BCM Building Materials and Construction Methods 2 — Questions and Answers
Question 1: Which roofing system type is most commonly used on low-slope commercial roofs in the US?
- Single-ply membrane (TPO, EPDM, or PVC) (Correct answer)
- Clay tile roofing
- Wood shake shingles
- Slate roofing
Correct answer: Single-ply membrane (TPO, EPDM, or PVC)
Single-ply membranes like TPO and EPDM dominate low-slope commercial roofing due to their ease of installation, cost-effectiveness, and performance.
Question 2: Post-tensioned concrete slabs use high-strength steel tendons to:
- Apply compressive pre-stress to the concrete after it cures, improving span capacity and crack control (Correct answer)
- Connect precast concrete panels at construction joints
- Reinforce concrete columns against seismic lateral loads
- Anchor curtain wall systems to the building structure
Correct answer: Apply compressive pre-stress to the concrete after it cures, improving span capacity and crack control
Post-tensioning applies compressive force to cured concrete via stressed tendons, counteracting tensile stresses and enabling thinner slabs with longer spans.
Question 3: The R-value of an insulation material measures its:
- Resistance to heat flow (thermal resistance) (Correct answer)
- Resistance to moisture absorption
- Fire resistance in minutes
- Compressive strength under load
Correct answer: Resistance to heat flow (thermal resistance)
R-value quantifies a material's resistance to conductive heat transfer; higher R-values indicate better insulating performance.
Question 4: Tilt-up construction is a concrete building technique where:
- Concrete wall panels are cast horizontally on the slab floor and then tilted up into vertical position (Correct answer)
- Precast panels are manufactured off-site and trucked to the project
- Concrete is pumped into vertically standing formwork systems
- Masonry walls are reinforced with horizontal grout lifts
Correct answer: Concrete wall panels are cast horizontally on the slab floor and then tilted up into vertical position
Tilt-up construction casts large concrete panels on the ground slab, then cranes tilt them vertically into position, making it efficient for industrial and warehouse buildings.
Question 5: The purpose of control joints in concrete flatwork is to:
- Create weakened planes where cracking occurs in a controlled, straight line (Correct answer)
- Provide expansion space for thermal movement in the slab
- Anchor the slab to the foundation walls
- Allow construction to pause between pours
Correct answer: Create weakened planes where cracking occurs in a controlled, straight line
Control joints are tooled or saw-cut into slabs to predetermine where shrinkage cracking will occur, keeping cracks at planned locations.
Question 6: Fly ash is commonly added to concrete mixes primarily because it:
- Improves workability, reduces permeability, and partially replaces Portland cement (Correct answer)
- Accelerates concrete strength gain in cold weather
- Increases the unit weight of the concrete mix
- Acts as an air-entraining agent for freeze-thaw resistance
Correct answer: Improves workability, reduces permeability, and partially replaces Portland cement
Fly ash, a coal combustion byproduct, is a pozzolanic supplementary cementitious material that improves concrete durability while reducing cement content and cost.
BCM Building Materials and Construction Methods 2
Which roofing system type is most commonly used on low-slope commercial roofs in the US?