Construction & Building Materials Flashcards

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

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.

What is the water-cement (w/c) ratio's primary influence on hardened concrete?

Answer: Strength and permeability

Lower w/c ratios produce denser cement paste with higher strength and lower permeability, per Abrams' law.

Which insulation material has the highest R-value per inch of thickness?

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).

In timber construction, what does the 'species group' classification primarily indicate?

Answer: Allowable design stresses

NDS species groups (e.g., Douglas Fir-Larch, Southern Pine) define allowable design values for bending, tension, compression, and shear.

What is the term for the gradual time-dependent deformation of concrete under sustained load?

Answer: Creep

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

Which type of glass provides the highest level of safety through a laminated interlayer that holds fragments together when broken?

Answer: Laminated glass

Laminated glass uses a polyvinyl butyral (PVB) interlayer that bonds glass plies together, retaining fragments and providing impact resistance.

What is the primary advantage of using precast concrete over cast-in-place concrete?

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.