1
NEVADA C-5 CONCRETE CONTRACTOR P R A C T I C E
COMPREHESIVE EXAMINATION ACADEMIC YEAR 2026 -
27 QUESTIONS CORRECT ANSWER AND RATIONALES
Q1.
Before placing concrete, what should be verified about the subgrade?
A. It is slightly wet and properly compacted
B. It is rough and uneven to increase bonding
C. It contains free-standing water
D. It is covered with vapor barrier only
⬛ Correct: A
Rationale: A firm, moist (not saturated) subgrade prevents absorption of mix water and supports
uniform slab thickness; uneven or muddy bases cause settlement cracks.
Q2.
Which material is commonly used to prevent bonding between a new slab and an existing one?
A. Epoxy resin
B. Grout
C. Plastic sheeting or bond-breaker compound
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D. Curing compound
⬛ Correct: C
Rationale: Bond breakers (poly film or chemical compounds) permit independent movement
where isolation is required.
Q3.
According to ACI 318, what is the minimum concrete cover for reinforcing steel cast against
earth?
A. 1 inch
B. 1 ½ inches
C. 3 inches
D. 2 inches
⬛ Correct: C
Rationale: Concrete directly exposed to earth or weather requires ≥ 3 in. cover for protection
against corrosion and fire.
Q4.
When installing reinforcement bars, laps should be—
A. Randomly spaced for strength
B. Overlapping by one-half bar diameter
C. Overlapping per design (typically 40 × bar diameter)
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D. Butt-welded without overlap
⬛ Correct: C
Rationale: Proper lap length ensures stress transfer between bars; default splice = 40 db unless
structural plans specify otherwise.
Q5.
What is the purpose of vibration during concrete placement?
A. To mix aggregates
B. To consolidate and remove entrapped air
C. To cool the mix
D. To prevent hydration
⬛ Correct: B
Rationale: Internal or surface vibration removes air voids, ensuring full contact with
reinforcement and forms for high strength.
Q6.
Excessive vibration can cause—
A. Increased strength
B. Segregation and loss of entrained air
C. Uniform texture
D. Improved curing
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⬛ Correct: B
Rationale: Over-vibration drives coarse aggregate downward and water upward, weakening the
surface.
Q7.
The typical maximum slump for floor slabs is—
A. 1 inch
B. 10 inches
C. 4 inches
D. 8 inches
⬛ Correct: C
Rationale: General-purpose concrete is workable at 3 – 5 in. slump; higher slumps risk
segregation unless plasticizers are used.
Q8.
Concrete should not be placed if ambient temperature is below—
A. 10 °F
B. 40 °F (4 °C)
C. 55 °F
D. 70 °F
NEVADA C-5 CONCRETE CONTRACTOR P R A C T I C E
COMPREHESIVE EXAMINATION ACADEMIC YEAR 2026 -
27 QUESTIONS CORRECT ANSWER AND RATIONALES
Q1.
Before placing concrete, what should be verified about the subgrade?
A. It is slightly wet and properly compacted
B. It is rough and uneven to increase bonding
C. It contains free-standing water
D. It is covered with vapor barrier only
⬛ Correct: A
Rationale: A firm, moist (not saturated) subgrade prevents absorption of mix water and supports
uniform slab thickness; uneven or muddy bases cause settlement cracks.
Q2.
Which material is commonly used to prevent bonding between a new slab and an existing one?
A. Epoxy resin
B. Grout
C. Plastic sheeting or bond-breaker compound
,2
D. Curing compound
⬛ Correct: C
Rationale: Bond breakers (poly film or chemical compounds) permit independent movement
where isolation is required.
Q3.
According to ACI 318, what is the minimum concrete cover for reinforcing steel cast against
earth?
A. 1 inch
B. 1 ½ inches
C. 3 inches
D. 2 inches
⬛ Correct: C
Rationale: Concrete directly exposed to earth or weather requires ≥ 3 in. cover for protection
against corrosion and fire.
Q4.
When installing reinforcement bars, laps should be—
A. Randomly spaced for strength
B. Overlapping by one-half bar diameter
C. Overlapping per design (typically 40 × bar diameter)
,3
D. Butt-welded without overlap
⬛ Correct: C
Rationale: Proper lap length ensures stress transfer between bars; default splice = 40 db unless
structural plans specify otherwise.
Q5.
What is the purpose of vibration during concrete placement?
A. To mix aggregates
B. To consolidate and remove entrapped air
C. To cool the mix
D. To prevent hydration
⬛ Correct: B
Rationale: Internal or surface vibration removes air voids, ensuring full contact with
reinforcement and forms for high strength.
Q6.
Excessive vibration can cause—
A. Increased strength
B. Segregation and loss of entrained air
C. Uniform texture
D. Improved curing
, 4
⬛ Correct: B
Rationale: Over-vibration drives coarse aggregate downward and water upward, weakening the
surface.
Q7.
The typical maximum slump for floor slabs is—
A. 1 inch
B. 10 inches
C. 4 inches
D. 8 inches
⬛ Correct: C
Rationale: General-purpose concrete is workable at 3 – 5 in. slump; higher slumps risk
segregation unless plasticizers are used.
Q8.
Concrete should not be placed if ambient temperature is below—
A. 10 °F
B. 40 °F (4 °C)
C. 55 °F
D. 70 °F
