BULK DENSITY AND VOIDS

HOW TO TEST AGGREGATE FOR BULK DENSITY AND VOIDS?

OBJECTIVE

Determination of unit weight or bulk density and void of aggregates.

EQUIPMENTS

Name	Capacity
1. Balance	Sensitive to 0.5% of weight of material
2. Cylindrical metal measure	Of 3 litre capacity (for fine aggregate) Of 15 litre capacity (for aggregate upto 40mm)
3. Tamping rod	16 mm dia. and 60 cm long

cylindrical metal measure used for bulk density and void test of aggregate

SAMPLE PREPARATION

• Take the required amount of test sample form the bulk sample using any sample reductionmethod.
• The test is normally carried out on dry material, but when bulking tests are required, material with a given percentage of moisture may be used.

A. PROCEDURE FOR COMPACTED BULK DENSITY

1. Measure the volume of the cylindrical metal measure by pouring water into the metal measure and record the volume “V” in litre.
2. Fill the cylindrical metal measure about one-third full with thoroughly mixed aggregate and tamp it 25 times using tamping bar.
3. Add another layer of one-third volume of aggregate in the metal measure and give another 25 strokes of tamping bar.
4. Finally fill aggregate in the metal measure to over-flowing and tamp it 25 times.
5. Remove the surplus aggregate using the tamping rod as a straightedge.
6. Determine the weight of the aggregate in the measure and record that weight “W” in kg.

CALCULATION FOR COMPACTED BULK DENSITY

Compacted unit weight or bulk density = W/V

Where,

W = Weight of compacted aggregate in cylindrical metal measure, kg

V = Volume of cylindrical metal measure, litre

CALCULATION OF VOIDS

The percentage of voids is calculated as follows

Percentage of voids = [(G – ϒ)/G]*100

Where

G = Specific gravity of the aggregate

ϒ = Bulk density in kg/litre

B. PROCEDURE FOR LOOSE BULK DENSITY

1. Measure the volume of the cylindrical metal measure by pouring water into the metal measure and record the volume “V” in litre.
2. Fill the cylindrical measure to overflowing by means of a shovel or scoop, the aggregate being discharged from a height not exceeding 5 cm above the top of the measure
3. Level the top surface of the aggregate in the metal measure, with a straightedge or tamping bar.
4. Determine the weight of the aggregate in the measure and record the weight “W” in kg.

CALCULATION FOR LOOSE BULK DENSITY

Loose unit weight or bulk density = W/V

Where,

W = Weight of loose aggregate in cylindrical metal measure, kg

V = Volume of cylindrical metal measure, litre

CALCULATION OF VOIDS

The percentage of voids is calculated as follows

Percentage of voids = [(G – ϒ)/G]*100

Where

G = Specific gravity of the aggregate

ϒ = Bulk density in kg/litre

RESULT

The bulk density is reported in kg/litre to the nearest 0.01 kg

The percentage of voids is reported to the nearest whole number.

Mention whether the aggregate is

(a) oven dry,

(b) saturated and surface dry or

(c) with a given percentage of moisture.


Note:- Maximum bulking of sand at moisture content of 4%