BCE Construction & Building Materials 3 — Questions and Answers
Question 1: What phenomenon causes concrete to crack due to chemical expansion when alkalis in cement react with silica in aggregates?
- Carbonation shrinkage
- Alkali-Silica Reaction (ASR) (Correct answer)
- Delayed ettringite formation
- Sulfate attack
Correct answer: Alkali-Silica Reaction (ASR)
ASR produces an expansive gel at the aggregate surface that absorbs moisture and swells, causing map cracking ('crazing') in concrete.
Question 2: What is the water-cement (w/c) ratio's primary influence on hardened concrete?
- Color and aesthetics
- Strength and permeability (Correct answer)
- Aggregate gradation
- Air content
Correct answer: Strength and permeability
Lower w/c ratios produce denser cement paste with higher strength and lower permeability, per Abrams' law.
Question 3: Which insulation material has the highest R-value per inch of thickness?
- Fiberglass batt
- Cellulose
- Closed-cell spray polyurethane foam (SPF) (Correct answer)
- Mineral wool
Correct answer: Closed-cell spray polyurethane foam (SPF)
Closed-cell SPF achieves approximately R-6 to R-7 per inch, significantly higher than fiberglass (R-3.2), cellulose (R-3.7), or mineral wool (R-3.7).
Question 4: In timber construction, what does the 'species group' classification primarily indicate?
- Fire resistance rating
- Moisture content at time of milling
- Allowable design stresses (Correct answer)
- Dimensional stability
Correct answer: Allowable design stresses
NDS species groups (e.g., Douglas Fir-Larch, Southern Pine) define allowable design values for bending, tension, compression, and shear.
Question 5: What is the term for the gradual time-dependent deformation of concrete under sustained load?
- Shrinkage
- Settlement
- Creep (Correct answer)
- Elastic rebound
Correct answer: Creep
Creep is the slow, plastic deformation of concrete under long-term compressive stress, even below the elastic limit.
Question 6: Which type of glass provides the highest level of safety through a laminated interlayer that holds fragments together when broken?
- Tempered glass
- Laminated glass (Correct answer)
- Wired glass
- Heat-strengthened glass
Correct answer: Laminated glass
Laminated glass uses a polyvinyl butyral (PVB) interlayer that bonds glass plies together, retaining fragments and providing impact resistance.
Question 7: What is the primary advantage of using precast concrete over cast-in-place concrete?
- Lower material cost
- Greater monolithic continuity
- Better quality control and faster site erection (Correct answer)
- Higher fire resistance
Correct answer: Better quality control and faster site erection
Precast elements are fabricated in controlled factory conditions yielding consistent quality, and their delivery to site allows rapid structural erection.
BCE Construction & Building Materials 3
What phenomenon causes concrete to crack due to chemical expansion when alkalis in cement react with silica in aggregates?