Rodded Unit Weight of Coarse Aggregate

Purpose

Determination of the unit weight of coarse aggregates in a compacted condition. This test method is applicable to aggregates not exceeding 15 cm (6 inches) in nominal size. The unit weight so determined is necessary for the design of a concrete mixture by the absolute value method.

Equipment and Materials

• Balance accurate to 0.05 kg (0.1 lb) with a range to at least 25 kg (64 lb)
• Straight steel tamping rod 16 mm (⅝ inch) in diameter and about 60 cm (24 inches) in length with one end rounded in a hemispherical tip
• Watertight metal bucket having approximately equal height-to-diameter ratio, but the height should always be between 80 to 150% of the diameter
• Quantity of oven dry aggregate sample should be at least 125% of the quantity required to fill the metal pail

Test Procedure

1. Calibrate the metal bucket to determine its volume by determining the net weight of water required to fill it and dividing it by the density of water. For this test procedure it is sufficiently accurate to accept the density of water at room temperature to be 998 kg/m3 (62.3 lb/ft3).
2. Rodding the aggregates. Fill the bucket one-third full and rod the aggregate layer with 25 strokes of the tamping rod, evenly distributed over the surface. Add another layer of aggregates so that the bucket is approximately two-thirds full and repeat the rodding procedure. The third layer of aggregates should fill the pail to overflowing. Again repeat the tamping procedure and strike off the excess with the tamping rod. Manually try to balance the depressions below the top of the bucket with slight projections above the top. When tamping the first lift, do not permit the rod to penetrate to the bottom of the bucket. However, the subsequent lifts should penetrate to the top of the previous lift.
3. The rodded unit weight is computed in kg/m3 (lb/ft3) from the net weight of the rodded aggregates in the bucket divided by its volume.

Computations

Calculate the rodded unit weight as follows:

MSSD = (G − T)(1 + A/100)/V

MSSD = the rodded unit weight of the saturated surface dry aggregate, kg/m3 (lb/ft3)

G = combined mass of the oven-dry aggregate and the bucket, kg (lb)

T = mass of the bucket alone, kg (lb/f)

V = volume of the bucket, m3 (ft3)

A = % absorption, determined by ASTM Method C 127

Calculate the rodded unit weight to the nearest 10 kg/m3 (1 lb/ft3). Conduct three tests. Average any two that do not differ by more than 40 kg/m3 (2.5 lb/ft3).