ACI Making and Curing Specimens Questions and Answers 1 — Questions and Answers
Question 1: According to ASTM C31/C31M, what is the required temperature range for the initial curing of standard-cured concrete cylinders with a specified strength of less than 6000 psi (40 MPa)?
- 50°F to 70°F (10°C to 21°C)
- 60°F to 80°F (16°C to 27°C) (Correct answer)
- 68°F to 78°F (20°C to 26°C)
- 70°F to 90°F (21°C to 32°C)
Correct answer: 60°F to 80°F (16°C to 27°C)
ASTM C31/C31M specifies that for standard-cured specimens, the initial curing temperature must be maintained between 60°F and 80°F (16°C and 27°C). This ensures that the concrete gains strength in a controlled environment, providing an accurate measure for acceptance testing.
Question 2: A technician is preparing to cast 6x12-inch concrete cylinders. The concrete has a slump of 3 inches. Which of the following consolidation procedures is correct?
- Fill the mold in two equal layers, rodding each layer 25 times.
- Fill the mold in three equal layers, rodding each layer 50 times.
- Fill the mold in two equal layers, vibrating for 5 seconds per layer.
- Fill the mold in three equal layers, rodding each layer 25 times. (Correct answer)
Correct answer: Fill the mold in three equal layers, rodding each layer 25 times.
For 6x12-inch cylinders, ASTM C31/C31M requires the mold to be filled in three approximately equal layers. Each layer must be rodded 25 times, penetrating the underlying layer by about 1 inch.
Question 3: Which of the following is an appropriate action immediately after molding and finishing a concrete test specimen?
- Leave the specimen uncovered to allow bleed water to evaporate quickly.
- Move the specimen to the final curing location in the laboratory.
- Place the specimen in its initial curing location, protected from moisture loss and disturbance. (Correct answer)
- Submerge the specimen in ice water to rapidly cool it to the required curing temperature.
Correct answer: Place the specimen in its initial curing location, protected from moisture loss and disturbance.
Immediately after molding, specimens must be moved to an initial curing environment that prevents moisture loss, maintains the specified temperature, and is free from vibrations or other disturbances that could affect the concrete's integrity.
Question 4: A field-cured specimen is primarily used to determine:
- The adequacy of the concrete mixture proportions for strength.
- Acceptance of the concrete for specified strength.
- The in-place strength of the concrete in the structure. (Correct answer)
- The quality control of the concrete producer.
Correct answer: The in-place strength of the concrete in the structure.
Field-cured specimens are stored as close as possible to the actual structure and receive the same curing and protection. Their test results are used to estimate the in-place strength, which helps in determining when a structure can be put into service or when forms can be removed.
Question 5: When rodding the top layer of a concrete cylinder, the tamping rod should penetrate the underlying layer by approximately how much?
- The rod should not penetrate the underlying layer.
- 1/2 inch (13 mm)
- 1 inch (25 mm) (Correct answer)
- 2 inches (50 mm)
Correct answer: 1 inch (25 mm)
To ensure proper consolidation and bonding between layers, ASTM C31/C31M requires the tamping rod to penetrate about 1 inch (25 mm) into the previously placed layer for all but the bottom layer.
Question 6: During the initial curing period, standard-cured specimens must be transported to the laboratory for final curing. This transport must occur within what timeframe after molding?
- Within 12 hours
- Within 24 hours
- Within 48 hours (Correct answer)
- Within 72 hours
Correct answer: Within 48 hours
According to ASTM C31/C31M, the initial curing period can last for up to 48 hours. After this period, the specimens must be transported to the laboratory for final, standard curing in a moist room or water tank.
ACI Making and Curing Specimens Questions and Answers 1
According to ASTM C31/C31M, what is the required temperature range for the initial curing of standard-cured concrete cylinders with a specified strength of less than 6000 psi (40 MPa)?