Unit Weight and Voids in Aggregate

ASTM C29 outlines standard procedures for the determination of unit weight and voids in aggregate.

Equipment:

1. Balance

2. Tamping rod (16mm dia. x 600mm length)

3. Cylindrical metal measure (capacity ≥ 14L for coarse aggregate ≤ 37.5mm, or 2.8L for fine aggregate)

Sample:

Aggregate dried to constant weight, preferably in an oven at 110±5°C.

Procedure:

1. Determine the empty weight of metal measure.

2. Fill the metal measure 1/3 full with dry sample and level the surface with fingers.

3. Rod the layer of aggregate with 25 evenly distributed strokes over the surface using tamping rod.

4. Fill the remaining space with sample and rod again as in step 3.

5. Fill the measure to overflowing and rod again as in step 3.

6. Level the surface of aggregate with finger until the slight projection of larger pieces of coarse aggregate is almost balance the larger voids present under the surface.

7. Determine the weight of measure with aggregate, then calculate the net weight of aggregate by subtracting the weight of empty measure. Record it as A (g).

Calculation:

1. Bulk density (unit weight), M = A/V

2. Void content = 100[(SW) - M]/(SW)