CO Structural Concrete Contractor Exam
Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A| Instant
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1. What is the primary purpose of reinforcing steel in a reinforced
concrete structural member?
A. To reduce the weight of the concrete
B. To increase concrete workability
C. To resist tensile stresses that concrete alone cannot adequately
carry
D. To prevent all cracking in concrete
Rationale: Concrete is strong in compression but comparatively weak
in tension. Reinforcing steel is placed where tensile stresses are
expected so the composite member can resist bending, tension, and
other structural forces more effectively.
, 2. Which property of fresh concrete is most directly affected by its
water-cement ratio?
A. Aggregate size
B. Workability and potential strength
C. Reinforcing bar diameter
D. Concrete color
Rationale: The water-cement ratio strongly affects fresh-concrete
workability and hardened-concrete properties. Excess water may
make concrete easier to place but generally reduces strength and
increases permeability after hardening.
3. What is the primary function of coarse aggregate in structural
concrete?
A. Provide chemical curing
B. Replace reinforcing steel
C. Provide bulk and contribute to the concrete's load-carrying
structure
D. Prevent cement hydration
Rationale: Coarse aggregate makes up a substantial portion of
concrete volume. It contributes to dimensional stability, stiffness, and
economy while becoming part of the hardened concrete matrix.
, 4. Before placing concrete against an existing concrete surface, what
should generally be done?
A. Cover the surface with loose dust
B. Apply motor oil
C. Clean and properly prepare the existing surface
D. Saturate it with excess mixing water
Rationale: Proper surface preparation promotes bond between new
and existing concrete. Dirt, laitance, oil, and other contaminants can
interfere with adhesion and reduce the effectiveness of the
connection.
5. What is concrete consolidation intended to accomplish?
A. Increase the water content
B. Remove entrapped air and ensure concrete surrounds
reinforcement and forms
C. Stop cement hydration
D. Reduce cement content
Rationale: Consolidation, commonly accomplished with vibration,
removes unwanted entrapped air and helps concrete flow around
reinforcement and into corners. Poor consolidation can produce
honeycombing, voids, and weak areas.
, 6. Which tool is commonly used to consolidate freshly placed
structural concrete?
A. Pipe wrench
B. Chalk line
C. Internal concrete vibrator
D. Hacksaw
Rationale: An internal vibrator transmits vibration into fresh concrete,
helping it flow around reinforcing bars and against form surfaces.
Vibrators must be used correctly to avoid segregation and other
placement problems.
7. What is the main purpose of concrete curing?
A. Increase evaporation
B. Remove reinforcement
C. Maintain conditions that allow cement hydration and proper
strength development
D. Reduce cement hydration
Rationale: Curing keeps concrete sufficiently moist and within an
appropriate temperature range so hydration can continue. Proper
curing improves strength, durability, abrasion resistance, and overall
concrete quality.
Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A| Instant
Download Pdf
1. What is the primary purpose of reinforcing steel in a reinforced
concrete structural member?
A. To reduce the weight of the concrete
B. To increase concrete workability
C. To resist tensile stresses that concrete alone cannot adequately
carry
D. To prevent all cracking in concrete
Rationale: Concrete is strong in compression but comparatively weak
in tension. Reinforcing steel is placed where tensile stresses are
expected so the composite member can resist bending, tension, and
other structural forces more effectively.
, 2. Which property of fresh concrete is most directly affected by its
water-cement ratio?
A. Aggregate size
B. Workability and potential strength
C. Reinforcing bar diameter
D. Concrete color
Rationale: The water-cement ratio strongly affects fresh-concrete
workability and hardened-concrete properties. Excess water may
make concrete easier to place but generally reduces strength and
increases permeability after hardening.
3. What is the primary function of coarse aggregate in structural
concrete?
A. Provide chemical curing
B. Replace reinforcing steel
C. Provide bulk and contribute to the concrete's load-carrying
structure
D. Prevent cement hydration
Rationale: Coarse aggregate makes up a substantial portion of
concrete volume. It contributes to dimensional stability, stiffness, and
economy while becoming part of the hardened concrete matrix.
, 4. Before placing concrete against an existing concrete surface, what
should generally be done?
A. Cover the surface with loose dust
B. Apply motor oil
C. Clean and properly prepare the existing surface
D. Saturate it with excess mixing water
Rationale: Proper surface preparation promotes bond between new
and existing concrete. Dirt, laitance, oil, and other contaminants can
interfere with adhesion and reduce the effectiveness of the
connection.
5. What is concrete consolidation intended to accomplish?
A. Increase the water content
B. Remove entrapped air and ensure concrete surrounds
reinforcement and forms
C. Stop cement hydration
D. Reduce cement content
Rationale: Consolidation, commonly accomplished with vibration,
removes unwanted entrapped air and helps concrete flow around
reinforcement and into corners. Poor consolidation can produce
honeycombing, voids, and weak areas.
, 6. Which tool is commonly used to consolidate freshly placed
structural concrete?
A. Pipe wrench
B. Chalk line
C. Internal concrete vibrator
D. Hacksaw
Rationale: An internal vibrator transmits vibration into fresh concrete,
helping it flow around reinforcing bars and against form surfaces.
Vibrators must be used correctly to avoid segregation and other
placement problems.
7. What is the main purpose of concrete curing?
A. Increase evaporation
B. Remove reinforcement
C. Maintain conditions that allow cement hydration and proper
strength development
D. Reduce cement hydration
Rationale: Curing keeps concrete sufficiently moist and within an
appropriate temperature range so hydration can continue. Proper
curing improves strength, durability, abrasion resistance, and overall
concrete quality.
