Curing, Protection & Quality Control Flashcards

Which chemical admixture is commonly used in hot weather concreting to offset the accelerating effect of high temperatures?

Answer: Set retarder

Set retarders slow hydration, compensating for the accelerated set caused by elevated concrete temperatures in hot weather.

The water-to-cementitious-materials ratio (w/cm) primarily affects which property of hardened concrete?

Answer: Compressive strength and durability

The w/cm ratio is the single most important factor controlling concrete compressive strength and long-term durability.

During cold weather concreting, the concrete temperature at the point of placement should be maintained at a minimum of:

Answer: 50°F (10°C)

ACI 306 requires concrete to be placed and maintained at a minimum of 50°F (10°C) to ensure adequate hydration in cold weather.

What is the primary purpose of fogging or misting water over fresh concrete in hot, dry, or windy conditions?

Answer: To reduce plastic shrinkage cracking by slowing evaporation

Fogging raises humidity immediately above the slab surface, reducing evaporation rate and thus preventing plastic shrinkage cracking.

A cylinder break at 28 days shows strength below the specified f'c. What is the first step in ACI-compliant quality control response?

Answer: Conduct additional testing such as cores per ACI 318

ACI 318 requires taking cores from the suspect area as the next investigative step before any remedial action is decided.

Which test is performed in the field to determine the air content of fresh concrete?

Answer: Pressure meter (Type B) test

The pressure meter (ASTM C231) is the most common field method for measuring air content in fresh concrete.

Plastic shrinkage cracking typically occurs during which phase of concrete construction?

Answer: Before the concrete has set while still in a plastic state

Plastic shrinkage cracks form when the evaporation rate from the surface exceeds the rate of bleed water supply, while concrete is still plastic.