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Bulk Density and Void Percentage Test for Aggregates

Bulk Density and Void Percentage Test for Aggregates


The bulk density and void percentage of aggregate can be evaluated using standard test methods of applicable codes such as ASTM C 29/C29M-17a, IS: 2386 (Part 3) – 1963, or BS 812-2:1995. The procedure provided in this article is based on the specification of ASTM standard ( ASTM C 29/C29M-17a). The bulk density or unit weight is the weight per unit volume (mass per unit volume or density). Voids in unit volume of aggregate are the space between particles in an aggregate mass not occupied by solid minerals.

The bulk density values determined based on this test can be used for many methods of selecting proportions for concrete mixtures. Added to that, the evaluation of the percentage of voids between particles in fine, coarse, or mixed aggregates is dependent on the bulk density. It is worth knowing that, aggregates in stockpiles contain absorbed and surface moisture (the latter affecting bulking), while this test method determines the bulk density on a dry basis.

Apparatus

1. Balance

 A balance sensitive to 0.5% of the weight of the sample to be weighed.

2. Tamping Rod

A straight metal tamping rod of cylindrical cross-section 16 mm in diameters maximum 75 cm long, rounded at one end.

Tamping Rod
Fig. 1: Tamping Rod

3. Cylindrical Metal Measure

The capacity of cylindrical metal measure conforms to the specifications of Table 1.

Table 1 Capacity of Measures

Nominal Maximum Size of Aggregate, mm Capacity of Measure, m^3 (L)
12.5 0.0028 (2.8)
25 0.0093 (9.3)
37.5 0.014 (14)
75 0.028 (28)
100 0.070 (70)
125 0.100 [100]
Cylindrical Measures of Different Sizes
Fig. 2: Cylindrical Measures of Different Sizes

4. Shovel or Scoop

A shovel or scoop of convenient size for filling the measure with aggregate

5. Equipment for Measuring Volume of Measure

It includes plate glass, grease, and thermometer, and balance.

Sample Preparation

  1. The size of the test sample ranges from 125% to 200 % of the amount required to fill the measure.
  2. Dry the aggregate sample to constant mass in an oven at 110±5 °C.
Aggregate Sample
Fig. 3: Aggregate Sample

Determination of Volume of Measure

  1. Evaluate the mass of the plate glass and measure the nearest 0.05 kg.
  2. Place a thin layer of grease on the rim of the measure to prevent leakage of water.
  3. Fill the measure with water and cover it with the plate glass in a manner to remove bubbles and excess water.
  4. Determine the mass of the water, plate glass, and measure to the nearest 0.05 kg.
  5. Measure the temperature of the water to the nearest 0.5 °C and specify its density from Table 2.
  6. Calculate the volume, V, of the measure using the following expression:

                                     V=(W-M)/D Equation 1

                                     F= D/(W-M) Equation 2

where:

V: volume of the measure, m^3

W: mass of the water, plate glass, and measure, kg

M: mass of the plate glass and measure, kg

D: density of the water for the measured temperature, kg/m^3, and

F: factor for the measure, 1/m^3

Table 2 Density of Water

Temperature, C kg/m^3
15.6 999.01
18.3 998.54
21.1 997.97
23.0 997.54
23.9 997.32
26.7 996.59
29.4 995.83
Determination Volume of Measure
Fig. 4: Determination Volume of Measure

Test Procedure

  1. Take the weight of the empty measure (W) to the nearest 0.05kg, as per procedure provided above.
  2. Fill the measure to in three layers and compact the aggregate in three layers using one of the three methods based on the aggregate size.

Method A Rodding for maximum aggregates size of 37.5 mm or less, Method B—Jigging for maximum aggregates size greater than 37.5 mm and not exceeding 125 mm, and Method C—Shoveling to determine the loose bulk density of the aggregate.

Method A: Rodding

Fill the measure with aggregate in nearly equal three layer. Apply 25 evenly distributed strokes of tapping rode to each layer surface. The rode should not hit the bottom of the measure during rodding of the layer, and penetrating the rod to into the first and second layer during rodding second and third layer need to be prevented.

Rodding Aggregate
Fig. 5: Rodding Aggregate

Method B: Jigging

Fill the measure with aggregate in nearly equal three layer. Compact each layer by placing the measure on a firm base, raising the opposite sides alternately about 50 mm, and allowing the measure to drop in such a manner as to hit with a sharp, slapping blow. Compact each layer by dropping the measure 50 times, 25 times on each side, and finally level the surface of the aggregate.

Method C: Shoveling

Fill the measure to overflowing by means of a shovel or scoop, discharging the aggregate from a height not to exceed 50 mm above the top of the measure. Prevent segregation of the particle sizes of which the sample is composed. Level the surface of the aggregate.

3. Finally, determine and record the mass of the measure plus its contents to the nearest 0.05 kg.

Calculations

1. Calculation of Compacted Bulk Density of aggregate

Bulk density (M)= (G-T) / V Equation 3

Or

Bulk density (M)= (G-T) / F Equation 4

where:

M: bulk density of the aggregate, kg/m^3,

G:  mass of the aggregate plus the measure, kg,

T:  mass of the measure, kg,

V: volume of the measure, m^3,

F:  factor for measure, m^3, computed from equation 2.

The bulk density determined by this test method is for aggregate in an oven-dry condition. If the bulk density in terms of saturated-surface-dry (SSD) condition is required, it can be computed using the following formula:

Mssd= M[1+(A/100)] Equation 5

where:

MSSD : bulk density in SSD condition, kg/m^3.

A: % absorption,

 2. Void Content

Calculate the void content in the aggregate using the bulk density determined by either the rodding, jigging, or shoveling procedure, as follows:

%Voids= 100[(SxW)-M]/ (SxW) Equation 6

where:

M: bulk density of the aggregate, kg/m^3,

S: bulk specific gravity

W: density of water, 998 kg/m^3.

Read More:

Aggregate Crushing Value Test – Determine Aggregate Crushing Strength



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