CTQP Concrete Field Inspector 3 — Questions and Answers
Question 1: What is the purpose of striking off (screeding) concrete immediately after placement?
- To initiate the curing process by sealing the surface
- To bring mortar to the surface for finishing
- To level the concrete to the desired grade or form elevation (Correct answer)
- To consolidate the concrete around reinforcement
Correct answer: To level the concrete to the desired grade or form elevation
Screeding removes excess concrete and brings the surface to the required grade or elevation defined by the forms or screeds.
Question 2: According to ACI 305, what maximum concrete temperature at point of delivery is typically recommended for hot weather concreting?
- 75°F (24°C)
- 85°F (29°C)
- 90°F (32°C) (Correct answer)
- 95°F (35°C)
Correct answer: 90°F (32°C)
ACI 305 recommends that fresh concrete temperature at delivery should not exceed 90°F (32°C) to minimize adverse hot weather effects.
Question 3: A concrete cylinder that is tested at 27 days instead of 28 days will typically show:
- Higher strength because of additional curing
- Lower strength due to insufficient hydration
- Slightly lower strength, acceptable if within specifications (Correct answer)
- No difference; strength gain stops before 28 days
Correct answer: Slightly lower strength, acceptable if within specifications
Concrete gains strength slightly day by day, so a 27-day result is marginally lower than 28-day, but many specs allow a ±1 day tolerance.
Question 4: What does a 'cold joint' in concrete indicate?
- A joint placed in cold weather to allow thermal contraction
- A plane of weakness formed when fresh concrete is placed against hardened concrete (Correct answer)
- An intentional construction joint with a keyway for shear transfer
- A crack formed due to freezing temperatures during curing
Correct answer: A plane of weakness formed when fresh concrete is placed against hardened concrete
A cold joint forms when fresh concrete is placed against a layer that has already set, resulting in a weak bond plane.
Question 5: Which of the following actions is NOT appropriate when concrete fails the slump test on arrival?
- Reject the load
- Allow the contractor to add water up to the maximum w/c ratio (Correct answer)
- Retest with a new sample from the same truck
- Document the failing result and notify the engineer
Correct answer: Allow the contractor to add water up to the maximum w/c ratio
Water should never be added to a delivered load in the field to adjust slump without written authorization and without exceeding the design w/c ratio.
Question 6: What is the purpose of a curing compound applied to a concrete surface?
- To increase the concrete's final compressive strength by 10–15%
- To retain moisture in the concrete to promote hydration (Correct answer)
- To harden the surface against abrasion immediately after finishing
- To prevent carbonation of the concrete surface
Correct answer: To retain moisture in the concrete to promote hydration
Curing compounds form a membrane that retains moisture needed for continued cement hydration, achieving design strength.
Question 7: When rodding a 4-inch diameter concrete cylinder, how many layers and rod strokes per layer are required per ASTM C31?
- 2 layers, 15 strokes each
- 2 layers, 25 strokes each
- 3 layers, 25 strokes each (Correct answer)
- 3 layers, 50 strokes each
Correct answer: 3 layers, 25 strokes each
ASTM C31 requires 4-inch diameter cylinders to be filled in 3 equal layers and rodded 25 times per layer.
CTQP Concrete Field Inspector 3
What is the purpose of striking off (screeding) concrete immediately after placement?