ATT Unit Weight & Voids Testing 2 — Questions and Answers
Question 1: When performing the unit weight test on coarse aggregate, how many layers are used when rodding a 1/2-cubic-foot measure?
- 1 layer
- 2 layers
- 3 layers (Correct answer)
- 4 layers
Correct answer: 3 layers
ASTM C29 requires three equal layers when rodding aggregate in a 1/2-cubic-foot measure.
Question 2: What is the purpose of striking off the surface of the measure after filling in the unit weight test?
- To remove excess fines
- To create a flat surface flush with the top of the measure (Correct answer)
- To compact the aggregate further
- To allow moisture to evaporate
Correct answer: To create a flat surface flush with the top of the measure
Striking off levels the surface flush with the rim so the volume of aggregate equals exactly the volume of the measure.
Question 3: In ASTM C29, what tool is used to strike off the surface of the measure after the final layer of aggregate is added?
- A flat trowel
- A straightedge or tamping rod (Correct answer)
- A rubber mallet
- A vibrating plate
Correct answer: A straightedge or tamping rod
A straightedge or the tamping rod is used to strike off aggregate flush with the top of the measure.
Question 4: If the unit weight of a fine aggregate is 100 pcf and the specific gravity is 2.65, what is the approximate void content?
- About 15%
- About 22%
- About 39% (Correct answer)
- About 48%
Correct answer: About 39%
Void content = (1 - UW / (SG × 62.4)) × 100 = (1 - 100/165.36) × 100 ≈ 39.5%.
Question 5: Which aggregate characteristic does a high void content typically indicate?
- Well-graded, angular particles
- Poorly graded or rounded particles with large interparticle spaces (Correct answer)
- High moisture absorption
- Low specific gravity
Correct answer: Poorly graded or rounded particles with large interparticle spaces
High void content usually indicates poorly graded or uniform-sized aggregate, or particles with shapes that do not pack efficiently.
Question 6: What must be done to the calibration mass used to determine the volume of the unit weight measure?
- It must be soaked in water for 24 hours before use
- It must be traceable to a standard and verified at appropriate intervals (Correct answer)
- It must weigh exactly 10 kg
- It must be stored at the test temperature
Correct answer: It must be traceable to a standard and verified at appropriate intervals
Calibration masses must be traceable to national standards and verified periodically to ensure accuracy of the measure volume calculation.
Question 7: When using the shoveling procedure in ASTM C29, aggregate is dropped from a height of approximately how many inches above the measure?
- 1 inch
- 2 inches (Correct answer)
- 4 inches
- 6 inches
Correct answer: 2 inches
ASTM C29 specifies that aggregate be dropped from a height of approximately 2 inches (50 mm) above the top of the measure when using the shoveling method.
ATT Unit Weight & Voids Testing 2
When performing the unit weight test on coarse aggregate, how many layers are used when rodding a 1/2-cubic-foot measure?