ATT Specific Gravity & Absorption 2 — Questions and Answers
Question 1: What does the term 'apparent specific gravity' represent for aggregates?
- Ratio of aggregate mass to the mass of an equal volume of water, excluding permeable pores (Correct answer)
- Ratio of aggregate mass to the mass of an equal volume of water, including all pores
- Ratio of SSD mass to the mass of an equal volume of water
- Ratio of dry mass to the total volume including surface moisture
Correct 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.
Question 2: In AASHTO T 85, what is the required soaking period for coarse aggregate before testing specific gravity?
- 12 ± 1 hours
- 24 ± 4 hours (Correct answer)
- 48 ± 4 hours
- 72 ± 4 hours
Correct answer: 24 ± 4 hours
AASHTO T 85 requires coarse aggregate to soak in water for 24 ± 4 hours before testing.
Question 3: When determining fine aggregate specific gravity by ASTM C128, the pycnometer is filled with water to what level after adding the aggregate?
- Halfway up the neck
- The calibration mark on the neck (Correct answer)
- Just below the rubber stopper
- 25 mL below the top
Correct answer: The calibration mark on the neck
The pycnometer is filled to its calibration mark to ensure a known, reproducible water volume.
Question 4: 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?
- The aggregate has zero absorption
- The aggregate absorbs water, since SSD > OD specific gravity (Correct answer)
- The aggregate releases water on drying, so SSD < OD specific gravity is expected
- The values indicate the aggregate is contaminated
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.
Question 5: For fine aggregate, what instrument is typically used to determine when SSD condition is achieved in ASTM C128?
- Nuclear moisture gauge
- Metal cone and tamping rod (Correct answer)
- Hydrometer
- Proctor compaction mold
Correct answer: Metal cone and tamping rod
ASTM C128 uses the cone test — the fine aggregate slumps when surface moisture is gone, indicating SSD condition.
Question 6: If the water temperature during a specific gravity test deviates from 23°C, what adjustment must the technician make?
- Reject the test and rerun it at exactly 23°C
- Apply a temperature correction factor from the standard table (Correct answer)
- Add 0.001 to the result for every degree above 23°C
- No adjustment is needed for temperatures within 5°C of 23°C
Correct 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.
Question 7: Which condition describes a fine aggregate sample that has been air-dried to approximately SSD but is slightly damp on the outside?
- Oven-dry condition
- Air-dry condition
- Saturated surface-dry condition (Correct answer)
- Wet condition
Correct answer: Saturated surface-dry condition
SSD condition means internal pores are saturated but no free moisture film exists on particle surfaces.
ATT Specific Gravity & Absorption 2
What does the term 'apparent specific gravity' represent for aggregates?