BCE Construction & Building Materials 3

Question 1

What phenomenon causes concrete to crack due to chemical expansion when alkalis in cement react with silica in aggregates?

Accepted Answer

Alkali-Silica Reaction (ASR)

Answer

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?

Accepted Answer

Strength and permeability

Answer

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?

Accepted Answer

Closed-cell spray polyurethane foam (SPF)

Answer

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?

Accepted Answer

Allowable design stresses

Answer

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?

Accepted Answer

Creep

Answer

Creep is the slow, plastic deformation of concrete under long-term compressive stress, even below the elastic limit.

BCE - Bachelor of Civil Engineering Practice Test