ATT Moisture Content & Specific Gravity 3 — Questions and Answers
Question 1: An aggregate is described as 'oven-dry.' Which statement best describes this condition?
- All evaporable moisture removed by heating to 110 ± 5°C (Correct answer)
- Surface dry but internal pores partially saturated
- Pores fully saturated, surface dry
- Air-dried at ambient temperature for 24 hours
Correct answer: All evaporable moisture removed by heating to 110 ± 5°C
Oven-dry (OD) condition means all evaporable water has been removed by drying at 110 ± 5°C to constant mass per ASTM C566.
Question 2: The Le Chatelier flask method is an alternative procedure for determining specific gravity of which material?
- Coarse aggregate retained on No. 4 sieve
- Fine aggregate passing the No. 4 sieve (Correct answer)
- Lightweight aggregate only
- Recycled concrete aggregate
Correct answer: Fine aggregate passing the No. 4 sieve
The Le Chatelier flask (volumetric flask) method can be used for fine aggregate specific gravity as an alternative to the pycnometer method.
Question 3: During the SSD cone test for fine aggregate, a properly SSD sample will:
- Slump and lose its molded shape when the cone is lifted (Correct answer)
- Retain its shape perfectly with no slumping
- Crumble completely into loose particles
- Flow freely like dry sand
Correct answer: Slump and lose its molded shape when the cone is lifted
At SSD, the fine aggregate cone slumps slightly when the mold is removed, indicating surface moisture is absent while internal pores are saturated.
Question 4: When computing the mix design batch weights, a technician must adjust aggregate quantities because stockpile moisture differs from SSD. Which quantity is adjusted upward when aggregates are wetter than SSD?
- Aggregate batch weight is increased; mix water is decreased (Correct answer)
- Cement content is increased
- Aggregate batch weight is decreased; mix water is increased
- No adjustment is needed
Correct answer: Aggregate batch weight is increased; mix water is decreased
Wet aggregates carry extra water, so aggregate batch weight increases to maintain the target SSD weight, and mix water addition decreases by the same free moisture amount.
Question 5: What is 'absorption capacity' of an aggregate as defined by ASTM?
- The percentage of water the aggregate will absorb to reach SSD from oven-dry (Correct answer)
- Total water in the aggregate at any given time
- Water retained on aggregate surface after drying
- Maximum water aggregate holds at complete saturation
Correct answer: The percentage of water the aggregate will absorb to reach SSD from oven-dry
Absorption is the increase in mass of oven-dry aggregate after soaking in water to reach SSD, expressed as a percentage of the OD mass.
Question 6: A coarse aggregate sample has an OD mass of 4,850 g and an SSD mass of 4,970 g. What is its absorption?
- 2.47% (Correct answer)
- 2.41%
- 1.98%
- 0.42%
Correct answer: 2.47%
Absorption = (4970 − 4850) / 4850 × 100 = 120 / 4850 × 100 ≈ 2.47%.
Question 7: Why is it important to remove entrapped air bubbles from the pycnometer during fine aggregate specific gravity testing?
- Trapped air inflates the measured water volume, causing an artificially low specific gravity result (Correct answer)
- Trapped air increases aggregate mass on the balance
- Bubbles cause the pycnometer to overflow before reading
- Air increases the SSD moisture content value
Correct answer: Trapped air inflates the measured water volume, causing an artificially low specific gravity result
Air bubbles occupy volume in the pycnometer and are counted as water, making the displaced water volume appear larger and yielding a falsely low specific gravity.
ATT Moisture Content & Specific Gravity 3
An aggregate is described as 'oven-dry.' Which statement best describes this condition?