Construction Concrete and Masonry 1 — Questions and Answers
Question 1: What is the standard water-to-cement ratio range for most structural concrete mixes?
- 0.20–0.30
- 0.35–0.45
- 0.45–0.60 (Correct answer)
- 0.65–0.75
Correct answer: 0.45–0.60
Most structural concrete uses a water-to-cement (w/c) ratio of 0.45–0.60; lower ratios increase strength while higher ratios improve workability but reduce strength.
Question 2: What is the purpose of rebar (reinforcing steel) in concrete?
- To increase concrete's compressive strength
- To resist tensile stresses that concrete cannot handle (Correct answer)
- To reduce the amount of cement needed
- To speed up the curing process
Correct answer: To resist tensile stresses that concrete cannot handle
Concrete is strong in compression but weak in tension; rebar is embedded to carry tensile forces and prevent cracking under loads.
Question 3: What is the minimum curing time for standard Portland cement concrete to achieve adequate strength?
- 1 day
- 3 days
- 7 days (Correct answer)
- 28 days
Correct answer: 7 days
Concrete should be cured for a minimum of 7 days for adequate strength development; however, the standard 28-day strength is used for design purposes.
Question 4: What does the designation 'f'c = 4000 psi' mean for concrete?
- The concrete weighs 4000 psi
- The specified compressive strength at 28 days is 4000 psi (Correct answer)
- The tensile strength is 4000 psi
- The concrete must be placed at 4000 psi pressure
Correct answer: The specified compressive strength at 28 days is 4000 psi
f'c denotes the specified compressive strength of concrete measured in pounds per square inch (psi) at 28 days after placement.
Question 5: What is the purpose of a slump test for concrete?
- To measure concrete compressive strength
- To measure the workability and consistency of fresh concrete (Correct answer)
- To determine aggregate size distribution
- To check for air entrainment content
Correct answer: To measure the workability and consistency of fresh concrete
The slump test measures the workability (flowability) of fresh concrete by measuring how much a cone of concrete settles after the cone mold is removed.
Question 6: What type of mortar joint is most water-resistant and recommended for exterior masonry?
- Struck joint
- Raked joint
- Concave (tooled) joint (Correct answer)
- Flush joint
Correct answer: Concave (tooled) joint
A concave (tooled) joint is the most weather-resistant mortar joint because the tooling compresses and seals the mortar surface, preventing water infiltration.
Construction Concrete and Masonry 1
What is the standard water-to-cement ratio range for most structural concrete mixes?