NETTCP Concrete Testing 3 — Questions and Answers
Question 1: What type of fracture pattern in a concrete cylinder indicates an unsatisfactory break and may require investigation?
- Cone fracture
- Cone and split fracture
- Columnar fracture with no well-formed cone (Correct answer)
- Cone and shear fracture
Correct answer: Columnar fracture with no well-formed cone
A columnar fracture with no well-formed cone (Type 5 or 6 per ASTM C39) may indicate improper end conditions or capping problems.
Question 2: At what temperature range must concrete test specimens be initially cured after demolding per AASHTO T 23?
- 50°F to 60°F (10°C to 15.5°C)
- 60°F to 80°F (15.5°C to 26.7°C)
- 73°F ± 3°F (23°C ± 1.7°C) (Correct answer)
- 65°F to 75°F (18.3°C to 23.9°C)
Correct answer: 73°F ± 3°F (23°C ± 1.7°C)
AASHTO T 23 requires standard curing at 73°F ± 3°F (23°C ± 1.7°C) after demolding.
Question 3: When sampling concrete from a transit mixer, after how many revolutions at mixing speed must sampling begin per AASHTO R 60?
- After 30 revolutions at mixing speed
- After 50 revolutions at mixing speed
- After 70 revolutions at mixing speed (Correct answer)
- After 100 revolutions at mixing speed
Correct answer: After 70 revolutions at mixing speed
Per AASHTO R 60, concrete must be mixed at least 70 revolutions at mixing speed before sampling.
Question 4: What is the purpose of the Kelly Ball test in fresh concrete testing?
- Measure air content by pressure method
- Measure consistency as a field alternative to the slump test (Correct answer)
- Determine unit weight of fresh concrete
- Measure bleeding rate of fresh concrete
Correct answer: Measure consistency as a field alternative to the slump test
The Kelly Ball test measures the penetration depth of a 30-lb ball to estimate consistency, serving as a quick field alternative to slump.
Question 5: How many individual samples must be composited to form one field sample for concrete testing per AASHTO R 60?
- 2 increments taken over 15 seconds
- 3 or more increments regularly spaced through the discharge (Correct answer)
- 5 increments taken at the start and end only
- A single continuous sample from the middle of the load
Correct answer: 3 or more increments regularly spaced through the discharge
AASHTO R 60 requires compositing 3 or more individual samples taken at regularly spaced intervals throughout the middle portion of the load.
Question 6: What minimum curing period is typically required before a 6×12-inch concrete cylinder can be removed from its mold?
- 8 hours
- 16 hours (Correct answer)
- 24 hours
- 48 hours
Correct answer: 16 hours
Cylinders should not be demolded before 16 hours to avoid damaging immature concrete.
Question 7: When using a pressure meter to measure air content in fresh concrete (AASHTO T 152), the aggregate correction factor is subtracted because:
- Aggregates absorb air during pressure testing
- Aggregates contain air voids that give false high readings (Correct answer)
- Aggregates compress under pressure inflating the result
- Aggregates displace water affecting the pressure gauge
Correct answer: Aggregates contain air voids that give false high readings
Porous aggregates contain voids that respond to pressure like entrained air, so the aggregate correction factor removes this error.
NETTCP Concrete Testing 3
What type of fracture pattern in a concrete cylinder indicates an unsatisfactory break and may require investigation?