ACI Certification Strength Testing Technician 2 — Questions and Answers
Question 1: When consolidating a 6×12 inch concrete cylinder by rodding per ASTM C31, how many equal layers are required?
- Two layers
- Three layers (Correct answer)
- Four layers
- Six layers
Correct answer: Three layers
ASTM C31 requires three equal layers when making 6×12 inch cylindrical specimens consolidated by rodding.
Question 2: What are the diameter and minimum length specified for the tamping rod used to consolidate standard concrete cylinder specimens per ASTM C31?
- 3/8-inch diameter, 18 inches long
- 5/8-inch diameter, 24 inches long (Correct answer)
- 3/4-inch diameter, 24 inches long
- 1-inch diameter, 30 inches long
Correct answer: 5/8-inch diameter, 24 inches long
ASTM C31 specifies a tamping rod that is 5/8 inch (16 mm) in diameter and at least 24 inches (600 mm) long with a hemispherical tip.
Question 3: When using an internal vibrator to consolidate concrete cylinder specimens per ASTM C31, the vibrator diameter must not exceed what fraction of the mold diameter?
- One-sixth
- One-fourth (Correct answer)
- One-third
- One-half
Correct answer: One-fourth
Per ASTM C31, the vibrator diameter shall not exceed one-fourth (1/4) of the diameter of the mold being filled.
Question 4: Per ASTM C31, what temperature range must be maintained during initial curing of concrete cylinder specimens in the field?
- 50–70°F (10–21°C)
- 60–80°F (16–27°C) (Correct answer)
- 65–90°F (18–32°C)
- 70–95°F (21–35°C)
Correct answer: 60–80°F (16–27°C)
ASTM C31 requires specimens to be maintained between 60°F and 80°F (16°C and 27°C) during the initial curing period.
Question 5: After the top surface of a freshly cast cylinder is struck off, it must be finished so that it departs from a true plane by no more than:
- 1/32 inch (0.8 mm)
- 1/16 inch (1.6 mm) (Correct answer)
- 1/8 inch (3 mm)
- 3/16 inch (5 mm)
Correct answer: 1/16 inch (1.6 mm)
The struck-off top surface must be finished level within 1/16 inch (1.6 mm) of a true plane per ASTM C31.
Question 6: Per ASTM C31, freshly cast concrete specimens must be protected from vibration, shock, and disturbance for a minimum of how long after molding?
- 4 hours
- 8 hours
- 16 hours
- 24 hours (Correct answer)
Correct answer: 24 hours
Specimens must not be disturbed or transported for the first 24 hours after molding to prevent damage to the fresh concrete microstructure.
Question 7: When making concrete beam specimens for flexural strength testing per ASTM C31, which consolidation method is permitted when the measured slump is 3 inches (75 mm) or greater?
- Rodding only
- Internal vibration only
- External vibration only
- Either rodding or internal vibration (Correct answer)
Correct answer: Either rodding or internal vibration
Per ASTM C31, when slump is 3 inches or more, consolidation may be achieved by either rodding or internal vibration.
ACI Certification Strength Testing Technician 2
When consolidating a 6×12 inch concrete cylinder by rodding per ASTM C31, how many equal layers are required?