Concrete Field Inspector Flashcards

What is the primary purpose of using a vibrator during concrete placement?

Answer: To eliminate entrapped air voids and achieve consolidation

Internal vibration consolidates fresh concrete by liquefying it momentarily so air voids escape and the mix fills the form completely.

According to ASTM C94, how many total drum revolutions are permitted at mixing speed before discharge?

Answer: 300 revolutions

ASTM C94 limits the total drum revolutions at mixing speed to 300 or the time limit of 90 minutes, whichever is reached first.

A field inspector observes the vibrator being inserted more than 18 inches apart. What is the likely consequence?

Answer: Under-consolidation leaving unvibrated zones

Vibrator insertion spacing exceeding the radius of action (typically 1.5× vibrator diameter) leaves poorly consolidated zones between insertions.

What does the water-to-cementitious materials ratio (w/cm) primarily control?

Answer: The strength and durability of hardened concrete

The w/cm ratio is the single most important factor governing concrete strength and durability — lower ratios yield stronger, more durable concrete.

In cold weather concreting, what minimum temperature must fresh concrete be maintained at during placement and protection per ACI 306?

Answer: 50°F (10°C)

ACI 306 requires fresh concrete to be maintained at a minimum of 50°F (10°C) during placement and for the required protection period.

Which of the following is a correct procedure when the slump test cone is lifted?

Answer: Lift straight upward in 5 ± 2 seconds without twisting

ASTM C143 requires the cone to be raised smoothly and vertically in 5 ± 2 seconds without lateral or twisting motion.

What does segregation in concrete refer to?

Answer: Separation of coarse aggregate from the mortar fraction

Segregation is the undesirable separation of the coarse aggregate from the mortar, often caused by improper handling, over-vibration, or excessive w/c ratio.