix design when the aggregate is to be batched by volume or by weight. Then it is necessary to know the mass of the aggregate that will fill the container of unit volume.

If we know the bulk density of aggregate material than we can easily calculate the mass required to fill a unit volume container.

Bulk Density also indicates the percentage of voids present in the aggregate material.

This percentage of voids effects the grading of the aggregate which is important in higher strength concrete.

AIM:

To determine the bulk density and percentage voids of aggregate.

APPARATUS:

•  Weighing Balance
•  Temping Rod
•  Measuring Cylinder
•  Shovel 

FIGURE:

 

Procedure:

1.   Take the weight of empty measure (W)

2.   Fill the measure with aggregates sample for about one third height and tamp evenly with 25 strokes of the rounded end of the tamping rod.

3.   Add a similar quantity of aggregate as second layer and tamp it evenly with 25 strokes.

4.   Fill the measure with a third layer of aggregate up to over following and tamp it with 25 strokes

5.   Strike off the surplus aggregate using the tamping rod as a straight edge. And take the weight (w1)

6.   Empty the measure and fill it again to over flowing by means of a shovel, the aggregate being discharged from a height not exceeding 5 cm above the top of the measure.

7.   Level the surface of the measure and weight it (w2).

CALCULATIONS:

Diameter of metal measure =

Volume of metal measure (v) = (W1-W)

Bulk density of compacted coarse aggregates = ——————–

V

Bulk density of loosely packed aggregates= (W2-W)/V

Percentage of voids =100x (Gs-r)/ Gs

Where Gs = Specific gravity of aggregate

r = Bulk density of aggregate in kg / liter.