Making and Curing Specimens Flashcards

What is the minimum concrete temperature range required for initial field curing of test cylinders per ASTM C31?

Answer: 60°F to 80°F (16°C to 27°C)

ASTM C31 Section 10.1 requires that test cylinders be maintained within 60°F to 80°F (16°C to 27°C) during the initial 24-hour field curing period to ensure proper early strength gain without temperature-induced variability.

For a 4×8-inch concrete test cylinder made from concrete with a slump between 1 and 3 inches, how many layers and rods per layer are required per ASTM C31?

Answer: Two layers, 25 rods per layer

ASTM C31 requires 4×8-inch cylinders to be filled in two approximately equal layers with 25 rods per layer for concrete with a slump greater than 1 inch.

What is the purpose of using a 'curing box' or insulated curing container when making test cylinders in cold-weather field conditions?

Answer: To maintain the cylinders within the 60–80°F (16–27°C) ASTM C31 initial curing temperature range by preventing heat loss to the cold environment

In cold weather, cylinders in insulated boxes (sometimes with a small heat source) are kept at the 60–80°F range required by ASTM C31, protecting early-age concrete from temperatures below 60°F that would slow hydration.

When is vibration consolidation required instead of rodding for concrete test cylinder preparation per ASTM C31?

Answer: When the concrete has a slump of 1 inch (25 mm) or less, or when specified by the engineer

ASTM C31 requires vibration consolidation when concrete slump is 1 inch (25 mm) or less because stiff concrete cannot be adequately consolidated by the standard rodding procedure.

What is the maximum height to which the initial fill should be above the top of the mold when making test cylinders, to allow for rodding without material loss?

Answer: Each layer should overfill the mold by approximately 10% to account for consolidation settling

ASTM C31 directs technicians to fill each layer so that after consolidation (rodding), the layer is at the intended depth; a slight 10% overfill accounts for the volume reduction from consolidation.

Per ASTM C31, what is the required identification information that must be marked on each test cylinder immediately after casting?

Answer: Project name or number, sample location/structural element, date and time of sampling, and specimen number within the test set

ASTM C31 requires immediate positive identification of each cylinder with project, location, sampling time and date, and specimen number to maintain chain of custody and link test results to the correct structural element.