Purpose
Determination of unit weight of coarse aggregate in compressed state. This test method is applicable to aggregates not exceeding 15 cm (6 in) in nominal size. The unit weight thus determined is essential for the design of a concrete mix by the absolute value method.
Tools And Materials
- Precise balance up to 0.05 kg (0.1 lb) with a limit of at least 25 kg (64 lb)
- straight steel tamping rod 16 mm (⅝ in) in diameter and approximately 60 cm (24 in) in length with one end rounded into a hemispherical tip
- Watertight metal buckets have an approximately equal height-to-diameter ratio, but the height should always be between 80 and 150% of the diameter
- The sample volume of oven-dried aggregates should be at least 125% of the volume required to fill the metal bucket
Testing Process
Calibrate the metal bucket to determine its volume by determining the net weight of water needed to fill it and dividing by the water’s density. For this test procedure, the density of water at room temperature is 998 kg/m. Accept is accurate enough3 (62.3 lb/ft3).
shattering the aggregate. Fill the bucket one-third full and distribute the composite layer evenly over the surface with 25 strokes of the tamping rod. Add another layer of aggregate so that the bucket is about two-thirds full and repeat the rodding process. The third layer of aggregate should fill the bucket to overflow. Repeat the tamping process again and remove the excess from the tamping rod. Try manually balancing the pits under the top of the bucket with slight projections from the top.
When tamping the first lift, do not allow the rod to penetrate the bottom of the bucket. However, subsequent lifts must enter on top of the previous lift.
Roded unit weight kg/m. is calculated in3 (lb/ft3) divided by the net weight of the rod aggregate in the bucket by its volume.
Computation
Calculate the rodded unit weight as follows:
Mssd = (g – t)(1 + a/100)/v
Mssd = rod unit weight of saturated surface dry aggregate, kg/m3 (lb/ft3)
g = combined mass of oven-dried aggregate and bucket, kg (lb)
T = mass of the bucket alone, kg (lb/f)
V = Volume of the bucket, m3 (ft.)3,
A = % Absorbance, ASTM Method C 127. determined by
Roded unit weight is calculated to the nearest 10 kg/m. do till3 (1 lb/ft3) do three tests. Average any two that do not vary by more than 40 kg/m3 (2.5 lb/ft3,
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