CCI Concrete Testing & Evaluation 2

Question 1

According to ASTM C138, what property of fresh concrete is determined by the unit weight test?

Accepted Answer

Air content (by calculation)

Answer

ASTM C138 measures the unit weight (density) of fresh concrete, which can be used to calculate air content when the theoretical density is known.

Question 2

A concrete mix design specifies a w/cm ratio of 0.45. If the cementitious content is 600 lb/cy, what is the maximum water content allowed per cubic yard?

Accepted Answer

270 lb

Answer

Maximum water = w/cm ratio × cementitious content = 0.45 × 600 lb = 270 lb per cubic yard.

Question 3

Which ASTM standard governs the making and curing of concrete test specimens in the field?

Accepted Answer

ASTM C31

Answer

ASTM C31 covers the standard practice for making and curing concrete test specimens in the field.

Question 4

During a slump test, a concrete sample collapses to one side rather than slumping evenly. This is called a _____ slump and indicates what condition?

Accepted Answer

Shear slump — possible segregation or poor cohesion

Answer

A shear slump where the top slides off to one side indicates poor cohesion and possible segregation, making the test invalid and requiring a retest.

Question 5

At what age is concrete typically first tested for compressive strength in standard field practice?

Accepted Answer

28 days

Answer

The standard acceptance age for compressive strength is 28 days, as concrete reaches approximately 99% of its design strength by that time under normal curing.

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CCI Concrete Testing & Evaluation 2