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

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.

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

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.

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

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.

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

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.

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

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.

ACI (American Concrete Institute Certification) Practice Test

ACI (American Concrete Institute Certification) Practice Test

ACI Certification Making and Curing Specimens 2