California Concrete Contractor License
Exam (C-8) Questions And Correct
Answers (Verified Answers) Plus
Rationales 2025 Q&A | Instant
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1. What is the minimum compressive strength required for concrete
used in residential slabs according to California building codes?
3000 psi
This strength ensures durability and structural integrity for typical
residential concrete slabs.
2. Which of the following admixtures is commonly used to accelerate the
setting time of concrete?
Calcium chloride
Calcium chloride is a common accelerator that reduces the curing
time of concrete.
3. What is the primary purpose of reinforcing steel (rebar) in concrete
construction?
To increase tensile strength
Concrete is strong in compression but weak in tension, so rebar is
used to improve tensile strength.
,4. How often should slump tests be performed on a concrete batch
during a pour?
At least once every hour
Regular slump tests ensure the consistency and workability of
concrete during the pour.
5. What is the typical water-cement ratio range for concrete used in
structural applications?
0.4 to 0.6
This ratio balances workability and strength; too much water
weakens concrete.
6. What is the maximum allowable slump for concrete used in footings?
4 inches
This ensures adequate workability without excessive water content
that could reduce strength.
7. Which type of cement is typically used for concrete exposed to sulfate
soils?
Type V Portland cement
Type V cement has high sulfate resistance, suitable for aggressive
soils.
8. What is the primary cause of plastic shrinkage cracks in concrete?
Rapid evaporation of water from the surface
Quick drying causes shrinkage and cracking before the concrete
hardens.
9. When curing concrete, what is the minimum recommended curing
period to achieve proper strength?
7 days
Proper curing for at least 7 days ensures hydration and strength
development.
, 10. Which tool is used to check the flatness and levelness of a
concrete slab?
Straightedge or laser level
These tools help ensure the slab meets the required tolerances.
11. What is the function of a vapor barrier under a concrete slab?
To prevent moisture migration from soil into the slab
This protects flooring materials and prevents slab moisture problems.
12. When should concrete be placed relative to the temperature?
Between 50°F and 90°F
Concrete placed in this temperature range cures properly without
freezing or excessive heat issues.
13. What is the typical thickness of a residential concrete slab-on-
grade?
4 inches
This thickness supports typical residential loads without excessive
material.
14. How long should concrete be protected from freezing
temperatures after placement?
At least 72 hours
Freezing can damage concrete before it gains strength, so protection
is critical.
15. What is the purpose of air entrainment in concrete?
To improve freeze-thaw durability
Entrained air creates small bubbles that relieve internal pressure
from freezing water.
16. What type of joint is used to control cracking due to shrinkage in
concrete slabs?
Control joint (or contraction joint)
Exam (C-8) Questions And Correct
Answers (Verified Answers) Plus
Rationales 2025 Q&A | Instant
Download Pdf
1. What is the minimum compressive strength required for concrete
used in residential slabs according to California building codes?
3000 psi
This strength ensures durability and structural integrity for typical
residential concrete slabs.
2. Which of the following admixtures is commonly used to accelerate the
setting time of concrete?
Calcium chloride
Calcium chloride is a common accelerator that reduces the curing
time of concrete.
3. What is the primary purpose of reinforcing steel (rebar) in concrete
construction?
To increase tensile strength
Concrete is strong in compression but weak in tension, so rebar is
used to improve tensile strength.
,4. How often should slump tests be performed on a concrete batch
during a pour?
At least once every hour
Regular slump tests ensure the consistency and workability of
concrete during the pour.
5. What is the typical water-cement ratio range for concrete used in
structural applications?
0.4 to 0.6
This ratio balances workability and strength; too much water
weakens concrete.
6. What is the maximum allowable slump for concrete used in footings?
4 inches
This ensures adequate workability without excessive water content
that could reduce strength.
7. Which type of cement is typically used for concrete exposed to sulfate
soils?
Type V Portland cement
Type V cement has high sulfate resistance, suitable for aggressive
soils.
8. What is the primary cause of plastic shrinkage cracks in concrete?
Rapid evaporation of water from the surface
Quick drying causes shrinkage and cracking before the concrete
hardens.
9. When curing concrete, what is the minimum recommended curing
period to achieve proper strength?
7 days
Proper curing for at least 7 days ensures hydration and strength
development.
, 10. Which tool is used to check the flatness and levelness of a
concrete slab?
Straightedge or laser level
These tools help ensure the slab meets the required tolerances.
11. What is the function of a vapor barrier under a concrete slab?
To prevent moisture migration from soil into the slab
This protects flooring materials and prevents slab moisture problems.
12. When should concrete be placed relative to the temperature?
Between 50°F and 90°F
Concrete placed in this temperature range cures properly without
freezing or excessive heat issues.
13. What is the typical thickness of a residential concrete slab-on-
grade?
4 inches
This thickness supports typical residential loads without excessive
material.
14. How long should concrete be protected from freezing
temperatures after placement?
At least 72 hours
Freezing can damage concrete before it gains strength, so protection
is critical.
15. What is the purpose of air entrainment in concrete?
To improve freeze-thaw durability
Entrained air creates small bubbles that relieve internal pressure
from freezing water.
16. What type of joint is used to control cracking due to shrinkage in
concrete slabs?
Control joint (or contraction joint)
