ACI Curing, Protection & Quality Control 2 — Questions and Answers
Question 1: What is the minimum curing period recommended by ACI 308 for concrete made with Type I/II cement under normal temperature conditions?
- 3 days
- 5 days
- 7 days (Correct answer)
- 14 days
Correct answer: 7 days
ACI 308 recommends a minimum of 7 days of curing for concrete made with Type I/II cement at normal temperatures.
Question 2: Which curing compound application method ensures the most uniform coverage on a freshly finished slab?
- Brush application in one direction only
- Spray application in two passes at right angles (Correct answer)
- Roller application from one end to the other
- Squeegee application in a single pass
Correct answer: Spray application in two passes at right angles
Spraying curing compound in two perpendicular passes ensures overlapping, uniform coverage with no missed areas.
Question 3: Hot weather concrete placement is generally considered to occur when ambient temperature exceeds what threshold?
- 75°F (24°C)
- 80°F (27°C)
- 90°F (32°C) (Correct answer)
- 100°F (38°C)
Correct answer: 90°F (32°C)
ACI 305 defines hot weather concreting conditions as those where ambient temperature exceeds 90°F (32°C).
Question 4: A slump test result that is 2 inches higher than specified most likely indicates which quality control problem?
- Insufficient aggregate gradation
- Excess water added at the jobsite (Correct answer)
- Over-vibration of the concrete
- Too much cementitious material
Correct answer: Excess water added at the jobsite
Excess slump beyond specification is the classic indicator of unauthorized water addition, which increases w/c ratio and reduces strength.
Question 5: Which type of curing blanket is most appropriate for protecting concrete from freezing temperatures?
- Single-layer burlap
- Polyethylene sheeting alone
- Insulating blankets with foam core (Correct answer)
- Wet sand cover
Correct answer: Insulating blankets with foam core
Insulating blankets with foam cores provide both moisture retention and thermal protection needed to prevent freezing.
Question 6: What does a low rebound hammer reading relative to the specified concrete strength indicate?
- The surface is too wet from curing
- The concrete may not have reached design strength (Correct answer)
- The aggregate is too coarse
- The concrete was over-vibrated
Correct answer: The concrete may not have reached design strength
A rebound hammer measures surface hardness; a low reading suggests the concrete may be weaker than the design strength.
Question 7: When should white-pigmented curing compound NOT be used?
- On slabs exposed to direct sunlight
- On surfaces that will receive a bonded overlay or coating (Correct answer)
- On flatwork in hot weather
- On slabs with a broom finish
Correct answer: On surfaces that will receive a bonded overlay or coating
Curing compounds form a membrane that prevents bond between concrete and subsequent overlays, adhesives, or coatings.
ACI Curing, Protection & Quality Control 2
What is the minimum curing period recommended by ACI 308 for concrete made with Type I/II cement under normal temperature conditions?