ACI Concrete Materials & Mix Proportioning 2

Question 1

What does a low water-to-cement (w/c) ratio primarily produce in hardened concrete?

Accepted Answer

Higher strength and lower permeability

Answer

A lower w/c ratio reduces the capillary porosity in hardened concrete, resulting in higher strength and lower permeability.

Question 2

Which type of Portland cement is specifically designed for use in sulfate-exposed environments?

Accepted Answer

Type V

Answer

Type V Portland cement has very low tricalcium aluminate (C3A) content, making it highly resistant to sulfate attack.

Question 3

Fly ash used as a supplementary cementitious material in concrete is a byproduct of:

Accepted Answer

Coal-fired power plants

Answer

Fly ash is a pozzolanic byproduct collected from the flue gases of coal-fired electric power plants.

Question 4

According to ACI mix design principles, what is the purpose of the 'trial batch' step?

Accepted Answer

To verify calculated proportions produce desired fresh and hardened properties

Answer

Trial batches confirm that calculated mix proportions achieve the target slump, air content, and compressive strength before full-scale production.

Question 5

What is 'bleeding' in fresh concrete?

Accepted Answer

Migration of mix water to the concrete surface

Answer

Bleeding occurs when water migrates upward through fresh concrete to the surface due to settlement of heavier solid particles.

(ACI) American Concrete Institute Concrete Finisher Practice Test