ATT Bulk Density, Voids & Organic Impurities 2 — Questions and Answers
Question 1: In the ASTM C29 rodding method for bulk density, how many times is the tamping rod inserted per layer?
- 10 times
- 15 times
- 25 times (Correct answer)
- 50 times
Correct answer: 25 times
ASTM C29 requires the rod to be inserted 25 times per layer, distributing the strokes evenly over the surface.
Question 2: What concentration of NaOH solution is used in the ASTM C40 organic impurities test?
- 1% by weight
- 3% by weight (Correct answer)
- 5% by weight
- 10% by weight
Correct answer: 3% by weight
ASTM C40 specifies a 3% sodium hydroxide (NaOH) solution by weight for detecting organic impurities in fine aggregate.
Question 3: What does a color darker than the reference standard in the ASTM C40 test indicate?
- The aggregate is free of organic impurities
- The aggregate may contain injurious organic impurities (Correct answer)
- The NaOH solution is too dilute
- The aggregate is suitable for all concrete applications
Correct answer: The aggregate may contain injurious organic impurities
A color darker than Organic Plate No. 3 indicates the fine aggregate may contain harmful organic impurities that could adversely affect concrete.
Question 4: How many approximately equal layers are used when filling the measure by the rodding method in ASTM C29?
- 1 layer
- 2 layers
- 3 layers (Correct answer)
- 4 layers
Correct answer: 3 layers
ASTM C29 requires the measure to be filled in three approximately equal layers, each rodded 25 times.
Question 5: How long must the ASTM C40 test sample stand after adding NaOH before comparing colors?
- 1 hour
- 6 hours
- 24 hours (Correct answer)
- 48 hours
Correct answer: 24 hours
ASTM C40 requires the sample and NaOH solution to stand for 24 hours before performing the color comparison.
Question 6: The rodding method in ASTM C29 is applicable for aggregates with a maximum particle size up to:
- 19 mm (3/4 in)
- 25 mm (1 in)
- 37.5 mm (1-1/2 in) (Correct answer)
- 50 mm (2 in)
Correct answer: 37.5 mm (1-1/2 in)
The rodding method applies to aggregate with a maximum particle size not exceeding 37.5 mm (1-1/2 in); larger sizes require the jigging method.
Question 7: Which formula correctly calculates void content (%) per ASTM C29, where S = bulk specific gravity, W = density of water, and M = bulk density?
- (S × W − M) / (S × W) × 100 (Correct answer)
- (M / W) × 100
- (W − M) / M × 100
- (S × M) / W × 100
Correct answer: (S × W − M) / (S × W) × 100
Void content equals the theoretical solid volume minus the actual bulk density, divided by the theoretical solid volume, times 100.
ATT Bulk Density, Voids & Organic Impurities 2
In the ASTM C29 rodding method for bulk density, how many times is the tamping rod inserted per layer?