Unit Weight & Voids Testing Flashcards

When calculating voids in aggregate using bulk specific gravity (dry basis), which formula is correct?

Answer: Voids (%) = [1 − (UW / (SG × 62.4))] × 100

ASTM C29 defines percent voids as [1 − (W / (S × D))] × 100, where W = unit weight, S = bulk specific gravity (dry), and D = density of water.

In the unit weight test, the measure is filled in three layers when rodding. How many rod strokes per layer are required for a 1/3-cubic-foot measure?

Answer: 25 strokes

ASTM C29 specifies 25 strokes of the tamping rod per layer for a 1/3-cubic-foot or smaller measure.

What is the correct moisture condition of aggregate specified for the standard unit weight test per ASTM C29?

Answer: Oven-dry (OD)

ASTM C29 specifies that aggregate shall be in the oven-dry condition when the unit weight and void content are determined.

A technician reports a unit weight of 1,680 kg/m³ for coarse aggregate. Converting to pounds per cubic foot, this is approximately:

Answer: 105 pcf

1 kg/m³ = 0.0624 lb/ft³; 1,680 × 0.0624 ≈ 104.8 pcf, which rounds to approximately 105 pcf.

Which aggregate property, when higher, generally leads to a higher unit weight for a given gradation?

Answer: Particle specific gravity

Higher particle specific gravity means denser particles, which increases unit weight even if gradation and packing remain the same.

What action should a technician take if the surface of the aggregate in the measure is below the rim after rodding the final layer?

Answer: Add aggregate until it slightly mounds above the rim, then strike off

If the surface is below the rim, additional aggregate should be added to slightly overfill the measure before striking off to the rim.

In ASTM C29 calibration of the measure, the plate glass used to seal the measure during water filling must be at least how thick?

Answer: 1/4 inch (6 mm)

ASTM C29 requires that the glass plate used during measure calibration be at least 6 mm (1/4 in.) thick to prevent flexing.