ATT Unit Weight & Voids Testing 3 — Questions and Answers
Question 1: In the unit weight test, why is it important to avoid vibrating the measure during filling?
- Vibration causes aggregate to absorb water
- Vibration increases packing beyond the standard procedure, giving artificially high results (Correct answer)
- Vibration heats the aggregate and changes its density
- Vibration causes fine particles to rise to the surface
Correct answer: Vibration increases packing beyond the standard procedure, giving artificially high results
External vibration compacts aggregate beyond what the standard procedure intends, producing a unit weight higher than the standardized result.
Question 2: What is the minimum size of measure required for aggregate with a nominal maximum size of 1.5 inches per ASTM C29?
- 1/10 cubic foot
- 1/2 cubic foot
- 1 cubic foot (Correct answer)
- 2 cubic feet
Correct answer: 1 cubic foot
ASTM C29 requires a 1-cubic-foot measure when the aggregate nominal maximum size is 1.5 inches.
Question 3: Which of the following conditions would cause the measured unit weight of coarse aggregate to be lower than the true value?
- Using a damp aggregate sample
- Failing to strike off surplus aggregate above the rim
- Having a dented or deformed measure that increases its volume (Correct answer)
- Rodding too many times per layer
Correct answer: Having a dented or deformed measure that increases its volume
A deformed measure with a larger-than-calibrated volume holds more aggregate, making the calculated unit weight (mass/volume) artificially low.
Question 4: The voids-in-aggregate formula uses the term 'W' to represent what quantity?
- Water content of the aggregate
- Bulk unit weight of the aggregate (Correct answer)
- Weight of the empty measure
- Specific gravity of water
Correct answer: Bulk unit weight of the aggregate
In ASTM C29, W is the bulk unit weight (unit weight) of the aggregate determined by the standard test.
Question 5: According to ASTM C29, what is the standard number of drops of the measure against the base when using the jigging compaction method?
- 25 drops per layer
- 50 drops per layer (Correct answer)
- 100 drops total
- 50 drops total for all layers
Correct answer: 50 drops per layer
The jigging method requires the measure to be raised and dropped 50 times per layer as specified in ASTM C29.
Question 6: If a technician uses the jigging method instead of rodding for fine aggregate, what effect does this typically have?
- Results are invalid because jigging is only for coarse aggregate
- Results may be slightly different but both are acceptable methods under ASTM C29 (Correct answer)
- Jigging always produces higher unit weights than rodding
- Jigging is required for fine aggregate with moisture content above 5%
Correct answer: Results may be slightly different but both are acceptable methods under ASTM C29
ASTM C29 permits both rodding and jigging; either method is acceptable and results may differ slightly but remain valid.
Question 7: A unit weight measure is calibrated by filling it with water at a known temperature. What property of water is used to calculate the volume of the measure?
- Surface tension
- Viscosity
- Unit weight (density) (Correct answer)
- Compressibility
Correct answer: Unit weight (density)
The unit weight (density) of water at the test temperature is used along with the mass of water to calculate the volume (V = mass/density).
ATT Unit Weight & Voids Testing 3
In the unit weight test, why is it important to avoid vibrating the measure during filling?