Building Engineering Construction Materials and Properties 2 — Questions and Answers
Question 1: The slump test performed on fresh concrete primarily measures which property?
- 28-day compressive strength
- Air content percentage
- Workability and consistency (Correct answer)
- Aggregate gradation
Correct answer: Workability and consistency
The slump test measures the consistency or workability of fresh concrete by recording how much a standard cone of concrete settles.
Question 2: Per ASTM C39, what is the standard age at which concrete cylinder specimens are tested for compressive strength?
- 7 days
- 14 days
- 28 days (Correct answer)
- 56 days
Correct answer: 28 days
ASTM C39 specifies 28 days as the standard testing age because concrete reaches approximately 99% of its design strength by then under normal curing conditions.
Question 3: The modulus of elasticity (Young's modulus) of structural steel is approximately:
- 10,000 ksi
- 29,000 ksi (Correct answer)
- 57,000 ksi
- 100,000 ksi
Correct answer: 29,000 ksi
The modulus of elasticity of steel is approximately 29,000 ksi (200 GPa), a constant value used in all structural steel deflection and stiffness calculations.
Question 4: Which ASTM standard governs the compressive strength testing of cylindrical concrete specimens?
- ASTM C150
- ASTM C39 (Correct answer)
- ASTM C31
- ASTM C78
Correct answer: ASTM C39
ASTM C39 covers the standard test method for compressive strength of cylindrical concrete specimens; C31 covers making and curing specimens.
Question 5: Reinforcing bar (rebar) in the US is designated by bar number. What does the bar number represent?
- Nominal diameter in inches
- Approximate diameter in eighths of an inch (Correct answer)
- Weight per linear foot in pounds
- Cross-sectional area in square inches
Correct answer: Approximate diameter in eighths of an inch
A rebar bar number equals the approximate diameter in eighths of an inch; for example, a #4 bar has a nominal diameter of 4/8 = 0.5 inches.
Question 6: What role does fly ash play when used in a concrete mix design?
- It replaces coarse aggregate to reduce weight
- It acts as a supplementary cementitious material (SCM) (Correct answer)
- It functions as a chemical accelerating admixture
- It is applied as a curing membrane after placement
Correct answer: It acts as a supplementary cementitious material (SCM)
Fly ash is a pozzolan that reacts with calcium hydroxide in concrete to form additional cementitious compounds, improving long-term strength and durability.
Question 7: The flexural strength (modulus of rupture) of concrete is approximately what percentage of its compressive strength?
- 50%
- 25%
- 10–15% (Correct answer)
- 1–2%
Correct answer: 10–15%
Concrete's modulus of rupture (fr ≈ 7.5√f'c in psi) is roughly 10–15% of its compressive strength, reflecting concrete's inherent weakness in tension.
Building Engineering Construction Materials and Properties 2
The slump test performed on fresh concrete primarily measures which property?