CPC CPC Construction Methods & Materials 2 — Questions and Answers
Question 1: What does the water-cement (w/c) ratio primarily control in a concrete mix design?
- Color and texture
- Workability only
- Strength and durability (Correct answer)
- Aggregate gradation
Correct answer: Strength and durability
The w/c ratio is the single most important factor controlling concrete compressive strength and durability; lower ratios produce stronger, more durable concrete.
Question 2: In post-tensioned concrete construction, when are the tendons typically stressed?
- Before concrete is placed
- After concrete has reached sufficient strength (Correct answer)
- During concrete placement
- Seven days before pouring
Correct answer: After concrete has reached sufficient strength
Post-tensioning tendons are stressed after the concrete has cured and reached the required strength, typically around 75% of design strength.
Question 3: Which type of formwork system uses large prefabricated panels that can be reused many times on repetitive floor plates?
- Stick-built formwork
- Flying form (table form) system (Correct answer)
- Single-use stay-in-place forms
- Earthen formwork
Correct answer: Flying form (table form) system
Flying forms (table forms) are large prefabricated assemblies that are flown by crane from floor to floor, reducing labor and increasing reuse cycles.
Question 4: What is the primary function of a vapor retarder placed under a concrete slab-on-grade?
- Improve concrete bond to subbase
- Prevent moisture migration from soil into the slab (Correct answer)
- Increase load-bearing capacity
- Provide thermal insulation
Correct answer: Prevent moisture migration from soil into the slab
A vapor retarder placed beneath slabs-on-grade prevents ground moisture from migrating upward through the concrete, protecting floor coverings and equipment.
Question 5: In structural steel erection, what is the purpose of a 'safety cable' installed between columns?
- Align columns during grouting
- Provide fall protection for ironworkers walking on beams (Correct answer)
- Tension the connection bolts
- Support the crane load line
Correct answer: Provide fall protection for ironworkers walking on beams
Safety cables (perimeter cables) are installed between columns to provide fall protection for ironworkers, as required by OSHA 1926 Subpart R.
Question 6: Which soil improvement technique involves injecting a grout mixture into loose granular soil to densify and strengthen it?
- Surcharge preloading
- Compaction grouting (Correct answer)
- Dewatering
- Dynamic compaction
Correct answer: Compaction grouting
Compaction grouting injects a stiff, low-slump grout under pressure to displace and densify surrounding loose granular soils.
CPC CPC Construction Methods & Materials 2
What does the water-cement (w/c) ratio primarily control in a concrete mix design?