CO Concrete Contractor Exam Practice
Questions And Correct Answers
(Verified Answers) Plus Rationale 2027
Q&A| Instant Download Pdf.
1. Which practice is most important before placing concrete into forms
to ensure that the finished member will have the intended
dimensions, alignment, and structural performance?
A. Increasing the cement content of the mixture
B. Verifying form dimensions, line, grade, bracing, cleanliness, and
release-agent application
C. Adding water immediately before placement to improve flow
D. Removing reinforcing steel to simplify consolidation
B. Verifying form dimensions, line, grade, bracing, cleanliness, and
release-agent application
Rationale: Proper form inspection ensures that concrete is placed into a
stable, correctly positioned mold and reduces defects caused by
movement, contamination, dimensional errors, or inadequate stripping
preparation.
2. What is the primary purpose of consolidating freshly placed
concrete with an internal vibrator?
,A. To intentionally separate coarse aggregate from mortar
B. To remove entrapped air and improve contact between concrete,
reinforcement, and forms
C. To accelerate cement hydration through mechanical heating
D. To reduce the amount of cement required in the mixture
B. To remove entrapped air and improve contact between concrete,
reinforcement, and forms
Rationale: Proper vibration consolidates concrete by removing
entrapped air and helping the material flow around reinforcement and
into form corners without unnecessarily changing the mixture
proportions.
3. Excessive vibration of a highly workable concrete mixture may result
in:
A. Improved air entrainment
B. Complete elimination of shrinkage cracking
C. Segregation of aggregate and paste
D. Increased reinforcement cover
C. Segregation of aggregate and paste
Rationale: Over-vibration can cause heavier aggregate to settle while
mortar and paste rise, producing segregation and potentially weakening
the uniformity and appearance of the hardened concrete.
4. Which condition is most likely to increase the risk of plastic
shrinkage cracking?
,A. Cool temperatures, high humidity, and low wind
B. Rapid surface moisture evaporation caused by heat, wind, and low
humidity
C. Continuous moist curing immediately after finishing
D. Low evaporation rates combined with fogging
B. Rapid surface moisture evaporation caused by heat, wind, and low
humidity
Rationale: Plastic shrinkage cracking occurs when water evaporates
from fresh concrete faster than bleed water can replace it, causing
tensile stresses to develop before the concrete has gained sufficient
strength.
5. What is the principal function of properly placed reinforcing steel in
conventional reinforced concrete?
A. To eliminate the need for concrete cover
B. To provide tensile resistance where concrete is relatively weak
C. To prevent all volume changes caused by temperature
D. To replace coarse aggregate in structural members
B. To provide tensile resistance where concrete is relatively weak
Rationale: Concrete performs well in compression but has comparatively
low tensile strength, so reinforcing steel is positioned to resist tensile
forces and improve structural capacity.
6. Before concrete is placed around reinforcing steel, which action is
essential?
, A. Coat all reinforcement with curing compound
B. Verify reinforcement size, location, spacing, support, cleanliness, and
required cover
C. Remove chairs and supports so the steel rests on the subgrade
D. Apply excess form oil directly to reinforcing bars
B. Verify reinforcement size, location, spacing, support, cleanliness, and
required cover
Rationale: Reinforcement must be installed according to the approved
design and adequately supported so it remains in the required position
during concrete placement and consolidation.
7. What is the primary purpose of concrete cover over reinforcing
steel?
A. To make finishing easier
B. To protect reinforcement and provide proper structural bond and
durability
C. To increase slump
D. To eliminate the need for consolidation
B. To protect reinforcement and provide proper structural bond and
durability
Rationale: Adequate cover helps protect reinforcing steel from
environmental exposure and corrosion while also ensuring proper bond
and structural performance.
Questions And Correct Answers
(Verified Answers) Plus Rationale 2027
Q&A| Instant Download Pdf.
1. Which practice is most important before placing concrete into forms
to ensure that the finished member will have the intended
dimensions, alignment, and structural performance?
A. Increasing the cement content of the mixture
B. Verifying form dimensions, line, grade, bracing, cleanliness, and
release-agent application
C. Adding water immediately before placement to improve flow
D. Removing reinforcing steel to simplify consolidation
B. Verifying form dimensions, line, grade, bracing, cleanliness, and
release-agent application
Rationale: Proper form inspection ensures that concrete is placed into a
stable, correctly positioned mold and reduces defects caused by
movement, contamination, dimensional errors, or inadequate stripping
preparation.
2. What is the primary purpose of consolidating freshly placed
concrete with an internal vibrator?
,A. To intentionally separate coarse aggregate from mortar
B. To remove entrapped air and improve contact between concrete,
reinforcement, and forms
C. To accelerate cement hydration through mechanical heating
D. To reduce the amount of cement required in the mixture
B. To remove entrapped air and improve contact between concrete,
reinforcement, and forms
Rationale: Proper vibration consolidates concrete by removing
entrapped air and helping the material flow around reinforcement and
into form corners without unnecessarily changing the mixture
proportions.
3. Excessive vibration of a highly workable concrete mixture may result
in:
A. Improved air entrainment
B. Complete elimination of shrinkage cracking
C. Segregation of aggregate and paste
D. Increased reinforcement cover
C. Segregation of aggregate and paste
Rationale: Over-vibration can cause heavier aggregate to settle while
mortar and paste rise, producing segregation and potentially weakening
the uniformity and appearance of the hardened concrete.
4. Which condition is most likely to increase the risk of plastic
shrinkage cracking?
,A. Cool temperatures, high humidity, and low wind
B. Rapid surface moisture evaporation caused by heat, wind, and low
humidity
C. Continuous moist curing immediately after finishing
D. Low evaporation rates combined with fogging
B. Rapid surface moisture evaporation caused by heat, wind, and low
humidity
Rationale: Plastic shrinkage cracking occurs when water evaporates
from fresh concrete faster than bleed water can replace it, causing
tensile stresses to develop before the concrete has gained sufficient
strength.
5. What is the principal function of properly placed reinforcing steel in
conventional reinforced concrete?
A. To eliminate the need for concrete cover
B. To provide tensile resistance where concrete is relatively weak
C. To prevent all volume changes caused by temperature
D. To replace coarse aggregate in structural members
B. To provide tensile resistance where concrete is relatively weak
Rationale: Concrete performs well in compression but has comparatively
low tensile strength, so reinforcing steel is positioned to resist tensile
forces and improve structural capacity.
6. Before concrete is placed around reinforcing steel, which action is
essential?
, A. Coat all reinforcement with curing compound
B. Verify reinforcement size, location, spacing, support, cleanliness, and
required cover
C. Remove chairs and supports so the steel rests on the subgrade
D. Apply excess form oil directly to reinforcing bars
B. Verify reinforcement size, location, spacing, support, cleanliness, and
required cover
Rationale: Reinforcement must be installed according to the approved
design and adequately supported so it remains in the required position
during concrete placement and consolidation.
7. What is the primary purpose of concrete cover over reinforcing
steel?
A. To make finishing easier
B. To protect reinforcement and provide proper structural bond and
durability
C. To increase slump
D. To eliminate the need for consolidation
B. To protect reinforcement and provide proper structural bond and
durability
Rationale: Adequate cover helps protect reinforcing steel from
environmental exposure and corrosion while also ensuring proper bond
and structural performance.
