Concrete Materials & Mix Proportioning Flashcards

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

Answer: Higher strength and lower permeability

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

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

Answer: Type V

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

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

Answer: Coal-fired power plants

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

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

Answer: To verify calculated proportions produce desired fresh and hardened properties

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

What is 'bleeding' in fresh concrete?

Answer: Migration of mix water to the concrete surface

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

What is the approximate specific gravity of normal-weight Portland cement?

Answer: 3.15

Portland cement has a specific gravity of approximately 3.15, which is used in absolute volume mix design calculations.

Silica fume added to concrete primarily improves which property?

Answer: Strength and reduced permeability

Silica fume is an extremely fine pozzolan that reacts with calcium hydroxide to form additional C-S-H gel, significantly improving strength and reducing permeability.