ACI Certification Making and Curing Specimens 2

Question 1

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

Accepted Answer

60°F to 80°F (16°C to 27°C)

Answer

40°F to 90°F (4°C to 32°C)

Answer

50°F to 70°F (10°C to 21°C)

Answer

70°F to 100°F (21°C to 38°C)

Question 2

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?

Accepted Answer

Two layers, 25 rods per layer

Answer

Three layers, 25 rods per layer

Answer

One layer, 50 rods

Answer

Two layers, 10 rods per layer

Question 3

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

Accepted 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

Answer

To cure the cylinders faster using supplemental heat to achieve early break results at 3 days

Answer

To prevent freeze-thaw cycling of cylinders once they are in the lab

Answer

To seal the cylinders from moisture loss only, without temperature control

Question 4

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

Accepted Answer

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

Answer

Only when the concrete has no slump (0 inches) and is a no-slump mix

Answer

Always, because vibration produces more consistent cylinders than rodding

Answer

Only when the concrete contains steel fibers or other reinforcing fibers

Question 5

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?

Accepted Answer

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

Answer

Fill to exactly the top mark with no overfill and strike off immediately

Answer

Overfill by 1 to 2 inches before rodding each layer

Answer

No specific overfill is required; fill until the layer depth is approximate

Question 6

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

Accepted Answer

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

Answer

Technician's name only

Answer

Batch ticket number only

Answer

Cylinder size (4×8 or 6×12) and break age only