Aggregate Bulk density and Voids test

What is Bulk Density of aggregate?

It is the mass of the unit volume of bulk aggregate material. The term volume includes the volume of the individual particle and the volume of the voids between the particles. Bulk density is used in weight and volume batching both.

What is Voids in Aggregate ?

It is a space between the individual particles and in a unit volume of the aggregate mass and is not occupied by the solid mineral matters. 

AIM

TO determination of Bulk density and void of aggregates.

APPARATUS 

1. Balance – Sensitive to 0.5% of weight of material

2. Cylindrical metal measure of 3, 15 & 30 litre capacity

Capacity  Size of largest particle
3 Liters 4.75 mm and under
15 Liters 4.75 mm to 40 mm
30 Liters More than 40 mm

3. Tamping rod 16 mm diameter and 60 cm long, Rounded at one end.

SAMPLE PREPARATION

Take the required amount of test sample form the bulk sample using any sample reduction method.

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

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

B. PROCEDURE FOR LOOSE BULK DENSITY

  • Measure the volume of the cylindrical metal measure (three times for average) by pouring water into the metal measure and record the volume “V” in liter.
  • Fill the cylindrical measure to overflowing by means of a scoop, the aggregate being discharged from a height not exceeding 5 cm above the top of the measure
  • Level the top surface of the aggregate in the metal measure, with a straightedge or tamping bar.
  • Determine the weight (three times for average) of the aggregate in the measure and record the weight “W” in kg.

Calculations

1. CALCULATION OF 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, liter

2. 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/liter

RESULTS

The bulk density is reported in kg/liter to the nearest 0.01 kg & The percentage of voids is reported to the nearest whole number.

Mention whether the aggregate is:

  1. Oven dry,
  2. Saturated and surface dry or
  3. With a given percentage of moisture.

REFERENCE  STANDARD

IS : 2386 (Part 3) – 1963 – Method of test for aggregates for concrete,

Technical Discussion

 The bulk density is more in compacted state as compared to the loose which shows that the bulk density greatly depends on the degree of compaction or how densely it is packed.       

 

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