Concrete Testing Flashcards

What type of fracture pattern in a concrete cylinder indicates an unsatisfactory break and may require investigation?

Answer: Columnar fracture with no well-formed cone

A columnar fracture with no well-formed cone (Type 5 or 6 per ASTM C39) may indicate improper end conditions or capping problems.

At what temperature range must concrete test specimens be initially cured after demolding per AASHTO T 23?

Answer: 73°F ± 3°F (23°C ± 1.7°C)

AASHTO T 23 requires standard curing at 73°F ± 3°F (23°C ± 1.7°C) after demolding.

When sampling concrete from a transit mixer, after how many revolutions at mixing speed must sampling begin per AASHTO R 60?

Answer: After 70 revolutions at mixing speed

Per AASHTO R 60, concrete must be mixed at least 70 revolutions at mixing speed before sampling.

What is the purpose of the Kelly Ball test in fresh concrete testing?

Answer: Measure consistency as a field alternative to the slump test

The Kelly Ball test measures the penetration depth of a 30-lb ball to estimate consistency, serving as a quick field alternative to slump.

How many individual samples must be composited to form one field sample for concrete testing per AASHTO R 60?

Answer: 3 or more increments regularly spaced through the discharge

AASHTO R 60 requires compositing 3 or more individual samples taken at regularly spaced intervals throughout the middle portion of the load.

What minimum curing period is typically required before a 6×12-inch concrete cylinder can be removed from its mold?

Answer: 16 hours

Cylinders should not be demolded before 16 hours to avoid damaging immature concrete.

When using a pressure meter to measure air content in fresh concrete (AASHTO T 152), the aggregate correction factor is subtracted because:

Answer: Aggregates contain air voids that give false high readings

Porous aggregates contain voids that respond to pressure like entrained air, so the aggregate correction factor removes this error.