CCI Construction Materials & Methods 2 — Questions and Answers
Question 1: What is the primary purpose of using a vapor barrier in a concrete slab-on-grade?
- To increase compressive strength
- To prevent moisture migration from the subgrade into the slab (Correct answer)
- To reduce curing time
- To improve surface finish
Correct answer: To prevent moisture migration from the subgrade into the slab
A vapor barrier (polyethylene sheet) prevents soil moisture from wicking upward through the concrete slab, protecting flooring systems and interior finishes.
Question 2: Which masonry unit classification indicates the highest structural quality per ASTM C90?
- Type S
- Grade N (Correct answer)
- Grade MW
- Type N
Correct answer: Grade N
ASTM C90 Grade N concrete masonry units are intended for general use including above- and below-grade applications exposed to moisture and weather.
Question 3: In structural steel fabrication, what does the term 'mill scale' refer to?
- A quality rating assigned at the rolling mill
- Iron oxide layer formed on hot-rolled steel during manufacturing (Correct answer)
- The dimensional tolerance marking on structural members
- A surface coating applied for corrosion protection
Correct answer: Iron oxide layer formed on hot-rolled steel during manufacturing
Mill scale is a flaky iron oxide layer that forms on the surface of hot-rolled steel during the manufacturing process and must be removed before painting.
Question 4: What concrete admixture type is used to reduce the water content required to achieve a given slump?
- Accelerator
- Water reducer (plasticizer) (Correct answer)
- Air-entraining agent
- Retarder
Correct answer: Water reducer (plasticizer)
Water-reducing admixtures (plasticizers) allow the same workability to be achieved with less water, improving the water-to-cement ratio and concrete strength.
Question 5: When inspecting reinforcing steel, 'No. 5 bar' refers to a rebar with a nominal diameter of:
- 3/8 inch
- 1/2 inch
- 5/8 inch (Correct answer)
- 3/4 inch
Correct answer: 5/8 inch
Rebar bar numbers correspond to the nominal diameter in eighths of an inch, so a No. 5 bar has a nominal diameter of 5/8 inch.
Question 6: Which type of Portland cement is specifically designed for use in environments with high sulfate exposure?
- Type I
- Type II
- Type III
- Type V (Correct answer)
Correct answer: Type V
Type V Portland cement has a very low tricalcium aluminate (C3A) content, making it highly resistant to sulfate attack from soil and groundwater.
Question 7: What is the standard curing period recommended for normal-strength Portland cement concrete to achieve adequate strength?
- 3 days
- 7 days
- 14 days
- 28 days (Correct answer)
Correct answer: 28 days
Portland cement concrete is conventionally tested and specified to reach its design compressive strength at 28 days of moist curing.
CCI Construction Materials & Methods 2
What is the primary purpose of using a vapor barrier in a concrete slab-on-grade?