Specific Gravity & Absorption Flashcards

What does the term 'apparent specific gravity' represent for aggregates?

Answer: Ratio of aggregate mass to the mass of an equal volume of water, excluding permeable pores

Apparent specific gravity excludes permeable pore space, using only the impermeable solid volume.

In AASHTO T 85, what is the required soaking period for coarse aggregate before testing specific gravity?

Answer: 24 ± 4 hours

AASHTO T 85 requires coarse aggregate to soak in water for 24 ± 4 hours before testing.

When determining fine aggregate specific gravity by ASTM C128, the pycnometer is filled with water to what level after adding the aggregate?

Answer: The calibration mark on the neck

The pycnometer is filled to its calibration mark to ensure a known, reproducible water volume.

An aggregate has a bulk SSD specific gravity of 2.62 and a bulk oven-dry specific gravity of 2.58. Which statement is correct?

Answer: The aggregate absorbs water, since SSD > OD specific gravity

When SSD specific gravity exceeds OD specific gravity, the permeable pores hold absorbed water, which is typical for absorptive aggregates.

For fine aggregate, what instrument is typically used to determine when SSD condition is achieved in ASTM C128?

Answer: Metal cone and tamping rod

ASTM C128 uses the cone test — the fine aggregate slumps when surface moisture is gone, indicating SSD condition.

If the water temperature during a specific gravity test deviates from 23°C, what adjustment must the technician make?

Answer: Apply a temperature correction factor from the standard table

ASTM C127/C128 provide temperature correction factors to adjust results when testing temperature differs from 23°C.

Which condition describes a fine aggregate sample that has been air-dried to approximately SSD but is slightly damp on the outside?

Answer: Saturated surface-dry condition

SSD condition means internal pores are saturated but no free moisture film exists on particle surfaces.